Composite material

Abstract

A rigid composite material (100, 200) for construction or fabrication is provided. The material comprises hemp (102, 202), biochar (104, 204) and a binder (106, 206). A sheet, board, brick or tile is also provided comprising the composite material. A method (300) of making a rigid composite material for construction is further provided. The method comprises forming a mixture (305) of hemp, biochar and a binder, and drying the mixture (320) to set the composite material.

Description

[0001] COMPOSITE MATERIAL

[0002] TECHNICAL FIELD

[0003] The present invention relates to a composite material, and in particular but not exclusively to a composite material for construction or fabrication.

[0004] BACKGROUND

[0005] Construction and fabrication materials are vital to enable buildings (for example, homes), furniture (for example, sofas, tables, chairs, shelves, drawers, benches, interior architecture) and other products to be constructed. Sheet materials such as fibreboard (for example, MDF), particleboard and plywood (and shaped products formed from those materials, for examples cylinders and blocks) are widely used as construction and fabrication materials.

[0006] However, such conventional construction and fabrication materials often have a high carbon footprint and are typically manufactured using petrochemical-based materials (for example, resins and binders) which can release environmentally harmful substances into the environment at the product’s end of life.

[0007] There is a need for alternative construction and fabrication materials which are more sustainable and have a lower environmental impact.

[0008] The present invention has been devised with the foregoing in mind.

[0009] SUMMARY OF INVENTION

[0010] According to a first aspect there is provided a rigid composite material for construction or fabrication. The composite material may comprise hemp, biochar and a binder. The hemp and biochar may be embedded in a matrix formed by the binder.

[0011] By using a combination of hemp and biochar with a binder to adhere the hemp and biochar together, the resulting composite material may have sufficient mechanical properties to be used as a construction or fabrication material whilst reducing or minimising an environmental impact of the material (both during and after a useful life of the composite material).

[0012] The hemp may provide the composite material with strength and durability. The biochar may provide a lightweight reinforcement to the composite material, which may improve mechanical properties without significantly increasing a density of the composite material. The biochar may also provide the composite material with fire retardant and thermal insulation properties, without requiring an additional component or coating which is typically petrochemical-based to provide fire retardancy. The hemp and / or the binder may provide the composite material with water-repellent properties. The combination of mechanical, fire-retardant and water-repellent properties may make the composite material particularly suitable for use as a construction or fabrication material, particularly where safety standards (for example, with regard to fire risk) need to be met.

[0013] The biochar may also result in the composite material being substantially carbon-negative. Biochar is substantially pure carbon and is therefore very stable. Biochar can remain in soil for thousands of years without decomposing, effectively locking away the carbon contained in the biochar (around 50% of the carbon originally present in the organic material from which the biochar is derived), rather than releasing the carbon after the composite material reaches end of life.

[0014] In contrast, many known biocomposite materials (for example, made from plant fibers) which may be used in construction or fabrication typically release carbon on decomposing after reaching end of life. Known biocomposite products may therefore be substantially carbon-neutral, but the carbon in the biocomposite is released at end of product life rather than locked away.

[0015] Biochar may also improve soil health, fertility and productivity. Biochar has a porous structure and a large surface area to volume ratio, providing habitat for beneficial soil microbes. Biochar can also increase the ability of soil to retain water and nutrients, which may indirectly lower emissions by reducing the need for emissive fertilizers. The composite material may therefore have a significantly reduced environmental impact relative to known construction or fabrication materials, remaining environmentally friendly even after the end of useful life of the material.

[0016] Biochar may also be produced from a wide variety of organic materials, including agricultural waste, forestry waste, and certain types of municipal waste, making it a widely available and widely applicable material.

[0017] In addition, both hemp and biochar may be produced sustainably. Hemp grows quickly and typically requires little in terms of pesticides or irrigation and can be grown locally in many locations throughout the world. That may indirectly reduce emissions by reducing or preventing the need to transport materials internationally. Biochar can be made from many different types of waste biomass, preventing it from decomposing and releasing carbon.

