WO1991010702A1

WO1991010702A1 - Polymer composition

Info

Publication number: WO1991010702A1
Application number: PCT/EP1991/000021
Authority: WO
Inventors: Wai Yen Chow; Michel Goguelin
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1990-01-15
Filing date: 1991-01-09
Publication date: 1991-07-25
Also published as: US5376701A; DE69111423D1; DE69111423T2; GB9000865D0; JPH05503726A; EP0511235A1; EP0511235B1; CA2073864A1

Abstract

Compositions suitable for producing mineral fibre reinforced thermoplastic composite materials by the wet-laid process comprise mineral fibres, matrix polymer and a coupling agent. The fibres are silanized with reactive silane groups capable of reacting with the coupling agent, for example a maleic anhydride grafted polyolefin, to improve adhesion between the fibres and matrix polymer in the final composite product. The composition excludes components which hinder the reaction between the silane groups and the coupling agent.

Description

Polymer composition.

The present invention essentially concerns a composition suitable for the preparation of a mineral fibre reinforced thermoplastic matrix polymer composite material, a composite material and a process for making same.

In the prior art, there is already known a surface treatment of glass fibres to improve adhesion with a polymeric matrix. Examples of this prior art are JP-A-57-038548 and JP-A-60-046951, which latter discloses a surface treatment of glass fibres by dipping them in an ammoniacal solution of a copolymer of maleic anhydride and vinylacetate or an ethylenic hydrocarbon of formula CnH_2n with n being from 2 to 5, and a silane coupling agent to provide silanized glass fibres.

In the prior art, there are also known mineral fibre reinforced polyolefin matrix composite materials, comprising mineral fibres, a polyolefin matrix and process aids. Most of them are prepared by a dry process based on melt extrusion. Ac co rd i ng to the melt extrusion process, all the components are mi xed together and extruded when the polymer component is molten to prepare the composition (see for instance JP-A-60-001236). The compositions are said to have excellent mechanical strength.

In the composition, the mineral fibres used, usually glass fibres, can be surface treated with a si lane compound, such as an aminosilane.

Different processes are described in order to improve the adhesion between a polyolefinic matrix and a fibrous reinforcing material. Thus, GB-1,378,873 describes the use of a blend of an aromatic monocarboxyLic acid or a carboxylic or polycarboxylic acid and a graft copolymer obtained by grafting an unsatu rated dicarboxylic acid onto a propylene in a melt mixing and extrusion process of polypropylene and fiberglass.

US-A-3,755,245 describes a composite obtained by injection moulding of a mixture of polypropylene, organic peroxide, a high molecular weight halogenated organic compound and aminosilane heated glass fibers.

Different processes are also described to prepare fiber glass with specific coatings intended to have improved adhesion with the polyolefinic matrix.

Thus, GB-A-1,174,943 describes inorganic fiber reinforced propylene polymer molding compositions wherein the fibers are coated with the reaction product of aminosilane with anhydride modified polyolefin.

US-A-4,426,469 describes a specific coating of fiber glass with a three component coating comprising a polyolefinic film forming agent, a silane and a bis-maleamic acid, and the use of these glass fibers to prepare blends with polyolefinic compounds which are treated by injection molding.

US-A-3,936,415 describes the preparation of glass fibers coated with a mixture of an organosilane coupling agent, an oxidized polyolefin and a carboxylated high molecular weight elastomer. These fibers are then dried and used for the production of reinforced polyolefinic matrix.

US-A-3,661,628 describes another type of coated fiber glass and their use after being dried and mixed with olefinic polymers to form articles through molding and extrusion.

Other similar melt extrusion prior art compositions are disclosed in JP-A-53-110645, JP-A-58-145750.

