METHOD FOR RECYCLING COAL FIBERS

Abstract

A method for recycling carbon fibers, comprising: producing a carbon fiber-reinforced plastic product, comprising a carbon fiber-reinforced plastic containing carbon fibers and a resin; drawing the carbon fiber-reinforced plastic during a heat treatment of the carbon fiber-reinforced plastic product; removing the resin from the carbon fiber-reinforced plastic, which is drawn and conveyed; adding a sizing agent to the carbon fibers obtained by removing the resin; and winding the carbon fibers removed from the resin, wherein the temperature of the heat treatment is equal to or higher than a glass transition temperature of the resin and lower than a thermal decomposition start temperature, and the temperature is below a thermal degradation temperature of the carbon fibers; the carbon fiber-reinforced plastic is drawn upstream while the carbon fibers are wound downstream.The removal of the resin comprises bringing a solvent into contact with the carbon fiber reinforced plastic by immersing the drawn carbon fiber reinforced plastic into the solvent, and subsequently injecting the solvent from the nozzle, which is connected to an injection device, towards the carbon fiber reinforced plastic, and the starting temperature of the thermal decomposition of the resin is a temperature which indicates a 5% weight loss in a weight change plot of a thermogravimetric analysis, which is obtained by increasing the temperature of the resin from 30 °C to 550 °C at 5 °C / minute under an air atmosphere.

Description

BACKGROUND Technical area

[0001] The present invention relates to a method for recycling carbon fibers. State of the art

[0002] Carbon fiber reinforced plastic (CFRP) is a lightweight yet very rigid material capable of withstanding high hydrogen pressure. Therefore, it is used for molded carbon fiber products, such as hydrogen tanks for fuel cell vehicles. Furthermore, CFRP products are used in a wide range of applications beyond containers and tanks, including sports, leisure, and recreational products, as well as aerospace components. However, the carbon fibers used in CFRP are expensive, and their production emits a significant amount of CO2 and requires complex disposal processes, resulting in a substantial environmental impact.Therefore, a method for collecting and recycling carbon fibers from used carbon fiber reinforced, plastically molded products is being investigated.

[0003] For example, WO 2018 / 212016 A1 discloses a process for obtaining carbon fiber substrates as recycled carbon fiber bundles from a carbon fiber reinforced plastic containing a plurality of carbon fiber substrates and a matrix resin, which is a manufacturing process of the recycled carbon fiber bundle in which the carbon fiber reinforced plastic is heated to thermally decompose the matrix resin to obtain a heat-treated product, and wherein the heat-treated product is broken to separate the plurality of carbon fiber substrates. SUMMARY

[0004] As disclosed in WO 2018 / 212016 A1, a process for collecting carbon fibers from carbon fiber-reinforced, plastically molded products is investigated. However, because WO 2018 / 212016 A1 proposes a step of comminuting the matrix resin, continuous carbon fibers cannot be obtained. Therefore, carbon fibers that can be reused for molded products requiring continuous carbon fibers cannot be obtained.

[0005] Furthermore, WO 2018 / 212016 A1 describes the heating of carbon fiber-reinforced plastic at high temperatures to thermally decompose the matrix resin. However, heating at high temperatures may potentially degrade or weaken the carbon fibers and reduce their strength. Additionally, heating the carbon fiber-reinforced plastic at high temperatures may alter the resin properties, such as solubility, and cause difficulties in resin removal during subsequent processes.

[0006] Furthermore, WO 2018 / 212016 A1 proposes preserving the carbon fibers by removing the matrix resin. However, it is assumed that by suppressing the deterioration or reduction of the matrix resin and dissolving the carbon fiber reinforced plastic, it is possible to reuse the carbon fiber reinforced plastic without removing the matrix resin.

[0007] The present embodiment was developed taking into account the problems described above. For example, the embodiment provides a method for recycling carbon fibers that can yield continuous carbon fibers. Furthermore, for example, the embodiment can provide a method for recycling carbon fibers that can yield continuous carbon fibers while suppressing the degradation or reduction of the carbon fibers. Furthermore, for example, the embodiment provides a method for recycling carbon fibers that can yield a carbon fiber-reinforced plastic while suppressing the degradation or destruction of the carbon fibers. Furthermore, for example, the embodiment provides a method for recycling carbon fibers that can yield a carbon fiber-reinforced plastic while suppressing the degradation of a resin.Furthermore, for example, the embodiment provides a method for recycling carbon fibers which can obtain a carbon fiber reinforced plastic while suppressing the deterioration of the carbon fibers and the resin.

[0008] One aspect of the present embodiment is as follows. (1) A process for recycling carbon fibers, comprising: Manufacturing a carbon fiber reinforced, plastically molded product comprising a carbon fiber reinforced plastic containing carbon fibers and a resin; and Drawing or stretching the carbon fiber reinforced plastic while heat treatment is being carried out on the carbon fiber reinforced, plastically formed product, wherein a heat treatment temperature is equal to or higher than a glass transition temperature of the resin and lower than a starting temperature of thermal decomposition, and the temperature is below a temperature of thermal deterioration of the carbon fibers. (2) The procedure according to (1), wherein the starting temperature of the thermal decomposition of the resin is a temperature which indicates a 5% weight loss in a weight change plot of a thermogravimetric analysis, which is obtained by increasing the temperature of the resin from 30°C to 550°C at 5°C / minute under a nitrogen atmosphere. (3) The procedure according to (1), where the starting temperature of the thermal decomposition of the resin is a temperature which indicates a 5% weight loss in a weight change plot of a thermogravimetric analysis, which is obtained by increasing the temperature of the resin from 30°C to 550°C at 5°C / minute under an air atmosphere. (4) The procedure according to one of (1) to (3), where the temperature of the heat treatment is below 400 °C. (5) The procedure according to one of (1) to (4), where the temperature of the heat treatment is equal to or below 360 °C. (6) The procedure according to one of (1) to (5), further comprising Removing the resin from the drawn or stretched carbon fiber reinforced plastic. (7) The procedure according to (6), where the removal of the resin involves bringing a solvent into contact with the carbon fiber reinforced plastic. (8) The procedure according to (7), wherein the solvent contains at least one liquid selected from an acidic solution, an organic solvent, an aqueous hydrogen peroxide, or an ionic liquid. (9) The procedure according to (7) or (8), where the solvent is an acidic solution. (10) The procedure according to one of (6) to (9), further comprising Winding or coiling the carbon fibers, which are removed from the resin. (11) The procedure referred to in (10), further comprising: Pulling or stretching the carbon fiber reinforced plastic during heat treatment; Removing the resin from the carbon fiber reinforced plastic that is drawn and transferred; and Winding or coiling the carbon fibers, which are removed from the resin, the carbon fiber reinforced plastic is pulled upstream, while the carbon fibers are wound upstream. (12) The method according to one of (1) to (5), further comprising cutting the drawn carbon fiber reinforced plastic. (13) The procedure according to one of (1) to (12), the heat treatment is carried out using supercritical steam. (14) The procedure according to one of (1) to (13), wherein the resin comprises a heat-curing or thermosetting resin or a thermoplastic resin. (15) The procedure according to one of (1) to (14), the resin comprises an epoxy resin.