[0018] Hemp itself may also improve the sustainability and reduce the environmental impact of the composite material. Hem grows quickly and densely (for example, hemp plants can reach up to 4 m in height in 3 to 4 months). Because of that rapid and dense growth, hemp can absorb CO2 at a high rate. Additionally, hemp plants absorb more CO2 than is required to grow them. According to some estimates, for every ton of hemp produced, 1.3 tons of CO2 is removed from the air. Almost every part of the hemp plant can also be used, reducing waste and reducing the need for other more carbon-intensive materials. Hemp may also improve soil health at the end of product life, by returning nutrients to the soil and preventing erosion to maintain a capacity of soil to act as a carbon sink. The composite material may comprise a hemp to biochar ratio of between substantially 20:80 and substantially 80:20 by weight, optionally comprising a hemp to biochar ratio of between substantially 40:60 and substantially 60:40 by weight. That may enable the composite material to achieve a good balance between the respective material properties of the hemp and the biochar, improving a performance of the composite material as a construction material. The hemp to biochar ratio may be selected depending on the desired properties (for example, mechanical and / or thermal properties) of the composite material.

[0019] The hemp may comprise fibers of hemp. Using fibers of hemp may provide a convenient way to incorporate hemp into the composite material to provide the composite material with sufficient mechanical properties. The fibers of hemp may have an average size of between substantially 0.5 mm and substantially 300 mm, or may have an average size of between substantially 1 mm and substantially 100 mm, or may have an average size of between substantially 2mm and substantially 5 mm.

[0020] The biochar may comprise particles of biochar. Using particles of biochar increases a surface area of the biochar, which may result in improved adhesion to the hemp and to the binder. The particles of biochar may be embedded in the binder in small areas between regions of hemp. That may improve mechanical properties of the composite material by reducing or minimising a size of areas of binder matrix (between hemp or biochar material reinforcement embedded in the binder matrix), which may be comparatively weaker than the hemp or biochar reinforcement. The particles of biochar may have a size (for example, an average size) of between substantially 50 pm and substantially 5 mm. The particles of biochar may have a size (for example, an average size) of between substantially 0.01 mm and substantially 1 mm, or may have an average size of between substantially 0.1 mm and substantially 0.5 mm.

[0021] The composite material may comprise a binder saturation of between substantially 1% and substantially 300%, or a binder saturation of between substantially 25% and substantially 250%, or a binder saturation of substantially 100%. A binder saturation may be a ratio of the binder weight to the total dry weight of other material in the composite material (for example, a composite material comprising a binder saturation of 100% would have equal weights of binder and dry material). A binder saturation may be selected to provide optimal adhesion without providing excess binder material which may compromise the mechanical properties of the composite material. The binder saturation may be selected depending on one or more of a hemp to biochar ratio of the composite material, a size of the hemp and / or the biochar used in the composite material, and the desired properties of the composite material.

[0022] The composite material may comprise a laminated structure having a plurality of layers.

[0023] At least one layer of the laminated structure may have a different composition to another layer. That may enable the composite material to provide different properties at different regions within the material. The properties may be tailored by tailoring the composition of the different layers of the laminated structure. For example, the laminated structure may comprise a sandwich construction comprising outer layers disposed either side of one or more inner layers. The outer layers may have a different composition to the one or more inner layers. For example, the outer layers may comprise a greater hemp to biochar ratio than the one or more inner layers. That may provide the outer layers with improved mechanical properties (for example, strength, toughness) whilst the one or more inner layers have improved thermal properties (for example, insulative properties). That may enable the laminated structure of the composite material to be used as an insulation construction material using the same underlying material components.

[0024] The binder may be or comprise a biodegradable binder. The binder may be or comprise one or more of starch, an animal-derived protein, a plant-derived protein, lignin, tannin, polylactic acid, cellulose and chitosan. Additionally or alternatively, the binder may be or comprise a mineral binder. The binder may be or comprise one or more of lime, natural hydraulic lime, a geopolymer or alkali-activated binder, a magnesium-based binder, and calcium sulfoaluminate cement.

[0025] Conventional sheet construction materials such as fibreboard (for example, MDF), particleboard and plywood typically use synthetic binders or adhesives derived from petrochemicals, many of which can release harmful substances such as formaldehyde (a known human carcinogen) and other toxic volatile organic compounds into the environment. Using a biodegradable and / or mineral binder may provide a non-toxic binder which does not emit harmful substances such as gases. That may significantly reduce a health risk associated with manufacturing or using the composite material relative to conventional construction materials. Using a biodegradable and / or mineral binder may also reduce or minimise an environmental impact of the composite material. Biodegradable binders can be derived from renewable sources, unlike synthetic binders that are often petrochemical-based. Biodegradable binders will also break down harmlessly in the environment on product end of life, and may do so without requiring industrial compositing apparatus or conditions. That may allow the composite material to be composted domestically (for example, using a conventional home composting system and / or under conventional domestic composting conditions). Mineral binders can be made from some of the most abundant elements on earth, and will return those non-toxic components to the environment at the end of product life. Using biodegradable and / or mineral binders may also utilize waste products from other industries. For example, lignin is a by-product of the paper and biofuel industries, while mineral binders can contain fly ash and slag.

