Synthetic resin degradation method

Abstract

[Problem] To provide an epoxy resin degradation method for degrading synthetic resins including an epoxy resin obtained by binding an epoxy resin monomer having an epoxy group with at least one of a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound that are capable of binding to an epoxy group. [Solution] The present invention involves mixing a synthetic resin, a base, and an organic solvent containing at least one of 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropylene urea, tetramethylurea, N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide.

Description

Synthetic resin decomposition method

[0001] The present invention relates to a method for decomposing synthetic resins, including epoxy resins obtained by bonding an epoxy resin monomer having an epoxy group with at least one of a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound, which are capable of bonding with the epoxy group.

[0002] Thermosetting resins are strong and stable resins and are used in a variety of applications, such as adhesives, packaging materials, and semiconductor encapsulation materials. Furthermore, the properties of thermosetting resins can be improved by mixing them with glass fibers, carbon fibers, etc.

[0003] As of 2019, thermosetting resins accounted for approximately 10% of total resin production, and due to their properties, they will continue to be an essential material in industrial society.

[0004] Epoxy resin, which is one type of thermosetting resin, is a thermosetting resin that has excellent electrical insulation properties, heat resistance, mechanical strength, etc., and is widely used as a material for various electrical components, electronic components, automobile components, etc. This epoxy resin can be obtained, for example, 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 then subjecting the mixture to a thermal curing treatment.

[0005] However, once cured, epoxy resins are difficult to soften or melt due to heat and have low solubility in solvents, making them difficult to decompose and posing problems such as environmental impact.

[0006] In response to this situation, methods for decomposing epoxy resins have been proposed. For example, Patent Document 1 proposes a decomposition method in which a cured epoxy resin containing silica is brought into contact with subcritical water in which at least one alkali selected from an alkali metal salt and an alkali metal hydroxide is coexisted to decompose the cured epoxy resin.

[0007] Furthermore, Non-Patent Document 1 proposes a method of decomposing an epoxy resin cured with a low-viscosity primary amine by heating it in toluene at 190°C using sodium hydroxide.

[0008] Furthermore, Non-Patent Document 2 proposes a method in which a non-networked epoxy resin cured with a low-viscosity primary amine is heated at 160°C using potassium tert-butoxide in 1,4-dioxane or a mixed solvent of tetrahydrofuran and toluene, and also proposes a method in which a cured epoxy resin cured with a low-viscosity primary amine and having some network formation is first pretreated by irradiating it with microwaves in 1,4-dioxane at 200°C, and then heated at 160°C using potassium tert-butoxide in a mixed solvent of tetrahydrofuran and toluene.

[0009] Non-Patent Document 3 proposes a method in which networked epoxy resin fallout is heated at 200° C. in an N-methylpyrrolidone solvent using a nickel complex catalyst and hydrogen molecules.

[0010] JP 2012-188466 A

[0011] Hongwei Sun, Alexander Ahrens, Gabriel Martins Ferreira Batista, Bjarke S. Donslund, Anne. K. Ravn, Emil Vincent Schwibinger, Ainara Nova Flores, Troels Skrydstrup ChemRxiv. DOI: 10.26434 / chemrxiv-2023-207wl.Rebecca C. DiPucchio, Katherine R. Stevenson, Ciaran W. Lahive, William E. Michener, and Gregg T. Beckham ACS Sustainable Chem. Eng. DOI: 10.1021 / acssuschemeng.3c04181. Yumeng Liao, Kohei Takahashi, and Kyoko Nozaki J. Am. Chem. Soc. DOI: 10.1021 / jacs.3c09061.

[0012] However, the methods for decomposing epoxy resins described in Patent Document 1 and Non-Patent Documents 1 to 3 have the problem that they require high temperatures and high pressures, and therefore a great deal of energy is required to dispose of a large amount of epoxy resin. Furthermore, these decomposition methods have the problem that they require the use of equipment that can withstand such high temperatures and high pressures.

[0013] Furthermore, the epoxy resin decomposition method described in Non-Patent Document 1 has the problem that, when a commercially available composite epoxy resin is used, the resin must be immersed in a 75% aqueous acetic acid solution at 70°C overnight before decomposition, resulting in low epoxy resin decomposition efficiency. The epoxy resin decomposition method described in Non-Patent Document 2 has the problem that the aforementioned pretreatment is required when a higher hardness epoxy resin cured product is used. In addition, the epoxy resin decomposition methods described in Non-Patent Documents 1 and 2 have the problem of low versatility, for example, they are not applicable to epoxy resin cured products that have been networked with more highly superior aromatic diamines. Finally, the epoxy resin decomposition method described in Non-Patent Document 3 has the problem of requiring the use of expensive and valuable transition metals as catalysts and the use of hydrogen gas.

