Method for decomposing vulcanized rubber

Abstract

The present invention addresses the problem of providing a method for efficiently decomposing a vulcanized rubber. The solution is a method for decomposing a vulcanized rubber, wherein a radical initiator selected from peroxides is made to act, in a solvent, on a vulcanized rubber or a composition containing the vulcanized rubber in an atmosphere containing an oxygen gas at 0-60°C to convert the same into a soluble decomposition product.

Description

How to decompose vulcanized rubber

[0001] The present invention relates to a method for decomposing vulcanized rubber.

[0002] Conventionally, vulcanized rubber products, such as tire rubber, have often been recycled as fuel in cement plants, resulting in increased carbon dioxide emissions. However, carbon dioxide emissions contribute to global warming, and therefore the development of new recycling technologies for vulcanized rubber products is needed to reduce carbon dioxide emissions and mitigate global warming. Vulcanized rubber is essentially cross-linked by sulfur and is generally insoluble and difficult to process. Therefore, to efficiently reuse vulcanized rubber, it is important to develop a technology that can decompose insoluble and difficult to process vulcanized rubber through reactions such as devulcanization (hereinafter, decrosslinking may be referred to as devulcanization) into soluble polymers that are highly soluble in solvents and easy to handle and process. Known methods for decomposing vulcanized rubber by devulcanization include (A) a method of heating to a high temperature (generally 180°C or higher) (Patent Document 1), (B) a method of adding a thiol compound (Patent Document 2), (C) a method of adding an alkali metal (Patent Document 3), (D) a method of adding a microorganism (Patent Document 4), and (E) a method of swelling vulcanized rubber in a solvent and then adding a peroxide (Patent Document 5), or a method of adding a peroxide to vulcanized rubber in a solvent and heating to 80°C or higher (Non-Patent Documents 1 and 2).

[0003] Japanese Patent Laid-Open No. 11-209511 Japanese Patent Laid-Open No. 54-117594 Japanese Patent Laid-Open No. 11-514020 Japanese Patent Laid-Open No. 2004-313031 Japanese Patent Laid-Open No. 2002-97386

[0004] J. Polym. Environ. , 2011, 19, 382-390 Polym. Degrad. Stab. , 2015, 118, 88-95

[0005] However, the above methods (A) to (E) have the following problems. For example, in method (A), heating vulcanized rubber to high temperatures is prone to side reactions, making it difficult to maintain the basic skeleton of the vulcanized rubber. In method (B), adding a sulfur compound increases the sulfur content, limiting the uses of the product. In method (C), adding an alkali metal is dangerous because alkali metals are highly reactive to moisture, etc. In method (D), using microorganisms, the reaction rate is slow and production efficiency is low. Furthermore, in method (E), using a peroxide, a large amount of solvent is required because the ratio of the total solids (mg) excluding the solvent after decomposition to the solvent (mL) is a basic condition of 1:30 or less. In addition, even in the method of heating to 80°C or higher, the yield of the desulfurized product is not sufficiently high.

[0006] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a method for decomposing vulcanized rubber that can efficiently advance devulcanization.

[0007] As a result of extensive research aimed at solving the above problems, the inventors of the present invention have discovered a novel fact that the decomposition reaction of vulcanized rubber using a radical initiator selected from peroxides in an atmosphere containing oxygen gas proceeds easily at relatively low temperatures (60°C or less) without swelling the vulcanized rubber or using a large amount of solvent, and have completed the present invention.

[0008] The gist of the present invention is as follows. <1> A method for decomposing vulcanized rubber, comprising reacting a radical initiator selected from peroxides with vulcanized rubber or a composition containing the vulcanized rubber in a solvent at 0 to 60°C in an oxygen gas-containing atmosphere to convert the vulcanized rubber or a composition containing the vulcanized rubber into a soluble decomposition product. <2> The method for decomposing vulcanized rubber according to <1>, wherein the rubber component of the vulcanized rubber is a rubber component containing at least one rubber selected from natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR). <3> The method for decomposing vulcanized rubber according to <1> or <2>, wherein the composition containing the vulcanized rubber is a tire rubber composition containing carbon black or silica. <4> The method for decomposing vulcanized rubber according to any one of <1> to <3>, wherein the peroxide is selected from acyl peroxides. <5> The method for decomposing vulcanized rubber according to <4>, wherein the acyl peroxide is selected from benzoyl peroxide, lauroyl peroxide, and acetyl peroxide. <6> The decomposition method according to any one of <1> to <5>, wherein the decomposition method uses a chlorinated hydrocarbon or an aromatic hydrocarbon as a solvent. <7> The decomposition method according to <6>, wherein the chlorinated hydrocarbon is a chlorinated hydrocarbon selected from chloroform or chlorobenzene. <8> The decomposition method according to <6>, wherein the aromatic hydrocarbon is ethylbenzene. <9> The decomposition method according to any one of <1> to <8>, wherein the vulcanized rubber has been subjected to a pretreatment step of washing with a solvent.

[0009] In a preferred embodiment of the method for decomposing vulcanized rubber of the present invention, typically, 50% by mass or more of the rubber component in the vulcanized rubber is converted into soluble decomposition products. Specifically, the soluble decomposition products are soluble polymers derived from the rubber component in the vulcanized rubber and compositions containing the same (hereinafter, sometimes referred to as soluble polymer compositions). "Soluble" means that the polymers can be dissolved in the solvent used. When the weight-average molecular weight of the soluble polymer is 200 to 200,000, the yield of reusable soluble polymers is improved, further improving the economic and environmental value of this decomposition method.

[0010] In another preferred embodiment of the method for decomposing vulcanized rubber of the present invention, the vulcanized rubber contains at least one rubber selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber. In this case, the decomposition method produces a soluble polymer containing an easily recyclable diene monomer, such as isoprene or butadiene, in its skeleton.

