Method of preparing carbon material precursors

Abstract

Method of Preparing Carbon Material Precursors A method of preparing a carbon material precursor for carbonisation. The method comprises the steps of a) providing a carbon material precursor comprising a lignin; b) treating the carbon material precursor with a crosslinking agent; and c) heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C. Also disclosed is such a method comprising a step b) of irradiating the carbon material precursor with UV light; and such a method comprising a step c) of treating the carbon material precursor with a crosslinking agent after heat treating the fibre. The use of the crosslinking agent and / or the UV treatment may improve the efficiency of the stabilisation of carbon material precursors and facilitate handling of the carbon fibre precursors during stabilisation and carbonisation steps. A method of producing a carbon material is also provided.

Description

[0001] METHOD OF PREPARING CARBON MATERIAL PRECURSORS

[0002] Field

[0003] The present invention relates to methods of preparing carbon material precursors for carbonisation, to methods of producing carbon materials from said carbon material precursors and to said carbon materials and carbon material precursors. In particular the present invention relates to methods of stabilising carbon material precursors comprising lignin, prior to carbonisation, for example carbon fibre precursors comprising lignin.

[0004] Background

[0005] Carbon based materials have become crucial for many technological developments in areas such as energy, aerospace, automobiles, catalysis and medicine. In particular, carbon fibres are commonly used for many structural applications such as in the aerospace, military, automobile and wind turbine industries.

[0006] Furthermore, carbon foams have become a very important class of carbon-based materials due to their porous structure which can be tuned depending on the final application. Therefore carbon foam materials have enormous potential in technological areas where a light weight and a large surface area are important for the function of the material, such as in electrodes for batteries, absorbents and structural panels for construction, automotives and aircraft.

[0007] Currently, the vast majority of carbon fibres are produced by heat treatment and pyrolysis of polyacrylonitrile (PAN) carbon fibre precursors which are synthesised from petroleum sources. There are several disadvantages with this use of PAN material as carbon fibre precursors, for example high cost, slow carbonisation and the detrimental environmental impact of the acrylonitrile production.

[0008] Lignin may provide a more environmentally benign alternative for carbon material production, for example carbon fibres or carbon foams. Lignin is a complex organic polymer present in the cell walls of pith, roots, fruit, buds and bark and, along with hemicellulose and cellulose, is one of the most abundant components of lignocellulosic biomass. However, lignin itself performs poorly during the typical melt spinning process used to form carbon fibre precursors, which makes industrial scale production extremely complicated and difficult. Lignin may also provide carbon fibre precursors of a relatively poor quality, for example such lignin-derived carbon fibre precursors may comprise voids which may adversely affect the physical properties of the carbon fibres produced from such precursors.

[0009] Therefore it would be highly desirable to improve the processability of lignin into carbon material precursors in order to ultimately improve the environmental profile of carbon fibre products. Several attempts have been made to modify lignin to improve processability in the formation of carbon fibre precursors and / or carbon fibres. For example, WO 2014 / 078120 A1 discloses a method involving esterification of a lignin precursor with an acid, acid anhydride, alkyl halide, or acyl halide, to form a reduced Tg (glass transition temperature) lignin. WO 2014 / 046826 A1 discloses a method of making a carbon fibre which involves heat treating a lignin precursor absent an active ingredient in an inert atmosphere to raise the Tg of the precursor.

[0010] However, no efficient and environmentally sound commercial process for manufacturing carbon material precursors and / or carbon materials, such as carbon fibres and / or carbon foams, from lignin has been established.

[0011] Summary of the Invention

[0012] Some methods of converting lignin into carbon fibre precursors involve melt-spinning, where a lignincontaining feedstock is softened by heat. The fibres obtained by this process may be stabilised by thermal treatment in air before carbonisation in an inert atmosphere. The stabilisation of a lignincontaining fibre is a key step in the process which renders the fibres resistant to fusing to each other, prior to its carbonisation in an inert atmosphere. This stabilisation step requires a very slow heating rate or long isothermal steps to allow for cross linkages to form within the lignin fibre. The relatively long time required for these steps limits the speed and efficiency by which carbon fibres can be manufactured, which represents a significant drawback to the use of lignin in carbon fibre production.

[0013] Furthermore, lignin-containing carbon fibre precursors may have a high fusibility of the fibres when exposed to temperature above the Tg of the lignin (100-170°C), which is detrimental to the efficient processing, handling and use of the carbon fibre precursors and carbon fibres.

[0014] Also, known methods may introduce voids into the lignin-containing carbon fibre precursors which can lead to defects and breakage of carbon fibres formed from the precursors.

[0015] Similar issues are found in the production of other carbon material precursors and carbon materials formed from said precursors, for example in the production of carbon foam precursors and carbon foams.

[0016] Therefore it would be highly desirable to improve the stabilisation of lignin-containing materials in order to ultimately improve the commercial viability of carbon material production from lignin.

[0017] It is one aim of the present invention, amongst others, to provide a method of preparing a carbon material precursor for carbonisation that addresses at least one disadvantage of the prior art, whether identified here or elsewhere, or to provide an alternative to existing methods. For instance, it may be an aim of the present invention to provide a method of preparing a carbon material precursor for carbonisation which improves the efficiency of the stabilisation of carbon material precursors containing lignin, for example to provide sufficiently stabilised carbon material precursors in a shorter time than known methods and / or using less energy than known methods and / or to provide a carbon material precursor or carbon material having improved properties compared to known methods.

[0018] According to aspects of the present invention, there is provided a method, a carbon material precursor and a carbon material as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and from the description which follows.

[0019] According to a first aspect of the present invention, there is provided a method of preparing a carbon material precursor for carbonisation, the method comprising the steps of: a) providing a carbon material precursor comprising a lignin; b) treating the carbon material precursor with a crosslinking agent; and c) heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C.

[0020] The inventors have found that the method of this first aspect, which involves treating the carbon material precursor comprising lignin with the crosslinking agent, may allow carbon materials, such as carbon fibres and / or carbon foams, to be produced more efficiently. For example, the time required for heat treating the carbon material precursor may be reduced and / or the energy required by the process may be reduced, due to the effect of the crosslinking agent used in step b). Also, the use of the crosslinking agent may reduce the fusability of carbon fibres precursors during heating steps, improving the efficiency of the stabilisation of said precursor fibres and facilitating handling of the carbon fibre precursors during stabilisation and carbonisation steps. The inventors have found that carbon fibre precursors comprising lignin which are not treated with the crosslinking agent as described herein cannot be put under tension during stabilisation, leading to relatively thick carbon fibre precursors strands. The method of the present invention allows carbon fibre precursors comprising lignin to be tensioned and therefore stretched during stabilisation to provide carbon fibre precursor strands with a lower diameter than would otherwise be possible, which is beneficial for the further processing of the precursors into carbon fibres.

