Thermoplastic vulcanizate resistant to compression set as well as preparation method and application of thermoplastic vulcanizate

Abstract

The invention discloses thermoplastic vulcanizate resistant to compression set as well as a preparation method and application thereof, and belongs to the technical field of rubber materials. The preparation method of the thermoplastic vulcanizate resistant to compression set comprises the following steps: carrying out primary mixing, primary vulcanization and granulation on olefin rubber, sulfur, an activator and an accelerant to obtain rubber particles; and carrying out secondary mixing and secondary vulcanization on highly saturated rubber, a polysulfide cross-linking agent, a catalyst, a filler and the rubber particles to obtain the compression set resistant thermoplastic vulcanized rubber. A sulfur cross-linked rubber particle phase is introduced into a polysulfur cross-linked high-saturation rubber phase, so that a multi-sulfur bond cross-linked network containing cross-linked rubber particles is constructed in matrix rubber. While the repeated processing performance of the cross-linked rubber material is reserved, the elasticity and compression permanent deformation resistance of the material in a medium and low temperature environment can be remarkably improved, and the cross-linked rubber material has a wide application prospect in preparation of high-performance rubber products.

Description

Technical Field

[0001] This application belongs to the field of rubber materials technology, and in particular relates to a thermoplastic vulcanizate resistant to compression set, its preparation method and application. Background Technology

[0002] Thermoplastic vulcanizates (TPVs) are a class of thermoplastic elastomers prepared through dynamic vulcanization blending technology. Their structure is characterized by a high content of cross-linked rubber microparticles as the dispersed phase and a small amount of thermoplastic resin (plastic) forming the continuous phase. Due to this unique structure and comprehensive performance advantages, TPVs are widely used in many fields such as automotive, electronics, and construction, and show a strong trend of continuous expansion. However, the elastic properties of existing TPV materials are significantly inferior to those of vulcanized rubber, especially at low temperatures, where their compression set performance is significantly insufficient. Furthermore, they exhibit large permanent residual deformation under large deformations, making them unsuitable for applications requiring large deformations and cyclic loading. Therefore, developing TPV materials with excellent low-temperature compression set resistance is of great significance for further expanding their application scenarios.

[0003] For example, the prior art with publication number CN113831614A improves the problem of poor filler dispersibility through emulsion co-flocculation process, and introduces low molecular weight polyisobutylene as a plasticizer. The prepared TPV has an embrittlement temperature as low as -75℃, and a compression set of 12.3% under room temperature conditions (23℃×170h). Patent CN117264333 A prepares EPDM / PP type TPV with an embrittlement temperature below -70℃ by introducing silicone rubber as a cold-resistant agent and 3-aminopropyltriethoxysilane-grafted polypropylene as a compatibilizer.

[0004] However, existing improved processes have various technical drawbacks: First, although the existing plasticizers can improve the low-temperature performance and flexibility of materials to a certain extent, they will lead to a decrease in the strength and heat resistance of the materials. Moreover, at low temperatures, plasticizers are prone to migration or crystallization, losing their plasticizing effect. Second, the amount of cold-resistant agent added is difficult to control precisely. Too much will affect other properties of the material, while too little will not significantly improve the low-temperature performance. Summary of the Invention

[0005] This application discloses a thermoplastic vulcanizate resistant to compression set, its preparation method and application, aiming to solve the technical problem of poor compression set performance of existing thermoplastic vulcanizates at low temperatures.

[0006] To achieve the above objectives, the technical solution of this application is:

[0007] The first aspect of this application provides a method for preparing a thermoplastic vulcanizate resistant to compression set, the method comprising:

[0008] Rubber granules are obtained by mixing, vulcanizing, and granulating olefin rubber, sulfur, activator, and accelerator in one step;

[0009] A thermoplastic vulcanizate resistant to compression set is obtained by secondary mixing and vulcanization of highly saturated rubber, polysulfide crosslinking agent, catalyst, filler, and rubber particles.

[0010] Preferably, in conjunction with the first aspect, the olefin rubber is one or more of the following: ethylene propylene diene monomer (EPDM) rubber with an unsaturated third monomer content higher than 7%, natural rubber, styrene-butadiene rubber, polybutadiene rubber, butyl rubber, nitrile rubber, styrene / butadiene block copolymer, polyisoprene rubber, polynorbornene, unsaturated polyester rubber with an unsaturated unit content higher than 10 wt.%, epoxidized butadiene rubber, epoxidized isoprene rubber, epoxidized styrene / butadiene block copolymer, and epoxidized styrene / isoprene block copolymer.