[0011] In another preferred embodiment of the method for decomposing vulcanized rubber of the present invention, the vulcanized rubber further contains carbon black. Even in this case, the vulcanized rubber can be efficiently decomposed, and the carbon black can be reused. Furthermore, in a preferred embodiment of the method for decomposing compounded rubber containing carbon black, the ratio of the total solid content (recovered carbon black component) (mg) to the solvent (mL) after decomposition of the compounded rubber is usually 1:25 or more, which reduces the amount of solvent used and is therefore advantageous from an economic and environmental perspective.

[0012] According to the present invention, the reaction can be carried out under mild conditions to convert vulcanized rubber into soluble decomposition products, and therefore an efficient method for decomposing vulcanized rubber can be provided.

[0013] The method for decomposing vulcanized rubber of the present invention will be described in detail below by way of example based on an embodiment thereof.

[0014] The method for decomposing vulcanized rubber of the present invention is characterized in that a radical initiator selected from peroxides is allowed to act on vulcanized rubber or a composition containing the same in a solvent at 0 to 60°C in an atmosphere containing oxygen gas, thereby converting the vulcanized rubber or a composition containing the same into a soluble decomposition product.

[0015] It is believed that the peroxide used in the method for decomposing vulcanized rubber of the present invention basically acts on the cross-linking sites formed by sulfur to sever the cross-linking bonds, and therefore, in the case of diene rubber, it is believed that its main chain skeleton is basically maintained even after the decomposition reaction.

[0016] <Radical Initiator> The radical initiator used in the present invention is selected from peroxides. Examples of peroxides include acyl peroxide, percarboxylic acid, dialkyl peroxide, and alkyl hydroperoxide. Among these, from the viewpoint of reaction rate, acyl peroxide and percarboxylic acid are preferably used, and acyl peroxide is more preferably used. Specific examples of acyl peroxides include benzoyl peroxide, toluoyl peroxide, chlorobenzoyl peroxide, dichlorobenzoyl peroxide, methoxybenzoyl peroxide, phthaloyl peroxide, acetyl peroxide, propanoyl peroxide, caprylyl peroxide, decanoyl peroxide, lauroyl peroxide, myristoyl peroxide, and stearoyl peroxide. Among acyl peroxides, from the viewpoints of reaction rate, availability, and the like, benzoyl peroxide, lauroyl peroxide, and acetyl peroxide are preferably used. From the viewpoints of reaction rate and peroxide stability, lauroyl peroxide is preferred over benzoyl peroxide. Examples of percarboxylic acids include perbenzoic acid, chloroperbenzoic acid, peracetic acid, and perpropionic acid. Examples of dialkyl peroxides include di-tert-butyl peroxide, dicumyl peroxide, and tert-butylcumyl peroxide, and examples of alkyl hydroperoxides include tert-butyl hydroperoxide and cumene hydroperoxide. These peroxides may be in the form of a hydrate from the viewpoints of safety, availability, and the like. By using a suitable initiator, vulcanized rubber can be efficiently decomposed under mild conditions.

[0017] <Decomposition Step> In the method for decomposing vulcanized rubber of this embodiment, vulcanized rubber or a composition containing the same is decomposed using a radical initiator selected from the peroxides described above.

[0018] (Vulcanized Rubber) The vulcanized rubber to be decomposed by the decomposition method of this embodiment contains, for example, a diene rubber having a crosslinking site containing a sulfur atom, and may further contain carbon black, silica, etc. The form of the vulcanized rubber is not particularly limited and may be, for example, powdered rubber. The powdered rubber can be obtained by cutting and pulverizing used rubber products such as waste tires. The pulverization process may include multiple steps, such as a preliminary pulverization step and a fine pulverization step. Furthermore, the particle size of the powdered rubber used may be adjusted by a classification step after the pulverization step. Furthermore, the composition containing the vulcanized rubber may be recycled waste rubber, used rubber products, etc. Waste rubber is not limited to rubber generated from rubber products, but refers to all discarded rubber, including unnecessary scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is fine rubber generated during the buffing process of, for example, retreading a tire, in which the tread portion remaining on the base tire is scraped. Peeled rubber is a long piece of rubber, for example, 1 to 2 cm wide, peeled from the surface of a rubber product such as a tire. Peeled rubber is produced by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Rubber products include final products such as tires, rubber hoses, and rubber conveyor belts, as well as rubber parts or components used in the manufacturing process of final products. Used tires may be, for example, tires to be retreaded, or may be tires discarded for some reason, such as waste tires generated from tire replacement or scrapping, or ELT (End-of-Life Tires) that have reached the end of their life as tires. As the composition containing vulcanized rubber, tire rubber containing carbon black or silica is preferred.

[0019] --Diene-Based Rubber-- The diene-based rubber is a rubber containing units derived from a diene-based monomer (diene-based units) and may further contain units derived from a copolymerizable comonomer. The units derived from the diene-based monomer enable the diene-based rubber to be crosslinked (vulcanized) and to exhibit rubber-like elongation and strength. Note that, although the diene-based rubber in the crosslinked rubber is usually present in a crosslinked state, a portion of the diene-based rubber may be uncrosslinked. Specific examples of diene-based monomers (diene-based compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds. Specific examples of the aromatic vinyl compounds include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. Examples of the diene rubber include isoprene-skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). The isoprene-skeleton rubber is a rubber whose main skeleton is an isoprene unit, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). Among these, the diene rubber preferably comprises at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber. When the diene rubber comprises at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber, a diene-based soluble polymer containing a skeleton such as isoprene or butadiene can be obtained, which is easily recyclable. The content of the diene rubber in the vulcanized rubber is not particularly limited, and is preferably in the range of, for example, 10 to 100% by mass. From the viewpoint of further improving the yield of the soluble polymer, a range of 30 to 100% by mass is more preferable.