[0009] According to one aspect of the present embodiment, for example, a method for recycling carbon fibers that can obtain continuous carbon fibers can be provided. Furthermore, according to one aspect of the present embodiment, for example, a method for recycling carbon fibers that can obtain continuous carbon fibers while suppressing the degradation or degradation of the carbon fibers can be provided. Furthermore, according to one aspect of the present embodiment, for example, a method for recycling carbon fibers that can obtain a carbon fiber-reinforced plastic while suppressing the degradation or degradation of the carbon fibers can be obtained.Furthermore, according to one aspect of the present embodiment, for example, a method for recycling carbon fibers can be provided which can obtain a carbon fiber-reinforced plastic while suppressing the deterioration of a resin. Furthermore, according to one aspect of the present embodiment, for example, a method for recycling carbon fibers can be provided which can obtain a carbon fiber-reinforced plastic while suppressing the deterioration of both the carbon fibers and the resin. List of characters Fig. 1 is an exemplary flowchart to describe a process according to the present embodiment; Fig. Figure 2 is a schematic cross-sectional view showing an exemplary configuration of a container 100 as a carbon fiber reinforced, plastically formed product; Fig. Figure 3 is a schematic diagram describing one step of the drawing process under heat in the present embodiment; Fig. Figure 4A is a graph representing an exemplary thermal property of an epoxy resin, where the graph (horizontal axis: temperature, vertical axis: weight loss rate) represents a weight change plot (curved line TG) of a thermogravimetric analysis obtained by increasing the temperature of the resin under a nitrogen atmosphere; Fig. Figure 4B is a graph representing an exemplary thermal property of an epoxy resin, where the graph (horizontal axis: temperature, vertical axis: weight loss rate) represents a weight change plot (curved line TG) of a thermogravimetric analysis obtained by increasing the temperature of the resin under an air atmosphere; Fig. Figure 5 is a graph representing a thermal property of carbon fibers, where the graph represents a strength ratio (tensile strength after heating / tensile strength before heating) when heating the carbon fibers in air at a predetermined temperature (300 °C, 400 °C, 500 °C) for a predetermined time period (horizontal axis); Fig. Figure 6 is a graph that represents a tensile shear strength ratio (tensile shear strength during heating / tensile shear strength before heating) at a predetermined temperature of the epoxy resin; Fig. Figure 7 is a schematic diagram describing a configuration of a test piece used in a tensile shear strength test to measure a Fig. 6 tensile shear strength ratio is used; Fig. Figure 8 is a photograph of the carbon fibers, observed using SEM after immersion of the carbon fiber reinforced plastic in concentrated sulfuric acid to dissolve and remove the resin; Fig. Figure 9 is a schematic diagram to describe one aspect of the present embodiment; Fig. Figure 10 is a schematic diagram to describe one aspect of the present embodiment; and Fig. Figure 11 is a schematic diagram to describe one aspect of the present embodiment. DETAILED DESCRIPTION

[0010] The present embodiment is a method for recycling carbon fibers, comprising a step of producing a carbon fiber-reinforced, plastically formed product containing a carbon fiber- and resin-containing carbon fiber-reinforced plastic, and a step of drawing the carbon fiber-reinforced plastic while heat treatment is performed on the carbon fiber-reinforced, plastically formed product. The heat treatment temperature is equal to or higher than the glass transition temperature of the resin and lower than the temperature of thermal decomposition, and the temperature is below the temperature of thermal deterioration or thermal degradation of the carbon fibers.

[0011] The following describes the present embodiment in detail.

[0012] The present embodiment is a method for recycling carbon fiber reinforced, plastically formed products.

[0013] A carbon fiber-reinforced, plastically molded product comprises a carbon fiber-reinforced plastic containing carbon fibers and a resin. The carbon fibers are continuous carbon fibers. The carbon fiber-reinforced, plastically molded product is not particularly limited and includes, for example, a container or tank. The container can, for example, be a hydrogen tank for storing hydrogen. In the following example, a container is mainly used as an example of a carbon fiber-reinforced, plastically molded product, but the present embodiment is not limited thereto. Although the present embodiment relates to a method for recycling carbon fibers, in the present invention the method for recycling carbon fibers is understood to be a method for producing carbon fibers and / or carbon fiber-reinforced plastics from a carbon fiber-reinforced, plastically molded product.

[0014] Fig. Figure 1 presents an exemplary flowchart to describe a process according to the present embodiment. As in Fig. As shown in Figure 1, the present embodiment comprises at least the step of manufacturing the shaped product and the step of drawing it under heat. Each step is described in detail below. (Step of manufacturing the shaped product)

[0015] A recycling process according to the present embodiment comprises a step of producing a carbon fiber reinforced, plastically molded product comprising a carbon fiber reinforced plastic which contains carbon fibers and a resin.

[0016] As described above, the carbon fiber reinforced plastically molded product is not particularly limited and includes, for example, a container or tank. The carbon fiber reinforced plastically molded product to be manufactured may, for example, be one that is subsequently used for specific purposes after manufacture and collection, and a defective product at the manufacturing stage.

[0017] Fig. Figure 2 is a cross-sectional view showing an exemplary configuration of a tank 100. Fig. Figure 2 shows a cross-sectional view taken along a surface that is parallel to and passes through the central axis of the tank 100. The central axis of the tank 100 corresponds to the axis that passes through the center of a circle of the main body of the tank, which has an approximately cylindrical shape. The tank 100 can be used, for example, for filling with gas, such as compressed hydrogen. For example, the tank 100, filled with compressed hydrogen, is mounted or attached to a fuel cell vehicle to supply hydrogen to a fuel cell.

