The present invention relates to sheet materials and processes for producing such sheet materials. More particularly, the present invention relates to flame retardant sheet materials containing tanned collagen; the sheet materials may be used as leather-based materials.

Natural leather and other materials may be used in transport applications to cover seating and other internal parts of ground, air and water vehicle cabins. The requirements for such applications include good mechanical properties, good flame-retardant properties and, especially for relatively high value vehicles, good softness and hand-feel.

A great deal of waste leather is produced annually by the leather industry. Waste leather may derive from animal hides with imperfections and from leather off-cuts.

Leather production generally starts from raw hide or skin, then“beamhouse operations”, which involve mechanical processing and chemical treatment to remove hair and non-collagenous components (e.g. fat, grease, non-collagenous structural proteins such as elastin and keratin, non-structural proteins such as mucins, mucoids, albumens and globulins and salts present within the hide/skin). The result is a collagenous material, that can be further processed. For thicker starting materials (i.e. hides, that may be up to 5 mm thick), a splitting operation may occur when the hide is in a swollen state, often at the “liming stage” (part of the beamhouse operations after the hair is removed and at a alkaline pH), to produce a final leather thickness of around 2.2 mm or thinner, and often 1.0 to 1.2 mm thick. The benefit of the splitting operation is that it produces at least two pieces per hide. The top split (carrying the leather grain) is most valuable. The lower split or splits are generally much less valuable: they may be used for suede leathers, but usually are used in the production of gelatine (e.g. for sausage casings) or for bi-cast leathers of low value.

After beamhouse operations, the hide/skin undergoes tanning which renders the collagen in the leather resistant to putrefaction and enhances hydrothermal stability through the introduction of chemical crosslinks. The stage in the process where the leather has just been tanned is known as“wet-blue,“wet-white” or“wet-tanned” depending on the type of tanning. After tanning, the hides and skins may be shaved to get them to a consistent, specified thickness. Usually this is completed through a shaving machine, which generates small leather fibres/particles as waste. Subsequently, the leather undergoes a secondary wet processing stage (commonly known as retan, dyeing and fatliquoring) where the leather is exposed to further chemistries to alter the aesthetics of the leather, is fat-liquored (to give softness) and dyed as required.

It is known to produce imitation or synthetic leather from polymer materials that can be embossed and made to look like natural leather. Such synthetic materials however do not have the fibrous structure, or hand-feel, of natural leather nor other beneficial properties such as tensile strength and elasticity. Flame retardants may be added to such materials, but fire and flame-retardant properties can nevertheless be problematic.

There have been attempts to use off-cuts and waste leather to form leather-based materials with similar appearance and hand-feel to natural leather. US-A-2007/0184742 (Coulson et al) discloses a composite material including leather, non-leather fibres, a binding agent and one or more additional components such as cushioning agents, softeners, processing aids and colorants.

GB-A-l 396 188 discloses a process of producing materials from fibres of waste leather and other materials. The leather is disintegrated into fibres and mixed with, for example, textile or wood-pulp fibres and the mixture impregnated with a binder and aggregated on a screen.

CN-A-103 233 324 discloses a low-cost collagen fibre reconstituted leather. The reconstituted leather comprises the following ingredients in percentage by weight:

collagen fibre 85 - 99% and viscose fibre 1 - 15%. CN-A-103 233 321 discloses spun-laced collagen fibre bonded leather as well as a manufacturing method and a spun-lace device.

CN-A-103 276 531 discloses a low-cost collagen fibre regenerated hide and a method of manufacturing the same. The regenerated hide consists of a double-layered web in which one layer of the web contains up to 100% by weight of a low-cost viscose fibre and the other layer is composed of collagen fibres.

WO-A-01/94673 discloses an artificial leather sheet material made by

hydroentanglement of waste leather fibres. WO-A-2005/118932 discloses a development of the materials of WO 01/94673 of leather sheet material made by hydroentangling a web of mixed reclaimed leather fibres and synthetic fibres of a meltable bicomponent material which are heated prior to entanglement to fuse and form a supporting network. During manufacture, a sheet of tissue paper is laid over the surface of the leather fibre web and hydroentanglement jets. The prior art processes have problems because they generally use waste leather shavings which contain short fibres that are no longer than 0.1 - 0.2 mm obtained at the wet-blue stage. The strength and durability of the composite sheet materials tends to depend on the length of the fibres used within the composite. In order to compensate for relative low strength, prior art materials may use other inexpensive fibres (which may have poor thermal or flame retardant properties) or a scrim of cotton or polyester. In practice therefore, the leather fibres/particles used in prior art composites are more to give an aesthetic effect and for marketing purposes than technical reasons. Furthermore, the tanning agents used are typically chromium compounds (used in about 85% of all leather produced). Unfortunately, chrome tannage has significant problems, especially for use in composite materials, including after-glow properties when exposed to flame, so that significant amounts of fire-retardant compounds (e.g. brominated compounds) have to be added to be effective. Such fire-retardant materials may not be well incorporated in the material and are typically salts that can become mobile during the life of the product; such large amounts of fire-retardant compounds have other disadvantages including promoting corrosion to metals and irritation to workers handling the material.