[0020] --Sulfur-- The vulcanized rubber basically contains sulfur. In the vulcanized rubber, sulfur is typically present as crosslinks in the diene rubber after crosslinking the diene rubber, but some of it may be free. The method for decomposing vulcanized rubber of the present invention primarily involves the action of a radical initiator to decompose the crosslinks, thereby decomposing the vulcanized rubber and producing a soluble polymer. While sulfur is generally believed to remain in the soluble polymer, even if free sulfur components remain in the solution, the sulfur components can be separated by a purification procedure such as reprecipitation to purify the soluble polymer. The sulfur content in the vulcanized rubber is not particularly limited, and is, for example, in the range of 0.1 to 10 parts by mass, preferably 1 to 5 parts by mass, per 100 parts by mass of the diene rubber.

[0021] --Carbon Black-- The vulcanized rubber may further contain carbon black. In the method for decomposing vulcanized rubber of the present invention, the vulcanized rubber is decomposed into soluble polymers in the decomposition step. Therefore, even if the vulcanized rubber contains carbon black, the carbon black can be easily separated and recovered after the decomposition step, for example, by solid-liquid separation. Therefore, even if the vulcanized rubber contains carbon black, the vulcanized rubber can be efficiently decomposed. The content of carbon black in the crosslinked rubber is not particularly limited, and is, for example, in the range of 10 to 150 parts by mass, preferably 30 to 120 parts by mass, per 100 parts by mass of the diene rubber.

[0022] --Other Components-- In addition to the diene rubber, carbon black, and sulfur described above, the vulcanized rubber may contain various components commonly used in the rubber industry, such as rubber components other than diene rubber, fillers other than carbon black (silica, calcium carbonate, etc.), silane coupling agents, antioxidants, softeners, processing aids, resins, surfactants, organic acids (stearic acid, etc.), zinc oxide (zinc white), vulcanization accelerators, crosslinking agents other than sulfur, etc.

[0023] (Amount of Radical Initiator) The amount of the radical initiator used is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and preferably 30 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the vulcanized rubber. If the amount of the catalyst used is 0.1 part by mass or more per 100 parts by mass of the compounded rubber, the decomposition reaction of the vulcanized rubber will further proceed, and if the amount of the catalyst used is 30 parts by mass or less per 100 parts by mass of the vulcanized rubber, it is preferable from the standpoint of cost.

[0024] (Reaction Conditions) The decomposition step is carried out in an oxygen-containing atmosphere in a solvent at a temperature between 0°C and 60°C. The oxygen gas concentration (vol %) in the reaction atmosphere is typically 1 to 100%, preferably 1 to 80%, and more preferably 5 to 50%, including the atmospheric oxygen concentration of approximately 20%. When the oxygen gas concentration is less than 100%, an inert gas such as nitrogen gas can be used as the remaining gas component. Generally, the higher the oxygen concentration, the more advantageous the decomposition reaction. However, since undesirable side reactions are more likely to occur, when the oxygen concentration is high, it is necessary to appropriately control the reaction time, reaction temperature, etc. On the other hand, using atmospheric air with an oxygen concentration of approximately 20% eliminates the need for separate oxygen gas, which is advantageous in terms of equipment and economy. When the amount of vulcanized rubber is small in an air atmosphere, the reaction can proceed even in a closed vessel with a sufficiently large internal volume. In this case, the internal volume of the reaction vessel is generally 50 parts by volume or more, more preferably 100 parts by volume or more, per part by volume of vulcanized rubber. When the decomposition reaction is carried out in a closed system, a large amount of vulcanized rubber requires a reaction vessel with a large internal volume, which is not desirable from an equipment perspective. Therefore, from an equipment perspective, it is preferable to carry out the reaction in a non-closed system that allows the flow of air, etc. To make the reaction system non-closed, methods such as opening a portion of the reaction vessel, installing a membrane that allows the flow of air, etc., or allowing air, etc., to overflow can be considered. Another advantageous embodiment is a method in which the reaction is carried out while continuously or intermittently blowing air, etc. into the solution. In this case, the blowing rate is not particularly limited, but is usually 1 to 1000 mL / min, preferably 2 to 500 mL / min, and more preferably 3 to 200 mL / min per gram of vulcanized rubber.

[0025] In this embodiment, a solvent is used for the decomposition of the vulcanized rubber. Any solvent that does not inhibit the decomposition reaction can be used as the solvent. Examples of such solvents include aromatic hydrocarbons (aromatic solvents), chlorinated hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, and nitriles. Specific examples of aromatic hydrocarbons include toluene, xylene, ethylbenzene, trimethylbenzene, and propylbenzene. Chlorinated hydrocarbons include chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethene, chlorobenzene, and dichlorobenzene. Aliphatic hydrocarbons include pentane, hexane, and octane. Alicyclic hydrocarbons include cyclohexane and cyclooctane. Ethers include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, dioxane, and benzonitrile. Among these, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoints of reaction rate, availability, and the like. Specific examples of such solvents include toluene, xylene, ethylbenzene, chloroform, chlorobenzene, and dichlorobenzene. Among aromatic hydrocarbons, ethylbenzene is preferred over toluene from the viewpoint of reaction rate. The solvent suitable for the decomposition reaction also depends on the type of vulcanized rubber. For example, when the vulcanized rubber is NR-based, IR-based, or BR-based, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoint of reaction rate, solubility of the product, etc., specific examples of which include toluene, ethylbenzene, chloroform, and chlorobenzene. On the other hand, for SBR-based vulcanized rubber, chlorinated hydrocarbons are more preferred from the viewpoint of reaction rate, etc., specific examples of which include chloroform and chlorobenzene. By using a preferred solvent, the decomposition of the vulcanized rubber progresses more easily, and a soluble polymer can be produced more efficiently. The amount of the solvent used is preferably 2 mL or more, more preferably 10 mL or more, per 1 g of the vulcanized rubber, and is preferably 100 mL or less, and more preferably 50 mL or less.If the amount of the solvent used is 2 mL or more per 1 g of the vulcanized rubber, the decomposition reaction of the vulcanized rubber is promoted, and if the amount of the solvent used is 50 mL or less per 1 g of the crosslinked rubber, it is preferable from the standpoint of cost.

