Ethylene propylene diene monomer composite material and preparation method thereof

Abstract

The invention belongs to the technical field of rubber materials, and particularly relates to an ethylene propylene diene monomer composite material and a preparation method thereof. The ethylene propylene diene monomer composite material comprises the following components in parts by weight: 100 parts of ethylene propylene diene monomer, 8-15 parts of a polyurethane prepolymer, 10-15 parts of a reinforcing agent, 50-80 parts of white carbon black, 2-5 parts of a dispersing agent, 0.8-1.2 parts of a vulcanization accelerator and 2-3 parts of a vulcanizing agent. The ethylene propylene diene monomer composite material disclosed by the invention has excellent mechanical properties and bonding strength, and also has relatively good flame retardant property.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber materials, and in particular relates to an EPDM rubber composite material and a preparation method thereof. Background Art

[0002] Rubber materials are an important strategic resource due to their unique high elasticity. They can maintain their original shape after large deformation. Among them, ethylene propylene diene monomer rubber (EPDM) is a terpolymer of ethylene, propylene and non-conjugated dienes. Its main chain is composed of saturated hydrocarbon structure. It is a non-crystalline rubber with poor self-reinforcement. Since the industrial production in the 1960s, it has been widely used in automotive sealing strips, building waterproof materials, wire and cable insulation layers and household products due to its excellent weather resistance, ozone resistance, chemical corrosion resistance and electrical insulation properties. However, traditional EPDM rubber also has inherent defects: its molecular chain is highly flexible but low in polarity, and when the ethylene content is high, it has a certain degree of crystallization, resulting in insufficient mechanical strength and poor bonding strength with extreme substrates such as metals and plastics; ultimately, the overall performance of the product deteriorates, making it difficult to meet the requirements of high-end fields for the comprehensive performance of materials.

[0003] In order to solve the above problems, domestic and foreign research has mostly optimized performance through filling modification, blending and compounding, and even dynamic vulcanization. Early research focused on adding reinforcing fillers such as carbon black and white carbon black. Although they can improve tensile strength, they will deteriorate the processing performance of the material. In recent years, the application of nanofillers such as graphene, carbon nanotubes and montmorillonite has become a hot topic, but the high surface energy of nanomaterials can easily lead to agglomeration, poor dispersion and high cost. Most importantly, traditional modification technologies often focus on a certain property (such as only enhancing mechanics or only improving flame retardancy), and cannot take into account the comprehensive performance of the material.

[0004] Therefore, in response to the above problems, it is urgent to develop rubber composites with high performance to meet the needs of industrial production and application. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, one of the objects of the present invention is to provide an EPDM rubber composite material.

[0006] One of the purposes of the present invention is achieved by the following technical solution: An EPDM rubber composite material comprises the following components by weight: 100 parts of EPDM rubber, 8-15 parts of polyurethane prepolymer, 10-15 parts of reinforcing agent, 50-80 parts of white carbon black, 2-5 parts of dispersing agent, 0.8-1.2 parts of vulcanization accelerator and 2-3 parts of vulcanizing agent.

[0007] Furthermore, the mass ratio of the polyurethane prepolymer, the reinforcing agent, and the silica is 1:(1~1.5):(5~6.5).

[0008] Further, the preparation process of the reinforcing agent includes the following steps: (1) Add glycerol, alkali metal carbonate, and 6-bromohexanal to solvent A for reaction. After the reaction is completed, purify to obtain intermediate 1; the structural formula of the intermediate 1 is ; (2) Add intermediate 1, pentamethylaniline, and glacial acetic acid to solvent B, stir and mix evenly, then add sodium cyanoborohydride for reaction. Concentrate, extract the reaction solution, and combine the organic phases. Then, dry, filter, concentrate, and purify to obtain the reinforcing agent; the structure of the reinforcing agent is .

[0009] The reinforcing agent uses glycerol as the matrix skeleton, introduces long-chain aliphatic hydrocarbon groups through flexible connection with ether bonds (-O-), and the terminal is bonded to the benzene ring of the aromatic ring structure through an amino group (-NH2).

[0010] Further, in step (1), the molar ratio of glycerol, alkali metal carbonate, and 6-bromohexanal is 1:(6~7.5):(3~3.3), and the concentration of glycerol in solvent A is 0.1 mol / L.