Known composite materials generally require further complex processing to apply the fat liquor, dyes and the flame retardant compounds, often using a number of chemical baths on a long production line. Good chemical fixation (including of brominated salts) may not be achieved. Flame retardant requirements are becoming more stringent and, unfortunately, there can be problems of delamination and adhesion failure in known materials, particularly to coatings applied. There is, therefore, a need for improved leather-based materials with good mechanical properties, good flame-retardant properties, that can be durably coated, with long life and good softness and hand-feel.

It is an aim of the present invention to address this need.

The present invention accordingly provides, in a first aspect, a process for producing a sheet material, the process comprising: a) providing tanned collagen fibres, b) providing inherently flame-retardant fibres, and c) entangling the tanned collagen fibres and flame-retardant fibres to form a fibre mixture.

Providing collagen fibres may comprise providing one or more leather pieces and defibrillating the leather pieces to form tanned collagen fibres.

The process may further comprise d) forming a layer of a sheet material from the fibre mixture. The process may comprise needle punching the sheet material to increase porosity.

In a preferred aspect, the present invention provides, a process for producing a sheet material, the process comprising: a) providing one or more tanned leather pieces, b) defibrillating the leather pieces to form tanned collagen fibres, c) providing inherently flame-retardant fibres, d) entangling the tanned collagen fibres and flame-retardant fibres to form a fibre mixture, and e) forming a layer from the fibre mixture, thereby forming the sheet material. One or more further layer may be formed on the sheet material if desired.

Preferably, one or more tanned leather pieces comprise tanned split leather pieces. This is advantageous, because using splits as the source allows relatively long fibres to be obtained, the long length of fibres improving the entanglement and the strength and other properties of the sheet material. Usually, the split leather pieces comprise lower split leather pieces. Lower split pieces are often a waste or low value material in leather making.

Thus, the process may further comprise a step of splitting a hide to form an upper split and the lower split. It is advantageous if the splitting of the hide is conducted at a pH in the range 10 to 13.

The process preferably further comprises a step of tanning the split pieces.

Tanning processes that may be used include (but are not limited to): vegetable tanning agents, based upon pyrogallol and catechol type compounds such as Mimosa, Tara, Quebracho, Chestnut; semi-alum tannage (a combination of vegetable tanning agent e.g. Mimosa extract and aluminium sulphate); semi-chrome (a combination of vegetable tanning agent e.g. Tara extract and chromium sulphate); isocyanate based tannage (e.g. X- Tan from Lanxess); trivalent chromium tanning, e.g. using chromium sulphate;

aluminium tanning, e.g. using aluminium sulphate; zirconium tanning, e.g. using zirconium sulphate; titanium tanning, e.g. using titanium sulphate; iron tanning, e.g. using iron sulphate; zeolite tanning, e.g. using sodium aluminium silicate (Coratyl G from

Pulcra); dichlorotriazine based tanning (e.g. F90 from Stahl); polyphosphate tanning e.g. using sodium polyphosphate; oxazolidine tanning (e.g. Zoldine ZE from Angus

Chemicals); or a mixture of two or more thereof.

Preferably, the step of tanning the split pieces comprises using a source of aluminium and/or a source of glutaraldehyde in the tanning process. The tanning agents may comprise aluminium triformate, aluminium sulphate and/or glutaraldehyde.

Entangling the collagen fibres and flame-retardant fibres is preferably by a process selected from spun-lacing, hydroentanglement, and air entanglement.

The preferred method of entangling the collagen fibres and flame-retardant fibres is hydroentanglement performed using high pressure water jets. The water jets may be 80 to 250 pm diameter hydroentangling jets at 0.2 to 1.9 mm apertures and pressure of 12 MPa (120 bar) to 70 MPa (200 bar), usually up to 30 MPa.

Thus, in a preferred embodiment there is provided a process for producing a sheet material, the process comprising: i) providing a hide, ii) providing that the hide is split to form an upper split and the lower split, iii) providing that at least the lower split leather pieces are tanned (preferably using a source of aluminium and/or a source of

glutaraldehyde), iv) providing that the tanned split leather pieces are fat-liquored

(preferably using a flame retardant fat liquor), v) defibrillating the tanned split leather pieces to form tanned collagen fibres (preferably having a length in the range 0.5 cm to 12 cm), vi) providing flame-retardant fibres, vii) entangling the tanned collagen fibres and flame-retardant fibres to form a fibre mixture, e) thereby forming at least one layer of the sheet material.

The hides may be bovine hides, preferably ox hide or buffalo hide. In a third aspect there is provided, a sheet material comprising inherently flame- retardant fibres entangled with tanned collagen fibres.