[0011] Preferably, in conjunction with the first aspect, the activator is zinc oxide and stearic acid;

[0012] The accelerator is one or more of the following: thiazoles, thiurams, sulfenamides, guanidines, and dithiocarbamates.

[0013] Preferably, in conjunction with the first aspect, the highly saturated rubber is one or more of the following: ethylene propylene diene monomer (EPDM) rubber with an unsaturated third monomer content of less than 7%, partially hydrogenated nitrile butadiene rubber with a C=C residual content of 5-10 wt.%, partially hydrogenated styrene-butadiene rubber with a C=C residual content preferably of 5-10 wt.%, unsaturated polyester rubber with an unsaturated unit content of 5-10 wt.%, brominated butyl rubber, and chlorinated butyl rubber.

[0014] Preferably, in conjunction with the first aspect, the catalyst is one or more of the following: 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 4-dimethylaminopyridine, triphenylphosphine, diphenylguanidine, di-o-toluidine, triphenylguanidine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, and N,N'-dicyclohexyl-2-benzothiazole sulfenamide;

[0015] The filler is one or more of carbon black, silica, carbon nanotubes, graphene, graphene oxide, calcium carbonate, and fly ash.

[0016] In conjunction with the first aspect, preferably, the primary mixing is either intensive mixing or open mixing;

[0017] If intensive mixing is used, the mixing temperature is 30-50℃ and the mixing time is 8-15 minutes; the crosslinking temperature is 140-180℃ and the time is the positive vulcanization time.

[0018] If open mixing is used, the mixing temperature is room temperature and the mixing time is 5-20 minutes.

[0019] In conjunction with the first aspect, preferably, the secondary mixing is either intensive mixing or open mixing;

[0020] If intensive mixing is used, the mixing temperature is 30-50℃ and the mixing time is 10-15 minutes; the crosslinking temperature is 140-180℃ and the time is the positive vulcanization time.

[0021] If open mixing is used, the mixing temperature is room temperature and the mixing time is 10-20 minutes.

[0022] In conjunction with the first aspect, preferably, the mass fractions of each preparation raw material added are as follows:

[0023] 100 parts of olefin rubber;

[0024] Sulfur 0.3-3 parts;

[0025] Activator 1-10 parts;

[0026] Accelerator 1-10 parts;

[0027] 30-300 parts of highly saturated rubber;

[0028] 3-6 parts of polysulfide crosslinking agent;

[0029] Catalyst 0.05-0.5 parts;

[0030] 20-150 parts of filler.

[0031] The second aspect of this application provides a thermoplastic vulcanizate resistant to compression set prepared by the preparation method described in the first aspect.

[0032] The third aspect of this application provides the use of the compression-resistant thermoplastic vulcanizate described in the second aspect in the preparation of rubber products.

[0033] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following:

[0034] The preparation method provided in this application introduces sulfur-crosslinked rubber particles into a polysulfide-crosslinked hypersaturated rubber phase via a stepwise crosslinking strategy. Using the hypersaturated rubber phase as the continuous phase and sulfur-crosslinked rubber particles as the dispersed phase, and since both the dispersed and continuous phases are rubber components, the stepwise sequential crosslinking introduces the dispersed phase into the continuous phase, creating a two-phase network structure with dynamic sulfur bond crosslinking. Simultaneously, polysulfide bond crosslinking is introduced into the hypersaturated rubber, significantly improving the material's mid-to-low temperature elasticity and resistance to compression set while retaining its repeatability. Furthermore, the raw materials used in this application are directly derived from the traditional rubber industry system, requiring no additional modification or complex pretreatment; the preparation process is simple, requiring no special processing equipment, and possesses good versatility and industrial application potential. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart illustrating the preparation process of the thermoplastic vulcanizate prepared according to the embodiments of this application. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0038] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0039] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0040] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0041] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0042] It should be noted that all raw materials and reagents in the embodiments of this application were purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0043] In a first aspect, embodiments of this application provide a method for preparing a thermoplastic vulcanizate resistant to compression set, the method comprising:

[0044] Rubber granules are obtained by mixing, vulcanizing, and granulating olefin rubber, sulfur, activator, and accelerator in one step;

[0045] A thermoplastic vulcanizate resistant to compression set is obtained by secondary mixing and vulcanization of highly saturated rubber, polysulfide crosslinking agent, catalyst, filler, and rubber particles.

