Method for processing composite materials and method for manufacturing composite materials

Abstract

The purpose of the present invention is to provide a method for processing a composite material which makes it possible to efficiently recover a reinforcing material without sacrificing quality and without doing environmental harm.　To fulfill this purpose, the present invention provides a method for processing a composite material which includes a step for immersing a composite material comprising resin and a reinforcing material in a decomposition solution which contains an oxidizable active species having sulfuric acid as a starting material, decomposing the resin by heating, and recovering the reinforcing material, said method being characterized by further including a step for supplying oxygen to the decomposition solution.

Description

[Technical Field]

[0001] The present invention relates to a method for treating a composite material, and more particularly to a method for treating a composite material quickly and efficiently, which is capable of recovering the reinforcing material from the composite material made of a resin and a reinforcing material. [Background technology]

[0002] Composite reinforcement materials (composites) are materials formed by combining a base resin with reinforcing materials such as carbon fiber, glass fiber, metal fiber, high-strength organic fiber, inorganic filler, metal filler, carbon nanotubes, and cellulose nanofiber. Due to their high strength, composites are widely used in a wide range of applications, from small molded products such as fishing rods to large products such as ships. In particular, in recent years, composites using carbon fiber as a reinforcing material (carbon fiber reinforced plastics) have been used in structural materials for aircraft and other applications, as they can reduce the weight of products. Furthermore, carbon fiber reinforced plastics are expected to play a major role in improving the fuel efficiency of automobiles and other vehicles. Carbon fiber, which is the reinforcing material for carbon fiber reinforced plastics, is currently produced in the tens of thousands of tons, but demand is expected to expand to 100,000 to 150,000 tons by 2020, with production expected to continue to increase thereafter.

[0003] However, the production of carbon fiber requires a huge amount of energy, and from the perspective of environmental impact, it is desirable to recycle carbon fiber reinforced plastics (particularly through material recycling). Although recycling technology for carbon fiber reinforced plastics has been put into practical use for limited applications, there is currently no technology in practical use that allows for repeated use as parts for automobiles or aircraft through material recycling.

[0004] Methods for separating and recovering a reinforcing material from a composite material made of a resin containing carbon fiber reinforced plastic and the reinforcing material include, for example, techniques disclosed in Patent Document 1 and Patent Document 2. The technology of Patent Document 1 involves burning and decomposing resin at high temperatures to form a composite material, and using the recovered inorganic matter as a raw material for the reinforcing material. Furthermore, the technology of Patent Document 2 involves using a carbon fiber composite material, decomposing the matrix by anodization using electrolytic treatment, and recovering the carbon fibers.

[0005] However, the technique of Patent Document 1 requires that the composite material be heated to 300 to 1000° C., which not only poses quality problems such as deterioration of the reinforcing material, but also poses environmental load problems due to high-temperature heating. Furthermore, in the technology of Patent Document 2, because the carbon fiber composite material is used as an anode (electrode), there is a limit to the amount of carbon fiber composite material that can be processed at one time. This means that it is not suitable as a method for industrially processing carbon fiber composite material, and because an electric current is applied to the carbon fiber composite material, quality problems such as deterioration of the reinforcing material may occur.

[0006] As described above, many material recycling technologies for composite materials composed of resin and reinforcing material have been proposed. However, there is no standardized process for processing composite materials efficiently without placing a burden on the environment and without degrading the quality of the reinforcing material, and the current situation is that most processes rely on landfill disposal or thermal recycling. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 7-33904 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-249386 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide a method for processing composite materials that can recover reinforcing materials efficiently and without degrading the quality, without imposing a burden on the environment. [Means for solving the problem]

[0009] As a result of investigations aimed at solving the above-mentioned problems, the inventors focused on the decomposition reaction of resins by oxidizing active species and discovered that by using a technique of immersing a composite material in a treatment solution containing oxidizing active species, the resin can be decomposed and the reinforcing material can be recovered without degrading its quality. Furthermore, the inventors also discovered that by using a treatment solution containing oxidizing active species obtained by electrolyzing a sulfuric acid solution as the treatment solution, the resin can be decomposed into water and carbon dioxide, facilitating the recovery of the reinforcing material, thereby enabling the recovery of the reinforcing material efficiently and without degrading its quality without imposing a burden on the environment. The oxidizing active species can be generated by adding hydrogen peroxide to sulfuric acid or by electrolyzing a sulfuric acid solution. Specific examples of the oxidizing active species include hydroxyl radicals, peroxosulfuric acid, and peroxodisulfuric acid.