[0021] Furthermore, the method may allow the use of more sustainable materials compared to known methods due to these improvements obtained with lignin-containing carbon material precursors.

[0022] It is believed that any type of lignin can be utilised in the method of this first aspect, for example lignin obtained from softwood, hardwood or grass / annual plants. Suitable lignin can be obtained from these sources using various known processes, for example the Kraft, organosolve or soda processes. In some embodiments, more than one type and / or source of lignin is used to provide the lignin of the composition. The steps of the method are suitably carried out in the order of step a) followed by step b) followed by step c).

[0023] In some embodiments, the carbon material precursor is a carbon fibre precursor and is in the form of a fibre. Such carbon fibre precursors are suitable and intended for use in forming carbon fibres, as described herein.

[0024] In some embodiments, the carbon material precursor is a hydrogel or an aerogel. Such hydrogels or aerogels are suitable and intended for use in forming carbon foams, as described herein.

[0025] Step b) of the method of this first aspect involves treating the carbon material precursor with a crosslinking agent. Treating the carbon material precursor with the crosslinking agent suitably involves contacting the outer surface of the carbon material precursor with the crosslinking agent. The crosslinking agent may be applied to the carbon material precursor by any suitable means, suitably to the outer surface of the carbon material precursor. Alternatively the carbon material precursor may be brought into contact with the crosslinking agent, for example by passing the carbon material precursor through a vessel containing the crosslinking agent.

[0026] Suitably step b) involves treating the carbon material precursor with a solution comprising the crosslinking agent. In such embodiments, the carbon material precursor may be passed through and / or immersed in the solution comprising the crosslinking agent. The solution suitably comprises at least 0.1 wt% of the crosslinking agent, suitably at least 0.5 wt% of the crosslinking agent or at least 1 wt%.

[0027] Suitably the solution comprises up to 30 wt% of the crosslinking agent, suitably up to 25 wt% or up to 20 wt% of the crosslinking agent.

[0028] Suitably the solution comprises from 0.1 to 30 wt% of the crosslinking agent, suitably from 0.5 to 25 wt% or from 1 to 20 wt% of the crosslinking agent.

[0029] The solution comprising the crosslinking agent is suitably an aqueous solution. Therefore the solution comprising the crosslinking agent suitably comprises an aqueous solvent.

[0030] Therefore step b) suitably involves treating the carbon material precursor with a aqueous solution comprising at least 0.5 wt% of the crosslinking agent. Suitably step b) involves immersing the carbon material precursor in the aqueous solution comprising at least 0.5 wt% of the crosslinking agent. Suitably step b) involves immersing the carbon material precursor in the aqueous solution of the crosslinking of at least 1 second or at least 5 seconds, and suitably for up to 5 minutes, up to 2 minutes or up to 1 minute. In embodiments wherein the carbon material precursor is a fibre (i.e. a carbon fibre precursor), step b) suitably involves immersing the carbon fibre precursor in the aqueous solution comprising at least 0.5 wt% of the crosslinking agent by passing the carbon fibre precursor through the solution.

[0031] Step b) may involve drying the carbon material precursor after treating the carbon material precursor with a solution comprising the crosslinking agent, suitably to substantially remove the solvent.

[0032] Step b) may provide a coating of the crosslinking agent on the carbon material precursor.

[0033] Suitably the crosslinking agent is selected from a diisocyanate, boric acid or a carboxylic acid.

[0034] Suitable diisocyanate crosslinking agents may be selected from methylene diphenyl diisocyanate, toluene diisocyanate, hexameth methylene diisocyanate, methylene dicyclohexyl diisocyanate (MDI), hydrogenated MDI and isophorone diisocyanate (IPDI).

[0035] Suitable carboxylic acids comprise at least two carboxylate groups. The carboxylic acid may be a dicarboxylic acid or a tricarboxylic acid. A suitable carboxylic acid may be selected from the dicarboxylic acids oxalic acid (ethanedioic acid), malonic acid (propanedioc acid), succinic acid (butanedioic acid), glutaric acid (pentanedioic acid). A suitable carboxylic acid may be selected from the tricarboxylic acids citric acid (2-hydroxypropane-1 ,2,3-tricarboxylic acid), aconitic acid (prop-1- ene-1 ,2,3-tricarboxylic acid), propane-1 ,2,3-tricarboxylic acid and trimesic acid (benzene-1 ,3,5- tricarboxylic acid). In some embodiments, the carboxylic crosslinking agent is citric acid.

[0036] The crosslinking agent may be selected from a diisocyanate, boric acid and citric acid.

[0037] In some embodiments, the method of this first aspect comprises, after step b), a step: b2) irradiating the carbon material precursor with UV light.

[0038] Suitably step b2) involves irradiating the carbon material precursor with UV light from a UV lamp. One example a suitable UV lamp comprises 6 W UV tubes which emit UV light at 365 nm and 254 nm.

[0039] The irradiating the carbon material precursor with UV light of step b2) is not intended to encompass irradiation with natural daylight.

[0040] Suitably step b2) involves irradiating the carbon material precursor with UV light for at least s minutes, suitably at least 10 minutes, at least 20 minutes or at least 30 minutes. Step b2) may involve irradiating the carbon material precursor with UV light for up to 10 hours, up to 8 hours or up to 6 hours. Suitably, step b2) involves irradiating the carbon material precursor with UV light for from 5 minutes to 8 hours, from 10 minutes to 6 hours or from 10 minutes to 4 hours. The inventors have found that irradiating the carbon material precursor with UV light in a step b2) as described above may provide a further improvement the stabilisation of the carbon precursor material which is beneficial to a subsequent process of carbonisation to form a carbon material. For example, step b2) may allow a higher amount of elongation of carbon fibre precursors and reduce the amount of breakages during carbon fibre production. Step b2) may also increase the carbon yield of a subsequent carbonisation process and / or increase the tensile strength of carbon fibres produced by such a process.