[0046] This invention utilizes a highly saturated rubber phase as the continuous phase and sulfur-crosslinked rubber particles as the dispersed phase. Since both the dispersed and continuous phases are rubber components, the dispersed phase is introduced into the continuous phase through stepwise sequential crosslinking, creating a two-phase network structure with dynamic sulfur bond crosslinking. Simultaneously, polysulfide bond crosslinking is introduced into the highly saturated rubber, significantly improving the material's mid-to-low temperature elasticity and deformation resistance while retaining its repeatability. Furthermore, the raw materials used in this application are directly derived from the traditional rubber industry system, requiring no additional modification or complex pretreatment; the preparation process is simple, requiring no special processing equipment, and possesses good versatility and industrial application potential.

[0047] In this embodiment, the olefin rubber is one or more of the following: ethylene propylene diene monomer (EPDM) rubber with an unsaturated third monomer content higher than 7%, natural rubber, styrene-butadiene rubber, polybutadiene rubber, butyl rubber, nitrile rubber, styrene / butadiene block copolymer, polyisoprene rubber, polynorbornene, unsaturated polyester rubber with an unsaturated unit content higher than 10 wt.%, epoxidized butadiene rubber, epoxidized isoprene rubber, epoxidized styrene / butadiene block copolymer, and epoxidized styrene / isoprene block copolymer. The olefin rubber refers to an olefin rubber containing unsaturated carbon-carbon double bonds or a functionalized olefin rubber. EPDM rubbers have different degrees of saturation; the olefin rubber used is EPDM rubber with a lower degree of saturation (unsaturated third monomer content not less than 7%); the highly saturated rubber used is EPDM rubber with a higher degree of saturation (unsaturated third monomer content not more than 7%).

[0048] In the embodiments of this application, the activator is preferably zinc oxide and stearic acid; the accelerator is preferably one or more of the following: thiazoles (dibenzothiazole disulfide), thiurams (tetramethylthiuram disulfide, tetramethylthiuram monosulfide), sulfenamides (N-cyclohexyl-2-benzothiazole sulfenamide), guanidines (diphenylguanidine), and dithiocarbamates (zinc dimethyl dithiocarbamate).

[0049] In this embodiment, the highly saturated rubber is one or more of the following: ethylene propylene diene monomer (EPDM) rubber with an unsaturated third monomer content of less than 7%, partially hydrogenated nitrile butadiene rubber with a C=C residual content of 5-10 wt.%, partially hydrogenated styrene-butadiene rubber with a C=C residual content preferably of 5-10 wt.%, unsaturated polyester rubber with an unsaturated unit content of 5-10 wt.%, brominated butyl rubber, and chlorinated butyl rubber.

[0050] In this embodiment, the catalyst is one or more of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 4-dimethylaminopyridine (DMAP), triphenylphosphine (PPh3), diphenylguanidine (DPG), di-o-toluidine (DOTG), triphenylguanidine (TPG), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), N-cyclohexyl-2-benzothiazole sulfenamide (CZ), and N,N'-dicyclohexyl-2-benzothiazole sulfenamide (DZ); the filler is preferably one or more of carbon black, silica, carbon nanotubes, graphene, graphene oxide, calcium carbonate, and fly ash. The polysulfide crosslinking agent is a sulfur-containing copolymer disclosed in the prior art of application publication number CN 112679758A.

[0051] It should be noted that the particle size of the rubber particles produced in the first step of the reaction is 10-1000 μm. In this application, the rubber particles are directly prepared by mechanical shearing and crushing, and the prepared particles are distributed in the micrometer range. After sieving and grading, they are used. Different particle phase sizes affect the properties of the final two-phase rubber material.

[0052] It should be noted that the preparation method provided in this application uses sulfur-crosslinked rubber as the target material. It introduces a low-compression-set particle phase and a polysulfide-crosslinked continuous phase through stepwise crosslinking. The raw materials are directly derived from the traditional rubber industry, requiring no modification or complex processing. The preparation process is simple, requires no special processing equipment, and has good versatility. This application proposes a new method for preparing thermoplastic vulcanizates resistant to medium and low temperature compression set. This method can prepare crosslinked rubbers with high resilience, resistance to compression set, and reprocessability, with low-temperature compression set performance significantly superior to traditional TPV materials.

