Method for manufacturing fibrous filler and reaction apparatus

Abstract

The present invention provides a method for manufacturing fibrous fillers that allows for the simple and rapid recovery of fibrous fillers from fiber-reinforced resin composite materials. [Solution] A method for producing a fibrous filler, comprising immersing a fiber-reinforced resin composite material, composed of at least reinforcing fibers and a thermosetting resin, in a mixed solution of an aprotic organic solvent having a boiling point of over 200°C at atmospheric pressure, to which a basic compound has been added, and raising the temperature of the mixed solution to over 200°C at atmospheric pressure to remove the resin component including the thermosetting resin from the fiber-reinforced resin composite material and recovering the fibrous filler composed of the reinforcing fibers.

Description

Technical Field

[0001] The present invention relates to a method for producing a fibrous filler and a reaction apparatus for recovering the fibrous filler. More specifically, the present invention relates to a method for producing a fibrous filler, in which a resin component is removed from a fiber-reinforced resin composite material using a solvent to recover the fibrous filler, and to a reaction apparatus for recovering the fibrous filler obtained by decomposing the fiber-reinforced resin composite material.

Background Art

[0002] Fiber-reinforced resin composite materials, which are composed of a matrix resin and a fibrous filler such as glass fiber or carbon fiber, are used in a wide range of fields from general household electrical appliances to aircraft and automobile parts. Most of the offcuts generated in the production process of these fiber-reinforced resin composite materials and product wastes are not effectively utilized, and the majority of them are disposed of by incineration or landfilling. From the standpoints of effective utilization of resources and prevention of environmental pollution, there is a demand for a technology for recovering fibrous fillers from fiber-reinforced resin composite materials.

[0003] As a conventional technology for recovering fibrous fillers from fiber-reinforced resin composite materials, for example, a method (pyrolysis method) in which a resin component is thermally decomposed in a high-temperature combustion furnace to recover the fibrous filler is known. However, there are problems that the fibrous filler is degraded in the pyrolysis step, and the thermal decomposition of the matrix resin produces exhaust gas containing organic and inorganic harmful compounds, which has not been effectively utilized.

[0004] On the other hand, as a method other than pyrolysis for recovering fibrous fillers, for example, Patent Document 1 discloses that a treatment liquid containing at least one catalyst selected from the group consisting of alkali metals, alkali metal compounds, phosphoric acid, phosphates, organic acids and organic acid salts, and at least one organic solvent selected from the group consisting of amide solvents, alcohol solvents, ketone solvents and ether solvents is used to dissolve a cured epoxy resin. A treatment method for dissolving a cured epoxy resin is disclosed.

[0005] Furthermore, Patent Document 2 discloses a carbon fiber recovery method for carbon fiber-reinforced plastic, in which carbon fibers are recovered by dissolving the resin portion using a dissolving solution, wherein the dissolving solution includes a mixed solvent obtained by mixing multiple types of organic solvents, including at least one type of alcohol-based solvent, and a catalyst, and the distance between the HSP value of the mixed solvent and the HSP value of the resin portion of the carbon fiber-reinforced plastic is set to a predetermined value or less.

[0006] Furthermore, Patent Document 3 discloses a method for producing a phenol compound from a thermosetting resin cured product, which includes a swelling step of bringing a thermosetting resin cured product A into contact with an organic solvent to swell the thermosetting resin cured product A and obtain a thermosetting resin cured product B, and a decomposition step of decomposing the thermosetting resin cured product B.

[0007] Furthermore, Non-Patent Document 1 describes a method for recovering bisphenol A in high yield from thermosetting epoxy resin using 1,3-dimethyl-2-imidazolidinone as a solvent and sodium tert-butoxide as a catalyst. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2001-172426 [Patent Document 2] Japanese Patent Publication No. 2019-209540 [Patent Document 3] Japanese Patent Publication No. 2024-165142 [Non-patent literature]

[0009] [Non-Patent Document 1] Yasunori Minami et al., "Degradation of stable thermosetting epoxy resins mediated by bases in amide solvents" Polymer Journal, vol. 57, pp. 149-162, 2025. [Overview of the project] [Problems that the invention aims to solve]

[0010] While the method described in Patent Document 1 certainly involves processing in a temperature range where carbon fiber degradation is minimal, using sodium hydroxide, which is the least expensive of the alkali metal compounds described in Patent Document 1 and also has superior solubility for epoxy resin cured products, presents the problem of the processing solution becoming highly viscous.

