Method for decomposing epoxy resin and method for recovering carbon fiber from carbon fiber composite material

Abstract

To provide a method for decomposing an epoxy resin which can decompose an epoxy resin even under a mild condition of an atmospheric pressure and a room temperature at low cost, and can prevent production of a compound having high environmental loads.SOLUTION: A method for decomposing an epoxy resin includes a first step of treating an epoxy resin with an acidic solution, and introducing an acidic functional group into the epoxy resin, a second step of treating the epoxy resin with a solution containing metallic ions, and forming a metal salt of the acidic functional group, and a third step of treating the metal salt with hydrogen peroxide, and decomposing the epoxy resin to which the metal salt of the acidic functional group has been introduced, wherein at least one of a sulfuric acid, a phosphoric acid, a nitric acid and a hydrochloric acid is used as the acidic solution used in the first step, and a solution containing at least one of an alkali metal, an alkali earth metal and a metal salt of transition metal is used as the solution containing the metal ions used in the second step.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for decomposing an epoxy resin and a method for recovering carbon fibers from a carbon fiber composite material using the method. [Background technology]

[0002] Epoxy resin is a thermosetting resin having excellent electrical insulation, heat resistance, mechanical strength, etc., and is widely used as a material for various electrical components, electronic components, automobile components, etc. Epoxy resin is obtained by mixing a prepolymer such as a copolymer of bisphenol A and epichlorohydrin with a curing agent such as a polyamine or an acid anhydride and performing a heat curing treatment. However, once cured, epoxy resin is difficult to soften or melt by heat and has low solubility in solvents, so it is difficult to decompose. For this reason, disposal of cured epoxy resin must be done by landfilling, which causes problems such as environmental burden. In addition, since it has low solubility in solvents and is difficult to decompose, analysis such as structural analysis of cured epoxy resin is also difficult.

[0003] In particular, carbon fiber composite materials containing carbon fibers and resin materials such as epoxy resins are used in applications such as aircraft and automobiles, and there is a demand for recycling the carbon fibers. In order to recycle the carbon fibers, methods for removing the epoxy resin contained in used carbon fiber composite materials and recovering the carbon fibers have been studied.

[0004] For example, Patent Document 1 proposes that epoxy resin can be dissolved by immersing carbon fiber reinforced plastic containing carbon fiber and epoxy resin in sulfuric acid with a concentration of 90 wt % or more and a temperature of 120° C. or more. In this method, it is said that an alkali scrubber, water scrubber, or the like is provided to remove the sulfur oxides and carbon monoxide that are generated.

[0005] Patent Document 2 proposes that the epoxy resin can be dissolved by immersing a carbon fiber composite material containing an epoxy resin in an organic acid or inorganic acid of 0.01 to 10 M at a temperature of 10 to 100° C., and then immersing it in an alkaline aqueous solution. In the examples of Patent Document 2, the epoxy resin is decomposed at 60 to 70° C.

[0006] Patent Document 3 proposes that epoxy resin can be dissolved by swelling the resin with a weak acid of pH 2 to 4 and then immersing a reinforced part in which reinforcing fibers are impregnated with epoxy resin in a mixture of hydrogen peroxide and an ionized liquid.

[0007] Patent Document 4 proposes that epoxy resins can be dissolved by immersing them in a mixed solution of an epoxy resin decomposition compound such as trimethylsilyl halogen or Fenton's reagent, an organic solvent, and a small amount of water at atmospheric pressure and room temperature.

[0008] Conventional methods for decomposing epoxy resins require high temperatures and high pressures to decompose the epoxy resins, which requires a lot of energy. In addition, it is necessary to use dedicated equipment that can withstand such high temperatures and high pressures. Furthermore, when acids such as sulfuric acid and nitric acid are used at high temperatures, compounds with high environmental impacts such as SOx and NOx are generated. When sulfuric acid is used for decomposition, a part of the epoxy resin is carbonized, making it difficult to completely decompose it. In the method of using a mixture of hydrogen peroxide and an ionized liquid as in Patent Document 3, the ionized liquid is expensive, and there is a problem that it is costly to treat a large amount of carbon fiber composite material. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent Publication No. 2022-102186 [Patent Document 2] JP 2019-136932 A [Patent Document 3] JP 2017-104847 A [Patent Document 4] JP 2021-155644 A Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a method for decomposing epoxy resins, which is capable of decomposing epoxy resins at low cost even under mild conditions such as atmospheric pressure and room temperature, and which produces almost no compounds that have a high environmental impact, and a method for recovering carbon fibers from carbon fiber composite materials using said method. [Means for solving the problem]