Generally, the weight percentage of flame-retardant fibres in the material may be in the range 1% to 60%, preferably in the range 1% to 40%, more preferably in the range 1% to 30% and most preferably in the range 1% to 20%. The lower end of the range may be 2%, 3%, 4%, or 5%. Thus, the weight percentage of flame-retardant fibres in the material may be in the range 2% to 60%, preferably in the range 3% to 40%, more preferably in the range 4% to 30% and most preferably in the range 5% to 20%.

Generally, the weight percentage of tanned collagen fibres in the material may be in the range 15% to 95%, preferably in the range 40% to 95% (other ranges may be 45% to 95%, or 43% to 93%), more preferably in the range 70% to 95% and most preferably in the range 80% to 95%.

The inherently flame-retardant fibres may have been treated before incorporation in the sheet material and/or may be composed of flame retardant materials, in particular inherently flame-retardant materials. The flame-retardant fibres may comprise an inorganic material, a flame-retardant treated natural fibre, and/or a flame-retardant polymer.

Examples of flame-retardant fibres may comprise a material selected from one or more of glass, carbon, silicon carbide, elongated carbonaceous Dow™ fibre (EDF), carbonised viscose or acrylic fibres (e.g. Panox™ generated through thermo-oxidative stabilisation of viscose or acrylic fibres), modacrylic (e.g. Kanecaron™ or Protex™), Zeroxy™, Lastan™ (an oxidised acrylic based fibre), flame retardant treated wool (e.g. wool fibre treated by the ZIRPRO™ process), Proban™ treated cotton fibres, fungal mycelium-derived fibres, novoloid fibres (phenolic fibres, e.g. Kynol™), oxidised poly(acrylonitrile) fibre (OPF), polyhydroquinone-diimidazopyridine (PIPD), aramid (para- or meta-), polybenzimidazole (PBI), polyphenylenebenzobisozazole (PBO), polyimide, polyphenylene sulfide (PPS, e.g. Procon™), melamine,

polytetrafluoroethylene (PTFE), poly(ether-etherketone) (PEEK), phenolic fibre, polyamide-imide (PAI), copolymer p-aramid fibre, poly(m-phenylene isophthal-amide) (PMIA), and poly(p-phenylene terephthal-amide) (PPTA).

The flame-retardant fibres may have a length in the range 100 pm to 10 cm, preferably in the range 500 pm to 6 cm, preferably 1 mm to 8 cm, more preferably in the range 1 mm to 4 cm. A good range is preferably 25 mm to 7.5 cm. Staple fibres may be 20 to 35 mm , preferably 2 cm to 6 cm in length. Preferably, the flame-retardant fibres are crimped in order to improve interlocking of the fibres after entanglement.

The flame-retardant fibres preferably have a limiting oxygen index (LOI) (e.g. measured in nitrogen/air) of 25 or greater, preferably 30 or greater and more preferably 35 or greater. Examples of good flame-retardant fibres are meta aramid (with LOI of around 30 to 32) or para-aramid (with LOI of around 28 to 32), and preferably PBI (which may have a very high LOI of above 45).

Preferably, the tanned collagen fibres are natural collagen fibres derived from animal leather. Natural collagen may include collagen from animal sources (for example bovine, porcine, ovine, caprine and/or kangaroo animal sources), and/or collagen that can be extracted from waste leather materials. As used in this specification, the term “collagen” includes modified collagens and collagen-like proteins.

Generally, the tanned collagen fibres may have a length in the range 250 pm to 20 cm, preferably in the range 1000 pm to 15 cm, more preferably in the range 1 cm to 15 cm, most preferably in the range 1 cm to 12 cm. In prior art processes, fibres are extremely short, usually 0.1 -0.2 mm long. Thus, they have very little chance of becoming well-entangled, which means that binder is typically required. In contrast, the present invention advantageously, uses relatively long fibres: the long length of fibres improves the entanglement and the strength and other properties of the sheet material especially when using lower splits as the source of fibres.

Generally, the tanned collagen fibres may have a width in the range 0.1 pm to 2000 pm, preferably in the range 1 pm to 500 pm, possibly in the range 10 pm to 50 pm, most preferably in the range 25 pm to 75 pm.

Sizes may refer to size (e.g. width and/or length) determined by microscope, by hydrodynamic methods or by coagulation methods.

In some embodiments, the material may comprise at least two layers. The layers may differ in weight percentage of collagen fibres. For example, a first layer may have collagen at 95% by weight to give hand-feel essentially indistinguishable from natural leather and a second layer at 50% by weight to provide for more flame-retardant fibres and/or polymer fibres.

Generally, the material may further comprise fat liquor. Preferably, the fat liquor may be a flame-retardant fat liquor or flame-retardant lubricant, preferably comprising a siloxane-base lubricant or halogenated fat liquor. The use of fat liquor may be advantageous so that the collagen fibres have their bound water replaced with a lubricant as they dry, to reduce or prevent the fibres sticking together and maintain flexibility. Halogenated fat liquors (e.g. Truposol FRF from Trumpler GmbH) and siloxane-based lubricants (e.g. Densodrin CD, BASF) may improve flame retardant properties.