[0011] The method described in Patent Document 2 is a method that makes it possible to recover carbon fibers from carbon fiber reinforced plastic consisting of carbon fibers and a resin part. However, it is necessary to calculate the HSP value of the mixed solvent according to the HSP value of the resin part and mix several types of organic solvents including an alcohol-based solvent. However, there was a problem that an appropriate mixed solvent could not be prepared when the HSP value of the resin part was unknown.

[0012] While the method described in Patent Document 3 is indeed capable of decomposing thermosetting epoxy, it is a complex process that requires a resin swelling step before the resin decomposition step, and there was room for improvement.

[0013] While the method described in Non-Patent Document 1 certainly makes it possible to recover carbon fibers from carbon fiber reinforced plastics consisting of carbon fibers and resin, the reaction time is required for some samples to be around 20 hours, and there was room for improvement.

[0014] Therefore, the present invention aims to provide a method for producing fibrous fillers that allows for the processing of fiber-reinforced resin composite materials, which consist of at least reinforcing fibers and a thermosetting resin, using a simple processing method without the use of expensive equipment or chemicals, and without the need for special pre-preparation of processing agents tailored to the resin constituting the fiber-reinforced resin composite material, thereby recovering fibrous fillers made of reinforcing fibers. [Means for solving the problem]

[0015] The present invention, which solves the above problems, consists of the following embodiments (1) to (7). (1) A method for producing a fibrous filler, comprising: immersing a fiber-reinforced resin composite material, composed of at least reinforcing fibers and a thermosetting resin, in a mixture of an aprotic organic solvent having a boiling point of over 200°C at atmospheric pressure, to which a basic compound is added; and raising the temperature of the mixture to over 200°C at atmospheric pressure to remove the resin component including the thermosetting resin from the fiber-reinforced resin composite material and recover the fibrous filler composed of the reinforcing fibers. (2) A method for producing a fibrous filler according to (1), wherein the basic compound is used in an amount of 0.1% by mass or more and 15% by mass or less relative to the aprotic organic solvent. (3) A method for producing a fibrous filler according to (1) or (2), wherein the basic compound is a potassium salt. (4) A method for producing a fibrous filler according to any one of (1) to (3), wherein the swelling rate of the thermosetting resin in relation to the aprotic organic solvent, as measured by differential scanning calorimeter (DSC) in accordance with JIS K7121 (1987), is 10% or more when immersed for 5 hours at a temperature of glass transition temperature of the thermosetting resin + 20°C. (5) A method for producing a fibrous filler according to any one of (1) to (4), wherein the aprotic organic solvent comprises 1,3-dimethyl-2-imidazolidinone. (6) A method for producing a fibrous filler according to any one of (1) to (5), wherein the step of removing the resin component containing the thermosetting resin from the fiber-reinforced resin composite material is performed at normal pressure and under reflux conditions of the aprotic organic solvent at its boiling point. A reaction apparatus for use in the method for producing a fibrous filler according to any one of (7) (1) to (6). [Advantageous Effects of the Invention]

[0016] According to the present invention, there can be provided a method for producing a fibrous filler, which does not require special preliminary preparation of a treating agent tailored to the resin constituting the fiber-reinforced resin composite material, treats the fiber-reinforced resin composite material by a simple treatment method, and recovers the fibrous filler; and a fibrous filler obtained by decomposing the fiber-reinforced resin composite material, which exhibits properties close to those of virgin reinforced fibers. [Mode for Carrying Out the Invention]

[0017] Hereinafter, exemplary embodiments for carrying out each aspect of the present invention will be described in detail.

[0018] (Reinforced Fiber) Examples of the reinforced fiber of the present invention include known reinforced fibers such as glass fiber, carbon fiber, basalt fiber, aramid fiber, alumina fiber, and "Kevlar (registered trademark)" fiber. One type thereof may be used alone, or two or more types may be used in combination.