[0010] The technology described above is a groundbreaking process that discovers a resin decomposition reaction caused by oxidizing active species generated by electrolysis of a sulfuric acid solution, and enables efficient recycling of composite materials consisting of resin and reinforcing material by immersing the composite material in a treatment solution containing oxidizing active species. Unlike landfill disposal or thermal recycling, this process allows for efficient processing of composite materials without placing a burden on the environment or reducing the quality of the reinforcing material. However, from the perspective of cost reduction, there has been a need to develop a process that can further accelerate the resin decomposition rate and recover the reinforcing material more efficiently.

[0011] Therefore, the present inventors conducted further intensive research into a method for treating a composite material, which includes a step of immersing a composite material composed of a resin and a reinforcing material in a decomposition solution containing oxidizing active species made from sulfuric acid, and heating the composite material to decompose the resin and recover the reinforcing material. As a result, they found that treatment efficiency can be significantly improved by further performing a step of supplying oxygen into the decomposition solution.

[0012] The present invention has been made based on the above findings, and the gist of the present invention is as follows. 1. A method for treating a composite material, comprising the steps of immersing a composite material composed of a resin and a reinforcing material in a decomposition solution containing an oxidizing active species made from sulfuric acid, and heating the decomposition solution to decompose the resin and recover the reinforcing material, A method for treating a composite material, further comprising the step of supplying oxygen into the decomposition solution.

[0013] 2. The method for treating a composite material described in 1 above, wherein the step of supplying oxygen into the decomposition solution is characterized by supplying oxygen when the composite material is immersed and / or heated.

[0014] 3. The method for treating a composite material according to 1 or 2 above, wherein the decomposition solution is a solution in which hydrogen peroxide is mixed with a sulfuric acid solution.

[0015] 4. The method for treating a composite material according to 1 or 2 above, wherein the decomposition solution is a solution obtained by electrolyzing a sulfuric acid solution.

[0016] 5. A method for treating a composite material according to any one of 1 to 4 above, characterized in that the step of supplying oxygen into the decomposition solution introduces an oxidizing gas, which is at least one elemental or mixed gas selected from oxygen, ozone, nitrous oxide, nitric oxide and nitrogen dioxide; a mixed gas of such elemental or mixed gas with an inert gas; air alone; or a mixed gas of such elemental or mixed gas with air, or adds peroxide, peracid, perchloric acid, permanganic acid, nitric acid and salts thereof.

[0017] 6. A method for processing a composite material described in any one of items 2 to 5, characterized in that the oxidizing gas introduced into the decomposition solution is a mixed gas containing 15 volume % or more of oxidizing gas, and the mixed gas is introduced into the decomposition solution at a rate of 0.01 NL / sec or more.

[0018] 7. The method for treating a composite material according to any one of items 2 to 6, wherein in the step of supplying oxygen, the composite material is immersed in the decomposition solution, the temperature of the decomposition solution is heated and maintained at 100°C to 200°C, and the oxidizing gas is introduced into the decomposition solution to decompose the resin component of the composite material, and after the decomposition, the reinforcing material is recovered by filtering, washing, and drying.

[0019] 8. The method for treating a composite material according to any one of claims 1 to 7, wherein the reinforcing material is a continuous fiber.

[0020] 9. The method for processing a composite material according to claim 8, wherein the step of recovering the reinforcing material is a step of winding the reinforcing material around a core material.

[0021] 10. The method for treating a composite material according to any one of claims 1 to 9, wherein the reinforcing material is composed of at least one material selected from the group consisting of carbon fiber, glass fiber, and metal fiber.

[0022] 11. A method for producing a composite material, comprising: combining a reinforcing material recovered by the method according to any one of the above items 1 to 10 with a resin. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a method for processing composite materials that can recover reinforcing materials efficiently and without degrading the quality, without imposing a burden on the environment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment for carrying out the method for treating a composite material of the present invention (hereinafter referred to as the "present embodiment") will be described in detail. Note that the present invention is not limited to the following description, and various modifications can be made within the scope of the gist of the present invention.