The sheet material may comprise surfactants (e.g. cationic or anionic or amphiphilic) and/or other lubricants. The materials may also include other additives to modify properties of the materials. Such additives may include, but are not limited to fragrances, dyes and/or pigments.

To still further improve flame-retar dancy, the material may further comprise a flame-retardant composition comprising a particulate material selected from one or more of aluminium trihydrate, magnesium hydroxide, huntite, hydromagnesite, vermiculite, ammonium polyphosphate, organically modified phyllosilicate (e.g. Cloisite™), and expanded graphite.

The sheet material may also include particles intended to provide porosity. The sheet material may, in some circumstances, further comprise additive polymer fibres selected from polyester, viscose, polyalkene (e.g. polyethylene and/or

polypropylene), and polyamide. The additive polymer fibres may be optionally present in an amount in the range lwt% to 25wt%. The preferred polymer fibres comprise polyester, more preferably fire retardant enhanced polyester. The sheet material may further comprise one or more web layers comprising a suitable material (e.g. thermoplastic polymer). The web layer may be on one of the surfaces of the sheet material and/or may be a web layer disposed between two layers of the sheet material.

The web may be of relatively open structure (e.g. a scrim) to aid entangling through the web. Suitable scrims may comprise flame-retardant fibres selected from one or more of glass, carbon, silicon carbide, elongated carbonaceous Dow™ fibre (EDF), carbonised viscose or acrylic fibres (e.g. Panox™ generated through thermo-oxidative stabilisation of viscose or acrylic fibres), modacrylic (e.g. Kanecaron™ or Protex™), Zeroxy™, Lastan™ (an oxidised acrylic based fibre), flame retardant treated wool (e.g. wool fibre treated by the ZIRPRO™ process), Proban™ treated cotton fibres, fungal mycelium-derived fibres, novoloid fibres (phenolic fibres, e.g. Kynol™), oxidised poly(acrylonitrile) fibre (OPF), polyhydroquinone-diimidazopyridine (PIPD), aramid (para- or meta-), polybenzimidazole (PBI), polyphenylenebenzobisozazole (PBO), polyimide, polyphenylene sulfide (PPS, e.g. Procon™), melamine,

polytetrafluoroethylene (PTFE), poly(ether-etherketone) (PEEK), phenolic fibre, polyamide-imide (PAI), copolymer p-aramid fibre, poly(m-phenylene isophthal-amide) (PMIA), and poly(p-phenylene terephthal-amide) (PPTA).the preferred material for the scrim comprises aramid (meta aramid or para aramid) or ceramic based. The scrim may have square apertures (the yam spacings), so that the strength is generally similar or equal in both warp and weft directions. To improve the appearance of the sheet material, the sheet material may be embossed. Embossing the sheet material would usually involve forming a coating on the surface of the sheet material and embossing the surface of the coating. Thus, coating may comprise top coating, and optionally embossing the sheet material. In additional or alternatively, coating may comprise back coating, optionally with a flame retardant liquid composition. Thus, back coating may be used to apply liquid based materials to the reverse side of the material to further improve fire retardant properties.

Alternately, the sheet material may comprise a coating that has been pre-embossed using an embossed release paper. The area density of the sheet material may be 20 g/m ² to 3500 g/m ² , preferably 20 g/m ² to 1500 g/m ² , more preferably 200 g/m ² to 700 g/m ² . Thus, the area density may in the range 100 g/m ² to 1000 g/m ² , preferably 110 g/m ² to 870 g/m ² , more preferably 130 g/m ² to 730 g/m ² , most preferably 190 g/m ² to 610 g/m ² .

Sheet materials according to the invention may be made by entangling processes. The materials may further comprise a binder, preferably a resinous binder.

Example of suitable binders include vinyl copolymers, vinyl-styrene, melamine- formaldehyde, polyurethane (PU) and/or acrylic binders. To provide enhanced flame retardant (FR) properties, the binder may comprise halogen (i.e. be halogenated) or another flame-retardant component. The binder may be solvent- or aqueous-based. The binder may contain cross-linking moieties e.g. isocyanates, carbodiimides, aziridines, polyurea, or others.

If present, the process may further comprise curing the binder (e.g. by drying, UV curing, radiation curing, depending on the nature of the binder).

Preferred and optional features of the third aspect are also preferred and optional features of the first and second aspects.

In a fourth aspect, the present invention provides, a leather-based material formed by the process of the second or third aspects. Embodiments of the present invention will now be described with reference to the following figures, in which:

Figure 1 shows micrographs of (a) 95% (by weight) collagen fibres entangled with 5% (by weight) polyester fibres, (b) 85% (by weight) collagen fibres entangled with 15% (by weight) polyester fibres, and (c) 85% (by weight) collagen fibres entangled with 15% (by weight) polyester fibres with an automotive type re-tan and finish.

