Preparation method of thermoplastic vulcanized rubber for automobile sealing strip based on modification of waste EPDM (ethylene-propylene-diene monomer)

Abstract

The invention relates to the technical field of recycling of high polymer materials and blending modification of elastomers, and discloses a preparation method of thermoplastic vulcanized rubber for automobile sealing strips based on waste EPDM (Ethylene-Propylene-Diene Monomer) modification, which comprises the following steps: carrying out high-shear mixing and pre-swelling on waste EPDM rubber powder, liquid high vinyl polybutadiene and a peroxide initiator to obtain a system A; uniformly mixing the primary polypropylene, the primary ethylene propylene diene monomer and the bridging agent dry powder master batch to obtain a system B; synchronously adding the system A and the system B into a main feeding hole of a double-screw extruder for melt blending and dynamic vulcanization reaction; the first antioxidant and the second antioxidant are mixed into a system C, the system C is pressed in through a side feeding opening for blending after dynamic vulcanization, devolatilization and pelletizing are conducted, and the thermoplastic vulcanized rubber is prepared. According to the invention, liquid high-vinyl polybutadiene and a peroxide initiator are adopted to carry out high-shear pre-swelling on the waste ethylene-propylene diene rubber powder, so that reactive alkadiene permeates into micropores of the waste rubber powder, and an interpenetrating network is formed through in-situ cross-linking polymerization during subsequent extrusion and heating.

Description

Technical Field

[0001] This invention relates to the field of polymer material recycling and elastomer blending modification technology, specifically a method for preparing thermoplastic vulcanized rubber for automotive sealing strips based on waste EPDM modification. Background Technology

[0002] Car doors and windows are equipped with numerous weatherstripping strips. With vehicle scrapping and production line cutting, a considerable amount of waste EPDM rubber is generated annually. Directly discarding it into landfills pollutes the environment and wastes resources. Industrially, this waste rubber is typically recycled. Processing waste rubber into thermoplastic vulcanizates is currently the mainstream approach.

[0003] Existing waste rubber recycling technologies mostly employ physical crushing and mixing methods. Workers grind the waste material into rubber powder of a specified mesh size, which is then directly mixed into polypropylene resin for extrusion granulation. This conventional process is very simple to operate and has high overall production efficiency. The processing does not require complex chemical reaction equipment. To facilitate extruder operation, paraffin-based rubber oil is often added to the formulation. Paraffin oil effectively lubricates the polymer macromolecular chains, significantly improving the initial melt flowability of the mixture. The resulting ordinary blend possesses a certain degree of basic flexibility while fully retaining the environmentally friendly processing advantages of thermoplastic resins, such as the ability to be repeatedly heated and injection molded.

[0004] Existing physical blending methods cannot access the internal structure of waste rubber powder. The original three-dimensional cross-linked network of waste rubber is a dead zone. Conventional paraffin oil only provides physical plasticization. Highly crystalline polypropylene cannot establish chemical bonds with inert waste rubber powder. Once subjected to tensile stress, microscopic slippage immediately occurs at the interface between the two phases, causing a sharp drop in macroscopic tensile strength. Adding peroxides to the system to induce dynamic vulcanization would lead to severe side reactions. In the high-temperature molten state, free radicals released from the initiator readily diffuse into the continuous polypropylene phase. They rapidly attack the hydrogen atoms on the tertiary carbon atoms of the polypropylene main chain, directly inducing β-chain scission degradation of polypropylene. With the long chains of the continuous phase broken, the material becomes a soft, unsupported rubber mass. Current feeding practices involve adding antioxidants and other additives all at once at the main feed port. The structural characteristics of hindered phenolic antioxidants make them highly susceptible to dissociation of phenolic hydroxyl hydrogens. These hydrogens, along with the initiator, are present in the high-temperature barrel, directly creating severe hydrogen abstraction competition. A large amount of free radicals, essential for dynamic vulcanization, are ineffectively consumed. The rubber phase cannot be fully cross-linked, and the antioxidant itself is also prematurely destroyed in the internal consumption, resulting in a significant reduction in the heat and oxygen aging resistance of the final product. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing thermoplastic vulcanized rubber for automotive sealing strips based on waste EPDM modification. This method solves the problems of existing technologies, such as the inability of waste rubber to establish effective chemical bonds with the polypropylene matrix leading to interfacial delamination, the easy initiation of severe chain scission degradation of continuous polypropylene by peroxides, and the severe hydrogen abstraction and internal consumption caused by the co-mixing of antioxidants and initiators at the front end.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing thermoplastic vulcanizate for automotive sealing strips based on waste EPDM includes the following steps:

[0008] S1. By weight, 30.0-45.0 parts of waste EPDM rubber powder, 15.0-25.0 parts of liquid high-vinyl polybutadiene and 0.5-1.5 parts of peroxide initiator are mixed under high shear and heated for pre-swelling to obtain pre-swelled dispersed phase system A;

[0009] S2. By weight, 20.0-30.0 parts of virgin polypropylene, 10.0-20.0 parts of virgin EPDM rubber and 2.0-5.0 parts of bridging agent dry powder masterbatch are mixed evenly to obtain continuous phase system B.

