Crosslinked body

Abstract

Provided is a crosslinked body suitable for material recycling and chemical recycling. The crosslinked body has a structural unit represented by chemical formula (I) and a crosslinking agent. In chemical formula (I), each of l, m, and n is a positive number, and R is a basic functional group. The order of each repeating structural unit represented by l, m, and n is not limited, and the bonding pattern may be an alternating, block, or random pattern. In addition, the crosslinking agent is bonded to each of the basic functional groups R of the two structural units.

Description

crosslinked body

[0001] This invention relates to a crosslinked material suitable for material recycling and chemical recycling.

[0002] In recent years, with stricter regulations on carbon dioxide emissions, sustainable materials are in demand. Crosslinked materials generally rely on strong covalent bonds, making recycling difficult. To address this problem, research is being conducted on crosslinked polymers using dynamic covalent bonds (for example, Non-Patent Document 1).

[0003] Dynamic covalent bonding refers to covalent bonds in an equilibrium system that can achieve reversible dissociation-bonding in response to specific external stimuli. Chemical systems that utilize dynamic covalent bonding are attracting attention as "dynamic covalent chemistry." Among crosslinked polymers, chlorine-based polymers, which contain chlorine atoms in their molecules, are considered particularly difficult to recycle because they generate acid during decomposition.

[0004] Takada, Toshikazu; Koyama, Yasuhito. Recycling of Crosslinked Polymers Using Dynamic Covalent Bonding. Polymer Science Vol. 57, May (2008), pp. 346-349.

[0005] The inventors of this invention conducted extensive research on crosslinked polymers containing chlorine, and as a result, discovered a crosslinked polymer suitable for material recycling and chemical recycling, thus completing the present invention.

[0006] The crosslinked material of the present invention comprises structural units represented by the following chemical formula (I) and a crosslinking agent. In the following chemical formula (I), l, m, and n are all positive numbers, and R is a basic functional group. The order of each repeating structural unit represented by l, m, and n is not limited, and the bonding mode may be alternating, in blocks, or random. The crosslinking agent is bonded to the basic functional groups R of the two structural units, respectively.

[0007]

[0008] The basic functional group R can include a nitrogen atom, and the ends of the crosslinking agent can be bonded to this nitrogen atom. The basic functional group R containing a nitrogen atom can be a functional group represented by the following chemical formula (II) or (III).

[0009]

[0010] In the above chemical formula (II), R １ R is a pyridyl group, a quinolyl group, or an isoquinolyl group, and these groups may have substituents. In the above chemical formula (III), R ２ , R ３ R is a functional group that is the same or different from each other, and is a hydrogen atom or an alkyl group, and these groups may have substituents, ２ and R ３ They may have a ring structure in which they are bonded to each other.

[0011] Furthermore, the basic functional group R containing a nitrogen atom can be a functional group represented by the following chemical formula (IV) or (V).

[0012]

[0013] In the above chemical formula (V), R ４ The group is a linear, branched, or cyclic alkyl or aryl group having 1 to 8 carbon atoms, and these groups may have substituents.

[0014] As a crosslinking agent, a compound having two or more substituteable halogen atoms can be used.

[0015] According to the present invention, a crosslinked material suitable for material recycling and chemical recycling can be provided.

[0016] This figure shows the fusion state of the crosslinked material of the example under multiple temperature conditions. This figure shows the fusion state of the crosslinked material of the comparative example under multiple temperature conditions.

[0017] (Crosslinked material) The crosslinked material of this embodiment comprises a structural unit represented by the following chemical formula (1) and a crosslinking agent that crosslinks a plurality of structural units.

[0018]

[0019] In the above chemical formula (1), each of l, m, and n is a positive number, and R is a basic functional group. The order of each repeating structural unit represented by l, m, and n is not limited, and the bonding mode may be alternating, block, or random. Both ends of the crosslinking agent are respectively bonded to the basic functional groups R of two structural units.

[0020] The basic functional group R can be a functional group containing a nitrogen atom. Specifically, examples of the basic functional group R containing a nitrogen atom include functional groups represented by the following chemical formulas (2) and (3).

