Removal of non-fibrous material from fibrous waste

Abstract

A method 100 of removing non-fibrous material from fibrous waste, the fibrous waste comprising leather and / or textile waste. Milled fibrous waste is inserted into a chamber 110 and dispersed such that

Description

TECHNOLOGICAL FIELD Examples of the disclosure relate to removal of non-fibrous material from fibrous waste. Some relate to removal of polymeric coating material from textile waste and / or leather waste. BACKGROUND Fibrous waste, such as textile waste and / or leather waste, can be recycled to produce materials for use in clothing, footwear, accessories or upholstery. However, the fibrous waste can include some non-fibrous material. For example, textile and leather materials often include polymer coatings such as polyurethane coatings, laminated layers, backings and / or treatments. These non-fibrous materials are therefore often present in the fibrous waste. Non-fibrous material within fibrous waste can cause difficulties when processing the waste, by fouling or damaging material or equipment. Furthermore, when recycling the fibrous waste to produce new materials, the presence of non-fibrous waste can diminish the quality, aesthetics, strength, haptics or other performance properties of the new material. Processing of fibrous waste comprising non-fibrous material is therefore generally avoided when producing new materials for use in clothing, footwear, accessories or upholstery. BRIEF SUMMARY According to various, but not necessarily all, examples there is provided a method of removing non-fibrous material from fibrous waste, wherein the fibrous waste comprises leather waste and / or textile waste, the method comprising: inserting milled fibrous waste into a chamber, the milled fibrous waste comprising fibres and non-fibrous particles; dispersing the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber; and following the dispersal, filtering the milled fibrous waste through a filtering apparatus to provide a fibrous feedstock with a reduced non-fibrous content relative to the fibrous waste, the filtering apparatus including a screen comprising a plurality of apertures, wherein the plurality of apertures are dimensioned to permit material with a size below a predetermined threshold to pass through. The non-fibrous material may comprise polymeric coating material. The non-fibrous material may comprise polyurethane. The method may further comprise milling the fibrous waste prior to inserting the fibrous waste into the chamber, such that the non-fibrous material of the fibrous waste is broken down into non-fibrous particles in the milled fibrous waste. The milling may comprise inserting the fibrous waste into a disc mill. The majority of the fibres of the milled fibrous waste may have a length of 1 mm to 10 mm. The dispersal of the milled fibrous waste in the chamber may comprise inducing a gas flow in the chamber. The gas flow may be induced using a vacuum, a fan, a pump and / or compressed gas. The chamber may be a vortex chamber configured to generate a vortex when a gas flow is induced in the chamber. The vortex chamber may comprise a vortex inducing section which is substantially conical in shape. The chamber may comprise a lower outlet for discharging heavier particles from the chamber and an upper outlet for discharging lighter particles from the chamber. A vacuum may be applied to the upper outlet to facilitate the discharge of particles through the upper outlet. The lower outlet may comprise a vortex breaker. The maximum extent of at least the majority of the apertures in the screen may be from 0.5 mm to 2 mm. The maximum extent of at least the majority of the apertures in the screen may be from 0.75 mm to 1.25 mm. The filtering apparatus may include a first outlet arranged to collect particles that have passed through the apertures in the screen and a second outlet arranged to collect the fibrous feedstock that has not passed through the screen. The screen may be a vibrating screen which is configured to vibrate to facilitate movement of the milled fibrous waste across the screen. The filtering apparatus may include only a single screen. Alternatively, the apparatus may comprise a first screen and a second screen, the first and second screens each comprising a plurality of apertures. The second screen may be located below the first screen. At least the majority of the apertures of the second screen may have a maximum extent (in one or both dimensions that are parallel to the plane of the screen) that is smaller than the maximum extent of substantially all of the apertures in the first screen. According to various, but not necessarily all, examples there is provided a method of removing non-fibrous material from fibrous waste, the method comprising: inserting milled fibrous waste into a chamber, the milled fibrous waste comprising fibres and non-fibrous particles; dispersing the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber; and following the dispersal, filtering the milled fibrous waste through a filtering apparatus to provide a fibrous feedstock with a reduced non-fibrous content relative to the fibrous waste, the filtering apparatus including a screen comprising a plurality of apertures, wherein the plurality of apertures are dimensioned to permit material with a size below a predetermined threshold to pass through. According to various, but not necessarily all, examples there is provided a fibrous feedstock produced using the method of any of the preceding paragraphs. According to various, but not necessarily all, examples there is provided a method of forming a composite sheet material, wherein the method comprises: forming the fibres of the fibrous feedstock produced in the method of any of the preceding paragraphs into a web; locating an arrangement comprising the web and a reinforcing material into a hydroentanglement apparatus, wherein the web defines a first layer of the arrangement and the reinforcing material defines a second layer of the arrangement; and subjecting the arrangement to successive hydroentanglement steps in the hydroentanglement apparatus to provide the composite sheet material, wherein subjecting the arrangement to successive hydroentanglement steps causes the fibres of the web to entangle with each other and causes a mechanical bond to form between the fibres of the web and the reinforcing material. According to various, but not necessarily all, examples there is provided a composite sheet material formed using the method of the preceding paragraph. According to various, but not necessarily all, examples there is provided a system for removing non-fibrous material from fibrous waste, wherein the fibrous waste comprises leather waste and / or textile waste, the system comprising: a dispersal apparatus for dispersing milled fibrous waste comprising fibres and non-fibrous particles, wherein the dispersal apparatus comprises a chamber and dispersal means, the dispersal means being configured to disperse the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber; and a filtering apparatus, wherein the filtering apparatus includes a screen comprising a plurality of apertures, the plurality of apertures being dimensioned to permit material with a size below a predetermined threshold to pass through the screen. According to various, but not necessarily all, examples there is provided a system for removing non-fibrous material from fibrous waste, wherein the fibrous waste comprises leather waste and / or textile waste, the system comprising: a dispersal apparatus for dispersing milled fibrous waste comprising fibres and non-fibrous particles, wherein the dispersal apparatus comprises a chamber and an agitator, the agitator being configured to disperse the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber; and a filtering apparatus, wherein the filtering apparatus includes a screen comprising a plurality of apertures, the plurality of apertures being dimensioned to permit material with a size below a predetermined threshold to pass through the screen. According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing at least part of one or more methods described herein. The description of a function and / or action should additionally be 5 considered to also disclose any means suitable for performing that function and / or action. Functions and / or actions described herein can be performed in any suitable way using any suitable method. According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims. While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function. BRIEF DESCRIPTION Some examples will now be described with reference to the accompanying drawings in which: FIG. 1 shows a method of removing non-fibrous material from fibrous waste; FIG. 2 shows an example dispersal apparatus; FIG. 3 shows an example filtering apparatus; FIG. 4 shows a schematic illustrating functionality of the example filtering apparatus; FIG. 5 shows a further method of removing non-fibrous material from fibrous waste; FIG. 6 shows an example system for removing non-fibrous material from fibrous waste; FIG. 7 shows a further example system for removing non-fibrous material from fibrous waste; FIG. 8 shows an example of milled fibrous waste; FIG. 9 shows an example of non-fibrous material separated from the fibrous waste; FIG. 10 shows a graph illustrating the percentage removal of non-fibrous material from fibrous waste derived from a first example of end-of-life aviation seat covers by cumulative number of passes over a screen of a filtering apparatus; FIG. 11 shows a graph illustrating the percentage removal of non-fibrous material from fibrous waste derived from a second example of end-of-life aviation seat covers by cumulative number of passes over a screen of a filtering apparatus; FIG. 12 shows a graph illustrating the percentage removal of non-fibrous material from fibrous waste derived from a first example of post-industrial composite waste by cumulative number of passes over a screen of a filtering apparatus; and FIG. 13 shows a graph illustrating the percentage removal of non-fibrous material from fibrous waste derived from a second example of post-industrial composite waste by cumulative number of passes over a screen of a filtering apparatus. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DETAILED DESCRIPTION In examples of the disclosure, a method of removing non-fibrous material from fibrous waste is provided. Furthermore, examples of the disclosure also provide a system for removing non-fibrous material from fibrous waste. In this disclosure, the fibrous waste may comprise a pliable fibrous material such as leather or textile, in the form of leather waste and / or textile waste. Leather waste may comprise end-of-life leather material. Textile waste may comprise end-of-life textile material. A pliable fibrous material may be considered to be a material that is suitable, for example, for clothing, footwear, fashion accessories, fabric cladding, fabric decorative coverings and / or upholstery. Fibrous waste includes post-agricultural fibrous waste (also known as pre-industrial fibrous waste), industrial fibrous waste, post-industrial fibrous waste, pre-consumer fibrous waste, and / or post-consumer fibrous waste. For instance, fibrous waste could include textile waste, leather waste, consumer products, footwear, fashion accessories, fabric cladding, fabric decorative coverings, upholstery materials, and / or seat covers. The fibrous waste described herein may comprise one or more than one of these waste material components. Leather waste includes for instance coated leather waste, leather footwear, leather clothing, leather upholstery, leather seat covers, leather fashion accessories, leather cladding, leather decorative coverings, and / or wet blue leather waste. The fibre structure of leather waste after disintegration consists of tightly packed bundles of collagen fibres, which in turn consist of even finer fibrils. This results in a range of fibre diameters from about 100 microns for the bundles to very fine fibres below 1 micron. Textiles are materials formed by intertwining or interlocking fibres. Textiles include woven fabrics, knitted fabrics, braided fabrics and non-woven fabrics. A non-woven fabric is defined as any fabric other than a woven fabric, a braided fabric or a knitted fabric, such as felt or a needle-punched structure. Animal hides such as leather are not considered as textiles, as they are not fabricated by intertwining or interlocking fibres. Animal hide fibres are thus not considered as textile fibres. Thus, in this specification, the term “textile” means the same as “non-leather textile”. Textile waste comprises textile fibres. Textile fibres are the primary raw materials used in textile manufacture. Textile fibres generally have a substantially uniform diameter throughout their length. In most, but not all, examples, textile fibres have a linear density of 1.5 - 3.3 dtex. Textile fibres include natural fibres, naturally derived fibres and / or synthetic fibres. Examples of natural fibres used in textile manufacture include wool, cotton, flax, bast and silk fibres. Examples of naturally derived fibres used in textile manufacture include bamboo, viscose and soybean fibres. Examples of synthetic fibres used in textile manufacture include polyester, nylon, polypropylene, polyamide, elastane, and acrylic fibres. Some, but not all, natural and naturally derived textile fibres, such as cotton, flax, bast or viscose, are cellulosic textile fibres. Cellulosic textile fibres comprise cellulose. Post-agricultural textile waste includes natural fibres, such as the natural fibres described above (e.g., wool, cotton, flax, bast or silk), which are grown and / or processed by the agricultural industry for use in the textiles industry supply chain, but are unsuitable (i.e., of insufficient quality) for processing in traditional textile manufacturing methods. The suitability of natural fibres for the textile industry is determined using a number of parameters, depending on the type of fibre. For instance, the suitability can be determined by measuring the fineness, length, shape, strength, density, lustre, colour, handle, parallelism, and / or the cleanliness of the fibres, and possibly also the number of naps or knots in the fibres. As an example, flax fibres that are discoloured and coarsened in texture by dew retting, or flax fibres that are shortened by mechanical retting, are deemed unsuitable for textile spinning processes. Such flax fibres are deemed as post-agricultural textile waste by the textile industry. Industrial textile waste is produced during textile processing, such as during the cleaning, carding, combing and / or spinning of fibres. The waste fibres produced during these processes are too short for use in traditional textile manufacturing methods, and are therefore deemed as industrial textile waste by the textile industry. Post-industrial textile waste includes material in which the textile fibres have been intertwined or interlocked, but the material is in a form that is unsuitable for use in traditional textile manufacturing methods. For example, the dimensions of the material may be too small for use in the textile industry. Post-industrial textile waste includes cuttings or trim waste from roll or sheet processing. Pre-consumer textile waste includes any textile product that has been produced, but is no longer commercially / economically viable. As an example, fabrics, garments or apparel that have passed their design season in many cases are no longer commercially viable. As a further example, fabrics, garments or apparel that have failed quality standards in areas such as appearance or material performance are no longer commercially viable. Post-consumer textile waste includes textile products that have been used and discarded. For instance, worn clothes, carpets or upholstery that have been disposed of by a user. Textile waste can thus include waste loose textile fibres, waste woven fabrics, waste knitted fabrics, waste braided fabrics, and / or waste non-woven fabrics. Textile waste in many, but not all, examples includes more than one type of textile fibre. In other words, the textile waste can be mixed or non-homogeneous. In some examples, the textile waste includes more than two types of textile fibres. Depending on the source, the textile waste can include several types of textile fibres in varying ratios. A different type of textile fibre is a fibre made from a different material. Example types of textile fibres include wool, cotton, viscose, flax, soybean, bamboo, silk, polyester, nylon, polypropylene, polyamide, elastane, acrylic, bast or modal fibres. The textile waste may include one or more, two or more, or three or more of these types of textile fibres. In some examples, the textile waste includes both i) synthetic fibres and ii) natural or naturally derived fibres. The textile waste may include 10-90 wt.% natural or naturally derived fibres and 10-90 wt.% synthetic fibres, such as 70 wt.% synthetic fibres and 30 wt.% natural or naturally derived fibres. Where the textile waste is derived from denim, the textile waste may include 50-98 wt.% cotton fibres and 2-50 wt.% synthetic fibres (e.g., polyester and / or elastane). A fibre refers to a thread-like structure, i.e., an elongated solid material which is able to intertwine with another fibre. A fibre may have a length substantially greater than its diameter. For instance, the length divided by the width (i.e., the aspect ratio) of a fibre may be significantly greater than one. The aspect ratio may be greater than 50. Non-fibrous material refers to a solid material which is not a fibre or is not made from fibres. A non-fibrous material may have a length to diameter ratio (i.e., aspect ratio) of less than 10. Fibrous waste, such as textile waste or leather waste, often includes non-fibrous material contaminants. Fibrous waste can therefore comprise fibres and non-fibrous material. The non-fibrous material is any material that is present within the fibrous waste which is not a fibre or is not made from fibres. The non-fibrous material may be a coating, a laminated layer, a foam backing and / or a treatment applied to pliable material present in the fibrous waste. The non-fibrous material is typically polymeric. Polymeric coatings, such as polyurethane coatings, polyester coatings and / or acrylic coatings may be applied to leather or textiles, and therefore may be present in leather waste or textile waste. The polymeric coatings are non-fibrous. Non-fibrous material is notable to be hydroentangled. Non-fibrous material is unsuitable for use in textile manufacturing processes (such as spinning, weaving or knitting). In summary, fibrous waste may comprise leather waste and / or textile waste. Fibrous waste comprises fibres and may also comprise a non-fibrous material. The presence of some non-fibrous material in fibrous waste diminishes the quality of materials produced using the fibrous waste. Fig. 1 illustrates a flow chart of an example method 100 of removing non-fibrous material from fibrous waste. Figs. 2 to 4 illustrate example elements of a system for performing the method of Fig. 1. In block 110 of Fig. 1, milled fibrous waste is inserted into a chamber, the milled fibrous waste comprising fibres and non-fibrous particles (i.e., particles of non-fibrous material). In some examples, the milled fibrous waste is inserted into a chamber by a conveyor (e.g., pneumatically). In some examples, the majority of the fibres of the milled fibrous waste have a length in the range of 1 mm to 10 mm. Preferably, the majority of the fibres of the milled fibrous waste have a length in the range of 3 mm to 5 mm. The non-fibrous particles of the milled fibrous waste may be substantially planar or substantially granular in shape. The chamber may be made from metal, such as steel. The steel may for example be powder coated mild steel or stainless steel. The chamber may include a ceramic coating, an antistatic coating and / or a static dissipative coating. The chamber may be equipotential bonded. An example chamber 252 is shown in Fig. 2. In block 120 of Fig. 1, the milled fibrous waste is dispersed in the chamber such that the milled fibrous waste becomes airborne in the chamber. It has been found that the dispersal causes separation of the fibres and the non-fibrous particles. The dispersal could also be referred to as aeration. The terms airborne and aeration used herein do not imply that the atmosphere in the chamber comprises air. Whilst airborne, gas flows between the fibres and the non-fibrous particles, which can loosen, disentangle and / or dissociate the fibres and non-fibrous particles, such that the degree of separation between fibres and between fibres and non-fibrous particles is increased. The milled fibrous waste may be dispersed in the chamber for at least 1 second, such as 1 - 60 seconds, 1-10 seconds, or 1 - 5 seconds. An example dispersal apparatus 250 comprising a chamber 252 is shown in Fig. 2. A dispersal means (not shown) may form part of the dispersal apparatus 250, the dispersal means being configured to disperse the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber. The dispersal means could also be referred to as an agitator. In some examples, such as the example of Fig. 2, the dispersal of the milled fibrous waste in the chamber 252 comprises inducing a gas flow in the chamber 252 to cause the milled fibrous waste to become airborne in the chamber 252. The dispersal means may induce the gas flow. The dispersal means may comprise a vacuum (i.e., a negative pressure differential), a fan, a pump and / or compressed gas. Where the dispersal means comprises a vacuum, the vacuum may be a low-pressure vacuum. In other examples, the dispersal means could for instance comprise a paddle wheel to cause the milled fibrous waste to become airborne in the chamber, and / or the dispersal means may comprise a release mechanism configured to release the milled fibrous material into the chamber from a height to cause the milled fibrous waste to become airborne in the chamber. In the example of Fig. 2 the chamber 252 is a vortex chamber 252 configured to generate a vortex 255 when a gas flow is induced in the chamber 252. The vortex could also be referred to as a cyclone. The chamber 252 comprises an inlet 254 for inserting the milled fibrous waste. The inlet 254 may be located at an upper end of the chamber. The terms upper and lower refer to the top half (by height) and lower half (by height) of the chamber 252 respectively. The example chamber 252 further comprises a lower outlet 258 for discharging heavier particles (i.e., the milled fibrous waste) from the chamber and an upper outlet 256 for discharging lighter particles (i.e., fine dust or foam) from the chamber. The milled fibrous waste discharged from the lower outlet 258 may be conveyed (e.g., pneumatically) to a filtering apparatus to carry out the step of block 130 of Fig. 1. Block 130 of Fig. 1 is described in the following paragraphs. The lighter particles (i.e., fine dust or foam) discharged from the upper outlet 256 may be conveyed (e.g., pneumatically) to a dust filter. Heavier particles have greater inertia and thus are more likely to hit the wall of the chamber, fall down the chamber 252, and exit through the lower outlet 258. Lighter fine dust or foam particles have lower inertia and thus are less likely to hit the wall of the chamber 252 