Easily decomposable resin, method for decomposing easily decomposable resin, and method for recovering fiber from fiber-reinforced resin

Abstract

To provide an easily decomposable resin that allows decomposition with low energy consumption.SOLUTION: An easily decomposable resin comprises an iron complex having a divalent or trivalent iron ion and a ligand, and a resin, wherein the iron complex is chemically bonded to the resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an easily decomposable resin, a method for decomposing an easily decomposable resin, and a method for recovering fibers from a fiber-reinforced resin. [Background technology]

[0002] It has long been known that when divalent iron (II) and hydrogen peroxide are mixed, hydroxyl radicals are generated, which oxidize organic matter, known as the Fenton reaction (see, for example, Non-Patent Document 1). It has also long been known that phthalocyanine iron decomposes hydrogen peroxide to generate active oxygen, which then oxidizes organic matter (see, for example, Non-Patent Documents 2 and 3). These technologies have been limited to applications in the decomposition and purification of organic compounds such as trichloroethylene contained in industrial wastewater (see, for example, Non-Patent Document 4) and in biochemical fields such as tumor removal (see, for example, Non-Patent Document 5), but have not been applied to the decomposition of strong, highly stable resins such as epoxy resins.

[0003] For example, Patent Document 1 proposes thermally expandable particles, a thermally dissociable compound, or an epoxy resin containing a thermally expandable compound as an adhesive using an easily decomposable resin. In Patent Document 1, when the thermally expandable particles are heated, the volume of the epoxy resin expands, facilitating peeling of the bonded portion and facilitating thermal dissociation, but thermal energy must be applied to break down the resin.

[0004] Furthermore, carbon fiber reinforced resins containing carbon fibers and resins such as epoxy resins are used in applications such as aircraft and automobiles, and there is a demand for recycling of carbon fibers. For example, Non-Patent Document 6 proposes a method of removing the resin from carbon fiber reinforced resins by pyrolysis or liquefaction dissolution, and recovering only the carbon fibers. In Non-Patent Document 6, a large amount of thermal energy is required to remove the resin, which may result in a decrease in the strength of the recovered carbon fibers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-153409 [Non-patent literature]

[0006] [Non-Patent Document 1] HJHFenton,Proc.Chem.SOC.1893,9,113 [Non-patent document 2] AHCOOK,Catalylic Properties of the Phthalocyanines PartI,J.Chem.SOC,1938,1761 [Non-patent document 3] AHCOOK,Catalylic Properties of the Phthalocyanines PartIII,J.Chem.SOC,1938,1774 [Non-patent document 4] Yasuhiko Takuma et al., Decomposition rate of volatile organic compounds by Fenton reaction, Tokyo Metropolitan Industrial Technology Center Research Report, No. 3, P86 (2008) [Non-patent document 5] Y.Wang,et al.,Multifunctional Polymeric Micelles with Amplified Fenton Reaction for Tumor ablation [Non-patent document 6] Toru Kamo, Current Status and Issues of Recycling of Carbon Fiber Reinforced Plastics (CFPR), Journal of the Japan Society of Material Cycles and Waste Management, Vol. 29, P. 133 (2018) Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a readily decomposable resin that can be decomposed with low energy consumption, a method for decomposing the readily decomposable resin, and a method for recovering fibers from a fiber-reinforced resin that contains the readily decomposable resin. [Means for solving the problem]

[0008] The present invention provides an easily decomposable resin comprising a resin and an iron complex having a divalent or trivalent iron ion and a ligand, wherein the iron complex and the resin are chemically bonded to each other.

[0009] In the easily decomposable resin, the ligand is preferably cyclopentadienyl, porphyrin, or phthalocyanine.

[0010] In the easily decomposable resin, the resin preferably contains at least one selected from the group consisting of epoxy resin, unsaturated polyester resin, urea resin, diallyl phthalate resin, and polyurethane resin.

