Update on the Technology and Applications of Polyaryletherketones

Update on the Technology and Applications of Polyaryletherketones

David Kemmish

Smithers Rapra Update

Update on the Technology and Applications of Polyaryletherketones David Kemmish

iSmithers – A Smithers Group Company Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.ismithers.net

First Published in 2010 by

iSmithers Shawbury, Shrewsbury, Shropshire, SY4 4NR, UK

©2010, Smithers Rapra

All rights reserved. Except as permitted under current legislation no part of this publication may be photocopied, reproduced or distributed in any form or by any means or stored in a database or retrieval system, without the prior permission from the copyright holder.

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ISBN: 978-1-84735-408-2 (Hardback) 978-1-84735-409-9 (ebook)

Typeset by Argil Services Printed and bound by Lightning Source Inc.

P

reface

Polyaryletherketones (PAEK) have been described as the world’s highest performance true thermoplastic polymers. It is now 30 years since the invention of Victrex PEEK (polyetheretherketone) and PAEK are found in niche applications in almost every industry sector. PAEK are produced by several suppliers and an ever increasing range of products has been developed. These include higher temperature variants such as PEK, PEKEKK, PEEKK and PEKK, and also compounds, blends, composites, films, shapes, coatings and medical grades. PAEK find applications in the automotive, chemical process, oil and gas, aerospace, medical device, telecommunications and electronics industries. They are often used because of a combination of properties which goes far beyond temperature resistance and includes resistance to wear, chemical environments, hydrolysis, sterilisation and fire, together with biocompatibility, purity, low smoke and toxic gas emission and electrical performance. This review provides an overview of key aspects of commercial PAEK technology including PAEK production, characterisation, product forms (compound, blends, composites, films, coatings and medical grades) and classes of application in each industry sector. It includes many of the major historical developments and discusses up-to-date information on manufacturers, products and applications. Various papers and patents are cited which represent some of the key aspects of PAEK technology.

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Update on the Technology and Applications of Polyaryletherketones

iv

C

ontents

1

Manufacturing and Polymerisation Chemistry ..................... 1 1.1 Polyaryletherketone (PAEK) Nomenclature .................... 1 1.2 PAEK Producers: Past, Present and Future...................... 2 1.3 Manufacturing of PAEK ................................................. 3

1.3.1 Nucleophilic Processes ....................................4 1.3.2 Electrophilic Processes ..................................12 2

Characterisation ................................................................ 17 2.1 General Characterisation .............................................. 17 2.2 Quality Control Tests ................................................... 17 2.3 Crystallinity.................................................................. 18

2.3.1 Crystalline Morphology ...............................19 2.3.2 Crystallisation Processes ...............................21 2.3.3 Measurement of Crystallinity .......................23 2.3.4 Melting Processes .........................................25 2.4 Molecular Weight ......................................................... 26 2.5 Chemical Structure ....................................................... 28 3

Properties and Processing of Unfilled Polyaryletherketones 33 3.1 Introduction ................................................................. 33 3.2 Properties ..................................................................... 34

3.2.1 Thermal Performance ...................................34 3.2.2 Mechanical Properties ..................................36 3.2.3 Chemical Resistance .....................................38

Update on the Technology and Applications of Polyaryletherketones

3.2.4 Radiation Resistance ....................................40 3.2.5 Fire, Smoke and Toxicity ..............................41 3.2.6 Purity ...........................................................43 3.2.7 Electrical Properties ......................................43 3.3 Processing Techniques .................................................. 44 3.3.1 Background ..................................................44 3.3.2 Drying ..........................................................44 3.3.3 Processing Temperatures, Thermal Stability and Rework...............................................44 3.3.4 Crystallisation and Annealing .......................45 3.3.5 Orientation ...................................................46 3.3.6 Surface Treatment and Joining Technologies 46 3.3.7 Laser Sintering ..............................................47 4

Product Forms ................................................................... 51 4.1 Standard Powders and Granules ................................... 51 4.2 Compounds .................................................................. 52 4.3 Composites................................................................... 56 4.4 Films ............................................................................ 59 4.5 Fibres ........................................................................... 60 4.6 Fine Powders and Coatings .......................................... 61 4.7 Stock Shapes................................................................. 62 4.8 Foams........................................................................... 62

5

Competitive Materials ....................................................... 65 5.1 Introduction ................................................................. 65 5.2 Amorphous Sulfones and Thermoplastic Polyimides .... 67 5.3 Polyphenylene Sulfide ................................................... 67 5.4 High-temperature Polyamides ...................................... 68 5.5 Polyphenylenes ............................................................. 68 5.6 Thermotropic Liquid Crystalline Materials .................. 70

vi

Contents

5.7 Perfluoropolymers ........................................................ 71 5.8 Amide Imides ............................................................... 72 5.9 Non-melting Imides ...................................................... 72 5.10 Polybenzimidazole ...................................................... 73 6

Polyaryletherketone Blends................................................. 75 6.1 Introduction ................................................................. 75 6.2 Blends with Polyarylethersulfones ................................ 75 6.3 Blends with Thermoplastic Imides ................................ 77

6.3.1 Polyetherimide (PEI) .....................................77 6.3.2 Extem ...........................................................78 6.3.3 Polysiloxane /Polyimides ..............................78 6.4 Blends with PPS ............................................................ 79 6.5 Blends with Polybenzimidazole (PBI) ............................ 79 6.6 Blends with Fluoropolymers ......................................... 80 6.7 Blends with Thermotropic Liquid Crystalline Polyesters (TLCP) ..................................................... 80 6.8 Blends with Polyphenylene ........................................... 80 6.9 Blends with Other PAEK .............................................. 81 7

Applications of Polyaryletherketones.................................. 85 7.1 Introduction ................................................................. 85 7.2 Industry Segmentation and Sales Volumes .................... 85 7.3 Aerospace ..................................................................... 88 7.4 Automotive and Transport ........................................... 92 7.5 Oil and Gas .................................................................. 94 7.6 Electronic Devices ........................................................ 96 7.7 Semiconductors and Displays ..................................... 101 7.8 Industrial .................................................................... 103 7.9 Food Processing.......................................................... 108 7.10 Consumer Applications ............................................ 109

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Update on the Technology and Applications of Polyaryletherketones

8

Medical Grades and their Applications............................ 113 8.1 Materials .................................................................... 113 8.2 Applications ............................................................... 116

8.2.1 Short-term Applications .............................116 8.2.2 Permanent Implants ....................................117 Abbreviations ........................................................................... 123 Appendix ................................................................................. 127 Index ........................................................................................ 133

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1

Manufacturing and Polymerisation Chemistry

1.1 Polyaryletherketone (PAEK) Nomenclature PAEK are commonly described in terms of an ‘E’ and a ‘K’ which refer to the sequence of ether and ketone units in the structure. The most common PAEK are polyaryletheretherketone (PEEK), polyaryletherketone (PEK) and polyaryletherketoneketone (PEKK). PEEKK and PEKEKK are also produced commercially. There are two basic manufacturing routes: nucleophilic and electrophilic. Some polymers (e.g., PEKK) are only made commercially by electrophilic processes whereas others (such as PEEK, PEK and PEKEKK) can be made by either route. Chain polarity and rigidity increase with the presence of ketone units and therefore thermal properties such as glass transition (Tg) increase with increasing ketone to ether (K/E) ratio. Hence we can say that Tg should increase in the order: PEEK < PEK ~ PEEKK < PEKEKK < PEKK. For linear, all-para chains without disrupted crystal structures the melting point (Tm) increases with Tg such that Tg (in K)/Tm (in K) ~ 2/3. This can become a problem when the melting point becomes so high that the material is hard to process or keep in solution during manufacturing. In some cases (notably PEKK) the melting point is deliberately reduced without a large effect on Tg. This is achieved, as we shall see, by incorporating non-para or non-crystallisable units in the polymer backbone. These limit the size of the crystals and reduce the melting point. There are also polyketone copolymers in which the structure cannot be represented by a single repeating unit. (In the field of PAEK,

1

Update on the Technology and Applications of Polyaryletherketones

polymers produced from more than one monomer but with a single repeating unit are not usually called copolymers.) Often the copolymer units contain sulfone or biphenyl which can be used to increase Tg and achieve other tailored effects.

1.2 PAEK Producers: Past, Present and Future In its present form PEEK was invented by Imperial Chemical Industries (ICI) in 1978 [1, 2], although Raychem had already manufactured PEK by an electrophilic process. PEEK was manufactured by the ICI Victrex business group (along with polyethersulfones and thermotropic liquid crystalline polymers). A 1000 tpa capacity PAEK plant (now owned by Victrex plc) was constructed at Thornton Cleveleys in the northwest of England. ICI also produced a large range of PEEK compounds through its LNP subsidiary, PEEK films (Stabar) and continuous carbon fibre PEEK composites (APC1 and APC2). The APC technology is now owned by Cytec. LNP was first purchased by Kawasaki, then by GE Plastics and is now owned by Sabic. In 1993 the ICI Victrex PEEK business was sold to a management buyout and subsequently Victrex plc was floated on the London Stock Exchange as an independent company. Victrex currently has 4250 tonnes capacity and is the leading supplier of PAEK. It produces nucleophilic PEEK, PEK (‘PEEK HT’) and, since May 2009, PEKEKK (‘Victrex ST’). Sales in 2008 were 2625 tonnes of resin having grown by around 40% in the previous four years. In value terms sales were £141 million with a profit before tax of £55 million. In the 1980s and early 1990s Hoechst manufactured nucleophilic PEEKK (Hostatec) and BASF produced electrophilic PEKEKK (Ultrapek). Both failed to achieve substantial sales and were withdrawn from the market. PEKK was originally developed by DuPont. It is now manufactured by Rallis in India which has 100 t of capacity and supplies material

2

Manufacturing and Polymerisation Chemistry

to Cytec for use in aerospace interiors and thermoplastic composites. It is available in both crystalline and amorphous forms. PEKK (OxPEKK) is sold for both industrial and medical applications by Oxford Performance Materials which has recently been acquired by Arkema. PEKK type resins are also available from Polymics under the tradename Arylmax. In 2005 Degussa (now Evonik) formed a joint venture with Jilin University (Jida Degussa) in China to produce PEEK (Vestakeep) and subsequently acquired the old Hoechst PEEKK technology. Jilin had produced PEEK in China since 1980 to supply military and nuclear applications at a time when export of PEEK from the west was banned. Evonik has 1000 tpa capacity in China. Gharda Chemicals in India produced PEEK using a novel electrophilic process and also polyether sulfones by rather more conventional routes. This business was acquired by Solvay in 2005 and subsequently Solvay has built a 500 t (expandable to 1000 t) nucleophilic PEEK (Ketaspire) plant at the Gharda site in India. Both Gharda and Jilin (as Changchun Jilin Super Engineering Plastics Research Co., JSEP) have continued some activities in PAEK. Gharda has patented a low-cost process to produce PEK. JSEP produces PEEKK and PEEK copolymers and has filed patents on various improvements to the polymerisation process. JSEP reports that it will have 1000 tpa production capacity in Liaoning China at the start of 2010. Recently Polymics has introduced as series of high Tg PAEK which are described as based on patented nucleophilic technology with proprietary monomers.

1.3 Manufacturing of PAEK There are two basic routes to PAEK: nucleophilic and electrophilic processes.

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Update on the Technology and Applications of Polyaryletherketones

1.3.1 Nucleophilic Processes The nucleophilic polyetherisation route involves the displacement of an activated halogen by phenoxide anions. For carbonyl monomers the halogen is generally fluoride but sulfone groups are more powerfully activating and chlorine is an adequate leaving group. The routes to PEEK, PEK, PEEKK and PEKEKK are shown below and are widely described in the literature [1-4]. Diphenylsulfone is used as a high-temperature solvent (typically at around 320 °C) and the phenate is produced in situ by reaction of the bisphenol with alkali metal carbonates. The general reaction is shown below where Ar is a ketone activated aromatic and M is usually sodium or potassium: FArF + HOAraOH + M2CO3 m 2MF + CO2 + H2O + –Ar–O–Ara– At the end of the polymerisation the solidified polymerisation mixture contains polymer, diphenylsulfone and alkali metal fluorides. The diphenylsulfone is removed with acetone and the metal fluorides by extraction with water. Side reactions may occur at the carbonyl (which may give rise to the observed yellow colouration in sulfuric acid) and also as a result of the abstraction of protons ortho to fluorine. Protic solvents cannot be used and a key discovery was that diphenylsulfone is a suitable solvent that can be used close to the melting point of the polymer. This produces high molecular weight, tough, melt-processable polymers that are soluble in sulfuric acid and is a key feature of the ICI patents. The molecular weight can be controlled by means of a small difluoride excess and prior preparation of the dipotassium derivative of the bisphenol is unnecessary. Early work on different PAEK can be found in a range of patents and papers from ICI (e.g., [1-4]). As explained later, precise Tg values and melting points (Tm) will be a function of heating and cooling rates, crystallinity, morphology, chain sequence and exactly where on the

4

Manufacturing and Polymerisation Chemistry

differential scanning calorimetry or dynamic mechanical thermal analysis trace is selected for measurement by the researcher. This means that great care should be taken in comparing results reported in different papers and published by different workers. Industrial users of PAEK should use the melting points and thermal properties published in manufacturers’ literature. Several routes were systematically compared by Jilin University and Chiba Institute of Technology who produced comparable samples of nucleophilic PEEK, PEEKK, PEKEKK, PEKK and PEKEKEEK [5]. Figure 1.1 shows the key fluoromonomers and bisphenols and Figure 1.2 illustrates how they are combined to produce the main classes of PAEK. Table 1.1 lists their glass transition and melting temperatures.

Table 1.1 Glass transition and melting temperatures Polymer (nucleophilic, all para substituted)

Tg °C

Tm °C

PEEK [5]

143

334

PEKEKEEK [5]

154

345

PEK [2]

154

367

PEEKK [5]

158

363

PEKEKK [5]

161

377

PEKEKK [2]

–

383

165

386

PEKK [5]

5

6

HO

HO

F

F

HO

OH

O C

O

C

F

C

O

C

C

OH

O

O

C

O

Dihydroxydiketone

Dihydroxybenzophenone

Hydroquinone

Difluorodiketone

Figure 1.1 Key Monomers

OH

F

Difluorobenzophenone

‘DHDK’

‘DHB’

‘HQ’

‘DFDK’

‘DFB’

Update on the Technology and Applications of Polyaryletherketones

PEK

PEEKK

PEKEKK

PEKK

DFB + DHB

DFDK + HQ

DFDK + DHB

DFDK + DHDK

O

O

O

O

O

C

O

O

C

O

C

O

O

n

O

C

O

C

O

C

n

n

C

O

C

O

Figure1.2 Nucleophilic routes to PEEK, PEK, PEEKK, PEKEKK, PEKK [2, 5]

PEEK

DFB + HQ

O

n

C

O

n

Manufacturing and Polymerisation Chemistry

7

Update on the Technology and Applications of Polyaryletherketones

The fluoride monomer is expensive and is generally made by FriedelCrafts acylation from fluorobenzene or a diazotisation route from diaminodiphenylmethane. There are a number of patents which describe routes to difluorobenzophenone filed by companies such as Ihara, Raychem, Rhone Poulenc, Asahi and ICI, which can be found summarised in more recent patents [6, 7]. The recent work includes Victex’s route from dinitrodiphenylmethane using tetramethylammoniumfluoride [7] and Inspecs’s route [6] based on the reaction of formaldehyde with fluorobenzene followed by nitric acid oxidation of difluorodiphenylmethane. However, process economics will be driven by production scale and this gives an advantage to the existing producers and processes. Various attempts have been made to use cheaper chloromonomers. ICI patented an Ullman ether condensation route in which copper is used to catalyse the halide displacement. However copper residues had to be carefully removed since they were detrimental to the thermal stability of the polymer. It also seems possible that the balance of side reactions is such that PAEK produced from chloromonomers will be somewhat different to PAEK produced by more conventional routes. More recently Gharda Chemical has filed patents [8] on a route to PEK from a chloromonomer. The low cost monomer (hydroxychlorobenzophenone) is prepared by reaction of 4-chlorobenzoylchloride with phenol. Much of the Chinese development of PAEK has been led by Professor Zhongwen Wu of Jilin University. This group has continued to innovate in the field as JSEP following the acquisition of their PEEK technology by Degussa/Evonik. Recently their focus has been on reducing costs and improving production processes. The author is grateful to Professor Wu for information on their latest developments. JSEP produces PEEKK using the route in reference [5]. PEEKK was made by Hoescht in the 1980s and has properties similar to PEK. JSEP states that the monomers are significantly less expensive than those used to produce PEK, since hydroquinone is cheap and the difluorodiketone can be made from fluorobenzene and terephthaloylchloride. It has also developed sulfolane as an

8

Manufacturing and Polymerisation Chemistry

alternative to the diphenylsulfone polymerisation solvent [9]. This lowers reaction temperature and shortens reaction time and also allows removal of both the polymerisation solvent and fluoride salts using only deionised water. The product (which is called S-PEEK) is reported to have a higher melt flow index for a given level of mechanical properties than conventional PEEK. One drawback of the nucleophilic routes described so far is that they produce a metal salt and solid solvent residue which needs to be removed from the system. In many condensation polymerisations the small molecule produced is volatile and can be removed directly from the reaction. The KF residue leads to reversibility of the reaction and transetherification. However, the low solubility of KF in diphenylsulfone means that a high molecular weight can still be achieved and the KF can be removed by extraction with water. Indeed extraction with water at very high temperatures has recently been used to produce ultrahigh-purity grades of PEEK [10]. These materials can have less than 1 ppm residual potassium and sodium. The nucleophilic route allows the production of a very wide range of copolymers produced from various bisphenols (e.g., dihydroxydiphenylsulfone and biphenol) together with a range of difluoromonomers (which are often synthesised from fluorobenzene) and chloromonomers such as dichlorodiphenylsulfone. There is an extensive academic and patent literature but, as yet, very little industrial use of these more advanced systems. However, at the time of writing, Polymics has introduced a patented series of resins (Arylmax P) with Tg in the range 180 to 240 °C and melting temperatures from 320 to 370 °C. These resins are described as being produced with classic nucleophilic chemistry and proprietary monomers. The simplest copolymers contain three monomers and are, in effect, copolymers of basic materials such as PEEK, PEK and PEKEKK. Sulfone groups are particularly effective at increasing Tg but reduce the melting point by limiting the size of the ketone-containing crystals. This also reduces overall crystallinity and rate of crystallisation. The sulfone-containing monomer may be very simple, such as dichorodiphenylsulfone, but it may also be designed to maximise

9

Update on the Technology and Applications of Polyaryletherketones

the increase in Tg while minimising the effect on crystallinity. For example, it is possible to produce a reasonably fast crystallising polymer with Tg in excess of 175 °C by adding the monomer shown in Figure 1.3 to a standard PEK polymerisation [11].

Cl

O

O

S

S

O

O

Cl

Figure 1.3 Monomer used to increase Tg

Crystalline copolymers can have enhanced Tg (over 200 °C) and their melting point is usually limited by the presence of non-crystallisable groups. Some are more complex than simple three-monomer copolymers of PEEK or PEK. Copolymers such as ITX (Tg ~ 175 °C) and HTX (Tg ~ 202 °C) [11, 12] were originally developed as matrix materials for use in thermoplastic composites for high-performance fighter aircraft. The HTX monomers are shown in Figure 1.4. An interesting feature of these and other copolymers is that their sequence distribution does not necessarily reflect the initial displacement of halogen by phenoxide. The scrambling of structures due to transetherification has been extensively investigated by workers at ICI and Louvain University [13, 14]. The polymerisation reaction is reversible and so fluoride and phenoxide anions can attack para to sulfone or carbonyl groups which were not part of the original halo monomer. The effect is the creation of chain sequences which would be expected from the reaction of fluoromonomer with fluoromonomer or phenoxide with phenoxide. In the system discussed above it would be possible to find many combinations of sequences of LKF, Bis S and BP. This affects properties and can lead

10

Manufacturing and Polymerisation Chemistry

to the presence of species of different melting points [15]. The rate of reaction at each site depends on the nucleophile, the activating group, the temperature and the solvent. Very complex structures can be developed. Transetherification can make it difficult to control the production of block copolymers. One approach is to join the blocks using high-temperature stable heterojunctions such as amide and imide.

F

O

O

C

C

F

‘LKF’

O HO

S

OH

‘Bis-S’

O HO

OH

‘BP’

Figure 1.4 HTX monomers

More recently copolymers have been developed for use in fuel cell membranes. Commercial membranes are often sulfonated fluoropolymers but sulfonated PAEK can also have a good level of performance. Victrex has designed polymers which consist of easyand hard-to-sulfonate blocks which make sulfonation in sulfuric acid easy to control [16]. For example a biphenol or hydroquinone residue is highly reactive to electrophiles and is easily sulfonated in concentrated sulfuric acid. In contrast phenylene groups deactivated

11

Update on the Technology and Applications of Polyaryletherketones

with carbonyl or sulfone are very much less reactive. Hence PEEK is easily sulfonated in sulfuric acid whereas PEK requires much more forcing conditions. The membranes can be further enhanced by the use of crystallisable blocks which act as crosslinks and reinforce the membranes in its hydrated state. There are also a very large number of papers describing attempts to crosslink PAEK, the production and polymerisation of cyclic PAEK, branched PAEK, fluorinated PAEK, functionalised reactive PAEK, surface-modified PAEK and PAEK incorporating liquid crystalline functionality. The academic background of the Jilin group means that they have published a large number of papers on modified PAEK and copolymers [17]. These include papers on low-viscosity cyclic PAEK for composite impregnation, liquid crystalline PAEK, hightemperature copolymers with biphenyl and crosslinkable PAEK - for example PAEK oligomers with terminal alkyne groups. Publications on related subjects can also be found from companies such as Victrex [18] and various academic groups around the world. However, none of these products is, as yet, commercially available.

1.3.2 Electrophilic Processes In the past electrophilic PEK and PEKEKK have been produced by Raychem and BASF, respectively. Currently the vast majority of the world’s supply of PAEK is made by nucleophilic routes. However, recent commercial electrophilic products include PEKK and Gharda’s ‘Gatone’ PEEK technology - which is now owned by Solvay. PAEK produced by these processes do not have fluorine end groups. PEKK is produced from diphenylether and phthaloyl chlorides [19]. It is one of the few PAEK that would be difficult to make by nucleophilic routes because of the obvious complexity of the monomer required. The high melting point of linear, 100% para PEKK means that commercial PEKK is actually made from both terphthaloyl (T) and isophthaloyl chloride (I). Crystalline PEKK is typically 80:20 T/I whereas the amorphous grades used for thermoforming are 60:40 T/I.

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Manufacturing and Polymerisation Chemistry

The isophthaloyl groups limit the size of crystals and hence reduce their melting point - together with crystallisation rate and overall crystallinity. If all three monomers are used together then the resulting backbone sequence is somewhat random. However it is possible to pre-react one of the acid chlorides and diphenylether and then use the other acid chloride in a second step to produce a more regular structure. PEKK chemistry is quite versatile. Polymics produces a series of PEKK resins with Tg in the range 167-172 °C, Tm 310-360 °C and crystallisation rates which can be tailored to suit particular applications. Gharda has developed a process to produce PEEK from phenoxyphenoxybenzoic acid by dehydration in methanesulfonic acid (see Figure 1.5). Such reactions are described in patents and literature from ICI, Victrex and Gharda [20, 21]. The monomer can be produced by oxidation of ethylphenoxyphenoxybenzene.

13

C O

O 14

Figure 1.5 Gharda route to PEEK

COOH

O

O

O

n

Update on the Technology and Applications of Polyaryletherketones

Manufacturing and Polymerisation Chemistry

References 1.

J. Rose and P. Staniland, inventors; ICI, assignee; US4320224, 1978.

2.

T.E. Attwood, P.C. Dawson, J.L. Freeman, L.R.J. Hoy, J.B. Rose and P.A. Staniland, Polymer, 1981, 22, 8, 1096.

3.

V.L. Rao, Journal of Macromolecular Science, Part B: Physics, 1995, 35, 4, 661.

4.

K. Dahl and V. Jansons in Polymers and Other Advanced Materials: Emerging Technologies and Other Business Opportunities, Eds., P.N. Prasad, J.E. Mark and T.J. Fai, Plenum Press, New York, NY, USA, 1995, p.69.

5.

M. Shibata, R. Yosomiya, J. Wang, Y. Zheng, W. Zhang and Z. Wu, Macromolecules Rapid Communications, 1997, 18, 2, 99.

6.

H. Rögl and M. Ungerank, inventors; Inspec Fibres, assignee; WO/2007/014692, 2007.

7.

J.H. Clark and D. Adams, inventors; Victrex, assignee; GB2323086, 1998.

8.

K. Gharda, A. Malte, S. Mathur, P. Joseph and A. Mathew, inventors; Gharda Chemicals Ltd., assignee; GB2446397, 2007.

9.

Z. Wu and D. Zhao, inventors; WO/2007/109932 A1, 2007.

10. J. Devine, S. Green, D. Kemmish and B. Wilson, inventors; Victrex, assignee; US7160980 B2, 2002. 11. D. Kemmish, A. Newton and P. Staniland, inventors; ICI, assignee; EP0397356 B1, 1990.

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Update on the Technology and Applications of Polyaryletherketones

12. J. Rose, E. Nield, P. McGrail and H. Colquhoun, inventors; ICI, assignee; EP0194062, 1986. 13. V. Carlier, J. Deveaux, R. Legras, A. Bunn and P. McGrail, Polymer, 1994, 35, 2, 415. 14. V. Carlier, J. Deveaux, R. Legras and P. McGrail, Polymer, 1994, 35, 2, 423. 15. A. Bunn, N. Clayden and D. Kemmish, Macromolecules, 1993, 26, 22, 6138. 16. P. Charnock, D. Kemmish, P. Staniland and B. Wilson, inventors; Victrex, assignee; EP1112301 B1, 1999. 17. For a complete list of recent JSEP publications see: www.jusep.com.cn/english/Recent.html. 18. I. Teasdale, E.C. Harper, P. Coppo, B. Wilson and M.L. Turner, Macromolecules Rapid Communications, 2006, 27, 23, 2032. 19. E. Brugel, inventor; DuPont, assignee; EP0225144 A2, 1986. 20. K. Gharda, P. Trivedi, V. Iyer, U. Vakil and S. Limaye, inventors; Gharda Chemicals Ltd, assignee; EP1170318 B1, filed 2001. 21. D. Kemmish and B. Wilson, inventors; Victrex, assignee; US6909015 B2, filed 2001.

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2

Characterisation

2.1 General Characterisation Many of the tests used to characterise polyaryletheretherketone (PEEK) are simple industry standard techniques to measure properties such as mechanical, rheological, colour, fire, smoke or toxicity performance. However, some techniques require a specific knowledge of the polyaryletherketone (PAEK) literature. These include the characterisation of crystallisation, crystallinity, crystalline morphology, melting, molecular weight and chemical structure. Manufacturers also tend to have a number of proprietary quality control tests.

2.2 Quality Control Tests The importance of ‘char particles’ (also known as ‘black specks’) was recognised very early in the development of PAEK. Companies such as Dresser Rand published papers illustrating the detrimental effect of black specks on the lifetime of compressor valve plates. Sufficiently large particles of char were shown to nucleate cracks under service conditions. Black specks are basically carbonised PEEK and can be produced during processing. Black speck number and size are important factors in determining the quality of a PAEK moulding. Gels are also important especially in the production of film, fibres and fine tubes. Both gels and black specks can result from excessive thermal history and it is important to avoid long residence times and hot spots. Colour is also important. Colour variations are particularly noticeable in components joined from different batches

17

Update on the Technology and Applications of Polyaryletherketones

or fibres woven into a single cloth.