and thus are more likely to exit through the upper outlet 256. The vortex chamber 252 therefore facilitates the removal of fine dust or foam particles, which are non-fibrous particles. A vacuum (i.e., a negative pressure differential) may be applied to the upper outlet to facilitate the discharge of fine dust particles or foam from the chamber. The lower outlet 258 may include a vortex breaker. The vortex chamber 252 may comprise a vortex inducing section 253 which is substantially conical in shape. In block 130 of Fig. 1, the milled fibrous waste is filtered through a filtering apparatus, to provide a fibrous feedstock with a reduced non-fibrous material content relative to the fibrous waste. In other words, the fibrous feedstock has a lower percentage by mass of non-fibrous material content relative to the fibrous waste or milled fibrous waste inputted at the start of the method 100 described herein. The filtering apparatus includes a screen comprising a plurality of apertures. The plurality of apertures are dimensioned to permit material with a size below a predetermined threshold to pass through. In other words, the apertures are dimensioned to allow pieces of material of a certain size to pass through the screen. The filtering apparatus may include a first outlet arranged to collect particles that have passed through the apertures in the screen and a second outlet arranged to collect the fibrous feedstock that has not passed through the screen. The milled fibrous waste may be passed over the screen for up to 5 minutes in total, up to 2 minutes in total, up to 1 minute in total, or up to 15 seconds in total. In some examples, the filtering step is repeated (i.e., the milled fibrous waste / fibrous feedstock may be passed over the screen) multiple times. For example, the filtering step may be repeated 2 to 10 times. The filtering step may be repeated 3 to 6 times. Preferably, the maximum extent of at least the majority of the apertures in the screen is from 0.5 mm to 2 mm (such as 1 mm) in one or both of the dimensions that are parallel to the plane of the screen. The maximum extent of at least the majority of the apertures in the screen may be at least 0.1 mm, at least 0.3 mm, at least 0.5mm or at least 1 mm in one or both of the dimensions that are parallel to the plane of the screen. The maximum extent of at least the majority of the apertures in the screen may be up to 1.5 mm, up to 2 mm, up to 3 mm, or up to 5mm in one or both of the dimensions that are parallel to the plane of the screen. In some examples, at least the majority of the apertures in the screen have a substantially circular shape. The screen may be substantially planar. The screen may have a total surface area of from 0.5 m2 to 10 m2, such as 2 m2. The screen may be made from perforated steel. In some examples, the screen is a vibrating screen which is configured to vibrate to facilitate movement of the milled fibrous waste across the screen. In other examples, the screen may be static and the movement of the milled fibrous waste across the screen may be facilitated by an airflow across the screen. In some examples a combination of an airflow and a vibrating screen could be utilized to facilitate the movement of the milled fibrous waste across the screen. The screen may be angled at a downward slope (relative to ground) to facilitate movement of the milled fibrous waste across the screen. The screen may be inclined relative to horizonal (i.e., relative to ground) at an angle of from 1° to 25°, from 2° to 15, or from 3° to 10°, such as 5°. The screen may vibrate back and forth substantially in line with the horizontal dimension of the downward slope. The vibrating screen could, for example, be suspended by torsion springs. A vibrating platform which is configured to vibrate to facilitate movement of particles across the platform may be provided beneath the vibrating screen, in order to direct the particles that have passed through the apertures in the screen toward the first outlet. The platform may be angled at a downward slope (relative to ground) to facilitate movement of the particles across the platform. The platform may be inclined relative to horizonal (i.e., relative to ground) at an angle of from 1° to 25°, from 2° to 15, or from 3° to 10°, such as 5°. The platform may vibrate back and forth substantially in line with the horizontal dimension of the downward slope. The vibrating platform could, for example, be suspended by torsion springs. In some examples, the filtering apparatus includes only a single screen. An example of a filtering apparatus with a single screen is the second example filtering apparatus 260 of Figs 6 and 7, which is described in further detail later in the description. In other examples, the filtering apparatus includes a further screen with a plurality of apertures. That is to say, in the other examples the filtering apparatus includes a first screen and a second screen, the first and second screens each comprising a plurality of apertures. An example of a filtering apparatus with first and second screens is the first example filtering apparatus 230 of Figs 3, 4, 6 and 7, which is described in further detail later in the description. The second screen may be located below the first screen, such that the fibres and non-fibrous material that pass through the first screen fall onto the second screen. The apertures of the first screen may have a maximum extent (in one or both dimensions that are parallel to the plane of the screen) that is larger, on average (mean or median), than the apertures of the second screen. At least the majority of the apertures of the second screen may have a maximum extent (in one or both dimensions that are parallel to the plane of the screen) that is smaller than the maximum extent of substantially all of the apertures in the first screen. Filtering the milled fibrous waste through a screen may comprise filtering the milled fibrous waste through the first screen and the second screen. In such examples, the screen apparatus may comprise first, second and third outlets, the first outlet being arranged to collect particles that have passed through the apertures in both the first and second screens, the second outlet being arranged to collect fibrous feedstock that has passed through the apertures in the first screen but not the apertures in the second screen, and the third outlet being arranged to collect material that has not passed through the apertures in either of (i.e., both) the firstand second screens. Both the first and second screens may be vibrating screens which are each configured to vibrate to facilitate movement of the milled fibrous waste across the screen. Both the first and second screens may be angled at a downward slope (relative to ground) as described previously. The first example filtering apparatus 230 is shown in Figs. 3 and 4. In the example of Figs. 3 and 4, the first example filtering apparatus 230 comprises an inlet 231, a flail 232, a vacuum generator 233, a first vibrating screen 234, a second vibrating screen 235, a vibrating platform / panel 236, a first outlet 239, a second outlet 238 and a third outlet 237. The first example filtering apparatus 230 includes a housing made from steel. The first example filtering apparatus 230 also comprises at least one motor that is arranged to cause the first and second screens 234, 235 and the vibrating platform 236 to vibrate. In use, the milled fibrous waste is fed into the first example filtering apparatus 230 via the inlet 231. Optionally, the pieces of milled fibrous waste are broken up by the flail 232, which is located in the inlet 231. The vacuum generator 233 generates at least a partial vacuum, which causes airborne dust to be removed from the pieces of milled fibrous waste that have entered the inlet 231. Each of the first and second screens 234, 235 and the vibrating platform 236 are angled (downwardly, relative to ground) to (gravitationally) guide material towards the first, second and third material outlets 239, 238, 237, respectively. The pieces of milled fibrous waste may land initially on the first vibrating screen 234. Each of the first and second vibrating screens 234, 235 may include a plurality of apertures (e.g., perforations) which are dimensioned to allow pieces of material of a certain size to pass through the screen 234, 235. The size of each of the apertures in the screens 234, 235 may depend on the fibre size that is desired after filtering. The size of each of the apertures in the second vibrating screen 235 has a maximum extent (in one or both dimensions that are parallel to the plane of the screen 235) that is smaller than the maximum extent of each of the apertures in the first vibrating screen 234. The maximum extent of each of the apertures in the second vibrating screen 235 might, for example, be 1.5 mm in one or both of the dimensions that are parallel to the plane of the screen 235. In use, the motor of the first example filtering apparatus 230 causes the first and second screens 234, 235 and the vibrating platform 236 to vibrate. This, coupled with the angled nature of the screens and platform 234, 235, 236, causes material to be conveyed along the screens and platform 234, 235, 236. Oversized pieces of material do not pass through the apertures in the first vibrating screen 234 and are conveyed into the third outlet 237. Appropriately sized pieces of material (i.e., a fibrous feedstock) pass through the apertures in the first vibrating screen 234 (e.g., while the screen 234 is vibrating) and do not pass through apertures in the second vibrating screen 235. These appropriately sized pieces of material (i.e., the fibrous feedstock) are conveyed into the second outlet 238. Undersized pieces of material and dust pass through the apertures in both the first vibrating screen 234 and the second vibrating screen 235, but do not pass through the vibrating platform 236 (which does not have any apertures for the pieces / dust to pass through). Due to the elongate nature of fibres, the fibres are less likely to pass through apertures in the second vibrating screen 235 when compared to the non-fibrous particles. The undersized pieces of material and dust that passes through the second vibrating screen 235 therefore includes a significant amount of non-fibrous particles. The undersized pieces of material and dust are conveyed into the first outlet 239 by the vibrating platform 236. Fig. 4 illustrates a schematic that includes arrows which show the movement of material along the first and second screens 234, 235 and the vibrating platform 236 of the first example filtering apparatus 230 into the first, second and third outlets 239, 238, 237. In effect, by conveying oversized pieces of material into the third outlet 237, the first example filtering apparatus 230 removes oversized pieces. By conveying undersized pieces of material and dust into the first outlet 239, the vibrating screen removes non-fibrous material from the milled fibrous waste to provide a fibrous feedstock. The undersized pieces of material and dust may be rejected (i.e., not be used to form new sheet materials). The undersized pieces of material and dust may be conveyed (e.g., pneumatically) through to a dust filter 270. Each of the first and second vibrating screens 234, 235 might be user-replaceable, such that one or both of the screens 234, 235 could be replaced with screen(s) having different characteristics, such as a different aperture size. This will change the manner in which the pieces of material are sorted into the first, second and third outlets 239, 238, 237. This enables the first example filtering apparatus 230 to provide a product with a selectable fibre output size. The first example filtering apparatus 230 of Figs. 3 &4 need not have first and second screens 234, 235. It may instead have only one screen comprising a plurality of apertures, wherein the plurality of apertures are dimensioned to permit material with a size below a predetermined threshold to pass through. The single screen may be the same as the second vibrating screen 235 of the first example filtering apparatus 230. The second example filtering apparatus 260 shown in Figs. 6 and 7 is an example of a filtering apparatus 260 with a single screen. The second example filtering apparatus 260 is similar to the first example filtering apparatus 230, with the following exceptions. The second example filtering apparatus 260 does not include the first vibrating screen 234 and does not include the third outlet 237 of the first example filtering apparatus 230. In some examples, the size of each of the apertures in the single screen of the second example filtering apparatus 260 (which is the same as the second screen 235 of the first example filtering apparatus 230, but with a different aperture size), might, for example, be 1 mm in at least one dimension measured parallel to the plane of the screen. The undersized pieces of non-fibrous material and dust that passes through the single screen of the second example filtering apparatus 260 of Figs. 6 and 7 may be conveyed (e.g., pneumatically) from the filtering apparatus 260 to a dust filter. Following filtering, at least 10 wt.