[0011] The present invention is a method for decomposing an epoxy resin, comprising a first step of treating an epoxy resin with an acidic solution to introduce an acidic functional group into the epoxy resin, a second step of treating an epoxy resin with a solution containing metal ions to form a metal salt of the acidic functional group, and a third step of treating an epoxy resin with hydrogen peroxide to decompose the epoxy resin into which the metal salt of the acidic functional group has been introduced, wherein the acidic solution used in the first step is at least one of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid, and the solution containing metal ions used in the second step is a solution containing at least one of metal salts of alkali metals, alkaline earth metals, and transition metals.

[0012] In the method for decomposing an epoxy resin, it is preferable that sulfuric acid is used as the acidic solution used in the first step.

[0013] In the epoxy resin decomposition method, it is preferable that the solution containing metal ions used in the second step is a solution containing at least one of Fe(II), Fe(III), Cu(II), and Li.

[0014] The present invention relates to a method for recovering carbon fibers from a carbon fiber composite material, comprising recovering carbon fibers from the carbon fiber composite material by using the above-mentioned method for decomposing an epoxy resin. Effect of the Invention

[0015] The present invention can provide a method for decomposing epoxy resins, which can decompose epoxy resins at low cost even under mild conditions such as atmospheric pressure and room temperature, and which hardly produces compounds that have a high environmental impact, and a method for recovering carbon fibers from carbon fiber composite materials using the method. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing an example of a procedure for a method for recovering carbon fibers from a carbon fiber composite material according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing an IR spectrum of the epoxy resin in Example 1. [Diagram 3] FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after treatment with a metal ion-containing solution in Example 1. [Figure 4] FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after hydrogen peroxide treatment in Example 1. [Diagram 5] FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after hydrogen peroxide treatment in Example 2 (an example of hydrogen peroxide decomposition at 25° C.). [Figure 6] FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after hydrogen peroxide treatment in Comparative Example 1. [Figure 7] FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after treatment with a Fenton reagent in Comparative Example 2. [Figure 8] FIG. 13 is a diagram showing the results of thermogravimetric analysis of CFRP after hydrogen peroxide treatment in Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0018] <How to decompose epoxy resin> The method for decomposing an epoxy resin according to this embodiment includes a first step of treating the epoxy resin with an acidic solution to introduce acidic functional groups into the epoxy resin, a second step of treating the epoxy resin with a solution containing metal ions to form a metal salt of the acidic functional groups, and a third step of treating the epoxy resin with hydrogen peroxide to decompose the epoxy resin into which the metal salt of the acidic functional group has been introduced. The acidic solution used in the first step is at least one of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid, and the solution containing metal ions used in the second step is a solution containing at least one of metal salts of alkali metals, alkaline earth metals, and transition metals.

[0019] As described above, in conventional epoxy resin decomposition methods, high temperature and high pressure are required to decompose the epoxy resin, and a lot of energy is required. In addition, it is necessary to use dedicated equipment that can withstand such high temperature and high pressure. Furthermore, when an acid such as sulfuric acid or nitric acid is treated at high temperature, compounds with high environmental load such as SOx and NOx are generated. On the other hand, the epoxy resin decomposition method according to the present embodiment is capable of decomposing the epoxy resin under mild conditions (e.g., atmospheric pressure, room temperature), and compounds with high environmental load are hardly generated. In addition, it is advantageous in that it is not necessary to use dedicated equipment that can withstand high temperature and high pressure. Even when a large amount of epoxy resin is treated, it is not necessary to use a large amount of energy. By acting hydrogen peroxide on the metal salt of the acidic functional group introduced into the epoxy resin, the epoxy resin can be decomposed at a higher speed than with a normal Fenton's reagent. In the case of decomposition using sulfuric acid, a part of the epoxy resin is carbonized and it is difficult to completely decompose it, but the carbonized components can also be decomposed by this method.