Figure 2 shows micrographs of the top layer of the samples as in Figure 1 (a) and (b).

Figure 3 shows micrographs of the bottom layer of the samples as in Figure 1. The materials have high tensile strength including meeting the requirements in terms of the force to break on elongation for items such as a footwear and seating.

The present invention is further illustrated by the following examples.

Examples Method A fusing only fibres) a. Weighing: raw staple tanned collagen fibres (one or more types of fibres may be used in order to provide the desired physical attributes of the finished product). Weighed amounts of fibres are provided in an amount to provide a finished material with area density 20 g/m ² to 1500 g/m ² (or higher if required). A density of 500 g/m ² is typically used for many purposes. In some embodiments, two or more layers may be prepared, with each layer having a different area density, the overall density will preferably be in the range indicated above by laying the webs of fibres in different densities on top of each other. Inherently fire-retardant fibres for use in the invention are fibres that are made of a fire-retardant material, have been treated with a fire-retardant composition and/or have undergone a process to render them fire retardant before use in the invention. PBI is a particularly suitable flame-retardant fibre for use in the invention. b. Blending: After the tanned collagen and FR fibres are weighed, they are blended. c. Opening: the blended fibres are carried by a belt to a hopper to fluff and open the material and blend further. d. Carding: the blend fibres are carded. Carding machines contain cylinders wrapped with fine metal pins and teeth that are used to stretch and comb the fibres. Carding is advantageous in the invention because it combs, opens, and aligns the fibres, removing hard clumps and creating a uniform, soft and fluffy web. After carding, the carded blend is formed into a web and wet laid or air laid onto a belt to be carried to the entangling stage. If two or more layers are to be formed, the different webs to form the different layers may be laid on top of one another at this stage. The air-laid or wet-laid web is compressed and then pre-wetted to remove air pockets before the hydroentangling process. e. Hydroentangling: High-pressure water jets are applied to the web of fibres, entangling them together to form a non-woven fabric and providing strength and integrity to the wet-laid or air-laid carded web of fibres from the previous operation. The water pressure usually increases from the first to the last water jet injectors. The pressure is typically 2200 psi (15 MPa), used to direct the water jets on top of the web, but can be as high as 10,000 psi (69 MPa). The high-pressure jet of water entangles the fibres in the web. The jets’ kinetic energy is primarily used in rearranging fibres inside the web, and secondly, during bounce back against the substrates, dissipating energy to the fibres. A vacuum inside the roller (typically 500 mbar (50 kPa) or greater) removes used water from the product, avoiding flooding of the product and consequently maintaining the effectiveness of the jets to move the fibres & cause entanglement. Hydro-entanglement may be performed on both sides of the web in a stepwise approach. If required, the first entanglement roll may be subjected to further hydroentanglement as necessary, to generate the desired amount of interwoven bonding and strength. The material may also pass over a second entanglement roller in an overturned direction in order to treat and, thereby, consolidate the other side of the fabric. Furthermore, additional webs of fibres can be hydroentangled on top of the initial hydroentangled material in order to build up thickness. f. Smoothing: The non-woven material may be finally subjected to a series of water jets at a much lower pressure (such as a pressure of 750 psi (5 MPa)) in order to smooth out the surface of the material from any irregular surface aspects caused through the higher-pressure water jets. g. Drying: After hydroentanglement, the newly formed non-woven composite fabric is dewatered typically through a pressing system to reduce the moisture content to 10 - 50wt% and further dried by being pulled over large drying cans or routed through a tunnel dryer to remove excess water and moisture before being wound into a large roll. The drying stage can be completed at temperatures ranging from 40 °C to 100 °C, typically at 70 °C for 3 - 12 minutes.

To improve strength and other properties, web layer (e.g. comprising a

thermoplastic polymer) may be used, preferably a scrim (having relatively open structure with apertures) with the fibres entangled around the web. A suitable scrim may comprise 85gsm 100% Meta-Aramid with the following construction details: Weave Pattern: Plain; Width (cm): 105 - 109; Weight (gsm): 80 - 90; Warp Sett (ends/dm): 80 - 90; Weft Sett (picks/dm): 76 - 88; Gauge (mm): 0.4 - 0.5; and Composition: 100% Meta-Aramid. Such a scrim has square apertures (the yam spacings), so that the strength is equal in both warp and weft directions.