[0019] Further, the shape of these reinforced fibers includes, for example, shapes of short fibers such as continuous fibers and chopped strands, and whiskers.

[0020] Carbon fibers can be suitably used in the present invention, and there is no particular limitation on usable carbon fibers. Known various carbon fibers, for example, carbonaceous fibers and graphitic fibers produced using polyacrylonitrile (PAN), pitch, rayon, lignin, hydrocarbon gas and the like can be used. Among them, PAN-based carbon fibers, which can be expected to improve mechanical properties, can be preferably used.

[0021] (Thermosetting Resin and Fiber-Reinforced Resin Composite Material) In the present invention, a fiber-reinforced resin composite material is a composite material composed of at least a thermosetting resin reinforced with the aforementioned reinforcing fibers. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, melamine resins, urea resins, and urethane resins, with epoxy resins and vinyl ester resins being particularly preferred. In particular, epoxy resins cured with amine compounds exhibit high various properties, and fiber-reinforced resin composite materials using carbon fibers as reinforcing fibers are widely used, including in aircraft applications. However, the lifespan of an aircraft is 20 to 30 years, and it is expected that many aircraft will reach the end of their service life in the future. Therefore, using epoxy resins cured with amine compounds as the matrix resin is preferable from the viewpoint of recycling needs.

[0022] Furthermore, since carbon fibers generally consume more energy during manufacturing than glass fibers and have a greater need for recycling, it is preferable to use fiber-reinforced resin composite materials that utilize carbon fibers as reinforcing fibers.

[0023] The matrix resin of the present invention may also be used with additives such as stabilizers, release agents, ultraviolet absorbers, colorants, flame retardants, flame retardant enhancers, lubricants, fluorescent whitening agents, phosphorescent pigments, fluorescent dyes, flow modifiers, impact resistance modifiers, crystal nucleating agents, inorganic and organic antibacterial agents, photocatalytic antifouling agents, and infrared absorbers.

[0024] (Aprotic organic solvent) The solvent used in the present invention is preferably a high-boiling point aprotic organic solvent. Specific examples include aromatic solvents such as naphthalene, 1-chloronaphthalene, biphenyl, tetralin, 1,4-diisopropylbenzene, and 1,3,5-triisopropylbenzene; ester solvents such as γ-butyrolactone and ε-caprolactone; amide solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and N-octyl-2-pyrrolidone; urea solvents such as 1,3-dimethyl-2-imidazolidinone; sulfone solvents such as sulfolane; and mixtures thereof or aqueous solutions. Among these, amide solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and N-octyl-2-pyrrolidone, and urea-based solvents such as 1,3-dimethyl-2-imidazolidinone are preferred because they exhibit excellent high-temperature stability and hardly denature even under basic conditions, eliminating the need to discard the solvent after each reaction, which is advantageous from the standpoint of raw material costs and LCA.

[0025] Of these, solvents with a high swelling rate for thermosetting resins are preferred from the viewpoint of improving the efficiency of resin decomposition. Specifically, a swelling rate of 10% or more, more preferably 20% or more, and even more preferably 40% or more, when immersed for 5 hours at a temperature of the glass transition temperature of the thermosetting resin + 20°C, as measured by differential scanning calorimeter (DSC) based on JIS K7121 (1987), is preferred. At the glass transition temperature of the thermosetting resin + 20°C, the thermosetting resin is in a rubbery state and can swell sufficiently in the solvent in a short time. If the swelling rate of the solvent is within the above range, the efficiency of resin decomposition can be improved, and the thermosetting resin can be decomposed in a shorter time than with conventional methods. Among these, 1,3-dimethyl-2-imidazolidinone is particularly preferred.

[0026] (Basic compounds) Examples of basic compounds include inorganic bases such as sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, calcium hydroxide, barium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, trisodium phosphate, disodium phosphate, and monosodium phosphate; organic bases such as 1,8-diazabicycloundecene, tetramethylethylenediamine, N,N-diisopropylethylamine, 4-dimethylaminopyridine, 1,4-diazabicyclo[2.2.2]octane, potassium tert-butoxide, sodium tert-butoxide, and potassium hexamethyldisilazide; and their hydrates and mixtures. Among these, inorganic bases are preferred, and potassium salts are more preferred because they exhibit superior efficiency in the resin decomposition reaction.