[0018] The tank 100 comprises a liner 10 (made of nylon resin), a carbon fiber-reinforced resin layer 20 as an outer shell, a valve-side base 30, an end-side base 40, and a valve 50. Furthermore, a protective layer 60 is arranged between the liner 10 and the carbon fiber-reinforced resin layer 20. The liner 10 has a hollow shape, which is provided with a space filled with hydrogen and has a gas barrier property to seal the inner space and prevent the hydrogen from escaping.

[0019] The carbon fiber-reinforced resin layer 20 is a resin layer designed to cover the outer surfaces of the liner 10 and the protective layer 60. The carbon fiber-reinforced resin layer 20 is designed to cover an outer surface of the protective layer 60. The protective layer 60 is designed to cover an inner surface of the carbon fiber-reinforced resin layer 20 and also parts of the bases 30 and 40. The primary function of the carbon fiber-reinforced resin layer 20 is to reinforce the liner 10 (reinforcing layer). The liner 10 is designed to cover an inner surface of the protective layer 60.

[0020] In Fig. 2 The valve-side base 30 has an approximately cylindrical shape and is inserted and secured between the liner 10 and the protective layer 60. An approximately cylindrical opening in the valve-side base 30 functions as an opening in the tank 100. In the present embodiment, the valve-side base 30 can be made of stainless steel, for example, but it can also be made of other metals, such as aluminum, or of resin. A screw with an external thread is formed in a column-shaped section of the valve 50 and is screwed through the external thread into a screw with an internal thread formed on an inner surface of the valve-side base 30, with the opening of the valve-side base 30 being closed by the valve 50. The end base 40 can be made of, for example, aluminum and is assembled such that a portion of it faces the outside orexposed to the outside in order to conduct heat from inside the tank to the outside.

[0021] The carbon fiber reinforced resin layer contains the carbon fibers and a resin (matrix resin).

[0022] The resin is not particularly limited and includes, for example, phenolic resin, urea resin, unsaturated polyester resin, vinyl ester resin, polyimide resin, bismaleimide resin, polyurethane resin, diallyl phthalate resin, epoxy resin, or a mixture thereof. In some embodiments, the epoxy resin is used. Any epoxy resin generally known in the technical field may be used. The epoxy resin is not limited and includes, for example, a bisphenol A-type epoxy resin, a bisphenol AD-type epoxy resin, a bisphenol F-type epoxy resin, a phenol novolac-type epoxy resin, a cresol novolac-type epoxy resin, or a glycidyl ester-type epoxy resin. The epoxy resin may be of the straight or linear chain type or of the branched type. One type of resin may be used alone, or two or more types may be used together or in combination.The resin can be, for example, a thermoplastic resin or a thermosetting resin. In some embodiments, the resin comprises the thermoplastic resin.

[0023] The carbon fibers can be produced using a process generally known in the technical field. It is only necessary that the carbon fibers are materials containing carbon as the main component and can, for example, be carbon fibers that use acrylic as a starting material, carbon fibers that use resin as a starting material, or carbon fibers that use polyvinyl alcohol as a starting material. In particular, PAN-based carbon fibers, produced using polyacrylonitrile fibers as a starting material, are used in some embodiments.

[0024] The carbon fiber-reinforced resin layer can be formed, for example, by a precision winding process. A product formed by precision winding can be manufactured by aligning multiple carbon fiber bundles as needed, impregnating the carbon fiber bundles with a matrix resin, and winding the carbon fiber bundles onto a rotating substrate or mold at a suitable angle by applying tension until a suitable thickness is achieved. (Step of pulling or stretching while heating)

[0025] The recycling process according to the present embodiment comprises a step of drawing the carbon fiber-reinforced plastic while a heat treatment is carried out on the carbon fiber-reinforced, plastically formed product. Furthermore, the temperature of the heat treatment is equal to or above a glass transition temperature and below a temperature of thermal deterioration of the resin, and the temperature is below a starting temperature of thermal decomposition of the carbon fibers.

[0026] The heat treatment in the present embodiment allows the resin in the carbon fiber-reinforced, plastically formed product to soften, while suppressing thermal degradation of the resin and a decrease in the strength of the carbon fibers. In the present embodiment, because the carbon fiber-reinforced, plastically formed product is heated to or above the glass transition temperature of the resin, the resin in the carbon fiber-reinforced, plastically formed product becomes softer. In this embodiment, because the carbon fiber-reinforced plastic is drawn or stretched during the heat treatment to soften the resin, the carbon fiber-reinforced plastic can be easily drawn from the carbon fiber-reinforced, plastically formed product.In particular, the carbon fiber-reinforced plastic can be drawn from the carbon fiber-reinforced, plastically formed product using a smaller tensile force. Using a small tensile force for drawing helps to suppress cracking and damage to the carbon fibers. Meanwhile, in the present embodiment, since the carbon fiber-reinforced, plastically formed product is heated to a temperature below the thermal decomposition start temperature, the thermal decomposition of the resin can be suppressed. By suppressing the thermal decomposition of the resin, excessive deformation and carbonization of the resin can be prevented, and as a result, even in a case where solution treatment is carried out in a subsequent process, the resin in the carbon fiber-reinforced plastic can be easily dissolved.Furthermore, by suppressing the thermal decomposition of the resin, the reduction in resin strength can be suppressed, and therefore the drawn carbon fiber-reinforced plastic can itself be used for other purposes or undergo desired treatments (such as cutting) without the step of resin removal. Moreover, in the present embodiment, since the carbon fiber-reinforced, plastically formed product is heated below the temperature of thermal degradation of the carbon fibers, the thermal degradation of the carbon fibers can be suppressed, and the reduction in the strength of the carbon fibers can likewise be suppressed.

[0027] As described above, in the recycling process according to the present embodiment, the carbon fiber reinforced plastic is drawn while a heat treatment is carried out on the carbon fiber reinforced, plastically formed product.

