Fiber-reinforced plastic and method for recovering the fibers contained therein.
A polymer compound with a diacylhydrazine skeleton in the FRP matrix facilitates easy recovery of fibers by decomposition in hypochlorous acid, addressing the inefficiencies of existing CFRP recycling methods and ensuring the fibers remain reusable.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- KANAGAWA UNIVERSITY
- Filing Date
- 2026-04-07
- Publication Date
- 2026-06-11
AI Technical Summary
Existing methods for recovering carbon fibers from discarded carbon fiber reinforced plastic (CFRP) are inefficient and costly, and there is a need for a method that allows for easy and cost-effective recovery of fibers in a reusable state.
Incorporating a polymer compound with a diacylhydrazine skeleton as the matrix in FRP, which can be decomposed by immersion in an aqueous solution of hypochlorous acid or its salt, allowing the fibers to be recovered without deterioration.
The method enables easy and effective recovery of fibers from FRP, maintaining their reusable state and reducing environmental and economic costs associated with disposal.
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Abstract
Description
Technical Field
[0001] The present invention relates to a fiber reinforced plastic and a method for recovering the fibers contained therein.
Background Art
[0002] Fiber reinforced plastic (hereinafter also referred to as FRP) is a composite material obtained by combining a plastic having a low elastic modulus and low strength but being lightweight with a reinforcing material such as glass fiber or carbon fiber having a high elastic modulus and high tensile strength to increase the strength. Since it exhibits good mechanical properties and the like, it is used in a wide range of fields such as transportation equipment, housing equipment, pools, and building materials. In particular, carbon fiber reinforced plastic (hereinafter also referred to as CFRP) using carbon fiber as a reinforcing material is said to be lightweight and have strength comparable to steel, and is widely used as a material to replace steel plates conventionally used in automobiles and aircraft.
[0003] However, due to its excellent durability and strength, FRP tends to cause problems in waste treatment. In addition, the carbon fiber used in CFRP is very expensive while exhibiting excellent properties, and if carbon fiber can be recovered from discarded CFRP and reused, it is very useful both environmentally and in terms of cost. Against this background, for example, in Patent Documents 1 to 5, various methods for recovering carbon fiber contained in CFRP without deteriorating it have been proposed. Such methods include chemical treatment such as decomposing the plastic in CFRP in the presence of high temperature and radicals, and physical treatment such as removing the plastic in CFRP by treating CFRP with superheated steam at 800°C or higher.
[0004] On the other hand, the present inventors have proposed poly(diacylhydrazine) as a polymer that does not deteriorate over time during use but can be rapidly decomposed at the time of disposal (see Patent Documents 5 and 6). This polymer exhibits a certain durability during use as a plastic, but can be easily decomposed in an aqueous solution of sodium hypochlorite at the time of disposal. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2001-240697 [Patent Document 2] Japanese Patent Publication No. 2007-246831 [Patent Document 3] Japanese Patent Publication No. 2011-122032 [Patent Document 4] Japanese Patent Publication No. 2020-114904 [Patent Document 5] Japanese Patent Publication No. 2006-022315 [Patent Document 6] Japanese Patent Publication No. 2011-052075 [Overview of the project] [Problems that the invention aims to solve]
[0006] This invention has been made in view of the above circumstances, and aims to provide a fiber-reinforced plastic in which the contained fibers can be easily recovered in a reusable state. [Means for solving the problem]
[0007] The inventors of the present invention have conducted extensive research to solve the above problems and have found that if an FRP contains a polymer compound having a diacylhydrazine skeleton represented by the following chemical formula (1) as a matrix, the matrix can be decomposed by a simple treatment of immersion in an aqueous solution of hypochlorous acid or its salt, allowing the fibers contained in the FRP to be recovered in a reusable state, while this polymer compound possesses sufficient durability as a matrix for the FRP. The present invention is based on the above findings and provides the following.
[0008] (1) The present invention is a fiber-reinforced plastic characterized by containing a polymer compound having a divalent group represented by the following chemical formula (1) as a matrix. [ka] (In the chemical formula (1) above, the wavy lines indicate bonds to other atoms.)