2.3 Crystallinity Crystallinity is key to the development of mechanical properties and good chemical resistance. It is what differentiates PAEK from cheaper, but higher Tg, amorphous materials such as polyethersulfones and polyetherimides. Fortunately in PEEK the degree of crystallinity tends to vary by only a small amount over quite a wide range of cooling rates. Typically it is in the range 30 to 35% but values from 0 to 40% are easily achievable with more extreme thermal histories. In practice many processors rely on reproducible thermal history to create a reproducible crystalline structure. In many cases this is perfectly adequate. However, cooling rates over about 700 °C per minute in PEEK will result in amorphous material and slow cooling rates result in the development of substantial extra crystallinity [1]. PEEK sheets below about 1 mm in thickness can often be made amorphous by quenching from the melt in iced water. However, the exact conditions will vary according to the polymer grade – generally lower molecular weights will crystallise faster. Other slower crystallising PAEK (such as commercial PEKK) will be more sensitive to cooling rate and relatively easy to quench to the amorphous state. It is not unusual to see a translucent brown skin on PAEK injection mouldings in cases where the mould temperature has been too low. This can be removed by annealing above Tg - but it is better to use a correct mould temperature. It is also possible to increase crystallinity through annealing with the objective of improving chemical resistance. However, such increases may also affect mechanical properties such as toughness and, if performed in air at high temperatures, may result in some oxidative degradation. Characterising crystallinity requires consideration of all the size scales in the crystalline structure. The most important number is the overall percentage crystallinity, but it can also be important to characterise

18

Characterisation

the spherulitic and lamellar morphology. This section starts with a discussion of crystalline structure and then moves on to the development of crystallinity and how it can be characterised. Finally we consider the nature and interpretation of melting processes.

2.3.1 Crystalline Morphology PEEK is the best characterised and most important PAEK and so morphology will be discussed in terms of PEEK. Other PAEK are generally quite similar but some of the important differences will be highlighted – such as the occurrence of polymorphism. In general terms PEEK shows the typical lamellar and spherulitic structures which are characteristic of many polymers. The crystalline structure of PEEK can be described at a number of different scales. The crystalline unit cell itself has a chain axis repeat length of about 1 nm. In fact the repeat unit in PEEK runs from carbonyl to ether since these groups are found to be crystallographically equivalent. The unit cells are the basic unit of the crystalline lamellae which are typically around 10 nm thick. Typically the lamellae themselves radiate out from a centre of nucleation to form spherulites which are around 1 to 10 μm in diameter. The unit cell dimensions depend slightly on crystallisation conditions but lamella thickness and spherulite size can vary a lot according to thermal history and also according to some of the characteristics of the polymer. The unit cell dimensions are important because they are used to calculate crystalline density which can then be used to determine percentage crystallinity using a simple two-phase model of crystalline and amorphous regions. X-ray-based unit cell determination is usually of considerable academic interest and the structures of all the common PAEK can be found in the literature [2, 3]. In fact PEEK and PEK were the first polymers to have their structures determined by pattern-fitting structure refinement (PFSR) [2, 3]. This technique produces more accurate unit cells by virtue of fitting X-ray peaks

19

Update on the Technology and Applications of Polyaryletherketones

all the way up their steep sides as well as at their maxima and also determines the position of atoms within the cell by fitting intensity data. The structures of PEEK and PEK are orthorhombic with a Pbcn space group. Chains are located at the corner and centre of each cell with edge to face phenyl interactions. The unit cell dimensions and corresponding densities for isotropic materials are given in Table 2.1. However, later work has shown that the unit cell dimensions of PEEK are somewhat dependent on crystallisation conditions and this explains why there are slight variations in the quoted densities for PAEK crystals [4]. X-ray analysis can also be used to measure crystalline orientation and crystallite perfection using the standard techniques of polymer crystallography.

Table 2.1 Unit cell parameters for isotropic PEEK and PEK by PFSR Polymer

c/nm

Densityg/cm3

a/nm

b/nm

PEEK [2]

0.7781

0.5922

1.0056

1.378

PEK [2]

0.765

0.597

1.009

1.413

PEKEKK and PEKK can have closely similar structures when crystallised from the melt with a small shift in diffraction peak positions to a lower angle with an increase in keto content - reflecting a change in unit cell parameters [5]. However polyaryletherketoneketone (PEKK) can exhibit a second structural form with face to face phenyl packing. This form is favoured by solvent crystallisation (e.g., in aspolymerised material), by cold crystallisation and by a higher 1,4 to 1,3 ratio. Solvent-crystallised PEK and PEKEKK have been reported to show both polymorphs [5]. The unit cells of seven oriented PAEK were compared by Blundell and Newton [6] who observed that the crystalline density remains almost unchanged at 1.400 g/cm3 with a standard deviation of 0.006.

20

Characterisation

The lamellar structure is typically probed by small-angle X-ray scattering and electron microscopy techniques. Thinner lamellae will melt at lower temperatures (because of the extra entropy increase involved in their melting) and so lamella thickness characterisation is important in the interpretation of melting processes. The simplest way to observe the spherulitic morphology of PAEK is by hot-stage microscopy. However, the nucleation density is often rather too high for optical microscopy and researchers sometimes rely on a small amount of oxidative thermal degradation to reduce this to convenient levels. There are other effects which can make hot-stage microscopy observations unreliable. A more direct method is to preferentially etch the amorphous phase and make direct scanning electron microscopy observations of the resulting structure [7, 8]. This can produce excellent results and has been used extensively to characterise the morphology of fibre-reinforced PAEK composites. It can be difficult to disentangle the effect of percentage crystallinity from spherulitic and lamellar morphology. For example, high-temperature crystallisation will give rise to lower nucleation density (larger spherulites) and higher crystallinity. However, it has been suggested that spherulite size influences the fracture mechanism in PEEK [9].

2.3.2 Crystallisation Processes Crystallisation processes in PEEK have been the subject of many academic papers [10-13]. However, the crystallisation of PEEK generally matches the classic behaviour of other polymers. The effect of time is described by Avrami kinetics (n ~ 3) and secondary crystallisation occurs after the spherulites have impinged. This secondary crystallisation results from an increase in the crystallinity within the spherulites and is probably related to the existence of the low-temperature melting peaks (LTMP) described later. A number of non-isothermal crystallisation models have been developed. The crystallisation rate of PAEK reaches a maximum between Tg and Tm. Crystallisation is driven by the rate of nucleation and the rate at which polymer chains can reel onto a nucleated crystalline surface.

21

Update on the Technology and Applications of Polyaryletherketones

At low temperatures the rate of nucleation is very high (it is easy to form a nucleus of critical size in a low-energy environment) but the rate of chain movement is slow. At high temperatures chains move very fast but it is difficult to nucleate new highly energetic chains onto a crystalline surface. Accordingly there is a maximum rate at intermediate temperatures. In the case of PEEK the maximum occurs at around 225 °C and the minimum crystallisation half-life is of the order of six seconds [1]. The overall percentage crystallinity is a product of the volume fraction of space filled by spherulites and the percentage crystallinity within those spherulites. An early, but highly relevant, model for non-isothermal PEEK crystallisation [14] showed that spherulites grow to completion in PEEK at cooling rates below about 700 °C per minute. Below that rate crystallinity increases very gradually with lower cooling rate until about 1 °C per minute when rather larger increases are seen in the degree of crystallinity. The rate of crystallisation will vary with molecular weight and nucleation density. Other PAEK will show similar generic behaviour but rates of crystallisation can very widely. In particular any unit in the chain that does not readily crystallise will retard the rate of crystallisation, reduce overall crystallinity and limit crystal size reducing the melting point. This effect can be used to limit Tm while maintaining Tg (as in PEKK) but excessively reduced crystallinity and crystallisation rate can cause problems with mould cycle times or properties such as fatigue and chemical resistance. Crystallisation rate can also be affected by a failure to melt the polymer at a high enough temperature. For example, PEEK that is melted below 390 °C shows faster crystallisation rates than when melted above 390 °C. This is because residual crystalline regions can persist up to the thermodynamic melting point (typically reported to be around 390 °C) and result in self-nucleation [15]. The crystallisation rate of PEEK is also known to decrease with thermal and thermal oxidative degradation [16]. Large reductions

22

Characterisation

in nucleation density are observed. With care this effect can be used as a sensitive method to assess degradation. Crystallinity can also be developed by annealing at a fixed temperature. This can be important in practical processing and is discussed in the processing section.

2.3.3 Measurement of Crystallinity The commonest techniques for measuring crystallinity are density, wide-angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Density measurement works very well with unfilled, void-free samples. Care must be taken not to change crystallinity as a result of mechanical yielding during sample preparation, for example during cutting. Density can be measured by using a density column or by weighing the sample in air and in water. Accuracy to at least three decimal places is required. Crystallinity is determined using a simple additive, two-phase model of crystalline and amorphous regions. This assumes that there is one unique crystalline density for a given PAEK. However, as described earlier, the density of 100% crystalline PAEK will vary according to the crystallisation conditions. This is unfortunate since it is usually differences in crystallisation conditions that give rise to real differences in crystallinity. This means that densities measured on samples crystallised at different temperatures should, strictly speaking, be used to calculate crystallinity with a crystalline density appropriate to each crystallisation temperature. It should also be remembered that PAEK chains close to the crystalline lamellae are constrained and that the two-phase model is only an approximation - there is also a constrained amorphous phase. Hence two samples with apparently identical percentage crystallinities calculated from a single crystalline density and a two-phase model could have different properties. However, in practice these effects are usually regarded as second order and a single crystalline density and a two-phase model are adopted. For example, the author tends to

23

Update on the Technology and Applications of Polyaryletherketones

use 1.4000 g/cm3 and 1.2642 g/cm3 for crystalline and amorphous PEEK, respectively. WAXS measurements are based on the ratio of the intensity of the crystalline peaks and the amorphous background. Fitting the amorphous background is best done with the help of a computer. Various corrections can be applied to obtain more accurate absolute crystallinities. However, most frequently we are interested in approximate absolute but accurate relative crystallinities and the corrections are not always necessary. The peak width can give information on crystal perfection - sharper peaks indicate more perfect crystals. Two-dimensional diffraction patterns of isotropic materials show rings corresponding to the diffraction peaks. Intensity variations within the rings can be used to assess crystalline orientation. WAXS only looks at material which can be penetrated by X-rays and so the depth of the analysis is limited. The patterns for filled systems can be hard to interpret but various methods have been developed - for example for use in continuous carbon-fibre composites. The FTIR method is based on the ratio of certain absorbances [17, 18]. It is especially useful for mapping the crystallinity of surfaces but it is unable to penetrate to any great depth within a sample. Measurement of local crystallinity variations can help assess variation in cooling rate and in the analysis of differential shrinkage and warpage. DSC is perhaps the most commonly used method, and the method most plagued with errors of interpretation [18]. The heats of fusion of 100% crystalline PAEK are easily determined by measurements on highly crystalline samples of known crystallinity. The heat of fusion for 100% crystalline PEEK, for example, is widely accepted to be 130 J/g1. It is tempting therefore to simply subtract the observed heat of crystallisation from the heat of fusion and use this to calculate the level of crystallinity present in the sample prior to the heating scan. However, there are three problems with this approach. The heating scan itself results in increases in the degree of crystallinity. These occur throughout the scan - not just during the easily identifiable

24

Characterisation

crystallisation process. Accordingly the heat of crystallisation can be seriously underestimated. In addition it is well known that heats of fusion and crystallisation are temperature dependent. Correction for this effect requires a detailed knowledge of the heat capacities of the liquid, amorphous glass and crystalline phases. Finally the wide temperature range between Tg and Tm makes is difficult to maintain a stable DSC baseline and judge appropriate peak integration limits. Hence the application of DSC to crystallinity determination is only simple when the sample is highly crystalline and does not change significantly before the onset of the melting process. For example it could work well with a sample that had been annealed at a high temperature close to Tm. It is possible to use DSC to determine lower levels of crystallinity but this requires expert interpretation. In these circumstances density, FTIR or WAXS may be the preferred option.

2.3.4 Melting Processes Data tables almost always show a single melting point for a given PAEK. However, there are a range of melting temperatures reflecting a range of crystal sizes and perfections. Industrial papers will tend to quote the temperature of maximum DSC endothermic heat flow, whereas academic papers may concentrate on the highest temperature melting process extrapolated to zero heating rate. Many PAEK samples show low-temperature melting processes either as discrete peaks or as shoulders on the main melting process. These LTMP are of great practical significance since they form just above any annealing temperature. They can therefore be used to determine information about the thermal history of a sample. They have even been used to assess the maximum temperature to which PEEK is exposed in wear applications. It should be noted, however, that subsequent heating above the annealing temperature will remove the associated lowtemperature melting process. Similarly stepwise cooling can result in a series of LTMP. The physical origin of LTMP has been the subject of much controversy

25

Update on the Technology and Applications of Polyaryletherketones

over a period of almost twenty years [19-39]. The two main interpretations are the following. 1. There is a single distribution of crystalline structure and the lower melting peaks represent the melting of the dominant crystal species. The upper peak is then the result of the recrystallisation process becoming unable to keep up with the rate of melting. (The lower peaks are small because rapid recrystallisation conceals ongoing melting resulting in a low net enthalpy change). 2. The LTMP result from the melting of smaller less perfect lamellae. These form just above annealing temperatures since the continuous rearrangement of the constrained amorphous phase gradually forms crystals which are stable at the annealing temperature. In the author’s opinion there is ample evidence for the existence of smaller, less perfect lamellae which form in the constrained amorphous phase between primary lamellae. It is perfectly reasonable that this would be so - since secondary crystallisation occurs in a constrained amorphous phase. Accordingly the second interpretation is favoured. However, it is also true that melting and recrystallisation occur during a heating scan and so the small LTMP may represent more of the lamella size distribution than the small size of the peak would suggest. In cold-crystallised samples there may be a lot more small lamellae than the size of the LTMP indicates (because melting is accompanied by a simultaneous crystallisation exotherm) and indeed the clearest evidence for the melting–recrystallisation interpretation comes from cold-crystallised materials.

2.4 Molecular Weight As with all thermoplastics it is important to characterise the molecular weight distribution of PAEK. In practice simple measurements such as melt flow index (MFI) and capillary rheometry are used to give an indication of molecular weight. The lower shear rate of MFI is

26

Characterisation

more relevant to extrusion processes whereas higher shear rates are more meaningful for processes such as injection moulding. The viscosity-shear rate relationship will change with molecular weight distribution. Early attempts to characterise the molecular weight of PEEK were hindered by its lack of solubility. Solution viscosity is typically measured in concentrated sulfuric acid. This technique is useful for small samples and samples that may lack thermal stability but it is not as sensitive as melt viscosity. Much effort was put into gel permeation chromatography (GPC) of sulfonated PEEK and the determination of Mark-Houwink parameters. Relationships were determined between melt viscosity and molecular weight [40]. Melt viscosity is related to molecular weight by: log10(MW) = -15.06 + 3.21 log10Mw where MV is the melt viscosity at 400 °C and a shear rate of 1000 s-1. It was also found that PEEK is soluble in solvents such as phenol/ trichlorobenzene [40] and that chlorophenol/dichlorobenzene can be used as a GPC solvent at just 40 °C [10]. GPC in these types of solvents has become a relatively standard technique. Polydispersity is typically between ~2 and 3 - as would be expected for a transetherified (i.e., reversible reaction) condensation polymer. More recently the use of triple detector GPC has provided true molecular weight as opposed to ‘equivalent molecular weight’ which needs to be corrected with Mark-Houwink constants. Although GPC provides more information it may be less sensitive to changes than a melt viscosity measurement. This is because of the power law dependence of MV on Mw and also difficulties in assessing the presence of high and low molecular weight tails. Recently a method has been developed to derivatise PAEK by reversible thioacetalisation. A wide range of PAEK can be solubilised in common solvents using this technique and GPC is one of the expected applications [41]. It is possible that this method will allow even more accurate GPC measurements as a

27

Update on the Technology and Applications of Polyaryletherketones

result of the simple solvent systems that can be used.

2.5 Chemical Structure In common with other materials the end groups and sequence distribution of PAEK can be determined by techniques such as nuclear magnetic resonance (NMR) and FTIR. There is a substantial amount of literature on this subject. However, whereas measurement of crystallinity is frequently necessary, it is relatively unusual for end users to be concerned with detailed information on chemical structure. It is easy to distinguish the basic PAEK by FTIR (e.g., measuring the relative intensity of the carbonyl infrared absorption) or by measuring the melting point and glass transition by DSC. Fluorine end groups are typically determined by 19F-NMR and can be compared with results on model compounds [42]. Hydroxyl end groups can be measured by FTIR - the levels in commercial polymers are very low. Fluorine is typically found to be a common end group, reflecting the use of excess fluoromonomer so as to avoid the presence of relatively unstable hydroxyl groups. 13C-NMR has been used in conjunction with model compounds to identify other end groups. 13

C-NMR can also be used to characterise the backbone sequence distribution of PAEK. In solvents such as trifluoromethanesulfonic acid the delocalised electron system of PAEK chains mean that NMR signals are extremely sensitive to sequencing information. Groups up to six rings removed from the observed carbon atom can show significant effects. In a series of five papers Bunn and co-workers have described how 13C-NMR can be used to sequence PAEK containing ether, ketone, sulfone, thio and biphenyl functionalities [43-47].

References 1.

28

D. Blundell, J. Chalmers, M. McKenzie and W. Gaskin, SAMPE Quarterly, 1985, 16, 4, 22.

Characterisation

2.

J. Hay, D. Kemmish, J. Langford and A. Rae, Polymer Communications, 1984, 25, 175.

3.

J. Hay, D. Kemmish and J. Langford, Polymer Communications, 1986, 27, 283.

4.

J. Hay, J. Langford and J. Lloyd, Polymer, 1989, 30, 3, 488.

5.

K. Gardner, B. Hsiao and K. Faron, Polymer, 1994, 35, 11, 2290.

6.

D. Blundell and A. Newton, Polymer, 1991, 32, 2, 308.

7.

R. Olley, D. Bassett and D. Blundell, Polymer, 1986, 27, 3, 344.

8.

D. Blundell, R. Crick, B. Fife, J. Peacock, A. Keller and A. Waddon, Journal of Materials Science, 1989, 24, 6, 2057.

9.

J. Chu and J. Shultz, Journal of Materials Science, 1990, 25, 8, 3746.

10. J. Hay and D. Kemmish, Plastics and Rubber Processing and Applications, 1989, 11, 29. 11. C. Velisaris and J. Seferis, Polymer Engineering and Science, 1986, 26, 22, 1574. 12. M. Jenkins, J. Hay and M. Terill, Polymer, 2003, 44, 22, 6781. 13. F.J. Medellín-Rodriguez and P.J. Phillips, Polymer Engineering and Science, 1996, 36, 5, 703. 14. D. Blundell and B. Osborne, SAMPE Quarterly, 1985, 17, 1. 15. Y. Lee and R. Porter, Macromolecules, 1988, 21, 9, 2770. 16. M. Day, T. Suprunchuk, J. Cooney and D. Wiles, Journal of Applied Polymer Science, 1988, 36, 5, 1097.

29

Update on the Technology and Applications of Polyaryletherketones

17. J. Chalmers, W. Gaskin and M. Mackenzie, Polymer Bulletin, 1984, 11, 5, 433. 18. A. Jonas, R. Legras and J. Issi, Polymer, 1991, 32, 18, 3364. 19. Y. Lee and R. Porter, Macromolecules, 1987, 20, 1336. 20. D. Blundell, Polymer, 1987, 28, 13, 2248. 21. D. Bassett, R. Olley and I. Raheil, Polymer, 1988, 29, 10, 1745. 22. S. Chang, Polymer Communications, 1988, 29, 138. 23. P. Cebe, Journal of Materials Science, 1988, 23, 10, 3721. 24. Y. Lee, R. Porter and J. Lin, Macromolecules, 1989, 22, 4, 1756. 25. M. Lattimer, J. Hobbs, M. Hill and P. Barham, Polymer, 1992, 33, 18, 3971. 26. K. Kruger and H. Zachmann, Macromolecules, 1993, 26, 19, 5202. 27. B. Hsiao, K. Gardner, D. Wu and B. Chu, Polymer, 1993, 34, 19, 3996. 28. C. Bas, P. Battesti and N. Alberola, Journal of Applied Polymer Science, 1994, 53, 13, 1745. 29. R. Verma, V. Velikov, R. Kander, H. Marand, B. Chu and B. Hsiao, Polymer, 1996, 37, 24, 5357. 30. T. Ko and E. Woo, Polymer, 1996, 37, 7, 1167. 31. R. Verma, H. Marand and B. Hsiao, Macromolecules, 1996, 29, 24, 7767.

30

Characterisation

32. C. Fougnies, P. Damman, D. Villers, M. Dosière, and M.H.J. Koch, Macromolecules, 1997, 30, 5, 1392. 33. D. Ivanov and A. Jonas, Macromolecules, 1998, 31, 14, 4546. 34. W. Wang, J. Shulz and B. Hsiao, Journal of Macromolecular Science Physics, 1998, B37, 5, 667. 35. D. Ivanov, R. Legras and A. Jonas, Polymer, 2000, 41, 10, 3719. 36. B. Sauer, W. Kampert, N. Blanchard, S. Threefoot and B. Hsiao, Polymer, 2000, 41, 3, 1099. 37. G. Georviev, P. Dai, P. Cebe and M. Capel, Journal of Materials Science, 2001, 36, 6, 1349. 38. C. Wei, M. Chen and F. Yu, Polymer, 2003, 44, 26, 8185. 39. M. Jenkins, J. Hay and N. Terrill, Polymer, 2003, 44, 22, 6781. 40. J. Devaux, D. Delimoy, D. Daoust, R. Legras, J. Mercier, C. Strazielle and E. Nield, Polymer, 1985, 26, 13, 1994. 41. P. Cross, P. McGrail, H. Colquhoun, F. Paoloni, P. Hodge and M. Ioannis, inventors; Cytec, assignee; GB2449750, 2008. 42. J. Devaux, D. Daoust, R. Legras, J. Dereppe and E. Nield, Polymer, 1989, 30, 1, 161. 43. R. Abraham, I. Haworth, A. Bunn and A. Hearmon, Polymer, 1990, 31, 4, 728. 44. R. Abraham, I. Haworth, A. Bunn and A. Hearmon, Polymer, 1990, 31, 1, 126. 45. R. Abraham, I. Haworth, A. Bunn and A. Hearmon, Polymer, 1989, 30, 11, 1969.

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Update on the Technology and Applications of Polyaryletherketones

46. R. Abraham, I. Haworth, A. Bunn and A. Hearmon, Polymer, 1988, 29, 6, 1110. 47. A. Bunn, British Polymer Journal, 1988, 4, 307.

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3

Properties and Processing of Unfilled Polyaryletherketones

3.1 Introduction Polyaryletherketones (PAEK) are generally described as hightemperature polymers. However, most PAEK applications rely on a combination of properties which extend well beyond temperature performance. Having said that, most ‘high-performance’ polymers are also high-temperature polymers and there are good reasons why that would be so. For example, it is difficult to have excellent frictional wear performance in a polymer that melts at low temperatures. The producers of PAEK typically publish properties and processing literature for each of their product grades which emphasise design data and precise use instructions. These should always be consulted. In this chapter we will review the basic properties and processing of PAEK but with an emphasis on underlying principles. Properties quoted are generally taken from manufacturers’ literature. Specific design numbers can always be obtained from producer websites and will, in any case, depend on the precise grade. Relative ease of processing is a property of PAEK which is often taken for granted. However, if PAEK were as hard to process as some polyimides or fluoropolymers then their market would be a lot smaller. PAEK are justifiably described as the highest performance true thermoplastic materials.

33

Update on the Technology and Applications of Polyaryletherketones

3.2 Properties 3.2.1 Thermal Performance The thermal performance of polymers is described in terms of both short- and long-term effects and can result from changes which are physical or chemical. Short-term performance is often expressed in terms of heat distortion temperature (HDT). This measures the temperature at which a material distorts by a certain amount under a particular stress. HDT provides less information than a plot of flexural modulus versus temperature but is convenient for quick comparisons of materials. In amorphous and unfilled crystalline materials HDT is close to Tg. In crystalline materials HDT can be enhanced to temperatures close to the melting point by the addition of reinforcing fibres. Table 3.1 summarises Tg, Tm and HDT values for some reinforced and unreinforced PAEK.

Table 3.1 Thermal properties of commercial PAEK PAEK

Tg/°C

Tm/°C

HDT unfilled/°C

HDT 30% glass/°C

PEEK

143

343

152

328

PEK

157

374

165

360

PEKEKK

162

387

172

380

PEKK* (crystalline)

163

360

175

*Note that PEKK chemistry is quite versatile. For example Polymics produce a grade of PEKK with a Tg of 172 °C In common with other plastics the effective modulus (deflection under load) of PAEK will change as a function of time, load and temperature. Creep modulus data in the form of strain measured as a function of time and temperature under a particular stress should be available from all suppliers of PAEK. The ratio of stress to strain then

34

Properties and Processing of Unfilled Polyaryletherketones

gives the apparent creep modulus which can be used in calculations relating to that temperature, time and stress. Thermochemical stability at elevated temperature is often characterised by a continuous use temperature (CUT) also known as relative temperature index (RTI) as defined by Underwriters Laboratory. This is basically the temperature at which 50% of properties are retained after 100,000 hours, although the data may be related to shorter periods. It is important to know which property was measured. Values for PAEK are typically in the range 180 to 260 °C depending on the property used and this can limit the range of suitable applications more than Tm or HDT. CUT is useful for comparisons between materials. Both aromatic C–H and C=O groups are more oxidatively stable than aliphatic C–H groups. In general, to achieve a high CUT a polymer should not contain aliphatic C–H. Some materials have high HDT but disappointing CUT for exactly this reason. For example, many Nylons have high melting points but relatively low CUT. PAEK only contain groups that exhibit a relatively high degree of oxidative stability. PAEK will degrade at elevated temperatures - especially in the presence of air. Degradation has been studied by a number of workers [1-6]. The mechanism is believed to involve homolytic scission at ether and carbonyl links followed by abstraction of hydrogen and inter- and intramolecular radical combination to produce crosslinks and furan derivatives. The non-volatile residue gradually loses hydrogen and oxygen and tends towards a black carbon-like char. In nitrogen at 500 °C there is a brief induction period followed by volatilisation of about 30% of the polymer. The volatile products contain phenol, dibenzofuran and various H- and OH-terminated oligomers, some of which contain furan units. The residual black ‘char’ material is rich in carbon and deficient in oxygen and hydrogen. Typical reactions are as follows: –Ar–O–Ar– m –Ar–OU + UAr– –Ar–CO–Ar– m 2ArU + CO

35

Update on the Technology and Applications of Polyaryletherketones

–ArU + –Ara– m –ArH + –AraU– –ArU + –AraU– m –ArAra< Crosslink Dibenzofuran units are formed by intramolecular radical combination. The presence of air leads to much faster rates of degradation due to the formation and decomposition of hydroperoxides: –ArH + O2 m –ArOOH –ArOOH m –ArOU + UOH Autoacceleration takes place in the presence of air due to the decomposition of ROOH. ROOH decomposition is classically accelerated by heat, light and metal ions such as cobalt, iron, manganese and copper which can provide electrons to the process: ROOH + Cu (II) m Cu(I) + H+ + ROOU ROOH + Cu(I) m Cu (II) + −OH + ROU We might also expect that any impurity that decomposes via radical processes more readily than PEEK would serve to initiate and accelerate degradation. These types of oxidative degradation reaction are classically represented in terms of two autoaccelerating, interacting cycles which may be interrupted at a variety of points. However, many standard stabilisers are too volatile and/or too unstable to operate well at PEEK processing temperatures.