[0020] The decomposition products produced by this method are soluble in water, and can therefore be used as a recycling method to recover carbon fibers and fillers from carbon fiber composite materials such as carbon fiber reinforced plastics (CFRP) by decomposing the epoxy resin contained in the carbon fiber composite materials and then washing with water.

[0021] In this method, at least the surface of the epoxy resin is oxidized by an acidic solution, and acidic functional groups (e.g., sulfonic acid groups, carboxyl groups, phosphoric acid groups, etc.) are introduced. When the epoxy resin with the acidic functional groups introduced is treated with a solution containing metal ions, an exchange reaction occurs between the hydrogen of the acidic functional groups and the metal ions to form a metal salt. The Fenton reaction occurs by reacting hydrogen peroxide with the epoxy resin with the metal salt of the acidic functional group. It is believed that the Fenton reaction that occurs in this way can decompose the epoxy resin more quickly than when a normal Fenton reagent is used.

[0022] The epoxy resin to be decomposed is not particularly limited as long as it is a thermosetting resin obtained by a thermosetting treatment of a curing agent and an epoxy group-containing compound (prepolymer) having an epoxy group. Examples of the epoxy resin include an epoxy resin obtained by a reaction between an amino group-containing compound having an amino group and an epoxy group-containing compound having an epoxy group, an epoxy resin obtained by a reaction between a carboxylic acid anhydride and an epoxy group-containing compound having an epoxy group, and an epoxy resin obtained by a reaction between a phenol resin and an epoxy group-containing compound having an epoxy group. The epoxy resin may contain a catalyst that promotes curing.

[0023] Examples of the amino group-containing compound that serves as a curing agent include 4,4-methylenebis(2,6-diethylaniline), diethylenetriamine, isophoronediamine, polyamidoamine, aliphatic polyamine, and dicyandiamide.

[0024] Examples of the carboxylic acid anhydride that serves as a curing agent include maleic anhydride, phthalic anhydride, and methylhexahydrophthalic anhydride.

[0025] Catalysts that accelerate curing include tertiary amines and imidazoles.

[0026] Examples of epoxy group-containing compounds (prepolymers) include bisphenol A type epoxy, bisphenol F type epoxy, and phenol novolac type epoxy.

[0027] In the first step, the epoxy resin is treated with an acidic solution to introduce acidic functional groups at least to the surface of the epoxy resin. In order to decompose the epoxy resin as completely as possible, the acidic functional groups may be introduced into the interior of the epoxy resin.

[0028] In the first step, the epoxy resin or a material containing the epoxy resin is immersed in an acidic solution at a predetermined temperature, pressure, and time. If necessary, the immersion liquid may be stirred. In addition to immersion, spraying, coating, and other methods may also be used.

[0029] The acid solution may be at least one of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid. Of these, sulfuric acid is preferred from the standpoint of its permeability into the resin and ease of generating acidic functional groups.

[0030] The acidic functional group to be introduced is a sulfonic acid group, a carboxyl group, a phosphoric acid group, a hydroxyl group, or the like.

[0031] The amount of the acidic solution used is preferably equal to or more than the mass of the epoxy resin, more preferably equal to or more than twice the mass. If the amount of the acidic solution used is less than the mass of the epoxy resin, the introduction reaction of the acidic functional group may not proceed easily. There is no upper limit to the amount of the acidic solution used, as long as it is not excessive.

[0032] The reaction temperature in the first step is, for example, in the range of 0 to 180° C., and preferably in the range of 20 to 160° C. If the reaction temperature is lower than 0° C., the reaction for introducing an acidic functional group may not proceed easily, whereas if the reaction temperature exceeds 180° C., sulfur trioxide may be generated, which may promote corrosion of the apparatus, etc.

[0033] The reaction pressure in the first step is, for example, atmospheric pressure (950 to 1030 hPa), and pressurization (for example, 1 to 2 atm) may be performed.