[0028] In the present embodiment, “drawing or stretching the carbon fiber-reinforced plastic” means drawing or stretching the carbon fiber-reinforced plastic in a continuous state from the carbon fiber-reinforced, plastically formed product, and also includes the concept of stripping the carbon fiber-reinforced plastic from the carbon fiber-reinforced, plastically formed product. In the present embodiment, since the carbon fiber-reinforced plastic is drawn in a state in which the resin in the carbon fiber-reinforced, plastically formed product is softened by heating, the carbon fiber-reinforced plastic can be drawn easily. When drawing the carbon fiber-reinforced plastic from the carbon fiber-reinforced, plastically formed product, a blade-shaped tool can be used to tear off the carbon fiber-reinforced plastic.Bringing the blade-shaped tool into contact with a part (resin part) between the carbon fiber reinforced plastic and the molded product, in order to separate the molded product and the carbon fiber reinforced plastic at a bonding section (resin part) between the molded product and the carbon fiber reinforced plastic, facilitates the separation of the carbon fiber reinforced plastic.

[0029] The process of drawing the carbon fiber reinforced plastic is not particularly limited, and, for example, drawing is possible by directly or indirectly connecting an end section of the carbon fiber reinforced plastic to a winding roll and rotating the roll.

[0030] Heat treatment can be carried out, for example, inside a heat treatment chamber. The carbon fiber-reinforced, plastically formed product is heated inside the chamber to soften the matrix resin. The heat treatment chamber can be a furnace or a heating device with a chamber that internally introduces and / or discharges the heating medium.

[0031] A process for drawing the carbon fiber reinforced plastic while heat treatment is being carried out on the carbon fiber reinforced, plastically formed product can, for example, be described in Fig. Figure 3 describes a method for arranging the carbon fiber-reinforced, plastically formed product in the heat treatment chamber and withdrawing a portion of the carbon fiber-reinforced plastic from the heat treatment chamber during the heat treatment process. The carbon fiber-reinforced plastic can, for example, be transferred to the outside through a discharge opening located on a part of the heat treatment chamber. This transfer of the carbon fiber-reinforced plastic can be successfully carried out, for example, by a transfer or conveying roller.

[0032] In the present embodiment, the temperature of the heat treatment is equal to or higher than the glass transition temperature and below the starting temperature of the thermal decomposition of the resin, and the heat treatment is below the temperature of the thermal degradation or deterioration of the carbon fibers.

[0033] In the present embodiment, the resin softens or softens upon heating the carbon fiber-reinforced, plastically formed product at or above the resin's glass transition temperature, and the carbon fiber-reinforced plastic can be drawn under a small tensile force. Furthermore, drawing with a small tensile force also ensures the suppression of cracking and damage to the carbon fibers. Heating the carbon fiber-reinforced, plastically formed product at a temperature below the resin's thermal decomposition start temperature ensures the suppression of thermal decomposition.By suppressing the thermal decomposition of the resin, excessive deformation and carbonization can be prevented. As a result, even in cases where solution treatment is performed in a subsequent process, the resin in the carbon fiber reinforced plastic can be easily dissolved using the solvent. Furthermore, suppressing the thermal decomposition of the resin prevents a reduction in its strength, and the drawn carbon fiber reinforced plastic can be used for other purposes or, in some cases, can undergo desired treatments (such as cutting) without the need for resin removal.

[0034] The starting temperature of thermal decomposition can be measured using a heat-weight measuring device.

[0035] In the present embodiment, the starting temperature of the thermal decomposition can be a temperature that indicates a 5% weight loss in a weight change plot of a thermogravimetric analysis, obtained by increasing the temperature of the resin from 30 °C to 550 °C at 5 °C / minute under a nitrogen atmosphere. Alternatively, the starting temperature of the thermal decomposition can be a temperature that indicates a 3% weight loss in a weight change plot of a thermogravimetric analysis, obtained by increasing the temperature of the resin from 30 °C to 550 °C at 5 °C / minute under a nitrogen atmosphere.The starting temperature of thermal decomposition can be a temperature that indicates a 1% weight loss in a thermogravimetric analysis plot obtained by increasing the resin temperature from 30 °C to 550 °C at a rate of 5 °C / minute under a nitrogen atmosphere. It is generally assumed that the aforementioned starting temperature of thermal decomposition under a nitrogen atmosphere is the starting temperature for the decomposition of a main chain and / or side chain of the resin.

[0036] In the present embodiment, the starting temperature of the thermal decomposition can be a temperature that indicates a 5% weight loss in a thermogravimetric analysis obtained by increasing the resin temperature from 30 °C to 550 °C at a rate of 5 °C / minute under an atmospheric atmosphere. The starting temperature of the thermal decomposition can be a temperature that indicates a 3% weight loss in a thermogravimetric analysis obtained by increasing the resin temperature from 30 °C to 550 °C at a rate of 5 °C / minute under an atmospheric atmosphere. The starting temperature of the thermal decomposition can be a temperature that indicates a 1% weight loss in a thermogravimetric analysis obtained by increasing the resin temperature from 30 °C to 550 °C at a rate of 5 °C / minute under an atmospheric atmosphere.In general, when heating is carried out in air, since oxidative deterioration progresses due to oxygen present in the air, the initial temperature of thermal decomposition measured in an air atmosphere is below the initial temperature of thermal decomposition measured in a nitrogen atmosphere, assuming that the weight loss ratios in the two atmospheres are the same.

[0037] In the present embodiment, a reduction in the strength of the carbon fibers can be suppressed by heating the carbon fiber-reinforced, plastically formed product below the temperature of thermal deterioration of the carbon fibers. The temperature of thermal deterioration of the carbon fibers can be defined as the lowest temperature at which a reduction in tensile strength or tensile strength of 1% or more occurs, in a case where the heat treatment of the carbon fibers is carried out in air. By measuring the tensile strength before and after the heat treatment of the carbon fibers used in the carbon fiber-reinforced plastic, a reduction in strength can be calculated.

[0038] In one embodiment, the temperature of the heat treatment can be equal to or higher than 100 °C, equal to or higher than 120 °C, equal to or higher than 140 °C, equal to or higher than 160 °C, equal to or higher than 180 °C, or equal to or higher than 200 °C. Furthermore, the temperature of the heat treatment can be below 400 °C, equal to or less than 390 °C, equal to or less than 380 °C, equal to or less than 370 °C, equal to or less than 360 °C, equal to or less than 350 °C, equal to or less than 340 °C, equal to or less than 330 °C, equal to or less than 320 °C, equal to or less than 310 °C, equal to or less than 300 °C, equal to or less than 290 °C, or equal to or less than 280 °C.In cases where the heat treatment temperature is equal to or above 100 °C, the resin in the carbon fiber reinforced plastic can be effectively softened. In cases where the heat treatment temperature is less than 400 °C, the thermal degradation of the resin in the carbon fiber reinforced plastic can be easily suppressed, and the deterioration of the carbon fibers can also be easily suppressed. The upper and / or lower limits of these numerical ranges can be conveniently combined to specify intended ranges.