Method B (using binder) a) As a modification to Method A above, the non-woven material can be provided with increased strength using a binder, usually in the form of a resin. This may be accomplished by passing the roll of material through a roller coater applying a resin (e.g. aqueous or solvent based). The resin may be curable (e.g. an isocyanate, carbodiimide, aziridine, polyurea, etc resin). Once the resin has sufficiently penetrated the roll, it may be cured (e.g. by air drying, heat drying, UV curing, radiation curing, etc). The properties of the resin, in particular the tensile strength at specific elongation values, can determine the degree of softness. For example, resins tested at 100% elongation: Resin A having a tensile strength of 5 MPa and Resin B having a tensile strength of 0.8 MPa; Resin B will have a softer handle than Resin A. Usually, a flame-retardant based resin may be used, such as a halogenated polyurethane (PU) type or an ethylene vinyl-chloride copolymer. b) A typical process would be as involve the roll of nonwoven being fed to a roller coater that applies 50 g/m ² of an aqueous PU resin that is allowed to penetrate through the roll. Subsequently, the web is dried at 80 °C through a tunnel dryer for 60 seconds. After drying, the roll would be rewound.

Method C (coating) a) The sheet material produced according to the above methods A and B may be coated. Because of the advantageous properties of the sheet material, traditional leather coating techniques may be used or to transfer type coating systems. With transfer type systems in particular care has to be used to ensure that the coating does not subsequently de-laminate, especially if the coating adhesive layer does not penetrate nor react well enough to give high adhesion values over time. The preferred method is therefore as follows: a. The sheet material is passed through a roller coater to apply an adhesion coat at an application level of 80 g/m ² , before being dried at 80 °C for 90 seconds. The sheet material is then again passed through a roller coater to apply a coloured basecoat at an application of 120 g/m ² before being dried at 80 °C for 120 seconds. Finally, the process is repeated with a colourless topcoat at an application of 40 g/m ² before being dried at 80 °C for 60 seconds. After coating, the sheet material may be embossed by passing through a rotopress having an engraved cylinder with an appropriate pattern at 80 °C to impart a permanent texture to the material.

The coating materials compositions may be as follows: 1) Adhesion coat: 10 parts of levelling agent (e.g. DRL 1261 from Dr Leather Ltd), 43 parts of water, 30 parts of Butyl Icinol (2-butoxyethanol), 9.5 parts of adhesion promoter (e.g. DRL 506 from Dr Leather Ltd), 7 parts of a PU binder (e.g. RU3961 from Stahl) and 0.5 parts of isocyanate crosslinker (e.g. Astacin Hardener Cl from BASF) 2) Coloured Basecoat: 65 parts Compact basecoat formulation (NLC Ltd), 30 parts pigment (e.g. PP-39-lxx range of pigments from Stahl) and 5 parts of isocyanate crosslinker (e.g. Astacin Hardener Cl from BASF)

3) Topcoat: 94 parts Compact topcoat formulation (NLC Ltd) and 6 parts of isocyanate crosslinker (e.g. Astacin Hardener Cl from BASF)

In each of the methods, particulates may be added either in the coatings stage or during the hydroentanglement process.

Sheet materials according to the invention achieve flame retardancy according to the following test: Aviation flame retardant (FR) tests include: a. Flammability - CS25.853 (a) Arndt 18 App.F Pt.I(a)(l)(ii) & (b)(4) 12 second edge test (Vertical); b. Heat Release - CS25.853 (d) Arndt 18 App.F Pt IV (e) & (g); c. Smoke Emission - CS25.853 (d) Arndt 18 App.F Pt V (a) & (b)

Train flame retardant (FR) tests include BS 6853: 1999, in which BS476-7 and Annex B and annex D.

Method D (using waste splits)

It is greatly advantageous to use waste splits (usually the lower split or splits) to generate fibres for use in the process of the invention. Lower spilts tend to be of relatively low value and to use them to provide a higher value sheet material as in the present invention is economically advantageous.

The splits, once obtained are fully degreased (leather is not always fully degreased of natural fat and oil), enzymatically treated (to ensure that the fibre structure is well opened-up) and tanned with a flame retardant friendly process, before further processing with a flame-retardant fat-liquor. The materials may be dyed if appropriate, and flame retardant compounds added so that they penetrate deep to the fibrillar level and therefore are better fixed. The leather is subsequently dried, staked and milled (to soften the leather and separate the fibres internally to provide softness and movement), before dry splitting (e.g. using dry splitter as produced by Atom) the material into 0.6 mm layers.

Once they are split to 0.6mm, the thin sheets of leather are defibrilliated which is easier than if they were full thickness. Defibrillation allows the fibres to be pulled apart and harvested, and does not tear the fibres, instead teasing the fibres out. The fibres are longer (typically 4 - 15 mm long), than in conventional processes, thus lending themselves to a better overall product.

The result is a stock of flame retardant leather fibres, that have all the necessary properties to be used in a hydroentangled (or mechanical assembled) material, as the fibres can be more easily integrated with inherently flame retardant fibres (around 50 mm on average and/or may be crimped (so that they entangle better). It is also advantageous in some application (e.g. for strength) to use scrim or fine scrim made of high tensile fibres (e.g. ceramic based fibres as made by Nextel (3M), or aramid). Furthermore, leather fibres obtained in this way provide a better base for the leather coatings to adhere and fix to the sheet material. Thus, there is reduced chance of delamination in final use.

The following beamhouse and re-tanning processes for the leather are used.