[0034] The reaction time in the first step may be appropriately determined depending on the reaction temperature, reaction pressure, etc. When the reaction temperature is room temperature (20 to 25° C.) and the reaction pressure is atmospheric pressure (950 to 1030 hPa), the reaction time may be in the range of, for example, 3 to 24 hours.

[0035] In the second step, the resulting product is treated with a solution containing metal ions to form metal salts of the acidic functional groups introduced in the first step.

[0036] In the second step, the epoxy resin or the material containing the epoxy resin having the acidic functional group introduced therein may be immersed in a solution containing metal ions at a predetermined temperature, pressure, and time. If necessary, the immersion liquid may be stirred. In addition to immersion, spraying, coating, and other methods may also be used.

[0037] The solution containing metal ions includes a solution containing at least one of metal salts of alkali metals, alkaline earth metals, and transition metals. Among these, a solution containing at least one of Fe(II), Fe(III), Cu(II), and Li is preferred from the viewpoint of efficient catalysis of the Fenton reaction.

[0038] The amount of metal ions used is preferably equal to or more than the mass of the epoxy resin, more preferably equal to or more than twice the mass. If the amount of metal ions used is less than the mass of the epoxy resin, the reaction of forming the metal salt may not proceed easily. There is no upper limit to the amount of metal ions used, as long as it is not excessive.

[0039] The reaction temperature in the second step is, for example, in the range of 0 to 100° C., and preferably in the range of 20 to 80° C. If the reaction temperature is below 0° C., the reaction for forming the metal salt may not proceed easily, and if it exceeds 100° C., the solvent may evaporate.

[0040] The reaction pressure in the second step is, for example, atmospheric pressure (950 to 1030 hPa), and pressurization (for example, 1 to 2 atm) may be performed.

[0041] The reaction time in the second step may be appropriately determined depending on the reaction temperature, reaction pressure, etc. When the reaction temperature is room temperature (20 to 25° C.) and the reaction pressure is atmospheric pressure (950 to 1030 hPa), the reaction time may be in the range of, for example, 30 seconds to 24 hours.

[0042] In the third step, the epoxy resin into which the metal salt of the acidic functional group has been introduced in the first and second steps is decomposed by treatment with hydrogen peroxide.

[0043] In the third step, the epoxy resin or the material containing the epoxy resin into which the metal salt of the acidic functional group has been introduced may be immersed in a solution containing hydrogen peroxide such as hydrogen peroxide solution at a predetermined temperature, pressure and time. If necessary, the immersion liquid may be stirred. In addition to immersion, spraying, coating and other methods may also be used.

[0044] As the hydrogen peroxide, for example, hydrogen peroxide solution, sodium percarbonate, etc. may be used.

[0045] The amount of hydrogen peroxide used is preferably equal to or more than the mass of the epoxy resin, more preferably equal to or more than twice the mass. If the amount of hydrogen peroxide used is less than the mass of the epoxy resin, the decomposition reaction of the epoxy resin may not proceed easily. There is no upper limit to the amount of hydrogen peroxide used, as long as it is not excessive.

[0046] The reaction temperature in the third step is, for example, in the range of 0 to 100° C., and preferably in the range of 20 to 80° C. If the reaction temperature is below 0° C., the decomposition reaction of the epoxy resin may not proceed easily, whereas if it exceeds 100° C., hydrogen peroxide may evaporate.

[0047] The reaction pressure in the third step is, for example, atmospheric pressure (950 to 1030 hPa), and pressurization (for example, 1 to 2 atm) may be performed.

[0048] The reaction time in the third step may be appropriately determined depending on the reaction temperature, reaction pressure, etc. When the reaction temperature is room temperature (20 to 25° C.) and the reaction pressure is atmospheric pressure (950 to 1030 hPa), the reaction time may be in the range of, for example, 30 seconds to 24 hours.

[0049] The epoxy resin decomposition method according to the present embodiment allows epoxy resin to be decomposed at low cost under mild conditions such as atmospheric pressure and room temperature. This method hardly produces compounds that have a high environmental impact. In addition, by using this epoxy resin decomposition method, components other than epoxy resin can be recovered from materials containing epoxy resin at low cost under mild conditions such as atmospheric pressure and room temperature.