[0025] <Resin decomposition and composite material recovery process> The composite material processing method of this embodiment includes a step of immersing a composite material composed of a resin and a reinforcing material in a decomposition solution containing oxidizing active species made from sulfuric acid, and heating the solution to decompose the resin and recover the reinforcing material (resin decomposition / composite material recovery step).

[0026] (composite material) The composite material of this embodiment refers to a material whose strength is improved by compounding a reinforcing material, which is a different material such as a fiber or a filler, into a resin (base material). The compounding method is not particularly limited, and may be a method that utilizes interactions such as hydrogen bonding or intermolecular forces, and may be dispersion, adhesion, bonding, adsorption, support, arrangement, etc. The composite material may further contain a base material, a reinforcing material, other additives, etc. The form of the composite material is not particularly limited, and after cutting or pulverizing it into a form suitable for treatment, it can be treated with a treatment solution containing an oxidizing active species.

[0027] The reinforcing material constituting the composite material is a material that is compounded or dispersed in the resin that is the matrix of the reinforced composite material. Examples of the reinforcing material include carbon fiber, glass fiber, metal fiber, organic high-strength fiber, inorganic filler, carbon nanotube, and cellulose nanofiber.

[0028] The reinforcing materials are classified into fibrous and particulate types, and although the definition is not clear, generally, those with a large aspect ratio (length / width) (for example, an aspect ratio of 100 or more, preferably 200 or more) are called fibrous, and those with a small aspect ratio (length / width) (for example, an aspect ratio of less than 200, preferably less than 100) are called particulate. Furthermore, fibrous reinforcing materials are divided into continuous fibers, which are several meters long and wound on a bobbin, and short fibers, which are several millimeters to several centimeters long. Continuous fibers are long fibers used in the form of unidirectional layers in which all the fibers are aligned parallel to each other, and can be used by knitting or weaving. Furthermore, by stacking unidirectional layers in various directions, it is possible to create plates with quasi-isotropy, orthotropy, and anisotropy. Therefore, if the reinforcing material can be recycled as continuous fiber, its uses will be greatly expanded, leading to the realization of a recycling-oriented society.

[0029] The carbon fiber is a fiber made by carbonizing acrylic fiber or pitch (a by-product of petroleum, coal, coal tar, etc.) at high temperatures. Glass fiber is made by melting and drawing glass into fibers. Metal fibers are made by processing metals such as stainless steel, aluminum, iron, nickel, and copper into threads using plastic processing (rolling, etc.), melt spinning, CVD, etc. The organic high-strength fibers are fibers made from resins such as polyamide, polyester, acrylic, polyparaphenylenebenzobisoxazole, and polyimide.

[0030] These fibers are processed into intermediate substrates such as continuous fibers or nonwoven fabrics, and then combined with the base material. Continuous fibers are long fibers used in unidirectional layers where all the fibers are parallel to one another and can be knitted or woven. Unidirectional layers can also be stacked in various directions to create quasi-isotropic, orthotropic, and anisotropic plates. Nonwoven fabric is a sheet-like material made by intertwining fibers without weaving them. Nonwoven fabric refers to fabric made by bonding or intertwining fibers through thermal, mechanical, or chemical action.

[0031] Examples of elements constituting the inorganic filler include elements in Groups 1 to 16 of the periodic table. While the elements are not particularly limited, elements in Groups 2 to 14 of the periodic table are preferred. Specific examples include Group 2 elements (Mg, Ca, Ba, etc.), Group 3 elements (La, Ce, Eu, Ac, Th, etc.), Group 4 elements (Ti, Zr, Hf, etc.), Group 5 elements (V, Nb, Ta, etc.), Group 6 elements (Cr, Mo, W, etc.), Group 7 elements (Mn, Re, etc.), Group 8 elements (Fe, Ru, Os, etc.), Group 9 elements (Co, Rh, Ir, etc.), Group 10 elements (Ni, Pd, Pt, etc.), Group 11 elements (Cu, Ag, Au, etc.), Group 12 elements (Zn, Cd, etc.), Group 13 elements (Al, Ga, In, etc.), and Group 14 elements (Si, Ge, Sn, Pb, etc.). Examples of inorganic compounds containing these elements include oxides (including composite oxides), halides (fluorides, chlorides, bromides, iodides), oxoacid salts (nitrates, sulfates, phosphates, borates, perchlorates, carbonates, etc.), compounds formed from the above elements and negative elements such as carbon monoxide, carbon dioxide, and carbon disulfide, as well as salts such as hydrocyanic acid, hydrocyanates, cyanates, thiocyanates, and carbides. One inorganic filler may contain one or more of the above elements. The multiple elements may be uniformly or unevenly distributed in the particles, and the surface of a particle of a compound of one element may be coated with a compound of another element. These inorganic fillers may be used alone or in combination. Among these, preferred inorganic fillers include, but are not limited to, at least one element selected from the group consisting of silica, zirconia, titanium, zinc, iron, copper, chromium, cadmium, carbon, tungsten, antimony, nickel, and platinum.