[0011] Further, in step (1), the alkali metal carbonate is potassium carbonate or sodium carbonate, and the solvent A is N,N-dimethylformamide; the reaction temperature is 90~110°C, and the time is 12~16 h.

[0012] Furthermore, after the reaction in step (1) is completed, it specifically includes the following steps: Add water to the reaction solution after the reaction is completed until solids precipitate.

[0013] Further, in step (2), the molar ratio of intermediate 1, pentamethylaniline, glacial acetic acid, and sodium cyanoborohydride is 1:(3~3.5):(3~4):(6~7.5), and the concentration of intermediate 1 in solvent B is 0.2 mol / L; the reaction time is 16~24 h; the solvent B in step (2) is methanol, and the solvent used for extraction is dichloromethane.

[0014] Further, the preparation steps of the polyurethane prepolymer are as follows: Weigh 30 parts of polytetrahydrofuran ether glycol, 15~18 parts of triphenyl isocyanate thiophosphate, 0.5~0.8 parts of triethylenediamine, and 1~2 parts of glycerol according to weight parts, and stir and react under an anhydrous system to obtain the polyurethane prepolymer.

[0015] Further, the temperature of the stirring reaction is 90~100°C, and the time is 18~24 h.

[0016] Another object of the present invention is to provide a method for preparing the above-mentioned ethylene-propylene-diene monomer (EPDM) rubber composite material, which is convenient and feasible to operate and is easy to realize industrial production.

[0017] The second object of the present invention is achieved by the following technical solution: The method for preparing the above-mentioned EPDM rubber composite material includes the following steps: a. According to the above weight parts, mix ethylene-propylene-diene monomer rubber, reinforcing agent, polyurethane prepolymer, white carbon black, and dispersant evenly, and then carry out mixing to obtain a mixed rubber. b. Add vulcanization accelerator and vulcanizing agent to the mixed rubber for mixing, and then obtain a preform through compression molding. The preform is vulcanized to obtain the EPDM rubber composite material.

[0018] Furthermore, the temperature of the mixing in step a is 125-135 °C, and the time is 12-15 min; the temperature of the mixing in step b is the same as that in step a, the time of the mixing is 3-5 min; the temperature of the vulcanization treatment is 170-180 °C, and the time is 6-8 min.

[0019] Furthermore, the dispersant is sodium stearate or potassium stearate; the vulcanization accelerator is N-cyclohexyl-2-benzothiazolyl sulfenamide or tetrabenzylthiuram disulfide; the vulcanizing agent is sulfur or dicumyl peroxide.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides an EPDM rubber composite material. By compounding and using ethylene-propylene-diene monomer rubber, polyurethane prepolymer, reinforcing agent and other auxiliary materials, the prepared composite material not only has high adhesion strength and mechanical properties, but also has good flame retardant properties.

[0021] On the one hand, the appropriate short branched chains contained in the reinforcing agent in the present invention can enhance the movement ability of the molecular chain and improve its dispersion uniformity in the rubber matrix; while the steric hindrance effect generated by the short branched chains effectively inhibits the excessive aggregation of macromolecules and forms a stable dispersed phase. This unique molecular structure enables the reinforcing agent to play an interfacial bridging role while endowing the composite material with excellent processing fluidity, and finally realizes the synergistic improvement of high cohesive energy, flame retardant properties and mechanical strength. On the other hand, the introduced aliphatic chain segments in the reinforcing agent produce physical entanglement with the non-polar main chain of ethylene-propylene-diene monomer rubber, the aromatic groups in the reinforcing agent form π-π conjugation with the rigid benzene ring in the polyurethane prepolymer, and at the same time, the polar sites of ether bonds and amino groups chemically crosslink with active functional groups such as isocyanate groups (-NCO) of polyurethane to construct a multi-scale interfacial bonding mechanism, significantly improving the adhesion strength and mechanical strength of the composite system.

[0022] 2. The present invention provides a method for preparing an EPDM rubber composite material, which is simple and feasible and is easy to realize industrial production. DETAILED DESCRIPTION

[0023] Below, in conjunction with specific embodiments, the present invention is further described. It should be noted that, under the premise of no conflict, the embodiments described below or the technical features can be arbitrarily combined to form new embodiments. The specific conditions not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, unless otherwise specified, are conventional products obtained through commercial channels.