[0026] The method for decomposing vulcanized rubber according to this embodiment is carried out at 0 to 60°C. By carrying out the decomposition step at 0 to 60°C, the decomposition reaction of the diene rubber in the vulcanized rubber can be carried out efficiently. From the viewpoint of the decomposition rate, the decomposition step is preferably carried out at 5°C or higher, more preferably 10°C or higher, and from the viewpoints of energy cost, environmental load, reaction equipment, etc., the decomposition step is preferably carried out at 50°C or lower, more preferably 40°C or lower. The decomposition reaction of the present invention basically proceeds smoothly at around room temperature (20 to 30°C), and therefore, another advantage of the decomposition method of the present invention is that no special equipment for heating or cooling is required.

[0027] The decomposition step can be carried out under any pressure, including reduced pressure, normal pressure, and increased pressure. For example, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 1 MPa, and even more preferably 50 kPa to 500 kPa.

[0028] In the decomposition reaction of the present invention, it is important to efficiently stir the raw materials, i.e., the vulcanized rubber, the radical initiator, and the solvent. Various conventionally known stirring methods can be used, such as a method using a magnetic stirrer, a method using a mechanical stirrer, or a method using a shaker. Furthermore, to promote the reaction, ultrasonic irradiation, microwave irradiation, light irradiation, or the like may be used in combination. These methods can also be used in combination.

[0029] (Decomposition Products) In the method for decomposing vulcanized rubber according to this embodiment, it is preferable that 50% by mass or more of the rubber component in the vulcanized rubber is decomposed into a soluble polymer having a weight-average molecular weight of 200 to 200,000, and more preferably into a soluble polymer having a weight-average molecular weight of 300 to 150,000, through the decomposition step. The weight-average molecular weight (Mw) can be measured by gel permeation chromatography (hereinafter sometimes referred to as GPC). After the decomposition step, insoluble carbon black is recovered. The recovered carbon black typically contains organic components derived from the vulcanized rubber. The proportion of the organic components in the recovered carbon black is preferably 5 to 35% by mass, and more preferably 7 to 25% by mass.

[0030] <Others> The method for decomposing vulcanized rubber according to this embodiment may further include other processes. Examples of such processes include pretreatment processes for the vulcanized rubber (e.g., a cutting process and a pulverization process). Examples of pretreatment processes for the vulcanized rubber include a process of washing with a solvent. Washing with a solvent can remove additives that may inhibit the decomposition reaction, such as antioxidants, remaining in the vulcanized rubber, thereby reducing the amount of initiator used. The type of solvent used in the pretreatment process is not particularly limited, but solvents that easily dissolve additives such as antioxidants are preferred. Specific examples include hydrocarbons such as toluene, ketones such as acetone, chlorinated hydrocarbons such as chloroform, and ethers such as tetrahydrofuran. The method for decomposing vulcanized rubber according to this embodiment can be carried out using any type of reactor, such as a batch reactor or a flow reactor.

[0031] <Separation and purification of product> The polymer product after the decomposition reaction can be recovered and purified by methods such as separating the insoluble component, mainly carbon black, by centrifugation, filtration, etc., followed by precipitation using a poor solvent, or removing impurities by column chromatography or preparative GPC. The obtained polymer product and the recovered carbon black, which is the insoluble component, can be reused as raw materials for compounded rubber, etc. In a suitable example of decomposing compounded rubber containing carbon black, the ratio of the recovered carbon black component (mg) to the solvent (mL) after the decomposition reaction is generally 1:25 or more, and preferably 1:20 or more.

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0033] <Analytical equipment, etc.> Gel permeation chromatography (hereinafter sometimes referred to as GPC): Analysis system: Shimadzu Corporation LabSolutions (liquid delivery unit: Shimadzu Corporation LC-20AB, column: Tosoh Corporation TSKgel Super HM-H × 2, detector: Shimadzu Corporation differential refractometer RID-10A, eluent: tetrahydrofuran, flow rate: 0.6 mL / min, measurement temperature: 40°C, weight average molecular weight (Mw) and number average molecular weight (Mn) are based on standard polystyrene) Nuclear magnetic resonance analyzer (hereinafter sometimes referred to as NMR): Bruker Corporation AVANCE III HD 600 (solvent: CDCl ３ )

[0034] <Preparation of Vulcanized Rubber Sample> (Vulcanized Rubber A) A rubber composition was prepared by blending 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 2 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.6 parts by mass of vulcanization accelerator CBS [N-cyclohexyl-2-benzothiazolylsulfenamide], 1.8 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] per 100 parts by mass of natural rubber, and the rubber composition was then heat-crosslinked to prepare a vulcanized rubber.

[0035] (Vulcanized Rubber B) 60 parts by mass of natural rubber and 40 parts by mass of butadiene rubber were blended with 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 2 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.6 parts by mass of vulcanization accelerator CBS [N-cyclohexyl-2-benzothiazolylsulfenamide], 1.8 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] to prepare a rubber composition, and the rubber composition was heated and crosslinked to prepare a vulcanized rubber.

[0036] (Vulcanized Rubber C) 40 parts by mass of natural rubber and 60 parts by mass of butadiene rubber were blended with 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 2 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.6 parts by mass of vulcanization accelerator CBS [N-cyclohexyl-2-benzothiazolylsulfenamide], 1.8 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] to prepare a rubber composition, and the rubber composition was heated and crosslinked to prepare a vulcanized rubber.

[0037] (Vulcanized Rubber D) A rubber composition was prepared by blending 50 parts by mass of carbon black, 2 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 1 part by mass of wax, 1 part by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 0.3 parts by mass of vulcanization accelerator DPG [1,3-diphenylguanidine], 0.5 parts by mass of vulcanization accelerator MBTS [dibenzothiazolyl disulfide], 0.5 parts by mass of vulcanization accelerator TBBS [N-t-butyl-2-benzothiazole sulfenamide], 1.5 parts by mass of sulfur, and 1 part by mass of antioxidant TMDQ [trimethyldihydroquinoline polymer] with 100 parts by mass of styrene-butadiene rubber, and the rubber composition was heated and crosslinked to prepare a vulcanized rubber. In the first decomposition step of the vulcanized rubber, the obtained vulcanized rubber was cut into pieces (about 5 mm square) or further frozen and crushed into pieces (about 1 to 2 mm square) and used.