[0021]

[0022] In the above chemical formula (2), R １ is a pyridyl group, a quinolyl group, or an isoquinolyl group, and these groups may have substituents. In the above chemical formula (3), R ２ , R ３ are the same or different functional groups, which are a hydrogen atom or an alkyl group, and these groups may have substituents, and R ２ and R ３ may have a ring structure in which they are bonded to each other.

[0023] In the above chemical formula (2) or (3), when there may be substituents, the substituents are not particularly limited, and examples include an alkyl group, an amino group, an aminoalkyl group, a carboxy group, a carboxyalkyl group, an acyl group, a hydroxyl group, an alkoxy group, an aryl group, an aryloxy group, a nitro group, a nitrile group, a heterocyclic group, a halogen atom, etc.

[0024] Specific examples of the above chemical formula (2) include the following chemical formula (4), and specific examples of the above chemical formula (3) include the following chemical formula (5).

[0025]

[0026] In the above chemical formula (5), R ４The group is a linear, branched, or cyclic alkyl or aryl group having 1 to 8 carbon atoms, and these groups may have substituents. These substituents are not particularly limited and include, for example, alkyl groups, amino groups, aminoalkyl groups, carboxyl groups, carboxyalkyl groups, acyl groups, hydroxyl groups, alkoxy groups, aryl groups, aryloxy groups, nitro groups, nitrile groups, heterocyclic groups, halogen atoms, and the like.

[0027] When the basic functional group R is a functional group represented by the above chemical formulas (4) and (5), the chlorine content in the structural unit represented by the above chemical formula (1) can be 20 to 50% by mass, and the sulfur content can be 0.1 to 3.0% by mass.

[0028] In a basic functional group R containing a nitrogen atom, one end of the crosslinking agent bonds to the nitrogen atom, forming a quaternary ammonium salt. By heating the crosslinked body to a predetermined temperature or higher, equilibrium is established between the cleavage and formation reactions of the bond between the nitrogen atom and the crosslinking agent, allowing for rearrangement of the crosslinking sites.

[0029] By rearranging the crosslinking points, material recycling described later can be performed, and by removing the crosslinking agent using a capture agent to capture the crosslinking agent, chemical recycling described later can be performed.

[0030] First, let's explain material recycling. Material recycling is a recycling method in which products destined for disposal are reprocessed through physical or chemical treatment and used as the same or different product. In this invention, material recycling can be achieved by reshaping a crosslinked body through heating.

[0031] When the crosslinked material of this embodiment is heated to a predetermined temperature or higher, one end of the crosslinking agent detaches from the basic functional group R (e.g., nitrogen atom) to which it was initially bound, and rebonds to another basic functional group R (e.g., nitrogen atom). By changing the bonding position of the crosslinking agent to the structural unit in this way, that is, by rearranging the crosslinking points, the crosslinked material can be reshaped, enabling material recycling.

[0032] Next, chemical recycling will be described. Chemical recycling is a recycling method in which products to be discarded are decomposed into low molecular weight substances or raw material units by chemical treatment and then reused as raw materials. In the present invention, chemical recycling can be achieved by treating the crosslinking agent separated from the crosslinked product with a capturing agent to return it to the uncrosslinked product.

[0033] When heating the crosslinked product of the present embodiment at a predetermined temperature or higher, a capturing agent for capturing the crosslinking agent is added in advance, so that the capturing agent can be bonded to both ends of the crosslinking agent, and a structural unit that is not crosslinked (that is, an uncrosslinked polymer) can be obtained. This structural unit (uncrosslinked polymer) can be used as a raw material for new products.

[0034] (Crosslinking agent) As the crosslinking agent, a known crosslinking agent can be appropriately employed. Here, as the crosslinking agent, it is preferable to use a compound having two or more replaceable halogen atoms. Examples of this compound include α,α'-dichloro-p-xylene, α,α'-dibromo-p-xylene, 1,6-dichlorohexane, 1,6-dibromohexane, 1,6-diiodohexane, 1,8-dibromooctane, 1,10-dibromodecane, 1,3,5-tris(bromomethyl)benzene, 1,2,4,5-tetrakis(bromomethyl)benzene, pentaerythritol tetrachloride, pentaerythritol tetrabromide, and the like.

