This invention relates to composite material and in particular to a composite material comprising natural or naturally derived fibres embedded in a resin.

Composite materials are used in a wide variety of applications from high performance aerospace, marine and automotive components to sports equipment, particularly in applications where their advantageous properties, namely their low weight, high strength and high stiffness, are desirable. The textile reinforcement in composite materials are typically (but not exclusively) woven or non woven. In non woven reinforcements, fibres or yarn tows are aligned by filament winding and stitched to form fibrous sheets, or randomly distributed in a non woven, chopped strand or needle- punched fibre mat. In woven reinforcements, yarn tows are interlaced uniformly into biaxial woven, single ply fabric which is arranged in a multiple ply stack to form a laminated composite. All of the reinforcements described are typically comprised of glass or carbon fibres, bonded together or embedded in a thermoplastic or thermosetting resin matrix. The use of carbon fibres as a reinforcement material in composites is well established particularly being used in areas where weight and strength are critical, for example in aerospace, marine or motor racing applications. The use of glass fibres as a reinforcement material in composites is well established in transport and building construction applications.

As 2D planar reinforcements, non-woven reinforcements and biaxial woven plied lay-up assemblages do not provide continuous fibre reinforcement within the composite material, resulting in resin-rich areas. Therefore, in high-performance aerospace, military, marine and some transport applications, three dimensionally reinforced woven glass and carbon preforms for composites have been developed to provide greater strength and dimensional tolerances. A three dimensional woven fabric generally consists of yarns oriented in three mutually orthogonal directions, for example where the warp and weft yarns of a woven structure are interlocked by binder warp yarns extending through the thickness of the structure. These structures are typically in the 1500 to 3000g/m ² range, but can be produced up to 5000g/m ² .

3D woven composites have a vast range of properties that are superior to traditional 2 D laminates. Different textile processes such as weaving, braiding, stitching and knitting can be used to manufacture a wide range of 3D structures. The 3D woven fabric composites are prefered for several reasons; Due to their enhanced mechanical properties, their ability to tailor fibrous properties into specific areas of the reinforcement combating localised stresses is an advantage. The 3D weaving process can also be used to produce complex near-net-shape structures that are manufactured flat, and extended to shape off-the-loom. The ability of the weave design to interlace yarns through intersections is an advantage. The manufacture of multiple layer and / or 3D woven preforms in one integrated piece eliminates the need for the ply lay-up process which can provide production efficiency and potentially cost-saving measures. Three of the most common 3D woven architectures are the orthogonal, layer interlock and multiple layer twill or satin weaves based on traditional constructions. In orthogonal weaves, the yarns extend in three mutually orthogonal directions to produce a 3D reinforced structure where binding threads extend through the layers from surface to surface. In layer or angle interlock weaves, layers of weft yarns are interlocked by warp yarns that contribute both to the X-Axis and the Z-Axis reinforcement by migrating through the total thickness at an angle of approx 45° one layer at a time.

Multiple layer twill or satin weaves are 3D reinforced derivatives of traditional 2D twill or satin constructions, where warp yarns interlink through a proportion of, or the total thickness in sequence with the natural interlacement pattern of the weave.

3D woven materials are complex constructions. They utilize conventional multishaft Industrial Dobby and Jacquard weaving technology to assemble yarns in thick, multiple layer stacks with designated warp yarn paths interlinking these layers together in the warp (0°) and through-the-thickness orientations. Yarn interlacement and levels of inherent crimp are present in these architectures, who's primary function is to reinforce.

Warp yarns are designated one, or a combination of the following roles: -

1. lnplane interlacement where yarns interlace within the layer of origin;

2. Low-crimp warp stuffer: to reinforce in the warp orientation;

3. Through-the-thickness interlink / interlocker: Warp yarns that migrate through a proportion of, or the total fabric thickness in a variety of perpendicular or angled stitches;

4. Selvedge yarns: To either stabilise inserted weft yarns or act as sacrificial yarn that will be assigned to waste after production;

5. Supplementary warp yarns: yarns that float until programmed to weave intermittently and provide specific reinforcement in key areas;

6. Tailored, localized or Through-intersection support: Yarns that are primarily arranged to interlace in a specific locality or over a designated area to contribute reinforcement. Yarns that are introduced to provide a specific functionality to the material for unique added value or benefit; or yarns that migrate through the intersection of a shaped structure to provide continual fibrous reinforcement, (e.g. in Structural X-profiles, I-Beam profiles or hollow-sectioned reinforcement;

7. Weft fill paths can operate in-plane or also interlace out-of plane across the fabric width.

However, while such materials are desirable from an engineering point of view, the fibres and resin matrix within such known synthetic composite materials cannot generally be separated for recycling at end of life and therefore must be disposed of in landfill. In the automotive industry in particular there has been a great desire, partly led by legislation, to utilise a much greater proportion of recyclable and natural materials and to minimise the amount of material that must be disposed of in landfill at the end of life.

