WO2003093354A1

WO2003093354A1 - Method of manufacturing a composite material_

Info

Publication number: WO2003093354A1
Application number: PCT/GB2003/001872
Authority: WO
Inventors: Kenneth Malcolm Seargeant
Original assignee: Victrex Manufacturing Limited
Priority date: 2002-05-02
Filing date: 2003-05-02
Publication date: 2003-11-13
Also published as: GB0210085D0; AU2003239662A1

Abstract

A method of manufacturing a composite material and such a material per se is described. The method comprises selecting a matrix material which may be a thermofusible material such as an engineering resin, with polyetheretherketone resin being preferred, and a filler material which may be fibrous and may be an inorganic or organic fibrous material. The method comprises contacting the matrix material and filler material in a liquid medium, for example water, so as to provide a mixture of the matrix material and filler material in the liquid medium and then contacting the mixture with a sieve so as to remove at least some of the liquid medium thereby to form a mass comprising matrix material and filler material. This mass may then be used to make articles by injection moulding or extrusion.

Description

METHOD OF MANUFACTURING A COMPOSITE MATERIAL

This invention relates to a composite material and particularly, although not exclusively, relates to a method of manufacturing a composite material.

Manufacture of composite materials by compounding long fibres into thermally melt fusible matrix materials, for example polymeric materials, and maintaining fibre length is fraught with problems. Low viscosity polymeric materials are considered to be easier to process than higher one's but ensuring good dispersion of fillers within such polymeric materials is still difficult. With higher viscosity polymeric materials, there is a tendency for mechanical forces from processing equipment to generate high forces in fibre/matrix mixtures that tend to break the fibrous material and/or necessitate very long processing times. For example, in known low cost composites made by compounding discontinuous fibres having initial fibre lengths of about 10mm with a matrix material, the fibres may have their lengths reduced to as low as 200μm by the processing equipment with consequential loss of potential mechanical properties. The reduction in length is particularly noticeable for relatively brittle fibres.

The abovementioned problems are particularly acute when compounding polyaryletherketones, for example polyetheretherketone, with fibres due to the relatively high viscosity of such polymers.

Additionally, many unsized fibrous materials ball-up with little mechanical agitation making it difficult to feed them into processing equipment, particularly at relatively high fibre weight fractions.

It is an object of the present invention to address the abovedescribed problems .

According to a first aspect of the invention, there is provided a method of manufacturing a composite material which comprises a matrix material and a fibrous or plate- like filler material, the method comprising:

contacting the matrix material and filler material in a liquid medium so as to provide a mixture of the matrix material and filler material in the liquid medium; and removing at least some of the liquid medium thereby to produce a mass comprising matrix material and filler material.

In the method, said liquid medium may be at a temperature of less than 0°C when said matrix material and filler material are initially contacted with the liquid medium. Preferably, however, said liquid medium is at a temperature of greater than 0°C. The temperature may be greater than 5°C, preferably greater than 10°C, more preferably greater than 15°C, especially 20°C or greater.

The temperature could be greater than 100°C. Suitably, however, the temperature is less than 100°C, preferably less than 80°C, more preferably less than 50°C, especially less than 30°C. Advantageously, said liquid medium may be at ambient temperature when said matrix material and filler material are initially contacted with liquid medium. Preferably, the liquid medium is at ambient pressure when said matrix material and filler material are initially contacted therewith and, preferably, at all times prior to removal of said liquid medium.

The method suitably involves mixing the matrix material and filler material in said liquid medium. Any suitable mixing means may be used. It is preferred to use a mechanical mixing means, for example a paddle mixer. Suitably, the mixing means is selected to minimise forces on the filler material which could size reduce the material detrimentally. During said mixing, the mixture may be maintained at a temperature in the range 10°C to 50°C, suitably at ambient temperature. Suitably, it is not necessary to apply heat to the mixture during its mixing.

Preferably, in the method, a slurry of said matrix material and said filler material in said liquid medium is produced. Thus, preferably, both the matrix material and filler material are substantially insoluble in said liquid medium. Preferably, said matrix material and filler material are substantially homogenously dispersed in said slurry.