3.2.2 Mechanical Properties Table 3.2 gives typical mechanical properties for PAEK. However, these are room temperature properties. It is interesting to note that by comparison with other engineering polymers they are very good

36

Properties and Processing of Unfilled Polyaryletherketones

but not exceptionally so. It is the retention of these properties at high temperatures and in aggressive environments that makes PAEK exceptional. Three Victrex grades of PEEK are included in the table to illustrate the effect of molecular weight. The grade code is roughly proportional to viscosity at moderate shear rates and so molecular weight increases in the order 90 < 150 < 450. It can be seen that this is reflected in an increasing elongation to break and notched Izod impact strength. However, tensile strength and modulus are slightly higher for lower molecular weights. This possibly reflects the higher level of crystallinity achieved in moulding lower molecular weight materials (they crystallise faster and hence the process starts at higher temperatures where more energy is available to rearrange entanglements into crystals).

Table 3.2 Mechanical properties of unfilled PAEK PEEK 90 G

PEEK 150 G

PEEK 450 G

PEK PEKEKK

PEKK (crystalline)

Tensile strength (MPa)

110

110

100

110

115

110

Tensile elongation (%)

15

25

45

20

20

12

Flexural modulus (GPa)

4.3

4.3

4.1

4.1

4.1

4.5

Unnotched Izod impact

No break

No break

No break

Notched Izod impact (kJ/m/m)

4.5

5.0

7.5

No break 6.0

6.0

Note that all data are based on ISO test methods except for PEKK which is based on ASTM methods.

37

Update on the Technology and Applications of Polyaryletherketones

The fatigue performance of PAEK is very good and this arises from their crystalline nature. The most important grades are available with elevated temperature fatigue data. Many applications rely on the ability of PAEK to survive in high-temperature fatigue environments in the presence of chemical solvents and gases. High-temperature environmental fatigue data are relatively hard to come by and the industry often relies on experience and application-specific testing. This has created a tendency to stick to known grades and sources of product once success in a particular application has been demonstrated. Wear resistance is excellent because of the relative hardness, resistance to fatigue and temperature and chemical resistance of PAEK. Wear resistance is important not just in applications such as thrust washers and gears but also in applications where generation of wear particles could become a problem. This applies in fields as diverse as silicon wafer manufacture [7] and bearing surfaces in orthopaedic implants [8]. In many plastics tribological failure is a result of melting, and the high melting point of PAEK is a particular benefit. Wear data are typically expressed as a wear rate at a given pressure and velocity and for a given counterface. Wear tests may also involve lubricants or exposure to different chemicals. Often the wear face temperature is uncertain and depends on the thermal characteristics of the specimen and test rig. This means that wear test data never represent fundamental material properties and are always dependent on test conditions. Many PAEK producers and speciality compounders have invested in wear test rigs to produce application-specific data. Special wear grades are available and these are discussed in Section 4.2.

3.2.3 Chemical Resistance The failure of plastics in chemical environments may occur through dissolving, swelling, environmental stress cracking (ESC) or actual chemical attack. Dissolving, swelling or ESC can be predicted by consideration of the materials solubility parameters but there are always limitations to this approach. The chemical resistance of PAEK

38

Properties and Processing of Unfilled Polyaryletherketones

was reviewed in a RAPRA report published in 1995 [9]. The semicrystalline structure of PAEK resists swelling and ingress of chemical environments and the dissolution of crystals is energetically unfavourable. It is important to ensure that components have achieved an adequate degree of crystallinity. If necessary this crystallinity can be increased through annealing. Factors such as loading, stress concentrations and residual stress from moulding can be very important. Materials suppliers produce extensive tables showing resistance to chemicals at various temperatures and stress levels. As etherketones, PAEK have superb resistance to hydrolysis - in contrast to many polymers based on hydrolysable groups, such as esters, amides and imides. There are extensive data for important classes of environment. These include automotive fluids, oilfield environments, jet fuel, hydraulic fluids, refrigerants and materials used in semiconductor processing. However, these tables often provide little or no explanation of the underlying mechanisms. There are several important classes of chemical which will attack PAEK. These include the following. UÊ >œ}i˜ÃÊqÊ Àœ“ˆ˜i]ÊV…œÀˆ˜iÊ>˜`Êy՜Àˆ˜iÊV>˜Ê>Ê>ÌÌ>VŽÊ*
Ê as would be expected from their ability to halogenate aromatic rings. UÊ -ÌÀœ˜}Ê>Vˆ`ÃÊqÊ*
ÊV>˜Ê«iÀvœÀ“ÊÜiÊˆ˜ÊÜi>ŽÊ>Vˆ`ÃÊLÕÌÊÛiÀÞÊÃÌÀœ˜}Ê acids can dissolve PAEK. Sometimes this is due to protonation of carbonyl groups but in other cases there is actual reaction at the aromatic rings. Often this involves a classic electrophilic attack. Concentrated sulfuric acid dissolves and sulfonates PEEK under mild conditions but forcing conditions are required to sulfonate phenylene groups which are deactivated by carbonyl or sulfone - as in PEK, for example. Concentrated nitric acid can nitrate PEEK. PAEK can also be attacked by Lewis acids such as FeCl3 - presumably by interaction with the carbonyl group. UÊ "݈`>̈ÛiÊ i˜ÛˆÀœ˜“i˜ÌÃÊ qÊ /…iÊ …ˆ}…‡Ìi“«iÀ>ÌÕÀiÊ œÝˆ`>̈ÛiÊ degradation of PEEK was discussed in Section 3.2.1. PAEK can

39

Update on the Technology and Applications of Polyaryletherketones

also be degraded by agents such as ozone. UÊ ˆ}…‡Ìi“«iÀ>ÌÕÀiÊ >Àœ“>̈VÃÊ qÊ
ÌÊ Ìi“«iÀ>ÌÕÀiÃÊ VœÃiÊ ÌœÊ ˆÌÃÊ melting point PEEK will dissolve in certain aromatic esters and ketones and materials such as benzophenone, diphenylsulfone and chloronaphthalene. Parachlorophenol dissolves PEEK at modest temperatures and solutions of chlorophenol/dichlorobenzene or phenol/trichlorobenzene have been used as solvents for gel permeation chromatography (GPC). PAEK will show some susceptibility to ESC in aromatic solvents at elevated temperatures and may even be slowly eroded by slight solubility effects. UÊ
“ˆ˜iÃÊqÊ*
ÊV>˜ÊLiÊ>ÌÌ>VŽi`ÊLÞÊܓiÊ>“ˆ˜iÃʇÊÃÕV…Ê>ÃÊ>˜ˆˆ˜iÊ at elevated temperatures. UÊ -œÛi˜ÌÃÊ̅>ÌÊV>˜Êˆ˜`ÕViÊVÀÞÃÌ>ˆÃ>̈œ˜ÊqÊ
ʏ>À}iʘՓLiÀʜvÊ«>«iÀÃÊ [10-16] report the solvent-induced crystallisation of amorphous PEEK. Most of these solvents operate by reducing Tg of the PEEK to below ambient temperature which then allows crystallisation. They typically have an H–C–X functionality, where X is electron withdrawing. Examples include chloroform, methylene chloride, tetrahydrofuran and chlorotoluene. Such solvents tend to have an enhanced ability to cause ESC in crystalline PEEK. Solvent crystallisation is an interesting phenomenon but, so far, has limited industrial application.

3.2.4 Radiation Resistance PAEK show excellent resistance to gamma rays, electrons, protons and neutrons. This is because the delocalisation of bonding electrons in the aromatic rings makes it unlikely that high-energy particles will break the polymer chain or create a free radical at or adjacent to the ring. The radiation resistance of PEEK has been well characterised for applications as diverse as nuclear power plants and satellites in geosynchronous orbit [17]. However, the environment of the radioactive exposure also has a significant effect. A number of papers

40

Properties and Processing of Unfilled Polyaryletherketones

have been published which look at the chemistry of radioactive degradation in vacuum and in the presence of oxygen. In particular Sasuga of the Japanese Atomic Energy Research Institute published a series of detailed studies [18-24]. As we would expect oxygen becomes involved in the free radical degradation mechanism and enhances the degradation process. Resistance to ultraviolet radiation is limited. This is because of the strong absorption of ultraviolet by the aromatic species. It can be addressed by coating the PAEK components or to some extent by incorporating ultraviolet absorbers of reflectors. Unfortunately many standard ultraviolet stabilisers are too volatile or lack the thermal stability required to work well in PAEK.

3.2.5 Fire, Smoke and Toxicity PAEK do not support combustion in air, have very low smoke emission and burn in excess oxygen to produce non-toxic gases such as carbon dioxide and water. This contrasts sharply with many other highperformance polymers which can produce highly toxic combustion products such as fluorochemicals, sulfur dioxide and nitrogencontaining compounds. PEEK 450 G has a V-0 flammability rating to 1.45 mm and extremely low smoke emission in National Bureau of Standards smoke chamber tests. However, the limiting oxygen index (LOI) of PEEK is not especially high (35%) in comparison to many other high-performance polymers. Fire performance can be enhanced by the addition of fillers [25] and the overall constructions used. Table 3.3 gives cone calorimetry data for unfilled PEEK at a variety of heat fluxes [26].

41

42 135

293

42

82

433

499

77.4

75

78

218

281

82

65.1

50

NI

NI

NI

NI

NI

No ignition (NI)

25

Smoke (m2/kg1)

Total heat release (MJ/m2)

Time to ignite (s)

Time (s)

Mass loss (%)

Heat flux (kW/m2)

Peak rate of heat release (kW/m2)

Table 3.3 Cone calorimetry results for unfilled PEEK [27]

Update on the Technology and Applications of Polyaryletherketones

Properties and Processing of Unfilled Polyaryletherketones

3.2.6 Purity A large number of PAEK applications require high degrees of product purity both in terms of metals and volatile organic components (outgassing). At first sight it is not obvious that PAEK should be very pure materials. They are condensation polymers made with large quantities of alkali metal salts or Lewis acids in volatile organic solvents such as diphenylsulfone. However, PAEK can be very pure due to the efficiency of the extraction processes used in their manufacture. Standard grades of Victrex PEEK pass the outgassing requirements of ASTM E 595-84 and contain low levels of residual metals. These properties help make PEEK ideal for applications in which contamination is critical. An early example was the use of PEEK in transport and storage wafer carriers for silicon wafer manufacturing. The high purity coupled with low wear particle generation was shown to lead to a higher yield of silicon wafer devices [7]. In addition there are more recent ultrapure grades in which metals are typically less than 1 ppm and residual polymerisation solvents have been reduced still further [27].

3.2.7 Electrical Properties PAEK can be used as good electrical insulators in a wide range of environments and over a wide range of temperatures. The polar nature of the carbonyl group means that materials such as fluoropolymers have superior dielectric constants and dissipation factors. However, relative to fluoropolymers, PAEK insulation offers lower toxicity in fire situations and more resistant mechanical properties. PAEK can have a relatively low comparative tracking index which measures susceptibility to electrical breakdown on the surface of an insulator. Possibly this reflects the relatively easy degradation of PAEK to carbonaceous char.

43

Update on the Technology and Applications of Polyaryletherketones

3.3 Processing Techniques 3.3.1 Background As true thermoplastics, PAEK can be processed using virtually all the standard technologies. In the early days many machines could not reach the required temperatures but there are now a very large number of competent processors. PAEK can be injection and compression moulded, extruded into film, sheet and fibre, powder and dispersion coated, blow moulded, laser sintered, converted into thermoplastic composites, welded, metallised, adhesively bonded and machined [28]. The generic principles of good thermoplastic processing invariably apply to PAEK. This section concentrates on concepts which are specific to PAEK. Processing of specific products, such as coatings or films, is covered in Chapter 4. The major manufacturers publish helpful and detailed processing guides. There are a number of academic studies of injection moulding which use techniques such as microbeam X-ray diffraction to investigate intricate structural variations in injection moulding [29-32] and orientation processes.

3.3.2 Drying PAEK typically absorb around 0.5% moisture. This has a negligible effect on properties and will not cause chemical changes during processing. However, it will cause splay marks and other processing problems. Accordingly PAEK are typically dried for 3 hours at 150 °C or 2 hours at 160 °C before processing.

3.3.3 Processing Temperatures, Thermal Stability and Rework Melt temperatures are typically 35 to 60 °C above the melting point but care is needed to avoid excessive thermal history - especially with higher melting point PAEK. At lower temperatures self-nucleation

44

Properties and Processing of Unfilled Polyaryletherketones

effects may become evident and lead to variation. Manufacturers will provide specific guidelines but under normal conditions the melt viscosity of PAEK is usually within the range typical of other thermoplastic materials. Each manufacturer will provide recommendations on thermal stability and acceptable hold times. In general PAEK should be expected to be reasonably stable - especially in the absence of air and metals such as copper. The stability of PAEK means that they can often be readily reworked and recycled - although in filled compounds the normal issues of progressive fibre breakage will apply. Recycled material may be found to contain higher levels of char particles or discoloration than virgin material.

3.3.4 Crystallisation and Annealing For injection moulding it is common to recommend mould temperatures of at least 160 °C to ensure the crystallisation of PEEK. Higher temperatures (e.g., 180 °C) are often preferable. PAEK with higher Tg will require correspondingly higher mould temperatures. Shrinkage will be a function of crystallinity and therefore will depend on tool temperature. Manufacturers publish grade-specific shrinkage values as a function of processing conditions. Shrinkages of 1.2 to 2.3% are typical for unfilled materials and are much lower, but often more anisotropic, for filled materials. The precise shrinkage always depends on process conditions and so moulds can be made slightly smaller than calculated and then adjusted accordingly. The crystallisation-induced shrinkage of PAEK can limit dimensional tolerances and give rise to problems with warpage. In some circumstances this can be an advantage for blends with amorphous materials and also materials such as PEKK. Annealing processes can be used to increase crystallinity in a poorly moulded part, to increase crystallinity to improve strength and chemical resistance, to remove stress before and after machining and to remove thermal history and so limit dimensional changes with

45

Update on the Technology and Applications of Polyaryletherketones

temperature. The components should be dry and heating and cooling should be slow to avoid distortion and stress. Hold temperatures are determined by objective. High temperatures are used to maximise crystallinity, whereas a temperature just above the use temperature is used to remove thermal history. A temperature just above Tg can be used to crystallise amorphous material. At high temperatures there is some risk of surface oxidation and embrittlement.

3.3.5 Orientation The most common orientation process is used to produce fibres and is described in research disclosures from ICI, academic literature and manufacturer processing guidelines. Melt spun fibres of PEKEKK have exhibited moduli as high as 13 GPa [33]. There are also a number of academic references to oriented material which, as expected, shows enhanced mechanical performance. Techniques such as solid-state extrusion [34] and die drawing have been applied to PEEK and a modulus of 11 GPa has been obtained [35]. Orientation processes are similar to those used for polyethylene terephthalate but there are some key differences in terms of orientation-induced crystallisation [36, 37]. The creation of biaxially oriented PEEK films was originally described by ICI [38] and has been extensively investigated by later workers [39]. Usually this involves a two-stage biaxial stretching. The first stage is achieved using stretching rolls and the second using a tenter frame stretcher. Finally the film is heat set under stress.

3.3.6 Surface Treatment and Joining Technologies PAEK can be both adhesively bonded and welded [40]. PAEK can be welded using standard techniques such as hot plate, friction and near field ultrasonic welding. However, high-energy inputs will be required to melt the polymer. Organisations such as the Welding Institute have published a number of papers in the field.

46

Properties and Processing of Unfilled Polyaryletherketones

Surface treatment prior to adhesive bonding typically consists of surface roughening and may be followed by acid etching or plasma, corona, ultraviolet or laser treatments. These increase surface functionality and improve bond strength. There are a number of recommended adhesives which are often based on epoxy resin chemistry. However, it should be remembered that many adhesives do not offer the very high-temperature performance of PAEK. It is worth noting that there is a considerable literature on highly controlled surface modifications of PAEK. These utilise chemical modification of the carbonyl and phenylene groups and can allow the attachment of various effect molecules, for example bioactive groups.

3.3.7 Laser Sintering Laser sintering of PAEK is a relatively recent development. EOS has launched a grade of PEEK powder which is suitable for this process [41]. Powder is built into a solid part by local melting using a focused laser beam. The parts are created layer by layer. Complex, highly accurate geometries can be achieved using three-dimensional computer-aided design data.

References 1.

J. Hay and D. Kemmish, Polymer, 1987, 28, 12, 2047.

2.

R.B. Prime and J.C. Seferis, Journal of Polymer Science, Part C: Polymer Letters, 1986, 24, 12, 641.

3.

A. Jonas and R. Legras, Polymer, 1991, 32, 15, 2691.

4.

M. Day, D. Sally and D.M. Wiles, Journal of Applied Polymer Science, 1990, 40, 9, 1615.

47

Update on the Technology and Applications of Polyaryletherketones

5.

M. Day, J.D. Cooney and D.M. Wiles, Journal of Applied Polymer Science, 1989, 38, 2, 323.

6.

M. Day, T. Suprunchuk, J.D. Cooney and D.M. Wiles, Journal of Applied Polymer Science, 1988, 36, 5, 1097.

7.

P. Jones, I. Emani, J. Goodman and K. Mikkelsen, Microcontamination, 1993, 29.

8.

J. Devine, inventor; Invibio Ltd, assignee; GB2435648A, 2006.

9.

G. Pritchard, Anti-Corrosion Polymers: PEEK, PEKK and orther Polyaryls, Rapra Review Report No.80, Rapra Technology, Shawbury, Shrewsbury, UK, 1995.

10. J. Hay and D. Kemmish, Polymer, 1988, 29, 4, 613. 11. B. Stuart and D. Williams, Polymer, 1994, 35, 6, 1326. 12. G. Mensitieri, A. Apicella, M. Del Nobile and L. Nicolais, Journal of Reinforced Plastics and Composites, 1993, 12, 11, 1138. 13. G. Mensitieri, A. Apicella, M. Del Nobile and L. Nicolais, Polymer Bulletin, 1991, 27, 3, 323. 14. G. Mensitieri, A. Apicella, M. Del Nobile, L. Nicolais and F. Garbassi, Journal of Materials Science, 1990, 25, 6, 2963. 15. G. Mensitieri, A. Apicella, M. Del Nobile and L. Nicolais, Polymer Engineering Science, 1989, 29, 24, 1786. 16. E. Stober, J. Seferis and J. Keenan, Polymer, 1984, 25, 12, 1845. 17. J. Funk and G. Sykes, SAMPE Quarterly, 1988, 19, 3, 19. 18. T. Sasuga and M. Hagiwara, Polymer, 1987, 28, 11, 1915.

48

Properties and Processing of Unfilled Polyaryletherketones

19. E. Hagazy, T. Sasuga, T. Nishii and T. Seguchi, Polymer, 1992, 33, 14, 2904. 20. E. Hagazy, T. Sasuga and T. Seguchi, Polymer, 1992, 33, 14, 2911. 21. O. Yoda, Polymer Communications, 1984, 25, 238. 22. T. Sasuga and M. Hagiwara, Polymer, 1987, 28, 11, 1915. 23. T. Sasuga, Polymer, 1988, 29, 9, 1562. 24. T. Sasuga and M. Hagiwara, Polymer, 1986, 27, 6, 821. 25. D. Kemmish and R. Leibfried, inventors; Victrex, assignee; WO01/62841 A2, 2001. 26. D. Kemmish in Proceedings of BCC Conference on Advances in Flame Retardency of Polymer Materials, Stamford, CT, USA, 1991. 27. J. Devine, S. Green, D. Kemmish and B. Wilson, inventors; Victrex, assignee; US7160980, 2002. 28. F. Mata, V. Gaitonde, S. Karnik, J. Paulo Davim, Journal of Materials Processing Technology, 2009, 209, 1980. 29. C.M. Hsiung and M. Cakmak, Journal of Applied Polymer Science, 1993, 47, 1, 125. 30. C.M. Hsiung, M. Cakmak and J.L. White, Polymer Engineering Science, 1990, 30, 16, 967. 31. C.M. Hsiung and M. Cakmak, Journal of Applied Polymer Science, 1993, 47, 1, 149. 32. Y. Ulcer, M. Cakmak and C. Hsiung, Journal of Applied Polymer Science, 1995, 55, 8, 1241.

49

Update on the Technology and Applications of Polyaryletherketones

33. C.M Hsiung and M. Cakmak, Polymer Engineering Science, 1991, 31, 3, 172. 34. Y. Lee, J.M. Lefebvre and R.S. Porter, Journal of Polymer Science: Polymer Physics Edition, 1988, 26, 4, 795. 35. A. Richardson, F. Ania, D.R. Rueda, I.M. Ward and F. Baltá Caleja, Polymer Engineering Science, 1985, 25, 6, 355. 36. D. Blundell, A. Mahendrasingam, D. McKerron, A. Turner, R. Rule, R. Oldman and W. Fuller, Polymer, 1994, 35, 18, 3875. 37. F. Daver, A. Blake and M. Cakmak, Macromolecules, 2009, 42, 8, 2626. 38. B. Griffin and I. Luscombe, UK Patent Office Research Disclosure No. 21601, 1981 and RD No. 20216, 1982. 39. M. Cakmak and M. Simhambhatla, Polymer Engineering Science, 1995, 35, 19, 1562. 40. S. Green, K. Cartwright and S. Mycock in Proceedings of Medical Polymers, Dublin, Ireland, 2004. 41. F. A. M. Pfister and M Leuterer inventors, EOS Assignee, US 2008/0258330

50

4

Product Forms

4.1 Standard Powders and Granules Unfilled polyaryletherketones (PAEK) are typically supplied as powders or granules - typical properties are listed in Chapter 3. Compounds will have been through a melt-compounding process and will be granular in form. Granules are easier to feed in many processes such as injection moulding. Unfilled granules may have been filtered to reduce the level of gels and black speck present in the product. PAEK are typically available in a range of viscosities. For example, Victrex polyaryletheretherketone (PEEK) is available as 450, 380, 150 and 90 grades. A lower number indicates a lower molecular weight and viscosity. It should be noted that short-term properties may not be the most sensitive indicator of molecular weight effects, and requirements such as long-term fatigue performance or complex environmental resistance should always be taken into account. In general the author believes that it is best to use the highest useable molecular weight. However, there are exceptions: it is not necessarily the case in processes that require high degrees of filler or fibre wetting, low degrees of fibre breakage or low process forces. It should also be noted that some granular grades are designed to be especially suitable for particular processes. For example, some Victrex grades (e.g., 380) are particularly suitable for extrusion processes in which very low levels of gels and black speck are required. Standard particle size powders are typically used as a feedstock for processes such as extrusion and compression moulding. There are

51

Update on the Technology and Applications of Polyaryletherketones

also fine powders which are used in products such as coatings which will be discussed later.

4.2 Compounds PAEK compounds contain fibres, fillers and other effect additives. A range of compounds is available from PAEK producers and general compounders. There are also speciality products produced by a number of custom compounders - such as RTP and Lehman and Voss. Polymics produces compounds based on PEEK, PEKK and their new high temperature PAEKs. As true thermoplastics, PAEK can be compounded using conventional single-screw and twinscrew equipment. The normal effects of fillers and additives apply in PAEK as they do in other thermoplastics. However, temperature is an important limitation. Many fillers, additives, fibre treatments, etc., are too volatile or thermally unstable to be used at 400 °C. In some cases these problems could be overcome by redesign of the molecules, for example to reduce volatility, but the size of the PAEK market is relatively small and so relatively unattractive to additive developers. Table 4.1 summarises some properties of compounds produced by Victrex plc. Glass and carbon fibres are the commonest reinforcements and are available in a range of base resin viscosities. The effects are exactly as expected. Carbon produces the highest strength and modulus with a relatively low density. Lower viscosity grades of PAEK allow for higher filler content with less fibre breakage and so the tensile strength and modulus of 90GL30 are somewhat higher than for 450GL30. However, longer term properties such as fatigue strength might benefit more from increased molecular weight. Figures A1-A4 in Appendix 1 show the fatigue performance, yield strength as a function of temperature, specific strength and coefficient of thermal expansion for a number of PAEK compounds and composites. Some of the standard ICI compounds have been extensively characterised in terms of their engineering design properties [1].

52

190

180

220

240

240

250

350

200

250

200

PEEK 150GL30

PEEK 450GL30

PEEK 90 GL60

PEEK 150CA30

PEEK 450CA30

PEEK 450CA40

PEEK HMF 40

PEK22 GL30

PEK 22 CA30

PEKEKK 45GL30

335 328 343 339 336 –

9.0 10 9.5 6.5 8.0 8.5

50 60 45 40 45 40

368 380

8.0 11

45 70

22

2.2

11.0

360 11 70

11

2.9

2.5

349 -

36

28

23

23

23

11.3

1.3

1.6

1.7

1.5

1.4

2.7

12.0

335

8.5

40

12.0

2.3 2.5

HDT (°C)

Notched Izod (kJ/m2)

Unnotched Izod (kJ/m2)

Flexural modulus (GPa)

Tensile elongation (%)

GL = glass fibre; CA = carbon fibre. Number after CA or GL = fibre content (%). PEEK molecular weight: 450 > 150 > 90 (150 and 90 are easy-flow grades). HMF grades combine high-flow resins with special compounding technology to achieve increased strength, stiffness and fatigue performance. Note that the grade codes are trademarks of Victrex plc.

190

Tensile strength (MPa)

PEEK 90GL30

Material

Table 4.1 Properties of some Victrex compounds

Product Forms

53

Update on the Technology and Applications of Polyaryletherketones

Long-fibre-reinforced compounds are available from organisations such as RTP. These materials are tough and yet lightweight and are particularly suitable for metal replacement. Long-fibre compounds might be expected to offer improved impact resistance, better creep and modulus retention at high temperature, improved dimensional stability and improved resistance to warpage as a result of reduced shrinkage. RTP and Oxford Performance Polymers offer compounds of polyaryletherketoneketone (PEKK). Glass bubbles can be used to reduce weight but there are also high specific gravity grades. Other fillers such a talc and mica reduce shrinkage and coefficients of expansion which can be useful in low-warpage grades. Fillers can be used to reduce the coefficient of thermal expansion such that it is comparable to that of metals. This can help with the direct replacement of metal components. Special wear grades are available. These are typically reinforced with carbon fibre and contain lubricants such as graphite and polytetrafluoroethylene (PTFE). Recently Victrex has introduced PTFE free wear grades. Various studies have related the wear of PEEK compounds to mechanical properties [2]. Aramid fibres are sometimes used to reduce counterface wear and fluoropolymer synthetic oils are also used. The processing temperatures of PAEK can push the thermal stability limits of fluoropolymers and suitable ventilation is required. PTFE is effective as an internal lubricant since it coats the wear surfaces and dramatically reduces the coefficient of friction. Graphite is often used in the presence of an external lubricant. A typical generic wear grade of PAEK might contain 10-15% of each of carbon fibre, graphite and PTFE (e.g., 15% carbon fibre and 15% PTFE). Some suppliers of such compounds quote a single wear factor for a given product of pressure and velocity. However, the failure mechanism depends on the combination of pressure and velocity. It has been shown that under high-pressure, low-velocity conditions, wear is predominantly cohesive. Under conditions of low pressure and high velocity (but the same overall pressure × velocity) the specific wear rate is much lower and this is due to an interfacial wear mechanism with polymeric film transfer [3]. Comparisons have been made using

54

Product Forms

pressure and velocity conditions relevant to real applications - such as automotive powertrains. Materials such as Victrex PEEK 450FC30 compare well with competing products [4]. Analysis of wear debris can show evidence of thermal oxidative degradation of PAEK under failure conditions [5]. The wear performance of PAEK compounds can be further improved by blending with polybenzimidazole; this blend is described later. Conductive compounds are very important in electronic applications. Many silicon chip and wafer handling processes require wellcontrolled static dissipation. This can be achieved using a variety of conductive fillers including milled carbon fibre, carbon black, metal fibres, indium tin oxide-coated glass and carbon nanotubes [6-10]. In general conductive compounds fall into three resistivity ranges. Definitions vary but, in general, 109-1011 ohm/sq is said to be ‘antistatic’, 107-109 ohm/sq is ‘dissipative’ and less than 106 ohm/sq is conductive. Often a particular resistivity range is required for the application. This can be difficult to achieve since resistivity changes rapidly as the filler concentration approaches the percolation threshold (roughly the point at which each fibre touches at least one other fibre to form a continuous conducting network). Various strategies have been developed to reduce this effect but it is often found that the precise resistivity also depends on the moulding conditions and the level, dispersion and distribution of the filler at the point in the moulding actually being measured. Nevertheless statically dissipative PAEK are a very important class of compounds. There are a number of manufacturers of conductive PEEK compounds. Victrex produces materials in the antistatic and dissipative ranges including a non-carbon-based, low out-gassing dissipative material. RTP manufactures a range of glass-reinforced and high-purity carbon nanotube compounds which are controlled to within narrow ranges of resistivity. Coloured materials and masterbatches can be obtained from a variety of compounders including RTP and Colorant Chromatics. Other speciality PAEK compounds include radio opaque, antimicrobial, magnetic, laser markable and authentication grades.