[0014] In view of the above circumstances, an object of the present invention is to provide a synthetic resin decomposition method that can efficiently decompose epoxy resins contained in synthetic resins under milder conditions than conventional decomposition methods.

[0015] As a result of intensive research into the above-mentioned problems, the inventors of the present invention have discovered the following revolutionary synthetic resin decomposition method for decomposing synthetic resins including epoxy resins.

[0016] A first aspect of the present invention for solving the above-mentioned problems is a synthetic resin decomposition method for decomposing a synthetic resin containing an epoxy resin obtained by bonding an epoxy resin monomer having an epoxy group, which is represented by at least one of chemical formulas (A1) to (A8), with at least one of a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound capable of bonding with the epoxy group, the synthetic resin decomposition method comprising a decomposition step of mixing the synthetic resin, a base, and an organic solvent containing at least one of 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, tetramethylurea, N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide, to decompose the epoxy resin contained in the synthetic resin.

[0017] Here, n in the above chemical formula represents any natural number.

[0018] According to the first aspect, the epoxy resin contained in the synthetic resin can be efficiently decomposed.

[0019] A second aspect of the present invention is the synthetic resin decomposition method according to the first aspect, characterized in that the amount of the organic solvent is 0.1 to 5 moles per unit mole of the epoxy resin monomer.

[0020] According to the second aspect, the epoxy resin contained in the synthetic resin can be decomposed more efficiently.

[0021] A third aspect of the present invention is the synthetic resin decomposition method according to the first aspect, characterized in that the base comprises at least one of sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium tert-butoxide, lithium tert-butoxide, potassium tert-butoxide, lithium bistrimethylsilylamide, sodium bistrimethylsilylamide, and potassium bistrimethylsilylamide.

[0022] According to the third aspect, the epoxy resin contained in the synthetic resin can be decomposed more efficiently.

[0023] A fourth aspect of the present invention is the synthetic resin decomposition method according to the first aspect, wherein the amount of the base is 2 to 12 equivalents relative to the amount of epoxy resin monomer structural units used to obtain the epoxy resin.

[0024] Here, the epoxy resin monomer structural unit is, as shown in the following chemical formula, an epoxy resin monomer used to obtain an epoxy resin from which two epoxy groups located at both ends have been removed.

[0025] In this chemical formula, R １ represents, for example, a carbon functional group such as dimethylmethylene, methylene, bistrifluoromethylmethylene, or 9,9-fluorenyl, or a sulfur functional group such as sulfonyl or sulfanyl. ２ represents, for example, hydrogen, a carbon functional group such as a methyl group, or a halogen such as bromine at any position on the benzene ring.

[0026] Specific examples of the epoxy resin monomer structural unit include those shown in the following chemical formulas (a1) to (a8) for the epoxy resin monomers of the above-mentioned chemical formulas (A1) to (A8). Note that the epoxy resin monomer structural unit for the epoxy resin monomer of chemical formula (A1) is that shown in chemical formula (a1), and the other units have a similar relationship.

[0027] Here, n in the above chemical formula represents any natural number.

[0028] According to the fourth aspect, the epoxy resin contained in the synthetic resin can be decomposed more efficiently.

[0029] A fifth aspect of the present invention is the synthetic resin decomposition method according to any one of the first to fourth aspects, characterized in that the diamine compound is a compound represented by any one of chemical formulas (B1) to (B7), the monoamine compound is a compound represented by the following chemical formula (B8), the acid anhydride is a compound represented by any one of chemical formulas (B9) to (B10), and the dithiol compound is a compound represented by the following chemical formula (B11).

[0030]

[0031] According to the fifth aspect, the epoxy resin contained in the synthetic resin can be decomposed more efficiently.

[0032] A sixth aspect of the present invention is the synthetic resin decomposition method according to the first aspect, characterized in that the reaction temperature in the decomposition step is in the range of 100°C to 160°C.

[0033] It is known that bisphenol A decomposes at high temperatures (190°C) (see Non-Patent Document 1). However, according to the sixth aspect, by carrying out the reaction at a low temperature (for example, 100 to 160°C), it is possible to recover the epoxy resin monomer (for example, bisphenol A) used to obtain the epoxy resin, which is generated during the decomposition of the epoxy resin, without decomposing it.