[0039] For example, the glass transition temperature of epoxy resin is approximately 100 °C to 200 °C, and the thermal decomposition start temperature is approximately 240 °C to 360 °C. Heating to a temperature equal to or above the thermal decomposition start temperature causes excessive thermal decomposition, and the resin's strength decreases significantly. Furthermore, excessive deformation and carbonization of the resin occur, making it difficult to dissolve and remove the resin using a solvent. Fig. Figure 4A relates to an exemplary epoxy resin, showing a weight change plot of the thermogravimetric analysis obtained by increasing the temperature of the resin from 30 °C to 550 °C at 5 °C / minute under a nitrogen atmosphere. Fig. 4A is a temperature that indicates a 5% weight loss, approximately 350 °C, which can be described as the starting temperature of thermal decomposition. Furthermore, it concerns Fig. 4B an exemplary epoxy resin, wherein a weight change plot of a thermogravimetric analysis obtained by increasing the temperature of the resin from 30 °C to 550 °C at 5 °C / minute under an air atmosphere is shown. Fig. 4A and Fig. 4B also represent turning points. In Fig. 4B is a temperature that indicates a 5% weight loss, approximately 340 °C, which in the present embodiment can be referred to as the thermal decomposition start temperature. As described above, when heating is carried out in air, because oxidative deterioration progresses due to oxygen in the air, the thermal decomposition start temperature measured in an air atmosphere is lower than the thermal decomposition start temperature measured in a nitrogen atmosphere, assuming the weight loss ratios in both atmospheres are the same. At a temperature equal to or above the thermal decomposition start temperature, thermal decomposition of the resin occurs excessively, allowing for excessive decomposition of the main chain and / or side chain of the resin and, in some cases, causing carbonization of the resin.When such thermal decomposition occurs, it becomes difficult to dissolve and remove the resin using the solvent. Furthermore, because the strength of the resin decreases, the carbon fiber-reinforced plastic itself can no longer be used. However, within a range specified in the present embodiment—within the glass transition temperature or higher and lower than the starting temperature of the thermal decomposition—because the resin can be softened while thermal decomposition is suppressed, a high-quality continuous carbon fiber-reinforced plastic can easily be obtained by drawing the carbon fiber-reinforced plastic in this state. Thermogravimetric analysis is a method for measuring the change in weight in a case where the temperature of the substance is changed according to a predetermined program.In the present embodiment, a thermogravimetric analysis can be carried out by measuring a change in weight in a case, wherein, for example, a sample of approximately 10 mg is placed in a container made of aluminium, aluminium oxide or platinum, and the temperature is increased at a constant heating rate (5 °C / minute).

[0040] In the present embodiment, with regard to more efficient suppression of the thermal decomposition of the resin, the temperature of the heat treatment can be 1 °C or more below the start temperature of thermal decomposition, 5 °C or more below the start temperature of thermal decomposition, 10 °C or more below the start temperature of thermal decomposition, 15 °C or more below the start temperature of thermal decomposition, 20 °C or more below the start temperature of thermal decomposition, 25 °C or more below the start temperature of thermal decomposition, or 30 °C or more below the start temperature of thermal decomposition.

[0041] Fig. Figure 5 is a graph representing the thermal properties of carbon fibers, where the graph depicts a strength ratio (tensile strength after heating / tensile strength before heating) when the carbon fibers are heated in air at a predetermined temperature (300 °C, 400 °C, 500 °C) for a predetermined time period (horizontal axis). As in Fig. As shown in Figure 5, it can be understood that the strength of the carbon fibers does not decrease even when the carbon fibers are heated to 400 °C. Similarly, it can be understood that the strength of the carbon fibers does not decrease when they are heated to 500 °C, a temperature used in conventional heat treatments. This is thought to result from oxidative degradation of the carbon fibers caused by heat and oxygen. It is generally assumed that in many cases, the starting temperature of the thermal decomposition of the resin is below the temperature of thermal degradation of the carbon fibers.

[0042] Fig. Figure 6 is a graph representing the tensile shear strength ratio at a predetermined temperature of the resin (epoxy resin, see [reference]). Fig. 4A and Fig. 4B). In particular, Fig. Figure 6 shows a tensile shear strength ratio (tensile shear strength during heating / tensile shear strength before heating (strength at 23 °C), vertical axis, • mark) at a predetermined temperature (23 °C, 100 °C, 150 °C, 250 °C, horizontal axis). The dotted line from 250 °C to 350 °C represents a virtual curved line. As in Fig. As shown in Figure 7, tensile shear strength is the strength that occurs when two plates are bonded by resin and an adhesive-bonded section is fractured by shear stress, which is a load that attempts to move the adhesives in opposite directions to each other. As shown in Figure 7, tensile shear strength is the strength that occurs when two plates are bonded by resin and a section bonded with adhesive is fractured by shear stress, which is a load that attempts to move the adhesives in opposite directions. Fig. As shown in Figure 6, the tensile shear strength decreases when the resin heating temperature is increased. In a state where the tensile shear strength decreases, the carbon fiber reinforced plastic can be drawn more easily. For example, in a case where the heating temperature is 150 °C, the tensile shear strength ratio is 0.2 or less, and the tensile shear strength during heating is 20% or less compared to the tensile shear strength before heating, indicating that the carbon fiber reinforced plastic can be drawn using less force.In the present embodiment, the temperature of the heat treatment can be a temperature at which the tensile shear strength ratio is 20% or less, a temperature at which the tensile shear strength ratio is 15% or less, a temperature at which the tensile shear strength ratio is 10% or less, or a temperature at which the tensile shear strength ratio is 5% or less.

[0043] In the present embodiment, the carbon fiber-reinforced, plastically formed product is not normally crushed or pulverized. Only a tubular section of a tank can be used as the carbon fiber-reinforced, plastically formed product. Metal components and the like in the carbon fiber-reinforced, plastically formed product can be removed before or after the heating step.