[0024] Example 1 An EPDM rubber composite material comprises the following components by weight: 100 parts of EPDM rubber, 12 parts of polyurethane prepolymer, 12 parts of reinforcing agent, 70 parts of white carbon black, 3 parts of sodium stearate, 1 part of N-cyclohexyl-2-benzothiazolyl sulfenamide and 2.5 parts of sulfur.

[0025] The preparation process of the polyurethane prepolymer comprises the following steps: weighing 30 parts of polytetramethylene glycol, 16 parts of triphenyl isocyanate thiophosphate, 0.6 parts of triethylenediamine and 1.5 parts of glycerol by weight, adding them into a reaction kettle, extracting for 10 minutes under a negative pressure of 0.1 MPa under stirring to remove moisture from the reaction system, then reacting at 95° C. for 20 hours, and cooling the reaction system to room temperature to obtain the polyurethane prepolymer.

[0026] The preparation process of the enhancer comprises the following steps: (1) Under nitrogen atmosphere, potassium carbonate (70 mmol), glycerol (10 mmol), and 6-bromohexanal (31 mmol) were added to 100 mL of N,N-dimethylformamide and stirred at 100 °C for 14 h; the reaction solution was poured into 500 mL of water to precipitate solids, which were filtered and the filter cake was purified by silica gel column chromatography (eluent: 80% petroleum ether, 20% dichloromethane) to obtain intermediate 1 (yield 35.41%). The characterization results of intermediate 1 are as follows: 1 H NMR (C 21 H 38 O6, 400 MHz, CDCl3) δ 9.65 (t, 3H), 3.75-3.73 (m, 1H), 3.53(d, 4H), 3.40(t, 6H), 2.43 (q, 6H), 1.59-1.49 (m,12H), 1.31-1.28 (m, 6H); the above results confirmed that the target product was obtained.

[0027] (2) Under a nitrogen atmosphere, pentamethylaniline (65 mmol), glacial acetic acid (65 mmol) and intermediate 1 (20 mmol) were added to 100 mL of methanol. After stirring evenly, sodium cyanoborohydride (140 mmol) was added, and the reaction was carried out at room temperature for 20 h; the reaction was quenched with saturated sodium bicarbonate solution, the mixed system was concentrated to remove most of the methanol, and then extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, concentrated, and purified by silica gel column chromatography (eluent: 95 v% n-hexane, 5 v% dichloromethane) to obtain the enhancer (yield 78.65%). The characterization results of the enhancer are as follows: 1 H NMR(C 54 H 89 N3O3, 400 MHz, CDCl3) δ6.36(s, 3H), 3.75 - 3.73 (m, 1H), 3.53(d, 4H), 3.40 - 3.35(m, 12H), 2.27(s, 9H),2.20(s, 18H), 2.14(s, 18H), 1.57 - 1.42 (m, 18H), 1.31 - 1.28 (m, 6H); The above results confirmed the obtained target product.

[0028] This example also provides a preparation method of the above ethylene-propylene-diene monomer (EPDM) rubber composite material, including the following steps: a. According to the said parts by weight, ethylene-propylene-diene monomer (EPDM) rubber, enhancer, polyurethane prepolymer, silica, sodium stearate were mixed evenly and put into an internal mixer, and kneaded at 130 °C for 13 min to obtain the kneaded rubber; b. The kneaded rubber was transferred to an open mill, N-cyclohexyl-2-benzothiazolesulfenamide and sulfur were added, kneaded at 130 °C for 4 min, and then molded into a preform by compression molding. Finally, the preform was vulcanized, the vulcanization temperature was 172 °C, and the vulcanization time was 7 min to obtain the ethylene-propylene-diene monomer (EPDM) rubber composite material.

[0029] Example 2 An ethylene-propylene-diene monomer (EPDM) rubber composite material, by weight, includes the following components: 100 parts of ethylene-propylene-diene monomer (EPDM) rubber, 8 parts of polyurethane prepolymer, 10 parts of enhancer, 50 parts of silica, 2 parts of potassium stearate, 0.8 part of tetrabenzylthiuram disulfide, and 2 parts of dicumyl peroxide.