[0032] Carbon nanotubes are carbon allotropes and are sometimes classified as a type of fullerene.

[0033] Cellulose nanofibers are wood cellulose fibers that have been thinned to a width of about 15 nanometers.

[0034] In this embodiment, the content of the reinforcing material in the composite material is preferably 10 to 80% by mass, with the reinforced composite material being 100% by mass. Preferably, the lower limit is 15% to 20% by mass, and the upper limit is 75% to 70% by mass.

[0035] The resin constituting the composite material is a resin used as the matrix of the composite material, and a thermoplastic resin or a thermosetting resin is used. Mixtures of these resins, as well as those containing secondary components of the resin components such as crystallized products, heat-treated products, oriented products, plasticizers, and modifiers, can also be used as the resin of the composite material.

[0036] The thermoplastic resin refers to a resin that becomes soft when heated to its glass transition temperature or melting point and can be molded into the desired shape. Generally, thermoplastic resins are difficult to machine, such as by cutting or grinding, and are therefore widely used in injection molding, in which the resin is heated to soften, then forced into a mold, cooled, and solidified to produce the final product. Examples of thermoplastic resins include super engineering plastics such as polyether ether ketone and polyether sulfone, polyethylene, polypropylene, polystyrene, ABS resin, vinyl chloride resin, methyl methacrylate resin, nylon, fluororesin, polycarbonate, and polyester resin.

[0037] Thermosetting resins are resins that polymerize when heated, forming a polymer network structure, hardening and becoming irreversible. To use them, relatively low-molecular-weight resins with sufficient fluidity are formed into a desired shape, then heated or otherwise reacted to harden them. Some adhesives and putties require a mixture of liquid A (base) and liquid B (hardener), but these are epoxy resins, a type of thermosetting resin, and a polymerization reaction occurs when they are mixed. Thermosetting resins are hard and resistant to heat and solvents. Examples include phenolic resins, epoxy resins, bismaleimide resins, polyimide resins, unsaturated polyester resins, vinyl ester resins, and polyurethanes.

[0038] In this embodiment, the resin content in the composite material is preferably 20 to 90 parts by mass, based on 100 parts by mass of the reinforcing material, and the lower limit is preferably 25 parts by mass or more, or 30 parts by mass or more, and the upper limit is preferably 85 parts by mass or less, or 80 parts by mass or less.

[0039] The composite material may contain other additives such as flame retardants, heat stabilizers, antioxidants, light absorbers, release agents, lubricants, various stabilizers, antistatic agents, dyes and pigments, and various reactants. In this embodiment, the content of the other additives in the composite material can be, for example, 0.01% by mass or less, or 80% by mass or less, with the reinforced composite material being 100% by mass.

[0040] (decomposition solution) In this embodiment, a decomposition solution containing oxidizing active species made from sulfuric acid is used. Here, the oxidizing active species contained in the decomposition solution are derived from sulfuric acid, and specifically, can be obtained by (a) electrolyzing a sulfuric acid solution or (b) mixing hydrogen peroxide with the sulfuric acid. In addition, acids other than sulfuric acid, such as hydrochloric acid and nitric acid, may be mixed.

[0041] The sulfuric acid used as the raw material for the oxidizing active species is a sulfuric acid solution consisting of sulfuric acid (H2SO4) and water (H2O). The concentration of sulfuric acid contained in the sulfuric acid solution is preferably 30 to 95 wt%, more preferably 50 to 80 wt%. If the sulfuric acid concentration is less than 30 wt%, it is not possible to obtain the amount of oxidizing active species necessary to decompose the base material of the reinforced composite material, and it takes a long time to decompose the base material.