Finally, GB-A-1 ,262,470 (= FR-1 ,598,204) discloses a surface treatment of inorganic surfaces to improve adhesion of organic coatings comprising a combination of an organosi loxane and of a copolymer of ethylene containing acid units. The disclosure of this document is very broad and the uses disclosed concern coating of any silicous product, such as glass, in the form of panels, pearls, fibres, and notably to provide safety window glass (see page 4, lines 19 to 29). The siloxane alone or a mixture of the siloxane and the ethylenic copolymer containing carboxylic acid groups are applied as a coating on the surface of the substrate (see page 4, lines 112 to 126). In the example given, the coating binder comprises the ethylenic copolymer containing acid functions dispersed in an aqueous solution, in which has been introduced gamma-aminopropyl-(triethoxy)-silane ; and a strand of fibre glass is immersed in the aqueous solution (page 59, lines 95 to 121).

This patent only discloses and suggests a possible blend of glass fibres with an olefin type resin by injection molding and si mp le ext rusi on ( page 4 , l i ne s 53 t o 60 ; page 6, l i nes 24 to 35).

A fully different way to prepare mineral fibres reinforced thermoplastic matrix composite materials is by a wet-laid process, and there is no suggestion in this GB document of the use of such silanized glass fibres in such a wet-laid process.

The wet-laid process for producing fibre rei nforced thermoplastic composites has been known for some years, and in general employs techniques commonly used in papermaking in the preliminary stages. Thus a mixture of reinforcing fibres, powdered thermoplastics materials and optionally dispersion aids, fillers, etc. is formed into a dilute slurry with water. The slurry is then passed to a papermaking type machine and delivered in a thin layer onto a moving mesh or "wire". The water is drained off through the wire to leave a thin web of thermoplastic particles in which are dispersed the reinforcing fibres. Because of the production method, the fibres, e.g. glass fibres, are arranged with th-eir longitudinal axes in the plane of the web.

The web is dried, for example using hot air, and the dried web is then converted into a fused product by heating to a temperature at which the thermoplastic particles melt and hence fuse into a continuous polymer matrix. Cooling and shaping, e.g. by pressing into a mould whilst the polymer is still molten result in a fibre-reinforced thermoplastic polymer composite material of generally good physical/mechanical properties. When such product is in the form of a flat two-dimensional sheet, it may be moulded into three-dimensional articles by flow moulding (hot-pressing) technique. Teachings relating to the wet-laid process may be found for example in US-A-4,481,075, US-A-4,645,565 and similar methods which also employ papermaking technology may be found for example in US-A-4,734,321.

It has long been recognized in the art that teachings relating to production of melt extrusion compositions cannot be extrapolated to formulate compositions for a wet-laid process in view of the different technical problems encountered in dispersing the composition components in an aqueous slurry. More particularly, the art of promoting fibre to polymer adhesion in a fused (continuous polymer phase) fibre reinforced composite (final product) which is produced by a dry melt extrusion process cannot be applied to a wet-laid process.

Final products prepared via the wet-laid process have many advantages over products obtained via the dry melt extrusion process. Thus, the reinforcing fibres in the mineral fibres reinforced polyolefin matrix composite often are subject to breakage when the composite is prepared by energy intensive methods such as extrusion and melt mixing. Although interfacial adhesion of fibres to polymer can increase mechanical properties, such fibre breakage always lead to mechanical properties far less than expected, because fibre length is decreased during the production process. In contrast, the wet-laid process allows the fibre to, maintain its integrity but interfacial adhesion of polymer to fibre is not achieved (resulting in mechanical properties also less than expected) because of the problems caused by the presence of water in the aqueous slurry used to lay down the composition.

So, there exists a performance need to achieve adhesion between fibres and the polymer matrix and to simultaneously retain fibre integrity. The prior art solutions have to be imp roved as rega rds t he adhes i on/ adhesi on rate between the i norgani c material (mineral fibre) and the thermoplastic (especially polyolefinic) matrix in the final composite material, as regards the length of inorganic material, with the purpose of improving the mechanical properties of the composite materials, of simplifying the method of preparation of improving the manufacturing rate.

A main purpose of the present invention is to solve the technical problem of improving sharply the adhesion between mineral fibres reinforcing a thermoplastic matrix in fused composite materials.

