WO2013011256A1

WO2013011256A1 - Method for manufacturing a nanocomposite material

Info

Publication number: WO2013011256A1
Application number: PCT/GB2012/000593
Authority: WO
Inventors: Michele MEO; Fulvio PINTO
Original assignee: The University Of Bath
Priority date: 2011-07-15
Filing date: 2012-07-13
Publication date: 2013-01-24
Also published as: GB201112224D0

Abstract

A method of manufacturing a nanocomposite material, comprising providing a fibre fabric; impregnating the fibre fabric with a solution containing nano-silica particles; drying the impregnated fabric leaving discrete nano-silica particles substantially evenly distributed on the surface of the fibres throughout the fabric structure so as to reinforce the fibres; and infiltrating the nano-silica reinforced fibre fabric with a polymeric thermoset resin material. Carbon nanotubes may be grown on the nano-silica reinforced fibre fabric prior to infiltrating with the resin. Also, a nanocomposite material so formed.

Description

Method for Manufacturing a Nanocomposite Material

FIELD OF THE INVENTION

The present invention relates to methods of manufacturing nanocomposite materials, and to nanocomposite materials so formed.

BACKGROUND OF THE INVENTION

A composite material includes two or more materials (e.g. reinforcing elements and a matrix) differing in form or composition. The materials act together but do not fully merge. A nanocomposite material is a composite material that further includes nano scale particles. Nanoparticles generally have a mean average particle diameter less than approximately 100 nm and have size dependent properties not observed in the same material at larger scales. However, for some materials the definition of a "nanoparticle" can extend to particles having dimensions as large as 800 - 900 nm.

In polymer matrix composites, nanoparticles are sometimes used as a "filler" in the polymer matrix to provide reinforcement to the finished nanocomposite material. The nanoparticles are mixed with the polymer matrix material, which is then used with a fibrous reinforcement to form a triphasic nanocomposite material.

Whilst the nanoparticles in triphasic nanocomposites have been shown to provide some additional reinforcement, the nanoparticles have a tendency to form agglomerates, which create new interphases and introduce areas of weakness into the final structure. Modifying the nanoparticles with the aim of avoiding agglomeration has been found to be expensive, time consuming and not particularly effective.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a method of manufacturing a nanocomposite material, comprising providing a fibre fabric; impregnating the fibre fabric with a solution containing nano-silica particles; drying the impregnated fabric leaving discrete nano-silica particles substantially evenly distributed on the surface of the fibres throughout the fabric structure so as to reinforce the fibres; and infiltrating the nano-silica reinforced fibre fabric with a polymeric thcrmoset resin material.

A further aspect of the invention provides a nanocomposite material, comprising a fibre fabric having discrete nano-silica particles substantially evenly distributed and on the surface of the fibres throughout the fabric structure so as to reinforce the fibres, and a polymeric thcrmoset resin matrix.

The invention is advantageous in that the substantially evenly dispersed nano-silica particles act to reinforce the fibres of the fibre fabric throughout the fabric structure. Applying the nano-silica prior to the resin matrix enables greater control over the nano-silica distribution, and the problems of agglomeration typically found in the prior processes are substantially avoided. The nano-silica also provides more reinforcement action than when used as a reinforcing "filler" in the matrix.

The nano-silica on the fibres increases the surface area in contact with the polymeric thcrmoset matrix giving rise to beneficial "nanoeffects" (e.g. crack pinning and crack deflection), which improve the mechanical and thermal properties of the final composite. The dimensions of the nano-silica are of the same magnitude as the radius of gyration of the polymer matrix, inducing the formation of a polymer interphase layer. Importantly, the nano-silica also acts to reinforce the fibres by modifying their mechanical properties thus strengthening the yarns of the fibres in the fabric. As a result, the final solid composite prepared by infiltrating the nano-silica reinforced fibre fabric with polymeric resin exhibits improved strength and toughness.