% of the non-fibrous material may be removed from the fibrous waste or milled fibrous waste inputted at the start of the method 100 described herein. At least 20 wt.%, at least 30 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, at least 90 wt.% or 100 wt.% of the non-fibrous material may be removed from the fibrous waste or milled fibrous waste inputted at the start of the method 100 described herein. The dispersal apparatus and the filtering apparatus (such as the example dispersal apparatus 250, and the first example filtering apparatus 230 or second example filtering apparatus 260) may form a system for removing non-fibrous material from fibrous waste. The milled fibrous waste may be conveyed (e.g., pneumatically) between the dispersal apparatus and the filtering apparatus. In some, but not necessarily all examples, the method 100 further comprises, prior to inserting the milled fibrous waste into the chamber, milling fibrous waste to provide the milled fibrous waste. The fibrous waste may be milled by a mill to disassemble the fibrous waste into individual fibres. The mill, such as the example mill 240 of Figs. 6 &7, may form part of the system for removing non-fibrous material from fibrous waste. The mill 240 may be an industrial mill, such as a hammer mill or a disk mill. The mill 240 may comprise a chamber that houses a plurality (e.g., two) toothed mill discs. The gap between the mill discs may be from 0.05 mm to 3 mm, and at least one of the discs may be rotated at between 300 rpm and 3000 rpm. One of the discs may rotate (e.g., at a fixed speed) while an adjacent disc remains stationary. The pieces of fibrous waste may be pneumatically conveyed between the discs (e.g., through suction). The milling process applies a shear and tear action to open the pieces of fibrous waste and dissemble them into individual fibres. In other examples, the milled fibrous waste may be provided pre-milled (i.e., the milling is carried out separately or in another location). The milling of the fibrous waste may be carried out at a temperature of up to 60 °C. In some examples, the mill is cooled to below room temperature (25 °C), or below 0 °C, to prevent softening of the fibres and / or the non-fibrous material. The mill may be cooled to -5 °C in some examples. It has been unexpectedly found that milling causes mechanical separation of the fibres and the non-fibrous material in the fibrous waste. Some non-fibrous material is denser than the fibres and therefore settles to the bottom of the mill once separated from the fibres during the milling process. The milled fibrous waste can therefore be removed whilst leaving non-fibrous material within the mill. The amount of non-fibrous material within the milled fibrous waste is therefore lower than the amount of non-fibrous material in the fibrous waste prior to milling. Figs. 5 and 6 illustrate an example method 300 and system 200 for converting fibrous waste to fibrous feedstock by removing non-fibrous material from the fibrous waste. The method 300 of Fig. 5 includes the method 100 of Fig. 1, along with a number of additional optional steps. Only one, only some, or all, of these additional optional steps may be incorporated into the method 100 of Fig. 1. Fig. 6 illustrates a schematic of a system 200 for performing aspects of the method 300 of Fig. 5. The system 200 receives, as its input, fibrous waste 20 comprising non-fibrous material. The incoming fibrous waste 20 may be substantially dry (for example, having a moisture content of 0 - 16 wt. %). The system 200 may comprise a shredder 210, a granulator 220, the first example filtering apparatus 230, a mill 240, a dispersal apparatus 250, the second example filtering apparatus 260, a dust filter 270 and a fibre storage receptacle / silo 280. The elements 210, 220, 230, 240, 250, 260, 270 and 280 may be pneumatically connected in that pressurized air and / or generated (partial) vacuums may be used to convey fibrous waste from one element to another element 210, 220, 230, 240, 250, 260, 270 and 280. Any number of intervening elements can exist between the elements 210, 220, 230, 240, 250, 260, 270 and 280, including no intervening elements. The system 200 need not comprise all of the illustrated elements 210,220,230, 240, 250, 260, 270 and 280 and might, in some embodiments, only comprise some of the illustrated elements 210, 220, 230, 240, 250, 260, 270 and 280. In some examples, the method 300 of Fig. 5 comprises shredding the fibrous waste 20 in a shredder, such as the example shredder 210 of Fig. 6, to provide shreds of fibrous waste. The shredding is demonstrated by block 310 of Fig. 5. The shredder 210 may be an industrial shredder, such as a double shaft shredder. The fibrous waste may be manually sorted prior to its insertion into the shredder 210, in order to remove foreign objects. In the example of Figs. 5 and 6, the fibrous waste is substantially dry (for example, having a moisture content of 0 -16 wt. %). The fibrous waste may comprise textile waste for example. The fibrous waste is shredded by the shredder 210 without dissembling the fibrous waste 20 into individual fibres. By way of example, each shred of fibrous waste that is output by the shredder 210 might be 200 mm x 30 mm. In some examples, following shredding, the shreds of fibrous waste are cut within a granulator, such as the example granulator 220 of Fig. 6, to provide pieces of reduced size (relative to the shreds of fibrous waste), which are suitable for milling. The granulating is demonstrated by block 320 of Fig. 5. The granulator 220 might comprise counter-rotating, toothed wheels that granulate the input shreds of material to provide the pieces of reduced size. The granulator 220 may have adjustable settings to change the size of the pieces of material that are output by the granulator 220, as indicated in Fig. 6. By way of example, the granulator 220 may be set to output pieces of material that have a particular maximum extent in any / every dimension. That is, in general, output pieces of material are not larger than the particular maximum extent in any dimension. For example, the maximum extent might be less than 10 mm in every dimension, such as 6 mm. The cutting of the shreds of fibrous waste within the granulator 220 may reduce the size of the fibres within the pieces of fibrous waste, such that the majority of the fibres have a length of less than 10 mm. In some examples, the cutting reduces the length of the majority of the fibres to 1 - 10 mm. Preferably, the cutting reduces the length of the majority of the fibres to 3 - 5 mm. The granulator 220 may include one or more cutting blades. The shreds of fibrous waste may be fed into the granulator 220 using a conveyor. In some examples, the method 300 of Fig. 5 further comprises filtering the fibrous waste prior to milling the fibrous waste. The filtering is demonstrated by block 330 of Fig. 5. The filtering 330 may be the same as the filtering 130 described in relation to Figs 1, 3, and 4, and the first example filtering apparatus 230 may be used, but the filtering 330 of the method 300 of Fig. 5 is carried out prior to the milling of the fibrous waste. Each of the apertures in the first vibrating screen 234 of the first example filtering apparatus 230 might have a maximum extent (in one or both dimensions that are parallel to the plane of the screen 234) that corresponds to setting of the granulator 220. For example, if the granulator 220 is set to output pieces of fibrous waste that have a maximum extent of 6 mm, each of the apertures in the first vibrating screen 234 may have a maximum extent (in one or both dimensions that are parallel to the plane of the screen) of 6 mm. Oversized pieces of material that enter the third outlet 237 may be conveyed (e.g., pneumatically) back to the granulator 220 for further cutting (i.e., recycled). The appropriately sized pieces of material may be conveyed (e.g., pneumatically) to the mill 240. The mill could also be referred to as a milling apparatus. In the examples of Figs. 5 and 6, the moisture content of the fibrous waste may be low (0 - 16 wt. %), so it is not necessary to dry the pieces of fibrous waste prior to milling. In some examples, the method 300 of Fig. 5 comprises milling the fibrous waste to provide the milled fibrous waste. The milling is demonstrated by block 340 of Fig. 6. The fibrous waste may be milled by a mill, such as the example mill 240 of Fig. 6, to disassemble the fibrous waste into individual fibres. The mill 240 may be an industrial mill, such as a hammer mill or a disk mill. The mill 240 may comprise a chamber that houses a plurality (e.g., two) toothed mill discs. The gap between the mill discs may be from 0.05 mm to 3 mm, and at least one of the discs may be rotated at between 300 rpm and 3000 rpm. One of the discs may rotate (e.g., at a fixed speed) while an adjacent disc remains stationary. The pieces of fibrous waste may be pneumatically conveyed between the discs (e.g., through suction). The milling process applies a shear and tear action to open the pieces of fibrous waste and dissemble them into individual fibres. It has been unexpectedly found that milling causes mechanical separation of the fibres and the non-fibrous material in the fibrous waste. Some non-fibrous material is denser than the fibres and therefore settles to the bottom of the mill once separated from the fibres during the milling process. The milled fibrous waste can therefore be removed whilst leaving non-fibrous material within the mill. The amount of non-fibrous material within the milled fibrous waste is therefore lower than the amount of non-fibrous material in the fibrous waste prior to milling. In some examples, the method 300 of Fig. 5 comprises inserting the milled fibrous waste into a chamber, such as the example chamber 252 of the dispersal apparatus 250 shown in Fig. 6 and Fig. 2, in the same way as described in relation to block 110 of Fig. 1. The insertion is demonstrated by block 350 of Fig. 5. In some examples, the method 300 of Fig. 5 comprises dispersing the milled fibrous waste in the chamber, such as the example chamber 252 of the dispersal apparatus 250 shown in Fig. 6 and Fig. 2, in the same way as described in relation to block 120 of Fig. 1. The dispersal is demonstrated by block 360 of Fig. 5. In some