JP7641310B2 - Method for decomposing epoxy resin and method for recovering carbon fiber from carbon fiber composite material - Google Patents

Description

The present invention relates to a method for decomposing epoxy resin and a method for recovering carbon fibers from carbon fiber composite materials using the method.

Epoxy resin is a thermosetting resin with excellent electrical insulation, heat resistance, and mechanical strength, and is widely used as a material for various electrical components, electronic components, and automobile parts. Epoxy resin can be obtained by mixing a prepolymer, such as a copolymer of bisphenol A and epichlorohydrin, with a hardener, such as a polyamine or an acid anhydride, and then performing a heat curing process. However, once cured, epoxy resin is difficult to soften or melt due to heat, and has low solubility in solvents, making it difficult to decompose. For this reason, the disposal of cured epoxy resin must be done by landfilling, which creates problems such as a burden on the environment. In addition, because it has low solubility in solvents and is difficult to decompose, it is also difficult to analyze the structure of cured epoxy resin.

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 carbon fibers. In order to recycle carbon fibers, methods are being considered for removing the epoxy resin contained in used carbon fiber composite materials and recovering the carbon fibers.

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, an alkali scrubber or water scrubber is provided to remove the sulfur oxides and carbon monoxide that are generated.

Patent Document 2 proposes that the epoxy resin can be dissolved by immersing a carbon fiber composite material containing the epoxy resin in an organic acid or inorganic acid at 0.01 to 10 M and 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.

Patent document 3 proposes that the 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.

Patent Document 4 proposes that epoxy resins can be dissolved by immersing them in a mixture 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.

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 specialized equipment that can withstand such high temperatures and pressures. Furthermore, when acids such as sulfuric acid and nitric acid are used at high temperatures, compounds that have a high environmental impact, such as SOx and NOx, are produced. When decomposition is performed using sulfuric acid, 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 ionized liquid as in Patent Document 3, the ionized liquid is expensive, and there is a problem that it is costly to process a large amount of carbon fiber composite material.

JP 2022-102186 A JP 2019-136932 A JP 2017-104847 A JP 2021-155644 A

The object of the present invention is to provide a method for decomposing epoxy resins at low cost, under mild conditions such as atmospheric pressure and room temperature, and with almost no generation of compounds that place a high burden on the environment, and a method for recovering carbon fibers from carbon fiber composite materials using said method.

The present invention is a method for decomposing an epoxy resin, comprising a first step of introducing an acidic functional group into the 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, and 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, in which 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.

In the method for decomposing an epoxy resin, it is preferable to use sulfuric acid as the acidic solution used in the first step.

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

The present invention is a method for recovering carbon fibers from carbon fiber composite materials, in which carbon fibers are recovered from carbon fiber composite materials using the above-mentioned epoxy resin decomposition method.

The present invention provides a method for decomposing epoxy resins at low cost and under mild conditions such as atmospheric pressure and room temperature, with little production of compounds that have a high environmental impact, and a method for recovering carbon fibers from carbon fiber composite materials using the method.

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. FIG. 2 is a diagram showing an IR spectrum of the epoxy resin in Example 1. FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after treatment with a metal ion-containing solution in Example 1. FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after hydrogen peroxide treatment in Example 1. FIG. 1 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.). FIG. 2 is a diagram showing an IR spectrum of an epoxy resin after hydrogen peroxide treatment in Comparative Example 1. FIG. 1 is a diagram showing an IR spectrum of an epoxy resin after Fenton's reagent treatment in Comparative Example 2. FIG. 13 is a diagram showing the results of thermogravimetric analysis of CFRP after hydrogen peroxide treatment in Example 3.

The following describes an embodiment of the present invention. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

<Method of decomposing 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 an acidic functional group 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 group, 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.

As described above, in conventional epoxy resin decomposition methods, high temperature and high pressure are required to decompose 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 acids such as sulfuric acid and nitric acid are 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 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 treating a large amount of epoxy resin, it is not necessary to use a large amount of energy. By reacting hydrogen peroxide with the metal salt of the acidic functional group introduced into the epoxy resin, the epoxy resin can be decomposed faster than with a normal Fenton's reagent. In the case of decomposition using sulfuric acid, 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.