Since the nano-silica is distributed throughout the fabric structure, the reinforcement action of the nano-silica is observed throughout the fabric. This contrasts with the prior processes in which the nano-particles are introduced, and remain, within the matrix, such that no mechanical reinforcement of the fibres takes place.

The resultant nanocomposite material exhibits improved toughness and stiffness, and the manufacturing method can be carried out at lower cost and in less time than the prior processes in which the nano-particles are introduced with the matrix. Typically, the dry fibre fabric will be partially impregnated with a resin binder to aid handling. The nano-silica beneficially "adheres" to the surface of the fibres. The presence of the binder on the fibre surface can increase the adhesion of the nano-silica particles on the fibres. The nano-silica particles preferably remain attached to the fibres after infiltrating with the resin, i.e. they substantially do not freely move into the matrix.

The fibre fabric may typically be a carbon fibre fabric but alternatively glass fibre fabrics or suitable other fibre fabrics could be used. The fibre fabric may take a wide variety of forms, including unidirectional, woven or 3-dimensional fibre substrates. The nano-silica particles typically have an average (mean) particle diameter less than approximately 100 nm. However, similar results may be achieved with larger nanoparticles up to 800 - 900 nm. For the purpose of this disclosure, "nano-silica" is considered to be silica particles having a mean particle diameter less than 900 nm. Typically, the nanoparticles will have a diameter of between 0.007 to 0.200 microns. The nano-silica solution may be an aqueous solution. The solution may, for example, be prepared by diluting an aqueous solution of colloidal silica with water to a desired nano-silica concentration. Using off-the-shelf colloidal silica brings about cost savings in the process. Using an aqueous solution is beneficial since the viscosity of the solution is low, which aids wetting of the fabric, and is easy to handle. The drying step is also uncomplicated as ventilation is straightforward and can be carried out at low temperatures.

Alternatively, the solution may be prepared by mixing nano-silica particles with a carrier liquid to a desired nano-silica concentration, preferably by stirring and or sonication. Sonication is a non-mechanical mixing process that uses sound (typically ultrasound). Other suitable forms of mechanical, and non-mechanical mixing may be used in addition to, or instead of, stirring and/or sonication.

The solution may contain nano-silica at a concentration of between 1 %wt to 25 %wt, preferably between 3 %wt to 20 %wt, more preferably between 5 %wt to 10 %wt, and most preferably approximately 5 %wt. The impregnation step may include wetting the fabric by spraying the solution towards the fabric. The spray may be directed to one or both sides of the fabric. The fabric may be arranged substantially vertically during the spraying step. The fabric may be sprayed with the solution until droplets appear on the fabric surface. The spraying process may be (semi-) automated or manual. An aqueous silica solution may have sufficiently low viscosity for spraying. The drying step may include providing a flow of warm air over the wet fabric.

Alternatively, the impregnation step may include wetting the fabric with the solution by a calendering process. The calendering process may include immersing a cylinder in a bath containing the nano-silica solution, removing the wet cylinder from the bath, and pressing the fabric into contact with the wet cylinder. Alternatively, the calendering process may include immersing the fabric in a bath containing the nano- silica solution, removing the wet fabric from the bath, and then pressing the wet fabric into contact with a cylinder. Preferably, the wet fabric is pressed between two dry cylinders (rollers) which may be made of polymeric material. Generally, the calendering process may be expected to yield improved wetting of the fabric as compared with the spraying process

The nano-silica solution used in the calendering process may be diluted with a solvent, preferably ethanol. The drying step may include placing the wet fabric in an oven to remove the solvent (and water). The calendering process may be (semi-) automated or manual.

The nano-silica particles attached to the surface of the fibres are preferably substantially free of agglomerates prior to infiltrating with the resin.

The infiltration step may include a resin infusion process, a resin film infusion process, or a resin transfer moulding process, for example, which may be carried out at ambient or elevated temperatures, and/or with vacuum assistance. The infusion process is not limited to those indicated above and other suitable techniques in which a flux of resin is forced through a preform may alternatively be used.