[0041] Step c) of the method of this first aspect involves heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C, suitably to a temperature of from 125°C to 300°C, for example from 150°C to 275°C.

[0042] Suitably, step c) involves heating the carbon material precursor at the temperature of from 100°C to 350°C for at least 30 minutes, suitably at least one hour or at least two hours.

[0043] Suitably step c) involves heating the carbon material precursor at the temperature of from 100°C to 350°C for up to 20 hours, suitably up to 15 hours

[0044] Suitably step c) involves heating the carbon material precursor to the temperature of from 100°C to 350°C at a heating rate of from 0.2 to 2°C per minute, suitably at a heating rate of from 0.5 to 1.5°C per minute.

[0045] Step c) may involve at least one isothermal period, wherein the carbon material precursor is maintained at a set temperature for a set amount of time. Suitably such a set amount of time for the isothermal period is at least 10 minutes, suitably at least 20 minutes or at least 30 minutes. The set temperature of the isothermal period may be a maximum temperature of from 100°C to 350°C to which the carbon material precursor is heated to, or may be a set temperature below said maximum temperature.

[0046] Step c) may involve more than one isothermal period. For example, step c) may involve a first heating period wherein the carbon material precursor is heated to at least a first temperature of from 100°C to 350°C followed by a first isothermal period at said first temperature for a set amount of time, and then a final heating wherein the carbon material precursor is heated to a maximum temperature of from 100°C to 350°C followed by a final isothermal period. The first temperature is suitably from 100°C to 200°C, for example from 125°C to 175°C. The maximum temperature is suitably from 200°C to 350°C, for example from 225°C to 300°C or from 225°C to 275°C.

[0047] Step c) may involve further heating periods and isothermal periods. For example, step c) may involve second and third heating periods to second and third temperatures of from 100°C to 350°C, respectively, followed by second and third isothermal periods, respectively, wherein the first, second and third temperatures are successively higher and are lower than the maximum temperature. Said first, second, third and maximum temperatures, when present, are suitably at least 10°C apart, suitably at least 20°C apart. Said temperatures may be up to 100°C apart, suitably up to 75°C apart. Each of the heating periods suitably involve heating at the rates discussed above. Each of the isothermal periods are suitably maintained for an amount of time as discussed above.

[0048] Suitably step c) stabilises the carbon material precursor for subsequent handling and carbonisation. Suitably step c) involves less time and / or a lower maximum temperature than a comparable method wherein step b) of treating the carbon material precursor with a crosslinking agent is not carried out. Therefore step c) suitably involves a lower overall amount of energy than a comparable method wherein step b) is not carried out.

[0049] In some embodiments, the method of this first aspect comprises, after step c), a step: d) treating the carbon material precursor with a second crosslinking agent.

[0050] Treating the carbon material precursor with the second crosslinking agent suitably involves contacting the outer surface of the carbon material precursor with the crosslinking agent. The second crosslinking agent may be applied to the carbon material precursor by any suitable means, suitably to the outer surface of the carbon material precursor. Alternatively the carbon material precursor may be brought into contact with the second crosslinking agent, for example by passing the carbon material precursor through a vessel containing the second crosslinking agent.

[0051] Suitably step d) involves treating the carbon material precursor with a solution comprising the second crosslinking agent. In such embodiments, the carbon material precursor may be passed through and / or immersed in the solution comprising the second crosslinking agent. The solution suitably comprises at least 0.1 wt% of the second crosslinking agent, suitably at least 0.5 wt% of the second crosslinking agent or at least 1 wt%.

[0052] Suitably step d) involves treating the carbon material precursor with a solution comprising at least 0.5 wt% of the second crosslinking agent.

[0053] Suitably the solution comprises up to 30 wt% of the second crosslinking agent, suitably up to 20 wt% or up to 10 wt% of the second crosslinking agent.

[0054] Suitably the solution comprises from 0.1 to 25 wt% of the second crosslinking agent, suitably from 0.5 to 20 wt% or from 1 to 15 wt% of the second crosslinking agent.

[0055] The solution comprising the second crosslinking agent is suitably a non-aqueous solution. Therefore the solution comprising the second crosslinking agent suitably comprises a non-aqueous solvent, suitably an organic solvent. Suitable organic solvents include hydrocarbon solvents, for example alkanes. A suitably solvent may be hexane. Therefore step d) suitably involves treating the carbon material precursor with a solution comprising an organic solvent and at least 0.5 wt% of the second crosslinking agent. Suitably step d) involves immersing the carbon material precursor in a solution comprising an organic solvent and at least 0.5 wt% of the second crosslinking agent.

[0056] In embodiments wherein the carbon material precursor is a fibre (i.e. a carbon fibre precursor), step d) suitably involves immersing the carbon fibre precursor in the solution comprising at least 0.5 wt% of the second crosslinking agent by passing the carbon fibre precursor through the solution.

[0057] Step d) may involve drying the carbon material precursor after treating the carbon material precursor with a solution comprising the second crosslinking agent, suitably to substantially remove the solvent.

[0058] The solution comprising the organic solvent may penetrate into the bulk of the carbon material precursor. Therefore in step d) the second crosslinking agent may penetrate into the carbon material precursor.

[0059] The second crosslinking agent may be selected from the crosslinking agents discussed above in relation to step b). Suitably the second crosslinking agent is selected from a diisocyanate, boric acid or a carboxylic acid.

[0060] Preferably the second crosslinking agent is a diisocyanate or a diisocyanate precursor. Suitable diisocyanate second crosslinking agents may be selected from methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI). A suitable diisocyanate precursor may be N,N'- (methylenebis(4,1-phenylene))bis(1 Hbenzo[d][1 , 2, 3]triazole-1 -carboxamide) (MDI-B).

[0061] Suitably the crosslinking agent used in step b) is a boric acid or a carboxylic acid as defined above and the second crosslinking agent used in step d) is a diisocyanate or a diisocyanate precursor.

[0062] In some embodiments, the carbon material precursor comprises a thermoplastic elastomer, suitably at least 10 wt% of a thermoplastic elastomer.