[0027] (Processing of fiber-reinforced resin composite materials) The processing of fiber-reinforced resin composite materials in this invention is a general term for the process of immersing the fiber-reinforced resin composite material in a mixture of an aprotic organic solvent with a boiling point exceeding 200°C at atmospheric pressure, to which a basic compound has been added, and then raising the temperature of the mixture to above 200°C at atmospheric pressure to remove the resin component containing the thermosetting resin from the fiber-reinforced resin composite material and recover the fibrous filler consisting of the reinforcing fibers. At temperatures below 200°C, the decomposition ability of the thermosetting resin tends to be poor. The upper limit of the reaction temperature is preferably below the boiling point of the aprotic organic solvent, and from the viewpoint of reaction efficiency, it is even more preferable to be under atmospheric pressure and reflux conditions at the boiling point of the aprotic organic solvent. By performing the reaction at atmospheric pressure, there are advantages such as not requiring special equipment such as pressure-resistant equipment, not requiring pressure operations such as pressure reduction or release, and being able to continuously recover fibers because it can be carried out in an open system.

[0028] The processing time cannot be specified in general, as it depends on the type and amount of fiber-reinforced resin composite material used, as well as the temperature and solvent. However, it is preferably 0.01 hours or longer, and more preferably 0.1 hours or longer. This preferred time allows for sufficient decomposition of the resin components in the fiber-reinforced resin composite material. On the other hand, there is no particular upper limit to the processing time, but sufficient decomposition can be achieved within 24 hours, preferably within 18 hours, and more preferably within 12 hours.

[0029] The concentration of the basic compound in the aprotic organic solvent during processing is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to the aprotic organic solvent. An example of an upper limit is 15% by mass or less, preferably 12% by mass or less, and more preferably 10% by mass or less.

[0030] Furthermore, basic compounds in aprotic organic solvents may be dissolved or partially insoluble, but dissolution tends to result in superior decomposition of the matrix resin. Here, dissolution refers to a homogenized liquid state in the aprotic organic solvent when the basic compound is a solid, and a homogenized liquid state when the basic compound is a liquid, without liquid-liquid separation. The state in which the basic compound is dissolved in the aprotic organic solvent is determined by its state at the point when the predetermined temperature is reached.

[0031] There are no particular restrictions on the form of the reaction apparatus, but it is preferable to use one in which the parts that come into direct contact with the solvent are made of corrosion-resistant materials such as Hastelloy (an alloy made of Ni, Cr, Mo, etc.) or SUS. Various known reaction methods, such as batch and continuous methods, can be used for the process.

[0032] Furthermore, the reaction apparatus for this processing step preferably has a stirring mechanism for stirring a mixture consisting of an aprotic organic solvent to which a basic compound has been added. Various stirring methods can be employed, such as a rotary stirring device, a pump-circulation stirring method in which the mixture is circulated by a pump, a bubbling method in which gas bubbles are used for stirring, and a shaking method in which the apparatus is shaken.

[0033] Furthermore, the mass ratio of fiber-reinforced resin composite material to aprotic organic solvent during processing cannot be generalized as it depends on the type of fiber-reinforced resin composite material used and the reaction temperature. However, a ratio of fiber-reinforced resin composite material to aprotic organic solvent of 1:1000 to 1:1 can be exemplified, and from the viewpoint of productivity, 1:100 to 1:2 is more preferable.

[0034] (Recovery of fibrous filler) In the method for producing the fibrous filler of the present invention, the fibrous filler, consisting of reinforcing fibers, can be separated and recovered from the reaction solution obtained by the above-described step (treatment of fiber-reinforced resin composite material). There are no particular restrictions on the method for separating and recovering the fibrous filler from this reaction solution, and any known method may be used, but a simple and preferred method is to separate the fibrous filler from the waste liquid by solid-liquid separation. Here, the waste liquid refers to the liquid phase portion containing at least an aprotic organic solvent, obtained by separating the fibrous filler from the reaction solution obtained by the above-described step.