55

Update on the Technology and Applications of Polyaryletherketones

4.3 Composites The term PAEK composite generally means a continuous fibre reinforced material and mostly refers to continuous carbon fibre reinforced products. These can come as unidirectional tape or woven cloth which is then used to form melt-processed components. Whereas compounds can be produced using standard twin-screw extrusion technology, the production of PAEK composites usually involves a proprietary process. Some processes do little more than bring the PAEK into contact with the fibre and leave the final forming process to individually wet the carbon fibres with polymer. Such products are relatively low cost and simple to produce but it can be difficult to make void-free, high-quality parts. The more advanced processes use a variety of techniques to produce low-void products in which there is a strong interface between the polymer and the fibre and a high degree of fibre distribution and wetting. It is possible to crudely assess the quality of the product by snapping a piece of tape and looking for loose fibre and evidence of fibre pull-out. Higher quality tapes will tend to break cleanly and show little evidence of unwetted fibres. More sophisticated tests involve polishing sections and microscopic examination. It is important to realise that mechanical properties in the fibre direction will be dominated by the fibre and may not be very sensitive to the quality of the impregnation. Accordingly it is useful to measure transverse properties such as transverse flexural and transverse tensile strength as a method of assessing the quality of pre-impregnated tape. Other key tests include damage tolerance measurements such as damage area and compression after impact. Impregnation methods include: UÊ `ˆÀiVÌʓiÌʈ“«Ài}˜>̈œ˜ÊQ££RÆ UÊ «ÀœViÃÃiÃÊ>ÃÈÃÌi`Ê܈̅Êۜ>̈iÊ«>Ã̈VˆÃiÀÃÊQ£ÓRÆ

56

Product Forms

UÊ «œÜ`iÀʈ“«Ài}˜>̈œ˜]ÊiˆÌ…iÀÊiiVÌÀœÃÌ>̈VʜÀÊ>µÕiœÕÃÊ`ˆÃ«iÀȜ˜Ê [13–17]; and UÊ wLÀiÊVœ‡“ˆ˜}ˆ˜}ÊQ£n]Ê£™R° The early technology (known as APC2) was pioneered by ICI and is now owned by Cytec. Cytec also acquired the DuPont technology and now offers a product range that includes both PEEK and PEKK. Other suppliers include Tencate (which acquired Phoenix TPC), Suprem (formerly Gurit and before that Sulzer), Schappe (comingled products), Toho Tenax and Ticona. Typically uniaxial preimpregnated sheet is around 120 to 100 μm thick. Recently Mitsuya has produced a 40 μm product using PEEK film which allows even more design flexibility. The benefits of thermoplastic composites include: UÊ …ˆ}…‡ÛœÕ“i]ʏœÜ‡VœÃÌʓ>˜Õv>VÌÕÀˆ˜}Ê«ÀœViÃÃiÃÆ UÊ i>ÃiʜvÊÀiVÞVˆ˜}Æ UÊ …ˆ}…Ê̅iÀ“œ«>Ã̈VÊ̜Õ}…˜iÃÃÊ>˜`Ê`>“>}iÊ̜iÀ>˜ViÆ UÊ ˜œÊÅivʏˆviʈÃÃÕiÃÆ UÊ ˜œÊ V…i“ˆÃÌÀÞÊ œVVÕÀÀˆ˜}Ê `ÕÀˆ˜}Ê «>ÀÌÊ v>LÀˆV>̈œ˜]Ê ˜œÊ ۜ>̈iÊ organic compounds; and UÊ Üi`ˆ˜}]ÊvÕȜ˜ÊLœ˜`ˆ˜}Ê>˜`ÊÀi«>ˆÀ° Table 4.2 summarises some basic properties of PEEK-based APC2 thermoplastic composites from Cytec. The properties of finished components can be tailored by controlling fibre orientation during the layup process. Full characterisation of a thermoplastic composite will include measurement of in-plane shear properties, open hole tensile and compressive failure, interlaminar fracture toughness and compression after impact. Cytec also produces TPC based on PEKK [20].

57

Update on the Technology and Applications of Polyaryletherketones

Table 4.2 Properties of PEEK thermoplastic composites In fibre direction

In transverse direction

Tensile strength (MPa)

2070

86

Failure strain

1.45

0.88

Tensile modulus (GPa)

138

10.2

2900

60

Failure strain

1.5

–

Tensile modulus (GPa)

172

10

AS4 carbon fibre

IM7 carbon fibre Tensile strength (MPa)

In spite of their advantages PAEK thermoplastic composites have made relatively slow progress since their invention in the 1980s. In many cases this has been due to a lack of fabrication technology and competition from newer toughened thermosets. PAEK also face competition from polyphenylene sulfide (PPS) composites which are much less expensive but have some limitations in terms of Tg and toughness. PPS composite parts have found a large number of aerospace applications – including the leading edges of Airbus wings. There are also industrial and oilfield applications which will be discussed later in this review. High-volume fabrication should be a key advantage for thermoplastic composites over thermosets. Conventional techniques include press lamination, autoclave lamination and thermoforming. Thermoforming can convert flat consolidated sheets into complex shapes. Autoclave lamination requires the use of expensive bagging materials (such as Kapton polyimide), lengthy heating and cooling cycles and expensive autoclaves. Accordingly a number of automated processes have been developed which do not need autoclaves.

58

Product Forms

In fibre placement with in situ consolidation, a robot lays down tape onto a tool as it is heated with hot gas, infrared radiation or lasers and is consolidated in situ. This process is operated by companies such as Automated Dynamics and Accudyne. Much effort has been put into perfecting the consolidation process which requires relatively voidfree and smooth tapes [21-24]. Other processes use automated layup (e.g., the FibreForge Relay Station) followed by press consolidation and thermoforming. Xperion Aerospace has created a continuous compression moulding process which can be used to make rails, beams and profiles. Icotec has developed a ‘composite flow moulding’ process [25] which allows the moulding of pultruded rods into articles such as screws, fasteners and bone plates while maintaining fibre length and orientation.

4.4 Films Film can be produced using a conventional single-screw extruder and coathanger die, preferably with closed loop control of thickness. The crystallinity of the film is controlled using the temperature of the casting rolls. PEEK films were first marketed by the ICI Stabar films group. Thicknesses were available down to about 25 μm, and a variety of processing techniques such as thermoforming were developed. More recently films have been produced by Ajedium, Lipp Terler and Sumitomo. In 2003 Ajedium launched a 6 μm film product. In 2007 Victrex started to produce Aptiv PEEK film in a range of thicknesses from 6 to 750 μm. The film is also available as tape coated with silicone or acrylic adhesives. Thicker sheet products are available from suppliers such as Ensinger and RTP. In June 2009 Oxford Performance Materials introduced OXPEKK Permetta film at thicknesses down to 25 μm in both amorphous and crystalline forms. PEEK film competes with polyimide and PTFE. In comparison to PTFE it offers much higher strength, modulus, abrasion and creep

59

Update on the Technology and Applications of Polyaryletherketones

resistance and lower density. The comparison with polyimide is more complex. PEEK has similar electrical, physical and thermal ageing performance. It offers lower moisture absorption which allows more stable properties and improves resistance to thermal shock. Hydrolysis resistance and resistance to strong alkalis are further advantages. PEEK films are available in very low thicknesses. The permeability of PEEK film to gases such as carbon dioxide, helium, hydrogen, nitrogen, oxygen and water vapour is also relatively low. Amorphous film can be thermoformed by heating to a temperature close to or above Tg for a few seconds. If the process is quick enough and if the tool temperature is below Tg then amorphous mouldings can be produced. However, longer heating times and higher tool temperatures will produce crystalline parts. The thermoforming of crystalline films requires temperatures close to the melting point and higher powered heaters. Adhesion to the film can be enhanced by surface treatment. The conventional method is corona discharge but more recently atmospheric pressure oxygen plasma treatments have been developed. The film can also be vacuum metallised to improve barrier performance, coated with copper for surface conductivity or with more advanced coatings such as sapphire. Mineral fillers can be used to provide higher modulus and to the control coefficient of thermal expansion in relation to particular coatings or specific applications.

4.5 Fibres Fibres were originally developed by ICI Fibres and the technology is now owned by Zyex Ltd in the UK. Zyex produce a wide range of monofilament, multifilament and staple fibres and can make hollow monofilaments and tubes. PEEK is the most common material but PEK and PEKK can also be used. The fibres are manufactured by extrusion and orientation and have good mechanical properties with

60

Product Forms

high strengths. They compete with fibres such as Kevlar, Vectran, polybenzimidazole (PBI) and PBO. Kevlar, PBO and PBI are nonmelting materials and offer obvious advantages in protective, fireresistant clothing. Kevlar and Vectran offer high orientation and very high strength due to their rigid rod character. However, PEEK fibres can have advantages in terms of chemical resistance (especially to hydrolysis and alkalis), flexural fatigue and abrasion resistance.

4.6 Fine Powders and Coatings Large particle size powders are used for processes such as compression moulding, but PAEK can also be obtained in a range of sizes down to about 10 μm [26] from suppliers such as Evonik and Victrex. These can be used for powder and dispersion coating and carbon composite impregnation. Victrex produces Vicote coatings for both powder and aqueous dispersion applications [27]. The coatings offer all the properties expected of PAEK. Abrasion and wear resistance can be exceptional – far superior to that of fluoropolymer coatings. Special wear-resistant [28] and electrostatic dissipative grades have been developed and there is a product line based on PEK [29]. Recently it has been claimed that coating performance in terms of adhesion, cracking and processability onto concave surfaces can be improved by using a base layer of amorphous PEKK [30]. A wide range of coating techniques can be used with fairly standard equipment. These include conventional electrostatic powder and dispersion spraying techniques and also flame spraying. Flame spraying is a one-step process in which the powder passes through a flame that melts the polymer particles before they are deposited on the substrate surface. This removes the size and location restrictions imposed by the use of ovens and offers much greater design freedom. Both Victrex and Evonik offer flame spray technology and collaborate with suppliers of flame spray equipment. A key requirement of PAEK coating is to avoid contamination with other materials since these can degrade at process temperatures and lead to defects in the coatings.

61

Update on the Technology and Applications of Polyaryletherketones

4.7 Stock Shapes Stock shapes can be made by extrusion or by compression moulding – although some smaller shapes are injection moulded. They can be used for prototyping, small production runs and even quite largevolume applications if the machining costs are acceptable. Companies such as Ensinger, Quadrant, Advanced Polymer Technologies, Vertec and Gehr produce a range of PEEK polymer and compound stock shapes. A wide range of sizes is available.

4.8 Foams Zotefoams and Victrex have collaborated to produce PEEK foams. The process uses Zotefoam’s nitrogen saturation technology to impregnate granules which are then used in conventional injection moulding equipment or in extrusion to produce foamed components [31]. According to the 2008 MuCell applications guidelines from Trexel, PEEK foams well with Mucell supercritical gas foaming technology.

References 1.

D. Moore, J. Smith and S. Turner, Plastics, Rubber and Composites Processing and Applications, 1994, 21, 1, 19.

2.

Z. Zhang, C. Breidt, L. Chang and K. Friedrich, Tribology International, 2004, 37, 3, 271.

3.

I. Griffiths, D. Kemmish, P. Tweedale, M. Morgan and R. Weidig in Proceedings of the SAE International Congress, Detroit, MI, USA, 1997, 970658.

4.

I. Griffiths, D. Kemmish and M. Morgan in Proceedings of the SAE International Congress, Detroit, MI, USA, 1998, 980716.

62

Product Forms

5.

M. Zhang, Z. Lu and K. Friedrich, Tribology International, 1997, 30, 2, 103.

6.

J. Sandler, P. Werner, M. Shaffer, V. Demchuk, V. Altstadt and A. Windle, Composites: Applied Science and Manufacturing, 2002, 33, 8, 1033.

7.

J. Sandler, P. Werner, M. Shaffer, R. Jaskulka, O. Jacobs, V. Altstadt and A. Windle, Wear, 2004, 257, 9, 1006.

8.

J. Sandler, P. Werner, M. Shaffer, R. Verdejo, F. Wollecke and V. Alstadt, Advanced Materials, 2005, 17, 23, 2864.

9.

J. Sandler, A. Windle, P. Werner, V. Alstadt and M. Shaffer, Journal of Materials Science, 2003, 38, 10, 2135.

10. D. Bangarusampath, H. Ruckdaschel, V. Altstadt, J. Sandler, D. Garray and M. Shaffer, Polymer, 2009, 50, 5803 11. F. Cogswell and D. Hezzell, inventors; ICI, assignee; US4549920, 1982. 12. F. Cogswell and U. Measuria, inventors; ICI, assignee; US4624886, 1985. 13. S. Mills, inventor; Philips Petroleum, assignee; US4900499; 1988. 14. J. O’Connor, J. Geibel and W. Beever, inventors; Philips Petroleum, assignee; US4792481, 1986. 15. D. Soules, inventor; Philips Petroleum, assignee; US5019427, filed 1989. 16. A. Vodermayer, J. Karger and H. Erlach, inventors; Sulzer, assignee; US6277238, 1999. 17. A. Vodermayer, J. Karger, H. Erlach and S. Kaufmann, inventors; Sulzer, assignee; US6372294, filed 1999.

63

Update on the Technology and Applications of Polyaryletherketones

18. P. McMahon and T. Chung, inventors; Hoechst Celanese, assignee; US4799985, 1986. 19. P. McMahon, T. Chung and L. Ying, inventors; Hoechst Celanese, assignee; US4818318, 1986. 20. J. Pratte, J. Bai and D. Leach in Proceedings of the 37th SAMPE Technical Conference, Seattle, WA, USA, 2005. 21. M. Lamontia and M. Gruber in Proceedings of 2007 SAMPE Conference, Baltimore, MD, USA, 2007. 22. M. Lamontia, M. Gruber, J. Tierney, J. Gillespie, B. Jensen and R. Cano in Proceedings of 2009 SAMPE Europe Conference, Paris, France, 2009. 23. A. Wood, D. Padey, J. Walling, R. Lenferink, S. Wijskamp, R. Day and J. Benn, SAMPE 2008, Long Beach, CA, USA, 2008. 24. R. Becker, A. Nettles, R. Bucinell, R. Langone and J. Mondo, SAMPE 2001, Long Beach, CA, USA, 2001. 25. U. Loher, J. Mayer, P. Tognini, T. Wegener and E. Wintermantel, inventors; Amsler Peter, assignee; WO96/19336, 1995. 26. A. Lucke and D. Steidl, inventors; Hoechst, assignee; US5247052, 1992. 27. I. Beckwith and J. Robinson, inventors; Victrex, assignee; WO2005/023893A2, 2004. 28. J. Robinson, inventor; Victrex, assignee; GB2437830, 2007. 29. B. Wilson and J. Robinson, inventors; Victrex, assignee; GB2425495, 2006. 30. T. Hsu, D. Berry and G. Butler, inventors; Polymics, assignee; WO2009/058362A1, 2008. 31. N. Witten and I. Tollett, inventors; Zotefoams, assignee; WO2006/100517A1, 2006. 64

5

Competitive Materials

5.1 Introduction More than 30 years after their invention, polyaryletherketones (PAEK) are present in almost every industry sector. However, world sales are only around 3000 tonnes per year. The high price (around £40 per kilogram) means that alternative materials will be used if possible. In some applications even more expensive polymeric materials such as polybenzimidazole or polyimides must be used to meet performance requirements. This chapter briefly reviews the main classes of competitive material and identifies, in general terms, their typical strengths and weaknesses. It should then be clear why PAEK are the material of choice as each of the application segments is reviewed in Chapters 7 and 8. Table 5.1 compares some of the basic properties of typical competitive materials. A more extensive review of many of these materials can be found in reference [1]. Here, emphasis is given to the more recent developments.

65

66

160

17-28

Polybenzimidazole

Polytetrafluoroethylene (PTFE)

25

86

Polyimide

Perfluoroalkoxy (PFA)

207

Polyphenylene

23

152

Polyphenylene (injection mouldable)

Fluorinated ethylene propylene (FEP)

85

152

120

Extem TPI

Polyphenylene sulfide

20

105

Polyetherimide

Polyamideimide

60

84

Polyethersulfone

300

325

~300

3.0

7.5

–

–

8

3.0

60

100

76

Polyphthalamide

100

100

0.6

0.6

0.2

6.5

3.1

8.3

6.0

5.0

3.7

3.5

3.3

2.6

2.3

3.9

>95

>95

>95

58

53

49

55

45

47

47

47

38

35

49

435

360

154

151

278

105

242

200

203

121

160

260

204

260

–

260

–

–

220

200–240

170

180

165

250

305

260

327

–

–

–

–

–

280

–

–

–

315

340

2.15

2.15

2.2

1.3

1.43

1.21

1.21

1.42

1.35

1.37

1.27

1.37

1.13

1.32

Tensile Flexural Limiting Tensile Continuous Tm//oC Density (g/cm3) Heat strength/ elongation/% modulus/ oxygen use distortion MPa index GPa temperature temperature (LOI)/% (HDT)/oC (CUT)/oC

Polyaryletheretherketone (PEEK)

Polymer

Table 5.1 Typical properties of unfilled competitive polymers (data from reference [1] and manufacturers’ literature) Update on the Technology and Applications of Polyaryletherketones

Competitive Materials

5.2 Amorphous Sulfones and Thermoplastic Polyimides Polyarylethersulfones are manufactured by companies such as Solvay, BASF and Sumitomo under trade names such as Udel, Radel, Epispire, Ultrason and Sumicaexcel. They are manufactured by nucleophilic polyetherisation routes in which the key monomer is usually dichlorodiphenylsulfone. In fact the chemistry is quite similar to that used in the manufacture of PAEK and the old ICI Victrex group manufactured both PAES and PAEK products. However, dichlorodiphenylsulfone is much less expensive than difluorobenzophenone. Accordingly PAES polymers can be much less expensive than PAEK. Tg values are typically in the range 180225 °C but the more advanced sulfones can have values around 265 °C. Thermoplastic imides are manufactured by Sabic under the trade names Ultem and Extem. Ultem (Tg of 217 °C) has been available for many years but Extem is a relatively recent family of sulfone-containing imides [2]. Extem offers very high Tg (up to 311 °C) together with relatively good chemical resistance for an amorphous resin. These materials have higher stiffness than PAEK between Tg of the PAEK and Tg of the sulfone or etherimide. The performance of the PAEK can be improved by adding reinforcing fibres but there remain some applications in which this performance window is critical. Since they are amorphous they undergo less shrinkage on cooling and this leads to better dimensional tolerance and stability. They are also relatively transparent. However, amorphous resins tend to have much lower chemical resistance, inferior fatigue performance and will lose useful properties immediately above Tg. These limitations of amorphous resins mean that it is usually obvious when a PAEK is required.

5.3 Polyphenylene Sulfide Polyphenylene sulfide (PPS) is a relatively inexpensive material made by the reaction of sodium sulfide and dichlorobenzene. It

67

Update on the Technology and Applications of Polyaryletherketones

has Tg of about 90 °C, a melting point of around 280 °C and is highly crystalline. Flow properties can be excellent, and over the years improved grades have offered increased molecular weight and toughness. Chemical resistance is broadly similar to PAEK and the LOI of 47% is significantly higher. However, toxic sulfur dioxide is produced in fire situations. In many ways PPS can be regarded at a low-temperature version of PAEK although with perhaps less toughness, greater flow and a greater tendency to flash in moulds. Chemical resistance and many key properties decrease significantly above Tg (90 °C).

5.4 High-temperature Polyamides When PAEK were first introduced they were often described as very high temperature polyamide (‘Nylon’)-like materials. However, there are some key differences. PAEK do not absorb large amounts of water, do not undergo hydrolysis and do not contain aliphatic hydrocarbon groups that tend to reduce long-term temperature stability and CUT. Until recently high-temperature Nylons have been based on hexamethylene terephthalamide (6T) units. However DSM has announced the introduction of Nylon 4T which is based on tetramethylene terephthalamide [3]. This may offer slightly higher temperature performance than 6T but the key differences with PAEK will remain.

5.5 Polyphenylenes Poylphenylenes were originally developed by Maxdem in California and subsequently by Mississippi Polymer Technologies (MPT). More recently MPT was bought by Solvay and the product is now sold under the trade name of Primospire. A pure paraphenylene would lack processability and so has to be substituted with phenylketone and/or copolymerised with unsubstituted metaphenylene [4-6]. In this way it is possible to produce both extrusion and injection

68

Competitive Materials

moulding grades. The advantages of polyphenylenes include: UÊ ÛiÀÞʅˆ}…ÊÃÌÀi˜}̅Ê>˜`ÊÃ̈vv˜iÃÃÊ܈̅œÕÌÊÀiˆ˜vœÀVi“i˜ÌÆÊ̅iÞÊ>ÀiÊ œvÌi˜ÊÀiviÀÀi`Ê̜Ê>ÃÊÃiv‡Àiˆ˜vœÀVˆ˜}Ê«œÞ“iÀÃÊ­-,*®Æ UÊ …ˆ}…ÊVœ“«ÀiÃÈÛiÊÃÌÀi˜}Ì…Æ UÊ œÕÌÃÌ>˜`ˆ˜}ʓiV…>˜ˆV>Ê«iÀvœÀ“>˜Viʈ˜ÊVÀޜ}i˜ˆVÊVœ˜`ˆÌˆœ˜ÃÆ UÊ ˆ˜…iÀi˜ÌÊy>“iÊÀiÈÃÌ>˜ViÊ­"ÊHÊx䯮Ê>˜`Ê>L>̈ÛiÊ«iÀvœÀ“>˜ViÆ UÊ V…i“ˆV>Ê ÀiÈÃÌ>˜ViÊ Ü…ˆV…Ê ˆÃÊ iÝVi«Ìˆœ˜>Ê vœÀÊ >˜Ê >“œÀ«…œÕÃÊ “>ÌiÀˆ>]ʜÕÌ«iÀvœÀ“ˆ˜}ÊܓiÊVÀÞÃÌ>ˆ˜iʓ>ÌiÀˆ>Ãʈ˜Ê>Vˆ`ÃÆ UÊ ˆÃœÌÀœ«ˆVÊ «iÀvœÀ“>˜ViÊ >˜`Ê `ˆ“i˜Ãˆœ˜>Ê ÃÌ>LˆˆÌÞÊ vÕÀ̅iÀÊ enhanced by low moisture absorption and coefficient of thermal iÝ«>˜Ãˆœ˜Æ UÊ ÌÀ>˜Ã«>Ài˜ÌÊ}À>`iÃÊ܈̅ÊiÝVi«Ìˆœ˜>ÊÃÕÀv>ViÊ}œÃÃɓˆÀÀœÀÊw˜ˆÃ…Ê >˜`Ê>iÃ̅ïVÃÆÊ>˜` UÊ `œÊ˜œÌʅ>ÛiʏˆµÕˆ`ÊVÀÞÃÌ>ˆ˜iÊV…>À>VÌiÀÊ>˜`ÊÜÊ`œÊ˜œÌÊŜÜÊ«œœÀÊ weld line strength, transverse properties, compressive strength or a fibrillated structure. Primospire has a fairly low HDT and the loss of properties above Tg is a disadvantage. With reinforcement (e.g., glass or carbon fibre) PAEK can match and exceed many of the properties of Primospire. However, the disadvantages of such reinforcement can include: UÊ >˜ˆÃœÌÀœ«Þ]Ê̜iÀ>˜ViÃÊ>˜`Ê`ˆ“i˜Ãˆœ˜>ÊÃÌ>LˆˆÌÞÆ UÊ ˆ˜viÀˆœÀÊÃÕÀv>ViÊw˜ˆÃ…Æ UÊ Vœ˜Ì>“ˆ˜>̈œ˜ÊLÞÊÀiˆ˜vœÀVi“i˜ÌÊÜi>ÀÊ«>À̈ViÃÊ­ŽiÞʈ˜Ê“i`ˆV>Ê >««ˆV>̈œ˜ÃÊ>˜`ÊÌiiÌÀœ˜ˆVÃ®Æ UÊ >LÀ>Ȝ˜Ê`ÕiÊ̜ÊwLÀiÃÊ­iëiVˆ>ÞÊ}>ÃîÆ

69

Update on the Technology and Applications of Polyaryletherketones

UÊ >}˜ïVÊ Àiܘ>˜ViÊ ˆ“>}ˆ˜}Ê ­,®Ê >˜`Ê 8‡À>ÞÊ ˆ“>}ˆ˜}Ê >ÀÌiv>VÌÃÆ UÊ œÜiÀÊiœ˜}>̈œ˜Ê>˜`ʈ“«>VÌÊ«iÀvœÀ“>˜ViÆ UÊ ˆ˜VÀi>Ãi`Ê`i˜ÃˆÌÞʇÊ܅ˆV…Ê“ˆ}…ÌÊLiÊVÀˆÌˆV>Êˆ˜Ê>iÀœÃ«>ViÆÊ>˜` UÊ iiVÌÀœ“>}˜ïVÊňi`ˆ˜}ÊivviVÌð Accordingly it is not difficult to identify niches where polyphenylenes would be favoured over PAEK.

5.6 Thermotropic Liquid Crystalline Materials Thermotropic liquid crystalline polyesters (TLCP) such as DuPont’s Zenite or Ticona’s Vectra have unique properties because a very high degree of orientation can develop under the action of shear. This arises because of the presence of rigid groups in the polymer backbone (often based on hydroxybenzoic acid) which form ordered domains in which the chains are aligned in the same direction. In general the advantages of TLCP are as follows: UÊ ÛiÀÞʅˆ}…ÊyœÜʈ˜ÌœÊ̅ˆ˜ÊÃiV̈œ˜ÃÆ UÊ Ã…œÀÌʓœÕ`ÊVœœˆ˜}Ê̈“iÃÊ܈̅ʘœÊy>ň˜}Æ UÊ œÜÊVœivwVˆi˜ÌÃʜvÊ̅iÀ“>ÊiÝ«>˜Ãˆœ˜]ʏœÜʓœˆÃÌÕÀiÊ>LÜÀ«Ìˆœ˜Ê >˜`ʅˆ}…Ê`ˆ“i˜Ãˆœ˜>ÊÃÌ>LˆˆÌÞÆ UÊ œÜÊy>““>LˆˆÌÞ]ÊӜŽiÊ>˜`Ê̜݈VÊ}>ÃÊi“ˆÃȜ˜Æ UÊ …ˆ}…ÊÀ>`ˆ>̈œ˜ÊÀiÈÃÌ>˜ViÆ UÊ …ˆ}…Ê /Ê>˜`Ê 1/Æ UÊ œÜÊ«iÀ“i>LˆˆÌÞÆ UÊ }œœ`ÊV…i“ˆV>ÊÀiÈÃÌ>˜ViÊ̜ʜÀ}>˜ˆVÊ܏Ûi˜ÌÃÆÊ>˜`

70

Competitive Materials

UÊ Vœ“«>̈LˆˆÌÞÊ܈̅ÊÃÕÀv>ViʓœÕ˜ÌÊÌiV…˜œœ}Þ]ʈ˜VÕ`ˆ˜}ʏi>`‡vÀiiÊ solder processes. However, the mouldings tend to be highly anisotropic, have low weld line strength and low toughness with a fracture behaviour resembling that of wood. As polyesters, TLCP are susceptible to hydrolysis by acids and bases.