[0063] Suitably, at least a part of the thermoplastic elastomer comprises functional groups which provide compatibility with lignin. Compatibility with lignin may be determined by the polarity of the polymer and / or functional groups within the polymer. Semi-polar polymers may provide acceptable compatibility with lignin. For example, polyester polyols and polyether polyols may have an appropriate polarity for compatibility with lignin. Said semi-polar polymers may provide parts or segments of the thermoplastic elastomer. Said semi-polar polymers, for example polyester polyols or polyether polyols may provide compatibility with lignin and enable the thermoplastic elastomer to combine with the lignin to provide a composition with the improved mechanical properties. Suitably the thermoplastic elastomer is a polymer comprising polyol groups. By “polymer comprising polyol groups” we mean that the polymer has been formed using a polyol, for example a polyester polyol or a polyether polyol. The polyol may be a diol, such as a polyethylene glycol, and the two hydroxyl groups of the diol may form bonds with other functional groups during formation of the polymer. The polymer comprising polyol groups may therefore not contain any free hydroxyl groups after formation of the polymer. This usage of the term “polyol” is in accordance with the common usage of the term in polymer chemistry.

[0064] In some embodiments, the thermoplastic elastomer is a block copolymer comprising at least two different block polymer components. Suitably the thermoplastic elastomer is a linear segmented block copolymer comprising at least two different block polymer components. Suitably one of said at least two different block polymer components provides a “soft segment” and another one of said at least two different block polymer components provides a “hard segment”. The terms hard and soft segments in relation to thermoplastic elastomer block copolymers would be known to the person skilled in the relevant art. Suitably the soft segment is chosen to be compatible with lignin, for example by comprising polyol groups. Suitably the soft segment comprises a polyol, suitably a polyether polyol or a polyester polyol. Polyether polyols are known in the art as polymers formed from the polymerisation of an epoxide, for example ethylene oxide. Suitable examples of polyether polyols include polyethylene glycol and polypropylene glycol. Said polyether polyols are diols. Polyester polyols are known in the art as polymers formed from the polymerisation reaction of a glycol (a diol) with a dicarboxylic acid. An example of a polyester polyol is polycaprolactone polyol.

[0065] Suitably the thermoplastic elastomer comprises material derived from sustainable biological sources. Said material may reduce the environmental impact of using a thermoplastic elastomer to blend with the lignin and maintain the favourable environmental benefits of using lignin to produce carbon fibre precursors and carbon fibres.

[0066] In some embodiments, the thermoplastic elastomer of the carbon material precursor is suitably a thermoplastic polyurethane.

[0067] Suitably the thermoplastic polyurethane is a block copolymer comprising a polyol, suitably in the soft segment. Such thermoplastic polyurethanes are block copolymers comprising alternating sequences of hard and soft segments. The hard segments are formed by the reaction of diisocyanates with short-chain diols and the soft segments are formed by reaction of diisocyanates with long-chain polyols. The hard segments of the thermoplastic polyurethane may therefore comprise carbamate groups (derived from the diisocyanates).

[0068] Suitably the thermoplastic polyurethane is a block copolymer comprising a polyether polyol or a polyester polyol. Said thermoplastic polyurethanes may alternatively be referred to as being formed using a polyol (for example a polyether polyol or a polyester polyol) or being derived from said polyol. The thermoplastic polyurethanes may therefore comprise said polyol (for example a polyether polyol or a polyester polyol) covalently bonded into larger polymer chains comprising other groups / segments.

[0069] An example of a suitable thermoplastic polyurethane is TPU Pearlthane ECO 12T95 supplied by Lubrizol.

[0070] The carbon material precursor may comprise at least 25 wt% of the thermoplastic elastomer, suitably at least 35 wt%, suitably at least 45 wt%.

[0071] The carbon material precursor may comprise up to 65 wt% of the thermoplastic elastomer, suitably up to 60 wt%, suitably up to 55 wt%.

[0072] The carbon material precursor suitably comprises 20 to 60 wt% of the thermoplastic elastomer, suitably from 40 to 60 wt% or from 45 to 55 wt%.

[0073] The carbon material precursor may comprise at least 35 wt% of the lignin, suitably at least 40 wt%, suitably at least 45 wt%.

[0074] The carbon material precursor may comprise up to 90 wt% of the lignin, suitably up to 75 wt%, up to 65 wt% or suitably up to 55 wt%.

[0075] The carbon material precursor suitably comprises 30 to 90 wt% of the lignin, suitably from 40 to 80 wt%, suitably from 40 to 60 wt% or from 45 to 55 wt%.

[0076] In some embodiments, the carbon material precursor comprises from 40 to 60 wt% of thermoplastic elastomer and from 40 to 60 wt% of lignin, suitably from 45 to 55 wt% of thermoplastic elastomer and from 45 to 55 wt% of lignin.

[0077] In some embodiments, the carbon material precursor comprises a third crosslinking agent. Suitably said third crosslinking agent is mixed within the bulk material of the carbon precursor material, suitably blended with the lignin and the thermoplastic elastomer, when present.

[0078] The third crosslinking agent may be a diisocyanate or a diisocyanate precursor, as described above, a diglycidyl ether compound, a carbodiimide compound, gluraraldehyde or a vinyl sulfone compound.

[0079] Suitable diglycidyl ether compounds may be selected from neopentyl glycol diglycidyl ether or a polyethyleneglycol diglycidyl ether (PEGDGE).

[0080] Suitable carbodiimide compounds may be selected from N,N'-Dicyclohexylcarbodiimide, N,N'- Diisopropylcarbodiimide, 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide, 1-cyclohexyl-(2- morpholinoethyl)carbodiimide. Suitable vinyl sulfone compounds may be selected from phenyl vinyl sulfone, divinyl sulfone and diphenyl sulfone.

[0081] The use of such third crosslinking agents may be particularly advantageous wherein the carbon material precursor comprises a thermoplastic elastomer, as described above, as such third crosslinking agent may improve the compatibility of the lignin and the thermoplastic elastomer and provide advantageous properties in subsequent processing.

[0082] The third crosslinking agent may be present in the carbon material precursor in an amount of at least 0.1 wt%, based on the total weight of the carbon material precursor, suitably at least 0.5 wt% or at least 1 wt%.

[0083] The third crosslinking agent may be present in the carbon material precursor in an amount of up to 10 wt%, based on the total weight of the carbon material precursor, suitably up to 7.5 wt% or up to 5 wt%.

[0084] The third crosslinking agent may be present in the carbon material precursor in an amount of from 0.1 to 10 wt%, based on the total weight of the carbon material precursor, suitably from 0.5 to 7.5 wt% or from 1 to 5 wt%.