[0010] S3. System A and System B are simultaneously added to the main feed port of the twin-screw extruder for melt blending and dynamic vulcanization reaction.

[0011] S4. By weight, 0.5-1.0 parts of the first antioxidant and 0.3-0.8 parts of the second antioxidant are mixed evenly to form system C. After dynamic vulcanization reaction, system C is forced into the barrel at the side feed port downstream of the main feed port of the twin-screw extruder for further blending. Then, vacuum devolatilization and extrusion pelletizing are performed to obtain thermoplastic vulcanized rubber.

[0012] By adopting the above technical solution, this invention addresses the difficulties in re-crosslinking waste rubber and the degradation of blend properties. It utilizes a liquid diene infiltration and in-situ crosslinking mechanism to improve the microstructure. In the high-shear pre-swelling stage of system A, liquid high-vinyl polybutadiene infiltrates into the crosslinking network pores of waste EPDM rubber, acting as a reactive swelling agent. When the material enters the extruder and is heated, the peroxide initiator decomposes thermally to generate primary alkoxy radicals RO·. These primary radicals abstract allyl hydrogen from the polybutadiene molecular chain, causing the high-vinyl side chain -CH=CH2 to undergo crosslinking polymerization. The reaction process involves: RO· + -CH2-CH(CH=CH2)- → ROH + -CH2-C·(CH=CH2)-. In this way, the newly generated polymer network forms an interwoven structure with the original crosslinking network of the waste rubber, improving the structural strength of the waste rubber powder and facilitating stress transfer during subsequent processing.

[0013] Building upon this, to prevent the degradation of the continuous phase polypropylene caused by the peroxide initiator, a bridging agent containing multiple unsaturated double bonds was introduced into system B. Under blending shear, this bridging agent accumulates at the interface between the waste rubber phase and the virgin polypropylene phase. When the peroxide initiator diffuses into the continuous phase, the double bonds in the bridging agent preferentially undergo addition reactions with free radicals, thereby consuming the escaped primary free radicals. This competitive reaction prevents free radicals from attacking the tertiary carbon atoms on the polypropylene molecular chain, thus inhibiting β-chain scission degradation; simultaneously, one end of the bridging agent crosslinks with the rubber phase, while the other end grafts onto the polypropylene molecular chain, strengthening the physical bonding at the interface between the two phases.

[0014] Furthermore, conventional processes often add antioxidants along with other additives, causing the phenolic hydroxyl groups of the antioxidants to readily undergo hydrogen abstraction reactions with peroxide free radicals, unnecessarily consuming the initiator. This invention adjusts the feeding sequence, physically isolating the dynamic vulcanization reaction zone and the antioxidant addition zone along the extruder axis. The peroxide completes the dynamic crosslinking of the rubber phase in the front-middle section of the extruder. Only after the crosslinking degree of system A reaches the predetermined requirement and the concentration of free radicals within the system is significantly reduced is system C added at the downstream feed port. This not only allows the antioxidant to retain its original anti-thermal-oxidative aging function but also avoids the mutual chemical consumption between the two additives.

[0015] Preferably, the weight ratio of each raw material component is as follows: 38.0 parts of waste EPDM rubber powder, 20.0 parts of liquid high vinyl polybutadiene, 1.0 part of peroxide initiator; 25.0 parts of virgin polypropylene, 15.0 parts of virgin EPDM rubber, 3.5 parts of bridging agent dry powder masterbatch; 0.8 parts of first antioxidant, and 0.5 parts of second antioxidant.

[0016] By adopting the above technical solution, limiting the specific proportion of raw materials helps to control the phase reversal of the blend system in the molten state, and ultimately disperses the vulcanized rubber particles in the continuous polypropylene phase, so as to take into account both the mechanical strength and processing fluidity of the material.

[0017] Preferably, the peroxide initiator is bis(tert-butylperoxyisopropyl)benzene; the first antioxidant is pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and the second antioxidant is tris(2,4-di-tert-butylphenyl)phosphite.

[0018] By adopting the above technical solution, since the half-life temperature of the peroxide initiator is close to the melting temperature of virgin polypropylene, the vulcanization reaction will only occur on a large scale after the resin has been fully melted and mixed. Simultaneously, the hindered phenolic antioxidant and phosphite antioxidant can respectively capture large molecular carbon free radicals and decompose hydrogen peroxides, achieving a combined antioxidant effect.