[0042] In the electrolysis of the sulfuric acid solution (a) above, platinum electrodes, carbon electrodes, etc. can be used, but in the electrolysis of a highly concentrated sulfuric acid solution, so-called diamond electrodes, in which a thin film of diamond is coated on the surface of a metal plate, can be used from the viewpoint of durability. As an electrolysis device for a sulfuric acid solution, it is preferable to use a diaphragm-type electrolysis cell using a diamond electrode.

[0043] The conditions for the electrolysis are as follows: in the case of a diamond electrode, the current density is 0.01 to 10 A / cm 2 The voltage may be set to 0.1 to 100 V, but may be changed as appropriate depending on the type of electrode, the sulfuric acid concentration of the sulfuric acid solution, the amount of the sulfuric acid solution, and the like.

[0044] The electrolysis must be carried out in a closed system, and is preferably carried out in a closed sulfuric acid solution circulation system while circulating a predetermined amount of sulfuric acid solution. The circulation method may be a method of passing the solution parallel to the electrode surface at a flow rate of 50 mL / min or more using a pump or the like, or a method of natural circulation by convection with the flow of gas generated by electrolysis.

[0045] The treatment time of the electrolysis may be appropriately changed depending on the amount of sulfuric acid solution, sulfuric acid concentration, flow rate of the sulfuric acid solution, current flow conditions, etc., but treatment for 0.5 to 10 hours per 1 L of sulfuric acid solution is preferred in terms of efficiently generating oxidizing active species.

[0046] In the case of a sulfuric acid electrolysis method in which electrolysis is performed using sulfuric acid solutions as the catholyte and the anolyte, sulfuric acid solutions of different concentrations may be used for both electrodes. In particular, in the present invention, a sulfuric acid solution containing oxidizing active species obtained by electrolyzing a sulfuric acid solution of a high concentration is effective in promoting the decomposition of the base material of a reinforced composite material, so it is preferable to increase the sulfuric acid concentration on the anode side and decrease the sulfuric acid concentration on the cathode side in order to extend the life of the electrodes.

[0047] The power source used for electrolyzing the sulfuric acid solution can be electricity from various possible devices, but it is preferable to use electricity generated from so-called renewable energy sources such as solar cells. In addition, the hydrogen (generated from the cathode) and oxygen (generated from the anode) generated by electrolysis can be collected and converted into electricity or heat.

[0048] Furthermore, when hydrogen peroxide is mixed with the sulfuric acid solution, the hydrogen peroxide is consumed, so it is preferable to add hydrogen peroxide as needed.

[0049] When the sulfuric acid solution is mixed with the water peroxide, it is preferable to mix the hydrogen peroxide with the sulfuric acid solution in an amount of 0.1 to 1.0 parts by weight per part by weight of sulfuric acid.

[0050] The decomposition solution containing the obtained oxidizing active species can be supplied to a treatment tank for decomposing the resin of the composite material by either a continuous method in which the solution is continuously supplied from an electrolysis device to the treatment tank using a pump or the like, or a batch method in which a sulfuric acid solution is circulated in a closed system, and after electrolysis, a treatment solution is collected from the system and supplied to the treatment tank. The collected treatment solution may also be combined with a device that can heat, cool, or pressurize it.

[0051] The decomposition solution used to treat the reinforced composite material can be reused, and the solution can be recovered, its concentration adjusted, and reused as a sulfuric acid solution to generate active oxidizing species again, further reducing the burden on the environment.

[0052] The decomposition solution containing the oxidizing active species is preferably heated to enhance the decomposition of the resin in the composite material. The heating temperature of the decomposition solution depends on the boiling point of the decomposition solution, but it is preferable to heat the solution to a temperature of 100°C or higher, more preferably 100 to 200°C, in order to efficiently decompose the resin in the composite material. The heating temperature may be a temperature below the boiling point of the sulfuric acid solution, and the solution is heated at atmospheric pressure or under an inert gas atmosphere. The treatment solution may be heated under increased or reduced pressure.

[0053] When the resin of the composite material is decomposed using the decomposition solution, it is preferable to charge the composite material and the treatment solution so that the weight ratio of the composite material to the treatment solution is 0.001 to 0.1, which allows the resin of the composite material to be completely decomposed and reinforcing materials such as reinforcing fibers to be recovered more reliably. The time for immersing the composite material in the decomposition solution is not particularly limited, and can be appropriately set depending on the concentration of the decomposition solution and the amount of resin.