The resin may be an epoxy resin, for example, or any other suitable thermosetting^' polymer. Preferably a toughened epoxy thermoset polymer is used. The method may further comprise growing carbon nanotubes on the nano-silica reinforced fibre fabric prior to infiltrating with the resin. It is known that carbon nanotubes (CNTs) can be grown on fibre fabric to provide reinforcement. The nano- silica reinforced fibre fabric has been found to provide an excellent substrate on which to gown CNTs, yielding unexpected results.

CNTs may be grown by a chemical vapour deposition (CVD) process, including thermal catalytic decomposition of a carbon-containing gas. The carbon-containing gas may include a hydrocarbon and/or the catalyst may be a metal. For example, CNTs may be grown by thermal decomposition of hydrocarbons (e.g. toluene or xylene) in the presence of a metal catalyst obtained by the decomposition of an organometallic compound, such as ferrocene.

The nano-silica particles attached to the surface of the fibres may act as initiating sites for the carbon nantotube growth. The substantially evenly distributed nano-silica particles attached to the surface of the fibres provide a substantially uniform carbon nanotube forest distribution, without any modification to the traditional CVD process.

The nano-silica particles act with the carbon-containing gas to grow carbon nanotubes having a length of up to several microns. In particular, it has been found that the nano- silica may act with ferrocene to enhance the growth of CNTs, giving the possibility to create longer nanotubes. The nano-silica CNT reinforced fibre fabric can be used to form an tetraphasic composite, after infiltrating with the resin matrix, having excellent mechanical properties.

The dry nano-silica reinforced fibre fabric may be infiltrated (preimpregnated) with the resin to form a "prepreg" prior to lay-up. The prepregs may be used in a "wet" lay- up to form composite parts in a conventional manner.

Alternatively, the dry nano-silica reinforced fibre fabric may be used in a "dry" lay-up followed by infiltrating with the resin to form composite parts in a conventional manner. 6

The dry nano-silica CNT reinforced fibre fabric may be arranged between prepregs in a "wet" lay-up.

The invention extends to all nanocomposite materials and nanocomposite material parts produced directly by the method. The nanocomposite materials may have nano-silica particles provided in an amount of up to approximately 40 % weight of the fibre fabric within the composite, preferably less than 20 %wt., further preferably less than 10 %wt., and most preferably approximately S %wt.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates a flow diagram showing the process steps for forming a triphasic nanocomposite;

Figure 2 illustrates a flow diagram showing the process steps for forming a tetraphasic nanocomposite;

Figure 3a illustrates a flow diagram showing the process steps for preparing nano- silica solutions;

Figure 3b illustrates a flow diagram showing the process steps for impregnating the carbon fibre fabric with the nano-silica solution; Figures 4a-c illustrate SEM images at xlOO, x370 and x2,200 magnification, respectively of the carbon fibre fabric prior to impregnating with the nano-silica solution;

Figures Sa-c illustrate SEM images at xlOO, x370 and x 13,000 magnification, respectively of the dried nano-silica reinforced carbon fibre fabric; Figures 6a-b illustrate SEM images at x9,000 and x 13,000 magnification, respectively of a dried nano-silica reinforced carbon fibre fabric, showing the particles attached all over the fibres surface and few agglomerates;

Figure 7 illustrates an X-RAY image of a dried nano-silica reinforced carbon fibre fabric, showing the substantially uniformly distributed particles and few agglomerates;

Figures 8a-c illustrate SEM images of the triphasic composite, showing the nano-silica remains attached to the fibres and only a small presence of Si atoms in matrix rich regions;

Figure 9 illustrates the effect of nano-silica particles (as %wt. of fibre fabric) on bending modulus of a laminate of the triphasic composite;

Figure 10 illustrates the effect of nano-silica particles (as %wt. of fibre fabric) on Young's modulus of a laminate of the triphasic composite;

Figure 1 1 illustrates the effect of nano-silica particles (as %wt. of fibre fabric) on Vickers hardness of a laminate of the triphasic composite; and Figure 12a-c illustrate SEM images at xl,300, x3,000 and x9,500 magnification, respectively of carbon nanotube growth on a dried nano-silica reinforced carbon fibre fabric.