[0009] (2) The present invention is also a fiber-reinforced plastic as described in item (1), which is a carbon fiber-reinforced plastic.
[0010] (3) The present invention also relates to the fiber-reinforced plastic described in item (1) or (2), wherein the polymer compound is a cured epoxy resin or a crosslinked vinyl polymer.
[0011] (4) The present invention also relates to a method for recovering fibers contained in fiber-reinforced plastic, characterized by immersing the fiber-reinforced plastic described in any one of items (1) to (3) in an aqueous solution of hypochlorous acid or a salt thereof to decompose the matrix, and separating and recovering the fibers contained in the fiber-reinforced plastic. [Effects of the Invention]
[0012] According to the present invention, a fiber-reinforced plastic is provided in which the contained fibers can be easily recovered in a reusable state. [Modes for carrying out the invention]
[0013] The following describes one embodiment of the fiber-reinforced plastic of the present invention and one embodiment of a method for recovering fibers contained in the fiber-reinforced plastic. It should be noted that the present invention is not limited in any way to the following embodiments and examples, and can be implemented with modifications within the scope of the present invention.
[0014] First, the fiber-reinforced plastic (FRP) of the present invention will be described. The fiber-reinforced plastic of the present invention is characterized by including a polymer compound having a divalent group represented by the following chemical formula (1) as a matrix. In the following chemical formula (1), the wavy bond represents a bond to another atom. The "polymer compound having a divalent group represented by the following chemical formula (1)" means a compound in which the structure represented by the following general formula (1) is included in the molecule of the polymer compound.
[0015]
Chemical formula
[0016] Generally, FRP is obtained by impregnating fibers such as glass fibers and carbon fibers with a matrix material, shaping it into a desired shape, and then curing it. Examples of such fibers include glass fibers, carbon fibers, aramid fibers, etc., and among them, carbon fibers are preferably mentioned. Examples of these fibers include unidirectional materials in which the fibers are arranged in one direction, woven fabrics such as plain weave, twill weave, and satin weave, and non-woven fabrics.
[0017] The material used as the matrix is not particularly limited, but preferably includes epoxy resins, curable compositions containing monomers having ethylenically unsaturated bonds, etc. These are impregnated into the above-mentioned fibers and cured by means such as heating to become the matrix of FRP. That is, the matrix is a cured product of an epoxy resin or a curable composition and is a highly cross-linked polymer compound. Strictly speaking, such a cured product may not be regarded as a polymer compound in some cases, but in the present invention, a polymer compound including such a cured product is called a polymer compound.
[0018] As described above, the polymer compound serving as the matrix contains the divalent group represented by the above chemical formula (1). This divalent group may be included in a cross-linking structure that cross-links polymer molecules during curing, or may be included in a monomer of an epoxy resin and be included in the main chain of the polymer molecule. Under the conditions under which the FRP of the present invention is normally used, this polymer compound is stable, and thus the FRP of the present invention exhibits excellent durability. On the other hand, the divalent group represented by the above chemical formula (1) decomposes through the following chemical reaction when contacted with an aqueous solution of hypochlorous acid or its salt. In the following chemical reaction formula, sodium hypochlorite is shown as hypochlorous acid or its salt, but it is not limited thereto.
[0019]
Chemical formula
[0020] That is, chemical species 1 containing the divalent group represented by the above chemical formula (1) is oxidized by sodium hypochlorite and converted into a highly reactive azodicarbonyl compound 2, and this azodicarbonyl compound 2 is immediately hydrolyzed and decomposed into two carboxylic acids and diimide 3. Through such a chemical reaction, the cross-linking structure that cross-linked polymer molecules is cleaved, or the main chain of the polymer molecule is slightly cleaved. As a result, the polymer compound serving as the matrix can no longer maintain the cured state, becomes solvent-soluble, and enters a state where it can be removed. As a result of the polymer compound being removed from the FRP in this way, the fibers contained in the FRP are recovered. The recovered fibers do not deteriorate even after undergoing this chemical treatment and remain in a reusable state.