[0011] The present invention is a method for decomposing a readily decomposable resin, which comprises treating a material containing the readily decomposable resin with hydrogen peroxide to decompose the readily decomposable resin.

[0012] The present invention is a method for recovering fibers from a fiber-reinforced resin, which comprises treating the fiber-reinforced resin containing the easily decomposable resin and fibers with hydrogen peroxide to decompose the easily decomposable resin and recover the fibers. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a readily decomposable resin that can be decomposed with low energy consumption, a method for decomposing a readily decomposable resin, and a method for recovering fibers from a fiber-reinforced resin that contains a readily decomposable resin. [Brief explanation of the drawings]

[0014] [Figure 1] 1 shows photographs of the states of test pieces of Examples 1 and 2 and Comparative Examples 1 to 3 before and after immersion in hydrogen peroxide water. [Figure 2] 1 is an image of a carbon fiber reinforced resin immersed in hydrogen peroxide water. [Figure 3] Scanning electron microscope (SEM) images of new and recovered carbon cloth. [Figure 4]1 shows energy dispersive spectroscopy (EDS) spectra obtained by EDS analysis of SEM images of new and recovered carbon cloths. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0016] <Easily degradable resin> The easily decomposable resin according to this embodiment includes a resin and an iron complex having a divalent or trivalent iron ion and a ligand, and the iron complex and the resin are chemically bonded to each other. The chemical bond between the iron complex and the resin is, for example, a covalent bond or an ionic bond.

[0017] The ligand constituting the iron complex is not particularly limited as long as it coordinates with the divalent or trivalent iron ion as the central metal, but preferred examples include cyclopentadienyl, porphyrin, phthalocyanine, etc. Examples of iron complexes having cyclopentadienyl, porphyrin, or phthalocyanine as the ligand include ferrocene, heme, and iron phthalocyanine.

[0018] Specific structural formulae of ferrocene, heme, and iron phthalocyanine are shown below: Note that the hydrogen atoms in the structural formulae may be substituted with other substituents. [ka]

[0019] The content of the iron complex in the easily decomposable resin is preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less. When the content of the iron complex in the easily decomposable resin satisfies the above range, the decomposition ability of the easily decomposable resin with hydrogen peroxide may be enhanced compared to when the content does not satisfy the above range. Furthermore, when the content of the iron complex is too high, the mechanical properties of the resin may be deteriorated.

[0020] The easily decomposable resin can be prepared by mixing a resin with an iron complex precursor. The mixing is preferably performed by heating, for example, in the range of 40°C to 80°C. The iron complex precursor, like the iron complex described above, contains a divalent or trivalent iron ion and a ligand. The ligand has a functional group capable of bonding with the resin. Examples of functional groups capable of bonding with the resin include silane groups, silanol groups, carboxyl groups, amino groups, ammonium groups, nitro groups, hydroxyl groups, carbonyl groups, thiol groups, sulfonic acid groups, sulfonium groups, boric acid groups, oxazoline groups, pyrrolidone groups, phosphate groups, nitrile groups, hydroxyl groups, carboxyl groups, silyl groups, and isocyanate groups.

[0021] The resin is not particularly limited, but is preferably a thermosetting resin when considering use as an adhesive or a resin constituting a fiber-reinforced resin. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, phenolic resins, urea resins, melamine resins, polyurethane resins, silicone resins, diallyl phthalate resins, alkyd resins, guanamine resins, polyimide resins, urea resins, melamine formaldehyde resins, phenol formaldehyde resins, furan resins, and xylene resins. Among these, it is preferable to include at least one resin selected from the group consisting of epoxy resins, unsaturated polyester resins, urea resins, diallyl phthalate resins, and polyurethane resins in terms of strength, adhesiveness, and the like.