examples, the method 300 of Fig. 5 comprises filtering the milled fibrous waste through a filtering apparatus, such as the second example filtering apparatus 260 shown in Figs. 6 &7, in the same way as described in relation to block 130 of Fig. 1. The dispersal is demonstrated by block 370 of Fig. 5. In this example, the second example filtering apparatus 260 has only one screen comprising a plurality of apertures, wherein the plurality of apertures are dimensioned to permit material with a size below a predetermined threshold to pass through. The second example filtering apparatus 260 shown in Figs. 6 and 7 is an example of a filtering apparatus with a single screen. The second example filtering apparatus 260 shown in Figs. 6 and 7 may be similar to the first example filtering apparatus 230 of Figs. 3 and 4, but the second example filtering apparatus 260 does not include the first vibrating screen 234 and does not include the third outlet 237 of the first example filtering apparatus 230 shown in Figs. 3 and 4. In some examples, the size of each of the apertures in the single screen of the second example filtering apparatus 260 (which is the same as the second screen 235 of the first example filtering apparatus 230, but with a different aperture size), might, for example, be 1 mm in at least one dimension measured parallel to the plane of the screen. The undersized pieces of non-fibrous material and dust that passes through the single screen of the second example filtering apparatus 260 of Figs. 6 and 7 may be conveyed (e.g., pneumatically) from the filtering apparatus 260 to a dust filter. As described in relation to block 130 of Fig. 1, the filtering provides a fibrous feedstock, which can optionally be conveyed (e.g., pneumatically) to fibre storage 280 as shown in Fig. 6. Due to the elongate nature of fibres, the fibres are less likely to pass through apertures in the screen of the filtering apparatus 260. The undersized pieces of material and dust that passes through the screen therefore includes a significant amount of non-fibrous particles, which are removed from the fibrous feedstock which has not passed through the screen. Fig. 7 illustrates a further system 300 for removing non-fibrous material from fibrous waste. The system 300 of Fig. 7 is similar to the system 200 of Fig. 6, however the system 300 of Fig. 7 is further adapted for the processing of wet fibrous waste. Wet fibrous waste could include leather waste such as wet blue leather. The system 300 includes the shredder 210, the granulator 220, the first example filtering apparatus 230, the mill 240, the second example filtering apparatus 260, the dust filter 270 and the fibre storage receptacles / silos 280. Each of these elements 210, 220, 230, 240,260, 270, 280 operates as explained above in relation to the processing of fibrous waste unless stated otherwise here. The method for processing the wet fibrous waste is the same as that described above, unless stated otherwise here. It can be seen in Fig. 7 that the system 300 illustrated in Fig. 7 further comprises a dryer 310 and a deduster 320. As explained above in relation to Fig. 6, the elements 210, 220, 230, 240, 250, 260, 270, 280, 310 and 320 may be pneumatically connected. Any number of intervening elements can exist between the elements 210, 220, 230, 240, 250, 260, 270. 280, 310 and 320, including no intervening elements. The system 300 need not comprise all of the illustrated elements 210, 220, 230, 240, 250, 260, 270, 280, 310 and 320 and might, in some embodiments, only comprise some of the illustrated elements 210, 220, 230, 240, 250, 260, 270, 280, 310 and 320. The fibrous waste 30 that is initially provided for processing by the system 300 of Fig. 7 may be wet. It may, for example, have a moisture content of 50 - 60 wt. %. In some examples, the fibrous waste 30 that is processed by the system 300, such as leather waste, may comprise shreddings 31 and shavings 32. If so, the shreddings 31 are input into the shredder 210 in the same manner as described in relation to Figs. 5 &6 above. The shavings 32 might be relatively small in size. In view of this, it might not be necessary to put those into the shredder 210. Instead, the shavings 32 might be put directly into the granulator 220 with the shreds of fibrous waste 30 that are output by the shredder 210. After possible shredding in the shredder 210, in some examples, the shreds of fibrous waste are cut within the granulator 220 in the same manner as described above in relation to Figs. 5 &6. It was explained above in relation to the system 200 of Fig. 6 that the moisture content of the pieces of fibrous waste output by the granulator 220 might be between 0 and 16 wt. %. However, the fibrous waste that is inserted into the granulator 220 of the system 300 of Fig. 7 might be wet and consequently the pieces of fibrous waste that are output by the granulator 220 might be wet. For example, if the moisture content of the fibrous waste prior to processing by the system is initially 50 - 60 wt. %, the moisture content of the pieces of fibrous waste output by the granulator 220 might also be 50 - 60 wt. %. That is, the moisture content of the fibrous waste output by the granulator 220 might be substantially the same as when the fibrous waste is fed into the shredder 210 and the granulator 220. The method for processing wet fibrous waste using the system 300 of Fig. 7 may therefore differ from the method for processing dry fibrous waste in that, after granulation, the pieces of wet fibrous waste may be dried using one or more dryers 310. The dryer(s) 310 may dry the fibrous waste. In some examples, if the pieces of fibrous waste output by the granulator 220 have a moisture content of 50 - 60 wt. %, they are dried by the one or more dryers 310 such that they have a moisture content of around 25 - 30 wt. % moisture. After possible processing by the shredder 210, the granulator 220 and / or the dryer 310, the pieces of fibrous waste are conveyed to and input into the filtering apparatus 230. The filtering apparatus 230 operates as described above in relation to Figs. 5 and 6. In some examples where the fibrous waste comprises leather waste, following granulation and filtering, the pieces of leather waste are milled by the mill 240 in the same manner as that described above in relation to Figs. 5 &6. The process for leather waste is different from textile waste in that the dust content is typically higher after milling (15-20 wt. % for leather waste, versus less than 2 wt. % for textile waste). It is also different in that milling by the mill 240 typically produces bundles of fibres when milling leather waste, rather than individual / discrete fibres when processing textile waste. The mill settings used when processing leather waste might be different to those used to process textile waste, as leather waste is denser than textile waste. The process for processing leather waste after milling is the same as described above in relation to in relation to Figs. 5 &6, other than there is an additional dedusting / scarification step by a deduster 320, due to the typically higher dust content of bundles of leather fibres versus individual textile fibres. Dedusting / scarification would typically be carried out after the bundles of leather fibres have been passed through the second example filtering apparatus 260 and prior to storage of the fibrous feedstock in the form of bundles of leather fibres in receptacles / silos 280. Fibrous waste examples As described previously, in the methods 100, 300 of Figs. 1 and 5, non-fibrous material is removed from the fibrous waste during milling and during filtering. It has been unexpectedly found that milling causes mechanical separation of the fibres and the non-fibrous material in the fibrous waste. Some non-fibrous material is denser than the fibres and therefore settles to the bottom of the mill once separated from the fibres during the milling process. The milled fibrous waste can therefore be removed whilst leaving non-fibrous material within the mill. The amount of non-fibrous material within the milled fibrous waste is therefore lower than the amount of non-fibrous material in the fibrous waste prior to milling. Fig. 8 is a microscope image of milled fibrous waste. In the example of Fig. 8, the fibres of the milled fibrous waste are leather fibres. A first example leather fibre from the sample of Fig. 8 has a length of 4600 pm and a width of 29 pm, and thus has an aspect ratio (i.e., length divided by width) of 159. A second example leather fibre from the sample of Fig. 8 has a length of 5470 pm and a width of 74 pm, and thus has an aspect ratio of 74. Fig. 9 is a microscope image of non-fibrous material separated from fibrous waste. The example non-fibrous material of Fig. 9 is non-fibrous material separated during milling, and is collected from the mill following milling. Similar non-fibrous material may be collected following milling, dispersal and filtering using the mill 240, the dispersal apparatus 250 and the second example filtering apparatus 260 of Figs. 6 &7. The non-fibrous material following milling, dispersal and filtering can be collected from the first outlet of the second example filtering apparatus 260. In the example of Fig. 9, the non-fibrous material is primarily particles of polymeric coating material. The polymeric coating material may be polyurethane coating material. A first example particle of non-fibrous material from the sample of Fig. 9 has a length of 506 pm and a width of 401 pm, and thus has an aspect ratio of 1.26. A second example particle of non-fibrous material from the sample of Fig. 9 has a length of 291 pm and a width of 193 pm, and thus has an aspect ratio of 1.51. A third example particle of non-fibrous material from the sample of Fig. 9 has a length of 320 pm and a width of 282 pm, and thus has an aspect ratio of 1.13. A fourth example particle of non-fibrous material from the sample of Fig. 9 has a length of 224 pm and a width of 78 pm, and thus has an aspect ratio of 2.87. A fifth example particle of non-fibrous material from the sample of Fig. 9 has a length of 533 pm and a width of 477 pm, and thus has an aspect ratio of 1.12. Tables 1 to 3 below illustrate the mass lost during the milling of various types of fibrous waste. Much of the mass lost during milling corresponds to loss of non-fibrous material as described in the paragraphs above. Table 1 illustrates the mass lost during the milling of fibrous waste in the form of split leather trim waste derived from footwear. Table 2 illustrates the mass lost during the milling of fibrous waste in the form of end-of-life aviation seat covers. The end-of-life aviation seat covers of Table 2 are made up of a composite sheet material first layer, a 190 gsm foam backing second layer and a 50 gsm fabric backing third layer. The composite sheet material first layer comprises a 60gsm -100 gsm woven polyester reinforcing material, a 100 - 500 gsm leather body of fibres on one side of the reinforcing material and a 100 - 500 gsm leather further body of fibres on the other side of the reinforcing material. Gsm is the grammage or area density of the material, measured in grams per square metre of material. Table 3 illustrates the mass lost during the milling of fibrous waste in the form of postindustrial composite waste. The post-industrial composite waste of Table 3 is a composite sheet material produced using the method of forming a composite sheet material described herein. The composite sheet material of Table 3 includes a 60 gsm -100 gsm woven polyester reinforcing material, a 100 gsm - 500 gsm leather body of fibres on one side of the reinforcing material and a 100 gsm - 500 gsm leather further body of fibres on the other side