[0050] Materials containing epoxy resins are not particularly limited, and examples thereof include electronic components such as electrical components, IC sealants, and printed wiring boards, carbon fiber composite materials, hydrogen tanks, automotive parts such as paints, aircraft fuselages, and adhesives.

[0051] <Method for recovering carbon fibers from carbon fiber composite materials> The method for recovering carbon fibers from a carbon fiber composite material according to this embodiment is a method for recovering carbon fibers from a carbon fiber composite material using the above-mentioned epoxy resin decomposition method. This method includes a first step of treating the carbon fiber composite material with an acidic solution to introduce an acidic functional group into the epoxy resin contained in the carbon fiber composite material, a second step of treating the carbon fiber composite material with a solution containing metal ions to form a metal salt of the acidic functional group, and a third step of treating the carbon fiber composite material with hydrogen peroxide to decompose the epoxy resin into which the metal salt of the acidic functional group has been introduced, in which at least one of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid is used as the acidic solution used in the first step, and at least one of metal salts of alkali metals, alkaline earth metals, and transition metals is used as the solution containing metal ions used in the second step.

[0052] FIG. 1 shows an example of the procedure for the method for recovering carbon fibers from a carbon fiber composite material according to this embodiment.

[0053] For example, first, a carbon fiber composite material (CFRP) is treated with an acidic solution to introduce an acidic functional group into the epoxy resin contained in the carbon fiber composite material (first step: introduction of an acidic functional group). In the first step, after the reaction, the material may be washed by a method such as immersion or spraying with water or an organic solvent.

[0054] Next, the epoxy resin is treated with a solution containing metal ions to form a metal salt of the acidic functional group introduced into the epoxy resin in the first step (second step: metal substitution). In the second step, after the reaction, the epoxy resin may be washed by immersion, spraying, or the like using water or an organic solvent.

[0055] Next, the epoxy resin into which the metal salt of the acidic functional group has been introduced in the first and second steps is decomposed by treatment with hydrogen peroxide (third step: hydrogen peroxide decomposition). In the third step, after the reaction, the carbon fibers can be recovered by washing using, for example, water, an organic solvent, or the like by immersion or spraying.

[0056] The carbon fiber composite material is not particularly limited as long as it is a composite material containing carbon fiber and epoxy resin, and examples thereof include carbon fiber reinforced plastic (CFRP) and hybrid fiber reinforced plastic containing glass fiber or aramid fiber other than carbon fiber.

[0057] According to the method for recovering carbon fibers from a carbon fiber composite material according to the present embodiment, it is possible to recover carbon fibers from a carbon fiber composite material at low cost and under mild conditions such as atmospheric pressure and room temperature. This method hardly produces any compounds that have a high environmental impact.

[0058] This specification includes the following embodiments.

[0059] (1) a first step of introducing acidic functional groups into an epoxy resin by treating with an acidic solution; a second step of treating with a solution containing metal ions to form a metal salt of the acidic functional group; a third step of treating with hydrogen peroxide to decompose the epoxy resin into which the metal salt of the acidic functional group has been introduced; Including, The acid solution used in the first step is at least one of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid; A method for decomposing an epoxy resin, wherein the solution containing metal ions used in the second step is a solution containing at least one of a metal salt of an alkali metal, an alkaline earth metal, and a transition metal.

[0060] (2) A method for decomposing an epoxy resin according to (1), comprising the steps of: A method for decomposing an epoxy resin, wherein sulfuric acid is used as the acidic solution used in the first step.

[0061] (3) A method for decomposing an epoxy resin according to (1) or (2), comprising the steps of: A method for decomposing an epoxy resin, wherein the solution containing metal ions used in the second step is a solution containing at least one of Fe(II), Fe(III), Cu(II), and Li.