[0035] (Method for producing structural unit) The chlorine-based polymer (the above chemical formula (1)) that is the structural unit of the crosslinked product of the present embodiment is obtained by introducing a chlorine atom and a basic functional group R into polyethylene.

[0036] When the basic functional group R is the above chemical formula (4), chlorosulfonated polyethylene (hereinafter referred to as CSM) is reacted with 3-hydroxypyridine to modify the chlorine atom of the SO ２ Cl group contained in CSM. Further, when the basic functional group R is the above chemical formula (5) and R ４ is a methyl group, CSM is reacted with 1-methylpiperazine to react the SO ２It is obtained by modifying the chlorine atom of the Cl group. Note that CSM is produced by dissolving or suspending polyethylene in a solvent and then subjecting it to chlorination and chlorosulfonation.

[0037] The solvent used for the modification of CSM may be any solvent that can dissolve CSM and does not inhibit the progress of the modification reaction. Examples of such solvents include aromatic hydrocarbon compounds (benzene, toluene, xylene, etc.), chlorine compounds (dichloromethane, chloroform, 1,1,2-trichloroethane, trichloroethylene, tetrachloroethylene, etc.), ether compounds (tetrahydrofuran, 1,4-dioxane, etc.), ester compounds (ethyl acetate, butyl acetate, etc.), ketone compounds (methyl ethyl ketone, methyl isobutyl ketone, etc.), and the like.

[0038] When modifying CSM, it is preferable to capture the acid generated in the modification reaction. Examples of such capturing agents include inorganic salts (sodium carbonate, potassium carbonate, magnesium oxide, etc.) and organic bases (triethylamine, pyridine, etc.).

[0039] The reaction conditions (reaction temperature, reaction pressure, reaction time) in the modification of CSM can be set as appropriate. For example, the reaction conditions can be set as follows: Reaction temperature: 0°C to 140°C; Reaction pressure: normal pressure to 1 MPa; Reaction time: 1 to 24 hours.

[0040] On the other hand, it is also possible to modify CSM without using a solvent. Specifically, a kneader can be used to knead CSM and a modifying agent (such as 3-hydroxypyridine). If necessary, heating can be performed during kneading.

[0041] (Method for producing a crosslinked product) As a method for producing a crosslinked product, a known method can be appropriately adopted. For example, a crosslinked product can be obtained by dissolving a chlorine-based polymer in an organic solvent, then mixing a crosslinking agent, distilling off the solvent, and then performing a heat treatment. On the other hand, a crosslinked product can be obtained by kneading a chlorine-based polymer and a crosslinking agent in a kneader and then performing a heat treatment. The conditions of the heat treatment described above can be appropriately determined according to the type of the crosslinked product.

[0042] The present invention will be specifically described by the following embodiments. However, the present invention is not limited to these embodiments.

[0043] (Example 1) As a polymer constituting the structural unit of the crosslinked body, a chlorine-based polymer having a structural unit represented by the following chemical formula (6) was prepared, and as a crosslinking agent, α,α'-dichloro-p-xylene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared. The chlorine-based polymer had a nitrogen content of 0.9% by mass, a chlorine content of 34% by mass, and a sulfur content of 1.0% by mass.

[0044]

[0045] (Example 2) A chlorine-based polymer and a crosslinking agent were prepared in the same manner as in Example 1, except that the crosslinking agent was changed to α,α'-dibromo-p-xylene (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0046] (Example 3) As the polymer constituting the structural unit of the crosslinked body, a chlorine-based polymer having a structural unit represented by the following chemical formula (7) was prepared, and α,α'-dichloro-p-xylene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared as the crosslinking agent. The chlorine-based polymer had a nitrogen content of 0.4% by mass, a chlorine content of 34% by mass, and a sulfur content of 0.9% by mass.