[0038] <Example of the first decomposition step> (Calculation of yield) The yield of the first decomposition step was calculated by adding a certain amount of an internal standard substance (hexamethyldisilane) to the reaction solution, then collecting a portion of the reaction solution, １ H NMR measurement was carried out to calculate the weight of the monomer skeleton of the solubilized rubber component, and the yield was calculated from the ratio of this weight to the weight of the monomer skeleton in the vulcanized rubber before the reaction (calculated from the compounding ratio of the vulcanized rubber) according to the following formula: Yield of the first decomposition step (%) = (Weight of the monomer skeleton of the rubber component solubilized after the reaction ÷ Weight of the monomer skeleton of the vulcanized rubber component before the reaction) × 100. For example, in the case of natural rubber, １ H NMR (CDCl ３In the case of the solubilized rubber (solvent), the proton signal of the internal standard (hexamethyldisilane) and the proton signal of the isoprene skeleton (alkenyl group) of the solubilized rubber component are observed around 0.04 and 5.13 ppm, respectively. The yield can be calculated from the ratio of the signal integral value of the isoprene skeleton to the signal integral value of the internal standard. The polyisoprene content of the natural rubber was assumed to be 93%.

[0039] Specific examples are described below. (Example 1) A mixture of 50 mg of the vulcanized rubber sample A, 7.4 mg of benzoyl peroxide (water-containing, 75% purity), and 0.8 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C (room temperature) for one day in a 5 mL Spitz vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement to be 89%. Furthermore, by GPC measurement of the reaction solution, the molecular weight was estimated to be Mw = 41,400, Mn = 16,900, and Mw / Mn = 2.4 (see Table 1).

[0040] (Examples 2 to 48) The decomposition reaction and analysis of the products were carried out in the same manner as in Example 1, while changing the reaction conditions (type of vulcanized rubber, type of radical initiator, type of solvent, reaction temperature, type of container, etc.). The results are shown in Tables 1 and 2.

[0041]

[0042]

[0043] (Notes for Tables 1 and 2) 1) The types of reaction vessels used are as follows (all reactions were carried out under sealed conditions): Examples 1 to 18, 29, 32: 5 mL Spitz-type vials Examples 19 to 28, 30, 31, 33 to 38, Comparative Example 1: 10 mL round-bottom vials Examples 39, 40: 20 mL round-bottom vials Examples 41 to 48: 150 mL flat-bottom vials 2) The radical initiators used are as follows: BPO: benzoyl peroxide LPO: lauroyl peroxide APO: acetyl peroxide 3) The solvents used are as follows: PhMe: toluene, Xy: xylene, CyH: cyclohexane, CHCl ３ : Chloroform, CHCl ２ CH ２ Cl: 1,1,2-trichloroethane, Cl ２ C=CCl ２ : tetrachloroethene, DCB: o-dichlorobenzene, PhCl: chlorobenzene, PhCN: benzonitrile, PhOMe: anisole, ｔ BuOMe: tert-butyl methyl ether, PhEt: ethylbenzene, THF: tetrahydrofuran, CDCl ３ : deuterated chloroform 4) Regarding temperature, 25°C indicates decomposition at room temperature, 30°C and 40°C indicate decomposition in a thermostatic bath, and 60°C indicates decomposition in an oil bath or water bath. 5) Regarding time, m indicates minutes, h indicates hours, and d indicates days. 6) The numbers in parentheses for the yield in the decomposition reaction of vulcanized rubbers B and C indicate the ratio of the yield of isoprene skeleton to that of butadiene skeleton. 7) Comparative Example 1 shows an example of a reaction performed under a nitrogen atmosphere using a deoxygenated solvent.

[0044] The results in Tables 1 and 2 demonstrate that compounded vulcanized rubbers containing natural rubber, butadiene rubber, and / or styrene-butadiene rubber and carbon black decompose in various solvents under air with a radical initiator such as acyl peroxide to yield soluble polymers. In particular, when acyl peroxide is used, the decomposition reaction proceeds smoothly even at room temperature. Furthermore, with regard to the type of rubber, styrene-butadiene rubber exhibits a greater solvent effect than natural rubber and butadiene rubber. The decomposition reaction proceeds more efficiently when chlorinated hydrocarbons such as chloroform or chlorobenzene are used as solvents. For example, with vulcanized rubber D containing styrene-butadiene rubber, the yield was 30% even after four days at 30°C in toluene (Example 38), whereas a high yield of 77% was achieved after one day at 30°C in chloroform (Example 35). In these decomposition reactions, the presence of oxygen is important, as shown in the following comparative example.

[0045] Comparative Example 1 In the reaction of Example 29 (vulcanized rubber A, benzoyl peroxide initiator, toluene solvent, 40°C, 6 hours), a deoxygenated solvent was used as the solvent and the reaction was carried out under a nitrogen atmosphere. As a result, the yield of the soluble polymer decreased from 83% to 3%.

[0046] The results of Comparative Example 1 show that the decomposition reaction proceeds in an air atmosphere, but hardly proceeds in a nitrogen atmosphere. The presence of oxygen in the air is thought to be extremely important for the progress of the decomposition reaction.

[0047] In decomposing compounded rubber containing carbon black, the carbon black can be separated by filtration, centrifugation, etc. to obtain a soluble polymer. Specific examples are shown below.

[0048] (Example 49) A mixture of 50 mg of the vulcanized rubber sample A, 7.4 mg of benzoyl peroxide (water-containing, 75% purity), and 0.8 mL of chlorobenzene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 1 day in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 94%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 42,900, Mn = 17,000, and Mw / Mn = 2.5. Chlorobenzene was added to the reaction solution, and insoluble solids were removed by filtration. The insoluble solids were washed with toluene. The insoluble solids were heated and dried under vacuum to recover the carbon black component (20 mg). Meanwhile, the filtrate and washings were combined and concentrated under reduced pressure to obtain a soluble polymer composition (P1) having an isoprene skeleton (30 mg). A portion of this was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition (P1) was calculated to be 65%, and by GPC measurement, the molecular weight was estimated to be Mw = 45,200, Mn = 18,300, and Mw / Mn = 2.5.