[0044] The heating process is not particularly limited. For example, it can be heating in air. Heat treatment in air is easy to carry out and is also advantageous in terms of cost. In particular, the present embodiment is effective because damage to the carbon fibers can be suppressed, even under conditions where oxygen is present in air or similar environments. Furthermore, the heat treatment can be carried out using supercritical steam. By using supercritical steam, the oxygen-containing fraction of air in a treatment atmosphere can be reduced, and thus decomposition and damage to the carbon fibers can be efficiently suppressed. For example, the heat treatment can be carried out by introducing supercritical steam at atmospheric pressure into an atmospheric pressure reaction vessel.Furthermore, the heat treatment is not particularly restricted, but can be carried out under an inert atmosphere, such as nitrogen. The heat treatment can also be carried out by introducing heated, supercritical steam and / or inert gas (such as nitrogen) into the heat treatment chamber.

[0045] In the carbon fiber recycling process according to the present embodiment, the carbon fiber-reinforced plastic drawn under heat during the drawing step remains in a bundled state formed by the carbon fibers and the matrix resin. As described above in the present embodiment, the carbon fiber-reinforced plastic can be reused directly, since the reduction in strength of the resin and the carbon fibers is suppressed. Furthermore, depending on the application, the resulting carbon fiber-reinforced plastic can be reused by desired processing treatments. For example, the processing treatment could involve cutting the carbon fiber-reinforced plastic into desired dimensions. For instance, a sheet-shaped product can be produced by hardening the cut carbon fiber-reinforced plastic, which is suitably mixed with binder resin and the like. (Step of removal)

[0046] The recycling process according to the present embodiment can include a step of removing the resin from the carbon fiber-reinforced plastic to obtain the carbon fibers. The method of removing the resin from the carbon fiber-reinforced plastic is not particularly restricted, but can involve dissolving and removing it using a solvent. Dissolving and removing the resin using a solvent can suppress the deterioration or degradation of the carbon fibers.

[0047] The following describes a step of loosening or dissolving and removing the resin using a solvent as an exemplary removal step.

[0048] The dissolving and removal step is a step of removing the resin in the drawn carbon fiber reinforced plastic by dissolving the resin using the solvent fluid.

[0049] In one embodiment, the resin in the drawn carbon fiber-reinforced plastic is removed during the dissolving and removal step. By bringing the carbon fiber-reinforced plastic into contact with the solvent, the resin can be dissolved and removed. Dissolving and removing the resin avoids thermal stress and suppresses the degradation or deterioration of the carbon fibers. In particular, removal using the solvent results in less degradation or deterioration of the carbon fibers than removal by thermal decomposition. Furthermore, in the present embodiment, since excessive deformation and carbonization of the resin are suppressed during the drawing step under heat, which is the preceding step, the resin in the carbon fiber-reinforced plastic can be dissolved efficiently.

[0050] Resin removal is carried out using a solvent capable of dissolving the resin in the carbon fiber reinforced plastic. The solvent simply needs to be one that can dissolve the resin and could, for example, be at least one liquid selected from an acidic solution, an organic solvent, an aqueous hydrogen peroxide solution, or an ionic liquid. These liquids can dissolve the resin and cause it to swell, thus facilitating its efficient removal. One type of solvent can be used alone, or two or more types can be used together or in combination.

[0051] The acidic solution can be, for example, phosphoric acid and sulfuric acid. The acidic solution can be, for example, a solution containing sulfuric acid (for example, with a density of 90% by mass or more), as described in the unexamined Japanese patent application with publication number 2020-37638, or a solution containing phosphoric acid, as described in the unexamined Japanese patent application with publication number 2020-50704. One type of acidic component can be used alone, or two or more types can be used together or in combination.

[0052] The organic solvent can be, for example, an aliphatic hydrocarbon-based solvent, an aromatic hydrocarbon-based solvent, an alcohol-based solvent, a ketone-based solvent, an ether-based solvent, an amide-based solvent, or an ester-based solvent. One type of organic solvent can be used alone, or two or more types can be used together or in combination. For example, the aliphatic hydrocarbon-based solvent could be pentane, hexane, heptane, or octane. The aromatic hydrocarbon-based solvent could be, for example, benzene, toluene, or xylene. An organic solvent comprising two or more of these components could be, for example, petroleum ether, white spirit, or ligroin.The organic solvent may include a decomposition catalyst. The decomposition catalyst may, for example, be an alkali metal compound, as described in the unexamined Japanese patent application with publication number 2020-45407.

[0053] The ionic liquid can, for example, be an ionic liquid comprising at least one cation selected from an imidazolium-based cation, a pyridinium-based cation, a pyrrolidinium-based cation, a quaternary ammonium-based cation, or a quaternary phosphonium-based cation. One type of ionic liquid can be used alone, or two or more types can be used together or in combination.

[0054] Fig. Figure 8 is a SEM-observed photograph of the carbon fibers, which were obtained by dissolving and removing the resin through immersion of the carbon fiber-reinforced plastic in concentrated sulfuric acid. The temperature of the concentrated sulfuric acid can be, for example, 100 °C to 300 °C. As in Fig. As stated in section 8, the resin can be efficiently removed from the carbon fiber-reinforced plastic using the solvent. Furthermore, no significant reduction or decrease in the strength of the carbon fibers was observed after resin removal using the solvent.

[0055] The dissolving and removal of the resin is achieved by bringing the solvent into contact with the carbon fiber-reinforced plastic. The method of bringing the solvent into contact with the carbon fiber-reinforced plastic is not particularly limited and includes, for example, an immersion process, a die coating method, a bar coating method, a roll coating method, or a engraving coating method. Among these, the immersion process is used in some embodiments. In particular, the solvent can be brought into contact with the carbon fibers by conveying the carbon fiber-reinforced plastic using a roller to immerse the carbon fiber-reinforced plastic in the solvent contained in a bath.In one embodiment, the drawn carbon fiber reinforced plastic can be immersed in the solvent during transport using a transport roller.

[0056] The degree of resin dissolution during the dissolution and removal process can be adjusted according to the type of solvent, treatment temperature, treatment time, or similar factors. The treatment time can be adjusted, for example, by the conveying speed of the carbon fiber-reinforced plastic. The treatment time is not particularly limited and can be appropriately adjusted according to the type of solvent, resin, and similar factors.

[0057] The temperature of the solution (liquid temperature) can be appropriately adjusted, taking into account the desired degree of dissolution and removal. For example, the temperature of the solution (liquid temperature) can be 20°C or higher, 40°C or higher, 60°C or higher, 80°C or higher, 300°C or lower, 250°C or lower, 200°C or lower, 150°C or lower, or 100°C or lower.