[0034] FIG. 1 shows chemical reaction formulas according to Examples 1 to 17. FIG. 2 is a table showing the reaction conditions and the yield of bisphenol A according to Examples 1 to 17. FIG. 3 shows a chemical reaction formula according to Example 18. FIG. 4 shows a chemical reaction formula according to Example 19. FIG. 5 shows a chemical reaction formula according to Example 20. FIG. 6 shows a chemical reaction formula according to Example 21. FIG. 7 shows a chemical reaction formula according to Example 22. FIG. 8 shows a chemical reaction formula according to Example 23. FIG. 9 shows a chemical reaction formula according to Example 24. FIG. 10 shows a chemical reaction formula according to Example 25. FIG. 11 shows a chemical reaction formula according to Example 26. FIG. 12 shows a chemical reaction formula according to Example 27. FIG. 13 shows a chemical reaction formula according to Example 28. FIG. 14 shows an SEM image of the surface of the carbon fiber of Example 29. FIG. 15 shows a chemical reaction formula according to Example 29. FIG. 16 shows an SEM image of the surface of the carbon fiber of Example 30. FIG. 17 shows a chemical reaction formula according to Example 30.

[0035] Hereinafter, an embodiment of the method for decomposing synthetic resins including epoxy resins according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiment.

[0036] (Embodiment 1) <<Method for Decomposing Synthetic Resins>> A method for decomposing synthetic resins containing epoxy resins according to this embodiment is a method for decomposing synthetic resins containing epoxy resins, which are represented by at least one of the following chemical formulas (A1) to (A8) and are obtained by bonding an epoxy resin monomer having an epoxy group with at least one of a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound capable of bonding to the epoxy group. The method includes a decomposition step of mixing the synthetic resin, a base, and an organic solvent containing at least one of 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, tetramethylurea, N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide to decompose the epoxy resin contained in the synthetic resin.

[0037] Here, n in the above chemical formula represents any natural number.

[0038] According to the synthetic resin decomposition method of this embodiment, epoxy resins can be efficiently decomposed at low reaction temperatures (e.g., 80 to 200° C.). In addition, when the reaction temperature is lower than 190° C. (e.g., 80 to 180° C.), epoxy resin monomers (e.g., bisphenol A) used to obtain the epoxy resins, which are generated when the epoxy resins are decomposed, can be recovered without being decomposed.

[0039] <Synthetic Resins> The synthetic resins to be decomposed by the synthetic resin decomposition method according to this embodiment (target synthetic resins) are not particularly limited as long as they are represented by at least one of the above chemical formulas (A1) to (A8) and include an epoxy resin obtained by bonding an epoxy resin monomer having an epoxy group with at least one of a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound capable of bonding with the epoxy group. That is, the target synthetic resin may be a resin obtained by bonding one type of epoxy resin monomer with one (only one type of compound) of a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound capable of bonding with the epoxy group, or a resin obtained by bonding multiple types of epoxy resin monomers with multiple types of compounds from a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound capable of bonding with the epoxy group. The proportion (by weight) of epoxy resin in the synthetic resin is not particularly limited, and a higher weight percentage of epoxy resin (e.g., 80 to 100 by weight) is preferred, and the resin may even be 100 by weight. The above-mentioned epoxy resins and synthetic resins can be produced by known production methods.

[0040] The diamine compound is not particularly limited as long as it is a compound having two nitrogen atoms bonded to at least one hydrogen atom. The monoamine compound is not particularly limited as long as it is a compound having one nitrogen atom bonded to two hydrogen atoms. The acid anhydride is not particularly limited as long as it is a compound formed by dehydration condensation of two oxo acid molecules. The dithiol compound is not particularly limited as long as it is a compound having two thiol groups. The imidazole compound is not particularly limited as long as it is a compound having an imidazole group.

[0041] Here, the diamine compound is, for example, a compound represented by chemical formulas (B1) to (B7), the monoamine compound is, for example, a compound represented by chemical formula (B8), the acid anhydride is, for example, a compound represented by chemical formulas (B9) to (B10), the dithiol compound is, for example, a compound represented by chemical formula (B11), and the imidazole compound is, for example, a compound represented by chemical formula (B12).

[0042]

[0043] The synthetic resin may contain components other than epoxy resin. Specifically, the synthetic resin may contain polyester, polyamide, polycarbonate, polyfluorocarbon, carbon fiber, glass fiber, water, etc. Even if the synthetic resin contains these components, the epoxy resin contained in the synthetic resin can be decomposed by the synthetic resin decomposition method according to the present invention.

[0044] <Base> In the synthetic resin decomposition method according to this embodiment, the base is not particularly limited. Examples of the base include sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium tert-butoxide, lithium tert-butoxide, potassium tert-butoxide, lithium bistrimethylsilylamide, sodium bistrimethylsilylamide, and potassium bistrimethylsilylamide. Only one of these may be used, or multiple types may be used. By using these bases, the synthetic resin can be decomposed more easily.