[0026] The composite material may comprise one or more oils or waxes. The one or more oils or waxes may comprise carnauba wax, candelilla wax, thistle oil, sunflower oil, soya oil, pine resin, beeswax, soy wax, linseed oil, tung oil, mineral oil, silicone or natural rubber. That may improve a water-repellency of the composite material, for example by sealing the composite material.

[0027] The one or more waxes may be disposed on a surface of the composite material. Additionally or alternatively, the one or more waxes may be dispersed through the composite material.

[0028] According to a second aspect, there is provided a sheet, board, brick or tile comprising the composite material of the first aspect. According to a third aspect, there is provided a method of making a rigid composite material for construction. The method may comprise forming a mixture of hemp, biochar and a binder. The method may also comprise drying the mixture to set the composite material. The method may comprise making the composite material of the first aspect.

[0029] The method may comprise forming the mixture into a desired shape.

[0030] Forming the mixture into a desired shape may comprise pressing the mixture. Pressing the mixture may comprise pressing the mixture for a predetermined time at a predetermined temperature.

[0031] Pressing the mixture may comprise heat-pressing the mixture. Heat-pressing the mixture may comprise pressing the mixture at a temperature of up to substantially 250°C. The temperature of the heat pressing may be selected or determined based on at least the binder used in the mixture.

[0032] The method may further comprise curing the mixture. The method may comprise curing the mixture for between substantially 1 minute and substantially 48 hours. Curing of the mixture may take place during and / or after forming the mixture, for example during and / or after pressing. A time and / or a temperature of the curing step may be selected or determined based on at least the binder used in the mixture

[0033] Features which are described in the context of separate aspects and embodiments of the invention may be used together and / or be interchangeable wherever possible. Similarly, where features are described in the context of a single embodiment for brevity, those features may also be provided separately or in any suitable sub-combination.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0036] FIG. 1 shows an embodiment of a rigid composite material for construction or fabrication comprising hemp, biochar and a binder, in accordance with the present invention;

[0037] FIG. IB shows an embodiment of a rigid composite material having a mineral binder, in accordance with the present invention;

[0038] FIG. 2 shows another embodiment of a composite material for construction or fabrication, in accordance with the present invention, comprising a laminated structure;

[0039] FIG. 3 shows an embodiment of a method of manufacturing the composite material shown in FIG.

[0040] 1; and FIG. 4 shows a particle size of biochar particles produced by grinding in the method of FIG. 3.

[0041] Like reference numerals in different Figures may represent like elements.

[0042] DETAILED DESCRIPTION

[0043] Biochar is a form of charcoal produced by charring organic matter. It is typically produced by performing pyrolysis, which involves heating biomass in a low-oxygen environment to prevent it from burning and / or decomposing. Pyrolysis results in a charcoal like material that is rich in carbon.

[0044] Figure 1 shows an embodiment of a rigid composite material 100 in accordance with the present invention. The composite material 100 may find particular use as an environmentally friendly alternative to materials such as fibreboard (for example, MDF), particleboard and plywood for use in construction and fabrication of homes, furniture and other products.

[0045] The composite material 100 comprises hemp 102, biochar 104 and a binder 106. In the embodiment shown, the composite material 100 comprises a hemp to biochar ratio of 50:50 by weight, with a binder saturation of 100%. The hemp 102 comprises hemp fibers having an average size (for example, a length) of substantially 3mm, while the biochar 104 comprises biochar particles having an approximate size (for example, a width or diameter) of substantially 1.0 mm or less. However, it will be appreciated the hemp 102 may alternatively comprise hemp fibers having any suitable size (for example between substantially 0.5 mm and substantially 300 mm), and the biochar 104 may alternatively comprise biochar particles having any suitable size (for example between substantially 0.01 mm and substantially 1 mm, or between substantially 50 pm and substantially 5 mm). The composite material 100 may also comprise any suitable hemp to biochar ratio (for example, between 80:20 and substantially 20:80 by weight), which may be selected upon desired properties of the composite material 100. The binder 106 may alternatively be provided at any suitable binder saturation (for example, between substantially 25% and substantially 250%).