[0047]

[0048] (Example 4) A chlorine-based polymer and a crosslinking agent were prepared in the same manner as in Example 3, except that the crosslinking agent was changed to 1,6-dichlorohexane (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0049] Using the chlorine-based polymers and crosslinking agents from each of the above examples, the chlorine-based polymers and crosslinking agents were mixed in a chloroform solution such that the molar ratio of the tertiary amine nitrogen in the piperazine group or the nitrogen in the pyridine group of the chlorine-based polymer to the crosslinking agent was 2:1. Next, after the chloroform was removed by distillation, crosslinked products were produced under the crosslinking conditions shown in Table 1 below.

[0050]

[0051] The chlorine-based polymers used in Examples 1 and 2 were prepared as follows. First, 25 g of CSM (product name "TOSO-CSM TS-530", manufactured by Tosoh Corporation) and 192 g of toluene were added to a flask (volume: 1 L) and dissolved. Next, 6.2 g of 1-methylpiperazine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the flask and stirred at 80°C for 3.5 hours.

[0052] Next, the solution in the flask was cooled to room temperature, and then the solution was added dropwise to methanol to obtain a precipitate. The obtained precipitate was washed with acetone, and the solvent was removed by vacuum drying to obtain the chlorine-based polymer represented by the above chemical formula (6).

[0053] The chlorine-based polymers used in Examples 3 and 4 were prepared as follows. First, 25 g of CSM (product name "TOSO-CSM TS-530", manufactured by Tosoh Corporation) and 332 g of toluene were added to a flask (volume: 1 L) and dissolved. Next, 2.9 g of 3-hydroxypyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the flask, and the mixture was stirred under reflux conditions for 6 hours.

[0054] Next, the solution in the flask was cooled to room temperature, and then the solution was added dropwise to methanol to obtain a precipitate. The obtained precipitate was washed with acetone, and the solvent was removed by vacuum drying to obtain the chlorine-based polymer represented by the above chemical formula (7).

[0055] (Comparative Example) As the polymer constituting the structural unit of the crosslinked body, CSM (product name "TOSO-CSM TS-530", manufactured by Tosoh Corporation) was prepared, and as the crosslinking agent (vulcanizing agent), dipentamethylenethuram tetrasulfide (product name "Noxellar TRA", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) was prepared. In addition, as additives, pentaerythritol (product name "Neurizer P", manufactured by Mitsubishi Chemical Corporation) and magnesium oxide (Kyowa Mag 150, manufactured by Kyowa Chemical Industry Co., Ltd.) were prepared.

[0056] A CSM composition was obtained by adding 4 parts by weight of magnesium oxide, 3 parts by weight of pentaerythritol, and 2 parts by weight of vulcanizing agent to 100 parts by weight of CSM and kneading the mixture using a kneader. A comparative example of a sulfur crosslinked body was obtained by pressing the CSM composition at 160°C for 15 minutes.

[0057] The gel fraction [%] was measured for each crosslinked material in Examples 1A to 1D, 2, 3, 4 and the Comparative Example. The gel fraction is the ratio of insoluble material when the crosslinked material is immersed in toluene at 30°C for 24 hours, and is calculated by the following formula (8).

[0058] Gel fraction = (M2 / M1) × 100 ... (8) M1: Initial mass of the crosslinked material [g] M2: Dry mass of the crosslinked material after immersion in toluene (drying conditions: 80°C, 2 hours)

[0059] The measurement conditions and results for the gel fraction are shown in Table 2 below. As shown in Table 2 below, the gel fractions of Examples 1A to 1D and 12 were all equivalent to those of the comparative example. The gel fractions of Examples 3 and 4 were in the range of 70 to 75%.

[0060]

[0061] (Evaluation of Material Recycling) Next, fragments of each crosslinked material (Example 1C and Comparative Example) were pressed for 30 minutes at temperatures of 120°C, 140°C, and 160°C, respectively, and the morphology of the fragments was observed. The results of this observation are shown in Figures 1 and 2. For the crosslinked material of Example 1C, as shown in Figure 1, the fragments fused together at temperatures of 140°C and 160°C. On the other hand, for the crosslinked material of the Comparative Example, as shown in Figure 2, the fragments did not fused together regardless of the temperature.