[0045] In the synthetic resin decomposition method according to this embodiment, the amount of base is not particularly limited, but it is preferable to react 2 to 12 equivalents, more preferably 2 to 8 equivalents, even more preferably 2 to 6 equivalents, and particularly preferably 3.5 to 4.5 equivalents, relative to the amount of epoxy resin monomer structural unit represented by at least one of the following chemical formulas (a1) to (a8) used to obtain the epoxy resin. The epoxy resin monomer structural unit may be constituted by one type of compound, or multiple types of compounds in amounts appropriate to the ratio used in synthesizing the epoxy resin, as long as it is one used to obtain the epoxy resin.

[0046] Here, n in the above chemical formula represents any natural number.

[0047] <Organic Solvent> In the synthetic resin decomposition method according to this embodiment, the organic solvent that can be used is not particularly limited as long as it contains at least one of 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, tetramethylurea, N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide. However, an organic solvent containing only 1,3-dimethyl-2-imidazolidinone is preferred. By using these organic solvents, the epoxy resin contained in the synthetic resin can be more easily decomposed. The organic solvent may be not only one of the above-mentioned compounds, but also a mixture of multiple compounds. The organic solvent may be composed solely of the above-mentioned compounds (100% by weight), or may contain substances other than the above-mentioned compounds.

[0048] The amount of the organic solvent is not particularly limited, but is preferably 0.1 to 5 molar concentration relative to the moles of epoxy resin monomer units of the synthetic resin, more preferably 0.2 to 2 molar concentration, and particularly preferably 0.25 to 1 molar concentration.

[0049] <Reaction Conditions for Decomposition Step> The decomposition of the synthetic resin according to this embodiment is carried out by mixing the synthetic resin with a base and an organic solvent containing at least one of 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, tetramethylurea, N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide.

[0050] The order of mixing (blending) these materials (substances) is not particularly limited, but examples include first mixing a synthetic resin and a base and then adding an organic solvent, or preparing a raw material composition that is a blend of a base and an organic solvent and then mixing this raw material composition with a synthetic resin.

[0051] The synthetic resin decomposition method according to this embodiment can be carried out in an inert gas (e.g., argon, nitrogen, etc.) atmosphere or an air atmosphere. The reaction temperature during decomposition of the synthetic resin (the reaction temperature during the decomposition step) is not particularly limited, but is preferably within a range of 80 to 200°C, since the epoxy resin contained in the synthetic resin can be easily decomposed. A reaction temperature during the decomposition step of 100 to 160°C is more preferable, since the epoxy resin contained in the synthetic resin can be more easily decomposed and the epoxy resin monomer (used to obtain the epoxy resin) produced during the decomposition of the epoxy resin can be recovered without decomposition. A reaction temperature during the decomposition step of 140 to 150°C is particularly preferable, since the epoxy resin contained in the synthetic resin can be more easily decomposed and the epoxy resin monomer (used to obtain the epoxy resin) produced during the decomposition of the epoxy resin can be recovered without decomposition.

[0052] The time required for the reaction step is not particularly limited, but is preferably in the range of 1 to 40 hours, more preferably in the range of 7 to 10 hours. In the decomposition step, it is preferable to stir the mixture of the synthetic resin, the base, and the organic solvent by a known means.

[0053] <<Method for recovering bisphenol A, etc.>> The synthetic resin decomposition products produced using the synthetic resin decomposition method according to this embodiment contain a specific bisphenol, a specific bisphenol ether, and low-molecular-weight oligomers and polymers derived from the curing agent that can be separated from these. Therefore, by using this synthetic resin decomposition method, bisphenol A can be recovered from epoxy resin. Note that the bisphenol ether can ultimately be subjected to a known hydrolysis reaction to obtain the specific bisphenol.

[0054] Next, the synthetic resin decomposition method according to the present invention will be explained more specifically and in detail with reference to examples, but the present invention is not limited to the following examples.

[0055] Examples (Entry) 1 to 17 To verify in detail the synthetic resin decomposition method according to this embodiment, an epoxy resin monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups was mixed with 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1, and the mixture was heated at 180°C for 5 hours to obtain a cured resin. The cured resin was then pulverized, and the resulting powdered epoxy resin (1) (a synthetic resin composed of 100% epoxy resin) was used to verify depolymerization.

[0056] In an argon atmosphere, a base and an organic solvent were sequentially added to a predetermined amount (0.10 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (1), and the reaction mixture was stirred under heating. The reaction mixture was then returned to room temperature (25°C), and hydrochloric acid was added to quench (terminate) the reaction.

[0057] Next, ethyl acetate was added to the reaction mixture, and the organic layer was extracted from the resulting two-layer solution, dried over magnesium sulfate, and evaporated under reduced pressure to obtain a crude product. The crude product was analyzed using mesitylene as an internal standard and deuterated chloroform. １ The yield of bisphenol A obtained according to the chemical reaction formula shown in Figure 1 was measured by H NMR, and the results are shown in Figure 2.

[0058] As can be seen from this figure, it was found that the powdered epoxy resin (1) can be easily decomposed by the synthetic resin decomposition method of this example.