[0085] In some embodiments, the carbon material precursor is a carbon fibre precursor comprising from 40 to 60 wt% of the lignin, from 40 to 60 wt% of a thermoplastic elastomer and from 0.1 to 10 wt% of a third crosslinking agent, suitably a diisocyanate or diisocyanate precursor.

[0086] According to a second aspect of the present invention, there is provided a method of preparing a carbon material precursor for carbonisation, the method comprising the steps of: a) providing a carbon material precursor comprising a lignin; b) irradiating the carbon material precursor with UV light; and c) heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C.

[0087] The steps of the method are suitably carried out in the order of step a) followed by step b) followed by step c).

[0088] The inventors have found that the step b) of irradiating the carbon material precursor with UV light may provide an increase in carbon yield in carbon materials after carbonisation of the carbon material precursors. In embodiments wherein the carbon precursor material is a fibre, step b) may advantageously increase the elongation of said fibres under tension and reduce the amount of fibre breakages. Also, the step of irradiating the carbon material precursor with UV light may shorten the time required for stabilising the precursor in step c). The carbon material precursor and the lignin may have any of the suitably features and advantages discussed in relation to the first aspect.

[0089] Suitably the carbon material precursor comprises at least 10 wt% of a thermoplastic elastomer, as defined in relation to the first aspect.

[0090] Step b) of the method of this second aspect is suitably as defined in relation to step b2) of the first aspect.

[0091] Step b) may be preceded by a step b1) of treating the carbon material precursor with a crosslinking agent. Step b1) is suitably as described in relation to step b) of the first aspect.

[0092] Step c) of the method of this second aspect is suitably as defined in the relation to step c) of the first aspect.

[0093] According to a third aspect of the present invention, there is provided a method of preparing a carbon material precursor for carbonisation, the method comprising the steps of: a) providing a carbon material precursor comprising a lignin; b) heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C; and c) treating the carbon material precursor with a crosslinking agent.

[0094] The steps of the method are suitably carried out in the order of step a) followed by step b) followed by step c).

[0095] The inventors have found that treating the carbon material precursor with a crosslinking agent after a heat treatment (stabilisation) step provides an improvement in the mechanical properties of the carbon material, for example carbon fibres, after carbonisation, for example an improvement in the Youngs modulus of the carbon material.

[0096] The carbon material precursor and the lignin may have any of the suitably features and advantages discussed in relation to the first aspect.

[0097] Suitably the carbon material precursor comprises at least 10 wt% of a thermoplastic elastomer, as defined in relation to the first aspect.

[0098] Step b) of the method of this third aspect is suitably as defined in the relation to step c) of the first aspect. Step c) of the method of this third aspect is suitably as defined in relation to step b) or step d) of the first aspect, suitably as defined in relation to step d) of the first aspect.

[0099] According to a fourth aspect of the present invention, there is provided a method of producing a carbon material, the method comprising the steps of:

[0100] 1) preparing a carbon material precursor for carbonisation according to the method of the first, second or third aspects;

[0101] 2) carbonising the carbon material precursor obtained in step 1) to provide the carbon fibre.

[0102] Suitably the steps of the method are carried out in the order step 1) followed by step 2).

[0103] Suitably, step 2) of the method comprises the steps of:

[0104] 2a) heating the carbon material precursor to a first temperature of from 100°C to 350°C in an atmosphere comprising oxygen;

[0105] 2b) heating the carbon material precursor to a second temperature of at least 800°C in an inert atmosphere.

[0106] Suitably step 2a) involves heating the carbon material precursor to a first temperature of at least 150 °C and suitably up to 350 °C, for example a temperature of approximately 250 °C, suitably at a heating rate of from 0.2 to 2°C per minute, suitably at a heating rate of from 0.5 to 1 .5°C per minute.

[0107] Suitably step 2b) involves heating the carbon material precursor to a second temperature of at least 800°C and suitably up to 2,000°C, for example a temperature of from 1 ,000 to 2,000°C, suitably approximately 1 ,000°C. Step 2b) may involve heating to such a temperature at a rate of from 0.5 to 50°C per minute or from 5 to 50°C per minute.

[0108] In some embodiments, the carbon material formed by the method of this fourth aspect is a carbon fibre.

[0109] In some embodiments, the carbon material formed by the method of this fourth aspect is a carbon foam.

[0110] According to a fifth aspect of the present invention, there is provided a material for use as a carbon material precursor, the material comprising a lignin; wherein the material comprises a coating and wherein the coating comprises a crosslinking agent.

[0111] The material of this fifth aspect may have any of the suitable features and advantages of the carbon material precursor described in relation to the first aspect. Suitably the material comprises at least 10 wt% of a thermoplastic elastomer.

[0112] The crosslinking agent may be as described in relation to the first aspect.

[0113] The coating on the material of this fifth aspect may be formed by a step b) of the method of the first aspect, or may be formed by a method of the first, second or third aspects of the present invention.

[0114] According to a sixth aspect of the present invention, there is provided a carbon material produced by a method of the fifth aspect.

[0115] In some embodiments, the carbon material of this sixth aspect is a carbon fibre.

[0116] In some embodiments, the carbon material of this sixth aspect is a carbon foam.

[0117] In some embodiments the methods of the present invention may be carried out as a continuous or semi-continuous process for producing, stabilising and carbonising carbon material precursors to provide carbon materials, in particular wherein the carbon material precursor is a carbon fibre precursor and the carbon material is a carbon fibre.

[0118] Examples

[0119] Materials: Alcell Organosolv hardwood lignin (TCA) and modified Kraft hardwood lignin (TCC) was obtained from Tecnaro GmbH. (Germany). Thermoplastic Polyurethane (TPU) (Lubrizol Estane Eco12T95) injection molding grade was supplied by Danquinsa GmbH, Germany. Methylene diphenyl diisocyanate (MDI), Toluene diisocyanate (TDI), boric acid and citric acid was obtained from Sigma Aldrich. Water used was at pure grade. N,N'-(methylenebis(4,1- phenylene))bis(1 Hbenzo[d][1 , 2, 3]triazole-1 -carboxamide) (MDI-B) was used as a crosslinker for TcA / TPU fibres since between 220-240°C, MDI isocyanate is liberated, linking TcA molecules through reaction with phenolic groups.