of the reinforcing material. The composite sheet material of Table 3 further comprises a 30 gsm -150 gsm polyurethane coating on the further body of fibres. Table 1 Material -Footwear split leather trim waste Mass in (g) Mass Out (g) Mass loss(g) Percentage mass loss Test 1 118 99 19 16.10 Test 2 167 147 20 11.98 Test 3 417 369 48 11.51 Test 4 298 266 32 10.74 Average 12.58 Table 2 Material - End of life aviation seat covers Mass in (g) Mass Out (g) Mass loss (g) Percentage mass loss Test 1 200 169 31 15.50 Test 2 384 343 41 10.68 Test 3 417 382 35 8.39 Average 11.52 Table 3 Material - Postindustrial composite waste Mass in (g) Mass Out (g) Mass loss(g) Percentage mass loss Test 1 292 246 46 15.75 Test 2 540 494 46 8.52 Test 3 385 356 29 7.53 Average 10.60 10 The dispersal and filtering of the milled fibrous waste described herein, such as in blocks 120, 130 of the method 100 of Fig. 1 and blocks 360 and 370 of the method of Fig. 5, further removes non-fibrous material from the milled fibrous waste to provide a fibrous feedstock. The dispersal of milled fibrous waste causes the milled fibrous waste 15 to become airborne. It has been found that the dispersal causes separation of the fibres and the non-fibrous particles. Whilst airborne, gas flows between the fibres and the non-fibrous particles, which can loosen, disentangle and / or dissociate the fibres and non-fibrous particles, such that the degree of separation between fibres and non-fibrous particles is increased. Furthermore, some non-fibrous fine dust particles can be removed by a vacuum (i.e., a negative pressure differential) during dispersal. The greater degree of separation between fibres and non-fibrous particles following dispersal facilitates separation of non-fibrous particles whilst filtering. Due to the elongate nature of fibres, the fibres are less likely to pass through apertures in the screen when filtering. The filtering therefore enables non-fibrous particles to be separated. Table 4 below illustrates the effect of the number of passes through the screen of the filtering apparatus, following dispersal. In the examples of Tables 4 to 7 below the milled fibrous waste is dispersed using the dispersal apparatus 250 of Fig. 2 and the filtering apparatus used is the second example filtering apparatus 260 of Figs. 6 and 7. Before each pass through the screen a sample of the material is separated on a laboratory sieve stack (sieve sizes 4 mm, 1 mm, 500 pm) and the mass / percentage of non-fibrous material and fibres was determined. Optical microscopy was used to confirm the identity of the collected material. The milled fibrous waste of Table 4 is derived from end-of-life aviation seat covers. The end-of-life aviation seat covers are made up of a composite sheet material first layer, a 190 gsm foam backing second layer and a 50 gsm fabric backing third layer. The composite sheet material first layer comprises a 60 gsm -100 gsm woven polyester reinforcing material, a 100 gsm - 500 gsm leather body of fibres on one side of the reinforcing material and a 100 gsm - 500 gsm leather further body of fibres on the other side of the reinforcing material. Table 4 Number of passes of milled fibrous waste through screen Initial mass of milled fibrous waste sample (g) Mass of fibre (g) Mass of non-fibrous material (g) Mass lost during measurement (g) Amount of fibre in milled fibrous waste sample (%) Amount of non-fibrous material in milled fibrous waste sample (%) Amount of milled fibrous waste sample lost during measurement (%) 0 10.0033 9.3167 0.6381 0.0486 93.14% 6.38% 0.49% 1 9.9967 9.4533 0.4831 0.0602 94.56% 4.83% 0.60% 2 9.9967 9.5333 0.3628 0.1006 95.37% 3.63% 1.01% 3 9.9933 9.5800 0.3275 0.0859 95.86% 3.28% 0.86% 4 10.0000 9.6533 0.2753 0.0714 96.53% 2.75% 0.71% As shown in Table 4, the filtering causes removal of the non-fibrous material. This is also demonstrated in Fig. 10 which is a plot of the results of Table 4, illustrating the percentage by mass of non-fibrous material removed after more passes over the screen of the filtering apparatus. It has been found that increasing the number of passes over the screen causes further removal of the non-fibrous material contaminants. Table 5 below illustrates the results of a repeat of the tests of Table 4. Fig. 11 is a plot of the results of Table 5, illustrating the percentage by mass of non-fibrous material removed after increasing numbers of passes over the screen of the filtering apparatus. Table 5 Number of passes of milled fibrous waste through screen Initial mass of milled fibrous waste sample (g) Mass of fibre (g) Mass of non-fibrous material (g) Mass lost during measurement (g) Amount of fibre in milled fibrous waste sample (%) Amount of non-fibrous material in milled fibrous waste sample (%) Amount of milled fibrous waste sample lost during measurement (%) 0 10.0067 8.3633 1.5462 0.0972 83.58% 15.45% 0.97% 1 9.9933 9.3400 0.6125 0.0408 93.46% 6.13% 0.41% 2 9.9933 9.4433 0.4847 0.0653 94.50% 4.85% 0.65% 3 10.0067 9.5267 0.4216 0.0584 95.20% 4.21% 0.58% 4 9.9900 9.6400 0.2995 0.0505 96.50% 3.00% 0.51% Table 6 below is similar to Tables 4 and 5, but shows the results of filtering a milled fibrous waste derived from post-industrial composite waste. The post-industrial composite waste is a composite sheet material produced using the method of forming a composite sheet material described herein. This composite sheet material from which the milled fibrous waste of Table 6 is derived includes a 60 gsm -100 gsm woven polyester reinforcing material, a 100 gsm - 500 gsm leather body of fibres on one side of the reinforcing material and a 100 gsm - 500 gsm leather further body of fibres on the other side of the reinforcing material. The composite sheet material from which the milled fibrous waste of Table 6 is derived further comprises a 30 gsm -150 gsm polyurethane coating on the further body of fibres. Fig. 12 is a plot of the results of Table 6, illustrating the percentage by mass of non-fibrous material removed after increasing numbers of passes over the screen of the filtering apparatus. Table 6 Number of passes of milled fibrous waste through screen Initial mass of milled fibrous waste sample (g) Mass of fibre (g) Mass of non-fibrous material (g) Mass lost during measurement (g) Amount of fibre in milled fibrous waste sample (%) Amount of non-fibrous material in milled fibrous waste sample (%) Amount of milled fibrous waste sample lost during measurement (%) 0 9.9933 9.5500 0.3698 0.0735 95.56% 3.70% 0.74% 1 10.0100 9.6833 0.2509 0.0757 96.74% 2.51% 0.76% 2 9.9933 9.5967 0.3151 0.0815 96.03% 3.15% 0.82% 3 10.0000 9.7433 0.2147 0.0420 97.43% 2.15% 0.42% 4 10.0067 9.7533 0.1774 0.0760 97.47% 1.77% 0.76% Table 7 below is similar to Table 6, but shows the results of filtering a milled fibrous waste derived from post-industrial composite waste, which is different from the postindustrial composite waste of Table 6. The post-industrial composite waste is a composite sheet material produced using the method of forming a composite sheet material described herein. This composite sheet material from which the milled fibrous waste of Table 7 is derived includes a 60 gsm -100 gsm woven fabric reinforcing material made from fire retardant synthetic fibres, a 100 gsm - 500 gsm leather body of fibres on one side of the reinforcing material and a 100 gsm - 500 gsm leather further body of fibres on the other side of the reinforcing material. The composite sheet material from which the milled fibrous waste of Table 7 is derived further comprises a first 30 gsm -150 gsm flame retardant polyurethane coating on the further body of fibres, along with a second 30 gsm -150 gsm polyurethane coating on the first flame retardant polyurethane coating. Fig. 13 is a plot of the results of Table 7, illustrating the percentage by mass of non-fibrous material removed after increasing numbers of passes over the screen of the filtering apparatus. Table 7 Number of passes of milled fibrous waste through screen Initial mass of milled fibrous waste sample (g) Mass of fibre (g) Mass of non-fibrous material (g) Mass lost during measurement (g) Amount of fibre in milled fibrous waste sample (%) Amount of non-fibrous material in milled fibrous waste sample (%) Amount of milled fibrous waste sample lost during measurement (%) 0 10.0133 8.9933 0.9151 0.1049 89.81% 9.14% 1.05% 1 10.0067 9.2567 0.6778 0.0722 92.50% 6.77% 0.72% 2 10.0000 9.4467 0.5093 0.0440 94.47% 5.09% 0.44% 3 10.0033 9.5000 0.4505 0.0529 94.97% 4.50% 0.53% 4 10.0000 9.5967 0.3373 0.0660 95.97% 3.37% 0.66% Composite sheet material formation A method of forming a composite sheet material from the fibrous feedstock produced using the methods 100, 300 of Figs. 1 or 5 is described below. The fibres of the fibrous feedstock produced using any of the methods described herein may be formed into a web. The web could also be considered as a body of fibres. The web may be in the form of a sheet. The web may be a non-woven web and the web can be formed by airlaying. In some examples, the web is needle punched once formed. Prior to (i.e., upstream of) forming the fibres into the web, the fibres for forming the web may be opened from a bale and / or a silo using a fibre opener. In some examples, the method further comprises blending the fibrous feedstock with additive fibres prior to (i.e., upstream of) forming the web. The inclusion of some additive fibres has been found to improve web stability during processing. In particular, these fibres can improve the stability of the web when forming the web into a roll, and therefore act as a process additive. In some examples, the additive fibres comprise bicomponent fibres, such as polylactic acid / polylactic acid bicomponent fibres, where each polylactic acid element has a different melting point, or polyethylene / polypropylene bicomponent fibres. The web may comprise 1 - 10 wt.% of the additive fibres. Preferably, the web comprises 2-5 wt.% of the additive fibres. The web may comprise predominantly (i.e., more than 50 wt.%) the fibres from the fibrous feedstock. Preferably, the web comprises at least 90 wt.% of the fibres from the fibrous feedstock. Most preferably, the web comprises at least 95 wt.