[0019] Preferably, the number average molecular weight of the liquid high-vinyl polybutadiene is 3050-4950, and the mass fraction of the 1,2-vinyl structure in the liquid high-vinyl polybutadiene is 61%-76%.

[0020] By employing the above technical solution, limiting the number-average molecular weight to this range allows polybutadiene to maintain a suitable flow state at room temperature, thereby penetrating into the interior of waste rubber powder. The higher content of 1,2-vinyl structures corresponds to a greater number of side-chain double bonds, which provides a basis for peroxide-induced cross-linking reactions and helps to improve the overall network density.

[0021] Preferably, the preparation method of liquid high-vinyl polybutadiene includes: mixing cyclohexane with 1,3-butadiene monomer in an anhydrous and oxygen-free environment with a protective gas, adding N,N,N',N'-tetramethylethylenediamine as a polarity modifier; adjusting the temperature to 30-40°C and injecting n-butyllithium initiator, then raising the temperature to 40-50°C and stirring at a constant temperature for 2-4 hours; after the system pressure drops to a constant value, adding isopropanol to terminate the reaction, and then removing the solvent and low molecular weight substances by vacuum distillation to obtain the product.

[0022] By employing the above technical solution, N,N,N',N'-tetramethylethylenediamine is introduced as a polarity modifier into the anionic polymerization system, primarily to alter the polarity of the active center, thereby encouraging the monomer to undergo a 1,2-addition reaction. This process control method is beneficial for adjusting the microstructure and molecular weight distribution of the product, obtaining materials with the desired vinyl content.

[0023] Preferably, the bridging agent dry powder masterbatch is composed of liquid trimethylolpropane trimethacrylate and hydrophilic fumed silica.

[0024] By adopting the above technical solution, the high specific surface area and porous characteristics of fumed silica are used to adsorb liquid trimethylolpropane trimethacrylate, thereby transforming the originally liquid additive into a dry powder state. This avoids the volatilization, uneven dispersion, and self-agglomeration that may occur when liquid multifunctional monomers directly enter the extruder.

[0025] Preferably, the preparation method of the bridging agent dry powder masterbatch includes: putting liquid trimethylolpropane trimethacrylate and hydrophilic fumed silica in a mass ratio of 7:3 into a high-speed mixer and shearing and mixing at 2000 rpm for 15 minutes at 25°C.

[0026] By adopting the above technical solution, and through this mass ratio and high-shear mixing at room temperature, the liquid monomer can better enter the silica pores and form a flowable powder, which is more conducive to accurate metering in actual production. When the material enters the extruder and is subjected to melt shearing, the internal monomers will be gradually released, continuously providing reactants for the grafting reaction at the interface.

[0027] Preferably, the specific process parameters in steps S1 and S2 are as follows: In step S1, high-shear mixing and pre-expansion heating are carried out in a high-speed kneader, with the blade speed set at 800-1000 rpm, and the actual material temperature of the system controlled at 80-90℃, and kneading is continued for 15-20 minutes; In step S2, mixing is carried out in a mixer, and mixing is carried out at 25-60℃ and a speed of 300 rpm for 5-10 minutes.

[0028] By adopting the above technical solution, the temperature and rotation speed conditions set in step S1 are conducive to the expansion of the pores of waste rubber powder under heating and shearing, thereby driving the penetration of liquid polybutadiene; while step S2 uses a lower temperature and rotation speed for mixing, mainly to prevent unnecessary physical agglomeration of the matrix resin due to excessive frictional heat.

[0029] Preferably, the specific process parameters for the dynamic vulcanization reaction in step S3 are as follows: the screw speed of the twin-screw extruder is set to 300-400 rpm; the temperature of the first to third zones of the barrel is set to 160-170℃; and the temperature of the fourth to seventh zones of the barrel is set to 195-205℃.

[0030] By adopting the above technical solution and setting the temperature of each zone of the extruder in a stepped manner, the polypropylene matrix gradually melts and initially mixes with the other components when the material passes through the first to third zones. After entering the fourth to seventh zones, the ambient temperature reaches the range where the initiator decomposes more rapidly, and the rubber phase undergoes a dynamic vulcanization reaction under the high shear of the twin-screw extruder. This stepwise temperature control method is beneficial for controlling the final size of the rubber particles.

[0031] Preferably, the specific process parameters for devolatilization and extrusion in step S4 are as follows: the side feed port is located in the eighth zone of the twin-screw extruder, and the temperature of the eighth zone is maintained at 190-195℃; the vacuum devolatilization zone is located in the ninth to eleventh zones of the twin-screw extruder, the temperature is set at 180-190℃, and the vacuum degree is controlled at -0.08 to -0.09MPa.

[0032] By adopting the above technical solution, antioxidants are added through side feeding in the cooling section at the rear of the extruder, and combined with the subsequent vacuum devolatilization operation, small molecule volatiles and residual monomers generated by the decomposition of the initiator can be extracted from the system. This is of substantial help in reducing the odor and volatile emission of the product.