Significant research into sustainable and bio-based composites has been carried out using non- woven fibre mat products comprising naturally derived fibres, such as flax, hemp and hybrid mixed fibre assemblies, with oriented fibre direction, or single layer woven plies that rely on the fibre/resin/adhesive interface targeting appropriate yet non-critical load bearing applications. There has been interest in 3D woven natural fibre based composites. However, a problem with such technology is the inherent variability and lack of consistency in the physical properties of natural fibres, such as flax, which leads to difficulty in providing 3D woven structures with predetermined and predictable mechanical properties.

Non-woven natural fibre mats for composite materials can be made from low-grade decorticated bast fibre or refined shive fibres. No refining or spinning is required. For weaving, the grade of raw material from the field varies between batch yield and country of origin. The sliver must be high quality and refined through numerous combings to produce a spun yarn sturdy enough for weaving. Currently, Western Europe produces the highest grade flax fibre for short fibre spinning and subsequent weaving, with Eastern European and Chinese suppliers offering mainly, but not exclusively lower grades. Sourcing the optimum yarns has posed several challenges in terms of the negotiation between quality, performance and cost. Sourcing a heavy yarn count, with low-medium twist in small - medium quantities for prototype production at low cost has been difficult to achieve. Cheaper flax yields exhibit poor fibre quality and are subject to increased fibrillation damage and fibre degradation during the weave process. An object of the present invention is to produce a naturally derived woven fabric for composite materials which overcomes the abovementioned problems.

According to a first aspect of the present invention there is provided a composite material comprising a 3D woven fabric embedded in a resin matrix, wherein at least a portion of the yarns in the fabric comprise regenerated cellulose fibres.

Regenerates cellulose fibres are manufactured from natural cellulose fibres, commonly extracted from the wood pulp of spruce timber (viscose) or hardwood trees (lyocell), cotton linter or bamboo, wherein the natural cellulose fibres are dissolved in an organic solvent and extruded to form regenerated cellulose fibres having consistent physical properties. The raw cellulose is changed physically but not chemically. Yarns are produced by extruding the cellulose solution, typically through a spinneret, then coagulating the filaments in an acid to produce a naturally derived, yet synthetically produced yarn. Regenerated cellulose fibres may be categorised under the following generic types; Viscose fibres, defined as a manufactured fibre of cellulose obtained by the viscose process, Lyocell fibres, defined as a manufactured fibre of cellulose obtained by extruding cellulose dissolved in an organic solvent, typically comprising N-Methylmorpholine N-oxide, Acetate fibre, which is defined as a manufactured fibre of cellulose ethanolate (acetate) wherein less than 92%, but at least 74% of the hydroxyl groups of the original cellulose are ethynolated (acetated), and other regenerated cellulose fibres manufactured from non traditional source of cellulose ( bamboo) and processed by either a viscose or lyocell process.

More specifically, the viscose process comprises dissolving pulp from wood, cotton or other natiral cellulosic material in sodium hydroxide, then mixing the resulting solution with carbon disulfide to form cellulose xanthate. The resulting viscose is extruded into an acid bath through a spinneret to form fibres. The acid converts the viscose back into cellulose.

The lyocell process differs from viscose fiber production in that a direct solvent process is used for the cellulose, the solvent typically comprising N-Methylmorpholine N-oxide. The Lyocell process is often preferred over the viscose process as it is more environmentally friendly as it avoids the polluting effects of carbon disulfide and other by-products of the viscose process.

The regenerated cellulose fibres do not require a sizing treatment (prior to 3D weaving) and achieve good thermal and adhesion compatibility with the resin matrix. Other attributes of the regenerated fibres include quality certified consistent production, where advanced clean processing techniques have been optimized, good fibre properties, and reduced cost compared to high-grade flax.

The regenerated fibres or filaments can be twisted or plied together or remain as a continuous filament yarn. Any coating applied to assist with any associated textile processing (for example, the twisting process during yarn production) may also be naturally derived.