A further main object of the present invention is to solve the technical problem of improving adhesion between mineral fibres and a thermoplastic, for example oleofinic, matrix in composite material, while allowing use of long mineral fibres, preferably having a length ranging between 6 and 50 millimetres and most preferably between 10 and 25 millimetres.

Another main object of the present invention is to solve the above technical problem of improving the adhesion between mineral fibres and a thermoplastic matrix in composite materials, whilst further allowing incorporation of large amounts of mineral fibres.

Yet another object of the present invention is to solve the technical problem of improving mechanical properties, notably impact strength, tensile and flexural strength, preferably improving the CHARPY impact strength up to 50 %, the tensile and flexural strength by a value ranging between 30 and 40 %, in composite materials.

All these objects of the present invention may be solved simultaneously for the first time by using a wet-laid process, which is very simple and low cost, thereby being applicable on the industrial scale.

Therefore, according to a first aspect, the present invention provides a composition suitable for the preparation, by a wet-laid process, of a mineral fibre reinforced thermoplastic matrix polymer composite material having improved adhesion between the mineral fibres and the matrix polymer, comprising mineral fibres, thermoplastic polymer and optionally process aids, characterized in that said mineral fibres are silanized mi ne ra l fibres containing reactive si lane groups, and in that said composition further comprises an adhesion-promoting coupling agent capable of reacting with the reactive si lane groups, to improve adhesion between the mineral fibres and the polymer; said composition not containing components which would hinder significantly the reaction between the coupling agent and the reactive silane groups under the processing conditions of the wet-laid process.

The thermoplastic polymer of the defined composition may be any thermoplastic which finds industrial use, for example polyolefins, polyamides or polyesters. Particularly preferred are the polyolefins such as polypropylene, and hereinafter the invention is described in terms of its applicability to polyolefins although it is to be understood that the particular embodiments described apply equally to other organic thermoplastic polymers.

According to a specific embodiment, the composition is characterized in that it is contained in a slurry, said composition being dispersed in the slurry, preferably at a content of from 0.1 to 5% by weight, e.g. about 0.5% by weight, said slurry being preferably an aqueous slurry.

Preferably, the coupling agent is a polyolefin modified with unsaturated carboxylic acid or anhydride groups, preferably having a content from 0.2 to 5 % by weight of grafted acid or anhydride groups, and most preferably from 0.5 to 2 % of grafted acid or anhydride groups. These acid or anhydride groups, which are grafted, are preferably derived from maleic, himic anhydride or acrylic acid.

According to a further embodiment, the composition is characterized in that the coupling agent has a molecular weight ranging between 5,000 and 250,000 , depending on the nature of the thermoplastic polymer, e.g. polyolefin, used to provide the matrix.

According to a special embodiment, the invention relates to a composition wherein the content of the mineral fibres ranges between 15 and 60 weight % ; preferably between 20 and 50 weight % with regard to the total weight of mineral fibres and thermoplastic fibres, e.g. polyolefin, the high mineral fibre content providing unexpected good mechanical properties. The mineral fibres are preferably glass fibres, and according to another aspect of the invention, the mineral fibres are long mineral fibres, preferably of a length ranging between 6 and 50 mm, most preferably between 10 and 25 mm. These are of course much longer than the fibres which are typically present in melt extruded composites. The mineral fibres may have a diameter of for example from 8 to 20, preferably from 10 and 17 micrometres.

According to another invention embodiment, the composition is characterized in that the mineral fibres have been silanized with a si lane surface coating selected from an aminosilane surface coating and a polysiloxane surface coating, which preferably represents less than about 1 % by weight of the total weight of the mineral fibres. Preferably, the mineral fibres e.g. glass fibres, are also treated with an ionic species which functions to reduce agglomeration of the fibres in aqueous slurry. Such treatment with ionic species may take place before or after the fibres are silanized. The total of ionic and silanized components on the mineral fibre is preferably no more than 1% by weight of the treated fibres. The ionic species which may be used to treat the fibres may be for example, an amphoteric or a cationic surfactant such as dialkyl dimethyl ammonium salts or alkylbetaines, these being partially linked to the fibre in the treatment.