5.7 Perfluoropolymers Fluoropolymers with fully fluorinated backbones can have high CUT and melting points. PTFE was the first commercially available fluoropolymer. Fluorine is a larger atom than hydrogen and forms a close-packed protective spiral around the carbon backbone. The resulting lack of polarity leads to very weak interchain interactions. Consequently PTFE is a very soft, low-friction material with a tendency to creep at low temperatures. In fact very high molecular weights are required to develop good mechanical properties and so the melt viscosity of PTFE is too high to be processed by conventional thermoplastic techniques. PTFE is processed using techniques which are similar to those used in powder metallurgy. PTFE has excellent chemical resistance (generally better than PAEK) and excellent ultraviolet resistance but is remarkably soft, weak and lacking in abrasion resistance and resistance to hard radiation. It is much more frequently used in compressive applications than those which require tensile or flexural performance. All fluoropolymers have a high LOI but produce toxic fumes in fire situations. FEP contains CF3 side groups due to copolymerisation with 10-12% hexafluoropropylene. The side groups tend to lock together and improve mechanical properties at processable molecular weights. FEP can be processed by extrusion, and its creep performance is better than that of PTFE. However steric stress due to the bulky side group reduces the CUT from 260 to 200 °C. PFA introduces a perfluoroalkoxy side chain - typically OC3F7. PFA can be injection moulded. Both PFA and FEP have PTFE-like chemical resistance and

71

Update on the Technology and Applications of Polyaryletherketones

are remarkably soft and weak by comparison to PAEK.

5.8 Amide Imides Torlon polyamideimide is produced by Solvay. It has a high melt viscosity and is reactive in the melt state. It can be moulded using heavy-duty injection moulding machines but must then be solid-state polymerised which increases HDT by about 30 °C and more than doubles the tensile strength. Tg is 275 °C and the HDT typically ranges from 278 to 284 °C depending on the grade. It is resistant to most common hydrocarbon and chlorinated solvents but can degrade in steam or hot caustics. It can also be attacked by some acids and amines. It can blister if the temperature is increased rapidly after it has absorbed moisture. However, it can have very good friction and wear performance and is used in many metal replacement applications.

5.9 Non-melting Imides DuPont markets a number of polyimides produced using the reaction of pyromellitic dianhydride and di-(4-aminophenyl)ether. These include grades of Kapton film and Vespel sintered parts. (It should be noted that Vespel is a trade name used for a number of very high performance materials including thermoplastics that are beyond the scope of this review. Here we concentrate on the classic materials such as the S grades.) Non-melting polyimide is typically a very highperformance material with no glass transition or melting point. HDT is about 360 °C and some parts can function continuously up to 260 and 315 °C in an inert atmosphere. However, these materials cannot be extruded or injection moulded and shapes are made by processes involving sintering and machining or direct forming to produce near net shape parts. Fillers such as graphite, PTFE and molybdenum disulfide can be used to obtain excellent wear performance. Radiation and fire resistance are excellent and outgassing very low. However, imides tend to be susceptible to hydrolysis by high-temperature water and to attack by alkalis and concentrated acids. The ideal

72

Competitive Materials

application has been described as a sliding electromechanical device which is exposed to radiation in a vacuum at a continuous working temperature of 315 °C. In this sort of situation non-melting polyimide can outperform PAEK. However, lack of processability affects part economics, especially for large production volumes.

5.10 Polybenzimidazole Polybenzimidazole is sold by PBI Performance Products under the trade name Celazole. It is one of those materials that, in many ways, outperforms PAEK. When it was first discovered it was described as having the processability of brick dust. However, a proprietary sintering process using temperatures in excess of 400 °C and metallurgical pressures has been developed. The resin can be moulded into stock shapes or directly moulded into finished articles. It is expensive. It finds application in seals and bearings, high-temperature industrial processes and as leading edges and ablative heat shields. There are also high-purity and electrostatic dissipative grades for electronic and silicon wafer manufacturing applications. Moulded polybenzimidazole has the highest compressive strength of any unfilled resin (400 MPa), Tg of 427 °C and HDT of 435 °C. It can withstand temperatures of 700 °C for several minutes. The LOI is 58%. However, it is degraded in hot aqueous acids. Polybenzimidazole can be solution spun into fibre and is extensively used in fightfighters’ clothing and other fire blocking applications.

References 1.

D. Kemmish, High Performance Engineering Plastics, Rapra Review Report No.86, Rapra Technology, Shrewsbury, Shawbury, UK, 1995.

2.

R. Odle and R. Galluci, Gallucci in Proceedings of the 61st SPE Antec Conference, Nashville, TN, USA, p.1853.

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Update on the Technology and Applications of Polyaryletherketones

3.

,°Ê,ՏŽi˜ÃÊ>˜`Ê,°Ê Àœ“L>V…]ʈ˜Ûi˜ÌœÀÃÆÊ -Ê*Ê
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5.

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6.

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74

6

Polyaryletherketone Blends

6.1 Introduction There have been many attempts to combine the performance advantages of polyaryletherketones (PAEK) with other materials. Blends may offer lower cost and/or be used to enhance some aspects of performance. It is a tribute to the processability and stability of PAEK that they can be used to improve the flow and processability of other high-temperature materials. Some blends are commercially successful. However, cost reduction can sometimes come with a complex mix of property trade-offs. End users may prefer to use a pure PAEK which has been characterised over many years. In addition specialist blends with complex formulations can have the effect of tying an end user to a single supplier. Successful blends are also limited to polymers which can survive the high processing temperatures associated with PAEK. There are some references to blends with nylons or polycarbonates in which we might question the process stability of the materials used. Thermal and morphological stability should be carefully checked when evaluating any PAEK blend. Not surprisingly the most frequently blended materials are those high-temperature polymers reviewed in Chapter 5.

6.2 Blends with Polyarylethersulfones Blends of PAEK and polyarylethersulfones (PAES) [1, 2] offer the potential for reduced cost, lower mould shrinkage and lower

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Update on the Technology and Applications of Polyaryletherketones

warpage but perhaps with somewhat reduced chemical resistance and, possibly, reduced fatigue resistance at higher levels of PAES. PAES and polyaryletheretherketone (PEEK) are not miscible but are fairly compatible. It is possible to form a fine dispersion of PAES in PAEK and so maintain a reasonable level of chemical resistance. The blends may also benefit from the higher modulus of PAES above Tg of PAEK. The organisations that produce their own PAES are best placed to use this technology because they have access to the raw material at cost. Without this advantage the production cost of PAEK has to be compared with the selling price of PAES. Solvay has recently filed a patent on fibre-reinforced blends of PAEK with polyphenylsulfones [2]. It appears to the author that PAES/PAEK blends may be the basis of some of Solvay Avaspire ‘modified PEEK’ product range and indeed some distributor literature describes Avaspire as PEEK/PPSU (polyphenylsulfone). Polyphenylene sulfide (PPS) is another possible component of some of these reduced cost but high performing blends - see Section 6.4. Solvay produces wear grades of Avaspire and Avaspire reinforced with glass and carbon fibres. These materials can offer more attractive economics than pure PEEK. Solvay states that material cost can be 30% lower but with the same mechanical performance and chemical resistance. Avaspire grades can be aimed at the cost-performance gap between PEEK and other high-performance crystalline polymers such as PPS, liquid crystalline polyesters (LCP) and high-temperature nylons. There can be property improvements in areas such as ductility. It is also possible to transetherify mixtures of PAEK and PAES, producing block copolymers [3]. Presumably these materials could be used to improve blend compatibility.

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PAEK Blends

6.3 Blends with Thermoplastic Imides 6.3.1 Polyetherimide (PEI) Many PAEK (e.g., PEEK, PEK) are miscible with PEI (Ultem) in all proportions [4, 5]. The result in an increase in Tg, reduced crystallisation rate, very little change in melting point and reduced overall crystallinity. Miscible polymer blends are fairly unusual and the PEEK/PEI combination has been extensively investigated [6-8]. The PEI (which is amorphous) has to be excluded from the crystalline phase and so crystallisation tends to further increase Tg due to the increased PEI content in the amorphous material. Depending on the crystallisation conditions there may be some evidence of phase separation of PEEK and PEI, or the creation of PEI-enriched regions. Table 6.1 gives melting point, Tg and heats of fusion for various PEEK/PEI compositions [4]. Interestingly the PEEK crystallinity seems to increase as PEI is added - probably due to the dilution effects of the PEI on PEEK chain entanglement.

Table 6.1 Thermal properties of PEEK/PEI blends PEEK (%)

Tg (°C)

Tm (°C)

100

142

343

80

155

340

70

161

340

60

168

340

50

176

340

40

183

340

0

215

–

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Update on the Technology and Applications of Polyaryletherketones

Blends of PAEK and PEI can offer increased Tg, good chemical resistance at the lower PEI levels and reduced cost relative to pure PAEK. In particular PEI can be used to build the heat distortion temperature (HDT) of PAEK. Such blends find uses where PAEKlike performance is required in combination with an improved HDT. There are also applications in which the PEI is used above its Tg as a melt adhesive. For example, laminates of copper foil and PEEK/ PEI blend films can be produced in which the copper adheres to the hot, amorphous blend which subsequently crystallises to produce a chemical and solder-resistant structure. Mitsubishi has produced flexible printed circuit boards based on this concept [9]. There are also situations in which PEI has been used to compatabilise PAEK with other PEI-miscible polymers. For example, PEN/PEI/PEEK ternary blends have been biaxially stretched [10, 11]. PEI is miscible with PEN and the PEEK is added to enhance the crystallisability of the blend and create a strain-hardening material. PEI has also been used to enhance the compatability of PEEK and polyethersulfone (PES) [12]. The PES can be encapsulated in a PEEK/PEI phase which further reduces the required amount of PAEK.

6.3.2 Extem Recently Victrex has launched an exclusive blend of PEEK and Extem called Victrex MAX Series. This appears to be based on a GE Plastics (Sabic) technology [13]. The blend offers many PEEK-like properties such as chemical resistance, hydrolytic stability, processability and wear resistance. Extem enhances performance between 150 and 275 °C (i.e., between Tg of PEEK and Tg of Extem) and improves dimensional stability.

6.3.3 Polysiloxane /Polyimides PEEK can be blended with polyimide/siloxane copolymers to produce materials with improved ductility. Such materials may be suitable

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PAEK Blends

for many applications, such as wire and cable insulation, where pure PEEK lacks the required flexibility [14].

6.4 Blends with PPS Since PPS is crystalline we should expect it to produce blends with much better chemical resistance than amorphous materials such as PAES. It should also allow very substantial cost reduction and can improve melt flow. Union Carbide filed patents on PEEK/PPS blends as early as 1982 [15]. Kureha has developed materials with improved compatibility, melt flow, formability and mechanical properties [16] Ticona has filed patents on improved PEEK/PPS blends and the most recent patent provides a good summary of the historical developments [17]. Solvay has filed patents on PEEK/PPS blends for use in bearing surfaces – under the conditions tested the blends perform as well as pure PEEK compounds [18]. It is possible that this technology is used in some of Solvay’s Avaspire grades.

6.5 Blends with Polybenzimidazole (PBI) PEEK/PBI blends were originally developed and marketed by Hoechst Celanese [19-21] and later PBI Performance Products. They have excellent properties and deliver some of the benefits of PBI in a meltprocessable form. The PBI is said to ‘immobilise’ the amorphous phase of PEEK. At the present time these blends are arguably the highest performing commercial thermoplastic materials for hightemperature wear applications. Starting in 2006, following a licence agreement with PBI Performance Products, they have been marketed worldwide as the Victrex T series and in Japan by PBI Performance Products. They are available unfilled, reinforced with glass and carbon fibre and as specially formulated wear grades. Victrex literature compares the wear factors, coefficient of friction and wear test counterface temperature very favourably with polyimides. However, melt processing requires high pressure and temperatures of around 450 °C - so these blends will only be used when conventional PAEK

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Update on the Technology and Applications of Polyaryletherketones

formulations are inadequate. Recently it has been discovered that polyaryletherketoneketone (PEKK) forms miscible blends with PBI [22]. Patents have also been filed on blends of PBI, PAEK and PEI [23].

6.6 Blends with Fluoropolymers PEEK and polytetrafluoroethylene (PTFE) are highly incompatible. However, fine PTFE powder is commonly added to PAEK to act as an internal lubricant in tribiological applications. The PTFE smears across the wear surface and reduces interfacial friction. This reduces interfacial forces and the heat build-up that can lead to failure by melting. PTFE is particularly suitable in applications where there is no external lubricant and the compounds are often reinforced with carbon fibre. PEEK can also be added to PTFE to improve the wear properties of PTFE - although other less expensive polymers can have similar effects. More recently PAEK and PTFE have been blended so as to produce melt-processable PTFE which has a number of interesting properties [24]. This is perhaps the most unlikely example of the use of PAEK to improve the melt-processability of an otherwise hard-to-process material.

6.7 Blends with Thermotropic Liquid Crystalline Polyesters (TLCP) TLCP can be used in small amounts to reduce the viscosity of many polymers [25] and reduced-viscosity products have been developed using PAEK [26]. Such blends might sometimes suffer from delamination and poor weld line strength depending on the amount of LCP used.

6.8 Blends with Polyphenylene A recent patent has reported partial miscibility of polyphenylenes

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PAEK Blends

with PEEK and an interesting combination of strength, impact resistance, stiffness, melt processablity, thermal stability and chemical resistance [27]. Possibly PAEK will find application as processing aids for polyphenylenes.

6.9 Blends with Other PAEK An unusual feature of PAEK blends is that they can be both miscible (as evidenced by a single intermediate Tg) and isomorphic (as evidenced by a single melting point). Hence PEEK can be blended with a wide range of PAEK to produce miscible and isomorphic blends - although it does not appear to be miscible with PEKK [28]. This behaviour probably results from the crystallographic equivalence of ether and ketone in the PEEK crystal structure. Miscibility and isomorphism can be used to tailor the crystallisation and melting behaviour of PAEK.

References 1.

L. Robeson and J. Harris, inventors; Union Carbide, assignee; US4624997, 1984.

2.

S. Weinberg, S. Shorrock and M. El Hibri, inventors; Solvay, assignee; US2009/0048379.

3.

I. Fukawa, T. Tanabe and H. Hachiya, Polymer, 1992, 24, 2, 173.

4.

J.E. Harris and L.M. Robeson, Journal of Applied Polymer Science, 1988, 35, 7, 1877.

5.

J. Harris, L. Robeson, M. Clifton, B. Eckstein and M. Matzner, inventors; Amoco, assignee; US5079309, 1989.

6.

A. Goodwin and G. Simon, Polymer, 1996, 37, 6, 991.

7.

H. Lee and W. Kim, Polymer, 1997, 38, 11, 2657.

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Update on the Technology and Applications of Polyaryletherketones

8.

B. Briscoe, B. Stuart and S. Rostami, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1993, 49, 753.

9.

K. Taniguchi and S. Yamada, inventors; Mitsubishi Plastics, assignee; WO02057343, 2001.

10. T. Tsunekawa, T. Toudaiji and G. Yamamura, inventors; Toray, assignee; JP2004123863. 11. X. Zhou and M. Cakmak, Polymer, 2006, 47, 18, 6362. 12. S. Rostami, inventor; ICI, assignee; US5071925, 1989. 13. A. Aneja, R. Gollucci, R. Odle and K. Sheth, inventors; GE, assignee; US0197739A1, 2007. 14. G. Haralur, G. Kailasam and K. Sheth, inventors; Cantor Colburn LLP, assignee; US0234060A1, 2009. 15. L. Robeson, inventor; Union Carbide, assignee; EP062830, 1982. 16. N. Nishihata and M. Tada, inventors; Kureha, assignee; EP1416015A1, 2003. 17. M. Ajbani, A. Auerback and K. Feng inventors; Ticona, assignee; WO 2009/128825 A1, 2009. 18. M. El-Hibri, E. Ryan, N. Harry, R. Empaynado and B. Stern, inventors; Solvay, assignee; WO2008/129059 A1, 2008. 19. L. Disano, B. Ward and E. Alvarez, inventors; Hoechst Celanese, assignee; EP0392855B1, 1990. 20. T. Andres, E. Alvarez, R. Hughes, W. Cooper and C. Wang, inventors; Hoechst Celanese, assignee; US5391605, 1993. 21. R. Hughes, inventor; Hoechst Celanese, assignee; US5844036, 1997.

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PAEK Blends

22. B. Dawkins, M. Gruender, G. Copeland and T. Hsu, inventors; PBI Performance Products, assignee; WO097709A1, 2008. 23. B. Dawkins, M. Gruender, G. Copeland and J. Zucker, inventors; PBI Performance Products, assignee; WO097675, 2008. 24. J. Lahijani, inventor, DuPont, assignee; US0016625, 2001. 25. F. Cogswell, B. Griffin and J. Rose, inventors; ICI, assignee; EP030417B2, 1980. 26. B. Wilson and D. Flath, inventors; Victrex, assignee; GB2424890, 2005. 27. N. Maljkvic, R. Chavers and M. El Hibri, inventors; Solvay, assignee; WO101847A2, 2007. 28. J. Harris and L. Robeson, inventors; Union Carbide, assignee; US4609714, 1984.

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Update on the Technology and Applications of Polyaryletherketones

84

7

Applications of Polyaryletherketones

7.1 Introduction Polyaryletherketones (PAEK) find applications in almost every industry sector with the possible exception of single-use packaging where they are much too expensive. Given the diversity of PAEK applications it seems remarkable that worldwide sales are only around 3000 tpa nearly 30 years after they were first introduced. However, they are only used when the benefits outweigh the price. This chapter reviews the main classes of PAEK applications. It is based on knowledge of the many press releases, application papers, manufacturers’ literature and presentations, conferences and trade shows over the last three decades. Emphasis is given to the newer classes of application and references are given to some of the key papers. As well as discussing applications in general terms each section gives specific examples based on recent press releases. The actual reasons for using PAEK can be very complex but an attempt is made to summarise some of the key points for each application - the lists of PAEK benefits are not exhaustive.

7.2 Industry Segmentation and Sales Volumes In general specific application examples can be classified into the following industry segments: UÊ
iÀœÃ«>ViÆ UÊ
Õ̜“œÌˆÛiÆ

85

Update on the Technology and Applications of Polyaryletherketones

UÊ "ˆÊ>˜`Ê}>ÃÆ UÊ iVÌÀœ˜ˆVÊ`iۈViÃÆ UÊ -i“ˆVœ˜`ÕV̜ÀÃÊ>˜`Ê`ˆÃ«>ÞÃÆ UÊ œœ`Ê«ÀœViÃȘ}ÆÊ>˜` UÊ œ˜ÃՓiÀ° Medical applications are discussed in Chapter 8. It is also possible to analyse applications by type (e.g., gears, valve components, etc.). To avoid repetition some application types (e.g., gears) are discussed in detail under only one industry although mention will be made of their applications across the range of industries. Victrex plc publishes annual reports which contain sales numbers by market segment and geography. In view of Victrex’s position as the leading producer, it seems likely that these reflect the position of the overall market. Figures 7.1-7.3 show Victrex’s reported sales by volume, industry sector and geography. It can be seen that Europe is the largest market. This reflects the strong automotive industry and, possibly, Victrex’s base in Europe. In 2008 Victrex reported total sales of 2625 tonnes and said that it was working on application developments with a potential annual sales volume of over 2900 tonnes.

86

Applications of Polyaryletherketones

Figure 7.1 Victrex sales volumes

Figure 7.2 Victrex sales by market segment

87

Update on the Technology and Applications of Polyaryletherketones

Figure 7.3 Victrex 2008 sales by geographic region

7.3 Aerospace Aerospace [1] was one of the earliest target application areas for PAEK. In part this was because the industry is relatively insensitive to material costs - especially if reduced component weight results in fuel savings. It was also driven by the interest in thermoplastic composites for high-performance military aircraft. Both HTX and ITX (see Chapter 1) were developed as matrix resins for military aircraft composites. "ÛiÀÊ̅iÊÞi>ÀÃÊ*
ʅ>ÛiÊ«Àœ}ÀiÃÈÛiÞÊÀi«>Vi`ʓiÌ>ÊVœ“«œ˜i˜ÌÃ]Ê traditional composites and plastics in aircraft. This has been driven by ease of fabrication, weight, mechanical properties, and resistance to jet fuels, hydraulic fluids and rain erosion together with fire smoke and toxicity performance. The limited ultraviolet (UV) resistance of PAEK has not ruled out >ÊiÝÌiÀˆœÀÊ>««ˆV>̈œ˜Ã°ÊˆiÀÃÊ>˜`ÊVœ>̈˜}ÃÊV>˜ÊLiÊÕÃi`Ê̜ÊÀi`ÕViÊ

88

Applications of Polyaryletherketones

̅iÊ ivviVÌÃÊ œvÊ 16°Ê "˜iÊ œvÊ Ì…iÊ i>ÀˆiÃÌÊ >««ˆV>̈œ˜ÃÊ Ü>ÃÊ ˆ˜iV̈œ˜Ê moulded radomes. PEEK has consistent electrical properties over a very wide range of temperatures. The radomes can be glass filled but are often unfilled on smaller high-speed aircraft. The PAEK can withstand extreme temperature variations and thermal shock as well as offering superb rain erosion resistance and resistance to impact. More recently RTP has introduced very long fibre-reinforced grades of PEEK which produce radomes with improved toughness and stiffness for high-speed launches of military weapon systems. Glass fibre-reinforced PEEK has been used to replace aluminium pylon fairings. These are low-load, non-structural parts, although good impact resistance is essential. The use of PEEK reduced both weight and cost and the fairings are some of the largest injection moulded PAEK components. A number of the fuel tank manhole covers on the A380 are made from carbon fibre-reinforced PEEK. The covers are painted with a fuel tank coating and an antistatic coating and covered with an aluminium sheet to conduct lightening strikes. PEEK was ideal because of weight reduction, ease of manufacture and dimensional stability. Glass-reinforced PEEK is used in injection moulded hubcaps on Boeing 777 aircraft. These caps, which are painted for UV resistance, must survive extremes of temperature, UV, ozone, flying debris, hard landings, jet fuel, de-icing solutions, hydraulic fluids and paint strippers. High-viscosity grades are used to ensure the impact performance of the outer walls of the hubcap whereas lower viscosity grades are used to mould internal electronic components with thinner wall sections. Inside aircraft the fire, smoke and toxicity performance of PAEK is often their key advantage versus other plastics. PAEK produce relatively little smoke and toxic gas in fire situations and they are used extensively in cabin structures. Polyaryletherketoneketone (PEKK) (often laminated with Tedlar) is used to make thermoformed cabin interior panels. Amorphous PEKK has the advantage of being thermoformable at relatively low temperatures which are compatible ܈̅ʫœÞۈ˜Þˆ`i˜iÊy՜Àˆ`iÊ­*6 ®Ê>˜`Ê̅iÊÛ>ÀˆœÕÃÊ>`…iÈÛiÃÊÕÃi`ʈ˜Ê the laminate. PEEK is found in window surrounds, passenger service units and lamp housings. Glass fibre-reinforced PEEK is used in the

89

Update on the Technology and Applications of Polyaryletherketones

hinge bracket assemblies of overhead storage compartments. In seats, PEEK has been used to replace magnesium alloy because it shows much better elastic recovery after impacts. It is used in lumbar support >`ÕÃÌiÀÃ]Ê …i>`ÀiÃÌÃÊ >˜`Ê Ãi>ÌLiÌÊ }Ո`iÃ°Ê >ÀLœ˜Ê wLÀi‡Àiˆ˜vœÀVi`Ê PEEK is used in injection moulded Airbus door handles because of its high specific strength and modulus versus aluminium. Glass fibre-reinforced PEEK is used in wire insulation stand offs to electrically isolate wire bundles while securing them to the aircraft structure. It is also used in wiring blocks. Amphenol has developed a silicon overmoulding process and produces a range of PAEK wiring and tubing clamps with silicon rubber clamping surfaces. These are 20% lighter than traditional metal clamps. PEEK cable ties are also available and Aplix has developed hook and loop fastening systems, which are likely to have applications across a range of industries. Wiring can be protected with convoluted PEEK tubing or braided tubes made from PEEK fibres. The braided tubes may also contain «œÞ«…i˜Þi˜iÊÃՏw`iÊ­**-®ÊwLÀiÃÊ̜ÊÀi`ÕViÊVœÃÌʜÀʓiÌ>ÊwLÀiÃÊÌœÊ increase mechanical and thermal performance. They are used in high-temperature aircraft engine environments. Various conduit interconnection devices are moulded from PEEK. Zodiac Aero ->viÌÞÊ -ÞÃÌi“ÃÊ …>ÃÊ «Àœ`ÕVi`Ê ˆ}…ÌÜiˆ}…ÌÊ V>ÀLœ˜Ê wLÀi‡Àiˆ˜vœÀVi`Ê backshells for the A380 leading to very substantial weight savings versus aluminium. PEEK propellers and impellers are used in a wide range of aerospace devices such as oil cooling systems and ventilation fans. The fatigue, creep and wear properties of PEEK lead to high reliability and long service lifetimes. Impeller housings have to contain debris in the event of an impeller failure and these housing can be much lighter when plastic impellers are used. PEEK is also resistant to the new }i˜iÀ>̈œ˜Êœvʈ˜ÃiV̈Vˆ`iÊyՈ`ðÊÕiÊÌ>˜ŽÊÛi˜ÌÃÊ>ÀiÊ«Àœ`ÕVi`ÊLÞʏœÃÌÊ core moulding. PEEK finds uses in unmanned aerial vehicles. The Allied Aerospace electric micro aerial vehicle uses PEEK because of its environmental resistance, low weight, mechanical properties and ease of fabrication

90

Applications of Polyaryletherketones

versus thermosets. Gas-assisted injection moulding is used to produce cost-effective components with excellent stiffness to weight ratios. -ˆÝÊ “ˆVÀœ“iÌÀiÊ *

Ê vˆ“Ê …>ÃÊ ÀiVi˜ÌÞÊ Ài«>Vi`Ê «œÞi̅ޏi˜iÊ terephthalate (PET) as a cover film for thermal-acoustic and burn̅ÀœÕ}…Ê ˆ˜ÃՏ>̈œ˜°Ê * /Ê v>ˆi`Ê Ì…iÊ ˜iÜÊ 

Ê y>“iÊ «iÀvœÀ“>˜ViÊ ÌiÃÌÃÊ>˜`Ê>ÌiÀ˜>̈Ûiʓ>ÌiÀˆ>ÃÊÃÕV…Ê>ÃÊ*6 Ê>˜`Ê«œÞˆ“ˆ`iÃÊÜiÀiÊ too dense or not available in the required film thicknesses. The film is installed using PEEK tape coated in an acrylic pressure-sensitive adhesive. PEEK fibre also finds application in high-temperature acoustic blankets based on the Helmholtz resonator effect [2].