[0059] Example 18 In an argon atmosphere, 384 mg (4.0 mmol) of sodium tert-butoxide and 2.0 mL of 3-dimethyl-2-imidazolidinone (DMI) were added sequentially to 589 mg (1.0 mmol, calculated relative to the molar weight of the epoxy resin monomer) of powdered epoxy resin (1), and the reaction mixture was stirred for 7 hours while heating at 150°C. Thereafter, the reaction mixture was returned to room temperature (25°C), and pure water was added to precipitate a solid. Next, the solid component was separated from the aqueous solution by decantation, and hydrochloric acid was added to the solid component.

[0060] Thereafter, organic matter was extracted from the solid component using acetic acid, and the solvent was removed by vacuum distillation to obtain a crude product. From the crude product, silica gel chromatography (developing solvent: a mixed solvent of hexane and ethyl acetate, volume ratio 6:4) was used to obtain bisphenol A (yield: 216 mg, 0.94 mmol, 94%) obtained according to the chemical reaction formula shown in Figure 3. In other words, it was found that the synthetic resin decomposition method of this example can easily and sufficiently decompose powdered epoxy resin (1). Bisphenol A: 1 H NMR (600 MHz, acetone-d6) δ 1.58 (s, 6H), 6.72 (AA'BB', 4H), 7.05 (AA'BB', 4H), 8.11 (br, 2H).

[0061] Example 19 In an argon atmosphere, 160 mg (4.0 mmol) of sodium hydroxide and 2.0 mL of 3-dimethyl-2-imidazolidinone (DMI) were added sequentially to 589 mg (1.0 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (1), and the reaction mixture was stirred for 7 hours while being heated at 150° C. Thereafter, the reaction mixture was returned to room temperature (25° C.), and pure water was added to precipitate a solid.

[0062] Next, the solid component was separated from the aqueous solution by decantation, and hydrochloric acid was added to the solid component. Subsequently, organic matter was extracted from the solid component using ethyl acetate, and the solvent was removed by distillation under reduced pressure to obtain a crude product. From the crude product, silica gel chromatography (developing solvent: a mixed solvent of hexane and ethyl acetate, volume ratio 6:4) was used to obtain bisphenol A (yield: 140 mg, 0.61 mmol, 61%), which was obtained according to the chemical reaction formula shown in Figure 4. In other words, it was found that powdered epoxy resin (1) can be easily decomposed by the synthetic resin decomposition method of this example.

[0063] Example 20 In an argon atmosphere, 38.4 mg (0.4 mmol) of sodium tert-butoxide and 0.2 mL of 3-dimethyl-2-imidazolidinone (DMI) were added sequentially to 59.1 mg (0.1 mmol, calculated relative to the molar weight of the epoxy resin monomer) of powdered epoxy resin (1), and the reaction mixture was stirred for 23 hours while heating at 150° C. Thereafter, the reaction mixture was returned to room temperature (25° C.), and 94.5 μL (1.0 mmol) of acetic anhydride was added, followed by stirring for 5 hours while heating at 100° C.

[0064] Ethyl acetate was then added to the reaction mixture, and the resulting solid precipitate was removed by filtration. The crude product was then distilled off under reduced pressure. From the crude product, silica gel chromatography (developing solvent: a mixed solvent of hexane and ethyl acetate, volume ratio 6:4) yielded bisphenol A diacetate (yield: 26.2 mg, 0.084 mmol, 84%), obtained according to the chemical reaction formula shown in Figure 5. This demonstrates that the synthetic resin decomposition method of this example can easily and effectively decompose powdered epoxy resin (1).

[0065] Example 21 In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups and 4,4'-diaminodiphenyl sulfone were mixed in a molar ratio of 2:1 and heated at 180°C for 5 hours to obtain a cured resin. The cured resin was then pulverized to obtain 467 mg (0.5 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (2) (synthetic resin consisting of 100% epoxy resin). To this was added 385 mg (4 mmol) of sodium tert-butoxide and 2.0 mL of 3-dimethyl-2-imidazolidinone (DMI), followed by stirring for 24 hours at 150°C. The reaction mixture was then returned to room temperature (25°C) and hydrochloric acid was added.

[0066] The organic matter was then extracted with ethyl acetate, and the solvent was removed by distillation under reduced pressure to obtain a crude product. This crude product was subjected to silica gel chromatography (developing solvent: a mixed solvent of hexane and ethyl acetate, volume ratio 7:3) to obtain bisphenol A (yield: 180.6 mg, 0.79 mmol, 79%), which was obtained according to the chemical reaction formula shown in Figure 6. This demonstrates that the synthetic resin decomposition method of this example can easily decompose networked epoxy resin (2).