[0046] In the embodiment shown, the binder 106 is a biodegradable starch-based binder, for example such as derived from potatoes, corn, wheat, tapioca or rice. The binder 106 may additionally or alternatively be or comprise any suitable biodegradable binder, for example a protein binder (such as derived from animal proteins, like casein or gelatin, or derived from plant proteins, like soy protein), a plant-derived binder (such as lignin or tannins), polylactic acid (for example, derived from plant starches such as corn or sugarcane), cellulose-based binders (for example methylcellulose or caboxymethyl cellulose), or chitosan (for example, derived from shells of insects or crustaceans, or from mushrooms). The binder 106 may additionally or alternatively be or comprise a mineral binder, for example lime (such as hydrated or hydraulic lime), a geopolymer or alkali-activated (such as derived from industrial waste products like fly ash or blast furnace slag), a magnesium-based binder (such as magnesium oxychloride or magnesium phosphate, which may be sourced from seawater or industrial waste such as from cement production), natural hydraulic lime, or calcium sulfoaluminate cement. The choice of binder or combination of binders may depend on required properties of the composite material 100 and its intended use, for example strength, flexibility, water-resistance etc. A balance of properties of the composite material 100 may be achieved by using a binder 106 comprising a combination of binder materials. Depending on the nature of the binder 106, the binder 106 may need to be dissolved in water or another solvent prior to being mixed with the hemp 102 and the biochar 104, although that is not essential and the binder 106 may be mixed directly with the hemp 102 and the biochar 104. Some binder materials may also be heat activated, although that is not essential.

[0047] The hemp 102 may impart or improve mechanical properties of the composite material 100, for example strength and toughness. The biochar 104 being provided as biochar particles may increase a surface of the area of the biochar 104 and improve its ability to bind with the hemp 102 and the binder 106, as well as allowing the biochar 104 to be more uniformly dispersed throughout the composite material 100 (for example, in the binder in small areas between hemp fibers). The biochar 104 may provide a lightweight reinforcement to the composite material 100, improving mechanical properties of the composite material 100 without increasing a density of the composite material 100. In addition, biochar 104 is an effective insulator with a low thermal conductivity, as well as being naturally fire retardant. By varying the hemp to biochar ratio of the composite material 100, the properties (for example, mechanical and / or thermal properties) of the composite material 100 may be varied accordingly. For example, a greater proportion of hemp 102 may increase a strength and / or toughness of the composite material 100, whilst a greater proportion of biochar 104 may improve thermal properties (such as reduced thermal conductivity and / or increased fire retardancy) of the composite material 100. The binder 106 acts to adhere the hemp 102 and the biochar 104 together in the composite material 100.

[0048] In the embodiment shown, a surface of the composite material 100 is substantially black or dark grey in colour. The overall colour of the composite material 100 is substantially due to the inclusion of the biochar 104, which has a substantially black colour. However, the colour of the composite material 100 may vary, for example between a white or light beige colour to a substantially black colour, depending on the hemp to biochar ratio. The binder 106 may also influence the colour of the composite material 100, with Figure IB showing a composite material 100 comprising a mineral binder and having a substantially white or light beige colour. The composite material 100 having a substantially black colour may be useful for heat absorption, for example if the composite material 100 is used as an external facade or cladding material for buildings in cooler climates.

[0049] A surface of the composite material 100 has a speckled visual appearance due to the size of the fibers of hemp 102 making them visible in the composite material. The lighter coloured fibers of hemp 102 provide a contrast to the predominant black colour provided by the biochar 104. In the embodiment shown, the fibers of hemp 102 are substantially randomly oriented in the composite material 100, providing the composite material 100 with substantially isotropic properties (for example, mechanical or thermal properties). Alternatively, the fibers of hemp 102 may be oriented or aligned in a specific direction, which may provide the composite material 100 with anisotropic or directional properties to provide improved performance in a desired direction through or along the composite material 100. The fibers of hemp 102 may also be provided in distinct layers with each layer of fibers oriented in a specific direction, although the fibers of different layers may not be aligned with one another. For example, the fibers of hemp 102 in adjacent layers may be oriented substantially perpendicular to one another, which may improve properties (for example, mechanical or thermal properties) in multiple directions through or along the composite material 100.