[0030] The preparation process of the polyurethane prepolymer includes the following steps: By weight, weigh 30 parts of polytetrahydrofuran glycol, 15 parts of triphenyl thiophosphate isocyanate, 0.5 part of triethylenediamine, and 1 part of glycerol, and add them to a reaction kettle. Under stirring, evacuate for 10 min at a negative pressure of 0.1 MPa to remove the moisture in the reaction system, and then react at 90 °C for 24 h. Cool the reaction system to room temperature to obtain the polyurethane prepolymer.

[0031] The preparation process of the reinforcing agent includes the following steps: (1) Under a nitrogen atmosphere, add potassium carbonate (60 mmol), glycerol (10 mmol), and 6-bromohexanal (30 mmol) to 100 mL of N,N-dimethylformamide, and stir at 90 °C for 16 h; pour the reaction solution into 500 mL of water, precipitate solids, and after filtration, purify the filter cake by silica gel column chromatography (eluent: 80 v% petroleum ether, 20 v% dichloromethane) to obtain intermediate 1 (yield 34.32%). The characterization results of intermediate 1 are the same as those in Example 1.

[0032] (2) Under a nitrogen atmosphere, add pentamethylaniline (60 mmol), glacial acetic acid (60 mmol), and intermediate 1 (20 mmol) to 100 mL of methanol. After stirring evenly, add sodium cyanoborohydride (120 mmol), and react at room temperature for 16 h; quench the reaction with saturated sodium bicarbonate solution, concentrate the mixed system to remove most of the methanol, then extract three times with dichloromethane, combine the organic phases, dry over anhydrous sodium sulfate, filter, concentrate, and purify by silica gel column chromatography (eluent: 95 v% n-hexane, 5 v% dichloromethane) to obtain the reinforcing agent (yield 77.23%). The characterization results of the reinforcing agent are the same as those in Example 1.

[0033] This example also provides a method for preparing the above ethylene-propylene-diene monomer composite material, which includes the following steps: a. According to the stated parts by weight, uniformly mix ethylene-propylene-diene monomer, reinforcing agent, polyurethane prepolymer, silica, and potassium stearate, and put them into a mixer, and knead at 125 °C for 15 min to obtain a kneaded rubber; b. Transfer the kneaded rubber to an open mill, add tetrabenzylthiuram disulfide and dicumyl peroxide, knead at 125 °C for 3 min, and then mold into a preform by compression molding. Finally, vulcanize the preform, the vulcanization temperature is 170 °C, and the vulcanization time is 8 min to obtain the ethylene-propylene-diene monomer composite material.

[0034] Example 3 An ethylene-propylene-diene monomer composite material, by weight, includes the following components: 100 parts of ethylene-propylene-diene monomer, 15 parts of polyurethane prepolymer, 15 parts of reinforcing agent, 80 parts of silica, 5 parts of sodium stearate, 1.2 parts of N-cyclohexyl-2-benzothiazolesulfenamide, and 3 parts of sulfur.

[0035] The preparation process of the polyurethane prepolymer includes the following steps: By weight, 30 parts of polytetrahydrofuran glycol, 18 parts of triphenyl thiophosphate isocyanate, 0.8 part of triethylenediamine, and 2 parts of glycerol are weighed and added to a reaction kettle. Under stirring, the moisture in the reaction system is removed by pumping under a negative pressure of 0.1 MPa for 10 min, and then the reaction is carried out at 100 °C for 18 h. The reaction system is cooled to room temperature to obtain the polyurethane prepolymer.

[0036] The preparation process of the reinforcing agent includes the following steps: (1) Under a nitrogen atmosphere, sodium carbonate (75 mmol), glycerol (10 mmol), and 6-bromohexanal (33 mmol) are added to 100 mL of N,N-dimethylformamide and stirred at 110 °C for 12 h; the reaction solution is poured into 500 mL of water to precipitate a solid, and after filtration, the filter cake is purified by silica gel column chromatography (eluent: 80 v% petroleum ether, 20 v% dichloromethane) to obtain Intermediate 1 (yield 34.95%). The characterization results of Intermediate 1 are the same as those in Example 1.