The ratio of the weight of filler material to matrix material in said mixture may be at least 0.1, suitably at least 0.5, preferably at least 1, more preferably at least 1.5, especially at least 2. The ratio is suitably less than 5, preferably less than 3.

The amount of said liquid medium in said mixture may be selected so that the matrix material and filler material can be intimately mixed in the method, suitably so that the matrix and filler materials are substantially uniformly dispersed throughout the liquid medium. The ratio of the weight of liquid medium to the weight of filler material may be at least 5, suitably 10 or more. Such relatively low ratios may be sufficient for filler materials having relatively short lengths to be dispersed. Where the filler material comprises relatively long fibres, the ratio may be higher - it may be 50, 100 or 150 or more. Preferably, however, the ratio is less than 500, more preferably less than 250, especially less than 200. ^•

Preferably, in the method, the filler material is separated, as far as possible, so that there are individual elements of said filler material in said mixture - that is, the mixture formed preferably does not include clumps of said filler material .

Preferably, in the method, the mixture of matrix material and filler material is contacted with a support and liquid medium removed from the mixture. Preferably, the support supports the forming composite material as liquid medium is removed therefrom. Preferably, the support includes openings therein via which said liquid medium may be removed, for example by said liquid medium passing from one side to an opposite side of said support . Said support is preferably perforate. It is preferably part of a sieve means.

Preferably, in the method, liquid medium is allowed to drain away from the forming composite material suitably under the action of gravity. Removal of liquid medium may be vacuum assisted. Suitably, a layer of composite material is formed on said support. In some situations, a further layer may be formed over said layer, for example by contacting said layer with more of said matrix material and filler material in said liquid medium.

Preferably, the method includes a drying stage. Preferably, after contact with said support and suitably after an initial amount of liquid medium has been removed, for example drained away, the formed composite material is dried. This may be effected by application of heat, suitably at a temperature which is greater than the boiling point of said liquid medium. Said temperature is preferably less than 300°C and, more preferably, is less than 200°C. Preferably, said formed composite material is dried in an oven.

The method may include a step of increasing the density of the formed composite material after at least some of said liquid medium has been removed from said mass. This may be achieved by use of a press or other compaction means . Said step of increasing the density may be carried out before or after said drying stage.

Said composite material may have a density of at least 0.05 g/cm³, suitably at least 0.10 g/cm³, preferably at least 0.15 g/cm³, more preferably at least 0.2 g/cm³, especially at least 0.3 g/cm³. The density may be less than 0.6 g/cm³, less than 0.5 g/cm³ or even less than 0.4 g/cm³.

In some embodiments, continuous sheets, (for example of thickness as low as 50μm) of the composite material may be formed, suitably using pressure to increase the density of the composite material. Parts having desired shapes may be stamped out of or otherwise formed from the sheets.

Alternatively, said composite material made in the method may be a prepreg. Said composite material may be divided up into smaller parts for example having a maximum dimension of less than 5cm, preferably less than 3.5cm, more preferably less than 2cm. Said smaller parts are preferably of a size such that they can feed processing apparatus, for example an injection moulder or extruder which may be used to produce articles from the composite material . The parts may have a maximum dimension of greater than 0.5cm, preferably greater than 1cm.

Said filler material suitably has an aspect ratio before contact with said matrix material of at least 5, preferably at least 10, more preferably at least 25. Where the filler material is fibrous, said aspect ratio may be greater than 50 or even greater than 100. The aspect ratio is suitably less than 50,000, preferably is less than 1,000, more preferably is less than 500 and, especially is less than 200.

Where said filler comprises a fibrous material, said material is suitably discontinuous. Thus, preferably greater than 95wt% of fibres in the material have a length before contact with said matrix material of less than 50mm, preferably less than 30mm, more preferably less than 15mm, especially less than 10mm.

The average of the maximum dimensions of said filler material before contact with said matrix material (e.g. the average length when said filler material is a fibrous material) may be at least 200 μm, suitably at least 1mm, preferably at least 2mm, more preferably at least 3mm. The average may be less than 100mm, preferably less than 50mm.

Said filler material may be selected from glasses, graphite-based materials, synthetic organic polymers, inorganic materials, minerals, metals and ceramics.

Examples of glasses includes silicic acid and other glass fibre products.

Examples of graphite-based materials include graphite platelets and carbon fibres.