[0053] It should be noted that the stepwise crosslinking method, which introduces pre-sulfur-crosslinked rubber particles with high size stability into a polysulfide-crosslinked highly saturated rubber matrix phase, avoids the limitation of irreversible monosulfide bonds widely distributed in traditional homogeneous vulcanizates. This method prepares a novel thermoplastic vulcanizate without a plastic phase, which significantly improves the medium and low temperature elasticity (low compression set) while maintaining the material's reprocessing capability, and has important industrial application value.

[0054] In this embodiment of the application, based on the rubber formulation and taking 100 parts of olefin rubber matrix as an example, the mass parts of each raw material added are as follows: 100 parts olefin rubber; 0.3-3 parts sulfur; 1-10 parts activator; 1-10 parts accelerator; 30-300 parts high-saturation rubber; 3-6 parts polysulfide crosslinking agent; 0.05-0.5 parts catalyst; and 20-150 parts filler. By controlling the amount of each raw material added, a thermoplastic vulcanizate with excellent comprehensive performance can be generated.

[0055] Thirdly, embodiments of this application also provide the application of the compression set resistant thermoplastic vulcanizate described in the second aspect in the preparation of rubber products. Specifically, because the aforementioned thermoplastic vulcanizate significantly improves low-temperature elasticity and deformation resistance while maintaining the material's reprocessability, it enhances the market competitiveness of rubber products when used in their preparation.

[0056] The technical solution of this application will be further described below with reference to specific embodiments.

[0057] Example 1

[0058] This embodiment provides a method for preparing compression-resistant thermoplastic vulcanizates, verifying the rubber particle content, polysulfide crosslinking agent dosage, catalyst type and dosage variables, specifically including:

[0059] S101: Ethylene propylene diene monomer (EPDM) rubber, zinc oxide, stearic acid, accelerator M, accelerator TT, and sulfur are added to an open mill in a weight ratio of 100:3:1:0.4:1.1:0.7 and mixed at room temperature for 10 minutes. The resulting compound A1 is molded at 150°C for the correct vulcanization time using a flat vulcanizing machine and further crushed to obtain cross-linked rubber particles (particle size of 10-800 micrometers) resistant to compression set, denoted as B1.

[0060] S102: Take the compression set resistant cross-linked rubber particles B1, EPDM rubber, polysulfide cross-linking agent, and catalyst according to the dosage in Table 1, add them to the open mill, mix at room temperature for 15 minutes, and add the corresponding compound C1 to C7 to the flat vulcanizing machine, and mold them at 150℃ for the correct vulcanization time to obtain the corresponding compression set resistant thermoplastic vulcanizates, marked as M1 to M7.

[0061] The specific raw material usage is shown in Table 1:

[0062] Table 1. List of Raw Material Consumption for Thermoplastic Vulcanizates M1 to M7

[0063]

[0064] Example 2

[0065] This embodiment provides a method for preparing compression-resistant thermoplastic vulcanizates, verifying the types of olefin rubbers, sulfur content, activator content, types and contents of accelerators, and particle size variations in the rubber powder. Specifically, it includes:

[0066] S201: Add olefin rubber, zinc oxide, stearic acid, accelerator, and sulfur to a two-roll mill according to the formula in Table 2 and mix at room temperature for 10 minutes; the resulting compound A2-A8 is molded at 150°C with the positive vulcanization time using a flat vulcanizing machine, further crushed, and sieved to obtain different types of cross-linked rubber particles resistant to compression set (particle size of 10-1000 micrometers), denoted as B2-B8.

[0067] S202: Take the compression set resistant cross-linked rubber particles B2-B8, EPDM rubber, polysulfide cross-linking agent, and catalyst CZ according to the dosage in Table 3, add them to the open mill, mix at room temperature for 15 minutes, and add the corresponding compound C8-C14 to the flat vulcanizing machine, and mold them at 150℃ for the correct vulcanization time to obtain the corresponding thermoplastic vulcanizates, marked as M8~M14.