Beamhouse The percentages in the following are weight % based on the weight of hides.

The hides are typically wet-salted (which is used as a preservation technique to reduce or prevent bacterial degradation)

The hides are machine de-salted before they begin wet processing

After desalting the hides are weighed, and loaded into a processing drum, with the following steps:

Stage 1 - Dirt Soak: An initial stage to rehydrate the hides fully. Add 200% water at 22°C, 0.3% sodium carbonate (to raise the pH), 0.1% bactericide ( e.g. Truposept BA from Trumpler GmbH), and 0.1% of an anionic dispersant/emulsifier in order to begin loosening the natural grease and fat within the fibre structure and ensure it is dispersed easily for removal (e.g. Pastosol F from Trumpler GmbH)). Run with drum constantly rotating for 60 minutes The liquor (the float of water and chemicals inside the drum) is checked to ensure that the pH is within a range of 8.5 - 10.0 and that the temperature is between 22 - 25°C

The drum is drained in order to allow the liquor that is full of residual salt, dirt and fats and other easily soluble proteins to be removed.

Stage 2 - Main Soak: The drum is refloated with 150% water at 23°C, 0.4% of a mixture of proteolytic enzymes (to accelerate the rehydration of the hide and to assist in the removal of non-structural proteins, proteoglycans, dirt and blood allowing liming chemicals to penetrate more easily (e.g. Trupowet PH from Trumpler GmbH), 0.1% Truposept BA), and 0.1% Pastosol F. The drum is run for 60 minutes, and the liquor is checked so that the NaCl concentration is below 3 by use of a hydrometer, that the pH is now in the zone of 9.0 - 10.0 and that the temperature remains between 22 - 25°C. The drum is drained once again

Stage 3 - Liming: 80% water at 23°C is added to the drum, 1.2% of lime (calcium hydroxide) to induce swelling through raising the pH (and consequently solubilising the remaining soluble non-collagenous proteins), 1.0% of a liming auxiliary compound that reacts with the prekeratinous proteins of the hair and ensures even distribution of the lime throughout the cross-section of the hide (e.g. Mollescal MF from BASF), and 0.5% sodium sulphide). This is run for 30 minutes. A further addition of 1.0% lime and 0.5% sodium sulphide, and run for a further 30 minutes. A further addition of 1.0% lime and 0.5% sodium sulphide is made and run for a further 30 minutes. Finally, a further 1.0% of lime is added along with a further 50% water at 28°C and run for a further 30 minutes. The float pH is checked to ensure it is greater than 12.3. The drum is set to automatically run for 5 minutes and remain stationary for 55 minutes, and this cycle is repeated for 12 to 18 hours (in order for all the hair to be destroyed and solubilised). The drum is drained and undergoes a washing cycle by adding 200% water at 23 °C and run for 25 minutes before being drained again.

At this point the hides are treated in the lime fleshing machine which uses a helical bladed cylinder, which removes any flesh and subcutaneous material from the underside of the hide.

The fleshed hides are passed through a lime splitting machine (such as the‘StarSplit’ machine made by GeMaTa SRL, Italy). The top split (with grain) is used in full leather production. The bottom, lower split, (mainly of very fibrous collagen), is separated and used for further processing. The use of the lower split is greatly advantageous owing to the very fibrous nature of the bottom split. It can be successfully defibrillated at later stage in the process better than other leather-based starting materials.

Deliming and Tannage.

The splits are weighed and reloaded into the drum for de-liming (to reduce the pH). 100% water at 30°C is added and the drum run for 30 minutes and drained to remove excess soluble calcium compounds. 100% water at 30°C is added to the drum, with 1% ammonium sulphate and run for 90 minutes. The pH of the liquor is checked to ensure it is between 8.5 - 9.0, and the cross-section of the split is checked (using phenolphthalein indicator solution) to ensure the pH through the cross-section is also between 8.5 - 9.0. The drum is drained. Bating

Proteolytic enzymes (typically pancreatic types) are added to remove any remaining non- collagenous proteins. This provides an advantageous opening up of the internal structure and results in freeing the fibres across the material. Usually, in prior processing splits are not often heavily bated if they are to become leather because the leather may tear easily, but in the present invention the resulting splits defibrillate better. The operation is completed by adding 50% water at 33°C and 1.5% pancreatic type bating enzyme (e.g. Trupozym CCK from Trumpler GmbH). The drum is run for 120 minutes. Without draining the drum, 1% of a strong non-ionic degreasing agent (e.g. Eusapon OC from BASF) is added and the drum is run for a further 90 minutes. This stage advantageously removes the natural fat remaining in the hide, and so further improves flame-retardancy. The drum is drained.