Examples of synthetic organic polymers include polyaramids and party oxidised polyacrylonitrile (PAN) materials .

Examples of inorganic materials include alumina.

The method is particularly useful wherein the filler material is brittle since it may reduce breakage of the material. The method may be particularly advantageously applied to brittle fibrous materials, for example glass fibres and/or inorganic fibres such as silicic acid fibre and/or alumina fibre. However, the method may also be used for preparing composites of tough fibres such as polyaramids, especially pulp or fibrillated forms.

In preferred embodiments, said filler material comprises one or more fibrous materials. Preferably, said filler material consists essentially of a single type of material .

Said liquid medium used in the method is preferably unreactive to the matrix material and filler material under the conditions of the method. Said liquid medium preferably has a boiling point of less than 200°C, preferably less than 150°C. The boiling point may be at least 50°C, preferably at least 80°C. Said liquid medium preferably comprises water. Whilst said liquid medium could include one or more co-solvents it preferably does not. Thus, preferably said liquid medium consists essentially of water.

Said matrix material may comprise any thermofusible material which is available in a particulate form, for example as a fine powder. It may comprise more than one material. Said thermofusible material may be a metal, for example aluminium or an alloy thereof. Preferably, however, said matrix material is a high temperature engineering resin. Examples are provided in Figure 1 of the accompanying drawings .

Said matrix material is preferably a polyether, especially an aromatic polyether, for example an aromatic polyetherketone or polyethersulphone . Preferred polyethers are those shown in Figure 1.

Said matrix material is preferably a polyarylether ketone or sulphone. Said matrix material is preferably a polyaryletherketone, with polyetherketone and polyetheretherketone being especially preferred.

Polyetheretherketone is the most preferred matrix material. Preferably, said matrix material consists essentially of polyetheretherketone.

Preferably, the matrix material contacted with said liquid medium in said method is a powder. Said matrix preferably has no particles having a dimension of greater than 2mm, preferably of greater than 1mm. The d₅₀ of the matrix material may be less than 500μm, preferably less than 250μm. The d₅₀ may be greater than lOμm, preferably greater than 25μm. In general, it is found that finer powders are advantageous as the amount of filler, especially fibrous filler, increases.

According to a second aspect of the invention, there is provided a composite material made in a method according to the first aspect.

The invention extends, in a third aspect, to a composite material as described in any statement herein per se.

According to a fourth aspect of the invention, there is provided a method of making an article by injection moulding or extrusion which comprises injection moulding or extruding a composite material according to said second or third aspects .

The method suitably involves injection moulding or extruding a composite material comprising a matrix material which is a polaryletherketone (especially polyetheretherketone) and a fibrous filler material especially one comprising glass and/or inorganic fibres. The method of the fourth aspect suitably involves use of injection moulder or extruder barrel temperatures of at least 100°C, preferably at least 200°C, more preferably at least 300°C and especially of at least 400°C.

According to a fifth aspect of the invention, there is provided an article made of a composite material as described herein and/or in a method as described herein.

Any feature of any aspect of any invention or embodiment described herein may be combined with any feature of any aspect of any other invention or embodiment described herein mutatis mutandis.

Specific embodiments of the invention will now be described, by way of example, with reference to Figure 1 which shows various engineering resins .

The following materials are referred to hereinafter.

Silicic acid fibre - BelCoTex (Trade Mark) fibre obtained from Belchem Fiber Materials GmbH of Germany.

The fibre is a continually melt drawn fibre which is chopped into predetermined lengths to provide a discontinuous fibre.

Saffil RF (Trade Mark) - alumina fibre obtained from Saffil Ltd of Cheshire, England - The fibre is made in a discontinuous manner and is further reduced in length by a secondary milling process. Saffil LA (Trade Mark) - alumina fibre as for Saffil RF except that the LA fibre is the longest fibre available from the supplier in bulk fibre form.

Kevlar (Trade Mark) - a polyaramid fibre obtained from Dupont .

PEEK™ 150PF - a low melt viscosity fine powder grade of polyetheretherketone obtained from Victrex Pic of Thornton Cleveleys, UK. The d₅₀ of the powder is approximately 50μm.