[0067] Example 22 In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups and 4,4'-diaminophenylmethane were mixed in a 1:1 molar ratio and heated at 180°C for 5 hours to obtain a cured resin. The cured resin was then pulverized to obtain 54.2 mg (0.1 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (3). To this was added 38.4 mg (0.4 mmol) of sodium tert-butoxide and 0.2 mL of 3-dimethyl-2-imidazolidinone (DMI), followed by stirring for 19 hours at 150°C. The reaction mixture was then returned to room temperature (25°C), and pure water was added to precipitate a solid component.

[0068] Next, the solid component was separated from the aqueous solution by decantation, and hydrochloric acid was added to the solid component. Subsequently, organic matter was extracted from the solid component using ethyl acetate, and the solvent was removed by distillation under reduced pressure to obtain a crude product. From the crude product, silica gel chromatography (developing solvent: hexane / ethyl acetate 6 / 4) was performed to obtain bisphenol A (yield: 22 mg, 0.095 mmol, 95%), which was obtained according to the chemical reaction formula shown in Figure 7. It was found that powdered epoxy resin (3) could be easily decomposed by the synthetic resin decomposition method of this example.

[0069] Example 23 In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups and aniline were mixed in a 1:1 molar ratio and heated at 110°C for 24 hours to obtain a cured resin. The cured resin was then crushed to obtain 87.2 mg (0.2 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (4). To this was added, in order, 77.5 mg (0.8 mmol) of sodium tert-butoxide and 0.4 mL of 3-dimethyl-2-imidazolidinone (DMI). The reaction mixture was then stirred for 7 hours at 150°C while being heated. The reaction mixture was then returned to room temperature (25°C), and hydrochloric acid (2 M, 0.8 mL) was added.

[0070] Subsequently, organic matter was extracted from the solid component using methylene chloride, and the solvent was removed by distillation under reduced pressure to obtain a crude product. From the crude product, silica gel chromatography (developing solvent: hexane / ethyl acetate 6 / 4) was performed to obtain bisphenol A (yield: 35 mg, 0.153 mmol, 76%), which was obtained according to the chemical reaction formula shown in Figure 8. It was found that powdered epoxy resin (4) can be easily decomposed by the synthetic resin decomposition method of this example.

[0071] Example 24: In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups and ethylenediamine were mixed in a 1:1 molar ratio and heated at 40°C for 24 hours, 80°C for 24 hours, and 100°C for 1 hour, yielding a cured resin. The cured resin was then crushed to obtain 80.2 mg (0.2 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (5). To this was added 77.3 mg (0.8 mmol) of sodium tert-butoxide and 0.4 mL of 3-dimethyl-2-imidazolidinone (DMI), followed by stirring at 150°C for 7 hours. The reaction mixture was then returned to room temperature (25°C), and hydrochloric acid (2 M, 0.8 mL) was added.

[0072] Subsequently, organic matter was extracted from the solid component using methylene chloride, and the solvent was removed by distillation under reduced pressure to obtain a crude product. From the crude product, silica gel chromatography (developing solvent: hexane / ethyl acetate 6 / 4) was performed to obtain bisphenol A (yield: 30 mg, 0.129 mmol, 65%), which was obtained according to the chemical reaction formula shown in Figure 9. It was found that powdered epoxy resin (5) can be easily decomposed by the synthetic resin decomposition method of this example.

[0073] Example 25: In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups and 2-methyl-1,3-imidazole were mixed in a 1:1 molar ratio and heated at 120°C for 2 hours and then at 180°C for 2 hours to obtain a cured resin. The cured resin was then crushed to obtain 84.7 mg (0.2 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (6). To this was added 77.1 mg (0.8 mmol) of sodium tert-butoxide and 0.4 mL of 3-dimethyl-2-imidazolidinone (DMI), followed by stirring for 19 hours at 150°C. The reaction mixture was then returned to room temperature (25°C) and then hydrochloric acid (2 M, 0.8 mL) was added.

[0074] Then, organic matter was extracted from the solid component using ethyl acetate, and the solvent was removed by distillation under reduced pressure to obtain a crude product. From the crude product, silica gel chromatography (developing solvent: hexane / ethyl acetate 6 / 4) was performed to obtain bisphenol A (yield: 37 mg, 0.162 mmol, 81%), which was obtained according to the chemical reaction formula shown in Figure 10. It was found that powdered epoxy resin (6) can be easily decomposed by the synthetic resin decomposition method of this example.