[0054] Furthermore, when the reinforcing material constituting the composite material is fibrous, it is preferable to align the treated reinforcing material in one direction while maintaining its length, or to orient it quasi-isotropically, or to arrange it randomly, in order to improve the quality of the composite material using the treated reinforcing material. Methods for aligning the treated reinforcing material in one direction include passing the treated reinforcing material through a nozzle of a certain shape in water or air to align and bundle the reinforcing material. Methods for orienting the material in a pseudo-isotropic manner include using a programmable robot or the like to align the fiber orientation in one direction and then fixing it with a resin or the like. Methods for orienting the fibers randomly include using a random mat manufacturing machine.

[0055] <Oxygen supply process> In this embodiment, in addition to the above-mentioned resin decomposition and composite material recovery process, a process of supplying oxygen into the decomposition solution is further included. In addition to the conventional process, by supplying oxygen to the decomposition solution, the decomposition rate of the resin that constitutes the composite material can be accelerated, so that high-quality reinforcing material can be recovered more efficiently than with conventional technologies without placing a burden on the environment.

[0056] The step of supplying oxygen to the decomposition solution is not particularly limited, but from the viewpoint of further increasing the decomposition efficiency, it is preferable to supply oxygen when the composite material is immersed and / or heated.

[0057] Examples of the oxidizing gas include oxygen, ozone, nitrous oxide, nitric oxide, nitrogen dioxide, fluorine, chlorine, chlorine dioxide, nitrogen trifluoride, chlorine trifluoride, silicon tetrachloride, and oxygen difluoride. Among these, from the viewpoint of safety, a single gas or a mixed gas of at least one selected from oxygen, ozone, nitrous oxide, nitric oxide, and nitrogen dioxide is preferable. These single gases or mixed gases can also be mixed with an inert gas. Furthermore, from the viewpoint of cost, atmospheric air is preferably used as the oxidizing gas, and a mixed gas of the single gases or mixed gases described above with air can also be used in the step of supplying oxygen to the decomposition solution.

[0058] The method for introducing the oxidizing gas into the decomposition solution is not particularly limited, and examples thereof include a method of bubbling the oxidizing gas into the reaction system. The oxidizing gas inlet may be a single inlet or a plurality of inlets, and the inlet may be made of a material such as plastic, metal, or glass that has excellent resistance to sulfuric acid. The means for introducing the oxidizing gas can be various means such as inserting it into the reaction system, connecting it directly to the reaction vessel, etc. The oxidizing gas can be introduced using a pump for supplying gas or an air header for storing the gas supplied from the pump, and it is more preferable to introduce the oxidizing gas by microbubbling.

[0059] Furthermore, the oxidizing gas introduced into the decomposition solution is a mixed gas containing 15% or more by volume of oxidizing gas, and it is preferable to introduce the mixed gas into the decomposition solution at a rate of 0.01 NL / sec or more. This is because the decomposition rate of the resin can be further increased. From the same viewpoint, it is preferable to introduce the mixed gas into the system (the decomposition solution) at a rate of 0.01 NL / sec or more from the start of treatment. More preferably, it is preferable to introduce the mixed gas into the system at a rate within the range of 0.01 NL / sec to 1 NL / sec from the start of treatment. Furthermore, in order to efficiently introduce the oxidizing gas into the decomposition solution, the oxidizing gas can be mechanically converted into microbubbles and then introduced.

[0060] Furthermore, methods for supplying oxygen other than by introducing the oxidizing gas include adding, to the decomposition solution, peroxides such as hydrogen peroxide, benzoyl peroxide, and peracetic acid, peracid, perchloric acid, permanganic acid, nitric acid, and salts thereof.

[0061] The peroxide, peracid, perchloric acid, permanganic acid, nitric acid, and salts thereof are preferably added to the decomposition solution at a rate of 0.01 mL / sec or more. This is because the decomposition rate of the resin can be further increased. From the same viewpoint, it is preferable to introduce the compound into the system (the decomposition solution) at a rate of 0.01 mL / sec or more from the start of treatment. More preferably, it is preferable to introduce the compound into the system at a rate within the range of 0.01 mL / sec to 1 mL / sec from the start of treatment.