[0037] (2) Under a nitrogen atmosphere, pentamethylaniline (70 mmol), glacial acetic acid (80 mmol), and Intermediate 1 (20 mmol) are added to 100 mL of methanol. After stirring evenly, sodium cyanoborohydride (150 mmol) is added, and the reaction is carried out at room temperature for 24 h; the reaction is quenched with saturated sodium bicarbonate solution, the mixed system is concentrated to remove most of the methanol, and then extracted three times with dichloromethane. The organic phases are combined, dried over anhydrous sodium sulfate, filtered, concentrated, and then purified by silica gel column chromatography (eluent: 95 v% n-hexane, 5 v% dichloromethane) to obtain the reinforcing agent (yield 78.16%). The characterization results of the reinforcing agent are the same as those in Example 1.

[0038] This example also provides a preparation method of the above ethylene-propylene-diene monomer (EPDM) rubber composite material, including the following steps: a. According to the described parts by weight, ethylene-propylene-diene monomer rubber, reinforcing agent, polyurethane prepolymer, silica white, and sodium stearate are mixed evenly and put into a mixer and kneaded at 135 °C for 12 min to obtain a kneaded rubber; b. The kneaded rubber is transferred to an open mill, N-cyclohexyl-2-benzothiazolyl sulfenamide and sulfur are added, and after kneading at 135 °C for 5 min, it is molded into a preform by compression molding, and finally the preform is vulcanized. The vulcanization temperature is 175 °C and the vulcanization time is 6 min to obtain the ethylene-propylene-diene monomer rubber composite material.

[0039] Comparative Example 1 This Comparative Example 1 is basically the same as Example 1, except that the reinforcing agent is omitted, and the others are the same as in Example 1.

[0040] Comparative Example 2 This comparative example 2 is basically the same as the example 1, except that in the process of preparing the polyurethane prepolymer, triphenyl isocyanate thiophosphate is replaced by hexamethylene diisocyanate, and the rest is consistent with the example 1.

[0041] Test Example 1 1. The mechanical properties of composite materials were tested using an electronic universal testing machine. The samples were cut into dumbbell-shaped specimens using a cutter and tested according to the national standard GB / T 528-2009; the speed was 500.0 mm / min, and the fixed force attenuation rate was 40.0%; 2. The tear strength is tested in accordance with GB / T 529-2008, using right-angle specimens; 3. Test the bonding strength according to GB / T11211-2009 "Determination of bonding strength between vulcanized rubber or thermoplastic rubber and metal"; 4. Shore A hardness is tested in accordance with GB / T 531.1-2008; 5. Flame retardant performance refers to GB / T 10707-2008 "Determination of Rubber Combustion Performance" standard, and the flame retardant performance is tested by limiting oxygen index tester. The test environment temperature is controlled at 23±2℃, and the humidity needs to be controlled at 45%-75%. The above test results are recorded in Table 1.

[0042] Table 1 It can be seen from the test results in Table 1 that the tensile strength, elongation at break, bonding strength, tear strength, etc. of Examples 1-3 of the present invention are significantly improved compared with Comparative Examples 1 and 2. The above results are attributed to the compounding of EPDM rubber, polyurethane prepolymer, reinforcing agent and other auxiliary materials in the present invention. The reinforcing agent has a unique molecular architecture, which gives the rubber composite material excellent processing fluidity, and achieves a synergistic improvement in high cohesive energy, flame retardant properties and mechanical strength. In addition, the reinforcing agent can not only generate physical entanglement with the non-polar main chain of EPDM rubber, but also form π-π conjugation with the rigid benzene ring in the polyurethane prepolymer, construct a multi-scale interface bonding mechanism, thereby significantly improving the mechanical strength and bonding strength of the composite system.

[0043] The materials of Examples 1-3 of the present invention have excellent flame retardant properties and are significantly better than those of Comparative Example 2. This is because the phosphorus element in the thiophosphoric acid triphenyl isocyanate introduced into the polyurethane prepolymer decomposes to generate acidic substances such as phosphoric acid and metaphosphoric acid when heated. These acids catalyze the dehydration of hydroxyl groups (-OH) in the rubber molecules to form a dense carbonized layer, which can give the rubber composite material good flame retardant properties.