[0021] The polymer compounds constituting the matrix are not limited as long as they have a divalent group represented by the above chemical formula (1). Examples of such polymer compounds include cured epoxy resins and crosslinked vinyl polymers. FRPs using these as matrices exhibit sufficient durability during use, while the matrix can be easily removed after use by the above treatment. Next, examples of such preferred polymer compounds will be described.
[0022] The cured epoxy resin is obtained by curing an epoxy resin containing polyepoxy compounds, polyol compounds, and a curing catalyst such as an amine. This uncured epoxy resin is impregnated into the aforementioned fibers, and then the epoxy resin is cured to produce FRP (fiber-reinforced plastic).
[0023] The polyepoxy compound and / or polyol compound constituting the epoxy resin contains a divalent group represented by the above chemical formula (1). As a result, the main chain of the polymer compound contained in the cured epoxy resin contains a divalent group represented by the above chemical formula (1).
[0024] For example, in conventional epoxy resins, bisphenol compounds such as bisphenol A are used as polyol compounds, and it is preferable to introduce a divalent group represented by the above chemical formula (1) into the molecule of such bisphenol compounds. Such bisphenol compounds can be obtained by the following synthesis route, for example. Although four types of bisphenol compounds are given as examples below for illustrative purposes, the present invention is not limited to these.
[0025] [ka]
[0026] [ka]
[0027] To synthesize polyphenol compounds such as bisphenol compounds, as described above, a phenol carboxylic acid hydrazide is synthesized, and then oxidatively condensed using an oxidizing agent such as bisacetoxyiodobenzene. Other examples of oxidizing agents that can be used here include potassium persulfate, potassium bisulfate, double salts of potassium sulfate, diacetoxyiodobenzene, bis(trifluoroacetoxy)iodobenzene, and iodosobenzene.
[0028] The bisphenol compound having a divalent group represented by the above chemical formula (1), obtained by the procedure described above, hardens by reacting with a polyepoxy compound in the presence of a base catalyst such as imidazole, for example, as shown below.
[0029] [ka]
[0030] As shown in the chemical reaction equation above, the main chain of the polymer compound in the hardened state contains a divalent group represented by chemical formula (1) above. This polymer compound is reduced in molecular weight as shown below when it comes into contact with an aqueous solution of hypochlorous acid or its salt. Since this low-molecular-weight compound is no longer a hardened product, it can be dissolved in a suitable solvent, and the fibers contained in the FRP can be recovered.
[0031] [ka]
[0032] Next, we will explain crosslinked vinyl polymers.
[0033] A crosslinked vinyl polymer is obtained by radical polymerization of (A) a monomer having ethylenically unsaturated bonds and (B) a crosslinking agent having two or more ethylenically unsaturated bonds and a divalent group represented by the above chemical formula (1) in its molecule. A liquid polymerizable composition is prepared by mixing (A) and (B) with a radical polymerization initiator, and this polymerizable composition is impregnated into fibers. The polymerizable composition is then heated to cure it, resulting in FRP. Such a crosslinking agent can be obtained, for example, by reacting (meth)acryloyl chloride and hydrazine in the presence of a base, as shown in the chemical reaction equation below. In this specification, (meth)acryloyl means acryloyl and / or methacryloyl.
[0034] [ka]
[0035] The crosslinking agent obtained as described above is polymerized with a monomer having ethylenically unsaturated bonds (e.g., a vinyl monomer) in the presence of a polymerization initiator such as azobisisobutyronitrile (AIBN) to form a crosslinked vinyl polymer. This crosslinked polymer has a divalent group represented by the above chemical formula (1) in the crosslinked portion, and the crosslinked portion is cleaved upon contact with an aqueous solution of hypochlorous acid or its salt. The vinyl polymer, with its crosslinked portion cleaved, is no longer a cured product and can be dissolved in a suitable solvent, making it possible to recover the fibers that were contained in the FRP.