[0058] The resin can be dissolved and removed by injecting the solvent into the carbon fiber reinforced plastic. That is, by applying injection pressure to the solvent to bring it into contact with the carbon fiber reinforced plastic, the resin can be removed using this pressure. The injection device used for this purpose is not particularly limited; for example, a high-pressure cleaning device can be used.

[0059] The nozzle pressure for injecting the solvent can be 1 MPa or higher, 5 MPa or higher, 8 MPa or higher, or 10 MPa or higher. At these pressures, the resin can be effectively removed from the carbon fiber-reinforced plastic. Alternatively, the nozzle pressure can be 30 MPa or less, 25 MPa or less, 22 MPa or less, or 20 MPa or less. At these pressures, damage to the carbon fibers caused by the solvent can be effectively suppressed. The distance between the nozzle and the carbon fiber-reinforced plastic (the injection target) can be 10 cm to 200 cm, or 30 cm to 100 cm, when the solvent is injected.

[0060] When dissolving and removing the resin, immersion in the solvent and injection of the solvent can be performed together. (Step of applying the sizing agent)

[0061] The recycling process according to the present embodiment can include a step of adding a sizing agent to the carbon fibers obtained by removing the resin.

[0062] After the removal step, the carbon fibers are essentially separated from all the resin, and the bundle of carbon fibers is separated into individual fiber forms. Applying the sizing agent to the carbon fibers allows them to be easily wound into a spool, and also suppresses fiber fuzzing and tangling.

[0063] The sizing agent is not particularly limited and includes, for example, epoxy resin, urethane resin, vinyl ester resin, polyamide resin, nylon resin, polyolefin resin (polyethylene and polypropylene), polyester resin, phenolic resin, or a mixture thereof. Among these, epoxy resin, urethane resin, vinyl ester resin, or polyolefin resin are used in some embodiments, and epoxy resin is used specifically in some embodiments. Using epoxy resin as the sizing agent can improve the adhesive properties of both carbon fibers and epoxy resin. One type of sizing agent can be used alone, or two or more types can be used together or in combination.

[0064] The application of the sizing agent to the carbon fibers is carried out by bringing the sizing agent into contact with the carbon fibers. The application method of the sizing agent is not particularly limited and includes, for example, a dipping method, a mold coating method, a rod coating method, a roller coating method, or an engraving coating method. Among these, the dipping method is used in some embodiments. In particular, the sizing agent can be applied to the carbon fibers by conveying the carbon fibers using a roller to immerse the carbon fibers in the sizing agent contained in a sizing bath. The sizing agent can be dispersed or dissolved in water or in an organic solvent, such as acetone, and can be used as a dispersion liquid or a solution.To increase the dispersibility of the sizing agent in order to improve liquid stability, a surfactant can be appropriately added to the dispersion liquid or solution.

[0065] The amount of sizing agent added to the carbon fibers, for example, is 0.1 to 10 parts by mass in a case where the total amount of carbon fibers and sizing agent is 100 parts by mass. If the amount added is within this range, suitable transport of the carbon fibers can be achieved, thereby ensuring sufficient rubfastness, which prevents pilling due to mechanical friction and the like. (Step of winding)

[0066] The recycling process according to the present embodiment can include a step of winding or rewinding the carbon fibers removed from the resin, which are obtained in the removal step. The winding or rewinding step of the carbon fibers is carried out after the removal step, and in a case where the addition of the sizing agent is included, the winding step can be carried out after the addition of the sizing agent.

[0067] Winding can be carried out, for example, using a winding roller. The winding roller is mounted with a drive unit that provides the necessary force to wind the carbon fibers. Additionally, several guide rollers can be mounted, each with its own drive unit to guide the rollers. The winding preload, which is a tensile force applied to the carbon fibers, can be kept as low as possible. By adjusting the winding preload within a suitable range, fiber breakage and winding deviation of the carbon fibers can be suppressed, resulting in longer, continuous fibers.

[0068] One embodiment comprises a step of drawing the carbon fiber-reinforced plastic while undergoing heat treatment, a step of removing the resin from the drawn carbon fiber-reinforced plastic, and a step of winding the carbon fibers removed from the resin, wherein the carbon fiber-reinforced plastic is drawn upstream and the carbon fibers are wound downstream. That is to say, in one embodiment, the drawing step is performed upstream while heating the carbon fiber-reinforced plastic, while the winding step is performed downstream, and between the upstream drawing step and the downstream winding step, a removal step and, in some cases, an application step of a sizing agent are performed.Furthermore, in one embodiment, the drawing step of the carbon fiber-reinforced plastic is carried out in the upper stream (upstream) under heating, while the winding step of the carbon fibers is carried out downstream. Between the drawing step in the upper stream and the winding step in the lower stream, a dissolving and removal step, and in some cases the application of the sizing agent, is performed. In such an embodiment, since the dissolving and removal step is carried out immediately after the drawing step under heating, and the carbon fiber-reinforced plastic can be brought into contact with the solvent at a high temperature, the resin can be efficiently removed using the solvent.Specifically, a portion (it may be an end section) of the carbon fiber-reinforced plastic is removed from the plastically molded carbon fiber-reinforced product. This removed portion is directly or indirectly connected to the winding machine, which applies preload to the carbon fiber-reinforced plastic and draws it into a continuous fiber state. The drawn carbon fiber-reinforced plastic is then separated from the resin using the solvent. The resulting carbon fibers, now free of resin, are wound onto the winding machine.

[0069] In the process of recycling the carbon fibers according to the present embodiment, which comprises the steps described above, suitable reusable carbon fibers can be efficiently obtained.

[0070] The following describes specific examples of the present embodiment with reference to Fig. 9 to Fig. 11. Although the following examples of the present embodiment, which are described in Fig. 9 to Fig. Figure 11 does not depict the step of manufacturing the molded product or the step of applying the sizing agent. The carbon fiber-reinforced, plastically formed product provided in the treatment step of each embodiment is one that is manufactured in the step of manufacturing the molded product. Furthermore, the step of applying the sizing agent can be included in the example of each embodiment, if desired.