[0062] (4) A method for recovering carbon fibers from a carbon fiber composite material, comprising recovering carbon fibers from the carbon fiber composite material by using the method for decomposing an epoxy resin according to any one of (1) to (3). EXAMPLES

[0063] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0064] [Preparation of epoxy resin] Bisphenol F type epoxy (manufactured by Mitsubishi Chemical, epoxy equivalent 176 g / eq) as an epoxy group-containing compound (prepolymer) and 4,4-methylenebis(2,6-diethylaniline) (Tokyo Chemical Industry) as a curing agent were mixed in a 2:1 (molar ratio) ratio and heated in a constant temperature bath at 160°C for 2 hours to produce a disk-shaped (marble-shaped) epoxy resin with a diameter of approximately 5 mm.

[0065] <Example 1> [Acid solution treatment of epoxy resin] Approximately 50 mg of epoxy resin was immersed in 1 mL of 98% concentrated sulfuric acid, and after 12 hours at room temperature (25°C), it was removed and washed with ultrapure water. The surface of the epoxy resin after immersion was analyzed using an infrared spectrometer (IR) (iS20, manufactured by Thermo Fisher Scientific). The results are shown in Figure 2. The upper part of Figure 2 shows the IR spectrum of the epoxy resin before treatment with the acidic solution, the middle part after treatment with the acidic solution, and the lower part after treatment with a metal ion-containing solution (metal salt treatment).

[0066] As a result, as shown in Figure 2 (middle), -1 , 1100cm -1 and 1030cm -1 A peak characteristic of sulfonic acid was detected in the vicinity, indicating that the surface of the epoxy resin was sulfonated.

[0067] [Metal ion-containing solution treatment of epoxy resin] Approximately 50 mg of epoxy resin treated with an acid solution was immersed in 1 mL of ultrapure water in which metal salts were dissolved at a concentration of 10 mg / mL, and after 12 hours at room temperature (25°C), it was removed and washed with ultrapure water. The metal salts used were potassium hydroxide, sodium hydroxide, cesium fluoride, ammonium acetate, calcium chloride, magnesium chloride, lithium chloride, iron (II) sulfate, iron (III) sulfate, copper (II) sulfate, aluminum sulfate, silver trifluoroacetate, and zinc nitrate. The results are shown in Figure 3.

[0068] After immersion, the epoxy resin surface was analyzed by IR, and it was found that all samples were converted to sulfonates, as shown in Figure 3. The distinction between sulfonic acid and sulfonates can be made by the 3500-1500 cm region of the IR spectrum. -1 The baseline elevation was evaluated based on the presence or absence of baseline elevation in sulfonic acid, but not in sulfonate (see the middle and bottom panels of Figure 2).

[0069] [Hydrogen peroxide treatment] Approximately 50 mg of the epoxy resin converted into the sulfonate was immersed in 5 mL of a 30% by mass aqueous solution of hydrogen peroxide and heated at 80°C for 20 minutes. The surface of the epoxy resin after heating was analyzed by IR to check whether the epoxy resin had decomposed. -1 and 750cm -1 If decomposition of the sulfonated epoxy resin occurs, the peak at 1500 cm originating from the normal epoxy resin inside is observed. -1 and 750cm -1 A peak should appear around this range. The results are shown in Figure 4.

[0070] As shown in Figure 4, peaks derived from the epoxy resin appeared especially when Li, Fe(II), Fe(III), and Cu were used as the metal, and weight losses of 2.4 mass%, 3.6 mass%, 4.0 mass%, and 2.0 mass%, respectively, were observed, indicating that the epoxy resin was decomposed.

[0071] <Example 2> [Investigation of shortening decomposition time] Iron (II) sulfate, which had the greatest decomposition effect, was used as the metal ion-containing solution, and "metal ion-containing solution treatment" was performed by varying the aqueous solution concentration, temperature, and immersion time. After that, "hydrogen peroxide treatment" was performed by changing the temperature. The conditions and results examined are shown in Tables 1 and 2, and Figure 5 shows the results of hydrogen peroxide treatment at 25°C as an example of the IR spectrum of an epoxy resin. In Tables 1 and 2, "〇" indicates "decomposition" and "×" indicates "not decomposed."

[0072] [Table 1]

[0073] [Table 2]

[0074] It was found that the fastest and lowest decomposition temperature was achieved by immersing the material in an 80 mg / mL aqueous solution of iron (II) sulfate for 30 seconds and then decomposing it in 30% hydrogen peroxide at 25°C for 30 seconds.