[0075] Example 26: In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups, 5.4 mL of 1,4-dioxane, and 1,3-di(mercaptomethyl)benzene were mixed in a 1:1 molar ratio with the epoxy monomer. Triethylamine (0.1 molar ratio with the epoxy monomer) was added and the mixture was heated at 75°C for 23 hours to obtain a cured resin. The cured resin was then crushed to obtain 259 mg (0.51 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (7). 196 mg (2.0 mmol) of sodium tert-butoxide and 1.0 mL of 3-dimethyl-2-imidazolidinone (DMI) were then added sequentially. The reaction mixture was then heated and stirred at 150°C for 7 hours. The reaction mixture was then returned to room temperature (25°C), and 379 μL (4.0 mmol) of acetic anhydride was added. The mixture was then heated and stirred at 100°C for 5 hours.

[0076] Ethyl acetate was then added to the reaction mixture, and the resulting solid precipitate was removed by filtration. The crude product was then distilled off under reduced pressure. From the crude product, silica gel chromatography (developing solvent: a mixed solvent of hexane and ethyl acetate, volume ratio 7:3) yielded bisphenol A diacetate (yield: 114 mg, 0.364 mmol, 72%), obtained according to the chemical reaction formula shown in Figure 11. This demonstrates that the synthetic resin decomposition method of this example can easily and effectively decompose powdered epoxy resin (7).

[0077] Example 27 In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups and hexahydroisobenzofuran-1,3-dione were mixed in a molar ratio of 1:1.6 and heated at 100°C for 10 minutes. Tetraphenylphosphonium bromide (0.75 mol% relative to the epoxy monomer) was then added, and the mixture was heated at 100°C for 10 minutes, followed by heating at 130°C for 4 hours to obtain a cured resin. The cured resin was then pulverized to obtain 117 mg of powdered epoxy resin (8) (0.2 mmol, calculated relative to the molar weight of the bisphenol A unit). To this was added 154 mg (1.6 mmol) of sodium tert-butoxide and 0.6 mL of 3-dimethyl-2-imidazolidinone (DMI), followed by stirring the reaction mixture for 19 hours while heating at 150°C.

[0078] The reaction mixture was then returned to room temperature (25°C), and hydrochloric acid was added. The organic matter was then extracted with ethyl acetate, and the solvent was removed by distillation under reduced pressure to obtain a crude product. From this crude product, silica gel chromatography (developing solvent: a mixed solvent of hexane and ethyl acetate, volume ratio 6:4) was used to obtain bisphenol A (yield: 42 mg, 0.18 mmol, 89%), obtained according to the chemical reaction formula shown in Figure 12. In other words, it was found that the synthetic resin decomposition method of this example can easily decompose the network epoxy resin (8) derived from the networked acid anhydride curing agent.

[0079] Example 28: In an argon atmosphere, an epoxy monomer in which the hydrogen atoms at both ends of bisphenol A were substituted with glycidyl groups was placed in a rotor and heated to 130°C while stirring. Bis(acetoacetoxy)zinc (molar ratio to the epoxy monomer: 0.05) was added and further stirred. After cooling the reaction mixture to 80°C, glutaric anhydride was mixed with the epoxy monomer in a 1:1 molar ratio. Air bubbles were removed by heating at 80°C while reducing the pressure. The reaction mixture was then heated at 130°C for 4 hours and then at 160°C for 2 hours to obtain a cured resin. The cured resin was then crushed to obtain 137 mg (0.3 mmol, calculated relative to the molar weight of the monomer) of powdered epoxy resin (9). 231 mg (2.4 mmol) of sodium tert-butoxide and 0.6 mL of 3-dimethyl-2-imidazolidinone (DMI) were then added sequentially. The reaction mixture was then stirred for 7 hours while heated at 150°C.

[0080] The reaction mixture was then returned to room temperature (25°C), and 2.4 mL of 2 M hydrochloric acid was added. The organic matter was then extracted from the solid component using ethyl acetate, and the solvent was removed by distillation under reduced pressure to obtain a crude product. Bisphenol A (yield: 48 mg, 0.201 mmol, 70%) was obtained from the crude product by silica gel chromatography (developing solvent: hexane / ethyl acetate 6 / 4) according to the chemical reaction formula shown in Figure 13. It was found that powdered epoxy resin (9) could be easily decomposed by the synthetic resin decomposition method of this example.

[0081] Example 29 In an argon atmosphere, 96.5 mg (1.0 mmol) of sodium tert-butoxide and 4.0 mL of 3-dimethyl-2-imidazolidinone (DMI) were added sequentially to 432 mg of a block of commercially available carbon fiber-reinforced epoxy resin (10) (Cat. No. JISK6850AJAA01), and the reaction mixture was stirred for 23 hours while heating at 150°C. The reaction mixture was then returned to room temperature (25°C), and 3.0 mL of 2 M hydrochloric acid was added to quench the reaction. Ethyl acetate was then added to the reaction mixture.