PEEK™ 450PF - a standard melt viscosity fine powder grade of polyetheretherketone obtained from Victrex Pic of Thornton Cleveleys, UK. Again, the d₅₀ of the powder is approximately 50μm.

PEEK™ 450P - standard melt viscosity coarse

(unmilled) grade of polyetheretherketone having a nominal particle size of 2mm x 2mm x 2 mm, obtained from Victrex ic.

Example 1 (Comparative)

6mm long silicic acid fibre as described above was dry mixed by tumbling with polyetheretherketone powder at several weight fractions. The resulting material at all fractions above 5wt% fibre balled up to produce a very low density, cotton wool like material that could only be fed into a compounding extruder by being rammed into the feed throat . Even then the material tended to compact to form a solid bridge ^■ above the feed screws preventing the material being fed into the process . Separate feeding via a screw feeder resulted in the same problem of balling and blocking.

Example 2 (Comparative)

A milled form of Saffil (RF) , was dry blended with PEEK™ 450P in fractions of 10wt% and 20wt% fibre. This was then compounded in a twin screw extruder, a 30mm APV. The resulting granulated compound was injection moulded into dumbbell test pieces for mechanical strength investigation. The resultant values obtained were much lower than that expected. The broken samples were ashed to determine the fibre lengths . The largest of these were seen to be <100μm. As a comparison, a lump of the original milled fibre was placed in a beaker of water and stirred gently so as to separate the fibres for optical microscopic investigation. It was seen that the fibres separated into a well-dispersed suspension very readily. The fibres were generally in the size 200-500 microns indicating that the compounding process used had broken the fibres substantially and may have resulted in the lower than expected mechanical properties seen.

Example 3 (General Procedure)

Varying amounts of unsized 6mm long silicic acid fibres as described in Example 1 were mixed with water in a plastic bucket to form a slurry. The ratio of the wt% of water to fibres may be varied according to the length of the fibres. For the shortest fibres the ratio may be 10:1; for longer fibres, the ratio may be 200:1 or more. Varying amounts of polyetheretherketone powder (PF grade PEEK™ powder from Victrex Pic, having a d₅₀ of approximately 50μm) were added to the mix under the action of a stirrer. The mixture was sieved using a 200mm round sieve (200μm mesh size) to allow the water to separate from the solid material and thereby form a pad (retained within the sieve) comprising fibre and polyetheretherketone. The pad was dried in an oven at a temperature of about 150°C.

In some cases, a layered product may be obtained. Formation of such a product is dependent upon the thickness of the pad, the lengths of fibres used and the manner in which the slurry is poured onto the sieve. For example, the shorter the fibre, the thinner the section of the pad and the more consistent the pouring of material onto the sieve, the less the layering. In a continuous process, the aforementioned may readily be controlled.

Examples 4 to 6

The general procedure of Example 3 was followed with variations as described below.

Example 4

A pad was prepared using 10wt% of a silicic acid fibre and 90wt% of PEEK™ 150PF (a finer grade comprising milled polyetheretherketone) .

The pad was pulled apart into clumps of approximately 10mm cubed. The material could be fed into an injection moulder directly (Example 4a) or could be densified using a hot press at about 400°C (wherein the polyetheretherketone is melted) and granulated in a single screw extruder (Example 4b) at a standard temperature used for processing polyetheretherketone. It should be noted that the pad thickness reduces significantly in the hot press as the polymer melts and so the density of the pad increases. In the extruder, the polyetheretherketone softens and flows rapidly and easily around the fibres to encapsulate them.

Example 5

The procedure of Example 4 was followed using 30wt% of silicic acid fibre and 70wt% of PEEK™ 450PF. The material was densified as described for Example 4b and the solid pad was cut up into 15mm squares using a band saw. This pre-melted and consolidated material was found to feed an injection moulder well.

Example 6

The procedure of Example 4 was generally followed except that PEEK™ 450PF (50wt%) was used with silicic acid fibre (50wt%) . The pad formed was cut up without compaction in a hot press or other densification step and cut, using a pair of scissors, into 15mm squares. The material could be fed directly into an injection moulder.

Example 7 - Testing of Materials

The tensile strength, elongation and tensile modulus of selected examples were assessed according to ASTM D638- 99 and the results are provided in Table 1 below. Table 1

In Table 1, no comparative example based on dry blended material is included due to the difficulties inherent in preparing and/or processing such materials.