[0049] (Example 50) 150 mg of the vulcanized rubber sample A, 23 mg of benzoyl peroxide (water-containing, 75% purity), and 2.4 mL of chlorobenzene were stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 2 days in a 100 mL round-bottom flask (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 94%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 37,800, Mn = 14,800, and Mw / Mn = 2.6. Chlorobenzene was added to the reaction solution, and insoluble solids were removed by filtration. The insoluble solids were washed with toluene. The insoluble solids were heated and dried under vacuum to recover the carbon black component (40 mg). Meanwhile, the filtrate and washings were combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (100 mg). A portion of this was sampled, and an internal standard (hexamethyldisilane) was added to the solution. １As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 62%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 41,800, Mn = 15,600, and Mw / Mn = 2.7. Furthermore, in order to purify the soluble polymer composition, a portion of the obtained soluble polymer composition was dissolved in tetrahydrofuran and added dropwise to methanol. The precipitated liquid polymer was separated, washed with methanol, and dried under reduced pressure to obtain purified soluble polymer composition (P2) (65 mg). A portion of it was sampled, and an internal standard substance (hexamethyldisilane) was added to the sample. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the purified soluble polymer composition (P2) was calculated to be 81%, and the molecular weights were estimated to be Mw = 45,800, Mn = 16,100, and Mw / Mn = 2.5 by GPC measurement.

[0050] (Example 51) A mixture of 200 mg of the vulcanized rubber sample A, 30 mg of benzoyl peroxide (water-containing, 75% purity), and 3.2 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 2 days in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and was found to be 89%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 38,300, Mn = 15,300, and Mw / Mn = 2.5. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Tetrahydrofuran was added to the separated insoluble solid, mixed, and further centrifuged to recover the insoluble carbon black component (70 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (147 mg). A portion of the polymer was sampled, and an internal standard (hexamethyldisilane) was added to the sample. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 69%, and by GPC measurement, the molecular weight was estimated to be Mw = 43,700, Mn = 16,300, and Mw / Mn = 2.7.

[0051] (Example 52) A mixture of 200 mg of the vulcanized rubber sample A, 30 mg of benzoyl peroxide (water-containing, 75% purity), and 3.2 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 60°C for 5 hours in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and was found to be 87%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 31,900, Mn = 13,400, and Mw / Mn = 2.4. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Tetrahydrofuran was added to the separated insoluble solid, mixed, and further centrifuged to recover the insoluble carbon black component (67 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (148 mg). A portion of the polymer was sampled, and an internal standard (hexamethyldisilane) was added to the sample. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 68%, and by GPC measurement, the molecular weight was estimated to be Mw = 35,200, Mn = 14,800, and Mw / Mn = 2.4.

[0052] (Example 53) A mixture of 200 mg of the vulcanized rubber sample A, 37 mg of lauroyl peroxide, and 3.2 mL of chloroform was placed in a 20 mL round-bottom vial (sealed) under an air atmosphere at 25°C for 2 days, and stirred with a magnetic stirrer using a Teflon (registered trademark) rotor to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 39,700, Mn = 16,000, and Mw / Mn = 2.5. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Tetrahydrofuran was added to the separated insoluble solid, mixed, and centrifuged again. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (74 mg). Meanwhile, the supernatant after centrifugation was combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (162 mg). A portion of the mixture was sampled, and an internal standard (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 61%, and by GPC measurement, the molecular weight was estimated to be Mw = 44,400, Mn = 17,000, and Mw / Mn = 2.6.

[0053] (Example 54) A mixture of 200 mg of the vulcanized rubber sample A, 37 mg of lauroyl peroxide, and 3.2 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 60°C for 5 hours in a 20 mL round-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and was found to be 87%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 31,900, Mn = 13,400, and Mw / Mn = 2.4. The reaction solution was concentrated under reduced pressure, diluted with tetrahydrofuran, and centrifuged to separate the insoluble solid. Toluene was added to the separated insoluble solid, mixed, and centrifuged again. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (76 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (159 mg). A portion of the mixture was sampled, and an internal standard (hexamethyldisilane) was added to the mixture. １As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 61%, and by GPC measurement, the molecular weight was estimated to be Mw = 27,600, Mn = 12,900, and Mw / Mn = 2.1.

[0054] (Example 55) A mixture of 1,000 mg of the vulcanized rubber sample A, 147 mg of benzoyl peroxide (water-containing, 75% purity), and 16 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 42,400, Mn = 14,900, and Mw / Mn = 2.8. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, and the mixture was further centrifuged. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (368 mg). Meanwhile, the supernatant liquid after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (731 mg). A portion of the mixture was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 64%, and by GPC measurement, the molecular weight was estimated to be Mw = 47,000, Mn = 15,600, and Mw / Mn = 3.0.

[0055] (Example 56) A mixture of 1,000 mg of the vulcanized rubber sample A, 147 mg of benzoyl peroxide (water-containing, 75% purity), and 16 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 85%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 25,400, Mn = 10,300, and Mw / Mn = 2.5. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, mixed, and further centrifuged. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (351 mg). Meanwhile, the supernatant after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (731 mg). A portion was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 61%, and by GPC measurement, the molecular weight was estimated to be Mw = 28,900, Mn = 10,700, and Mw / Mn = 2.7.

[0056] (Example 57) A mixture of 1,000 mg of the vulcanized rubber sample A, 183 mg of lauroyl peroxide, and 16 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 85%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 27,100, Mn = 10,900, and Mw / Mn = 2.5. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, mixed, and further centrifuged. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (392 mg). Meanwhile, the supernatant after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (782 mg). A portion was sampled, and an internal standard substance (hexamethyldisilane) was added to the sample. １As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 58%, and by GPC measurement, the molecular weight was estimated to be Mw = 30,100, Mn = 11,100, and Mw / Mn = 2.7.