The proportion of coupling agent in the inventive composition preferably ranges between 0.5 and 25 weight %, preferably between 1 and 15 weight %, with regard to the total weight of the mineral fibres, the thermoplastic polymer, e.g. po lyo l ef i n and the coupling agent.

According to another embodiment of the invention, the composition is characterized in that it further comprises a dispersant for promoting dispersion of mineral fibres in water preferably in a content ranging between 0.05 and 15 weight %, more preferably 1 to 10 weight %, based on the total weight of the mineral fibres. The dispersant will of course be compatible with the coupling agent, in the sense that it does not hinder significantly the reaction between the coupling agent and the reactive silane groups on the mineral fibres. Preferably, the dispersant is an ionically charged polymer, not containing functional groups, such as amino or hydroxy groups, which would de-activate the coupling agent, or not containing acid groups which would preferentially react with silanized mineral fibres. Such a dispersant is, for example, an aliphatic ester amide.

According to a further embodiment of the invention, the composition is characterized in that the thermoplastic polymer which, in the final product, constitutes the matrix of the composite material, is in powder form having preferably a grain size of from 100 to 1000, more preferably 300 to 800 micrometers.

In the composition of the invention, the thermoplastic polymer powder may be optionally partially replaced with a polyolefin pulp, i.e. a fibrill ated polyolefin. This may be present, for example, in an amount of from 0 to 20 weight %, e.g. 1 to 20 weight %, more preferably 2 to 10 weight % based on the total of fibres, thermoplastic polymer, coupling agent and pulp.

Further, the invention concerns a composition characterized in that it further comprises a flocculant, preferably in a content ranging between 0.5 and 2 weight %, based on the total dry content of the composition ; and/or an anti-oxidant, preferably in a content ranging between 1 and 2 weight % based on the total dry content of the composition.

It is a feature of the inventive compositions, and of the processes in which they may be used in order to reach the target fused matrix reinforced composites, that they do not contain components, e.g. process aids, which would hinder the reaction between the reactive silane groups on the mineral fibres and the coupling agent. Hindrance of the reaction is here intended to include preferential reactions when the thermoplastic polymer is melted, and prior reactions which would "kill" the reactive species in the silanizing groups and the coupling agent.

The composition according to the invention may be in the form of a mixture, e.g. in an aqueous slurry, or in the form of a dried web of polymer particles, coupling agent and silanized mineral fibres which will be permeable to air. The advantageous effect of the improved adhesion between thermoplastic polymer component and fibre component will only be seen, though, when the web has been converted to a solid composite material wherein the thermoplastic is fused into a continuous matrix in intimate contact with the fibres. Such conversion includes the step of heating the composition to a temperature at least equal to the melting point of the thermoplastic matrix polymer.

Furthermore, the invention relates to a wet-laid process for preparing a mineral fibre reinforced polyolefin matrix composite material, which includes forming a drained web from an aqueous slurry, characterized in that the aqueous slurry is prepared with a composition as above defined, preferably said composition constituting from 0.1 to 5 weight % of the slurry. Preferably, the web is heated to a temperature sufficient to melt the polyolefin and shaped to obtain a shaped composite material.

Further aims, objects, purposes and advantages of the invention will appear from the illustrative examples given herebelow. In the examples, all the percentages are given by weight unless otherwise stated.