The decomposition products produced by this method are soluble in water, and can 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.

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 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 when hydrogen peroxide acts on 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.

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

Examples of amino group-containing compounds that act as curing agents include 4,4-methylenebis(2,6-diethylaniline), diethylenetriamine, isophoronediamine, polyamidoamine, aliphatic polyamines, and dicyandiamide.

Examples of carboxylic acid anhydrides that serve as hardeners include maleic anhydride, phthalic anhydride, and methylhexahydrophthalic anhydride.

Catalysts that accelerate curing include tertiary amines and imidazoles.

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

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

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

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

The acidic functional groups that can be introduced include sulfonic acid groups, carboxyl groups, phosphoric acid groups, and hydroxyl groups.

The amount of acidic solution used is preferably equal to or greater than the mass of the epoxy resin, and more preferably equal to or greater than twice the mass. If the amount of acidic solution used is less than the mass of the epoxy resin, the reaction for introducing acidic functional groups may not proceed smoothly. There is no upper limit to the amount of acidic solution used, so long as it is not excessive.

The reaction temperature in the first step is, for example, in the range of 0 to 180°C, preferably in the range of 20 to 160°C. If the reaction temperature is below 0°C, the reaction for introducing acidic functional groups may not proceed smoothly, and if it exceeds 180°C, sulfur trioxide may be generated, which may accelerate corrosion of the equipment, etc.

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 also be performed.

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 set to, for example, a range of 3 to 24 hours.

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

In the second step, the epoxy resin or a material containing the epoxy resin to which an acidic functional group has been introduced is immersed in a solution containing metal ions at a specified temperature, pressure, and time. If necessary, the immersion liquid may be stirred. In addition to immersion, other methods such as spraying and coating may also be used.

Examples of solutions containing metal ions include solutions containing at least one of metal salts of alkali metals, alkaline earth metals, and transition metals. Of these, solutions containing at least one of Fe(II), Fe(III), Cu(II), and Li are preferred from the standpoint of efficiently catalyzing the Fenton reaction.

The amount of metal ions used is preferably equal to or greater than the mass of the epoxy resin, and more preferably equal to or greater than twice the mass. If the amount of metal ions used is less than the mass of the epoxy resin, the reaction to form the metal salt may not proceed smoothly. There is no upper limit to the amount of metal ions used, as long as it is not excessive.

The reaction temperature in the second step 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, the reaction to form the metal salt may not proceed smoothly, and if it exceeds 100°C, the solvent may evaporate.

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 also be performed.

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 set to, for example, a range of 30 seconds to 24 hours.

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.

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

For example, hydrogen peroxide solution, sodium percarbonate, etc. can be used as hydrogen peroxide.

The amount of hydrogen peroxide used is preferably equal to or greater than the mass of the epoxy resin, and more preferably equal to or greater 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 smoothly. There is no upper limit to the amount of hydrogen peroxide used, so long as it is not excessive.

The reaction temperature in the third step 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, the decomposition reaction of the epoxy resin may not proceed smoothly, and if it exceeds 100°C, the hydrogen peroxide may evaporate.

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 also be performed.

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 set to, for example, a range of 30 seconds to 24 hours.

The epoxy resin decomposition method according to this embodiment allows epoxy resin to be decomposed at low cost under mild conditions such as atmospheric pressure and room temperature. This method produces almost no 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.

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

<Method for recovering carbon fibers from carbon fiber composite material>
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.

Figure 1 shows an example of the procedure for recovering carbon fibers from a carbon fiber composite material according to this embodiment.

For example, first, a carbon fiber composite material (CFRP) is treated with an acidic solution to introduce acidic functional groups into the epoxy resin contained in the carbon fiber composite material (first step: introduction of acidic functional groups). After the reaction in the first step, the material may be washed by, for example, immersion or spraying with water or an organic solvent.