[0044] The above embodiments are only preferred embodiments of the present invention, and the scope of protection of the present invention cannot be limited thereby. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. An ethylene-propylene-diene monomer rubber composite material, characterized in that, By weight parts, it includes the following components: 100 parts of ethylene propylene diene monomer rubber, 8 - 15 parts of polyurethane prepolymer, 10 - 15 parts of reinforcing agent, 50 - 80 parts of white carbon black, 2 - 5 parts of dispersant, 0.8 - 1.2 parts of vulcanization accelerator, and 2 - 3 parts of vulcanizing agent.

2. The ethylene-propylene-diene rubber composite according to claim 1, wherein The preparation process of the reinforcing agent includes the following steps: (1) Glycerol, an alkali metal carbonate, and 6-bromohexanal are added to solvent A for reaction. After the reaction is completed, intermediate 1 is obtained through purification; the structural formula of the intermediate 1 is ; (2) Add intermediate 1, pentamethylaniline, and glacial acetic acid into solvent B. After stirring and mixing evenly, add sodium cyanoborohydride for reaction. Concentrate the reaction solution, extract it, and combine the organic phases. Then, obtain the enhancer through drying, filtration, concentration, and purification; the structure of the enhancer is .

3. The ethylene-propylene-diene rubber composite according to claim 2, wherein In step (1), the molar ratio of glycerol, alkali metal carbonate, and 6 - bromohexanal is 1:(6 - 7.5):(3 - 3.3), and the concentration of glycerol in solvent A is 0.1 mol / L.

4. The ethylene-propylene-diene rubber composite according to claim 2, characterized in that, In step (1), the alkali metal carbonate is potassium carbonate or sodium carbonate, and the solvent A is N,N - dimethylformamide; the reaction temperature is 90 - 110°C, and the time is 12 - 16 h.

5. The ethylene-propylene-diene monomer rubber composite according to claim 2, wherein In step (2), the molar ratio of intermediate 1, pentamethylaniline, glacial acetic acid, and sodium cyanoborohydride is 1:(3 - 3.5):(3 - 4):(6 - 7.5), and the concentration of intermediate 1 in solvent B is 0.2 mol / L; the reaction time is 16 - 24 h; the solvent B is methanol; the solvent used for extraction is dichloromethane.

6. The ethylene-propylene-diene rubber composite material according to claim 1, wherein The preparation steps of the polyurethane prepolymer are as follows: By weight parts, weigh 30 parts of polytetrahydrofuran ether glycol, 15 - 18 parts of triphenyl thiophosphate isocyanate, 0.5 - 0.8 parts of triethylenediamine, and 1 - 2 parts of glycerol, and stir - react under an anhydrous system to obtain the polyurethane prepolymer.

7. The ethylene-propylene-diene rubber composite material according to claim 6, wherein The temperature of the stirring reaction is 90 - 100°C, and the time is 18 - 24 h.

8. The preparation method of the ethylene-propylene-diene monomer rubber composite material according to any one of claims 1 to 7, characterized in that, It includes the following steps: a. According to the said weight parts, mix ethylene propylene diene monomer rubber, reinforcing agent, polyurethane prepolymer, white carbon black, and dispersant evenly, and then carry out mixing to obtain a mixed rubber. b. Add vulcanization accelerator and vulcanizing agent to the mixed rubber for mixing, and then obtain a pre - product through compression molding. Vulcanize the pre - product to obtain an ethylene propylene diene monomer rubber composite material.

9. The preparation method of the ethylene-propylene-diene rubber composite material according to claim 8, characterized in that, The temperature of the mixing in step a is 125 - 135°C, and the time is 12 - 15 min; the temperature of the mixing in step b is the same as that in step a, and the mixing time is 3 - 5 min; the temperature of the vulcanization treatment is 170 - 180°C, and the time is 6 - 8 min.

10. The preparation method of the ethylene-propylene-diene rubber composite material according to claim 8, characterized in that, The dispersant is sodium stearate or potassium stearate; the vulcanization accelerator is N - cyclohexyl - 2 - benzothiazole sulfenamide or tetrabenzyl thiuram disulfide; the vulcanizing agent is sulfur or dicumyl peroxide.

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