œ“«>Ài`Ê ÌœÊ Ì…iÀ“œÃiÌÃ]Ê *
Ê Ì…iÀ“œ«>Ã̈VÊ Vœ“«œÃˆÌiÃÊ …>ÛiÊ relatively few aerospace applications. Potential application areas include fuselage panels, fasteners, floor beams, door and fuel tank access panels, spars, ribs, thermal and fire barriers and stiffeners. œÜiÀÊVœÃÌÊ**-ÊÃÞÃÌi“Ãʅ>ÛiÊLii˜ÊÀ>̅iÀʓœÀiÊÃÕVViÃÃvՏÊ>˜`Ê>ÀiÊÕÃi`Ê in the leading edges of wings and a variety of ribs, panels and beams. Generally thermoplastics are used when the need for large numbers of the same component allows cost-effective automated production. They also offer advantages in terms of toughness, damage tolerance >˜`ÊÀiVÞV>LˆˆÌÞ°Ê*
Ê>ÀiÊÕÃi`Ê܅i˜Ê**-ʏ>VŽÃÊiˆÌ…iÀÊ̅iÊÀiµÕˆÀi`Ê temperature or impact performance. Existing structures include floor panels and floor structures (e.g., on the A440M), engine thermal protection covers and air inlet struts. Icotec has developed a range of composite fasteners, bolts, nuts, inserts and brackets. These are much lighter and have higher specific strength than aluminium or titanium. They do not corrode and have properties (such as coefficient of thermal expansion) that match those of composite structures. Although generally small in size, large numbers of these components are used and very substantial weight Ã>ۈ˜}ÃÊ V>˜Ê LiÊ >V…ˆiÛi`°Ê œÀÊ iÝ>“«i]Ê >Ê ˜iÜÊ v>ÃÌi˜ˆ˜}Ê ÃœṎœ˜Ê for hydraulic lines in the Airbus A400M results in a 9.4 kg weight reduction per fastening by replacing titanium bolts with composite bolts. The parts are electrically insulating, do not corrode and are easier to install.

91

Update on the Technology and Applications of Polyaryletherketones

7.4 Automotive and Transport In the early days automotive applications were often considered to be too cost sensitive for PAEK. Today there are many niche automotive applications and PEEK can be found in almost every car in the world. œÜiÛiÀ]Ê}œL>Ê>Õ̜“œÌˆÛiÊÃ>iÃÊ>ÀiÊ«ÀœL>LÞʏiÃÃÊ̅>˜Ê£äääÊÌ«>ÆÊ small amounts of PEEK are being used to great effect. The use of PAEK is particularly prevalent in Europe - especially in Germany. In 2005 Europe accounted for 70% of Victrex’s automotive sales reflecting the level of innovation in the European industry. PAEK will only be used if they are the most cost-effective solution. High-volume injection moulded components offer great design flexibility and are often less expensive than their machined metal counterparts. PAEK offer wear, thermal and engine oil resistance together with weight and noise reduction. They are recyclable and environmentally friendly. It seems inevitable that the continued trend towards more efficient, higher engine temperature, lower weight, safer and quieter automobiles will drive the development of many more PAEK components. Transmission components were amongst the earliest applications. These benefited from the thermal, wear and transmission fluid resistance of PEEK together with cost reduction and design freedom.

œ“«ï˜}ʓ>ÌiÀˆ>ÃÊÃÕV…Ê>ÃÊ«œÞˆ“ˆ`iÃÊ>˜`Ê«œÞ>“ˆ`iˆ“ˆ`iÃÊÜiÀiÊ often more expensive to fabricate. Applications include seal rings, thrust washers, bearing retainers and cages, bearings, bushings and vœÀŽÊ«>`ðÊ-iv‡ÕLÀˆV>Ìi`Ê­«œÞÌiÌÀ>y՜Àœi̅ޏi˜iÊ­*/ ®‡Vœ˜Ì>ˆ˜ˆ˜}®Ê PEEK thrust washers are able to function for a time in the absence of external lubrication and this can be very useful in emergencies or under unusual driving conditions. Many of the wear studies mentioned in Chapter 3 were targeted at wear in transmission-type environments [3, 4]. PAEK washers, gaskets, bearings and bushings also find application the engine itself. -i>ÊÀˆ˜}ÃÊ>˜`ÊvÀˆV̈œ˜ÊÜ>ÅiÀÃÊ>ÀiÊÕÃi`ʈ˜ÊVÕÌV…ÊVœ“«œ˜i˜ÌðÊ/…iÊ friction washer shows a stable coefficient of friction throughout the

92

Applications of Polyaryletherketones

lifetime of the component. PEEK is used in the vanes and vane tips of vacuum pumps because of its wear resistance, sealing performance and the cost reduction associated with a moulded component. PEEK is also used in oxygen sensors, steering column sleeves, lamp sockets and fuel management systems. Recently PEEK film has started to be used in thrust washers in seat motors and a series of PEEK-lined, high-pressure quick connectors have been introduced. PEEK coatings have been applied to single-piece solid steel stampings to produce cost-effective cylinder gaskets. Higher temperature PAEK and PAEK blends have been used in turbocharger components.
˜Ìˆ‡œVŽÊLÀ>Žˆ˜}ÊÃÞÃÌi“Ê­
-®ÊÌ>««iÌÃÊ>˜`Ê«Õ˜}iÀÃÊÜiÀiÊ>˜œÌ…iÀÊ early application for carbon fibre-reinforced PEEK. Many of the ܜÀ`½ÃÊ
-Ê LÀ>Žˆ˜}Ê ÃÞÃÌi“ÃÊ ÀiÞÊ œ˜Ê *

°Ê /…iÊ Vœ“«œ˜i˜ÌÃÊ >ÀiÊ strong and resist automotive fluids but they are also of low weight allowing rapid switching of the brakes with minimal noise. More recently PEEK has found uses in electrical parking brake gears and brake wear indicators. In recent years gears have been a growing application area. PAEK gear applications are not just confined to the automotive industry but in many cases their development is being driven by automotive applications. These include worm gears for steering adjustment, air conditioning, seat adjustment and electronic power steering systems. Benefits include reduced cost versus metal gears, design flexibility, reduced weight, ability to run without lubrication [5], corrosion resistance and much lower noise due to higher internal damping. In many cases lower performance materials cannot be ÕÃi`°ÊœÀÊiÝ>“«i]ÊÃi>ÌÊ>`ÕÃ̓i˜ÌÊ}i>ÀÃÊLi˜iwÌÊvÀœ“Ê̅iÊÃÌÀi˜}Ì…Ê and toughness of PEEK such that the seat still works even after severe crashes, allowing removal of the passengers. In some parts of the world car interiors can become extremely hot and gears controlling the air conditioning and other systems must still function reliably. Recently Metaldyne has chosen PEEK to replace metal in its balance shaft module gears. Balance shaft modules are used to reduce the vibration associated with four cylinder engines. The reduced weight results in up to a 9% reduction in power consumption, and levels

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Update on the Technology and Applications of Polyaryletherketones

of noise and vibration have been improved. The design of plastic gears depends on the availability of empirical data at real torques, temperatures, speeds and environmental conditions. Victrex plc has developed gear test rigs specifically for PAEK applications [6] and is able to provide application-specific design data. The highly instrumented rigs are capable of running at up to 6000 rpm at ̜ÀµÕiÃʜvÊÕ«Ê̜ÊÈäÊ “°Ê>ˆÕÀiʓœ`iÃÊV>˜ÊLiÊVœ“«iÝʈ˜VÕ`ˆ˜}ÊÀœœÌÊ fracture, pitting, pitch line fracture and plastic yielding. Interestingly PEEK-PEEK gear combinations have been shown to outperform PEEK–steel gear combinations.

7.5 Oil and Gas PAEK have been used in the oil and gas industries for over twenty years [7, 8]. Recently there has been increased interest because of the ever increasing challenges of oil and gas extraction. It is not ՘ÕÃÕ>Ê̜Êw˜`ÊÌi“«iÀ>ÌÕÀiÃÊ>˜`Ê«ÀiÃÃÕÀiÃʜvÊ£{äÊ*>Ê>˜`ÊÓääÊc Ê combined with hydrogen sulfide, methane, brine, carbon dioxide and crude oil. Under these conditions devices such as seals, backup rings and connectors can simply extrude out of their location. Hightemperature stiffness and strength together with wear, abrasion, chemical, temperature, creep, fatigue and permeation resistance are key properties. Extraction depths may exceed 3000 m and any equipment failures can result in extremely expensive shutdowns. Accordingly the industry is willing to use the very highest performance materials such as PEK and PEKEKK as well as PEEK. It is worth noting that PAEK find many of the same applications in geothermal energy production which also faces high temperatures and pressures in a superheated water environment. Typical applications include: UÊ `>Ì>ʏœ}}ˆ˜}Ê̜œÃÆ UÊ Ãi˜ÃœÀʅœÕȘ}ÃÆ

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Applications of Polyaryletherketones

UÊ `>Ì>Ê>˜`Ê«œÜiÀÊV>LiÃÆ UÊ iiVÌÀˆV>ÊVœ˜˜iV̜ÀÃÆ UÊ Li>Àˆ˜}Ã]ÊLÕň˜}ÃÆ UÊ Ãi>Ã]ÊL>VŽÕ«ÊÀˆ˜}ÃÆ UÊ Vœ“«ÀiÃÜÀÊVœ“«œ˜i˜ÌÃÆ UÊ iiVÌÀˆV>ÊÃÕL“iÀÈLiʫՓ«ÃÆ UÊ i“Li``i`Ê À>`ˆœ‡vÀiµÕi˜VÞÊ ˆ`i˜ÌˆwV>̈œ˜Ê ­, ®Ê Ì>}ÃÊ ÌœÊ ÌÀ>VŽÊ `œÜ˜…œiÊiµÕˆ«“i˜ÌÆ UÊ V>LiÊ̈iÃÆÊ>˜` UÊ i˜iÀ}އ>LÜÀLˆ˜}ÊëÀˆ˜}ÃÊvœÀÊÃi>ˆ˜}ÊÃÞÃÌi“ð œÀÊiÝ>“«i]ÊÀii˜iÊ/Üii`ÊÕÃiÃÊLœÌ…Ê*

Ê>˜`Ê* Ê̜ʫÀœ`ÕViÊ injection moulded outer connector shells. The PAEK serves as an electrical insulator with excellent strength and corrosion and creep ÀiÈÃÌ>˜Vi°Ê ˆvvœÀ`Ê-«Àˆ˜}Ê œ“«>˜Þʅ>ÃÊ`iÛiœ«i`Êi˜iÀ}އ>LÜÀLˆ˜}Ê springs based on PEEK monofilament from Zyex. They offer a number of advantages including a much lower level of shaft damage should the seal fail and the spring come into contact with the shaft. More recently there have been a number of developments which use extruded PAEK pipes [9-11]. Victrex plc has developed extrusion technology to produce pipes with diameters ranging from 7 to 250 mm. The pipes have much superior properties versus conventional “>ÌiÀˆ>ÃÊÃÕV…Ê>ÃÊ*
££Ê>˜`Ê*6 °Ê/…iÃiʈ˜VÕ`iʏœÜÊ«iÀ“i>LˆˆÌÞ]ʏœÜÊ sensitivity to rapid gas decompression, erosion and wear resistance and high strength, creep and fatigue performance. They are being used as liners in a range of umblicals to replace conventional materials which are limited in terms of temperature and collapse resistance as well as chemical (especially permeation) resistance. In comparison to steel umbilicals, PEEK-lined hoses offer lower weight, excellent bend resistance, long continuous lengths and better corrosion resistance in

95

Update on the Technology and Applications of Polyaryletherketones

some environments. In 2008 Kutting UK Ltd., launched a range of PEEK-lined hoses following a joint development with Victrex, plc. ˜Ê
«ÀˆÊÓää™Ê7iÃÌiÀ˜Ê>Vœ˜Ê>՘V…i`Ê>ʘiÜÊ*

‡L>Ãi`ʏˆ˜iÀÊvœÀÊ downhole applications - called Extremetube. This followed eight years of research into the best materials for liner applications. There are also a number of patents on even more challenging >««ˆV>̈œ˜ÃÊvœÀÊ«ˆ«iÃÊQ£ÓR°ÊœÀÊiÝ>“«i]Ê
ÊV>ˆ“i`Ê>Ê*

Ê«ˆ«iÊ wrapped in continuous carbon fibre PEEK composite for use as an œˆwi`ÊÀˆÃiÀ°Ê-ÕV…ÊÀˆÃiÀÃÊVœÕ`ÊLiÊÃiÛiÀ>ÊŽˆœ“iÌÀiÃʏœ˜}Ê>˜`Ê̅iˆÀÊ near neutral buoyancy and excellent environmental resistance would allow recovery of oil from the deep oceans. The specific mechanical properties of composite pipes mean that they may also find uses as drill pipes. It seems inevitable that the need for PAEK will continue to increase as oil and gas extraction becomes more demanding.

7.6 Electronic Devices In the early days PAEK found applications in high-performance connectors and wiring systems. The connectors were used in military or downhole (oil and gas) equipment. PEEK insulated wiring was used in nuclear power applications because of its radiation resistance and ability to operate in high-temperature, chemical environments. It was used in critical systems because of its relatively good performance in extreme circumstances such as loss of coolant accidents. It found uses in military and mass transit applications where low flammability and low smoke and toxic gas emissions were critical. It was also used in magnet and winding wire for motors. All these classes of applications remain important and many will grow in the future. "ÛiÀÊ Ì…iÊ >ÃÌÊ `iV>`iÊ Ì…iÀiÊ …>ÛiÊ Lii˜Ê >Ê ˜Õ“LiÀÊ œvÊ ÌÀi˜`ÃÊ `ÀˆÛˆ˜}Ê increased use of PAEK in new classes of electronics applications. The Waste Electrical and Electronic Equipment (WEEE) and Restriction œvÊ>â>À`œÕÃÊ-ÕLÃÌ>˜ViÃÊ­,œ-®Ê`ˆÀiV̈ÛiÃÊÀiÃÌÀˆVÌÊ̅iÊÕÃiʜvʅi>ÛÞÊ

96

Applications of Polyaryletherketones

metals, including lead, in electrical and electronic equipment. This is causing the industry to use lead-free solders which have significantly …ˆ}…iÀÊ«ÀœViÃÃÊÌi“«iÀ>ÌÕÀiÃÊ­ÌÞ«ˆV>ÞÊÓÈä‡ÎääÊc ÊversusÊÓÎäÊc ®Ê and longer exposure times. Many electronic devices are assembled using surface mount technology. Any plastic components must survive lead-free solder temperatures with adequate dimensional stability, outgassing, strength, creep, toughness and impact properties. Higher temperature materials are therefore replacing lower temperature ones ÃÕV…Ê>ÃÊ«œÞ«Àœ«Þi˜iÊ­**®]Ê* /]Ê*
ÈÈÊ>˜`Ê* /°Ê**-ÊV>˜ÊÃÕÀۈÛiÊ Ãœ“iʏi>`‡vÀiiÊ܏`iÀÊ«ÀœViÃÃiðʈµÕˆ`ÊVÀÞÃÌ>ˆ˜iÊ«œÞiÃÌiÀÃÊ­ *®Ê can offer the necessary temperature performance but may lack mechanical performance such as weld line strength. PAEK, however, have excellent temperature and outgassing performance and are w˜`ˆ˜}Ê>Ê܈`iÊÀ>˜}iʜvÊ>««ˆV>̈œ˜ÃÊQ£ÎR°Ê-œ“iʜvÊ̅iÃiʅ>ÛiÊ̅iÊ potential to become more than just the classic niche types of PAEK application. In addition to environmental concerns other industry trends which favour the use of PAEK include: UÊ i“«…>ÈÃÊ œ˜Ê ÃÞÃÌi“ÃÊ VœÃÌÃÊ ‡Ê …ˆ}…‡ÛœÕ“iÊ Vœ“«œ˜i˜ÌÃÊ V>˜Ê LiÊ «Àœ`ÕVi`ÊLÞʈ˜iV̈œ˜Ê“œÕ`ˆ˜}Æ UÊ “ˆ˜ˆ>ÌÕÀˆÃ>̈œ˜Ê‡Ê“ˆVÀœ“œÕ`ˆ˜}Ê>˜`Ê̅ˆ˜‡Ü>ÊVœ“«œ˜i˜ÌÃÊÕȘ}Ê …ˆ}…‡yœÜÊ}À>`iÃÆ UÊ œ˜}iÀʏˆvï“iÃ]Ê}Ài>ÌiÀÊ«Àœ`ÕVÌÊÀiˆ>LˆˆÌÞ]ÊLiÌÌiÀÊi˜ÛˆÀœ˜“i˜Ì>Ê ÀiÈÃÌ>˜ViÆ UÊ i˜iÀ}ÞÊÃ>ۈ˜}Æ UÊ ÕÃiʜvʅˆ}…ÊvÀiµÕi˜VˆiÃÊ>˜`Ê܈ÀiiÃÃÊVœ““Õ˜ˆV>̈œ˜Æ UÊ “œÀiÊVœ“«iÝʓՏ̈v՘V̈œ˜>Ê`iۈViÃÊ܈̅Êψ`ˆ˜}]ÊÀœÌ>̈˜}Ê>˜`Ê yˆ«ÊVœÛiÀÃÆÊ>˜` UÊ Üiˆ}…ÌÊÀi`ÕV̈œ˜°

97

Update on the Technology and Applications of Polyaryletherketones

Traditional connector applications have been extended to various iiVÌÀœ˜ˆVÊ`iۈViÊVœ˜˜iV̜ÀðÊœÀÊiÝ>“«i]ÊVœ>݈>ÊV>LiÊVœ˜˜iV̜ÀÊ housings are used in the transmission of high-volume, high-frequency data. PEEK offers stable dielectric properties over a wide range of temperatures and frequencies and this can be further enhanced by the use of mineral fillers. PEEK also offers advantages in flexible printed circuit connectors. These are becoming much smaller and ÀiµÕˆÀiÊiÝVii˜ÌÊyœÜÊV…>À>VÌiÀˆÃ̈Vðʘʓ>˜ÞÊV>ÃiÃÊ *ʓ>ÞÊLiÊ̅iÊ material of choice but PEEK can offer very good weld line strength and impact resistance. Many of the new applications are in mobile phones. Although PEEK is an expensive material, overall system cost and performance are improved. PEEK is being used as a gasket material for secondary batteries. These batteries power timing and memory functions while the primary batteries are removed. They are directly mounted on the phone circuit boards using automated soldering processes. The gaskets must maintain mechanical integrity while surviving leadfree soldering temperatures in the presence of battery electrolytes. Mobile phone hinges can be made from carbon fibre-reinforced PEEK because of its wear performance, stiffness and mechanical strength. PEEK shows less torque loss over 100,000 cycles than injection moulded metal powder, injection moulded magnesium or alternative «>Ã̈VÃÊÃÕV…Ê>ÃÊ*"°ÊÌʈÃÊ>ÃœÊ«œÃÈLiÊ̅>Ìʈ˜iV̈œ˜Ê“œÕ`i`Ê*

Ê components will be less expensive than components produced by metal injection moulding (MIM). Indeed PEEK should always be Vœ˜Ãˆ`iÀi`Ê>ÃÊ>˜Ê>ÌiÀ˜>̈ÛiÊ̜Ê>˜ÞÊÊVœ“«œ˜i˜Ì°Ê-“>‡ÃV>i]Ê high-power speakers convert over 95% of their energy input to heat and can reach operational temperatures which rival even lead-free ܏`iÀˆ˜}ʇʈ˜ÊiÝViÃÃʜvÊÓÈäÊc °Ê*

Êw“ÊV>˜ÊLiÊÕÃi`Ê̜ʫÀœ`ÕViÊ speaker diaphragms with excellent dynamic fatigue performance and chemical resistance. Moisture resistance and processability are LiÌÌiÀÊ̅>˜ÊvœÀÊܓiÊVœ“«ï˜}Ê«œÞˆ“ˆ`iÊw“ðÊ-ˆ“ˆ>ÀÞÊ* /Êw“Ê can be replaced in some electrical condenser microphones because of dynamic mechanical strength and resistance to solder reflow temperatures.

98

Applications of Polyaryletherketones

PAEK find many uses as internal components for office equipment such as copiers, printers and projectors. PEEK gears and bushings are used in high-temperature environments such as copier heating rollers or the fusing sections of laser printers. PEEK roller coatings offer ˆ˜VÀi>Ãi`ÊÜi>ÀÊÀiÈÃÌ>˜ViÊ>˜`ÊÌi“«iÀ>ÌÕÀiÊ«iÀvœÀ“>˜Vi°Ê-«ˆÌÊw˜}iÀÃÊ are pointed components used to separate paper from rollers. The tips have to remain sharp but with very little adhesion to toner. PEEK …ˆ}…‡Ìi“«iÀ>ÌÕÀiÊ돈ÌÊw˜}iÀÃÊV>˜ÊLiÊ«iÀy՜Àœ>ŽœÝÞÊ­*
®ÊVœ>Ìi`Ê >ÌÊÌi“«iÀ>ÌÕÀiÃÊLiÌÜii˜Ê>LœÕÌÊÎÎäÊ>˜`ÊÎÈäÊc ]Ê܅ˆV…ÊܜՏ`ÊÀՏiÊ out most other plastics. The use of PAEK allows the design of faster (higher temperature) equipment with a long life and high reliability. PEEK is used in the lamp holder assemblies of digital projectors. The projectors have become smaller but users expect higher brightness and longer lifetimes. PEEK survives the very high temperatures involved (both heat distortion temperature (HDT) and continuous ÕÃiÊÌi“«iÀ>ÌÕÀiÊ­ 1/®Ê>Àiʈ“«œÀÌ>˜Ì®°ÊÌÊ>ÃœÊ…>ÃÊÛiÀÞʏœÜʜÕÌ}>ÃȘ}Ê which would otherwise gradually cloud the system optics. PEEK film finds uses as a substrate for flexible printed circuit boards. Mitsubishi has developed a blend of PEEK and polyetherimide (PEI) in which the slow crystallisation characteristics can be utilised to fuse layers of circuit without the need for adhesives. This is a potentially œÜ‡VœÃÌÊÀœÕÌiÊ̜ʓՏ̈>ÞiÀÊVˆÀVՈÌÃÊQ£{R°Êˆ“ÊV>˜Ê>ÃœÊ«ÀœÛˆ`iÊ>Ê useful moisture barrier in applications such as membrane switches. There are also a number of niche applications such as environmentally ÀiÈÃÌ>˜ÌÊ, ÊÌ>}ð Examples of recent electronic applications are given in Table 7.1.

99

100 -œ`iÀÊÀiÈÃÌ>˜Vi]ʓˆVÀœ‡œÛiÀ“œÕ`ˆ˜}Ê܈̅Ê*

 Environmental Resistance

-ˆ“Տ>Ê/iV…ʘV° "iÊ7œvvÊ-iœŽ>˜}

>L>ÃÃi Golden Valley Products Kyocera VP Plast Talisman

Mobile phone slide hinge - coating

Mobile phone microphone spacer - film

Tweeter membrane - film

Membrane switch - film

Heat roller gears - PEEK

Micro connector - PEEK + glass

*ÀœÌiV̈ÛiÊ/>«iÊÚÊ "-É

Ê>Î

Mechanical stability at elevated temperatures

Moisture barrier, chemical and temperature resistance

Rigidity/weight ratio, acoustic properties

-œ`iÀÊÀiÈÃÌ>˜ViʇÊÀi«>Vi`Ê* /

Wear resistance, lubricity, bonding strength

, ÊÌ>}ÃÊi˜V>«ÃՏ>Ìi`ʈ˜Ê*

Êw“ÊÃÕÀۈÛiÊ̅iÊ painting cycle on a truck production line

"/
Ê ˆiiÌÀœ]Ê À>∏

Radio frequency tags - film

-Õ«iÀˆœÀÊ>VœÕÃ̈VÊ«Àœ«iÀ̈iÃÊversus PP, paper, >Õ“ˆ˜ˆÕ“°Ê>̈}ÕiÊ«iÀvœÀ“>˜Vi

Benefits of PAEK

Audio Technology Engineering

Manufacturer

-«i>ŽiÀÊVœ˜iʇÊw“

Application

Table 7.1 Examples of recent electronic applications

Update on the Technology and Applications of Polyaryletherketones

Applications of Polyaryletherketones

7.7 Semiconductors and Displays PAEK have established a number of important roles in the production of semiconductors and displays. Their benefits in terms of low particle generation (wear resistance), purity, chemical resistance and mechanical stability at high temperatures have been recognised for over two decades [15]. Even small differences in device yield as a result of lower contamination can justify the use of PAEK. This led to the use of PEEK wafer baskets when wafers were only >ÀœÕ˜`Ê̅Àiiʈ˜V…iÃʈ˜Ê`ˆ>“iÌiÀ°Ê-ˆ˜ViÊ̅>ÌÊ̈“iÊ̅iÀiʅ>ÛiÊLii˜Ê>Ê number of industry trends which have further increased the PAEK market. Wafers have moved to 30 cm and now 45 cm diameters. Decreased circuit line width and spacing have increased the need for accuracy and increased the sensitivity of devices to contamination and electrostatic discharge. Process temperatures have increased and the ever smaller integrated circuits have become harder to handle. PAEK are used in equipment for handling and transport, cleaning, iÌV…ˆ˜}]ÊV…i“ˆV>Ê“iV…>˜ˆV>Ê«œˆÃ…ˆ˜}É«>˜>ÀˆÃ>̈œ˜Ê­ *®Ê>˜`ÊÌiÃÌÊ and burn in. Victrex has introduced ultrahigh-purity grades of PEEK for critical applications. Wafer transport and storage were originally achieved using baskets made from pure PEEK. These had low levels of wear particle generation when wafers were inserted or removed, could handle hot wafers and had low levels of ionic impurities which could potentially act as a silicon dopant, reducing device yield. Later the carriers ÜiÀiÊ “>`iÊ ÕȘ}Ê iiVÌÀœÃÌ>̈VÊ `ˆÃÈ«>̈ÛiÊ ­ - ®Ê }À>`iÃÊ œvÊ *

Ê to avoid damage to the circuits being grown on the wafers. More recent transportation devices take the form of enclosed robotically …>˜`i`ÊLœÝiÃʎ˜œÜ˜Ê>ÃÊvÀœ˜Ìʜ«i˜ˆ˜}Ê՘ˆÌ>ÀÞÊ«œ`ÃÊ­"1*®°Ê"1*Ê >ÀiÊÌÞ«ˆV>Þʓ>`iÊvÀœ“Ê“>ÌiÀˆ>ÃÊÃÕV…Ê>ÃÊ«œÞV>ÀLœ˜>ÌiÊ­* ®ÊLÕÌÊ Ì…iÊ Ü>viÀÊ Vœ˜Ì>VÌÊ Vœ“«œ˜i˜ÌÃÊ >ÀiÊ - Ê }À>`iÃÊ œvÊ *

°Ê ˜Ìi}ÀˆÃÊ «Àœ`ÕViÃÊ>˜Ê>`Û>˜Vi`ÊÜ>viÀÊÌÀ>˜Ã«œÀÌÊV>ÀÀˆiÀÊÕȘ}Ê* ʜÛiÀ“œÕ`i`Ê with conductive PEEK compounds. The use of two distinct materials œ«Ìˆ“ˆÃiÃÊ LœÌ…Ê VœÃÌÊ >˜`Ê «iÀvœÀ“>˜Vi°Ê /…iÊ * Ê ˆÃÊ ÌÀ>˜Ã«>Ài˜ÌÊ >˜`Ê tough and can be moulded to very high dimensional tolerances. The >`Û>˜Ì>}iÃʜvÊ*

ʈ˜Ê"1*ÊV>˜ÊLiÊÃՓ“>ÀˆÃi`Ê>ÃÊvœœÜÃ\

101

Update on the Technology and Applications of Polyaryletherketones

UÊ œÜÊ«>À̈ViÊ}i˜iÀ>̈œ˜Ê`ÕiÊ̜ÊÜi>ÀÆ UÊ - Ê«iÀvœÀ“>˜ViÆ UÊ …ˆ}…Ê«ÕÀˆÌÞÊ>˜`ʏœÜʜÕÌ}>ÃȘ}ʈ˜ÊÛ>VÕՓÃÆ UÊ >LˆˆÌÞÊ̜ʅ>˜`iʅœÌÊÜ>viÀÃÆ UÊ ˜œÊ>``ˆÌˆÛiÃʇÊi°}°]Ê̜Êi˜ÃÕÀiÊwÀiÊÀiÈÃÌ>˜ViÆÊ>˜` UÊ Vœ“«iÝÊ}iœ“iÌÀˆiÃÊV>˜ÊLiÊ«Àœ`ÕVi`ÊLÞʈ˜iV̈œ˜Ê“œÕ`ˆ˜}° In addition there are a number of types of robotic wands which are used to handle the wafers. These need high modulus and creep resistance, good abrasion characteristics, temperature resistance, œÜÊ Üiˆ}…ÌÊ >˜`Ê - Ê V>«>LˆˆÌÞ°Ê *

É*œÞLi˜âˆ“ˆ`>✏iÊ ­* ®Ê blends (Victrex T series) have been used as end effector pads in these applications because of their combination of temperature and wear resistance. These ‘robotic hands’ pick up the wafers at very high temperature and need high purity, exceptional abrasion resistance and a very smooth finish. Wafer cleaning equipment (wands, wafer cleaning chucks, etc.) require good resistance to cleaning fluids such as peroxide and acids together with dimensional stability.