[0050] The composite material 100 has a substantially smooth surface, making it easy to handle and work with. For a composite material 100 having a larger hemp fiber size or a larger biochar particle size, the composite material 100 may have a slightly rougher surface texture upon initial manufacture compared to a composite material 100 having a smaller hemp fiber size or a smaller biochar particle size. However, the composite material 100 can be machined and / or finished to reduce a surface roughness of the composite material 100, for example, via sanding or buffing, and / or via the application of an oil or wax to the surface of the composite material 100. The oil or wax may alternatively or additionally be dispersed throughout the composite material 100, and may be included at a saturation of up to substantially 10%, for example between substantially 1% and substantially 5% (where saturation refers to a ratio of the oil or wax weight to the total weight of the dry components in the composite material 100). The inclusion of an oil or wax may also further improve a water-repellency of the composite material 100 by acting to seal the composite material 100, although that is not essential. The oil or wax may be one or more of carnauba wax, candelilla wax, thistle oil, sunflower oil, soya oil, pine resin, beeswax, soy wax, linseed oil, tung oil, mineral oil, silicone or natural rubber.

[0051] In the embodiment shown, the composite material 100 is formed as a sheet or board. That may be particularly convenient for use in construction or fabrication as a direct alternative to conventional sheet materials such as fibreboard, particleboard and plywood. A sheet or board of the composite material 100 having dimensions of 150 mm x 200 mm x 18 mm has a weight of approximately 200 g. In comparison, a sheet or board of MDF having the same dimensions has a weight of between approximately 335 g and approximately 400 g, given a typical range of densities for MDF of between approximately 620 kg m'3and 750 kg m'3. However, a weight and / or density of the composite material 100 may vary depending on the hemp to biochar ratio, the binder and the binder saturation. It will also be appreciated the composite material 100 may alternatively be formed directly in any suitable shape, for example a tile, a brick, or an arbitrary desired shape (discussed further below).

[0052] Figure 2 shows another embodiment of a composite material 200 in accordance with the present invention. The composite material 200 is substantially similar to the composite material 100 described with respect to Figure 1, with like reference numerals indicating like elements.

[0053] The composite material 200 comprises a laminated structure having a plurality of layers. In the embodiment shown, the composite material 200 comprises a first layer 200b, a second layer 200b, and a third layer 200c. The second layer 200b forms an inner layer disposed or sandwiched between the first layer 200a and the third layer 200c which form respective outer layers of the composite material 200. However, it will be appreciated the composite material 200 may have any suitable number of layers (for example, 2, 4, 5, 6 or more etc).

[0054] Each layer 200a-200c comprises hemp 202, biochar 204 and binder 206 substantially as described with respect to Figure 1. In the embodiment shown, the first layer 200a and the third layer 200c each comprise a greater hemp to biochar ratio than that of the second layer 200b. The first layer 200a and the third layer 200c have substantially the same composition, although that is not essential. That may result in the outer layers 200a, 200c having improved mechanical properties (for example, strength and / or toughness) relative to the inner layer 200b, which itself may have improved thermal properties (for example, increased fire retardance and / or lower thermal conductivity) than the outer layers 200a, 200c. In the embodiment shown, the binder 106 is the same for each of the layers 200a-200c and is provided at the same binder saturation, although that is not essential, and alternatively one or more of the layers 200a- 200c may use a different binder 106 and / or a different binder saturation to the other layers. That may enable the properties of each layer of the composite material 100 to be tailored as desired, which may enable the composite material to be employed in a wide variety of end uses.

[0055] Figure 3 shows an embodiment of a method 300 of manufacturing the rigid composite material 100, 200 described above in accordance with the present invention.