[0120] Example 1 : Fibres stabilised with MDI blocked crosslinkers

[0121] Stabilisation experiments were carried out in a Binder laboratory furnace by heating the test fibres to 250°C using a heating rate of 1 °C / min. Isothermal steps and heating ramps were combined in order to find the optimum temperature profiles for stabilisation. Carbonisation experiments were carried out using a tubular furnace heating from room temperature to 1000-1200°C.

[0122] N,N'-(methylenebis(4,1-phenylene))bis(1 Hbenzo[d][1 , 2, 3]triazole-1 -carboxamide) (MDI-B) was used as crosslinker for TcA / TPU fibers since, between 220-240°C MDI isocyanate is liberated, linking TcA molecules through reaction with phenolic groups.

[0123] MDI-B has the following structure:

[0124]

[0125] In order to test the effect of MDI-B on the stabilisation and the carbonisation of TcA / TPU fibres following samples were prepared (Table 1).

[0126] Table 1 - samples prepared using MDI-B crosslinker

[0127] Amount of Amount of TPU

[0128] Sample lignin (g) (g) Amount of MDI Total (g)

[0129] TcA-TPU-5-5 / 5% MDI

[0130] B 19 19 2 40

[0131] TcA-TPU-5-5 / 3%

[0132] MDI-B 19.4 19.4 1.2 40

[0133] TcA-TPU-5-5 / 2%

[0134] MDI-B 19.6 19.6 0.8 40

[0135] TcA-TPU-5-5 / 1 %

[0136] MDI-B 19.8 19.8 0.4 40

[0137] During the stabilisation step the fibres did not melt however, it was observed that the fibres elongate if a minimal stress is applied due to the loss of tenacity of the fibres during the heating process. To improve the tenacity several isothermal steps during the stabilisation were incorporated. The tests were carried out in a furnace holding the fibres with paper clips. The fibres heated directly from room temperature to 180°C showed a high degree of deformation. However, when the samples were heated until 170°C over 2 hours, deformation and elongation of the fibres was observed. Therefore, the experiment was continued with heating to 250°C at a heating rate of 1 °C / min. Isothermal steps were carried out for 2 hours at 180°C, at 200°C and at 250°C. The samples kept their approximate initial length during every stage of the stabilization process. However, after heating at 250°C the length of the fibres reduced, possibly due to some shrinkage caused by a crosslinking process as the MDI-B reacted with the TcA / TPU fibres. Dynamic mechanical analysis (DMA) was carried out in order to measure the evolution of the mechanical properties of the fibres during the stabilization process. Figure 1 shows the storage and loss modulus of TcA-TPU-5-5 / 3% MDI-B fibre as a function of the temperature for the TcA-TPU-5- 5 / 3% MDI-B fibre. Both the storage and loss modulus decrease with the temperature, indicating a loss of tenacity on heating to 150°C. After this point the fibres reached maximum elongation and approximately 50% of the fibres failed. The results showed a large drop in the storage modulus at lower temperatures (80-100°C).

[0138] In order to address this decrease in the properties of the fibres, the fibres were coated with a 5- 10 wt% solution of MDI in hexane. The fibres were dipped in the solution for 1 minute and then dried in air.

[0139] Figure 2 shows the storage and loss modulus of a TcA-TPU-5-5 / 3% MDI-B fibre coated with a MDI solution. The storage modulus of the fibre increased at 100°C, indicating a crosslinking reaction at that temperature range. With this coating it was possible to continue the DMA analysis until 250°C, without the fibre breaking. The following stabilization temperature profiles were established in these experiments:

[0140] 1) heating from room temperature to 150°C (heating rate 1 °C / min), then isothermal for 2 hours;

[0141] 2) heating from 150°C to 170°C (heating rate 1 °C / min), isothermal for 2 hours;

[0142] 3) heating from 170°C to 200°C (heating rate 1 °C / min), isothermal for 2 hours;

[0143] 4) heating from 200°C to 250°C (heating rate 1 °C / min), isothermal for 2 hours.

[0144] Figure 3 shows SEM images of the precursor fibres comprising different amounts of MDI-B, after treating with the MDI solution and stabilisation as described above. Figure 6 shows the morphology of the fibres as a function of the MDI-B content. Although, there is no phase separation observed, the roughness of the fibres increases with the addition of MDI-B due to the MDI-B is incorporated in powder form.

[0145] The stabilised fibres produced as described above were then carbonised by heating from room temperature to a temperature of from 1 ,000°C to 2,000°C in an inert atmosphere of nitrogen. The temperature was increased to said temperature at a rate of 5 to 50°C per minute.

[0146] Figure 4 shows SEM images of the carbon fibres produced from carbon fibre precursors comprising different amounts of MDI-B. Figure 4 shows the morphology of the carbon fibres produced form the samples TcA-TPU-5-5 / 3% MDI-B and TcA-TPU-5-5 / 5% MDI-B. The fibres show a clear crosssection with no voids indicating a good carbonisation behaviour. Figure 5 shows thermogravimetric analysis (TGA) results for the TcA-TPU-5-5 / MDI-B samples. The TGA results showed an increase of the carbon yield of the fibres with the addition of MDI-B. The carbon yields approached that of PAN precursor fibres.

[0147] Example 2: Stabilisation and carbonisation experiments of TcA / TPU and TcC / TPU multifilaments

[0148] One of the problems associated with the stabilisation of several fibres at once is that they stick together due to the softening that can occur on the fibre surface during stabilisation. In an attempt to solve this problem, the fibres were coated with a solution of a diisocyanate in an organic solvent prior to heat stabilisation. The precursor fibres were formed of 50 wt% TCA lignin and 50 wt% TPU (TCA- TPU 50-50). The diisocyante used was TDI and the solvent was hexane. The amounts of TDI used and further details of the fibres and heating profile are provided in Table 2. The fibres were dipped in a 10-20 wt% solution of TDI in hexane for 1 minute and then dried in air.

[0149] Table 2. Coatings prepared for TcA / TPU fibres samples.

[0150] The precursor fibres did not show the usual sticking effect during stabilisation, due to the coating of crosslinking agent. Therefore is was possible to heat stabilise multiple fibres together and also to subsequently carbonise multiple fibres together. This may provide process efficiency improvements in the production of such carbon fibres. Figure 6 shows a photograph and SEM images of TcA / TPU derived carbon fibres produced by this method involving coating with TDI followed by heat stabilisation.