[0062] The crosslinked material of Example 1C underwent re-fusion, indicating that it can be applied to material recycling. As shown in Table 1 above, Examples 1A, 1B, and 1D have the same crosslinked structure as Example 1C, differing only in processing time and temperature. Therefore, the crosslinked materials of Examples 1A, 1B, and 1D can also be fused into small fragments using the same process and can be applied to material recycling.

[0063] In the case of the crosslinked bodies of Examples 2, 3, and 4, after pressing the fragments at 160°C for 30 minutes, the morphology of the fragments was observed. It was found that the fragments fused together in all cases, indicating that they can be applied to material recycling.

[0064] (Evaluation of chemical recycling) The chemical recycling of the crosslinked material of Example 1C was evaluated. Specifically, after immersing the crosslinked material fragments in two types of solvents, the presence or absence of dissolution of the fragments was confirmed by heating at 120°C for 3 hours. The two types of solvents prepared were a solvent without a scavenger for capturing the crosslinking agent (o-xylene only) and a solvent containing a scavenger (o-xylene containing 5% by mass of 1-methylpiperazine (scavenger)).

[0065] The dissolution state of the fragments was observed. Here, the state before and after heat treatment was observed when the crosslinked material (fragments) was immersed in a solvent of o-xylene alone, and the state before and after heat treatment was observed when the crosslinked material (fragments) was immersed in a solvent of 1-methylpiperazine and o-xylene.

[0066] When the crosslinked material (fine fragments) was immersed in a solvent containing only o-xylene, the crosslinked material only swelled due to the solvent and did not dissolve. On the other hand, when the crosslinked material (fine fragments) was immersed in a solvent containing o-xylene containing 1-methylpiperazine, the crosslinked material dissolved completely upon heat treatment.

[0067] The observations described above indicate that heating the crosslinked material caused the scavenging agent, 1-methylpiperazine, to undergo an exchange reaction with the crosslinking sites of the crosslinked material and bond, returning the chlorine-based polymer, which is the structural unit of the crosslinked material, to an uncrosslinked state and dissolving in the solvent. Therefore, it was found that the crosslinked material of Example 1C can be applied to chemical recycling. As shown in Table 1 above, Examples 1A, 1B, and 1D have the same crosslinked structure as Example 1C, differing only in processing time and temperature. Therefore, the crosslinked materials of Examples 1A, 1B, and 1D can also be dissolved using the same process and are applicable to chemical recycling.

[0068] The crosslinked materials of Examples 2, 3, and 4 were also immersed in a solvent containing a scavenging agent (o-xylene containing 5% by mass of 1-methylpiperazine (scavenging agent)) and heated at 120°C for 3 hours. As a result, all of the crosslinked materials dissolved. Therefore, it was found that the crosslinked materials of Examples 2, 3, and 4 can also be applied to chemical recycling.

Claims

1. Having a structural unit represented by the following chemical formula (I) and a crosslinking agent, Each of l, m, and n is a positive number, R is a basic functional group, the order of each repeating structural unit indicated by l, m, and n is not limited, the bonding mode may be alternating, block-like, or random, and the crosslinking agent is bonded to the basic functional group R of two of the structural units, respectively, in the crosslinked product.

2. The crosslinked body according to claim 1, characterized in that the basic functional group R contains a nitrogen atom, and the end of the crosslinking agent is bonded to the nitrogen atom of the basic functional group R.

3. The crosslinked body according to claim 2, characterized in that the basic functional group R is a functional group represented by the following chemical formula (II) or (III). In the above chemical formula (II), R １ R is a pyridyl group, a quinolyl group, or an isoquinolyl group, and these groups may have substituents, in the above chemical formula (III), ２ , R ３ R is a functional group that is the same or different from each other, and is a hydrogen atom or an alkyl group, and these groups may have substituents, ２ and R ３ They may have a ring structure in which they are bonded to each other.

4. The crosslinked body according to claim 2, characterized in that the basic functional group R is of the following chemical formula (IV) or (V). In the above chemical formula (V), R ４ The group is a linear, branched, or cyclic alkyl or aryl group having 1 to 8 carbon atoms, and these groups may have substituents.

5. The crosslinked body according to claim 1, characterized in that the crosslinking agent is a compound having two or more replaceable halogen atoms.

Images