COMPARATIVE EXAMPLE 1

Composite material from a polypropylene matrix, commercially available glass fibres having ionic surfactant species (diameter of 10 microns, a length of 13 mm), and a cationic dispersant, by a wet-laid meth od

In 7 liters of water containing 3 g of a cationic di spersan based on fatty acid (Cartaspers ^® DS1 of Sandoz), 30 g of glass fibres which is sized to have good dispersion in aqueous medium (reference HW618 supplied by OWENS CORNING FIBERGLAS EUROPE) having an average length of 13 mm and 10 microns diameter, are added with strong stirring. 6 g of synthetic pulp are then introduced with moderate stirring. After suitable dispersion 64 g of polypropylene powder, of mean particle size 700 microns are added. After dilution until the suspension contains about 5 g of solids per liter, the mixture forming a "slurry" is then admitted on a wire screen, dewatered then dried according to the conventional papermaking technique. A sheet of 700 g/m² is thus obtained which comprises sufficient cohesion to be handled, stored, transported and in which the various components of the formulation have been perfectly retained.

To make a final industrial product from this sheet, about

7 of such sheets may for example be superposed and, after having effected preheating up to a temperature of the order of 180ºC to 210ºC, the assembly may be moulded under pressures of 40 to

100 kg/cm² for a cycle less than 30 seconds.

COMPARATIVE EXAMPLE 2 Composite material made from the same composition as example 1, but with silanized glass fibres

This example differs from the preceding one in that the glass fibres are 10 microns diameter, 13 mm long and are sized with a silane to promote adhesion as well as dispersion in aqueous medium (reference EC 690/2 by Vetrotex).

COMPARATIVE EXAMPLE 3

Composite material from the same compos i t i on as in example 1, but with 6 % of coupling agent

This example differs from example 1 in that 6 g of an unsaturated carboxylic acid modified polyolefin having 0.4 % of grafted carboxylic acid chains from maleic acid origin (reference Exxelor^® 2011 by Exxon Chemical) is added into the aqueous solution and the amount of polypropylene is reduced to 58 g.

INVENTION EXAMPLE 4

Composition material from the same composition as in example 2, but with 6 % of coupling agent of example 3

This example differs from example 2 in that 6 g of Ex xe lo r^® 2011 is added into the aqueous solution and the amount of polypropylene is reduced to 58 g.

It has to be noted that the dispersant used in examples

1, 2, 3 and 4 are all "friendly" to adhesion.

INVENTION EXAMPLE 5 Same composition as in example 4, but with additional flocculant

This example differs from example 4 in that 1 g of flocculant (reference X8494 by Dow Chemical) is added into the aqueous solution. INVENTION EXAMPLE 6

Composite material from a composition as in example 4, but with use of inert carbon black

This example differs from example 4 in that the PP granules is filled with 1 g of carbon black. The black PP granules can be produced by first melt mixing white PP granules with carbon black masterbatch (reference P30PPH by Cabot) followed by grinding.

COMPARATIVE EXAMPLE 7

Composite material from a composition as in example 5, but with use of a dispersant containing hydroxy functional groups

This examples differs from example 5 in that 2 g of carbon black dispersed in water at 0.35 % slurry concentration (containing a dispersant with hydroxy functional groups) (reference Tincolor BS by GMC) is added into the aqueous solution.

COMPARATIVE EXAMPLES 8, 9

Influence of glass fibres content These examples differ from example 1 in that 20 g and

40 g of glass fibres are used respectively and the amounts of polypropylene are adjusted accordingly to 68 g and 48 g.

INVENTION EXAMPLES 10, 11 and 12

Influence of variation of glass fibres and polypropylene content

These examples differ from example 4 in that 20 g, 40 g and 50 g of glass fibres are used respectively and the amounts of polypropylene are adjusted accordingtly to 68 g, 48 g and 38 g. INVENTION EXAMPLES 13, 14 and 15

Influence of the length of glass fibres These examples differ from example 10, 4 and 11 in that the glass fibres are 25 mm long, 10 microns in diameter, and are sized similarly to EC 690/2 (reference R16EX20 by OWENS CORNING FIBERGLAS EUROPE). INVENTION EXAMPLES 16, 17 and 18

Influence of glass fibres on adhesion

These examples differ from examples 10, 4 and 11 in that the glass fibres are 16 microns diameter, 13 mm long, and are sized similarly to EC 690/2 (reference R16EX25 supplied by OWENS CORNING FIBERGLAS EUROPE).