[0151] Example 3: UV assisted Stabilisation of TCA / TPU multifilament precursor fibres with boric acid

[0152] Boric acid was used as a crosslinking agent in a similar process to that described above, wherein the organic solution of the diisocyanate was replaced with aqueous solutions of boric acid of different concentrations - 2, 5 and 10%. The precursor fibres were TCA-TPU 50:50. The effects of the different coating solutions were tested with regards to the crosslinking ratio (via FTIR analysis) and the carbon yield (via TGA).

[0153] Figure 7 shows the TGA results for the stabilised fibres after pretreatment in increasing concentration of boric acid (concentration in wt%, aqueous solution)

[0154] Figure 8 shows SEM images of the stabilised fibres after boric acid coating and heat stabilisation (using the procedure described in Example 2). The stabilised fibres retained a desired cylindrical shape and exhibited reduced fusion at higher concentrations of the boric acid coating solution.

[0155] The addition of UV light as a pretreatment was also investigated. The fibres were exposed to a UV light source (365nm / 254nm, 6-watt tubes) for 30 mins. Figure 9 shows the carbon yield of fibres as a function of concentration of boric acid in the coating solution and UV light treatment. The carbon yield for the TDI treatment of Example 2 is given as a point of reference. The carbon yield was significantly increased when combining boric acid coating and UV light irradiation, giving a carbon yield of 46%.

[0156] The effect of tension during stabilization was also investigated. The test fibres were hung in a multifibre tow with increasing weight. The maximum load before failure of the fibres was recorded. The elongation and final diameter of the fibres after tension were studied with varying crosslinker amount.

[0157] The fibres were stretched and their diameter contracted during the stabilization (Table 3). It was found that the use of boric acid coating limited the fusion of the fibres. The use of UV light allowed for higher amounts of elongation (up to 500 % elongation for UV treated-BA 1 % and BA 2%. UV light was also beneficial to the success rate of the stabilization with a decreased amount of breakages.

[0158] Table 3: Influence of the concentration of Boric Acid on the elongation and the diameter of the fibres without (a) and with (b) UV light exposure.

[0159]

[0160]

[0161] Finally, the effect of the stabilization method on the melting properties of the materials was tested by DSC. Figure 10 shows the melting events of the TCA / TPU blends after coating with various concentrations of boric acid followed by UV treatment and heat stabilisation treatment (as described above). The combined effect of the reactive coating and UV was beneficial to the efficiency of the stabilization by reducing the meltability of the material. Figure 11 shows SEM images of carbon fibres produced following carbonization of these carbon fibres treated with boric acid and UV light. The carbonisation successfully produced lignin-based carbon fibres with a retained cylindrical shape and minimal fusion between filaments.

[0162] Figure 12 shows the minimum diameter obtained for each carbon fibre composition with and without UV treatment prior to heat stabilization. The stabilization method was successful in stretching the fibres from 90 pm down to 20 pm or less.

[0163] Figure 11 shows the tensile strengths obtained for the carbon fibre precursors. Using this stretching method, the fibres obtained a tensile strength of 1 .05 + / - 0.1 GPa. This value is comparable to that of the state of the art.

[0164] Example 4: Stabilisation of TCA / TPU 3D printed beams using TDI and boric acid:

[0165] 3D printed beams of TCA / TPU were prepared by melt extrusion. TPU and lignin (50-50 w%t) were compounded and shaped into 1.75 mm filament in a melt extruder, between 160 to 200°C. The filament was processed into beams in a fusion deposition modelling set-up.

[0166] Figure 14 shows photographic images of the 3D printed beams after coatings at various concentrations of boric acid solutions and heat stabilisation. The images show that the higher concentration of boric acid in the coating solution allowed the shape of the 3D printed beam to be retained and therefore may allow for the carbonisation of relatively complex 3D structures for use in functional applications. Such carbon material may provide useful components, for example in sensors or batteries.

[0167] Example 5: Stabilisation and carbonisation of freeze-dried lignin-based hydrogels by TDI reactive coating for functional applications

[0168] Freeze-dried lignin-based hydrogels were prepared with three different amounts of PEGDGE. Three samples of hydrogels were prepared from solutions of organosolv lignin (TCA), which were produced by mixing 0.8 g (28.57 wt%) of TCA with 2 ml of a 3.3 mol I1NaOH solution. The solutions were magnetically stirred and left overnight (for 24 h) at 60°C to allow the complete dissolution of the TCA in the NaOH solution. The three solutions were loaded with varying amounts of PEGDGE crosslinking agents (0.4 g, 0.6 g and 0.8 g, respectively) to form the hydrogels. The hydrogel samples were labelled 0.4 HG, 0.6 HG and 0.8 HG, according to the PEGDGE content. Figure 15 shows SEM micrographs of the hydrogels after freeze drying, stabilisation and carbonisation for 0.4 HG, 0.6 HG and 0.8 HG. Figure 15 shows the morphology of the freeze-dried lignin-based hydrogels with the three different amounts of PEGDGE. All the hydrogels showed a macro porous structure with interconnected channels in a 3D arrangement. This morphology is typically observed in porous carbon materials derived from lignin. The structure was kept intact after thermal stabilisation. This processing step is necessary to avoid the fusion of lignin during the heat treatment. Finally, the carbonised materials retain a 3D, interconnected and complex structure with voids and pores. The size of the voids is dependent on the concentration of crosslinking agent, with smaller ones for a higher concentration.

[0169] Figure 16 shows FTIR spectra of (a) pristine lignin, (b) 0.4 HG, (c) 0.6 HG and (d) 0.8 HG after stabilisation.

[0170] Example 6: Stabilisation and carbonisation of TCA / TPU single fibres using citric acid / UV light

[0171] Single carbon precursor fibres were prepared as follows. TPU and lignin (50-50 %wt) were compounded and spun into 25 pm fibres in a melt extruder, at temperature between 160 and 200°C. The fibres were then coated with aqueous solutions of citric acid (CA). Concentrations of 0, 2, 5, 10 and 20 wt% citric acid were tested. The coating was carried out by immersing the fibres in the aqueous solution of citric acid at 50°C for 5 min, followed by drying and exposure to UV light for 1 hour. The coated fibres were then heat stabilized in air using a temperature ramp of 1 °C per min and isothermal steps of 1 h each at 100°C, 150°C, 170°C and 200°C.