[0056] At step 305, the method 300 comprises forming a mixture of hemp 102, biochar 104 and a starch-based binder 106. As described above, the biochar 104 is provided as biochar particles, and the hemp 102 is provided as hemp fibers. In the embodiment shown, the biochar particles have an approximate size of substantially 1.0 mm or less. The biochar particles may be formed by processing biochar (pyrolyzed organic material) to produce particles of a desired size. For example, biochar may be ground or milled to produce biochar particles. In the embodiment shown, the biochar particles are produced by grinding biochar using a Eureka Mignon Specialita coffee grinder, although any suitable grinding or milling machine may alternatively be used. The size of the biochar particles produced by the grinding is shown in Figure 4, with ruler markings provided to show the size. A more selective range of biochar particle sizes may be provided, for example by passing the biochar particles through one or more meshes or sieves after grinding to separate biochar particles by size (e.g., sizes capable of passing through each mesh or sieve from sizes not capable of passing through each mesh or sieve). For example, a pair of meshes may be used to define an upper limit and a lower limit for the range of particle sizes desired, although that is not essential. Alternatively, the grinding process may be tailored to produce a substantially uniform distribution of particles having a desired average size, which may be validated by measuring the particle sizes resulting from the grinding process (for example, by conventional particle size measuring techniques such as dynamic image analysis, laser diffraction (also known as static light scattering or SLS), dynamic light scattering etc.).

[0057] The hemp fibers may be formed by chipping, grinding and sifting to produce and select hemp fibers of a desired size or range of sizes). In the embodiment shown, the hemp fibers are hemp shivs produced by East Yorkshire Hemp, having a size of approximately 3 mm, although any suitable hemp fibers may alternatively be used.

[0058] The hemp 102, biochar 104 and binder 106 is combined and mixed to ensure a substantially even distribution of the respective components through the mixture. The components may be mixed manually or may be mixed using a machine (for example, mixing according to a pre-determined mixing program).

[0059] At step 310, the method 300 optionally comprises forming the mixture of hemp 102, biochar 104 and binder 106 into a desired shape. In the embodiment shown, the mixture is placed into a mould having the desired shape. The mould is shaped to produce an item of composite material having a substantially rectangular shape, for example a board, sheet or tile, having dimensions of approximately 100 mm x 150 mm x 20 mm. However, that is not essential, and the mould may have any suitable shape (for example a circular shape, a hemispherical shape or hemispherical shell shape, a cubic or cuboidal shape, a cylindrical shape or cylindrical shape, or an arbitrary desired shape) and any suitable dimensions (for example, height, width and / or thickness). The mould may be lined with a release agent, for example silicone (such as a silicone spray or silicone sheet) to ensure release of the mixture from the mould.

[0060] At step 315, the method 300 optionally comprises pressing the mixture in the mould to form the composite material 100. In the embodiment shown, the mixture is pressed at room temperature (substantially 20°C), although depending on the binder used the mixture may be pressed at any suitable temperature, for example up to 250°C. Pressing the mixture whilst applying an elevated temperature may enable the binder to flow and adhere to the hemp 102 and the biochar 104 throughout the mixture. In some embodiments, the elevated temperature may also activate the binder 106 (if necessary) to begin curing the binder 106, although that is not essential. For example, in an alternative embodiment, the mixture may be pressed at substantially 170°C for substantially 150 s. The heat applied during pressing may activate a starch-based binder such as a tapioca starch binder and cause the binder 106 to adhere to the hemp 102 and the biochar 104 and set more quickly. Alternatively, the mixture may be pressed and subsequently cured (if necessary) as described below. The mixture may be pressed using a hydraulic press. In the embodiment shown, the mixture is pressed under approximately 10 tonnes of force, leading to an applied pressure of substantially 6.7 MPa in a mould having an area of 100 mm x 150 mm. However, any suitable pressure may be applied to the mixture in the mould. The mixture is pressed in the mould for substantially two hours, although the mixture may alternatively be pressed for any suitable length of time, for example between substantially 1 minute and substantially 48 hours. The thickness of the composite material 100 may be controlled during the pressing process (for example, by controlling an applied pressure or by controlling a distance between a pressing component and an opposing surface of the mould).

[0061] At step 320, the method 300 comprises drying (and optionally cooling) the pressed composite material 100, in order to allow the binder 106 to harden and set to secure the hemp 102 and the biochar 104 in the matrix of binder 106. In the embodiment shown, the composite material 100 is removed from the mould and placed on a perforated drying rack. A weight is placed on the board to prevent warping during drying, although that is not essential. However, it will be appreciated the composite material 100 may be dried (and optionally cooled) in any suitable manner. For example, drying the composite material 100 may comprise placing the composite material 100 in an environment having suitable ventilation and humidity to enable the composite material 100 to dry.