Such regenerated cellulose fibres, typically produced by the manufacturer to produce a yarn having consistent properties, have increased suitability in engineering composite applications. Such fibres do not necessarily require pre-treatment before being woven and can achieve good thermal and adhesion compatibility with the resin matrix. Therefore the use of regenerated cellulose fibres provides guaranteed attributes in terms of consistency in production, fibre properties, and quality certification.

Said regenerated cellulose fibres may comprise one or more of rayon, viscose rayon, lyocell, regenerated bamboo fibres or cellulose acetate.

In one embodiment, the woven fabric comprises an orthogonal weave wherein at least a portion of the interlocking yarns comprise regenerated cellulose fibres. The woven fabric may comprise substantially orthogonally woven warp and weft yarns arranged in layers interlinked by binding yarns extending through the layers, wherein said binding yarns comprising regenerated cellulose fibres The warp and weft yarns may comprise a natural fibre, preferably a cellulosic based fibre, such as flax Alternatively, or additionally, at least a portion of the warp and weft yarns may comprise regenerated cellulose fibres

In an alternative embodiment, substantially all of the yarns in the woven fabric comprise regenerated cellulose fibres

In a further embodiment, the woven fabric comprises an angle interlock weave where warp yarns interlock weft yarns as they sequentially migrate through-the-thickness of the material

The resin matrix may comprise an epoxy or polyester resin Alternatively the resin matrix may comprise a bioresin matrix, such as a furfuryl alcohol derived resin, which may be produced from agricultural waste Alternatively the resin matrix may comprise a soy-bean derived resin

In a further aspect of the invention, there is provided a three dimensional woven preform for a composite material, wherein at least a portion of the yarns of the preform comprise regenerated cellulose fibres

According to a further aspect of the present invention there is provided a three dimensional woven fabric comprising a plurality of yarns arranged in three mutually orthogonal directions, wherein at least a portion of the yarns comprise regenerated cellulose fibres Preferably the yarns extending through the structure (Z direction) comprise regenerated cellulose fibres Additionally the yarns extending in the warp and weft (X and Y) directions comprise regenerated cellulose fibres Alternatively the warp and weft yarns may comprise a cellulosic based natural fibre, such as flax

An embodiment of the present invention will now be described, by way of example only

With the implementation of EU directives on waste and end of life disposal strategies, there has been a surge of activity driven by the European Automotive Industry to introduce Natural Fibre Reinforced Composites (NFRC) as a substitute to glass-fibre reinforced plastic (GRP), where appropriate With sustainable, lower environmental production impact and lightweight attributes, matched with low cost in comparison to glass fibre yams as driving factors, natural fibre non woven materials have been implemented for use in acoustic insulation, interior trim and secondary non-critical vehicle parts such as parcel shelves and door inserts Plied lay-up woven laminates are currently being developed Material data is continually being generated allowing greater usage and integration into further applications

In an embodiment of the present invention an angle interlock 3D woven preform is produced from viscose rayon fibre warp and weft yarn tows arranged in layers of either straight stuffer yarns or interlacing yarns interlocked by a series of viscose rayon angle interlock binding yarns Interlocking warp yarns of the structure may contribute both to the X-Axis and the Z-Axis reinforcement by migrating through the total thickness at an angle of approx 45° one layer at a time This forms a structure with equal yarn path lengths between binding layers and provides a uniform preform surface for consolidation in a mould tool

The woven viscose rayon fabric is embedded in a resin matrix formed from a two-part epoxy resin based on an epoxide derived from the reaction of bis-phenol A with epichlorohydrin, an Araldite LY- 564 and a cycloaliphatic amine curing agent, Aradur HY 2954 which consisted of Tetrafunctional amine - 3,3/ -dιmethyl-4,4/ -dodicyclohexyl-methane is used to define the matrix A mixing ratio of 100 35 by weight of epoxide to curing agent was used to create a stoichiometrically balanced epoxy resin

In an alternative embodiment, thermally recyclable embodiment, a thermosetting bioresin, BioRez™ from TransFurans Chemicals bvba, can be employed as a matrix material The Furan resin, supplied as a one component system is based on furfuryl alcohol derived from Hemi-cellulose C5 sugars produced from agricultural waste An added advantage of this resin system is its inherent flame retardant properties which is desirable for natural fibre composites