DETAILED DESCRIPTION OF EMBODEVIENT(S)

Figure 1 illustrates a flow diagram showing the process steps for forming a triphasic nanocomposite by direct fabric impregnation. In the process, silica nano-particles 1 are directly impregnated into a fibrous reinforcement 2 comprising a woven carbon fibre fabric and, once dry, the nano-silica reinforced carbon fibre fabric is infiltrated with a polymeric resin matrix 3 to form a triphasic nanocomposite material 4.

Figure 2 illustrates a flow diagram showing the process steps for forming a tetraphasic nanocomposite. The process includes identical steps of directly , impregnating the fibrous reinforcement 2 with silica nano-particles 1 and further includes the step of 8

growing carbon nanotubes S on the nano-silica sites prior to infiltrating with the polymeric resin matrix 3 to form a tetraphasic nanocomposite 6.

The steps involved in manufacturing the triphasic nanocomposite 4 and the tetraphasic nanocomposite 6 will now be described in detail. Figure 3a illustrates a flow diagram showing processes 100 for preparing nano-silica solutions for directly impregnating the carbon fabric. The process starts with cutting and preparing layers of carbon fibre fabric at step 101. The carbon fibre fabric is of conventional type woven from a yarn of many thousands of carbon fibres twisted together. Commonly available carbon fibre fabric may have a twill weave or plain weave pattern, for example, but any other suitable carbon fibre fabric, or any other suitable fibre fabric, may be used in this process.

Next at step 102 solutions containing nano-silica particles are prepared. The solutions are dependent upon the chosen fibre fabrics and on the methods used to impregnate the fabric. In this example, the nano-silica particles are prepared in an aqueous solution. Using a water carrier is beneficial since it has relatively low viscosity leading to improved wetting of the carbon fibre fabric, and is relatively easy to process since drying of the impregnated carbon fibre fabric may be carried out at relatively low temperatures with straightforward ventilation.

Figure 3a illustrates two examples of how aqueous nano-silica solutions may be prepared. In the first example nano-silica particles 103 are chosen as the raw material and water is chosen as the carrier to obtain the required concentration of nano-silica in solution at step 104. The nano-silica particles require mixing in the water carrier and in the first example the mixing is performed at step 10S by one hour of mechanical stirring to eliminate agglomerates in the silica nano-particles followed by one hour of sonication at step 106.

In the second example an aqueous solution of colloidal silica at 40% wt. 13 is chosen as the raw material and is mixed with water at step 114 to obtain the required concentration of nano-silica particles in solution. Of course, aqueous colloidal silica solutions at different concentrations are available, and it is a matter of choice whether to select the dry silica nano-particles 103, or the aqueous colloidal silica solution 113, 9

as the raw material for the doping solutions. The process then continues with impregnating the carbon fibre fabric with the prepared doping solutions at step 201 which will now be described in detail with reference to Figure 3b.

Figure 3b illustrates a flow diagram showing two alternative processes for impregnating the carbon fibre fabric with the prepared nano-silica solutions. In the first example, the impregnation technique involves pressure spraying 201 and in the second example, the impregnation technique involves calendering 211.