[0035] Examples of solid-liquid separation methods include using a filter, separating the fibrous packing material from the liquid phase using a centrifuge, and methods combining these. However, the method is not limited to these, as it yields at least a liquid phase containing an aprotic organic solvent and a solid portion containing the fibrous packing material. Additionally, steps for washing the fibrous packing material with water or an organic solvent, or drying, may be added as needed. Furthermore, phenols, aromatic amines, and other compounds can be separated and recovered from the waste liquid obtained through this process. [Examples]

[0036] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0037] (Main ingredient) • "SumiEpoxy®" ELM434 (Tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd., hereinafter also referred to as ELM434). • “jER(registered trademark)” 828 (Diglycidyl ether of bisphenol A, manufactured by Mitsubishi Chemical Corporation; hereinafter also referred to as jER828). • “jER(registered trademark)” 825 (Diglycidyl ether of bisphenol A, manufactured by Mitsubishi Chemical Corporation; hereinafter also referred to as jER825). • Epiclon® 830 (Diglycidyl ether of bisphenol F, manufactured by DIC Corporation; hereinafter also referred to as EP830).

[0038] (Hardening agent) • "Seika Cure (registered trademark)" S (4,4'-diaminodiphenylsulfone, manufactured by Seika Co., Ltd., also referred to as DDS below.) HN-2200 (a mixture of 1,2,3,6-tetrahydro-3-methylphthalic anhydride and 1,2,3,6-tetrahydro-4-methylphthalic anhydride, manufactured by RESONAC Co., Ltd.) • Dicyandiamide (manufactured by Mitsubishi Chemical Corporation; hereinafter also referred to as DICY).

[0039] (Treatment solution for evaluating recyclability) • Potassium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter also referred to as KOH). • Sodium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter also referred to as NaOH). • Potassium tert-butoxide (manufactured by Kanto Chemical Co., Ltd., hereinafter also referred to as t-BuOK). • Benzyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter also referred to as BzOH). • 1,3-Dimethyl-2-imidazolidinone (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter also referred to as DMI) • Triethylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter also referred to as TEG). • N-methyl-2-pyrrolidone (manufactured by Kuraray Co., Ltd., hereinafter also referred to as NMP). • N-ethyl-2-pyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter also referred to as NEP).

[0040] (Reinforced fiber) • Carbon fiber bundle (Toray Industries, Inc.'s "Torayca®" T700SC-12k-50C, hereinafter also referred to as CF).

[0041] (Resin content measurement) The resin content (Rr) was calculated for the prepared fiber-reinforced resin composite material from the mass (M0) before the heating program (a) and the smallest mass (M1) up to the end of the heating program (b). Equipment: Hitachi High-Tech Science Corporation STA7000 Measurement atmosphere: Under a nitrogen stream Temperature rise program: (a) Hold at programmed temperature of 50°C for 1 minute (b) Heat from a programmed temperature of 50°C to 500°C at a heating rate of 25°C / min, and hold at 500°C for 30 minutes. Resin content: Rr=(M0-M1) / M0×100

[0042] (Resin decomposition rate measurement) The resin decomposition rate was calculated from the resin content (Rr) measured for each reference example of the fibers after the decomposition process and solid-liquid separation process described below, and from the mass (M0) before heating program (a) and the smallest mass (M1) up to the end of heating program (b) when heated according to the heating program below. Equipment: Hitachi High-Tech Science Corporation STA7000 Measurement atmosphere: Under a nitrogen stream Temperature rise program: (a) Hold at programmed temperature of 50°C for 1 minute (b) Heat from a programmed temperature of 50°C to 500°C at a heating rate of 25°C / min, and hold at 500°C for 30 minutes. Resin decomposition rate: 100-{(M0-M1) / M0×100} / Rr×100

[0043] (CF yield) The CF yield was obtained by weighing the mass of the fibrous filler that had been dried after the decomposition process and calculating the ratio of the mass of CF contained in the fiber-reinforced resin composite material used in the decomposition process based on the resin content.