[0062] At step 325, the method 300 optionally comprises curing the binder 106 of the composite material 100 (if necessary). Curing the binder 106 comprises subjecting the composite material 100 to a substantially consistent temperature for a pre-determined length of time in order to optimise or enhance properties of the binder 106. In the embodiment shown, curing the binder 106 comprises applying a temperature of substantially 21°C for substantially 120 hours (5 days). Alternatively, curing the binder 106 may comprise applying a temperature of substantially 21°C for substantially 6 hours, for example if the mixture has been heat pressed (such as at 170°C as described above). However, curing the binder 106 may comprise curing the binder 106 at any suitable temperature for any suitable length of time, for example between substantially 20°C and substantially 250°C for between substantially 1 minute and substantially 200 hours (the time and temperature of the curing process may depend on the binder used). For polymeric binders, curing may form cross-links between polymer chains in order to improve mechanical properties (for example, strength, toughness, hardness) of the material. In some embodiments, drying and curing (steps 320 and 325) may take place substantially simultaneously.

[0063] At step 330, the method 300 optionally comprises finishing the composite material 100. For example, the composite material 100 may cut to size or sanded, or edge detailing may be applied. In some embodiments, an oil or wax may be applied as a sealant or finish, for example to make the surface of the composite material 100 more water-repellent.

[0064] For embodiments in which the composite material comprises a laminated structure having a plurality of layers (as described above with respect to the composite material 200 shown in Figure 2), each of the individual layers may be formed separately or individually as set out with respect to the method 300. The formed layers may then be adhered together, for example using a binder to act as an adhesive between the layers (such as a lignin, cellulose or starch-based binder). Alternatively, the layers may be integrally formed with one another. The layers may be arranged on top of one another during the forming process, and may then be pressed or cured together to form the laminated composite material 200.

[0065] From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of construction or fabrication materials, in particular composite construction or fabrication materials, and which may be used instead of, or in addition to, features already described herein.

[0066] Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

[0067] Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom. For the sake of completeness, it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, and any reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

CLAIMS1. A rigid composite material for construction or fabrication, comprising hemp, biochar and a binder.

2. The composite material of claim 1, comprising a hemp to biochar ratio of between substantially 20:80 and substantially 80:20 by weight, optionally comprising a hemp to biochar ratio of between substantially 40:60 and substantially 60:40 by weight.

3. The composite material of claim 1 or of claim 2, wherein the biochar comprises particles of biochar having an size of between substantially 50 pm and substantially 5 mm.

4. The composite material of any preceding claim, comprising a binder saturation of between substantially 1% and substantially 300%, optionally comprising a binder saturation of between substantially 25% and substantially 250%, further optionally comprising a binder saturation of substantially 100%.

5. The composite material of any preceding claim, comprising a laminated structure having a plurality of layers.

6. The composite material of claim 5, wherein at least one layer has a different composition to another layer.

7. The composite material of claim 1 or of claim 2, wherein the binder comprises a biodegradable binder.

8. The composite material of claim 3, wherein the binder comprises one or more of starch, an animal-derived protein, a plant-derived protein, lignin, tannin, polylactic acid, cellulose and chitosan.

9. The composite material of any preceding claim, wherein the binder comprises a mineral binder.

10. The composite material of claim 5, wherein the binder comprises one or more of lime, natural hydraulic lime, a geopolymer or alkali-activated binder, a magnesium-based binder, and calcium sulfoaluminate cement.

11. The composite material of any preceding claim, further comprising one or more oils or waxes, optionally wherein the one or more oils or waxes comprise carnauba wax, candelilla wax, thistle oil, sunflower oil, soya oil, pine resin, beeswax, soy wax, linseed oil, tung oil, mineral oil, silicone or natural rubber.

12. The composite material of claim 11, wherein the one or more waxes are disposed on a surface of the composite material or are dispersed through the composite material.

13. A sheet, board, brick or tile comprising the composite material of any of claims 1 to 12.

14. A method of making a rigid composite material for construction, comprising: forming a mixture of hemp, biochar and a binder; and drying the mixture to set the composite material.

15. The method of claim 14, further comprising forming the mixture into a desired shape.

16. The method of claim 15, wherein forming the mixture into a desired shape comprises pressing the mixture.

17. The method of claim 16, where pressing the mixture comprises heat-pressing the mixture, optionally heat-pressing the mixture at a temperature of up to substantially 250°C.

18. The method of any of claims 14 to 17, further comprising curing the mixture, optionally curing the mixture for between substantially 1 minute and substantially 48 hours.

Images