Then, 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 resin may be washed by, for example, immersion or spraying with water or an organic solvent.

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 methods such as immersion or spraying with water or an organic solvent.

There are no particular limitations on the carbon fiber composite material, so long as it is a composite material containing carbon fiber and epoxy resin, but examples include carbon fiber reinforced plastic (CFRP) and hybrid fiber reinforced plastic containing glass fiber or aramid fiber other than carbon fiber.

The method for recovering carbon fibers from carbon fiber composite materials according to this embodiment makes it possible to recover carbon fibers from carbon fiber composite materials at low cost and under mild conditions such as atmospheric pressure and room temperature. This method produces almost no compounds that have a high environmental impact.

This specification includes the following embodiments:

(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;
The 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.

(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.

(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.

(4) A method for recovering carbon fibers from a carbon fiber composite material, comprising recovering carbon fibers from the carbon fiber composite material using the epoxy resin decomposition method described in any one of (1) to (3).

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.

[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 molar ratio of 2:1 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.

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 spectroscopy (IR) measurement device (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 the acidic solution treatment, the middle part shows the IR spectrum after the acidic solution treatment, and the lower part shows the IR spectrum after the metal ion-containing solution treatment (metal salt treatment).

As a result, as shown in FIG. 2 (middle), peaks characteristic of sulfonic acid were detected near 1200 cm ^-1 , 1100 cm ^-1 and 1030 cm ^-1 , indicating that the surface of the epoxy resin was sulfonated.

[Treatment of epoxy resin with metal ion-containing solution]
Approximately 50 mg of epoxy resin treated with an acid solution was immersed in 1 mL of ultrapure water in which a metal salt was dissolved at a concentration of 10 mg/mL, and after 12 hours at room temperature (25°C), it was taken out and washed with ultrapure water. As the metal salts, 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 were used. The results are shown in Figure 3.

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. Sulfonic acid and sulfonate salts were distinguished by the presence or absence of an increase in the baseline at 3500-1500 cm ^-1 in the IR spectrum. Sulfonic acid shows an increase in the baseline, while sulfonate salts do not show an increase in the baseline (see the middle and bottom rows of Figure 2).

[Hydrogen peroxide treatment]
Approximately 50 mg of the epoxy resin converted into the sulfonate salt 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 for decomposition of the epoxy resin. Decomposition was determined based on the presence or absence of peaks near 1500 cm ^-1 and 750 cm ^-1 in the IR spectrum. If decomposition of the sulfonated epoxy resin had occurred, peaks near 1500 cm ^-1 and 750 cm ^-1 originating from the normal epoxy resin inside should appear. The results are shown in Figure 4.

As shown in Figure 4, peaks derived from the epoxy resin appeared when Li, Fe(II), Fe(III), and Cu were used as metals, 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.

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

It was found that the fastest decomposition at a low 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.

<Comparative Examples 1 and 2>
[Comparative experiment with prior art]
Experiments were conducted to decompose epoxy resins that had been "treated with an acidic solution" 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 treated epoxy resin 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.

Regardless of which reagent was used, no decomposition of the epoxy resin was observed in the samples after one hour.

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 the epoxy resin by treatment with an acidic solution and metals in the form of metal salts.

Example 3
[Preparation of CFRP]
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, and heated in a thermostatic chamber at 170° C. for 2 hours to produce a CFRP with an epoxy resin fraction of 25% by mass.

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

Approximately 25 mg of the acid solution-treated CFRP was immersed in 5 mL of ultrapure water in which metal salts were 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.

Approximately 25 mg of CFRP converted to sulfonate was immersed in 5 mL of 30% by weight aqueous hydrogen peroxide solution, 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 (TG8120, manufactured by Rigaku), and the presence or absence of decomposition of the epoxy resin was examined from the weight loss when heated to 600°C. The results are shown in Figure 8.

When heated to 600°C, the weight loss of the CFRP after decomposition 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.

As described above, in the examples, epoxy resin was decomposed 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 (4)

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