[0044] (Solvent reusability) Solvent reusability was evaluated by comparing the peak area derived from the solvent obtained from H-NMR before and after the reaction, using only the solvent and base, stirring for the same amount of time as the reaction at a predetermined reaction temperature and pressure, and according to the following criteria. A: The peak area derived from the solvent after the reaction is 98% or more compared to before the reaction. B: The peak area derived from the solvent after the reaction is 90% or more compared to before the reaction. C: Solvent-derived peak area after reaction is less than 90% compared to before reaction.

[0045] (Production cycle) The production cycle was evaluated according to the following criteria. A: No special operations such as pressure reduction or release are required, and there is virtually no pipe blockage during CF recovery, no deposits on the decomposition liquid interface or reaction vessel walls, making it easy to recover CF and decomposition liquid. B: Although pressure manipulation such as pressure reduction and release is necessary, there is almost no pipe blockage during CF recovery, and no deposits on the decomposition liquid interface or reaction vessel walls, making it easy to recover CF and decomposition liquid. C: During CF recovery, either or both of the following occur: pipe blockage, deposits on the decomposition liquid interface, or reaction vessel walls, making it difficult to recover either or both of the CF and the decomposition liquid.

[0046] (Reference example 1) ELM434 (70 parts by mass), jER828 (10 parts by mass), EP830 (20 parts by mass), and DDS (45.2 parts by mass) were mixed to form a resin raw material. This resin raw material was impregnated into carbon fiber (CF) arranged in one direction and set in a mold at 90°C, heated from 90°C to 180°C for 60 minutes, and then heated at 180°C for 2 hours to cure the resin, thereby obtaining a sheet-like carbon fiber reinforced resin composite material. This was hereafter referred to as CFRP-1, and was cut into strips of about 40 mm in length for use in the examples and comparative examples. The resin content of CFRP-1, measured using the same procedure as described above for resin decomposition rate measurement, was 40% by mass.

[0047] (Reference example 2) A resin raw material was prepared by mixing 100 parts by mass of jER825, 80 parts by mass of HN-2200, and 3 parts by mass of DY080 (manufactured by Huntsman) as a curing accelerator. This resin raw material was impregnated into CF-1, which was arranged in one direction and set in a mold, at 60°C. The resin was then heated from 60°C to 160°C for 40 minutes, and then heated at 160°C for 1 hour to cure the resin, thereby obtaining a sheet-like fiber-reinforced resin composite material. This was designated as CFRP-2 and was cut into strips approximately 40 mm in length for use. The resin content of CFRP-2, measured using the same procedure as described above for the resin decomposition rate measurement, was 40% by mass.

[0048] (Reference example 3) A resin raw material was prepared by mixing 100 parts by mass of jER828, 7 parts by mass of DICY, and 1 part by mass of "OMICURE®" U-24M (manufactured by Huntsman) as a curing accelerator. This resin raw material was impregnated into CF-2, which was arranged in one direction and set in a mold, at 60°C. The resin was then heated from 60°C to 150°C for 80 minutes, and then heated at 150°C for 1 hour to cure the resin, thereby obtaining a sheet-like fiber-reinforced resin composite material. This was designated as CFRP-3 and was used after being cut into strips approximately 40 mm in length. The resin content of CFRP-3, measured using the same procedure as described above for measuring the resin decomposition rate, was 40% by mass.

[0049] (Example 1) <Disassembly process> KOH (1g), DMI (99g), and CFRP-1 (3g) were added to a stainless steel reaction vessel with reflux equipment at the top, and the temperature was raised to 222°C and heated for 3 hours. After the reaction, DMI (100g) was added to dilute the mixture, and the contents were recovered.

[0050] <Solid-liquid separation process> The contents were removed from the top of the reaction vessel and filtered at room temperature to recover the solid portion containing carbon fibers. The solid portion was then washed with NMP (100g) and water (100g), and dried to recover the carbon fibers.

[0051] (Example 2) The procedure was carried out in the same manner as in Example 1, except that CFRP-1 was replaced with CFRP-2, and the carbon fibers were recovered.

[0052] (Example 3) The procedure was carried out in the same manner as in Example 1, except that CFRP-1 was replaced with CFRP-3, and the carbon fibers were recovered.