[0068] The specific raw material usage is shown in Tables 2 and 3:

[0069] Table 2. List of Raw Material Consumption for Crosslinked Rubbers B2-B8 with Resistance to Compression Set

[0070]

[0071]

[0072] Table 3: List of Raw Material Consumption for Thermoplastic Vulcanizates M8 to M14

[0073]

[0074] Example 3

[0075] This embodiment provides a method for preparing compression-resistant thermoplastic vulcanizates, verifying the type of high-saturation rubber, the type and amount of filler, the type of processing equipment, and the processing time, specifically including:

[0076] S301: Ethylene propylene diene monomer (EPDM) rubber, zinc oxide, stearic acid, accelerator M, accelerator TMTD, and sulfur are added to an open mill at a weight ratio of 100:3:1:0.4:1.1:0.7 and mixed at room temperature for 10 minutes. The resulting compound A9 is molded at 150°C for the correct vulcanization time using a flat vulcanizing machine and further crushed to obtain cross-linked rubber powder rich in dynamic sulfur bonds (particle size of 10-500 micrometers), denoted as B9.

[0077] S302: Take the amount of cross-linked rubber powder B9 rich in dynamic sulfur bonds, high saturated rubber, catalyst CZ and filler according to the dosage in Table 4, add them to the open mill or internal mixer and mix for a certain time. The resulting compound C15 to C20 are added to the flat vulcanizing machine and molded at 150°C for the positive vulcanization time to obtain the corresponding thermoplastic vulcanizates, marked as M15 to M20.

[0078] The specific raw material usage is shown in Table 4:

[0079] Table 4: List of Raw Material Consumption for Thermoplastic Vulcanizates M15 to M20

[0080]

[0081] *O indicates mixing using an open mill; I indicates mixing using an internal mixer.

[0082] Meanwhile, to verify the comprehensive performance of the thermoplastic vulcanizates resistant to compression set prepared in the above embodiments, this application provides the following comparative examples for detailed illustration.

[0083] Comparative Example 1

[0084] This application provides a comparative method for preparing vulcanizates, specifically including:

[0085] EPDM rubber, zinc oxide, stearic acid, accelerator M, accelerator TT, sulfur, polysulfide crosslinking agent, and catalyst CZ were added to an open mill in a weight ratio of 100:1.2:0.4:0.16:0.44:0.28:1.2:0.2 and mixed at room temperature for 15 minutes. The resulting compound, DC1, was then added to a flat vulcanizing machine and molded at 150°C for the normal vulcanization time to obtain a control vulcanized rubber, labeled DM1.

[0086] Comparative Example 2

[0087] This application provides a comparative method for preparing commercially available thermoplastic vulcanizates, specifically including:

[0088] TPV granules with low hardness (55A) and high elasticity, prepared by dynamic vulcanization technology using polypropylene and EPDM rubber as raw materials, were directly hot-pressed to prepare relevant test samples, which were marked as TPV-55.

[0089] Comparative Example 3

[0090] This application provides a comparative method for preparing vulcanizates, specifically including:

[0091] According to the formula in Table 5, olefin rubber and various rubber additives were added to the open mill and mixed at room temperature for 15 minutes. The resulting compound DC2 to DC4 were added to the flat vulcanizing machine and molded at 150°C for the correct vulcanization time to obtain the comparative vulcanized rubber, labeled as DM2 to DM4.

[0092] The specific raw material usage is shown in Table 5:

[0093] Table 5. Comparison of Raw Material Consumption for Vulcanizates DM2 to DM4

[0094]

[0095] Comparative Example 4

[0096] This application provides a comparative method for preparing vulcanizates, specifically including:

[0097] EPDM rubber, zinc oxide, stearic acid, accelerator M, accelerator TMTD, sulfur, carbon black, polysulfide crosslinking agent, and catalyst CZ were added to an internal mixer in a weight ratio of 100:1.2:0.4:0.16:0.44:0.28:32:1.2:0.2 and mixed at 40°C for 10 minutes. The resulting compound, DC5, was added to a flat vulcanizing machine and molded at 150°C for the correct vulcanization time to obtain a control vulcanized rubber, labeled DM5.

[0098] Comparative Example 5

[0099] This application provides a comparative method for preparing vulcanizates, specifically including:

[0100] According to the formula (EPDM rubber, brominated butyl rubber, zinc oxide, stearic acid, accelerator M, accelerator TMTD, sulfur, carbon black, polysulfide crosslinking agent, and catalyst CZ in a weight ratio of 50:50:1.2:0.4:0.16:0.44:0.28:40:1.2:0.2), the mixture was mixed at room temperature on an open mill for 20 minutes. The resulting compound, DC6, was added to a flat vulcanizing machine and molded at 150°C for the normal vulcanization time to obtain a control vulcanized rubber, labeled as DM6.