[0022] The epoxy resin may be an epoxy group-containing compound (prepolymer) having epoxy groups, or may contain such a prepolymer and a curing agent. Examples of epoxy group-containing compounds (prepolymers) include bisphenol A type epoxy, bisphenol F type epoxy, and phenol novolac type epoxy. Examples of curing agents include amino group-containing compounds such as 4,4-methylenebis(2,6-diethylaniline), diethylenetriamine, isophoronediamine, polyamidoamine, aliphatic polyamine, and dicyandiamide, as well as carboxylic acid anhydrides such as maleic anhydride, phthalic anhydride, and methylhexahydrophthalic anhydride. The epoxy resin may also contain a catalyst that promotes curing. Examples of catalysts that promote curing include tertiary amines and imidazole.

[0023] Unsaturated polyester resins are synthesized, for example, by condensation polymerization of unsaturated polyesters such as maleic anhydride or isophthalic acid and polyhydric alcohols such as ethylene glycol. Urea resins are synthesized, for example, by condensation reaction of urea and formaldehyde. Diallyl phthalate resins are synthesized, for example, by polymerizing diallyl phthalate monomers, which are esters of phthalic acid and allyl alcohol. Polyurethane resins are synthesized, for example, by polyaddition of diisocyanates or polyisocyanates with active hydrogen-containing compounds such as polyhydric alcohols and amines.

[0024] The readily decomposable resin of this embodiment can be used as an adhesive or as a resin contained in a fiber-reinforced resin. Conventionally, decomposing resins such as epoxy resins requires heating, which consumes a large amount of thermal energy. However, the readily decomposable resin of this embodiment can be easily decomposed by hydrogen peroxide without heating. Therefore, by using the readily decomposable resin of this embodiment, decomposition can be achieved with low energy consumption.

[0025] The readily decomposable resin of this embodiment may be subjected to a hydrophilization treatment before being subjected to a decomposition treatment with hydrogen peroxide water. The hydrophilization treatment of the readily decomposable resin improves the affinity between the surface of the resin and the hydrogen peroxide decomposition liquid, thereby improving the decomposition efficiency. Examples of hydrophilization treatment methods include ultraviolet light irradiation, plasma treatment, acid treatment, and alkali treatment.

[0026] <Method for decomposing easily decomposable resin> The method for decomposing a decomposable resin according to this embodiment is a method for decomposing a decomposable resin by treating a material containing the decomposable resin with hydrogen peroxide. It is believed that the Fenton reaction occurs when hydrogen peroxide acts on a material containing the decomposable resin, thereby decomposing the decomposable resin.

[0027] In the hydrogen peroxide treatment, the material containing the readily decomposable resin according to this embodiment may be immersed in a solution containing hydrogen peroxide, such as aqueous hydrogen peroxide, at a predetermined temperature, pressure, and time. The immersion liquid may be agitated as needed. Other methods, such as spraying and coating, may also be used instead of immersion. Light irradiation may also be used as needed. Light irradiation reduces iron ions oxidized by the Fenton reaction, generating hydroxyl radicals again during this process, thereby improving decomposition efficiency. Visible light with a wavelength shorter than approximately 550 nm is desirable, and sunlight, LED light, laser light, or a gas lamp such as xenon can be used as a light source.

[0028] As the hydrogen peroxide, for example, hydrogen peroxide water, sodium percarbonate, etc. may be used.

[0029] The amount of hydrogen peroxide used is preferably 5% or more relative to the mass of the easily decomposable resin. If the amount of hydrogen peroxide used is less than 5% relative to the mass of the easily decomposable resin, it may take a long time to decompose the easily decomposable resin. There is no particular upper limit to the amount of hydrogen peroxide used, as long as it is not excessive.

[0030] The reaction temperature in the treatment with hydrogen peroxide is, for example, in the range of 0 to 100° C., preferably in the range of 20 to 80° C. If the reaction temperature is below 0° C., it may take a long time to decompose the easily decomposable resin, and if it exceeds 100° C., the hydrogen peroxide may evaporate.

[0031] The reaction pressure in the treatment with hydrogen peroxide is, for example, atmospheric pressure (950 to 1030 hPa), and may be pressurized (for example, 1 to 2 atm).