[0053] (Example 4) In Example 1, the decomposition process was carried out in the same manner as in Example 1, except that the preparation ratios were KOH (5g), DMI (95g), and CFRP-1 (3g), and carbon fibers were recovered.

[0054] (Example 5) In Example 4, the procedure was carried out in the same manner as in Example 4, except that KOH was replaced with t-BuOK, and carbon fibers were recovered.

[0055] (Example 6) In Example 4, the procedure was carried out in the same manner as in Example 4, except that KOH was replaced with NaOH, and carbon fibers were recovered.

[0056] (Example 7) In Example 4, the procedure was carried out in the same manner as in Example 4, except that DMI was replaced with NMP and the reaction temperature was 202°C, and carbon fibers were recovered.

[0057] (Example 8) In Example 7, the procedure was carried out in the same manner as in Example 7, except that KOH was replaced with NaOH, and carbon fibers were recovered.

[0058] (Example 9) In Example 4, the procedure was carried out in the same manner as in Example 4, except that DMI was replaced with NEP and the reaction temperature was 218°C, and carbon fibers were recovered.

[0059] (Comparative Example 1) In Example 6, the procedure was carried out in the same manner as in Example 6, except that DMI was replaced with BzOH and the reaction temperature was 205°C, and carbon fibers were recovered.

[0060] (Comparative Example 2) In Example 6, the procedure was carried out in the same manner as in Example 6, except that DMI was replaced with TEG and the reaction temperature was 285°C, and carbon fibers were recovered.

[0061] (Comparative Example 3) <Disassembly process> KOH (5g), NMP (95g), and CFRP-1 (3g) were added to an autoclave, heated to 240°C, and processed by heating for 3 hours. After the reaction, the mixture was allowed to cool and the pressure returned to atmospheric pressure before diluting with NMP (100g) and collecting the contents.

[0062] <Solid-liquid separation process> The contents were removed from the top of the reaction vessel and filtered at room temperature to recover the solid portion containing carbon fibers. The solid portion was then washed with NMP (100g) and water (100g), and dried to recover the carbon fibers.

[0063] (Comparative Example 4) In Comparative Example 3, the procedure was carried out in the same manner as in Comparative Example 3, except that the reaction vessel was an autoclave with a 10 mm diameter outlet at the bottom, and carbon fibers were recovered.

[0064] [Table 1]

[0065] [Table 2] [Industrial applicability]

[0066] The fibrous filler obtained in this invention can be mixed with a resin using commonly known methods to obtain a fiber-reinforced resin composite material. This fiber-reinforced resin composite material has excellent mechanical properties and moldability, making it suitable for use in various electrical and electronic components, automotive parts, aircraft parts, and the like.

Claims

1. A method for producing a fibrous filler, comprising immersing a fiber-reinforced resin composite material, composed of at least reinforcing fibers and a thermosetting resin, in a mixture of an aprotic organic solvent having a boiling point exceeding 200°C at atmospheric pressure, to which a basic compound is added, and raising the temperature of the mixture to above 200°C at atmospheric pressure to remove the resin component including the thermosetting resin from the fiber-reinforced resin composite material and recover the fibrous filler composed of the reinforcing fibers.

2. The method for producing a fibrous filler according to claim 1, wherein the basic compound is used in an amount of 0.1% by mass or more and 15% by mass or less relative to the aprotic organic solvent.

3. The method for producing a fibrous filler according to claim 1, wherein the basic compound is a potassium salt.

4. A method for producing a fibrous filler according to claim 1, wherein the swelling rate of the thermosetting resin in the aprotic organic solvent, as measured by differential scanning calorimeter (DSC) in accordance with JIS K7121 (1987), is 10% or more when immersed for 5 hours at a temperature of glass transition temperature of the thermosetting resin + 20°C.

5. The method for producing a fibrous filler according to claim 1, wherein the aprotic organic solvent comprises 1,3-dimethyl-2-imidazolidinone.

6. A method for producing a fibrous filler according to claim 1, wherein the step of removing the resin component containing the thermosetting resin from the fiber-reinforced resin composite material is performed at atmospheric pressure and under reflux conditions of the aprotic organic solvent at its boiling point.

7. A reaction apparatus used in a method for producing a fibrous filler according to any one of claims 1 to 6.

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