œ“«œ˜i˜ÌÃÊÕÃi`ʈ˜Ê̅iÊiÌV…Êi˜ÛˆÀœ˜“i˜Ìʅ>ÛiÊ̜Ê܈̅ÃÌ>˜`Ê«>Ó>Ê processing with a number of gas chemistries. PAEK can result in cost savings versus materials such as quartz, ceramics, PBI and polyimides. Ultra high-purity polyaryletheretherketone (PEEK) can be used to reduce contamination by metal ions. *

ʈÃÊÕÃi`Ê̜ʓ>ŽiÊ *ÊÀiÌ>ˆ˜ˆ˜}ÊÀˆ˜}ðÊ/…iÃiÊ>ÀiÊÕÃi`Ê̜ʅœ`Ê the wafers in place while they are polished by abrasive and corrosive V…i“ˆV>Ê ÏÕÀÀÞ°Ê /…iÊ *Ê Àˆ˜}ÃÊ }À>`Õ>ÞÊ Üi>ÀÊ >Ü>ÞÊ >˜`Ê Ì…iˆÀÊ lifetime can also be limited by the formation of an inner edge groove as a result of wafer impact against the inner diameter of the ring. Wear debris must not cause undesirable effects such as scratching or ՘iÛi˜Ê«œˆÃ…ˆ˜}°Ê˜ÊVœ“«>ÀˆÃœ˜Ê̜Ê**-ÊÀˆ˜}Ã]Ê*

ÊÀˆ˜}Ãʅ>ÛiÊLii˜Ê found to have much lower wear rates and equivalent defect rates.

102

Applications of Polyaryletherketones

>LÀˆV>̈œ˜Êv>VˆˆÌÞÊ`œÜ˜Ìˆ“iÃÊV>˜ÊLiÊÀi`ÕVi`ÊLiV>ÕÃiÊ̅iÀiʈÃʏiÃÃÊ need to replace the rings and this leads to substantial cost savings. ˆ˜>ÞÊ ÌiÃÌÊ >˜`Ê LÕÀ˜Ê ˆ˜Ê ÜVŽiÌÃÊ “ÕÃÌÊ LiÊ >LiÊ ÌœÊ ÃÕÀۈÛiÊ Ì…iÊ ÌiÃÌÊ conditions with a high degree of tolerance and dimensional stability.

- Ê }À>`iÃÊ œvÊ *
Ê >ÀiÊ ÕÃiÊ Ìœ}i̅iÀÊ ÜˆÌ…Ê «ÀiVˆÃˆœ˜Ê ˆ˜iV̈œ˜Ê moulding for fine connector arrays. Blends of PAEK with amorphous polymers, or less crystalline polymers such as PEKK, can offer a lower tendency to warp and higher dimensional tolerance. Examples of semiconductor process applications are given in Table 7.2.

7.8 Industrial Valves and compressors were amongst the earliest applications areas for PAEK. In static applications the temperature and chemical resistance, coupled with excellent mechanical performance make PAEK suitable for a wide range of metal replacement applications such as housings, linings, thrust washers and seals. However, there are also many moving parts which benefit from excellent dynamic fatigue resistance and wear resistance, with or without lubrication, together with dimensional stability and low-cost fabrication. Valve components depend on fatigue performance. PAEK compounds can outperform nylons due to superior mechanical properties at temperature, lower moisture absorption and better chemical resistance. PEEK compressor valve plates combine toughness with high thermal and dimensional stability. When PAEK components do fail they tend to do less downstream damage than their metal equivalents.

103

104

- ]ʏœÜÊ«>À̈ViÊ}i˜iÀ>̈œ˜]ʜÕÌ}>ÃȘ}]Ê«ÕÀˆÌÞ]ʈ“«ÀœÛi`Ê wafer yield High purity, low wear, smooth finish, temperature performance ,i`ÕViÃÊÜi>ÀÊ«>À̈ViÊ}i˜iÀ>̈œ˜]ÊLiÌÌiÀʏˆvï“iÊ̅>˜Ê*/ Excellent dimensional stability and tolerance across a range of conditions. Lighter than ceramics with better impact resistance

,i«>Vi`Ê**-]ÊLiÌÌiÀÊ«>ÀÌʵÕ>ˆÌÞ]Ê«>̈˜}ÊivwVˆi˜VÞ]ʏœ˜}iÀÊ«>ÀÌÊ life Metal-free flow path with strength and superior chemical resistance

Gudeng Precision Industrial

Piper Plastics

King Polytechnic

Piper Plastics

/ÀiiLœÀ}Ê-i>ˆ˜}Ê -œṎœ˜Ã

"À̘iÀ

AEM-Evertech

œ`iÀÊ*Àœ`ÕVÌÃ

7>viÀÊV>ÃÃiÌÌiÊ‡Ê - Ê*



End effectors - PEEK/PBI

-«ˆ˜É`ˆ«ÊiµÕˆ«“i˜Ì

iÀ>“ˆV‡wi`ÊÌiÃÌÊÜVŽiÌÃ

PEEK energised seals

-i“ˆVœ˜`ÕV̜ÀÊVi>˜ÊÀœœ“Ê shelf system

Holder components for chemical plating machines

-«Àˆ˜}Êii“i˜Ìʈ˜Ê…ˆ}…‡ purity quick disconnect coupling

High purity, low wear particle generation

High purity, all polymer, chemical resistance versus metal

Reduced wear, reduced downtime

Benefits of PAEK

Gudeng Precision Industrial

Manufacturer

*ÊÀˆ˜}ÃʇÊ*



Application

Table 7.2 Examples of semiconductor process applications

Update on the Technology and Applications of Polyaryletherketones

Applications of Polyaryletherketones

Applications in compressors include suction and discharge valves, bearings and piston rings, labyrinth seals, vanes, cams, scroll compressor tip seals, valve plates, poppet valves, star gears and rotors. Use of PAEK typically results in efficiency gains, improved reliability and increased lifetimes. The slight plastic flow of PAEK versus metals means that some types of seal, such as scroll compressor tip seals, will be able to bed into their environment and respond to a degree of wear and damage. PAEK can also reduce noise and vibration levels. -ÕV̈œ˜Ê>˜`Ê`ˆÃV…>À}iÊÛ>ÛiÃÊ>ÀiʓÕV…ʏiÃÃʓ>ÃÈÛiÊ̅>˜Ê̅iˆÀÊÃÌiiÊ or aluminium counterparts and this produces less noise and increases efficiency. PAEK also find uses in pump rotors, impellers and gears. Replacement of stainless steel can result in reduced wear and noise, more consistent running and improved operating efficiency. Recently Ensinger has introduced PEEK/PBI for compression vanes in a new line of high-rotation pneumatic tools. The vanes needed exceptional wear resistance and modulus at high temperatures together with excellent resistance to oils and grease. The vanes were previously made from a phenolic thermoset which was more expensive and time consuming to process and required lubrication inside the compression chamber. "ÛiÀʓ>˜ÞÊÞi>ÀÃÊ*
ʅ>ÛiÊvœÕ˜`Ê>Ê܈`iÊÀ>˜}iʜvÊ>««ˆV>̈œ˜Ãʈ˜Ê ÌiÝ̈iÊ>˜`ÊÜi>ۈ˜}ÊiµÕˆ«“i˜Ì°Ê-ÕV…ÊiµÕˆ«“i˜ÌʓÕÃÌÊÃÕÀۈÛiÊÛiÀÞÊ high-speed operation, high frictional wear, high process temperatures, steam and dyeing chemicals. PAEK compounds (some of which are continuous carbon fibre composites) have relatively low moments of inertia and this both saves energy and allows even faster operation of the machines. Applications include bearings, bushings, sleeves, lubricant-free wear plates, yarn and thread guides with overmoulded ceramic inlays, belts chain parts, valves, gears, seal rings, sensors, washers, wire protection and pump components. Recently PEEK has been used to coat woven glass fusion pressing belts to improve wear resistance and increase lifetime.

105

Update on the Technology and Applications of Polyaryletherketones

PAEK have great potential in membrane separation processes and there are a substantial number of patents describing ways to produce membranes and control membrane porosity. Porogen has recently launched a series of hollow fibre PAEK membranes for use at high temperature in aggressive environments. The membranes can be used to remove volatile organic compounds from air or industrial gas streams, to remove heavy hydrocarbons and acid gases from natural gas and in a variety of other high-temperature gas filtration processes. PAEK film is suitable for a range of seals, bearings and liners. PEEK film has recently been used to replace metal in Makatec’s heat exchangers. The film is spiral wound in a design that reduces cost and improves performance. PAEK coatings can be used to produce very hard wearing and environmentally resistant surfaces. PAEK (especially PEEK) are widely used in chemical analytical equipment because of their purity and resistance to temperature and a wide range of chemicals. A surprisingly high proportion of analytical chemists, especially chromatographers, are familiar with *

°Ê œ“«>˜ˆiÃÊÃÕV…Ê>ÃÊ1«V…ÕÀV…Ê-Vˆi˜ÌˆwVʓ>Žiʓ>˜ÞÊÌÞ«iÃʜvÊ specialist fittings including inert PAEK porous filters. A variety of PEEK tubing and heat shrinkable PEEK can be obtain from Zeus. Examples of recent industrial applications are given in Table 7.3.

106

Plate and frame modules in membrane filtration systems Discharge valve in linear compressors Pressure regulator diaphragm liner - film

Application Replacement for metal poppets in compressor valves

œ>̈˜}ÊvœÀÊ}œvÊL>ÊVœÀiÊ mould PEEK balls for check valves and bearings Hydraulic valve poppets

Reduced energy consumption versus steel, heat insulating, lower noise, fatigue and chemical resistance

Àii«ÊÀiÈÃÌ>˜ViʇÊÀi«>Vi`Ê*/

LG Electronics

ˆÀVœÀʘÃÌÀՓi˜Ì>̈œ˜Ê Technologies

Alfa Laval

œ“«ÀiÃÈÛiÊÃÌÀi˜}̅]Êi˜ÛˆÀœ˜“i˜Ì>ÊÀiÈÃÌ>˜Vi]ÊÃiv‡ sealing Ease of processing, mechanical properties, environmental resistance, food contact approval

Benefits of PAEK Impact resistance, increased range of applications, lower weight, better corrosion resistance, design flexibility, cost reduction -VÀ>ÌV…Ê>˜`ÊÜi>ÀÊÀiÈÃÌ>˜Vi]ÊÀii>ÃiÊ«Àœ«iÀ̈iÃ]ÊiÝÌi˜`i`Ê service life

œÀÀœÃˆœ˜Ê>˜`ÊÜi>ÀÊÀiÈÃÌ>˜Vi]Ê̜Õ}…˜iÃÃ

Bosch Rexroth

Parkway Products

-՘}Êޜ՘}Ê*ÀiVˆÃˆœ˜

Manufacturer Performance Plastics

Table 7.3 Examples of recent industrial applications

Applications of Polyaryletherketones

107

Update on the Technology and Applications of Polyaryletherketones

7.9 Food Processing The most commonly used grades of unfilled PAEK (e.g., Victrex PEEK and PEK), films, some filled grades and some coatings have food contact approval for repeated contact from regulatory bodies ˆ˜Ê ̅iÊ 1-
Ê >˜`Ê ÕÀœ«i°Ê œÜiÛiÀ]Ê Ì…iÃiÊ >««ÀœÛ>ÃÊ >ÀiÊ ÃÕLiVÌÊ ÌœÊ composition requirements and extraction tests on the final article. In Europe the extraction tests require measurement of specific PAEK monomers. There are also approvals for water contact and for use in dairy equipment. It is important to check the status of each specific grade with the manufacturer - for example, it would be possible to “>ŽiÊ>Ê}À>`iʜvÊ՘wi`Ê*

Ê܅ˆV…Ê`ˆ`ʘœÌʓiiÌÊ
ÊÀiµÕˆÀi“i˜ÌÃ°Ê In general, however, there will be a PAEK which is suitable for food contact use in a given application. PAEK (especially PEEK) find extensive uses in food processing equipment. The advantages of PEEK include: UÊ …ˆ}…‡Ìi“«iÀ>ÌÕÀiʓiV…>˜ˆV>Ê«iÀvœÀ“>˜ViÆ UÊ ÀiÈÃÌ>˜ViÊ̜ʅˆ}…‡«ÀiÃÃÕÀiÊÃÌi>“]ʅÞ`ÀœÞÈÃ]ÊÜ>ÌiÀÊÜvÌi˜iÀÃÊ>˜`Ê Vi>˜ˆ˜}ÊyՈ`ÃÆ UÊ Üi>ÀÊÀiÈÃÌ>˜ViÊ܈̅œÕÌʏÕLÀˆV>̈œ˜Êi>`ˆ˜}Ê̜ÊÀi`ÕVi`ʏÕLÀˆV>˜ÌÊ Vœ˜Ì>“ˆ˜>̈œ˜Æ UÊ “>ÃÃÊ«Àœ`ÕV̈œ˜ÊLÞʈ˜iV̈œ˜Ê“œÕ`ˆ˜}Æ UÊ Ài`ÕVi`ÊiµÕˆ«“i˜Ìʓ>ˆ˜Ìi˜>˜ViÆÊ>˜` UÊ ˜œÊ“iÌ>ÊVœ˜Ì>“ˆ˜>̈œ˜]ÊVœÀÀœÃˆœ˜Ê>˜`Êy>Žˆ˜}° Espresso machines have contained PEEK in steam contact components (boiler pins, steam faucets and filters) for some years. However, most food contact applications are found in food processing factories. PEEK is used in food conveyor belt chains because of its ability to ÃÕÀۈÛiʅˆ}…ÊÌi“«iÀ>ÌÕÀiÃÊ>˜`Ê>}}ÀiÃÈÛiÊVi>˜ˆ˜}ÊÀi}ˆ“iðÊ-ˆ“ˆ>ÀÞÊ *

Êv>LÀˆVÃÊܜÛi˜ÊvÀœ“ÊwLÀiÃÊLÞÊVœ“«>˜ˆiÃÊÃÕV…Ê>ÃÊ-iv>ÀÊ>ÀiÊÕÃi`Ê

108

Applications of Polyaryletherketones

to replace polyester because of steam and temperature resistance. PEEK fibres can also replace metal bristles in cleaning brushes. PEEK bushes and gears can reduce downtime and maintenance requirements. Helical PEEK gear wheels are used in spray heads for cleaning equipment because of their temperature and chemical resistance. PEEK also finds uses in scraper blades, pump impellers, housings and sensors. Examples of recent food processing applications are given in Table 7.4.

7.10 Consumer Applications Although PAEK are expensive, there are some applications in which the general public comes into close contact with PEEK. "˜iʜvÊ̅iÊi>ÀˆiÃÌÊVœ˜ÃՓiÀÊ>««ˆV>̈œ˜ÃÊÜ>ÃÊ̅iÊÕÃiʜvÊ*

ÊwLÀiÊ in tennis racquet strings. These strings offer playing characteristics close to those of natural gut, low dynamic stiffness, minimal tension loss after stringing, the ability to hold tension for exceptionally long periods and performance levels that are maintained at extremes of Ìi“«iÀ>ÌÕÀiÊ>˜`ʅՓˆ`ˆÌްʈLÀiÃÊ>ÀiÊ>ÃœÊÕÃi`Ê>ÃÊÃÌÀˆ˜}ÃÊvœÀʓÕÈV>Ê instruments such as violins. The strings show low internal damping, low inharmonicity and are unaffected by humidity changes. The superior toughness and fatigue strength of PEEK has led to its use in digital motors for Dyson vacuum cleaners. This helps double the life of the motor, which can be one of the first components to wear out. The fan spins at 100,000 rpm. The fan and rotor assembly is fixed on a shaft using PEEK spacers and PEEK bearing cages are used in the motor assembly. PEEK finds uses in portable stoves for camping and mountain climbing where it offers temperature resistance and high strength VœÕ«i`Ê܈̅ÊÈ}˜ˆwV>˜ÌÊÜiˆ}…ÌÊÀi`ÕV̈œ˜°Ê-܈ÌV…ˆ˜}ÊvÀœ“Ê“>V…ˆ˜ˆ˜}Ê metal to injection moulding helped to reduce manufacturing costs.

109

110 Temperature, wear, hydrolysis resistance, dimensional stability

Temperature resistance, mechanical strength, chemical resistance Wear, release and mechanical properties for aggressive cooking environments such as bacon, burgers and pizza crusts

High-temperature, high speed-performance without lubrication. Resistance to cleaning chemicals High-temperature sensor, completely encapsulated for optimum hygiene

Digmesa Ag -iˆÊ“L /œvÌiœÀ}Ê
ÉTaconic International

-
" 9>“>ŽÞÕÊ …>ˆ˜Ê œ°

Endress and Hauser

œÜʓiÌiÀÊvœÀÊۈÃVœÕÃÊyՈ`ÃÊÃÕV…Ê as oil and syrup

Digital fill level sensor

Helical gears for industrial cleaners

œœ`ÊVœœŽˆ˜}Ê>˜`Ê«ÀœViÃȘ}ÊLiÌÃÊ - PEEK coating

Espresso machine steam faucet

œœ`ÊVœ˜ÛiޜÀÊV…>ˆ˜Ã

œ˜`ÕV̈ۈÌÞÊÃi˜ÃœÀ

-Ìi>“Ê>˜`ʅÞ`ÀœÞÈÃÊÀiÈÃÌ>˜Vi]ÊVi>˜ˆ˜}ÊyՈ`Ê resistance

Temperature and chemical resistance

Non-stick, high temperature and pressure, good adhesion to steel core, low wear resulting in extended valve life and reduced downtime

Benefits of PAEK

ÕœÀÌi˜

Manufacturer

œ˜iÊÛ>ÛiÊvœÀÊ̜“>̜ʫÀœViÃȘ}ÊqÊ PEEK overmoulded steel core

Application

Table 7.4 Examples of recent food processing applications

Update on the Technology and Applications of Polyaryletherketones

Applications of Polyaryletherketones

œ>̈˜}ÃÊ>ÀiÊÕÃi`ʈ˜ÊVœœŽˆ˜}ÊiµÕˆ«“i˜ÌÊÃÕV…Ê>ÃÊ ÕVŽœœÊ˜`ÕÃÌÀˆ>½ÃÊ rice cooker. Historically aluminium cookers have been susceptible to corrosion and PEEK coatings have the ability to resist scratching by rice scoops and scrubbers. Advanced Mechanical Technology Inc., has used PEEK coatings to create longer lasting wear plates in its gymnasium treadmills.

References 1.

A. Wood, J. Walling and D. Padier in Proceedings of a RAPRA Polymers in Defence and Aerospace Conference, /œÕœÕÃi]ÊÀ>˜Vi]ÊÓääÇ°

2.

°Ê
ޏi]ʈ˜Ûi˜ÌœÀÆÊiÝViÊ œÀ«œÀ>̈œ˜°]Ê>ÃÈ}˜iiÆÊ7"Ê 107533 A2, 2006.

3.

I. Griffiths, D. Kemmish, P. Tweedale, M. Morgan and R. Weidig in Proceedings of the SAE International Congress, iÌÀœˆÌ]Ê]Ê1-
]Ê£™™Ç]ʙÇäÈxn°

4.

I. Griffiths, D. Kemmish and M. Morgan in the Proceedings of the SAE International Congress]Ê iÌÀœˆÌ]Ê]Ê1-
]Ê£™™n]Ê 980716.

5.

R. Weidig and J. Rosler, SAE Technical Paper Series, 2001, 1, 1142.

6.

1°Ê->˜Ìˆ>}œÊ>˜`Ê °Ê7i>iʈ˜Ê̅iÊ*ÀœVii`ˆ˜}ÃʜvÊ̅iÊ International Conference on Gears, Garching, Germany, 2005.

7.

°Ê-“>Êˆ˜ÊProceedings of the Oilfield Engineering with Polymers Conference, London, UK, 2008.

8.

°Êi>Žˆ˜Ê>˜`Ê°Ê-“>Êˆ˜ÊProceedings of High Performance Plastics, Vienna, Austria, 2005.

111

Update on the Technology and Applications of Polyaryletherketones

9.

D. Brademeyer, H. Massillonm, M.J. El-Hibri, B. Alexander, °
°Ê-ÌiÀ˜]Ê °Ê>ŽœÛˆVÊ>˜`Ê,° °Ê …>ÛiÀÃ]ʈ˜Ûi˜ÌœÀÃÆÊ-œÛ>Þ]Ê >ÃÈ}˜iiÆÊ7"££™ÈÇÈ]ÊÓään°

10. ,°/°ÊiˆLvÀˆi`]Ê°Ê-“>Ê>˜`Ê
°Ê7œœ`]ʈ˜Ûi˜ÌœÀÃÆÊ6ˆVÌÀiÝ]Ê >ÃÈ}˜iiÆÊ *£™{x{Ι]ÊÓääÈ° 11. ,°/°ÊiˆLvÀˆi`]Ê°Ê*iÀ˜ˆVi]Ê°Ê-“>]Ê°Ê6œi`“>˜Ê>˜`Ê
°Ê 7œœ`]ʈ˜Ûi˜ÌœÀÃÆÊ6ˆVÌÀiÝÊ>˜Õv>VÌÕÀˆ˜}ÊÌ`°]Ê>ÃÈ}˜iiÆÊ 7"äÓÎÓxx]ÊÓääÇ° 12.
°°Ê ÀiۈŽÊ>˜`Ê"°
°ÊÀÞÌ>]ʈ˜Ûi˜ÌœÀÆÊ
Ê"vvŜÀiÊ-ÞÃÌi“Ã]Ê >ÃÈ}˜iiÆÊ7"™™ÈÇxÈ£]Ê£™™™° 13. °Ê …i˜]Ê°ÊÀœÃÃÊ>˜`Ê °Êi>Žˆ˜Êˆ˜ÊProceedings of the Surface Mount Technology Conference]Ê"À>˜`œ]Ê]Ê1-
]Ê 2007. 14. °Ê/>˜ˆ}ÕV…ˆÊ>˜`Ê-°Ê9>“>`>]ʈ˜Ûi˜ÌœÀÃÆʈÌÃÕLˆÃ…ˆÊ*>Ã̈VÃ]Ê >ÃÈ}˜iiÆÊ7"äÓäxÇÎ{Î]ÊÓä䣰 15. P. Jones, I. Emami, J. Goodman and K. Mikkelsen, Microcontamination, 1993, 11, 29.

112

8

Medical Grades and their Applications

8.1 Materials The classification of medical-grade plastics is quite complex. Broadly speaking, three classes of application are defined by ISO 10993 and hence three classes of appropriate material are offered by manufacturers. The most demanding class (often referred to as ‘permanent’ or ‘implant’ grade) is used in over 30 day implantable applications. There are also less than 30 day, ‘prolonged’ implantable applications and short-term, ‘limited use’ applications. ISO 10993-1 provides a table which specifies tests according to the type of body contact and the duration of the application. Many of these tests are discretionary. It should be remembered that it is devices, not materials, which are approved. It has to be this way since a material which is excellent for one application could be completely unsuitable for another. Materials suppliers will usually lodge data files with organisations such as the FDA that can be used by device manufacturers to gain device approvals. Such files will contain grade-specific manufacturing information as well as in vivo and in vitro test results. Polyaryletherketones (PAEK) have been used for many years in secondary medical devices such as surgical instruments. The use of PAEK in implantable devices was first patented by ICI in 1987 [1]. ICI developed a number of high-value medical applications based around its polyhydroxybutyrate resorbable products (later part of Zeneca Biopolymers) but was relatively inactive in implantable PAEK. In the meantime BASF developed a number of applications based on PEKEKK, but it was not until 1999 that Victrex launched

113

Update on the Technology and Applications of Polyaryletherketones

an implantable grade of polyaryletheretherketone (PEEK) through its Invibio Ltd., subsidiary. Since that time Invibio’s PEEK Optima has become one of the major medical device plastics [2] along with ultrahigh molecular weight polyethylene (UHMWPE) and bioabsorbable materials such as polylactic and glycolic acids. Recently Victrex plc has split into two divisions: Invibio and Victrex Polymer Solutions. In the first half of 2008/2009 Invibio sales were £17.6 million with a profit of £10.2 million. According to the 2009 interim results from Victrex plc, over two million devices containing Invibio’s PEEK Optima have been implanted since its launch in 1999. PAEK (PEEK in particular) offer a number of advantages including: UÊ ˜œÊÀii>ÃiʜvʓiÌ>Êˆœ˜ÃÊ܅ˆV…ÊV>˜ÊÌÀˆ}}iÀÊ>iÀ}ˆVÊÀi>V̈œ˜Ãʈ˜Ê some people; UÊ ˜œÊ>ÀÌiv>VÌÃʈ˜Ê8‡À>ÞÊVœ“«ÕÌi`Ê̜“œ}À>«…ÞÊ­ /®Ê>˜`ʓ>}˜ïVÊ resonance imaging (MRI); UÊ ˆ“>}ˆ˜}Ê«Àœ«iÀ̈iÃÊ̅>ÌÊV>˜ÊLiÊÌ>ˆœÀi`ÊÕȘ}Ê>``ˆÌˆÛiÃÊÃÕV…Ê>ÃÊ barium sulfate or tantalum wire in continuous fibre-reinforced materials; UÊ “œ`ՏÕÃÊ̅>ÌÊV>˜ÊLiÊÌ>ˆœÀi`Ê̜ÊLiÊVœÃiÀÊ̜ÊLœ˜iÊ̅>˜Ê“iÌ>ÃÆ UÊ ÃÌiÀˆˆÃ>LˆˆÌÞÊ܈̅ÊÃÌi>“]Ê}>““>ÊÀ>`ˆ>̈œ˜Ê>˜`Êi̅ޏi˜iʜ݈`iÆ UÊ œÜiÀÊ`i˜ÃˆÌÞÊ>˜`ÊVœ˜`ÕV̈ۈÌÞÊ̅>˜Ê“iÌ>ÃÆ UÊ iÃÃʏˆŽiÞÊ̜ÊLiʘœÌˆVi`Ê܅i˜ÊVœÃiÊ̜Ê̅iÊΈ˜ÆÊ>˜` UÊ i>ÃiʜvÊvœÀ“>̈œ˜Êˆ˜ÌœÊVœ“«iÝÊÅ>«iÃÊ>˜`Ê«Àœ`ÕVÌÊvœÀ“ð Long-term implantable grades of PAEK (PEEK) meeting regulatory requirements are available from Invibio (Optima), Solvay (Solviva Zeniva) and Oxford Performance Materials (grades of polyaryletherketoneketone (PEKK)). Material for prolonged

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applications can be obtained from Invibio, Solvay or Evonik (Vestakeep M). Typically these are manufactured to the standards of good manufacturing practice as defined by ISO 13485. In some ways the product ranges are similar to industrial-grade materials but they are produced to even higher standards and levels of testing. In particular end users need to be confident that the material they receive is the same as the original material that underwent biocompatibility testing. This requires careful control of change (or even ‘no change’) and excellent quality control, material traceability and packaging. Products available from Invibio include the following: UÊ *

Ê"«Ìˆ“>ÊqÊ/…ˆÃʈÃÊ̅iʜÀˆ}ˆ˜>Ê}À>`iʜvʈ“«>˜Ì>LiÊ*

Ê launched in 1998. It is available in a variety of forms including stock shapes, glass and carbon fibre-reinforced compounds and radio-opaque grades. It is tested to the standards of ISO 10993 including genotoxcity, hemolysis, cytotoxicity, biostability, sensitisation, pyrogenicity and chemical analysis. It also meets the requirements of USP Class VI. UÊ ˜`œˆ}˜Ê qÊ /…ˆÃÊ ˆÃÊ >˜Ê ˆ“«>˜Ì>LiÊ Vœ˜Ìˆ˜ÕœÕÃÊ V>ÀLœ˜Ê wLÀiÊ composite which is used for the replacement of metals in high sustained or cyclic load applications. The ability to control fibre direction means that mechanical properties can be tailored for specific applications. It is supplied as a pre-impregnated tape or as rods that can be heat-formed through processes such a composite flow moulding. UÊ œÌˆÃÊ qÊ
Ê Üi>ÀÊ }À>`iÊ vœÀÊ Li>Àˆ˜}Ê >««ˆV>̈œ˜ÃÊ >}>ˆ˜ÃÌÊ …>À`Ê counter-faces such as metal and ceramics. Designed for arthroplasty (joint formation) devices. UÊ *

‡ >ÃÈÝÊqÊ/…ˆÃʈÃÊ`iÈ}˜i`ÊvœÀÊLœœ`ʜÀÊ̈ÃÃÕiÊVœ˜Ì>VÌʜvÊ less than 30 days. It meets USP Class VI and the relevant parts of ISO 10993 (cytotoxicity and sensitisation). Applications include catheters, laparoscopes and endoscopes.