In the spray assisted technique 201 the prepared and cut dry carbon fibre fabric sample is arranged in a substantially vertical orientation within a laminar flow hood at step 202. At step 203 a conventional spray apparatus is arranged to spray directly towards a surface of the carbon fibre fabric. The spray head is set at a certain distance from the fabric surface, depending on the fabric dimensions, in order to wet the entire fabric sample. At step 204, the spray system is activated until droplets start to appear on the fabric surface, indicating that the fabric sample is fully wet. Steps 202 to 204 may be repeated by rotating the fabric sample through 180 degrees such that the opposite surface of the carbon fibre fabric faces towards the spra head. Alternatively, the spray system may include two oppositely facing spray heads so as to spray the carbon fibre fabric sample simultaneously from both sides. Spraying under pressure drives the nano-silica solution deep into the carbon fibre fabric structure. At step 20S the wet fabric is left in the hood in a warm air flow in order to remove the excess of solution. In this example, the wet fabric was left to dry for approximately one hour. The temperature of the warm air flow and the time to dry will be dependent upon the carbon fibre fabric and the solution used. During the drying process, the excess of aqueous solution evaporates from the carbon fibre fabric leaving the nano- silica particles substantially evenly distributed on the surface of the fibres throughout the fabric structure of the carbon fibre.

In the calendering technique 211 a bath is filled at step 212 with a solution comprising approximately 50% by volume of the aqueous nano-silica solution previously prepared, and approximately 50% by volume of ethanol. Two alternative calendering techniques are presented here, the first making use of dry cylinders, or rollers, at step 213 and the second using wet cylinders, or rollers, at step 223.

With the dry cylinder calendering technique 213, the carbon fibre fabric is soaked in the bath containing the aqueous nano-silica ethanol solution for approximately three to five minutes at step 214. The wet fabric is then removed from the bath and passed through a pair of dry calendering rollers in order to remove the excess of solution and the larger nano-silica particle agglomerates at step 215. The calandering rollers may be made of polymeric material.

In the alternative wet cylinder calandering technique 213, the cylinder is bathed in the solution for approximately fifteen minutes in order to fully wet the cylinder at step 224 and then the edge of the fabric is positioned between the cylinders rollers of the calandering system, which then proceeds to squeeze the fabric and wet it with the solution at step 22S. Regardless of which calandering technique is used, the wet fabric is then placed in an oven in order to remove the ethanol and excess aqueous solution at step 236. For example, the wet fabric may be in the oven for approximately one hour at lOO'C.

Regardless of whether the pressure spraying process or the calandering process is used to impregnate the fabric, the dried nano-silica reinforced carbon fibre fabric may then proceed to composites manufacturing at step 300. Figures 4a to 4c illustrate SEM images at xlOO, x370 and x2,200 magnification, respectively of the carbon fibre fabric prior to impregnating with the nano-silica solution. For comparison Figures Sa to Sc illustrate similar SEM images at x 100, x370 and xl3,000 magnification, respectively of the dried nano-silica reinforced carbon fibre fabric. As can clearly be seen from Figure S, the nano-silica particles are substantially evenly distributed on the surface of the carbon fibres throughout the carbon fibre fabric structure, with few agglomerates.

Figures 6a and 6b illustrate SEM images at x9,000 and x 13,000 magnification, respectively of the dried nano-silica reinforced carbon fibre fabric showing the silica- nano-particles present all over the fibres¹ surfaces. It is important that that the silica- nano- articles are attached all over the fibre surface and throughout the fibre structure of the woven carbon fibre fabric, and are not merely provided on the outer surfaces of the fabric.

Figure 7 illustrates an X-ray image of the dried nano-silica reinforced carbon fibre fabric showing the silica nano-particles distributed substantially evenly on the entire carbon fibre fabric area with just a few agglomerates of the silica nano-particles characterised by small dimensions.

The composites manufacturing at step 300 may use any of a wide variety of well known techniques for forming carbon fibre reinforced polymeric resin composite materials and parts. The resin material is preferably an epoxy, but other suitable matrix materials known in the art may similarly be used, depending on the application.