[0062] Furthermore, as described above, it is also effective to heat the decomposition solution to 100°C to 200°C, maintain the temperature, immerse the composite material in the decomposition solution, and mechanically stir the entire system in the reaction system that decomposes the matrix resin of the composite material.

[0063] <Recycling of composite materials (manufacturing of composite materials)> In this embodiment, the composite material can be recycled using the reinforcing material recovered by the composite material processing method of this embodiment described above. For example, the reinforcing material from which the resin has been removed can be recycled by washing and drying it, and the recycled reinforcing material can be combined with a base material to regenerate (manufacture) a reinforced composite material.

[0064] <Winding process> In order to recover the reinforcing material of a reinforced composite material as continuous fibers, the matrix is ​​decomposed to extract a portion of the reinforcing material, which is then tied to a core, and the matrix is ​​further decomposed while the reinforcing material is wound up, allowing for recycling. In this case, the reinforcing material may be washed with water or dried. The reinforcing material may be washed with water or dried before being wound up, or may be washed with water or dried after being wound up. A step of washing and drying the reinforcing material may be provided between the disassembling step and the winding step. [Example]

[0065] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0066] (Preparation of decomposition solution containing oxidizing active species) Diamond electrodes were used as electrodes, and while the electrodes were water-cooled, sulfuric acid aqueous solution with a sulfuric acid concentration of 30 to 70 wt% was electrolyzed in a diaphragm-type electrolysis cell while circulating the solution in the electrolysis cell using a pump (KNF diaphragm liquid pump SIMDOSFEM1.02KT), producing more than 500 mL of decomposition solution containing oxidizing active species. Electrolysis was mainly performed at a constant current of 0.1 to 5.0 A / cm. 2 The circulating treatment was carried out for 10 to 500 minutes at a current of 1. The total concentration of oxidizing active species in the electrolyzed sulfuric acid aqueous solution was measured by reacting potassium iodide (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) with the oxidizing active species to liberate iodine, and then titrating the total iodine concentration with a sodium thiosulfate standard solution (a reagent manufactured by Wako Pure Chemical Industries, Ltd.).

[0067] [Examples and Comparative Examples] In Examples 1 to 8 and Comparative Examples 1 to 4, CFRP pressure tanks were used as the composite material. CFRP pressure tanks were created by using epoxy resin as the base material, applying it to a reinforcing material, and then winding it around a core material using a filament winder. The pressure tanks were then produced by curing at 150°C for 30 minutes. In Examples 10 to 13 and Comparative Examples 7 to 9, a carbon fiber reinforced plastic plate (CFRP, a medium-temperature curing epoxy resin-based prepreg manufactured by Toho Tenax Co., Ltd.) was used as the composite material, and the resin was decomposed and the reinforcing material (carbon fiber) was recovered by immersing it in the following decomposition solution.

[0068] In Example 1, a solution in which 98% concentrated sulfuric acid and 30% hydrogen peroxide solution were mixed in a weight ratio of 3:1 was used as the decomposition solution. In Examples 2 and 10, a solution in which 64% concentrated sulfuric acid and 30% hydrogen peroxide solution were mixed in a weight ratio of 3:1 was used as the decomposition solution. In Examples 3 to 9 and 11 to 13, a solution prepared by treating sulfuric acid of a predetermined concentration with a diamond electrode under the electrolysis conditions shown in Table 1 at a constant current for a predetermined time was used as the decomposition solution. In Examples 1 to 8 and 10 to 12, gas was introduced in the decomposition step by bubbling air directly into the decomposition tank through a pipe. In Examples 8 and 13, the hydrogen peroxide solution was introduced dropwise into the decomposition tank in the decomposition step. In Comparative Example 1, a solution in which 98% concentrated sulfuric acid and 30% hydrogen peroxide solution were mixed in a weight ratio of 3:1 was used as the decomposition solution. In Comparative Examples 2 and 7, a solution in which 64% concentrated sulfuric acid and 30% hydrogen peroxide solution were mixed in a weight ratio of 3:1 was used as the decomposition solution. In Comparative Examples 3 to 6 and 8 to 9, a solution prepared by treating sulfuric acid of a predetermined concentration with a diamond electrode under the electrolysis conditions shown in Table 2 at a constant current for a predetermined time was used as the decomposition solution. In Comparative Example 6, gas was introduced in the decomposition step by bubbling air directly into the decomposition tank through a pipe.