[0101] This application tests the comprehensive properties of the thermoplastic vulcanizates prepared in the above embodiments:

[0102] Recycling method: Take thermoplastic vulcanizates M1~M20 and control vulcanizates DM1~DM6 respectively, and conduct application tests such as tensile, tear, abrasion resistance and fatigue resistance. Then, take the used thermoplastic vulcanizates M1*~M20* and the used control vulcanizates DM1*~DM6* and cut them into pieces. The corresponding fragments are hot-pressed at 150℃ for 5 minutes to obtain the corresponding recycled thermoplastic vulcanizates N1~N20 and recycled control vulcanizates DN1~DN6.

[0103] Performance testing: Performance tests were conducted on thermoplastic vulcanizates M1-M20, control vulcanizates DM1-DM6, recycled thermoplastic vulcanizates N1-N20, and recycled control vulcanizates DN1-DN6. The specific test methods are as follows:

[0104] Tensile strength test: The test was conducted on a U-CAN UT-2060 tensile testing machine, according to ISO 37-2005, at room temperature, and at a tensile rate of 500 mm / min. At least 5 parallel tests were performed, and the average value was taken.

[0105] Elongation at break: The test was conducted on a U-CAN UT-2060 tensile testing machine, according to ISO 37-2005, at room temperature, and at a tensile rate of 500 mm / min. At least 5 parallel tests were performed, and the average value was taken.

[0106] Gel content test: The gel content was determined by an equilibrium swelling experiment. The specific experimental steps are as follows: A rubber sheet with a mass of m0 was immersed in toluene, and the solvent was changed every 24 hours. After immersion for 72 hours, the swelling equilibrium was fully reached. The sample was then dried in a vacuum oven at 60℃ until constant weight, and the mass was recorded as m1. Each sample was tested three times. The gel content (GF) was calculated according to equation (1-1): GF = m1 / m0 × 100%;

[0107] Compression set test: The test is conducted using a compression set mold. The test standard is GBT 7759.1-2015, and the test method A is adopted. The sample size is (29.0±0.5) mm in diameter and (12.5±0.5) mm in thickness. The compression ratio is 25%. The test temperatures are -30℃, 25℃, and 80℃. At least 3 parallel samples are tested, and at least 3 test sites are taken for each sample. The average value is then taken.

[0108] The tensile strength recovery rate and elongation at break recovery rate of recycled thermoplastic vulcanizates N1 to N7 and recycled control vulcanizate DN1 are calculated, and the calculation formula is as follows:

[0109] Tensile strength recovery rate = Tensile strength of recycled vulcanizate ÷ Tensile strength of unused vulcanizate × 100%;

[0110] Elongation at break recovery rate = Elongation at break of recycled vulcanizate ÷ Elongation at break of unused vulcanizate × 100%;

[0111] The specific test results are shown in Table 6:

[0112] Table 6. Summary of performance test results for thermoplastic vulcanizates M1-M7, comparative vulcanizate DM1, and commercial TPV.

[0113]

[0114]

[0115] As shown in Table 1 and the formulation of the comparative sample, M2 has the same formulation as the comparative sample DM1. DM1 is a homogeneous vulcanizate sample prepared by directly adding a polysulfide crosslinking agent to traditional sulfur-cured rubber, while M2 is a two-phase sample prepared through stepwise sequential crosslinking. Table 2 shows that compared to the comparative vulcanizate DM1, vulcanizate M2 has a higher gel content (>95%). M2 can be rapidly reprocessed at 150℃, and the recovery rate of tensile strength and elongation at break of the reprocessed and recycled sample is close to 100%, while the comparative sample DM1 requires further reprocessing and recycling. More importantly, M2 has a lower compression set at room temperature and 80℃, indicating better dimensional stability. The above experiments demonstrate that by introducing an effective sulfur vulcanization system (low sulfur, high accelerator) crosslinked particulate phase into polysulfide crosslinked high-saturation rubber through stepwise sequential crosslinking, the prepared thermoplastic vulcanizate possesses rapid reprocessing capability, excellent recyclability, and excellent resistance to compression set at medium and low temperatures. In contrast, although commercial TPV has excellent reprocessing capabilities, due to the presence of the plastic phase, its compression set at low temperatures is significantly higher than that of M2, indicating that M2 has a clear advantage in elasticity and dimensional stability at medium and low temperatures.