The composites manufacturing may be conducted at ambient or elevated temperatures and/or at ambient or elevated pressures. Purely as one example of the available composites manufacturing techniques, the vacuum assisted resin film infusion (VARFT) method may be employed. In this purely exemplary embodiment, eight nano-silica reinforced carbon fabric plies prepared by the pressure spraying technique were arranged on a mould tool with a pre-catalysed resin film. A vacuum bagging procedure was used to apply positive pressure and the composite was manufactured in an oven or autoclave to apply heat to melt and cure the resin film. Details of this well known technique and its alternatives will be well known to those skilled in the art and so will not be discussed further here. The exemplary eight ply laminate comprised approximately 60 %WL carbon fibre.

After the composites manufacturing at step 300 the resultant triphasic nanocomposite underwent extensive experimental testing. Figures 8a to 8c illustrate SEM images of the triphasic composite, showing the nano-silica 1 remains attached to the carbon fibres reinforcement 2. Further X-ray analysis indicates a small presence of Si atoms in resin rich areas indicating that the silica nano-particles remain attached to the fibres and are not dispersed within the resin matrix 3.

Figure 9 illustrates the effect of the nano-silica particles, expressed as percentage weight of the fibre fabric, on the bending modulus of the eight ply laminate sample of the composite. For the three-point bending test the samples were prepared according to ASTM D790. Fabric samples prepared by doping with silica solutions so as to contain from 5 %wt. to 20 %wt. nano-silica particles (as %wt. of fibre fabric) were compared with neat samples (no silica doping) having an equal amount of fibres (60% fibre content in the laminate) and obtained with the same lay-up sequence. As can be seen from Figure 9, samples prepared with fabrics impregnated with S %WL silica nano-particles show an increase of almost 50% in the bending modulus compared to the neat samples. Increasing the concentration (as %wt. of fibre fabric) of nano-particles within the fabric from 5%wt. to 20 %wt. leads to only a small further increase of the bending modulus of the composite laminate samples tested. The substantial increase in the bending modulus due to the presence of the nano-silica reinforcement is thought to be due to the beneficial "nano effects" of crack pinning and crack deflection brought about through the increased surface area of the fibres in contact with the resin matrix due to the nano-silica particles attached to the fibres surface. Figure 10 illustrates the effect of the nano-silica particles on Youngs modulus of the eight ply laminate sample of the composite. For the tensile test the samples were prepared according to ASTN D3039 and triphasic nanocomposite samples prepared by doping with silica solutions so as to contain 5 %wt. and 10 %wt. nano-silica particles (as %wt. of fibre fabric), respectively, were compared with neat samples (no silica doping) having an equal amount of fibres (60% fibre content in the laminate) and obtained with the same lay-up sequence. As can be seen from Figure 10, samples prepared with fabrics impregnated with 5 %wt. silica nano-particles (as %wt. of fibre fabric) show an increase of approximately 32% in Youngs modulus. Increasing the amount of nano-particles from 5%wt. to 10 %wt. (as %wt. of fibre fabric) leads to only a small further increase in the Youngs modulus of the composite laminate samples tested. The tensile test indicates that the nano-silica reinforcement of the carbon fibres is highly effective. Accordingly, it can be seen that the nano-silica enhances the mechanical properties of the carbon fibre reinforced polymeric laminate, confirming what was observed during the three point bending test. Figure 11 illustrates the effect of nano-silica particles on Vickers Hardness of the laminate plies. The VS Vickers Hardness test was conducted on both parallel fibres and perpendicular fibres and Figure 11 illustrates the substantial increase in hardness for the perpendicular fibres due to the addition of nano-silica particles at an amount of 5 %wt. (as %wt. of fibre fabric). Increasing the nano-silica concentration appears to have a relatively minor effect beyond 5 %wt. and the increase in hardness for the parallel fibres was significantly lower than that for the perpendicular fibres.