[0057] (Example 58) A mixture of 1,000 mg of the vulcanized rubber sample A, 183 mg of lauroyl peroxide, and 16 mL of chloroform was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 5 days in a 150 mL flat-bottom vial (sealed), to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement, and the yield was calculated to be 85%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 23,200, Mn = 9,800, and Mw / Mn = 2.4. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation. Toluene was added to the separated insoluble solid, mixed, and centrifuged again. The insoluble solid was heated and dried under vacuum to recover the insoluble carbon black component (381 mg). Furthermore, the supernatant after centrifugation was combined and concentrated under reduced pressure, resulting in a soluble polymer composition having an isoprene skeleton (798 mg). A portion of this was sampled, and an internal standard substance (hexamethyldisilane) was added to the mixture. １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 60%, and by GPC measurement, the molecular weight was estimated to be Mw = 27,200, Mn = 10,500, and Mw / Mn = 2.6.

[0058] (Example 59) A mixture of 6000 mg of the vulcanized rubber sample A, 886 mg of benzoyl peroxide (water-containing product, 75% purity), and 100 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 4 days in a 1000 mL flat-bottomed vial (unsealed) equipped with a PTFE membrane having a pore size of 0.2 µm, to carry out a decomposition reaction. １By H NMR measurement, the yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 45,800, Mn = 14,800, and Mw / Mn = 3.1. The reaction solution was diluted with tetrahydrofuran, and the insoluble solid was separated by centrifugation and dried by heating under vacuum to recover the insoluble carbon black component (2,257 mg). Meanwhile, the supernatant was concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (4,460 mg). By adding an internal standard substance (hexamethyldisilane), １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 66%, and by GPC measurement, the molecular weight was estimated to be Mw = 51,100, Mn = 16,700, and Mw / Mn = 3.1.

[0059] (Example 60) A mixture of 6000 mg of the vulcanized rubber sample A, 886 mg of benzoyl peroxide (water-containing product, 75% purity), and 110 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 25°C for 4 days in a 1000 mL flat-bottomed vial (unsealed) equipped with a PTFE membrane having a pore size of 0.45 µm, to carry out a decomposition reaction. １ By H NMR measurement, the yield of the soluble polymer composition produced by decomposition of the vulcanized rubber was calculated to be 80%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 50,400, Mn = 15,900, and Mw / Mn = 3.2. The reaction solution was diluted with toluene, and the insoluble solid was separated by centrifugation and dried by heating under vacuum to recover the insoluble carbon black component (2,304 mg). Meanwhile, the supernatant was concentrated under reduced pressure to obtain a soluble polymer composition having an isoprene skeleton (4,351 mg). By adding an internal standard (hexamethyldisilane), １ As a result of H NMR measurement, the proportion of isoprene skeletons in the soluble polymer composition was calculated to be 66%, and by GPC measurement, the molecular weight was estimated to be Mw = 51,400, Mn = 16,200, and Mw / Mn = 3.2.

[0060] The soluble polymer obtained by the decomposition process of the present invention basically maintains the polymer skeleton in the raw vulcanized rubber. For example, decomposition of vulcanized rubber sample A can selectively obtain cis-polyisoprene.

[0061] For example, the NMR data of the purified soluble polymer composition (P2) obtained by the decomposition reaction of vulcanized rubber sample A in Example 50 was as follows: 1 H NMR (CDCl3): δ(ppm) 1.68 (s, 3H, CH3), 2.00-2.09 (m, 4H, CH2), 5.12 (t, J = 6.2 Hz, 1H, =CH) 13 C NMR (CDCl3): δ(ppm) 23.5, 26.4, 32.2, 125.0, 135.2 observed １ H and １３ C NMR data indicates that the resulting soluble polymer has a cis-polyisoprene backbone, maintaining the basic structure of the polymer component in the vulcanized rubber.

[0062] (Example 61) A mixture of 100 mg of vulcanized rubber sample A, 14.8 mg of benzoyl peroxide, and 1.6 mL of toluene was stirred with a magnetic stirrer using a Teflon (registered trademark) rotor in an air atmosphere at 60°C for 1 hour in a 10 mL vial (sealed) to carry out a decomposition reaction. １ The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement to be 68%. Furthermore, the molecular weights were estimated by GPC measurement to be Mw = 57,900, Mn = 15,100, and Mw / Mn = 3.8.

[0063] Example 62 A decomposition reaction was carried out in the same manner as in Example 61, except that the decomposition reaction time was changed to 2 hours instead of 1 hour, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 87%, and the molecular weights of the soluble polymer were estimated to be Mw = 64,600, Mn = 21,200, and Mw / Mn = 3.0.

[0064] (Example 63) In Example 61, except that 18.4mg of lauroyl peroxide is used instead of 14.8mg of benzoyl peroxide, decomposition reaction is carried out in the same manner as in Example 61, and product analysis is carried out.As a result, the yield of soluble polymer can be calculated as 85%, and the molecular weight of soluble polymer is estimated as Mw=59800, Mn=21600, Mw / Mn=2.8.Comparing the yield of soluble polymer with that of Example 61, when using benzoyl peroxide, it is 68%, but when using lauroyl peroxide, it is 85%, and it is found that when using lauroyl peroxide, decomposition reaction proceeds faster.

[0065] (Example 64) In Example 63, except that the time of decomposition reaction is changed to 2 hours instead of 1 hour, decomposition reaction is carried out in the same manner as in Example 63, and product analysis is carried out.As a result, the yield of soluble polymer can be calculated as 88%, and the molecular weight of soluble polymer is estimated as Mw=37100, Mn=14800, Mw / Mn=2.6.Comparing the molecular weight of soluble polymer with that of Example 62, when using benzoyl peroxide, Mw=64600, Mn=21200, Mw / Mn=3.0, but when using lauroyl peroxide, Mw=37100, Mn=14800, Mw / Mn=2.6, it is found that using lauroyl peroxide makes decomposition reaction proceed faster, and obtains low molecular weight soluble polymer.