Vacuum Assisted Resin Transfer Moulding (VARTM) can be used to create the viscose rayon composites Flexible tooling allowed 100 KPa pressure to compact the viscose rayon preform Epoxy resin is injected under 75KPa at 75°C and the furan resin under 100KPa at 110 ⁰ C Wet out of the preforms occurs after 7 5 and 10 5 minutes respectively After wet-out the viscose rayon/epoxy is ramped to 100°C at 0 64°C/mιn and held isothermal for 60 minutes A post cure of 8hrs at 145°C brings the composite to full cure The viscose rayon/furan composite is de-moulded 20mιns after wet-out and B staged at 145°C for 60 mm

Testing

Flexural tests have been carried out as per ISO14125 using a three point bend configuration with 10mm diameter rollers Five samples were tested per composite and all samples failed within 30-180 seconds Fibre volume fraction tests were carried using the density buoyancy technique on a Mettler Toledo XS64 at 17 4°C At least three specimens were tested per material

The flexural results of the viscose rayon composites are given in table 1 below A of 40% fibre volume fraction (V, ) was found for the viscose composites The 6 7 GPa flexural modulus equalled the epoxy composites performance whilst a drop of 23% in flexural strength was observed An encouraging flexural strength value of 168 5 MPa was observed for the angle interlock viscose epoxy composite These results were achieved without any treatment to the yarns to improve interfacial properties between yarn and matrix, and without strength enhancing additives (such as nano-clay particles ) to the resin

Table 3: Flexural results on viscose rayon composites along the warp direction.

These results compare favourably with other work conducted in flax soy resin composites by Huang where unidirectional yarn composites possessing 48% (V, ) obtained values of 82-117 MPa and 4.7- 7.6 GPA in flexural stress and flexural modulus respectively. Huang also reports that flax fabric reinforced composites with 4 layers of laminate ply and possessing a 43% composite (V _f ) obtained flexural stress values of 20.9 - 25.2 MPa in the warp orientation and 0.7- 1.29 GPa in flexural modulus. A glass fibre laminated composite using bio-based resin and possessing a 45% (V^ ) was found to achieve flexural strength of 260 MPa and flexural modulus of 11.3GPa. Results from Oksmanand Heijenrath and Peijs state flax composite mats with a 47% can (V, ) obtain similar stiffness to glass fibres using epoxy and polypropylene matrix but with reduced strength.

In this instance, viscose epoxy and viscose furan composites with a much reduced composite volume fraction (V _f ) have reached 65% and 50% respectively of the properties of glass fibre composites. This provides significant motivation to generate a full range of tensile, flexural and toughness data from viscose composites.

Other suitable regenerated cellulose yarns for use in such 3D woven fabrics may be lyocell, regenerated bamboo fibres or cellulose acetate or any other variety of rayon.

Modified Dobby and Jacquard weave technology can produce orthogonal, angle interlock, twill, satin and near-net shaped woven prototypes. Preforms and composites with volume fractions in the range of 40% can generate significant mechanical property data and prototypes using flax and synthetically modified natural fibres. The use of viscose rayon negates some of the disadvantages of flax fibres such as batch variability, the need for alkali or enzyme pre-treatment, and inconsistency in production. Epoxy and furan resin systems were utilised successfully in the production of VARTM processed viscose composites. Vacuum infusion processing method was successfully used with epoxidised soy-bean bio-derived resin matrix (in conjunction with Prof R Wool at Centre of Composite Materials, University of Delaware, USA). Flexural strength and flexural modulus results are encouraging when compared with leading non-woven research. A natural fibre composite material in accordance with the present invention can be used to form curved composite parts for high performance applications, such as components of racing cars, for example demonstrator barge boards/side pods (as seen in the Worlds First Sustainable Racing Car in conjunction with Warwick Innovative Manufacturing Research Centre, 2008-09). With enhanced properties in the through-the-thickness (Z-Axis), these can be assigned to a variety of prototype applications for the automotive, transport, building and infrastructure sectors and beyond. A range of well established angle interlock, orthogonal and twill 3D woven fabric architectures have been fabricated in flax and viscose rayon yarns for this purpose. Preform fibre volume densities have been obtained using the Mettler Toledo XS64 density buoyancy technique. Fibre volume densities in the range of 27% - 47% have been recorded for a range of 3- 7 layer structures.

Tailored towards more demanding structural components, with development these cellulose-based materials aim to demonstrate enhanced mechanical properties compared with non-woven, stitched or plied woven laminates used currently. With additional advantages of renewable supply, near-net shaping and future capability for volume production, cellulose based composites position themselves as a key material within future composite applications. Examples include: generation of composite specimens for generation of mechanical property data, near-net shaped prototypes for transport, thick reinforcement panel prototypes and shaped structural sections for building and infrastructure and aerodynamic parts for racing cars.

The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.