[0075] <Comparative Examples 1 and 2> [Comparative experiment with prior art] Experiments were conducted to decompose epoxy resin that had been "acid solution treated" under the same conditions using an aqueous hydrogen peroxide solution (Comparative Example 1) and a Fenton's reagent (aqueous hydrogen peroxide solution + aqueous iron sulfate solution) (Comparative Example 2) (both experiments were conducted at room temperature (25°C) using a 30% by mass aqueous hydrogen peroxide solution). The surface of the epoxy resin after treatment was analyzed by IR to check for decomposition. The results of the experiment using the aqueous hydrogen peroxide solution are shown in Figure 6, and the results of the experiment using the Fenton's reagent are shown in Figure 7.

[0076] Regardless of which reagent was used, no decomposition of the epoxy resin was observed in the samples after 1 hour.

[0077] These results show that the coexistence of hydrogen peroxide and metal ions is necessary for the decomposition of epoxy resin. In addition, it was found that the decomposition of epoxy resin is achieved quickly and at low temperatures by the presence of acidic functional groups formed in epoxy resin by acidic solution treatment and metals in the form of metal salts.

[0078] <Example 3> [CFRP fabrication] The carbon fiber bundle was impregnated with an uncured epoxy resin containing a bisphenol-type epoxy group-containing compound and an amine-based curing agent. It was heated in a thermostatic chamber at 170°C for 2 hours to produce a CFRP with an epoxy resin fraction of 25% by mass.

[0079] [Disassembly of CFRP] Approximately 600 mg of the CFRP obtained above was immersed in 100 mL of 98 mass % concentrated sulfuric acid, and after 30 seconds at 140°C, it was taken out and washed with ultrapure water.

[0080] Approximately 25 mg of the CFRP treated with the acid solution was immersed in 5 mL of ultrapure water in which a metal salt had been dissolved at a concentration of 80 mg / mL, and after leaving it at room temperature (25°C) for 1 minute, it was removed and washed with ultrapure water.

[0081] Approximately 25 mg of the CFRP converted into sulfonate was immersed in 5 mL of a 30 mass% aqueous solution of hydrogen peroxide, and after 1 minute at room temperature (25°C), it was removed and washed with ultrapure water. The decomposed CFRP was subjected to thermogravimetric analysis using a thermogravimetric differential thermal analyzer (Rigaku, TG8120), and the presence or absence of decomposition of the epoxy resin was investigated from the weight loss when heated to 600°C. The results are shown in Figure 8.

[0082] The weight loss of the CFRP after decomposition when heated to 600℃ was 1.2% by weight, which was smaller than the 25% by weight before decomposition. This result confirmed the decomposition of the epoxy resin in the CFRP.

[0083] As described above, in the Examples, it was possible to decompose the epoxy resin at low cost under mild conditions such as atmospheric pressure and room temperature. In addition, there was almost no generation of compounds that have a high environmental impact.

Claims

1. A first step of introducing acidic functional groups into an epoxy resin by treating with an acidic solution; a second step of treating with a solution containing metal ions to form a metal salt of the acidic functional group; a third step of treating with hydrogen peroxide to decompose the epoxy resin into which the metal salt of the acidic functional group has been introduced; Including, The acid solution used in the first step is at least one of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid; A method for decomposing an epoxy resin, comprising the steps of: using a solution containing at least one of a metal salt of an alkali metal, an alkaline earth metal, and a transition metal as the solution containing metal ions used in the second step.

2. The method for decomposing an epoxy resin according to claim 1, Epoxy resin decomposition method, characterized in that sulfuric acid is used as the acidic solution used in the first step.

3. The method for decomposing an epoxy resin according to claim 1, A method for decomposing an epoxy resin, comprising the steps of: using a solution containing at least one of Fe(II), Fe(III), Cu(II), and Li as the solution containing metal ions used in the second step.

4. A method for recovering carbon fibers from a carbon fiber composite material, comprising recovering carbon fibers from the carbon fiber composite material by using the method for decomposing an epoxy resin according to any one of claims 1 to 3.

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