[0172] Figure 17 shows carbon yields of the citric acid / UV treated and heat stabilised fibres after carbonisation. Carbonisation was carried out by heating the precursor fibres from room temperature to 1 ,000°C up to 2,000°C in nitrogen. Temperature ramps of 5 to 50°C per minute were used. The results show that a combination of citric acid and UV light was beneficial to the carbon yield. The addition of 10 to 20 wt% of citric acid increased the carbon yield up to 35%. The use of UV light allows the amount of citric acid to be reduced down to 2 wt% whilst still obtaining a good carbon yield.

[0173] Figure 18 shows DSC analyses of the citric acid / UV treated and heat stabilised fibres. The coating with the 20 wt% solution of citric acid provides a decrease of the melting event in the fibres, which become infusible. The carbonised fibres present no voids, are cylindrical and reach a diameter of 7.5 pm. Figures 19 and 20 show the mechanical properties of the carbon fibres according to their diameters, which were produced from precursor fibres coated with 10 and 20 wt% solutions of citric acid, respectively. Example 8: Post stabilisation treatment

[0174] Precursor fibres of TCA-TPU 50-50 were heat stabilized under tension, as described above, and then treated with a solution of TDI in hexane. The fibres were then carbonised in two steps as follows: heating from room temperature to 250°C at 1 °C per min in air and then heating from 250°C to 1 ,000°C in a nitrogen atmosphere.

[0175] Figure 21 shows the mechanical properties of the carbon fibres after said post stabilisation treatment with hexane / TDL It is believed that said post stabilisation treatment allows for in-situ crosslinking of the fibres during carbonisation to provide carbon fibres which exhibit the 272 GPa modulus noted in Figure 21 .

[0176] Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0177] Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of’ or “consists essentially of’ means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% by weight, typically less than 3% by weight, more typically less than 1 % by weight of non-specified components.

[0178] The term “consisting of’ or “consists of’ means including the components specified but excluding addition of other components.

[0179] Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to encompass or include the meaning “consists essentially of’ or “consisting essentially of’, and may also be taken to include the meaning “consists of’ or “consisting of’.

[0180] For the avoidance of doubt, wherein amounts of components in a composition are described in wt%, this means the weight percentage of the specified component in relation to the whole composition referred to. For example, “wherein the carbon material precursor comprises 30 to 90 wt% lignin” means that 30 to 90 wt% of the carbon material precursor is provided by lignin.

[0181] The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention as set out herein are also to be read as applicable to any other aspect or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each exemplary embodiment of the invention as interchangeable and combinable between different exemplary embodiments.

[0182] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0183] All of the features disclosed in this specification (including any accompanying claims, and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0184] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0185] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims1. A method of preparing a carbon material precursor for carbonisation, the method comprising the steps of: a) providing a carbon material precursor comprising a lignin; b) treating the carbon material precursor with a crosslinking agent; and c) heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C.

2. The method according to claim 1 , wherein step b) involves treating the carbon material precursor with a solution comprising at least 0.5 wt% of the crosslinking agent,3. The method according to claim 1 , wherein the solution comprising at least 0.5 wt% of the crosslinking agent comprises an aqueous solvent.

4. The method according to any one of the preceding claims, wherein the crosslinking agent is selected from a diisocyanate, boric acid or a carboxylic acid.

5. The method according to any one of the preceding claims, wherein the method comprises, after step b), a step: b2) irradiating the carbon material precursor with UV light.

6. The method according to any one of the preceding claims, wherein step c) involves heating the carbon material precursor at the temperature of from 100°C to 350°C for at least one hour.

7. The method according to any one of the preceding claims, wherein step c) involves heating the carbon material precursor to the temperature of from 100°C to 350°C at a heating rate of from 0.2 to 2°C per minute.

8. The method according to any one of the preceding claims, wherein the method comprises, after step c), a step: d) treating the carbon material precursor with a second crosslinking agent.

9. The method according to claim 8, wherein step d) involves treating the carbon material precursor with a solution comprising at least 0.5 wt% of the second crosslinking agent.

10. The method according to claim 9, wherein the solution comprising at least 0.5 wt% of the second crosslinking agent comprises an organic solvent.11 . The method according to any one of the preceding claims, wherein the carbon material precursor comprises at least 10 wt% of a thermoplastic elastomer, preferably wherein the thermoplastic elastomer of the carbon material precursor is a thermoplastic polyurethane.

12. The method according to any one of the preceding claims, wherein the carbon material precursor comprises at least 40 wt% of the lignin.

13. The method according to any one of the preceding claims, wherein the carbon material precursor comprises at least 30 wt% of the thermoplastic elastomer.

14. The method according to any one of the preceding claims, wherein the carbon material precursor comprises a third crosslinking agent.

15. A method of preparing a carbon material precursor for carbonisation, the method comprising the steps of: a) providing a carbon material precursor comprising a lignin; b) irradiating the carbon material precursor with UV light; and c) heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C.

16. A method of preparing a carbon material precursor for carbonisation, the method comprising the steps of: a) providing a carbon material precursor comprising a lignin; b) heat treating the carbon material precursor obtained from step b) by heating the carbon material precursor at a temperature of from 100°C to 350°C; and c) treating the carbon material precursor with a crosslinking agent.

17. The method according to any one of the preceding claims, wherein the carbon material precursor is a carbon fibre precursor and is in the form of a fibre.

18. The method according to any one of claims 1 to 16, wherein the carbon material precursor is a hydrogel or an aerogel.

19. A method of producing a carbon material, the method comprising the steps of:1) preparing a carbon material precursor for carbonisation according to the method of any one of claims 1 to 16;2) carbonising the carbon material precursor obtained in step 1) to provide the carbon fibre.

20. The method according to claim 19, wherein step 2) comprises the steps:2a) heating the carbon material precursor to a first temperature of from 100°C to 350°C in an atmosphere comprising oxygen;2b) heating the carbon material precursor to a second temperature of at least 800°C in an inert atmosphere.21 . The method according to claim 19 or claim 20, wherein the carbon material is a carbon fibre.

22. The method according to claim 19 or claim 20, wherein the carbon material is a carbon foam.

23. A material for use as a carbon material precursor, the material comprising a lignin; wherein the material comprises a coating and wherein the coating comprises a crosslinking agent.

24. A carbon material produced by the method of claim 19 or claim 20.

25. The carbon material of claim 24, which is a carbon fibre.

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