[0032] The reaction time in the treatment with hydrogen peroxide 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 set in the range of 30 seconds to 300 hours, for example.

[0033] According to the method for decomposing easily decomposable resins of this embodiment, easily decomposable resins can be decomposed with low energy consumption, and this method produces almost no compounds that have a high environmental impact.

[0034] Materials containing easily decomposable resins are used in, for example, electronic components such as electrical parts, IC sealants, and printed wiring boards, fiber-reinforced resins, hydrogen tanks, automotive parts such as paints, aircraft fuselages, and adhesives.

[0035] <Method for recovering fibers from fiber-reinforced resin> The method for recovering fibers from fiber-reinforced resin according to this embodiment is a method for treating a fiber-reinforced resin containing the easily decomposable resin according to this embodiment and fibers with hydrogen peroxide to decompose the easily decomposable resin and recover the fibers.

[0036] In the hydrogen peroxide treatment, for example, the fiber-reinforced resin may be immersed in a solution containing hydrogen peroxide, such as aqueous hydrogen peroxide, at a predetermined temperature, pressure, and time. The immersion liquid may be stirred as needed. The amount of hydrogen peroxide, reaction temperature, reaction pressure, reaction time, and the like are as described above. Light irradiation may be performed as needed. The wavelength and light source of the light irradiation are as described above. Furthermore, a hydrophilization treatment may be performed as needed before the hydrogen peroxide treatment. After the decomposition of the easily decomposable resin, the fibers can be recovered by washing, for example, with water, an organic solvent, or the like by immersion or spraying.

[0037] The fiber reinforced resin is not particularly limited as long as it is a composite material containing the easily decomposable resin according to this embodiment and fibers, but examples include carbon fiber reinforced plastics (CFRP) and hybrid fiber reinforced plastics containing inorganic fibers other than carbon fibers, such as glass fibers, boron fibers, and magnesium oxide fibers.

[0038] The method for recovering fibers from fiber-reinforced resin according to this embodiment makes it possible to decompose easily decomposable resin and recover fibers from the fiber-reinforced resin with low energy consumption. This method hardly produces any compounds that have a high environmental impact.

[0039] The present specification includes the following embodiments.

[0040] (1) The composition includes a divalent or trivalent iron ion, an iron complex having a ligand, and a resin, An easily decomposable resin, wherein the iron complex and the resin are chemically bonded to each other.

[0041] (2) The easily decomposable resin according to (1) above, wherein the ligand is cyclopentadienyl, porphyrin, or phthalocyanine.

[0042] (3) The easily decomposable resin according to (1) or (2) above, characterized in that the resin contains at least one selected from the group consisting of epoxy resin, unsaturated polyester resin, urea resin, diaryl phthalate resin, and polyurethane resin.

[0043] (4) A method for decomposing an easily decomposable resin, comprising treating a material containing the easily decomposable resin according to any one of (1) to (3) above with hydrogen peroxide to decompose the easily decomposable resin.

[0044] (5) A method for recovering fibers from a fiber-reinforced resin, comprising treating a fiber-reinforced resin containing the easily decomposable resin according to any one of (1) to (3) above and fibers with hydrogen peroxide to decompose the easily decomposable resin and recover the fibers. [Example]

[0045] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0046] <Examples 1 to 4> [Preparation of easily degradable resin] A prepolymer of aminoferrocene (Tokyo Chemical Industry Co., Ltd.) and a two-component curing epoxy resin (GM-6800, manufactured by Blenny Giken Co., Ltd.) were mixed in a commercially available glass reagent bottle in the mass ratios listed in Examples 1-4 in Table 1. A stirrer tip was placed in the glass bottle, and the mixture was stirred for 2 hours on a hot stirrer heated to 50°C. After stirring, the curing agent for the two-component curing epoxy resin was added to the glass reagent bottle in the mass ratios listed in Examples 1-4 in Table 1 and stirred. In Examples 1 and 2, the resulting mixture (easily decomposable resin) was dropped onto a hot plate heated to 70°C and allowed to harden for 2 hours to prepare pellet-shaped test specimens. In Examples 3 and 4, the resulting mixture (easily decomposable resin) was dropped onto a silicone mold (50 mm x 5 mm x 2 mm) placed on a hot plate heated to 70°C and allowed to harden for 2 hours to prepare rod-shaped test specimens.