[0116] Comparing the mechanical properties of M1-M3 reveals that with increasing rubber particle content, the tensile strength of the thermoplastic vulcanizate increases while the elongation at break decreases. This is attributed to the filling effect of the rubber particles, which increases the network modulus and crosslinking density. Furthermore, with increasing the amount of compression set resistant rubber particles, the compression set of the thermoplastic vulcanizate at different temperatures decreases, indicating improved dimensional stability. Comparing the results of M2 and M4 also shows that increasing the content of the polysulfide crosslinking agent leads to a significant increase in the compression set of the thermoplastic vulcanizate at room temperature and 80°C, attributed to the introduction of more easily exchangeable polysulfide bonds.

[0117] The comparison of the results for M2, M5, and M6 in Table 6 also shows that the amount of catalyst CZ significantly affects the compression set resistance and reprocessing properties of thermoplastic vulcanizates. With the increase of catalyst CZ, the compression set of thermoplastic vulcanizates decreases, but the mechanical property retention rate of the reprocessed samples decreases. This is because the catalyst can improve the degree of crosslinking of polysulfide crosslinking agents to highly saturated rubber, thereby improving the integrity of the overall crosslinking network, but it can also lead to the formation of some irreversible monosulfide bonds.

[0118] Comparing the results of M2 and M7 in Table 6 reveals that the type of catalyst also affects the compression stability and reprocessing properties of thermoplastic vulcanizates. DBU, as an organic base, accelerates the nucleophilic addition reaction between active sulfur and rubber double bonds by activating polysulfide crosslinking agents through strong basicity and nucleophilicity. CZ, on the other hand, crosslinks rubber by generating sulfur free radicals through activation of polysulfide to attack the carbon-carbon double bonds on the rubber molecular chain. Because the former is more conducive to retaining more polysulfide bonds and can itself catalyze the exchange of polysulfide bonds through Lewis basicity, the stability of the resulting crosslinked network is not as good as that of CZ.

[0119] The above experiments demonstrate that by introducing highly stable rubber particles prepared using an effective sulfur vulcanization system (low sulfur, high accelerator) into highly saturated polysulfide-crosslinked rubber through a stepwise sequential crosslinking method, the resulting sulfur-vulcanized two-phase rubber not only avoids the drawback of traditional homogeneous vulcanized rubber's inability to be repeatedly processed, but also exhibits excellent dimensional stability at medium and low temperatures (low compression set). This example shows that by controlling the amount of pre-crosslinked rubber particles, the amount of polysulfide crosslinking agent, and the type and amount of catalyst, the compression set and reprocessing performance of thermoplastic vulcanizates can be effectively adjusted.

[0120] The above test methods were used to conduct corresponding performance tests on thermoplastic vulcanizates M8-M14 and control vulcanizates DM2-DM4. Specific test results are shown in Tables 7 and 8.

[0121] Table 7. Summary of performance test results for thermoplastic vulcanizates M8-M14 and comparative vulcanizates DM2-DM4

[0122]

[0123]

[0124] As shown in Table 7, the optimal addition amount of each substance was selected based on the above embodiments. Compared with the one-step mixing of Comparative Example 3, it was found that its low-temperature compression set performance was significantly lower than that of the step-by-step sequential addition in the embodiments, and it did not have the ability to be reprocessed.

[0125] Table 8. Summary of performance test results for thermoplastic vulcanizates M15-M20 and comparative vulcanizates DM5-DM6

[0126]

[0127] As shown in Table 8, the optimal addition amount of each substance was selected based on the above embodiments. Compared with the one-step mixing of Comparative Examples 4 and 5, it was found that the low-temperature compression set performance was significantly lower than that of the step-by-step sequential addition in the embodiments, and it did not have the ability to be reprocessed.

[0128] Therefore, this application proposes a stepwise sequential crosslinking method to introduce highly stable rubber particles prepared by crosslinking with an effective sulfur vulcanization system (low sulfur, high accelerator) into highly saturated rubber. The interfacial crosslinking of the two-phase network is achieved by activating the polysulfide crosslinking agent with a catalyst. The prepared sulfur-vulcanized two-phase rubber avoids the irreversible monosulfide bonds widely distributed in traditional homogeneous vulcanized rubber, achieving excellent reprocessing capability. Furthermore, unlike traditional thermoplastic vulcanizates, it does not require the introduction of a plastic phase, exhibiting excellent medium- and low-temperature dimensional stability (low compression set). In summary, this application proposes a novel method for preparing thermoplastic vulcanizates resistant to medium- and low-temperature compression set, and prepares a large class of vulcanized rubber compositions that combine excellent reprocessing performance and low compression set, showing broad application prospects in rubber product manufacturing.