It will be appreciated from Table 1 that compaction of the composite appears to improve its mechanical properties. It is also noted that lower viscosity matrix material (PEEK™ 150PF is lower viscosity than 450PF) flows more easily and tends to produce composites of higher strength. Also, in general, increasing the level of fibres improves some of the mechanical properties.

Examples 8 to 16

Saffil RF alumina fibres and polyetheretherketone powder were slurried together in water using a water to fibre weight ratio of about 20:1. The mixture was sieved as described in Example 3 to give a dense pad which was dried. The density of the pad is dependent inter alia on fibre lengths - for the finest fibre grade the density is about 0.3g/cc. The pad could be broken up by hand to give small flock-like granules which could be fed directly into an injection moulder or pre-granulated in an extruder (Example 10)

The relative amounts of fibres and polyetheretherketone were varied in respective examples and tensile strength, elongation and tensile modulus assessed as described for Example 7. Results are provided in Table 2 below. Table 2

CO c

CD O

m

CO

I m m

c m r

CO c

CD CO

m

CO

I m m

c m r

Referring to Table 2, the Example 15 and 16 materials were too stiff to process in the sample mould. However, the samples could be processed by other means. For example, the material of example 16 was made into a 150 x

150 x 10 mm plaque.

It will be appreciated from Table 2 that progressively higher strength and stiffness materials were obtained with increasing fibre fractions showing that the process described is an advantageous way of making materials from otherwise difficult to handle fibrous materials.

Example 17

Saffil LA (42wt%) was slurried with PEEK™ 150PF (58wt%) and pads of material produced as described above. The pads were cut up into 15mm cubes and these low density cubes were fed without further consolidation into an injection moulder and test pieces formed and tested as described in Example 7. Results are provided in Table 3. The dry strength of the pad improved with the longer fibres as did the tensile strength of the final material when compared to Example 12 which was similar but had a higher fibre fraction.

Table 3

Example 18 (Comparative)

Twaron (Trade Mark) pulp (a fibrillated polyaramid fibre) was dry blended with PEEK™ 150PF powder at 1,3 & 5% w/w of the Kevlar. The subsequent mix was fed into a twin screw compounder. The 1% material fed well; however as the fraction increased towards 5% w/w, the bulk density of the compound dropped sufficiently to cause feeding problems and resulted in erratic production. At even higher loading fractions feeding standard equipment would be difficult. Results for 5% w/w loading were: Tensile Strength 99Mpa; elongation 11.3%; Stiffness 4.4GPa

Example 19

Kevlar pulp 50% w/w was slurried with PEEK 150 PF fine powder as before at a ratio of 1:1 w/w (100:1 water to fibre w/w) . The mixture was stirred and strained following the procedure described in Example 3 and the pad formed dried. Again the pad was cut up into 10mm squares and fed into an injection moulder. The density was sufficiently high to cause no feeding difficulty but the resulting product was too stiff to injection mould past the gate on the test piece tool. However, as the material flowed as far as the gate, it is believed that it would be possible to make products using such high fibre to powder ratio mixtures .

Example 20

The procedure of Example 19 was used with a fibre fraction of 15% w/w and the balance being PEEK™ 450 PF.

Acceptable dog bone test pieces were made having tensile strength of 109MPa, tensile modulus 4.9 GPa and elongation of 4.4%.

Example 21

In order to reduce any tendency of a fine pitch based powder (Kureha milled fibre M111F) to settle during the preparation of a composite, a small amount of a highly fibrillated polyaramid fibre (Twaron 1091 obtained from Teijin Twaron bv) was incorporated as described below.

Into 10 litres of water was added 50g of Twaron 1091 and 450g Kureha milled fibre M115F after which 500g of PEEK 150PF was added. The material was drained out on to a sieve and dried overnight in an oven. This material without further treatment was injection moulded to form ASTM tensile bars and tested as previously described. Results: Tensile Strength 149MPa; Tensile Modulus 14-GPa; Elongation 1.2%. Example 22

A procedure similar to that of Example 21 was followed using 10 litres of water into which was added 36g of the Twaron, 480g of the Kureha M115F with 648g of PEEK 150PF and stirred. Again the material was drained and dried before injection moulding. Results: Tensile Strength 154MPa; Tensile Modulus 13.0GPa; Elongation 1.7%. Flexural Strength 234MPa; Flexural Modulus 11.3G; Elongation 2.3%.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference .

All of the features disclosed in this specification

(including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features . The invention is not restricted to the details of the foregoing embodiment (s) . The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of manufacturing a composite material which comprises a matrix material and a fibrous or plate-like filler material, the method comprising:

contacting the matrix material and filler material in a liquid medium so as to provide a mixture of the matrix material and filler material in the liquid medium; and

removing at least some of the liquid medium thereby to produce a mass comprising matrix material and filler material .

2. A method according to claim 1, wherein said liquid medium is at a temperature of greater than 0°C and less than 100°C when said matrix material and filler material are initially contacted with the liquid medium.

3. A method according to claim 1 or claim 2, which includes mixing the matrix material and filler material in said liquid medium.

4. A method according to claim 3, wherein during said mixing, the mixture is maintained at a temperature in the range 10°C to 50°C.

5. A method according to any preceding claim, wherein, in the method, a slurry of said matrix material and said filler material in said liquid medium is produced.

6. A method according to any preceding claim, wherein the ratio of the weight of filler material to matrix material in said mixture is in the range 0.1 to 5.

7. A method according to any preceding claim, wherein the ratio of the weight of liquid medium to the weight of filler material before liquid medium is removed is at least 5.

8. A method according to any preceding claim, which involves contacting the mixture of matrix material and filler material with a support and removing liquid medium from the mixture.

9. A method according to claim 8, wherein the support includes openings therein via which said liquid medium is removed.

10. A method according to claim 8 or claim 9, wherein said support is part of a sieve means.

11. A method according to any preceding claim, which involves allowing said liquid medium to drain away from the forming composite material under the action of gravity.

12. A method according to any preceding claim, which involves a drying stage.

13. A method according to any preceding claim, which includes a step of increasing the density of the formed composite material after at least some of said liquid medium has been removed from said mass.

14. A method according to any preceding claim, wherein said mass formed in the method is divided up into smaller parts.

15. A method according to any preceding claim, wherein said filler material has an aspect ratio before contact with said matrix material of at least 5.

16. A method according to any preceding claim, wherein said filler material is a fibrous material.

17. A method according to any preceding claim, wherein 95wt% of fibres in the filler material have a length before contact with said matrix material of less than 50mm.

18. A method according to any preceding claim, wherein said filler material is selected from glasses, graphite based materials, synthetic organic polymers, inorganic materials, minerals, metals and ceramics.

19. A method according to claim 18, wherein glasses include silicic acid and other glass fibres; graphite based materials include graphite platelets and carbon fibres; synthetic organic polymers include polyaramides and partly oxidised polyacrylonitrile materials; and inorganic materials include alumina.

20. A method according to any preceding claim, wherein said filler material comprises inorganic fibres.

21. A method according to any preceding claim, wherein said filler material comprises a polyaramid.

22. A method according to any preceding claim, wherein said liquid medium comprises water.

23. A method according to any preceding claim, wherein said matrix material comprises a particulate thermofusible material .

24. A method according to any preceding claim, wherein said matrix material is a high temperature engineering resin.

25. A method according to any preceding claim, wherein said matrix material is an aromatic polyether.

26. A method according to any preceding claim, wherein said matrix material is a polyetherketone or polyethersulphone .

27. A method according to any preceding claim, wherein said matrix material is polyetheretherketone or polyetherketone .

28. A method according to any preceding claim, wherein the matrix material contacted with said liquid medium in said method is a powder.

29. A composite material made in a method according to any of claims 1 to 28.

30. A composite material comprising a matrix material which is a polyetherketone or polyethersulphone in combination with a filler material.

31. A material according to claim 30, wherein said filler material comprises polyaramid fibres.

32. A material according to claim 30 or claim 31, wherein said filler material comprises pulp or fibriliated forms of a polyaramid.

33. A method of making an article by injection moulding or extrusion which comprises injection moulding or extruding a composite material according to any preceding claim.

3 . An article made of a composite material and/or by a method as described in any of claims 1 to 33.