The splits undergo a series of washes, where the drum is filled with 200% water at 28°C and run for 20 minutes before it is drained. This is repeated a further two times. The splits are then tanned, which stabilises the collagen so that it will be resistant to microbial/bacterial degradation, whilst also conferring a degree of hydrothermal stability. As previously noted, chrome tanning is not the optimum method for flame retardant leather. We have surprisingly discovered that a modified tannage with a mixture of a source of aluminium and glutaraldehyde is better for flame retardant properties, and is achieved as follows:

The drum is filled with 30% water at 30°C, along with 9% (wt) sodium chloride and run for 30 minutes. The salt content of the liquor is checked using a hydrometer to ensure a Baume reading of at least 6 is achieved (this is to ensure irreversible acid swelling of the collagen does not occur when the pH is later reduced). A total of 1% sulphuric acid and 0.5% formic acid is added in 4 equal portions every 15 minutes whilst the drum is running. The pH of the liquor is checked and ensured to be less than or equal to pH 2.5. With the correct pH, the drum is continued running for a further 45 minutes.

To the rotating drum, 3% modified glutaraldehyde (e.g. Relugan GTW from BASF) and 2% aluminium triformate (e.g. Novaltan AF from Zschimmer and Schwarz GmbH) is added. The run continues for a period of 120 minutes to gain penetration through the cross-section of the split. The pH is gently raised by adding 4% of sodium bicarbonate (commercial grade applied as a 10% wt solution in water) added in 8 equal additions over a 3 hour period. The drum is allowed to continue to run for a further 3 hours and the pH of the float checked to be at pH 5.4 - 5.8, and the cross-section checked with bromocresol green indicator solution to determine the pH is through the entire cross-section of the material. The raising of the pH indicates that the collagen has become reactive to the tanning agents and that a tanning mechanism has been achieved. To easily test for this, a sample of the split is subjected to hydrothermal shrinkage temperature test (IUP/16) to achieve at least a shrinkage temperature of 80°C. The drum is drained. 100% water at 30°C is added and the drum run for 15 minutes, before it is drained again and the splits removed.

The splits are piled and left for 72 hours, in order to age and fully cross-link with the collagen. Further processing with flame retardant auxiliaries and fat-liquor (which ensures the fibres do not stick together once the split is fully dried), possibly dye, is conducted.

Excess moisture is removed from the splits (by setting out and sammying).

The splits are placed in a drum and processed as follows:

125% water at 50°C is added to the drum and run for 15 minutes. The liquor of the drum is checked to ensure it is between pH 5.5 - 6.0. Extra sodium bicarbonate may be added as necessary. 10% of a flame retardant fat-liquor (e.g. Tuposol FR) is added to the drum that has been pre-emulsified with 40% water at 50°C. The drum is run for a period of 60 minutes. Optionally, dyestuff can be added is required. A total of 1.5% formic acid (diluted in water) is added to the drum in 5 equal additions to slowly reduce the pH to pH 4.0 over a period of 50 minutes. The fat-liquor be fully exhausted at this stage, and the drum is the continued running for a further 20 minutes.

The drum is drained. 200% water at 30°C is added to the drum, which is run for 15 minutes. The drum is drained.

50% water is added at 30°C and 20% of a halogenated flame retardant compound is added (e.g. Sellatec SAFE from TFL, Italy) and run for 45 minutes.

The drum is drained and the splits removed from the drum.

The splits are piled and allowed to age for 24 hours.

The splits are toggle dried, to ensure that they are dried flat and to ensure that the flame retardant compound remains attached to the fibrils of the fibre structure. The splits are put through a dry-splitting machine (StarSplitter from GeMaTa of Italy). The splits are split to a thickness of 0.7 mm They are passed through a through feed staking machine (such as a Syncro staker from Cartigliano) to soften the splits, and to achieve the effect of allowing the fibres to be well separated internally through the cross-section.

The splits are defibrillated using existing shredding and defibrillating equipment used in the textile recycling industry to produce a feedstock of pre-made, flame retardant leather fibres. The collagen fibres may be used in the process of the invention, as set out in Methods A, B and C.

Method E (back coating). Back coating may be used to apply liquid based materials to either coat the reverse side of the material, or to impregnate a fibrous sheet material from the reverse side. Thus, the sheet material may undergo application of a liquid flame retardant formulation in a process as follows: a. Ensure the sheet material is dry. b. Pass through a back coater, such as a rollercoater, where a flame retardant formulation is applied. The back coating process being as follows: i. The material is set in to the rollercoater (e.g. Easystar 1800 machine from GeMaTa SRL, Italy) utilising a 8L Roller (Gemata SRL, Italy) in‘Forward’ rolling format. ii. A formulation of a flame retardant halogenated product such as Leather

Seal Concentrate™ (LSC™) (Flameseal Inc) at a loading level of 300 gm ² is applied using the roller coater. iii. Resting (e.g. by passing the material through the conveyor system), without heating, to allow the flame retardant liquid to impregnate throughout the fibre structure, for two minutes. Dry in a drying tunnel at 80°C to remove the liquid carrier of the formulation. c. The material can then be, optionally, top-coated, on the top surface, to provide aesthetic appeal as described in Method C.