[0036] [ka]
[0037] Examples of monomers possessing ethylenically unsaturated bonds include ethylene, styrene, acrylic acid, acrylic acid esters, methacrylic acid esters, acrylamide, N-substituted acrylamide, N,N-disubstituted acrylamide, acrylonitrile, butadiene, vinyl acetate, and the like.
[0038] Furthermore, polymerization initiators include those that generate radicals upon heating, such as persulfates like sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides like hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide; and azo compounds such as azonitrile compounds, azoamidine compounds, cyclic azoamidine compounds, azoamide compounds, alkylazo compounds, 2,2'-azobis(2-amidinopropane)dihydrochloride, and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride.
[0039] A method for recovering fibers contained in the fiber-reinforced plastic of the present invention is also part of the present invention. The method for recovering fibers contained in the fiber-reinforced plastic of the present invention is characterized by immersing the fiber-reinforced plastic of the present invention in an aqueous solution of hypochlorous acid or its salt to decompose the matrix, thereby separating and recovering the fibers contained in the fiber-reinforced plastic. As this has already been explained, a detailed explanation will be omitted here.
[0040] Furthermore, when immersing FRP in an aqueous solution of hypochlorous acid or its salt to decompose the matrix, it is preferable to make the aqueous solution flow by stirring or other means. At this time, the fibers to be recovered may be scattered by the water flow, so in order to prevent this, it is desirable to contain the FRP to be decomposed in an appropriate net-type container. [Examples]
[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.
[0042] • Synthesis of diacryloylhydrazine [ka]
[0043] 19 mL (235 mmol) of acrylate chloride was dissolved in 30 mL of tetrahydrofuran. To this solution, an aqueous solution prepared by dissolving 10 g (255 mmol) of sodium hydroxide and 5.0 mL (103 mmol) of hydrazine monohydrate in 70 mL of water was added dropwise over 40 minutes, and the mixture was stirred for 3 hours. The precipitated solid was collected by filtration. After vacuum drying the obtained solid, it was recrystallized with ethyl acetate-hexane to obtain colorless crystalline diacryloylhydrazine. The yield was 4.7 g (33% yield).
[0044] A polymerizable composition was prepared by mixing N,N-dimethylacrylamide (DMA), diacryloylhydrazine (DAH), and 2,2'-azobisisobutyronitrile (AIBN) in a molar ratio of 95:5:2. Next, a 1 mm gap was created between two PTFE sheets, and a carbon fiber sheet (CF sheet) was sandwiched in this gap. The polymerizable composition prepared in the above procedure was then poured into the CF sheet to impregnate it. The CF sheet impregnated with the polymerizable composition was heated at 40°C for one day, and then heated at 100°C for 3 hours to prepare CFRP. The obtained CFRP was then washed with diethyl ether.
[0045] The CFRP obtained using the above procedure was wrapped in a polyester net and suspended in a 5% sodium hypochlorite aqueous solution, while the solution was stirred. After two days from the start of stirring, the CFRP matrix had disappeared, and a sheet of carbon fibers could be recovered. Observation of the recovered carbon fiber sheet with an electron microscope confirmed that the carbon fibers constituting the sheet were undamaged. From the above, it can be seen that, according to the FRP of the present invention, the matrix can be easily removed from the FRP, and the fibers contained in the FRP can be recovered in a reusable state.
Claims
1. A fiber-reinforced plastic characterized by containing a polymer compound having a divalent group represented by the following chemical formula (1) as a matrix. 【Chemistry 1】 (In the chemical formula (1) above, the wavy lines indicate bonds to other atoms.)
2. The fiber-reinforced plastic according to claim 1, which is a carbon fiber-reinforced plastic.
3. The fiber-reinforced plastic according to claim 1 or 2, wherein the polymer compound is a cured epoxy resin or a crosslinked vinyl polymer.
4. A method for recovering fibers contained in fiber-reinforced plastic, characterized by immersing the fiber-reinforced plastic according to any one of claims 1 to 3 in an aqueous solution of hypochlorous acid or a salt thereof to decompose the matrix, and separating and recovering the fibers contained in the fiber-reinforced plastic.