[0066] Example 65 A decomposition reaction was carried out in the same manner as in Example 61, except that an ethylbenzene solvent was used instead of the toluene solvent, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 87%, and the molecular weight of the soluble polymer was estimated to be Mw = 35,800, Mn = 14,000, and Mw / Mn = 3.0. When the yield of the soluble polymer was compared with the yield in Example 61, the yield was 68% when a toluene solvent was used, but 87% when an ethylbenzene solvent was used, indicating that the decomposition reaction proceeded more quickly when an ethylbenzene solvent was used.

[0067] Example 66 The decomposition reaction was carried out in the same manner as in Example 65, except that the decomposition reaction time was changed to 2 hours instead of 1 hour, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 88%, and the molecular weight of the soluble polymer was estimated to be Mw = 35,300, Mn = 13,900, and Mw / Mn = 2.5. When the molecular weight of the soluble polymer was compared with that of Example 62, when a toluene solvent was used, the values ​​were Mw = 64,600, Mn = 21,200, and Mw / Mn = 3.0, but when an ethylbenzene solvent was used, the values ​​were Mw = 35,300, Mn = 13,900, and Mw / Mn = 2.5. It was found that the decomposition reaction proceeded more quickly when an ethylbenzene solvent was used, and a soluble polymer with a lower molecular weight was obtained.

[0068] (Example 67) A decomposition reaction was carried out in the same manner as in Example 65, except that 18.4 mg of lauroyl peroxide was used instead of 14.8 mg of benzoyl peroxide in Example 65, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 88%, and the molecular weights of the soluble polymer were estimated to be Mw = 43,300, Mn = 17,000, and Mw / Mn = 2.5.

[0069] Example 68 The decomposition reaction was carried out in the same manner as in Example 67, except that the decomposition reaction time was changed to 2 hours instead of 1 hour, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 88%, and the molecular weights of the soluble polymer were estimated to be Mw = 27,600, Mn = 11,700, and Mw / Mn = 2.4.

[0070] (Example 69) As a pretreatment step, 10 g of the vulcanized rubber sample A was immersed in 100 mL of toluene solvent and shaken and stirred at room temperature for one day to dissolve the additives in the vulcanized rubber. After that, the vulcanized rubber was removed from the solution and dried under reduced pressure. A mixture of 200 mg of the vulcanized rubber sample A after the pretreatment step, 7.3 mg of lauroyl peroxide, and 3.2 mL of chloroform was placed in a 30 mL vial (sealed) and stirred with a magnetic stirrer using a Teflon (registered trademark) rotor at room temperature under an air atmosphere for one day to carry out a decomposition reaction. １The yield of the soluble polymer produced by decomposition of the vulcanized rubber was calculated by H NMR measurement and found to be 84%. Furthermore, by GPC measurement, the molecular weight was estimated to be Mw = 70,200, Mn = 20,700, and Mw / Mn = 3.4. Without the pretreatment step, under the same decomposition reaction conditions, the yield of the soluble polymer was 11%, demonstrating that the pretreatment step accelerates the decomposition reaction.

[0071] (Example 70) Pretreatment and decomposition reaction were carried out in the same manner as in Example 69, except that the decomposition reaction time was changed to 2 days instead of 1 day, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 86%, and the molecular weight of the soluble polymer was estimated to be Mw = 57,100, Mn = 17,700, and Mw / Mn = 3.2. When the pretreatment step was not performed, the yield of the soluble polymer was 13% under the same decomposition reaction conditions, demonstrating that the pretreatment step promotes the decomposition reaction.

[0072] Example 71 Pretreatment and decomposition reaction were carried out in the same manner as in Example 69, except that 40 mL of acetone solvent was used instead of 100 mL of toluene solvent in the pretreatment step of Example 69, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 83%, and the molecular weights of the soluble polymer were estimated to be Mw = 67,800, Mn = 21,100, and Mw / Mn = 3.2.

[0073] Example 72 Pretreatment and decomposition reaction were carried out in the same manner as in Example 71, except that the decomposition reaction time was changed to 2 days instead of 1 day, and the product was analyzed. As a result, the yield of the soluble polymer was calculated to be 84%, and the molecular weights of the soluble polymer were estimated to be Mw = 62,500, Mn = 18,600, and Mw / Mn = 3.4.

[0074] The present invention can provide an efficient method for decomposing vulcanized rubber, which is useful for chemical recycling of vulcanized rubber, and therefore the present invention is highly useful and has great industrial significance.

Claims

1. A method for decomposing vulcanized rubber, comprising reacting vulcanized rubber or a composition containing same with a radical initiator selected from peroxides in a solvent at 0 to 60°C in an atmosphere containing oxygen gas to convert the rubber into a soluble decomposition product.

2. The decomposition method according to claim 1, wherein the rubber component of the vulcanized rubber is at least one rubber component selected from the group consisting of natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR) and styrene-butadiene rubber (SBR).

3. The method according to claim 1, wherein the composition containing vulcanized rubber is a composition selected from tire rubber containing carbon black or silica.

4. The method according to claim 1, wherein the peroxide is a peroxide selected from acyl peroxides.

5. The method for decomposing according to claim 4, wherein the acyl peroxide is selected from the group consisting of benzoyl peroxide, lauroyl peroxide and acetyl peroxide.

6. The method according to claim 1, wherein the decomposition method is a method using a chlorinated hydrocarbon or an aromatic hydrocarbon as a solvent.

7. The method according to claim 6, wherein the chlorinated hydrocarbon is selected from the group consisting of chloroform and chlorobenzene.

8. The method according to claim 6, wherein the aromatic hydrocarbon is ethylbenzene.

9. The decomposition method according to claim 1, wherein the vulcanized rubber is a vulcanized rubber that has been subjected to a pretreatment step of washing with a solvent.

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