All the composite materials obtained from the above examples 1 to 18 are submitted to measure of the mechanical propertips, comprising measure of the Flexural Modulus according to DIN 53457 ; flexural strength according to DIN 53452, tensile strength according to DIN 53455 and unnotched CHARPY impact strength according to DIN 53453.

All the results obtained are set forth in the table given herebelow.

The data set forth in the attached table are used to illustrate :

a) comparative example 1 versus comparative example 2 shows that silanization of Fiber Glass (FG) alone cannot increase properties. The impact strength was increased, but no simultaneous improvement in strength ;

b) comparative example 3 versus comparative example 1 shows that coupling agent alone cannot increase properties ;

c) invention example 4 versus comparative examples, 1, 2 and 3 shows that the combined effect of silanization of FG and coupling agent is the only way to achieve increase of both impact and strength properties. The dispersant used in comparative examples 1, 2, 3 and 4 are all "friendly" to adhesion ;

d) invention example 5 versus invention example 4 shows that the particular flocculant used in invention example 5 is again "friendly" to adhesion ;

e) example 6 versus example 4 shows that inert carbon black is also "friendly" to adhesion ;

f) comparative example 7 versus examples 4, 5 and 6 shows that although the flocculant and the carbon black are

"friendly" to adhesion, the presence of a very "unfriendly" dispersant in the carbon black completely kills the adhesion. The dispersant used contains hydroxy functional groups ;

g) comparative examples 8, 1, and 9 show that wi t hout adhesion, impact and strength properties enhancement due to increase of fibre glass content starts to Level off at 40 % FG level (compare examples 1 and 9) ;

h) invention examples 10, 4, 11, and 12 show that with adhesion, all the mechanical properties continue to increase with increase of glass fibre content even up to 50 % level ;

i) invention examples 13, 14, and 15 show that 10 microns, 25 mm long fibre glass with sizing similar to the EC 690/2 when mixed with coupling agent (Exxelor^® ) can yield composites with very high properties via adhesion ; j) invention examples 16, 17, and 18 show that thicker (16 microns versus 10 microns) fibre glass with sizing similar to the EC 690/2 when mixed with coupling agent (Exxelor^®) can also yield composites with very high properties via adhesion.

The conditions of drying of the web in the wet-laid process ensure chemical reaction between the coupling agent and the reactive silane groups. An optimal complementary chemical reaction may occur when the thermoplastic polymer is molten.

Claims

1. A composition suitable for the preparation, by a wet-laid process, of a mineral fibre reinforced thermoplastic matrix polymer composite material having improved adhesion between the mineral fibres and the matrix polymer comprising mineral fibres, thermoplastic polymer and optionally process aids, characterized in that said mineral fibres are silanized mineral fibres containing reactive silane groups, and in that said composition further comprises an adhesion-promoting coupling agent capable of reacting with the reactive silane groups, to improve adhesion between the mineral fibres and the polymer; said composition not containing components which would hinder significantly the reaction between the coupling agent and the reactive silane groups, under the processing conditions of a wet-laid process.

2. The composition of claim 1, characterized in that it is in the form of an aqueous slurry, said composition being dispersed in the slurry, preferably at a content of from 0.1 to 5% by weight.

3. The composition of claim 1 or 2, characterized in that the coupling agent is a polyolefin modified with unsaturated ca rboxy l i c acid or anhydride groups, preferably having a content from 0.2 to 5 % by weight of grafted acid or anhydride groups, and most preferably from 0.5 to 2 % of grafted acid or anhydride groups.

4. The composition of claim 3, characterized in that the coupling agent has a molecular weight ranging between 5,000 and 250,000, depending on the nature of the thermoplastic polymer used to provide the matrix.

5. A composition according to any one of claims 1 to 4, characterized in that the content of the mineral fibres ranges between 15 and 60 weight % ; preferably between 20 and 50 weight % with regard to the total weight of mineral fibres and thermoplastic polymer, the high mineral fibre content providing unexpectedly good mechanical properties.