[0129] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0130] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a thermoplastic vulcanizate resistant to compression set, characterized in that, The preparation method includes: Rubber granules are obtained by mixing, vulcanizing, and granulating olefin rubber, sulfur, activator, and accelerator in one step; A thermoplastic vulcanizate resistant to compression set is obtained by secondary mixing and vulcanization of highly saturated rubber, polysulfide crosslinking agent, catalyst, filler, and rubber particles.

2. The method for preparing the compression-resistant thermoplastic vulcanizate according to claim 1, characterized in that, The olefin rubber is one or more of the following: ethylene propylene diene monomer (EPDM) rubber with an unsaturated third monomer content higher than 7%, natural rubber, styrene-butadiene rubber, polybutadiene rubber, butyl rubber, nitrile rubber, styrene / butadiene block copolymer, polyisoprene rubber, polynorbornene, unsaturated polyester rubber with an unsaturated unit content higher than 10 wt.%, epoxidized butadiene rubber, epoxidized isoprene rubber, epoxidized styrene / butadiene block copolymer, and epoxidized styrene / isoprene block copolymer.

3. The method for preparing the compression-resistant thermoplastic vulcanizate according to claim 1, characterized in that, The activator is zinc oxide and stearic acid; The accelerator is one or more of the following: thiazoles, thiurams, sulfenamides, guanidines, and dithiocarbamates.

4. The method for preparing the compression-resistant thermoplastic vulcanizate according to claim 1, characterized in that, The highly saturated rubber is one or more of the following: ethylene propylene diene monomer (EPDM) rubber with an unsaturated third monomer content of less than 7%, partially hydrogenated nitrile butadiene rubber with a C=C residual content of 5-10 wt.%, partially hydrogenated styrene-butadiene rubber with a C=C residual content preferably of 5-10 wt.%, unsaturated polyester rubber with an unsaturated unit content of 5-10 wt.%, brominated butyl rubber, and chlorinated butyl rubber.

5. The method for preparing the compression-resistant thermoplastic vulcanizate according to claim 1, characterized in that, The catalyst is one or more of the following: 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 4-dimethylaminopyridine, triphenylphosphine, diphenylguanidine, di-o-toluidine, triphenylguanidine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, and N,N'-dicyclohexyl-2-benzothiazole sulfenamide. The filler is one or more of carbon black, silica, carbon nanotubes, graphene, graphene oxide, calcium carbonate, and fly ash.

6. The method for preparing the compression-resistant thermoplastic vulcanizate according to claim 1, characterized in that, The first mixing process is either intensive mixing or open mixing. If intensive mixing is used, the mixing temperature is 30-50℃ and the mixing time is 8-15 minutes; the crosslinking temperature is 140-180℃ and the time is the positive vulcanization time. If open mixing is used, the mixing temperature is room temperature and the mixing time is 5-20 minutes.

7. The method for preparing the compression-resistant thermoplastic vulcanizate according to claim 1, characterized in that, The secondary mixing process is either intensive mixing or open mixing. If intensive mixing is used, the mixing temperature is 30-50℃ and the mixing time is 10-15 minutes; the crosslinking temperature is 140-180℃ and the time is the positive vulcanization time. If open mixing is used, the mixing temperature is room temperature and the mixing time is 10-20 minutes.

8. The method for preparing the thermoplastic vulcanizate resistant to compression set according to claim 1, characterized in that, The mass fractions of each of the preparation raw materials added are as follows: 100 parts of olefin rubber; Sulfur 0.3-3 parts; Activator 1-10 parts; Accelerator 1-10 parts; 30-300 parts of highly saturated rubber; 3-6 parts of polysulfide crosslinking agent; Catalyst 0.05-0.5 parts; 20-150 parts of filler.

9. A thermoplastic vulcanizate resistant to compression set prepared by any one of the preparation methods of claims 1-8.

10. The use of the thermoplastic vulcanizate of claim 9, which is resistant to compression set, in the preparation of rubber products.

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