[0069] After the composite materials were treated in each example and comparative example, the reinforcing material (carbon fiber) was recovered from the treatment solution and observed. No resin component of the composite material was found to be present. Therefore, it was determined that the resin constituting the composite material had been completely decomposed. The strength of the reinforcing material (carbon fiber) recovered from the decomposition solution was measured using a universal tensile tester (Shimadzu Corporation EZ Test Series Shimadzu Compact Tabletop Tester EZTest-5N) at a tensile speed of 1.5 mm / min and 23°C. The ratio of the strength of the recovered carbon fiber to the original strength of the reinforcing material (carbon fiber) was then calculated (recycled fiber strength ratio: the value obtained by dividing the strength of the reinforcing material recovered from the decomposition solution by the original strength of the reinforcing material). The ratio of the strength of the reinforcing material recovered from the decomposition solution to the original strength of the reinforcing material was 0.9 to 1.2, confirming that there was little decrease in strength due to the recycling process.

[0070] For each example and comparative example, the sulfuric acid concentration in the decomposition solution, the total concentration of oxidizing active species contained in the decomposition solution, the weight ratio of the composite material (CFRP) used in the decomposition treatment to the decomposition solution, the type and amount of oxidizing gas introduced, the heating temperature of the decomposition solution, and the time required for complete decomposition of the resin are summarized in Tables 1 and 2.

[0071] [Table 1]

[0072] [Table 2]

[0073] The results in Tables 1 and 2 show that in each example, the time required for complete decomposition of the resin was several times shorter than in the other examples, and that supplying oxygen to the decomposition solution significantly improved the treatment efficiency. [Industrial Applicability]

[0074] According to the present invention, it is possible to provide a method for processing composite materials that can recover reinforcing materials efficiently and without degrading the quality, without imposing a burden on the environment.

Claims

1. A method for treating a composite material, comprising the steps of immersing a composite material composed of a resin and a reinforcing material in a decomposition solution containing an oxidizing active species made from sulfuric acid, and heating the composite material to decompose the resin and recover the reinforcing material, further comprising the step of supplying oxygen into the decomposition solution; A method for treating a composite material, wherein the step of supplying oxygen into the decomposition solution comprises supplying oxygen when the decomposition solution is heated.

2. 2. The method for treating a composite material according to claim 1, wherein the decomposition solution is a solution in which hydrogen peroxide is mixed with a sulfuric acid solution.

3. 2. The method for treating a composite material according to claim 1, wherein the decomposition solution is a solution obtained by electrolyzing a sulfuric acid solution.

4. 2. The method for treating a composite material according to claim 1, wherein the step of supplying oxygen into the decomposition solution is characterized by introducing an oxidizing gas which is at least one elemental or mixed gas selected from oxygen, ozone, nitrous oxide, nitric oxide, and nitrogen dioxide; a mixed gas of any of the elemental or mixed gases with an inert gas; air; or a mixed gas of any of the elemental or mixed gases with air, or by adding peroxide, peracid, perchloric acid, permanganic acid, nitric acid, or salts thereof.

5. 2. The method for processing composite materials according to claim 1, wherein the oxidizing gas introduced into the decomposition solution is a mixed gas containing 15% by volume or more of the oxidizing gas, and the mixed gas is introduced into the decomposition solution at a rate of 0.01 NL / sec or more.

6. 5. The method for treating a composite material according to claim 4, wherein in the step of supplying oxygen, the composite material is immersed in the decomposition solution, and the resin component of the composite material is decomposed while the oxidizing gas is introduced into the decomposition solution while heating and maintaining the temperature of the decomposition solution at 100°C to 200°C, and after the decomposition, the reinforcing material is recovered by filtering, washing, and drying.

7. 2. The method of claim 1, wherein said reinforcing material is continuous fiber.

8. 8. The method for processing a composite material according to claim 7, wherein the step of recovering the reinforcing material is a step of winding the reinforcing material around a core material.

9. 2. The method for treating a composite material according to claim 1, wherein the reinforcing material is at least one selected from the group consisting of carbon fiber, glass fiber, and metal fiber.

10. A method for producing a composite material, comprising compounding a reinforcing material recovered by the method according to any one of claims 1 to 9 with a resin.

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