[0071] Fig. Figure 9 is a schematic diagram describing one aspect of the present embodiment. In the Fig. In the embodiment shown in Figure 9, the drawing step under heating is performed upstream, followed by the removal step (immersion in the solvent), and then the winding step is performed downstream. Specifically, a carbon fiber-reinforced, plastically formed product 200 is housed in a device 210 suitable for heat treatment, such as a heat treatment chamber, and the carbon fiber-reinforced plastic is drawn under heat treatment (drawing step under heating). In the heat treatment chamber, a container or tank is mounted on a shaft or shaft, which can be driven by rotation, and the carbon fiber-reinforced plastic is drawn from the tank while being heated. Next, the drawn carbon fiber-reinforced plastic is immersed in a solvent 230 (removal step).The carbon fibers removed from the resin are then wound up (winding step). The conveying method for the carbon fiber-reinforced plastic or carbon fibers between each step is not particularly restricted and can, for example, use a guide roller, a winding roller, or a spindle roller. Furthermore, although not shown, the application of the sizing agent can be performed after the removal step and before the winding step. Additionally, a drying step for the carbon fibers can be performed after the removal step and after the sizing agent application step.

[0072] Fig. Figure 10 is a schematic diagram describing one aspect of the present embodiment. Fig. Step 10 involves the removal process, which is carried out by injecting the solvent onto the drawn carbon fiber-reinforced plastic. Specifically, in Fig. 10. A solvent 250 is injected from a nozzle 240, which is connected to an injection device (not shown) in the direction of the drawn carbon fiber-reinforced plastic, to remove the resin from the carbon fibers. By moving the nozzle injecting the solvent and the carbon fiber-reinforced plastic, the solvent can be brought into contact with the entire carbon fiber-reinforced plastic. A plurality of nozzles can be arranged. Furthermore, although not shown, the step of applying the sizing agent can be carried out after the removal step and before the winding step. A drying step of the carbon fibers can also be carried out after the removal step and after the application of the sizing agent.

[0073] Fig. Figure 11 is a schematic diagram describing one aspect of the present embodiment. Fig. 11. The removal step is carried out by a combination of immersion in the solvent and injection of the solvent. In particular, in Fig.11. The drawn carbon fiber-reinforced plastic is immersed in the solvent 230, and then the solvent 250 is injected from the nozzle 240, which is connected to an injection device (not shown), towards the carbon fiber-reinforced plastic to remove the resin from the carbon fibers. By combining immersion in the solvent and injection of the solvent, the resin can be removed more efficiently. Furthermore, although not shown, the step of applying the sizing agent can be carried out after the removal step and before the winding step. Additionally, a step of drying the carbon fibers can be carried out after the removal step and after the application of the sizing agent.

[0074] According to a carbon fiber recycling process of the embodiment described above, high-quality carbon fibers suitable for recycling can be efficiently obtained. The carbon fibers obtained are applicable to a wide range of uses.

[0075] The upper and / or lower limits of the number ranges described in this description can each be combined as desired to specify the intended ranges. For example, the upper and lower limits of the number ranges can be combined as desired to specify intended ranges, and the lower limits of the number ranges can be combined as desired to specify intended ranges.

[0076] Throughout this description, any mention of "an embodiment," "an embodiment," or "a form of embodiment" means that a specific feature, structure, or property described with respect to the embodiment is included in at least one embodiment. Accordingly, the quoted phrases and their variations described throughout this description do not necessarily all refer to the same embodiment.

[0077] Although the present embodiment has been described in detail above, the specific structure is not limited to this embodiment, and possible modifications of the design which do not deviate from the concept of the present invention are included in the disclosure. Reference symbol list 10 liners 20 Carbon fiber reinforced resin layer 30 Valve-side base 40 End-side base 50 valve 60 protective layer 100 containers or tanks 210 Heat treatment device (heat treatment chamber) 220 Carbon fiber reinforced, plastically molded product 230 solvent 240 nozzle 250 solvent QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2018 / 212016 A1 [0003, 0004, 0005, 0006] JP 202037638

[0051] JP 202050704

[0051] JP 202045407

[0052]

Claims

[1] A process for recycling carbon fibers, comprising: Producing a carbon fiber reinforced plastic molded product comprising a carbon fiber reinforced plastic containing carbon fibers and a resin; and Drawing the carbon fiber reinforced plastic while performing a heat treatment on the carbon fiber reinforced plastic molded product, wherein a temperature of the heat treatment is equal to or higher than a glass transition temperature of the resin and lower than a thermal decomposition start temperature, and the temperature is below a thermal degradation temperature of the carbon fibers. [2] The method according to claim 1, wherein the thermal decomposition starting temperature of the resin is a temperature indicating a 5% weight loss in a weight change plot of a thermogravimetric analysis obtained by raising the temperature of the resin from 30°C to 550°C at 5°C / minute under a nitrogen atmosphere. [3] The method according to claim 1, wherein the thermal decomposition starting temperature of the resin is a temperature indicating a 5% weight loss in a weight change plot of a thermogravimetric analysis obtained by raising the temperature of the resin from 30°C to 550°C at 5°C / minute under an air atmosphere. [4] A process according to any one of claims 1 to 3, wherein the temperature of the heat treatment is below 400 °C. [5] A method according to any one of claims 1 to 4, wherein the temperature of the heat treatment is equal to or less than 360 °C. [6] The method of any one of claims 1 to 5, further comprising removing the resin in the drawn carbon fiber reinforced plastic. [7] The method of claim 6, wherein removing the resin comprises contacting a solvent liquid with the carbon fiber reinforced plastic. [8] The method according to claim 7, wherein the dissolving liquid contains at least one liquid selected from an acidic solution, an organic solvent, an aqueous hydrogen peroxide, or an ionic liquid. [9] A method according to claim 7 or 8, wherein the dissolving liquid is an acidic solution. [10] A method according to any one of claims 6 to 9, further comprising winding the carbon fibers removed from the resin. [11] The method of claim 10, further comprising: Drawing the carbon fiber reinforced plastic during heat treatment; Removing the resin in the carbon fiber reinforced plastic, which is drawn and transferred; and Winding up the carbon fibers, which are removed from the resin, where the carbon fiber reinforced plastic is pulled upstream while the carbon fibers are wound downstream. [12] The method of any one of claims 1 to 5, further comprising cutting the drawn carbon fiber reinforced plastic. [13] A process according to any one of claims 1 to 12, wherein the heat treatment is carried out using superheated steam. [14] A method according to any one of claims 1 to 13, wherein the resin comprises a thermosetting resin or a thermoplastic resin. [15] A method according to any one of claims 1 to 14, wherein the resin comprises an epoxy resin.

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