[0047] In Examples 1-4, as shown below, aminoferrocene reacts with epoxy resin (prepolymer) to form a chemical bond between aminoferrocene and epoxy resin. [ka]

[0048] <Comparative Examples 1 and 4> [Preparation of epoxy resin] A prepolymer and curing agent of a two-component curing epoxy resin (GM-6800, manufactured by Blenny Giken) were mixed in a 50 mL glass reagent bottle in the mass ratios shown in Comparative Examples 1 and 4 in Table 1. A stirrer tip was placed in the glass bottle, and the mixture was stirred on a hot stirrer heated to 50°C. A pellet test piece was prepared from the obtained epoxy resin in Comparative Example 1 in the same manner as in Example 1, and a rod-shaped test piece was prepared in Comparative Example 4 in the same manner as in Example 3.

[0049] <Comparative Examples 2 and 3> [Preparation of a mixture of epoxy resin and ferrocene] Ferrocene (Tokyo Chemical Industry Co., Ltd.) and a prepolymer of a two-component curing epoxy resin (GM-6800, manufactured by Blenny Giken Co., Ltd.) were mixed in a commercially available glass reagent bottle in the mass ratios shown in Comparative Examples 2 and 3 in Table 1. A stirrer tip was placed in the glass bottle, and the mixture was stirred for 2 hours on a hot stirrer heated to 50°C. After stirring, the curing agent for the two-component curing epoxy resin was added to the glass reagent bottle in the mass ratios shown in Comparative Examples 2 and 3 in Table 1, and the mixture was stirred. The resulting mixture (a mixture of epoxy resin and ferrocene) was dropped onto a hot plate heated to 70°C and left to harden for 2 hours, producing pellet test pieces.

[0050] [Hydrogen peroxide treatment (1)] The test pieces of Examples 1 and 2 and Comparative Examples 1 to 3 were immersed in 10 mL of a 35% aqueous solution of hydrogen peroxide (Tokyo Chemical Industry Co., Ltd.) placed in a 50 mL glass bottle, and allowed to stand in that state for 24 hours.

[0051] FIG. 1 shows photographs of the test pieces of Examples 1 and 2 and Comparative Examples 1 to 3 before and after immersion in hydrogen peroxide. The test piece of Example 1, which was immersed in hydrogen peroxide for 24 hours, disintegrated in the hydrogen peroxide. The test piece of Example 2, which was immersed in hydrogen peroxide for 24 hours, remained in a spongy state, but disintegrated when light pressure was applied with a metal rod after removal from the hydrogen peroxide. The test pieces of Comparative Examples 1 to 3 maintained their pellet shape even after immersion in hydrogen peroxide for 24 hours. The test pieces of Comparative Examples 1 to 3 did not disintegrate even when pressure was applied with a metal rod after removal from the hydrogen peroxide.

[0052] [Hydrogen peroxide treatment (2)] The test pieces of Examples 3 and 4 and Comparative Example 4 were immersed in a 35% aqueous solution of hydrogen peroxide (Tokyo Chemical Industry Co., Ltd.) and allowed to stand for 3 hours. The test pieces of Examples 3 and 4 and Comparative Example 4 were then washed with ion-exchanged water, after which they were placed on a three-point bending test fixture (Imada BT-500N) with a support distance of 40 mm. A three-point bending test was performed at a speed of 10 mm / min using a load detector (digital force gauge, Imada ZTS500N) to measure the bending strength. The bending strength of the test pieces before immersion in the hydrogen peroxide solution was also measured in the same manner. These results are summarized in Table 1.