6. The composition of any one of the preceding claims, characterized in that the mineral fibres are long mineral fibres, preferably of a length ranging between 6 and 50 mm, most preferably between 10 and 25 mm.

7. The composition of any one of claims 1 to 6, characterized in that mineral fibres have a diameter ranging between 8 and 20, preferably between 10 and 17 micrometres.

8. The composition of any one of claims 1 to 7, characterized in that the mineral fibres have been silanized with a silane surface coating selected from an aminosilane surface coating and a polysiloxane surface coating, which preferably represents less than 1 % by weight of the total weight of the mineral fibres.

9. The composition of any one of claims 1 to 8, characterized in that the mineral fibres are glass fibres.

10. The composition of any one of claims 1 to 9, characterized in that the content of coupling agent ranges between 0.5 and 25 weight %, preferably between 1 and 15 weight %, with regard to the total weight of the mineral fibres, the thermoplastic polymer and the coupling agent.

11. The composition of any one of claims 1 to 10, characterized in that the silanized mineral fibres are additionally treated with an ionic species, preferably such that the mineral fibres constitute at least 99 weight % of the silanized ionic species-treated mineral fibres.

12. The composition of claim 11, characterized in that the ionic species comprises an amphoteric or cationic surfactant, preferably selected from dialkyldimethyl ammonium salts and alky Ibetaines.

13. The composition of any one of claims 1 to 12, characterized in that it further comprises a dispersant for promoting dispersion of mineral fibres in water, preferably in a content ranging between 0.05 and 15 weight % based on the total weight of the mineral fibres.

14. The compositon of claim 13, characterized in that the dispersant is an ionically charged polymer, not containing functional groups such as amino or hydroxy groups which would de-activate the coupling agent, and not containing acid groups which would preferentially react with silanized mineral fibres.

15. The composition of claim 13 or 14, characterized in that the dispersant comprises an aliphatic ester amide.

16. The composition of any one of claims 1 to 15, characterized in that the thermoplastic polymer of the composite material is in powder form, preferably having a grain size of from 100 to 1000 micrometres, more preferably from 300 to 800 micrometres.

17. The composition of any one of claims 1 to 16, characterized in that it further comprises a polyolefin pulp, preferably in a weight content of from 1 to 20, more preferably from 2 to 10 % based on the total weight of fibres, thermoplastic polymer, coupling agent and pulp.

18. The composition of any one of claims 1 to 17, characterized in that it further comprises a flocculant, preferably in a content ranging between 0.5 and 2 weight %, based on the total dry content of the composition ; and/or an anti-oxidant, preferably in a content ranging between 1 and 2 weight % based on a total dry content of the composition.

19. The composition of any one of claims 1 and 3 to 18, when dependent on claim 1, characterized in that it is in the form of an air-permeable web.

20. The composition of any one of the preceding claims, characterized in that the thermoplastic polymer comprises a polyolefin.

21. The composition of claim 20, characterized in that the polyolefin comprises polypropylene.

22. A solid mineral fibre reinforced thermoplastic polymer matrix composite material in which the polymer comprises a continuous fused matrix, characterized in that it has been prepared from the composition as defined in any one of claims 1 to 21 by a process which includes the step of heating the composition to a temperature of at least the melting temperature of the thermoplastic polymer.

23. A wet-laid process for preparing a mineral fibre reinforced thermoplastic polymer matrix composite material, which includes forming a drained web from an aqueous slurry, characterized in that the aqueous slurry is prepared with a composition as claimed in any one of claims 1 to 21, preferably said composition constituting from 0.1 to 5% of the slurry.

24. The process of claim 23, characterized in that the web is heated to a temperature sufficient to melt the thermoplastic polymer and shaped to obtain a shaped composite material.

25. The process of claim 24, characterized in that the shaped material comprises a two-dimensional sheet.

26. The process of claim 24, characterized in that the shaped material comprises a three-dimensional artefact.