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PAEK are frequently used without surface modification. There are a significant number of papers and patents which describe PEEK modified with fillers such as hydroxyapatite (HA) or calcium phosphates, titanium coatings or even biomimetic protein and peptide sequences. Some of these are described in reference [2]. However, in HA-filled PAEK there is a trade-off between mechanical properties and modified biocompatibility. Various attempts have been made to overcome this limitation - for example by using HA coatings or HA whiskers [3, 4]. Biological modifications would be subject to extremely complex regulatory approval. In fact unmodified PEEK has been shown to be comparable in vitro with the bone forming capacity of titanium [5]. Recently PEEK fibres have been evaluated for biocompatibility with encouraging results [6] and porous PEEK materials are under development [7].

8.2 Applications Medical applications [2, 8, 9] of PAEK can be divided into shortterm medical devices (less than a day), prolonged (less than 30 day) implants and permanent implants. There are a very large number of patents relating to designs for permanent PAEK implants.

8.2.1 Short-term Applications Many short-term and prolonged medical devices are fabricated from PAEK. This has a lot to do with ease of repeated sterilisation, mechanical properties, purity (low extractables) and resistance to a very wide range of environments. Applications include: UÊ /ÕLˆ˜}Ê>˜`ÊV>̅iÌiÀÃʇÊvœÀÊiÝ>“«i]ÊvœÀÊÃÌi˜ÌÊ`iˆÛiÀÞʈ˜Ê“ˆ˜ˆ“>ÞÊ invasive surgery; UÊ i>̇ÅÀˆ˜Ž>LiÊÌÕLˆ˜}ÊvœÀÊ܈Àˆ˜}Ê«ÀœÌiV̈œ˜Æ

116

Medical Grades and their Applications

UÊ -ÌiÀˆˆÃ>LiÊ`ˆ>}˜œÃ̈VÊ`iۈViÃÆ UÊ ÀÕ}Ê`iˆÛiÀÞÆ UÊ œœ`ʓ>˜>}i“i˜ÌʇÊvœÀÊiÝ>“«i]Ê`ˆ>ÞÈÃÊiµÕˆ«“i˜ÌÆ UÊ >«>ÀœÃVœ«iÃÆ UÊ -ÕÀ}ˆV>Êˆ˜ÃÌÀՓi˜ÌÃÆ UÊ -ÕÀ}ˆV>Ê…i>`ÊÀiÃÌÀ>ˆ˜ÌÃÆ UÊ ˜`œÃVœ«iÃÆ UÊ ˜`œÃVœ«ÞÊV>“iÀ>ʅœÕȘ}ÃÆ UÊ i˜Ì>Ê̜œÃÆ UÊ iVÌÀœÃÕÀ}ˆV>Ê`iۈViÃÆ UÊ
˜>Þ̈V>ÊiµÕˆ«“i˜ÌÆ UÊ …Àœ“>̜}À>«…ÞÆÊ>˜` UÊ ˆœ‡…>â>À`ʅ>˜`ˆ˜}°

8.2.2 Permanent Implants Spinal implants were amongst the earliest permanent applications. They were developed to stabilise the lumbar or cervical spine and facilitate fusion of the vertebrae after surgery for degenerative disc disease or spinal instabilities. Conventionally these devices are made out of titanium. However, metal implants are radio-opaque and cause MRI artefacts which hinder the assessment of bone growth and the extent of fusion. Moreover it has been suggested that stress shielding effects can inhibit bone growth. Accordingly PAEK spinal devices were marketed by Accromed (now DePuy) following a series of clinical studies which started in 1989. Initially both PEEK and PEKEKK were considered and found to be very similar - although PEKEKK

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offered slightly higher strength. However, following the withdrawal of PEKEKK by BASF in 1995, PEEK became the dominant PAEK in implant applications. There are now a wide range of PEEK spinal devices manufactured by companies such as DePuy, Stryker, Medtronic and Pioneer Surgical. The key advantage remains compatibility with radiographic and MRI. The devices can be further improved by using radio-opaque dots which allow precision location. Bone pins, screws and plates have traditionally been metallic and require high strength and modulus. The availability of implantable grades of continuous carbon fibre PAEK means that it is now possible to use polymeric materials in mechanically demanding applications. The properties of such implants can be carefully tailored to meet the needs of the application. Metal implants have been associated with a reduction in bone quality due to stress shielding and there are concerns about the long-term effects of exposure to metal ions. Moreover polymeric implants can be more easily adjusted to fit the patient’s unique bone structure during surgery. The Icotec ‘composite flow moulding’ process allows the production of a family of innovative pins, screws and plates while maintaining fibre length and orientation Q£äR°ÊˆÝ>̈œ˜Ê`iۈViÃʅ>ÛiÊ>ÃœÊLii˜Ê`iÛiœ«i`ÊvœÀʏˆ}>“i˜ÌÃÊqÊvœÀÊ example, the spiked washers produced by Mathys. In some applications (such as ligament fixation) complete radiotranslucency would be a disadvantage but in these circumstances special contrast additives can be used to ensure optimum radiological definition [11]. Joint replacement applications include both static structural components and the need for wear-resistant moving surfaces. Applications can be small scale (such as the finger implant stems made by Mathys) or be targeted at large-scale mechanically demanding joints. Hip prostheses have been an obvious target - although the existing technology is long established and works reasonably well. The ability to tailor the stiffness of the femoral stem reduces stress shielding effects and the excellent fatigue resistance of PAEK-based materials allows long-term durability. Such non-metallic implants >ÀiÊ>ÃœÊi>ÈiÀÊ̜ʈ˜Ã«iVÌÊLÞÊÌiV…˜ˆµÕiÃÊÃÕV…Ê>ÃÊ,]Ê8‡À>ÞÃÊ>˜`Ê /°Ê The Bradley Stem was developed as early as 1986 and consisted of

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a tapered metallic core with a carbon fibre PEEK outer layer. More recently Zimmer developed the Epoch stem using PEKEKK which was converted to PEEK via an FDA 510 (k) application in 2002. The PEEK used in this Epoch system is believed to have been based on Gatone (electrophilic) resin from Gharda Chemicals [2]. The well-documented wear performance of PEEK and its compounds has led to considerable interest in its use for arthroplasty bearing surfaces. Target applications include acetabular cups in hip joints. Interest has been driven by the well-documented deficiencies of the existing metals, ceramics and polymers and there are numerous papers examining the wear performance of PAEK for these applications [1216]. Wear is superior to conventional materials such as UHMWPE. Recently Invibio has developed grades suitable for wear applications against hard counterfaces such as metals and ceramics [17, 18]. There has been considerable interest in the dental applications of PAEK - partly due to the allergic tissue reactions that can be caused by metal ions. The adjustable stiffness, processability and thermal conductivity are also advantages together with the ability to hide the colour of PAEK implants which may be close to the surface of the gum. Applications include dental implant posts, cups and healing caps. Unlike titanium, PAEK can be sculpted by dentists to fit individual patients. The majority of craniomaxillofacial procedures use titanium implants. However, titanium in these applications has a number of disadvantages. These include: UÊ Ã̈vv˜iÃÃÊÀi>̈ÛiÊ̜ÊLœ˜iʇʏi>`ˆ˜}Ê̜ʫœÃÈLiÊvÀ>VÌÕÀiÃÊ`ÕiÊÌœÊ stress shielding; UÊ ÛˆÃˆLˆˆÌÞÊ̅ÀœÕ}…Ê̅iÊΈ˜Æ UÊ «>ˆ˜Ê`ÕiÊ̜Ê՘˜>ÌÕÀ>ÊiÛiÃʜvʅi>ÌÊÌÀ>˜ÃviÀÆ UÊ œ˜}‡ÌiÀ“ÊÀii>ÃiʜvʓiÌ>Êˆœ˜ÃÆÊ>˜` UÊ ˆ˜ÌiÀviÀi˜ViÊ܈̅ʈ“>}ˆ˜}ÊÌiV…˜ˆµÕið

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PAEK can help to avoid all these disadvantages. Moreover it is relatively easy to produce computer-designed implants based on structural information from individual patients. The mechanical reliability of PAEK has led to their use in a variety of devices. For example, they are being evaluated in applications such as heart valves [19] and by Impella AG as rotors for bi-ventricular, intra-cardiac pump systems which can be inserted into the heart to replace heart-lung machines. PAEK also find applications as housings for implantable medical devices such as heart pacemakers [20, 21].

References 1.

R.M. Turner, M.S. Swerdlow and B. Bate, inventors; ICI, assignee; US 4662887, 1985.

2.

-°°ÊÕÀÌâÊ>˜`Ê°Ê iۈ˜i] Biomaterials, 2007, 28, 32, 4845.

3.

G. Converse, T. Conrad and R. Roeder, Journal of the Mechanical Behaviour of Biomedical Materials, 2009, 2, 627.

4.

S. Vedova, P. Robotti, A. Fabbri, D. Zeni, D. Amato and B. Monelli in Proceedings of the World Biomaterials Congress, Amsterdam, The Netherlands, 2008.

5.

K. Sagomonyants, M. Jarman-Smith, J. Devine, M. Aronow >˜`Ê°ÊÀœ˜œÜˆVâ]ÊBiomaterials, 2008, 29, 11, 1563.

6.

M. Jarman-Smith, M.P. McFetridge and N. Pierre in the Transactions of the 8th World Biomaterials Congress, 2008, Poster P-Sat-K-675.

7.

P. McFetridge, N. Pierre and M. Jarman-Smith in Transactions of the World Biomaterials Congress, Amsterdam, The Netherlands, 2008.

8.

°Ê-ˆ˜âʈ˜ÊProceedings of Medical Plastics 2003, Copenhagen, Denmark, 2003.

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9.

M. Jarman-Smith, Medical Device Technology, 2008, 19, 6, 12.

10. U. Loher, J. Mayer, P. Tognini, T. Wegener and E. Wintermantel, inventors; Amsler Peter, assignee; WO19336, 1995. 11. M. DeLangen, S. Green and J. Schlegel, inventors; Invibio Ltd., assignee; GB2438282, 2005. 12. S. Scholes and A. Unsworth, Journal of Engineering in Medicine, 2009, 223, 1, 13. 13. S. Scholes, I. Inman, A. Unsworth and E. Jones, Journal of Engineering in Medicine, 2008, 222, 3, 273. 14. S. Scholes and A. Unsworth, Journal of Engineering in Medicine, 2007, 221, 3, 281. 15. S. Scholes and A. Unsworth, Journal of Materials Science: Materials in Medicine, 2009, 20, 1, 163. 16. T. Brown, Q. Bao, T. Schwenke and M. Wimmer in Transactions of the World Biomaterials Congress, Amsterdam, The Netherlands, 2008 17. °Ê iۈ˜iÊ>˜`Ê°Ê-ˆ˜â]ʈ˜Ûi˜ÌœÀÃÆʘۈLˆœÊÌ`°]Ê>ÃÈ}˜iiÆÊ WO050082A1, 2008. 18. J. Devine, inventor; Invibio Ltd., assignee; GB2435648A, 2007. 19. J. Devine, J. Schlegel and R. Groeger, inventors; Invibio Ltd., assignee; GB2452518, 2007. 20. S. Green, inventor; Invibio Ltd., assignee; WO2009968914, 2009. 21. M. Warwick, S. Green and D. Hawks, inventors; Invibio Ltd., assignee; WO2009068915, 2009. 121

Update on the Technology and Applications of Polyaryletherketones

122

A

bbreviations

ABS

Anti-lock braking system

APC

Aromatic polymer composite

APC1

Aromatic polymer composite generation 1

APC2

Aromatic polymer composite generation 2

Bis S

Bisphenol S

CA

Grade code for carbon fibre reinforced material

CMP

Chemical mechanical polishing/planarisation

13

Carbon-13 nuclear magnetic resonance

CT

Computed tomography

CTE

Coefficient of thermal expansion

CUT

Continuous use temperature

DHB

Dihydroxybenzophenone

DSC

Differential scanning calorimetry

ESC

Environmental stress cracking

ESD

Electrostatic dissipative

FEP

Fluorinated ethylene propylene

19

Fluorine-19 nuclear magnetic resonance

FOUP

Front opening unitary pod

FTIR

Fourier transform infrared spectroscopy

GL

Glass fibre

GPC

Gel permeation chromatography

HA

Hydroxyapatite

HDT

Heat distortion temperature

C-NMR

F-NMR

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Update on the Technology and Applications of Polyaryletherketones

HTX

High temperature crystalline polymer

ITX

Intermediate temperature crystalline polymer

JSEP

Jilin Super Engineering Plastics Research Co., Changchun

KF

Potassium fluoride

LCP

Liquid crystalline polyesters

LKF

Long chain difluoride monomer

LOI

Limiting oxygen index

LTMP

Low-temperature melting peak(s)

MFI

Melt flow index

MIM

Metal injection moulding

MRI

Magnetic resonance imaging

Mw

Weight average molecular weight

NMR

Nuclear magnetic resonance

PA11

Polyamide 1,1

PA66

Nylon 6,6

PAEK

Polyaryletherketone(s)

PAES

Polyarylethersulfones

PBI

Polybenzimidazole

PBO

Poly(p-phenylene benzobisoxazole)

PBT

Polybutyleneterephthalate

PC

Polycarbonate

PEEK

Polyaryletheretherketone

PEEKK

Polyaryletheretherketoneketone

PEEK HT

Victrex Tradename for PEK – HT commonly taken to mean ‘high temperature’

PEI

Polyetherimide

PEK

Polyaryletherketone

PEKEKK

Polyaryletherketoneetherketoneketone

PEKK

Polyaryletherketoneketone

124

Abbreviations

PEN

Polyethylenenaphthalate

PET

Polyethylene terephthalate

PFA

Perfluoroalkoxy

PFSR

Pattern-fitting structure refinement

PP

Polypropylene

PPS

Polyphenylene sulfide

PTFE

Polytetrafluoroethylene

PVDF

Polyvinylidene fluoride

RFID

Radio frequency identification

RoHS

Restriction of hazardous substances

RTI

Relative temperature index

S-PEEK

Tradename of new JSEP PEEK

SRP

Self-reinforcing polymers

Tg

Glass transition temperature(s)

TLCP

Thermotropic liquid crystalline polyesters

Tm

Melting temperature

TPI

Thermoplastic polyimide

UHMWPE Ultrahigh molecular weight polyethylene UV

Ultraviolet

WAXS

Wide angle X-ray scattering

WEEE

Waste electrical and electronic equipment

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126

A

ppendix

Appendix 1 Properties of Polyaryletherketone (PAEK) Compounds and Composites Figures A1-A4 are reproduced from A. Wood, J. Walling and D. Padier in Proceedings of the Polymers in Defence and Aerospace Conference, 2007, Toulouse, France, by permission of Victrex, plc and Smithers Rapra.

Figure A1 Yield strength as a function of temperature for Victrex polyaryletheretherketone (PEEK) and related compounds

127

Figure A2 Dynamic fatigue properties of Victrex PEEK compounds at 5 Hz and 23 °C

Update on the Technology and Applications of Polyaryletherketones

128

Figure A3 Coefficient of linear thermal expansion (CTE) of Victrex PEEK-based materials in comparison with other common aerospace materials

Appendix

129

Figure A4 Specific strength of Victrex PEEK-based materials in comparison with other common aerospace materials

Update on the Technology and Applications of Polyaryletherketones

130

Appendix

Appendix 2 Trademarks The author and publisher acknowledge that the names of products used in this review, except where they are recognised chemical names, are invariably trademarks of their respective manufacturers. In the field of PAEK this includes but is not limited to: Evonik: Vestakeep, Vestakeep M Solvay: Solviva, Zeniva, Ketaspire, Avaspire, Gatone Victrex: Victrex PEEK, PEEK-HT, T-Series, Max-Series, ST, Vicote, Aptiv, all the grade codes in Table 4.1 Invibio: PEEK Optima, Endolign, Motis, PEEK Classix Oxford Performance Materials: OxPeKK and Permetta JSEP: S-PEEK Polymics: Arylmax.

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132

I

ndex

A Abrasion resistance 61 Amide imides 72 Amines 40 Annealing 39, 45 temperature 26 Anti-lock braking system tappets 93 Aromatic polymer compound technology 2 Aromatic polymer compound technology – 2nd Generation 2, 57 Aromatic polymers, high-temperature 40 Avrami kinetics 21

B Biaxial stretching, two-stage 46 Biphenol 9, 11 Bradley stem 118

C Catheters 115 Char particles 17, 35 Chemical mechanical polishing/planarisation 101 retaining rings 102 Chemistry, nucleophilic 9 Chloromonomers 9 13 C-Nuclear magnetic resonance spectroscopy 28 Coathanger die 59 Coatings, fluoropolymer 61

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Update on the Technology and Applications of Polyaryletherketones

Comparative tracking index 43 Composite flow moulding 118 Composites, thermoplastic 3 Compounds, long-fibre-reinforced 54 Compression moulding 51, 62 Cone calorimetry 42 Continuous use temperature 35, 68, 70-71 Corona discharge 60 Creep modulus 34-35 Crystalline morphology 19 Crystalline polymer, intermediate temperature 88 Crystallinity 18, 23, 37 Crystallinity, degree of 24, 39 Crystallisation, solvent-induced 40

D Degradation mechanism, free radical 41 Degree of orientation 70 Dibenzofuran 36 Dichlorobenzene 67 Dichlorodiphenylsulfone 9, 67 Die drawing 46 Differential scanning calorimetry 5, 23-25, 28 Difluorobenzophenone 6 Difluorodiketone 6, 8 Difluoromonomers 9 Dihydroxybenzophenone 6 Dihydroxydiketone 6 Dihydroxydiphenylsulfone 9 Diphenylether 12 Diphenylsulfone polymerisation 9 Dispersion spraying 61 Dupont 2, 57, 72 Dynamic mechanical thermal analysis 5

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Index

E Electromagnetic shielding effects 70 Electrophilic processes 1, 3, 12 Electrostatic powder 61 Endolign 115 Environmental stress cracking 38, 40 EOS GmbH 47 Ethylphenoxyphenoxybenzene 13 Extem 67, 78 Extremetube 96 Extrusion 27, 51, 60, 62, 68, 71 solid-state 46

F Fabrication, high-volume 58 Failure, tribological 38 Fluorinated ethylene propylene 71 Fibreforge relay station 59 Fibre placement 59 Fillers, mineral 60 Flame spraying 61 Fluorobenzene 8-9 Fluoromonomer 10 Fluoropolymers 33, 61, 71, 80 19 F-Nuclear magnetic resonance spectroscopy 28 Fourier transform infrared spectroscopy 23-25, 28 Friedel-Crafts acylation 8 Front opening unitary pods 101

G Gatone 12 Gears, balance shaft modules 93 Gel permeation chromatography 27, 40 Gharda Chemicals 3, 8, 12, 13, 14 Glass fibre-reinforced peek 89-90

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Update on the Technology and Applications of Polyaryletherketones

Glass transition temperature 1, 5, 9-10, 21-22, 25, 28, 46, 58, 60, 67-69, 72, 76

H Halogens 39 Heat distortion temperature 34, 69, 70, 72, 78, 99 Helical PEEK, gear wheels 109 Helmholtz resonator effect 91 Hydrolysis 72 Hydroquinone 6 residue 11

I ICI compounds 52 Icotec ‘composite flow moulding’ process 118 Imides, non-melting 72 Imides, thermoplastic 67, 77 Impregnation methods 56 direct melt 56 fibre co-mingling 57 powder impregnation 57 volatile plasticisers for 56 Inherent flame resistance 69 Injection moulding 27, 44-45, 51, 68, 97 Interfacial wear mechanism 54 Invibio PEEK Optima 114 Isomorphism 81 Isophthaloyl chloride 12

K Kapton polyimide 58

L Lamellar structure 21 Lamination, autoclave 58

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Index

Laparoscopes 115 Laser sintering 47 Lewis acids 39, 43 Limiting oxygen index 41, 66, 68, 69, 71, 73 Liquid crystalline polyesters 76, 97-98 thermotropic 70-71, 80 Liquid crystalline polymers, thermotropic 2 Low-temperature melting peaks 21, 25-26

M Magnetic resonance imaging 70, 114 Mark-Houwink constants 27 Mark-Houwink parameters 27 Materials, thermoplastic 33 Melt flow index 26 Melt viscosity 27 Metal injection moulding 98 Microscopy, hot-stage 21 Miscibility 81 Mississippi Polymer Technologies 68 Molybdenum disulfide 72 Motis 115 Mucell supercritical gas foaming technology 62

N Nitrogen saturation technology 62 Non-isothermal PEEK, crystallisation of 22 Nuclear magnetic resonance spectroscopy 28 Nucleophilic technology 3 Nylon 4t 68

O Orientation process 46, 60 Oxidative environments 39

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Update on the Technology and Applications of Polyaryletherketones

P Paraphenylene 68 Pattern-fitting structure refinement 19 PEEK blend with polybenzimisazole 105 blend with polyphenylsulfide 79 carbon fibre-reinforced 89-90, 96 crystallinity 77 electrostatic dissipative grades of 101 film 59, 99, 106 foams 62 impellers 90 modified 76 optima 114, 115 propellers 90 thermoplastic composites 58 victrex 51 PEEK-Classix 115 PEK, polymerisation of 10 PEKK, amorphous 89 Perfluoropolymers 71 Phthaloyl chlorides 12 Plasma treatments, atmospheric pressure oxygen 60 Plastics, medical-grade 113 Plungers 93 Polyamides, high-temperature 68 Polyaryletherketone (PAEK) blends 75 film 106 nomenclature 1 producers 2 spinal devices 117 thermoplastic composites 58, 91 unfilled 33, 51, 108 Polyaryletherketoneketone 20 Polybenzimidazole 55, 65, 73, 79

138

Index

Polyetherimide 77, 78 miscible polymers 78 Polyetherisation routes, nucleophilic 67 Polyethersulfones 2 Polyimides 33, 65 Polyimides, thermoplastic 67 Polyketone copolymers 1 Polymer blends, miscible 77 Polymer crystallography 20 Polymer, high temperature crystalline 88 monomers 11 Polymerisation 4 condensation 9 residual 43 Polymers, high-performance 33 Polymers, self-reinforcing 69 Polymics 13, 52 Polyphenylene 68-69, 80 Polyphenylene sulfide 67-68, 79 Polypropylene 97 Polytetrafluoroethylene 54, 71, 92 Press consolidation 59 Press lamination 58 Primospire 68-69 Processes, nucleophilic 1, 3-4 Processing, thermoplastic 44

R Radiation resistance 40 Recrystallisation 26 Relative temperature index 35 Resins, amorphous 67 Restriction of hazardous substances 96 Rheometry, capillary 26 Routes, nucleophilic 9, 12 RTP 89

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Update on the Technology and Applications of Polyaryletherketones

S Scanning electron microscopy 21 Self-nucleation 44 Single-screw extruder 59 Small-angle x-ray scattering 21 Solvent, polymerisation 9 Solvents, protic 4 Spinal implants 117 Stability, thermal and morphological 75 Stock shapes 62 for prototyping 62 Stress concentrations 39 Stress, residual 39 Stress shielding 119 Strong acids 39 Sulfonated fluoropolymers 11 Sulfones, amorphous 67 Surface treatment 46-47, 60

T Terephthaloylchloride 8 Thermal ageing 60 Thermoforming 58-59 Thermoplastics 52 Thioacetalisation, reversible 27 Torlon polyamideimide 72 Twin-screw extrusion technology 56

U Ultem 67 Ultrahigh molecular weight polyethylene 114 Ultraviolet resistance 88 Unfilled competitive polymers 66

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Index

V Vespel 72 Vicote coatings 61 Victrex max series 78 Victrex t series 102

W Wafer cleaning equipment 102 Waste electrical and electronic equipment 96 Welding Institute 46 Welding, friction 46 Welding, hot plate 46 Welding, near-field ultrasonic 46 Wide-angle x-ray scattering 23-25

X X-ray analysis 20 X-ray computed tomography 114 X-ray diffraction, microbeam 44 X-ray imaging artefacts 70

Z Zeneca biopolymers 113 Zotefoams 62

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Published by iSmithers, 2010

PolyArylEtherKetones (PAEK) have been described as the world’s highest performance true thermoplastic polymers. It is now 30 years since the invention of Victrex PEEK (PolyEtherEtherKetone) and PAEK are found in niche applications in almost every industry sector. PAEK are produced by several suppliers. As the market has grown an ever increasing range of products forms has been developed. These include higher temperature variants such as PEK, PEKEKK, PEEKK and PEKK and also compounds, blends, composites, films, shapes, coatings and medical grades. PAEK find applications in the automotive, chemical process, oil and gas, aerospace, medical device, telecommunications and electronics industries. They are often used because of a combination of properties which goes far beyond temperature resistance and includes resistance to wear, chemical environments, hydrolysis, sterilisation and fire together with biocompatibility, purity, low smoke and toxic gas emission and electrical performance. This review provides an overview of all the key aspects of PAEK technology including their production, characterisation, product forms (including compound, blends, composites, films, coatings and medical grades) and classes of application in each industry sector. It includes the many of the key historical developments and discusses up to date information on manufacturers, product forms and applications.

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