[0053] [Table 1]

[0054] As shown in Table 1, the bending strength before immersion in hydrogen peroxide solution was similar in Examples 3 and 4 and Comparative Example 4. However, in Examples 3 and 4, the bending strength after immersion in hydrogen peroxide solution for 3 hours was reduced by approximately 60% to 80% compared to the bending strength before immersion in hydrogen peroxide solution. On the other hand, in Comparative Example 4, the bending strength after immersion in hydrogen peroxide solution for 3 hours was reduced by just under 20% compared to the bending strength before immersion in hydrogen peroxide solution. It was found that in Examples 3 and 4, the strength was significantly reduced even by immersion in hydrogen peroxide solution for only a short period of time.

[0055] <Example 5> [CFRP fabrication] 10.605 g of a prepolymer of a two-component curing epoxy resin (GM-6800, manufactured by Blenny Giken) and 1.182 g of aminoferrocene (Tokyo Chemical Industry Co., Ltd.) were mixed in a 50 mL glass reagent bottle. A stirrer tip was placed in the glass bottle, and the mixture was stirred for 2 hours on a hot stirrer heated to 50 °C. After stirring, 3.0195 g of the curing agent for the two-component curing epoxy resin was added to the glass reagent bottle at room temperature and stirred. 0.5 g of the resulting mixture (easily degradable resin) was added dropwise to a 50 mm x 50 mm carbon cloth sheet (twill weave, DIY Material Shop, 0.5 g) fixed on a Teflon (registered trademark) plate. The carbon cloth sheet was then pressed down with the Teflon sheet to impregnate the easily degradable resin. The mixture was then heated on a hot plate at 80 °C for 3 hours to obtain a single-layer CFRP.

[0056] [Recovering carbon fiber from CFRP] The obtained CFRP was immersed in 100 mL of a 35% aqueous solution of hydrogen peroxide (Tokyo Chemical Industry) placed in a 500 mL glass bottle. Figure 2 shows an image of the CFRP immersed in hydrogen peroxide. After immersion in hydrogen peroxide for 72 hours, the resin in the CFRP had dissolved, and only the carbon cloth could be separated and recovered.

[0057] The new and recovered carbon cloths were subjected to SEM-EDS analysis using a scanning electron microscope (SEM-EDS, Hitachi, Ltd., "SU3500") at an accelerating voltage of 15 kV. Figure 3 shows SEM images of the new and recovered carbon cloths. Figure 4 shows EDS spectra obtained by EDS analysis of the SEM images of the new and recovered carbon cloths. As shown in Figure 3, the surface condition of the carbon fibers constituting the recovered carbon cloth was visually identical to that of the carbon fibers constituting the new carbon cloth. Furthermore, as shown in Figure 4, almost no iron (Fe) components were detected on the surface of the carbon fibers constituting the recovered carbon cloth. This suggests that the easily decomposable resin in the CFRP was decomposed and removed by treating the CFRP of the example with hydrogen peroxide.

Claims

1. The composition includes a divalent or trivalent iron ion, an iron complex having a ligand, and a resin, An easily decomposable resin, wherein the iron complex and the resin are chemically bonded to each other.

2. 2. The easily decomposable resin according to claim 1, wherein the ligand is a cyclopentadienyl, a porphyrin, or a phthalocyanine.

3. 2. The easily decomposable resin according to claim 1, wherein the resin comprises at least one selected from the group consisting of epoxy resin, unsaturated polyester resin, urea resin, diallyl phthalate resin, and polyurethane resin.

4. A method for decomposing a readily decomposable resin, comprising treating a material containing the readily decomposable resin according to any one of claims 1 to 3 with hydrogen peroxide to decompose the readily decomposable resin.

5. A fiber-reinforced resin comprising the easily decomposable resin according to any one of claims 1 to 3 and fibers is treated with hydrogen peroxide to decompose the easily decomposable resin and recover the fibers. A method for recovering fibers from a fiber-reinforced resin.

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