% of the fibres from the fibrous feedstock. Where the fibres from the fibrous feedstock are formed into a web using airlaying, the blending of the fibres from the fibrous feedstock with the additive fibres may be carried out by agitators in airlay forming heads. In examples where the fibres of the fibrous feedstock are formed into a web using airlaying, the fibres may be airlaid onto a support material. The support material is preferably a tissue material. The tissue material may have a weight per unit area (i.e., grammage) of 10 to 25 gsm, such as 18 gsm. In some examples, the web has a weight per unit area of 50 gsm - 500 gsm. Preferably, the web has a weight per unit area of 100 - 300 gsm. Most preferably, the web has a weight per unit area of 140 - 240 gsm. In examples where the web comprises comprise synthetic bicomponent fibres, the formed web may be inserted into and heated in an oven to cause partial melting of the bicomponent fibres. In some examples, the formed web is heated to 140 °C - 170 °C in the oven. The formed web may be heated in the oven for 20 - 110 seconds. The heating of the web including synthetic bicomponent fibres has been found to stabilise the web. The stabilisation of the web enables the web to be processed more readily. Otherwise, the web is more likely to fall apart during processing, for example during winding of the web into a roll, during the formation of the web in an airlaying process, and / or during unwinding of the web roll prior to hydroentanglement. Following the formation of the web, the web may be formed into a roll. The method further comprises locating an arrangement comprising the web and a reinforcing material into a hydroentanglement apparatus. The arrangement may be in the form of a sheet, and can be formed on a support by laying a sheet of the web onto a sheet of the reinforcing material. The web defines a first layer of the arrangement, and the reinforcing material defines a second layer of the arrangement. The reinforcing material is in the form of a sheet. The reinforcing material could also be considered as a reinforcing structure. The reinforcing material may comprise a structure defined by a fabric. The fabric could be a woven fabric, a knitted fabric, a braided fabric, or a non-woven fabric. Alternatively, the reinforcing material may comprise a structure defined by a combination of a woven fabric, a knitted fabric, a braided fabric, and / or a non-woven fabric. The fabric of the reinforcing material is preferably a durable fabric. A durable fabric is suitable for multiple cycles of use and washing, as opposed to disposable fabric, which is not suitable for repeated use and / or washing cycles. A durable fabric is suitable for use in clothing, footwear, accessories and / or upholstery. A durable fabric may be tear resistant (for instance greater than 10 N tear strength as measured by BS EN ISO 3377-2 2016 using a double-edged tear) and may have high tensile strength (for instance a tensile strength of greater than 7 N / mm as measured by tensile strength test BS EN ISO 3376-2002). The fabric of the reinforcing material could be a recycled fabric. In some examples, the reinforcing material has a different weight per unit area to the web, and preferably has a lower weight per unit area than the web. In other examples, the reinforcing material has the same weight per unit area as the web. The reinforcing material may have a weight per unit area of 50 gsm - 200 gsm. Preferably, the reinforcing material has a weight per unit area of 60 gsm -100 gsm. The reinforcing material may comprise virgin fibres and / or recycled fibres. The reinforcing material may comprise natural, naturally derived, and / or synthetic fibres. In some examples, the reinforcing material comprises splittable fibres. The splittable fibres of the reinforcing material may comprise at least two different fibres arranged in distinct segments across the cross-section of the splittable fibre. For example, the at least two different fibres may comprise polyester fibres and polyamide fibres, which may be microfibres. In some examples, the arrangement includes a further web on the opposite side of the reinforcing material to the web. In such examples, the web defines a first layer of the arrangement, the reinforcing material defines a second layer of the arrangement, and the further web defines a third layer of the arrangement. The second layer is between the first and third layers in this example (i.e., the further web is on the opposite side of the reinforcing material to the web). The further web may be the same as the web described above. Alternatively, the further web may have different weight per unit area to the web, a different structure to the web, and / or have a different composition to the web. The method further comprises subjecting the arrangement to successive hydroentanglement steps in the hydroentanglement apparatus. The hydroentanglement steps include exposing the arrangement to high pressure jets of liquid over a surface of the arrangement In some examples, the liquid is water. The jets may be directed firstly onto a first face of the arrangement, and subsequently onto a second opposite face of the arrangement. The jet pressure applied to the surface of the arrangement may be 180 - 380 bar. Subjecting the arrangement to successive hydroentanglement steps causes the fibres of the web to entangle with each other. Accordingly, the fibres of the web interlock with each other by entanglement. Subjecting the arrangement to successive hydroentanglement steps also causes a mechanical bond to form between the fibres of the web and the reinforcing material. This bond is caused by some of the fibres of the web being pushed by the high-pressure jets of liquid into gaps in the reinforcing material. Subjecting the arrangement to successive hydroentanglement steps may also dislodge non-fibrous particles from the fibres of the web to reduce the amount of non-fibrous material contaminants in the web. In some examples, in the hydroentanglement apparatus the arrangement is supported on a porous conveyor, which may be the support on which the arrangement is formed, and advanced through one or more treatment stations. In other examples, in the hydroentanglement apparatus the arrangement is supported on a porous drum, which may be the support on which the arrangement is formed, and advanced through one or more treatment stations. The one or more treatment stations comprise liquid outlets for subjecting the arrangement to high pressure jets of such liquid. In some examples, the method comprises subjecting the arrangement to successive hydroentanglement steps, wherein in each such hydroentanglement step the arrangement is exposed to high pressure jets of liquid over a surface of one of the faces of the arrangement. In other examples, the method comprises subjecting the arrangement to successive hydroentanglement steps, wherein in each such hydroentanglement step the arrangement is exposed to high pressure jets of liquid over a surface of each of the respective faces. Each of the successive hydroentanglement steps on one or each face of the arrangement may be carried out at a different treatment station in the apparatus. In such examples, the conveyor or the drum is arranged to support and advance the arrangement through each of the respective treatment stations. The composite sheet material may then be dried, for instance by heating the composite sheet material in an oven. Following the hydroentanglement steps, the composite sheet material is formed. The composite sheet material comprises a body of fibres including fibres interlocked with each other by entanglement, wherein the body of fibres comprises fibres derived from fibrous waste, such as leather waste or textile waste. The composite sheet material further comprises a reinforcing material, wherein at least some of the fibres of the body of fibres are mechanically bonded to the reinforcing material. The reinforcing material forms an intrinsic part of the material (e.g., as opposed to being a backing layer). For example, it may be that the reinforcing material and the fibres of the body of fibres cannot be separated from each other without the use of one or more tools. The body of fibres defines a first layer of the composite sheet material, and the reinforcing material defines a second layer of the composite sheet material. In examples where, prior to hydroentanglement, the arrangement comprises the further web, the composite sheet material formed following hydroentanglement comprises a further body of fibres. The further body of fibres includes fibres interlocked with each other by entanglement. At least some of the fibres of the further body of fibres are mechanically bonded to the reinforcing material. At least some of the fibres of the further body of fibres are also mechanically bonded to the body of fibres through gaps in the reinforcing material. The further body of fibres defines a third layer of the composite sheet material. The second layer of the composite sheet material is between the first and third layers. In some examples following hydroentanglement (i.e., downstream of hydroentanglement) the composite sheet material may be subject to treatments. The 36 treatments can produce materials suitable, for example, for clothing, footwear, accessories and upholstery applications and / or can improve the appearance and handling of the composite sheet material. Typical treatment steps include impregnation, colouring, treating with softening oils, drying, buffing, sueding and surface finishing. The composite sheet material may also be mechanically or chemically treated to add new functions to the material, such as waterproofing or fire retardancy. Impregnation can wash away non-fibrous material contaminants from the body of fibres. Buffing can abrade away non-fibrous material contaminants from the surface of the body of fibres. Except for the aforesaid finishing treatments, no adhesive is necessary to structurally bond the fibres. Thus, the composite sheet material may be substantially without any adhesive bonding of the fibres, the mechanical interlocking of the fibres caused by hydroentanglement being the predominant means of attaining and maintaining the integrity of the structure. In some examples, the composite sheet material comprises a coating, for example a polymeric coating. The coating may be a water based. Accordingly, the method may comprise applying such a coating to the composite sheet material following hydroentanglement and one or more of the treatments described above. The coating may be applied following drying and buffing of the composite sheet material. The composite sheet material may have a thickness of 0.5 - 2.5 mm. Preferably, the composite sheet material has a thickness of 0.7 mm - 1.6 mm, such as 1.2 mm. The composite sheet material may have a weight per unit area of over 250 gsm. Preferably, the composite sheet material has a weight per unit area of 350 gsm - 600 gsm, such as 450 gsm. Once used or discarded, the composite sheet material described herein may be considered as leather waste if the composite sheet material contains leather fibres, and be considered as textile waste if the composite sheet material contains textile fibres. A composite sheet material containing both leather and textile fibres would be considered as both leather waste and textile waste. There is thus described a method of removing non-fibrous material from fibrous waste, a system for removing non-fibrous material from fibrous waste, and a method of forming a composite sheet material with a number of advantages as described above and below. Milling of the fibrous waste removes heavier and denser non-fibrous particles, and also facilitates separation of fibres and non-fibrous particles during dispersal by disassembling the fibrous waste into individual fibres. The dispersal of the milled fibrous waste removes some fine non-fibrous dust and facilitates filtering of the milled fibrous waste by separating the fibres and non-fibrous particles. Filtering the milled fibrous waste through a screen removes fine particles which includes a significant amount of non-fibrous particles. It has been found that various aspects of the system and method therefore work synergistically to provide a fibrous feedstock with a reduced amount of non-fibrous material. The method of removing non-fibrous material from fibrous waste is a dry process and does not involve water or other solvents. The systems and methods can be used on a wide variety of types of fibrous waste and also mixtures of different types of fibrous waste, including contaminated fibrous waste. The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to ‘comprising only one...’ or by using ‘consisting.’ In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’, or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. For example, different types of fibrous waste could be used, different milling methods or apparatuses could be used, different dispersal methods or apparatuses could be used and / or different filtering methods or apparatuses could be used. Different sized apertures could be used depending on the fibrous waste. Input. Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. The term ‘a,’ ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon.