In addition, dynamic mechanical analysis (DMA) tests were carried out on the eight ply laminates produced by the spraying and the calandering impregnation techniques. The DMA tests were conducted in three point bending mode at 1 Hz frequency and the specimens were heated up to 140 C with a 2°C per minute ramp. The results revealed that the storage modulus was generally higher for the calandering sample as compared with the pressured spray samples, indicating that the calandering technique is probably the more efficient in terms of toughening the materials. However, it is expected that improvements in the spray technique may yield similar results to the calandering techniques. The DMA results also revealed that embedding the silica nano-particles within the carbon fabrics decreases the damping properties (tan δ) of the laminate from 0.2 to 0.15. Glass transition temperature does not seem to be affected by the nano doping processes.

Additionally, the nano-silica reinforced carbon fibre fabric has been found to provide an excellent substrate on which to grow carbon nanotubes. It is known that carbon nanotubes (CNTs) can be grown on carbon fibre fabric to provide reinforcement, generally out of the plane of the fibres. CNTs may be grown by a chemical vapour deposition (CVD) process, including thermal catalytic decomposition of a carbon containing gas. For example, CNTs may be grown by thermal decomposition of hydrocarbons (e.g. toluene or xylene) in the presence of a metal catalyst obtained by the decomposition of an organometallic compound, such as ferrocene.

The nano-silica particles attached to the surface of the fibres have been found to act as excellent initiating sites for CNT growth. The substantially evenly distributed nano- silica particles attached to the surface of the fibres provide a substantially uniform carbon nanotube forest distribution, without any modification to the traditional CVD processes.

The nano-silica particles act with the carbon containing gas to grow CNTs having a length of up to several microns. In particular, it has been found that the nano-silica may act with the ferrocene to enhance the growth of CNTs, giving the possibility to create longer nanotubes. Figures 12a-c illustrate SEM images at x 1,300, x3,000 and x9,500 magnification, respectively of carbon nanotube growth on the nano-silica reinforced carbon fibre fabric.

The nano-silica CNT reinforced carbon fibre fabric can be used to form a tetraphasic composite, after infiltrating with the resin matrix, giving excellent mechanical properties. In particular, the CNTs may increase the damping properties of the nano composite, which may partially or fully reverse the decreasing effect of the nano-silica noted above.

The nano-silica CNT reinforced carbon fibre fabric may be arranged between prepregs in a "wet" layup during composite manufacturing.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method of manufacturing a nanocomposite material, comprising providing a fibre fabric; impregnating the fibre fabric with a solution containing nano-silica particles; drying the impregnated fabric leaving discrete nano-silica particles substantially evenly distributed and on the surface of the fibres throughout the fabric structure so as to reinforce the fibres; and infiltrating the nano-silica reinforced fibre fabric with a polymeric thermoset resin material.

2. A method according to claim 1, wherein the nano-silica solution is an aqueous solution.

3. A method according to claim 2, wherein the solution is prepared by diluting an aqueous solution of colloidal silica with water to a desired nano-silica concentration.

4. A method according to claim 1, wherein the solution is prepared by mixing nano-silica particles with a carrier liquid to a desired nano-silica concentration, preferably by stirring and/or sonication.

5. A method according to any preceding claim wherein the solution contains nano-silica at a concentration of between 1 %wt to 25 %wt, preferably between 3 %wt to 20 %wt, more preferably between 5 wt to 10 %wt, and most preferably approximately 5 %wt.

6. A method according to any preceding claim, wherein the impregnation step includes wetting the fabric by spraying the solution towards the fabric.

7. A method according to claim 6, wherein the spray is directed to one or both sides of the fabric.

8. A method according to claim 6 or 7, wherein the fabric is arranged substantially vertically during the spraying step.

9. A method according to any of claims 6 to 8, wherein the fabric is sprayed with the solution until droplets appear on the fabric surface.

10. A method according to any of claims 6 to 9, wherein the drying step includes providing a flow of warm air over the wet fabric.