[0082] First, carbon fibers were separated from the obtained solution. The carbon fibers were removed, washed thoroughly with water, methanol, and acetone, in that order, and vacuum dried at room temperature (25°C). The carbon fibers were then dried at 115°C, and the mass of the carbon fibers was measured to be 285 mg. The surfaces of the recovered carbon fibers were also measured with an SEM. The results are shown in Figure 14. Analysis of the SEM images revealed that the carbon fibers were recovered without damaging their surfaces.

[0083] Next, the organic layer was extracted from the remaining solution after recovering the carbon fibers and evaporated under reduced pressure. Gas chromatography analysis using styrene as an internal standard revealed that 0.115 mmol of bisphenol A was obtained according to the chemical reaction formula shown in Figure 15. This demonstrates that the synthetic resin decomposition method of this example can easily decompose the epoxy resin (10) contained in commercially available carbon fiber-reinforced epoxy resins.

[0084] Example 30 In an argon atmosphere, 98.1 mg (1.0 mmol) of sodium tert-butoxide and 4.0 mL of 3-dimethyl-2-imidazolidinone (DMI) were added sequentially to 534 mg of a block of commercially available glass fiber-reinforced epoxy resin (11), and the reaction mixture was stirred for 23 hours while heating at 150°C. The reaction mixture was then returned to room temperature (25°C), and 3.0 mL of 2 M hydrochloric acid was added to quench the reaction. Ethyl acetate was then added.

[0085] First, the glass fibers were separated from the obtained solution. The glass fibers were then removed, thoroughly washed with water, methanol, and acetone, in that order, and vacuum dried at room temperature (25°C). The glass fibers were then dried at 115°C, and their mass was measured, yielding a value of 347 mg. The surfaces of the recovered glass fibers were also analyzed using an SEM. The results are shown in Figure 16. Analysis of the SEM images revealed that the glass fibers were successfully recovered without damaging their surfaces.

[0086] Next, the organic layer was extracted from the remaining solution after recovering the glass fibers and evaporated under reduced pressure. Then, gas chromatography analysis using styrene as an internal standard revealed that 0.318 mmol of bisphenol A was obtained according to the chemical reaction formula shown in Figure 17. This demonstrates that the synthetic resin decomposition method of this example can easily decompose the epoxy resin (11) contained in commercially available glass fiber-reinforced epoxy resins.

[0087] (Other Embodiments) From the above-described examples, it will be understood by those skilled in the art that even epoxy resins included in the present invention but not described in the examples can be decomposed by using the synthetic resin decomposition method of the present invention.

[0088] Furthermore, from the above examples, it will be understood by those skilled in the art that even a base that is included in the present invention but not described in the examples can decompose an epoxy resin included in the present invention by using the synthetic resin decomposition method of the present invention.

[0089] Furthermore, from the above examples, it will be understood by those skilled in the art that even organic solvents that are included in the present invention but not described in the examples can be used to decompose epoxy resins included in the present invention by using the synthetic resin decomposition method of the present invention.

Claims

1. A method for decomposing a synthetic resin containing an epoxy resin obtained by bonding an epoxy resin monomer represented by at least one of chemical formulas (A1) to (A8) and having an epoxy group, and at least one of a diamine compound, a monoamine compound, an acid anhydride, a dithiol compound, and an imidazole compound capable of bonding to the epoxy group, the method comprising: mixing the synthetic resin, a base, and an organic solvent containing at least one of 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, tetramethylurea, N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide to decompose the epoxy resin contained in the synthetic resin, the method being characterized by having a decomposition step. (n in the above chemical formula represents an arbitrary natural number.) 2. The method for decomposing a synthetic resin according to claim 1, wherein the amount of the organic solvent is in a molar concentration of 0.1 to 5 moles per unit mole of the epoxy resin monomer.

3. The method for decomposing a synthetic resin according to claim 1, wherein the base contains at least one of sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium tert-butoxide, lithium tert-butoxide, potassium tert-butoxide, lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amide, and potassium bis(trimethylsilyl)amide.

4. The amount of the base is 2 to 12 equivalents relative to the amount of the epoxy resin monomer structural unit represented by at least one of chemical formulas (a1) to (a8) used to obtain the epoxy resin, and the method for decomposing a synthetic resin according to claim 1 is characterized by this. (n in the above chemical formula represents an arbitrary natural number.) 5. The diamine compound is a compound represented by chemical formulas (B1) to (B7), the monoamine compound is a compound represented by chemical formula (B8), the acid anhydride is a compound represented by chemical formulas (B9) to (B10), the dithiol compound is a compound represented by chemical formula (B11), and the imidazole compound is a compound represented by chemical formula (B12). The method for decomposing a synthetic resin according to any one of claims 1 to 4, characterized by this.

6. The method for decomposing a synthetic resin according to claim 1, wherein the reaction temperature in the decomposition step is in the range of 100°C to 160°C.

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