Claims

1. A method of removing non-fibrous material from fibrous waste, wherein the fibrous waste comprises leather waste and / or textile waste, the method comprising:inserting milled fibrous waste into a chamber, the milled fibrous waste comprising fibres and non-fibrous particles;dispersing the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber; andfollowing the dispersal, filtering the milled fibrous waste through a filtering apparatus to provide a fibrous feedstock with a reduced non-fibrous content relative to the fibrous waste, the filtering apparatus including a screen comprising a plurality of apertures, wherein the plurality of apertures are dimensioned to permit material with a size below a predetermined threshold to pass through.

2. A method according to claim 1, wherein the non-fibrous material comprises polymeric coating material.

3. A method according to claim 1 or 2, wherein the non-fibrous material comprises polyurethane.

4. A method according to any of the preceding claims, wherein the method further comprises milling the fibrous waste prior to inserting the fibrous waste into the chamber, such that the non-fibrous material of the fibrous waste is broken down into non-fibrous particles in the milled fibrous waste.

5. A method according to claim 4, wherein the milling comprises inserting the fibrous waste into a disc mill.

6. A method according to any of the preceding claims, wherein the majority of the fibres of the milled fibrous waste have a length of 1 mm to 10 mm.

7. A method according to any of the preceding claims, wherein the dispersal of the milled fibrous waste in the chamber comprises inducing a gas flow in the chamber.

8. A method according to claim 7, wherein the gas flow is induced using a vacuum, a fan, a pump and / or compressed gas.

9. A method according to claim 7 or 8, wherein the chamber is a vortex chamber configured to generate a vortex when a gas flow is induced in the chamber.

10. A method according to claim 9, wherein the vortex chamber comprises a vortex inducing section which is substantially conical in shape.

11. A method according to any of the preceding claims, wherein the chamber comprises a lower outlet for discharging heavier particles from the chamber and an upper outlet for discharging lighter particles from the chamber.

12. A method according to claim 11, wherein a vacuum is applied to the upper outlet to facilitate the discharge of particles through the upper outlet.

13. A method according to claim 11 or 12 when dependent on claim 9, wherein the lower outlet comprises a vortex breaker.

14. A method according to any of the preceding claims, wherein the maximum extent of at least the majority of the apertures in the screen is from 0.5 mm to 2 mm.

15. A method according to claim 14, wherein the maximum extent of at least the majority of the apertures in the screen is from 0.75 mm to 1.25 mm.

16. A method according to any of the preceding claims, wherein the filtering apparatus includes a first outlet arranged to collect particles that have passed through the apertures in the screen and a second outlet arranged to collect the fibrous feedstock that has not passed through the screen.

17. A method according to any of the preceding claims, wherein the screen is a vibrating screen which is configured to vibrate to facilitate movement of the milled fibrous waste across the screen.

18. A fibrous feedstock produced using the method of any of the preceding claims.

19. A method of forming a composite sheet material, wherein the method comprises:forming the fibres of the fibrous feedstock produced in the method of any of the preceding claims into a web;locating an arrangement comprising the web and a reinforcing material into a hydroentanglement apparatus, wherein the web defines a first layer of the arrangement and the reinforcing material defines a second layer of the arrangement; andsubjecting the arrangement to successive hydroentanglement steps in the hydroentanglement apparatus to provide the composite sheet material, wherein subjecting the arrangement to successive hydroentanglement steps causes the fibres of the web to entangle with each other and causes a mechanical bond to form between the fibres of the web and the reinforcing material.

20. A composite sheet material formed using the method of claim 19.

21. A system for removing non-fibrous material from fibrous waste, wherein the fibrous waste comprises leather waste and / or textile waste, the system comprising:a dispersal apparatus for dispersing milled fibrous waste comprising fibres and non-fibrous particles, wherein the dispersal apparatus comprises a chamber and dispersal means, the dispersal means being configured to disperse the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber; anda filtering apparatus, wherein the filtering apparatus includes a screen comprising a plurality of apertures, the plurality of apertures being dimensionedto permit material with a size below a predetermined threshold to pass through the screen.

22. A method of removing non-fibrous material from fibrous waste, the method5 comprising:inserting milled fibrous waste into a chamber, the milled fibrous waste comprising fibres and non-fibrous particles;dispersing the milled fibrous waste in the chamber such that the milled fibrous waste becomes airborne in the chamber; and10 following the dispersal, filtering the milled fibrous waste through afiltering apparatus to provide a fibrous feedstock with a reduced non-fibrous content relative to the fibrous waste, the filtering apparatus including a screen comprising a plurality of apertures, wherein the plurality of apertures are dimensioned to permit material with a size below a predetermined threshold to15 passthrough.

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