11. A method according to any of claims 1 to 5, wherein the impregnation step includes wetting the fabric with the solution by a calendering process.

12. A method according to claim 11, wherein the calendering process includes immersing a cylinder in a bath containing the nano-silica solution, removing the wet cylinder from the bath, and pressing the fabric into contact with the wet cylinder.

13. A method according to claim 11, wherein the calendering process includes immersing the fabric is a bath containing the nano-silica solution, removing the wet fabric from the bath, and then pressing the wet fabric into contact with a cylinder.

14. A method according to any of claims 11 to 13, wherein the nano-silica solution is diluted with a solvent, preferably ethanol.

15. A method according to any of claims 11 to 14, wherein the drying step includes placing the wet fabric in an oven.

16. A method according to any preceding claim, wherein the nano-silica particles attached to the surface of the fibres are substantially free of agglomerates prior to infiltrating with the resin.

17. A method according to any preceding claim, wherein the infiltration step includes a resin infusion process, preferably selected from the group including resin infusion processing, resin film infusion processing, or resin transfer moulding processing.

18. A method according to any preceding claim, wherein the nano-silica particles remain attached to the fibres after infiltrating with the resin.

19. A method according to any preceding claim, wherein the fibre fabric is a carbon fibre fabric.

20. A method according to any preceding claim, wherein the thermoset resin is an epoxy resin.

21. A method according to any preceding claim, further comprising: growing carbon nanotubes on the nano-silica reinforced fibre fabric prior to infiltrating with the resin.

22. A method according to claim 21 , wherein the nano-silica particles attached to the surface of the fibres act as initiating sites for the carbon nantotube growth.

23. A method according to claim 22, wherein the substantially evenly distributed nano-silica particles attached to the surface of the fibres provide a substantially uniform carbon nanotube forest distribution.

24. A method according to any of claims 21 to 23, wherein the carbon nanotubes are grown by a chemical vapour deposition process.

25. A method according to claim 24, wherein the chemical vapour deposition process includes thermal catalytic decomposition of a carbon-containing gas.

26. A method according to claim 25, wherein the nano-silica particles act with the carbon-containing gas to grow carbon nanotubes having a length of up to several microns.

27. A method according to claim 25 or 26, wherein the carbon-containing gas includes a hydrocarbon, and/or wherein the catalyst is a metal.

28. A method according to any of claims 1 to 20, wherein the dry nano-silica reinforced fibre fabric is infiltrated with the resin to form a prepreg ply.

29. A method according to claim 28, further comprising arranging a stack of the prepreg plies.

30. A method according to any of claims 1 to 20, wherein the dry nano-silica reinforced fibre fabric is arranged in a stack of fibre plies prior to infiltrating with the resin.

31. A method according to any of claims 21 to 27, wherein the dry nano-silica reinforced fibre fabric with the carbon nanotubes is arranged in a stack of fibre plies prior to infiltrating with the resin.

32. A method according to claim 31, wherein the stack of fibre plies includes a ply of the dry nano-silica reinforced fibre fabric with the carbon nanotubes sandwiched between prepreg plies.

33. A method according to claim 32, wherein the. prepreg plies are prepared according to the method of claim 28.

34. A method according to any of claims 29 to 33, further comprising consolidating the stack of plies and curing the resin to form a composite parti

35. A nanocomposite material, comprising a fibre fabric having discrete nano- silica particles substantially evenly distributed on the surface of the fibres throughout the fabric structure so as to reinforce the fibres, arid a polymeric thermoset resin matrix.

36. A material according to claim 35, wherein the nano-silica particles are provided in an amount of up to approximately 40 % weight of the fibre fabric, preferably less than 20 %wt., further preferably less than 10 %wt., and most preferably approximately S wt.

37. A material according to claim 35 or 36, wherein the fibre fabric is a carbon fibre fabric.

38. A material according to any of claims 35 to 37, further comprising carbon nanotubes on the nano-silica reinforced fibre fabric.