[0033] This invention provides a method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification. It has the following beneficial effects:

[0034] 1. This invention employs a high-shear pre-swelling technique using liquid high-vinyl polybutadiene and a peroxide initiator to treat waste ethylene propylene diene monomer (EPDM) rubber powder. This achieves the technical effect of allowing reactive dienes to penetrate into the micropores of the waste rubber powder, forming an interwoven network through in-situ cross-linking polymerization during subsequent extrusion heating, thus reconstructing the internal structural strength of the waste rubber powder. Compared to existing technologies that involve direct physical blending or plasticization with conventional non-reactive oils, this invention overcomes the shortcomings of these methods, which fail to establish new cross-linking bonds within the waste rubber powder, resulting in poor compatibility of the blended system and a significant decrease in the mechanical properties of the finished product.

[0035] 2. This invention employs a technical solution of introducing a dry powder masterbatch containing a multi-double-bond bridging agent into the continuous phase of polypropylene. This achieves the technical effect of the bridging agent at the interface preferentially undergoing an addition reaction with diffused free radicals, simultaneously grafting polypropylene molecular chains onto the rubber phase. Compared to the existing technology of directly performing dynamic peroxide vulcanization within the polypropylene matrix, this invention overcomes the shortcomings of initiators easily attacking the tertiary carbon atoms of the polypropylene main chain, causing severe chain scission and degradation, which leads to the material losing melt strength and basic load-bearing capacity.

[0036] 3. This invention employs a technical solution of forcibly introducing a compounded antioxidant through a side feed port downstream of the dynamic vulcanization reaction zone of the extruder. This achieves the technical effect of introducing the antioxidant after the rubber phase crosslinking is basically completed and the concentration of free radicals in the system has decreased, thus preserving its effective activity. Compared with the existing technology that mixes and adds the antioxidant and initiator at the front end of the extruder in one go, this invention solves the problem that phenolic antioxidants are prone to prematurely engaging in competitive hydrogen abstraction reactions with free radicals, causing mutual consumption of additives and a sharp shortening of the thermo-oxidative stability period of the blend. Attached Figure Description

[0037] Figure 1The following are rheological performance and matrix degradation verification test diagrams of the test examples of the present invention, wherein (a) is a bar graph of melt flow rate distribution of some examples and comparative examples, and (b) is a graph showing the relationship between complex viscosity and angular frequency of the samples of Example 1 and Comparative Example 4.

[0038] Figure 2 The following are test diagrams for verifying the crosslinking network and antioxidant retention rate of the test examples of the present invention. (a) is a comparative distribution diagram of gel content of some examples and comparative examples, and (b) is a differential scanning calorimetry oxidation induction period test curve of the samples of Example 1 and Comparative Example 3 under constant temperature conditions of 200℃.

[0039] Figure 3 The diagram shows the evolution of macroscopic static mechanical properties and phase verification test results of the test examples of this invention. (a) shows the tensile strength and 100% constant elongation stress columnar distribution of each evaluation specimen, and (b) shows the typical engineering stress-strain response curves of Example 1 and the core comparative material under uniaxial tension.

[0040] Figure 4 This is a test diagram for the macroscopic application verification of constant compressive permanent deformation rate in the test examples of this invention. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0043] Waste EPDM rubber powder is produced by mechanically crushing automotive sealing strip waste at room temperature. It has not undergone chemical desulfurization and degumming treatment, and its particle size ranges from 40 to 60 mesh.

[0044] The virgin polypropylene is an isotactic polypropylene homopolymer, which can be made from polypropylene resin of grade T30S produced by China Petroleum & Chemical Corporation (CAS No. 9003-07-0). Its isotacticity is greater than or equal to 95%, the melt flow rate at 230℃ and 2.16 kg load is 2.0-5.0 g / 10 min, and the density is 0.90-0.91 g / cm³. 3 .

[0045] Virgin ethylene propylene diene monomer (EPDM) rubber is a random copolymer of ethylene, propylene, and 5-ethylidene-2-norbornene. It can be produced by Dow Chemical under the brand name NORDEL IP 4760P, CAS number 25038-36-2, in which the mass fraction of ethylene is 60%-70%, the mass fraction of 5-ethylidene-2-norbornene is 4%-5%, and its Mooney viscosity ML(1+4) at 125℃ is 40-60.

[0046] The CAS number for bis(tert-butylperoxyisopropyl)benzene is 25155-25-3, and its purity is greater than or equal to 96%.

[0047] The CAS number for trimethylolpropane trimethacrylate is 3290-92-4, and its purity is greater than or equal to 95%.

[0048] Fumed silica is hydrophilic with a specific surface area of ​​180-220 m². 2 / g, CAS number is 112945-52-5.

[0049] The CAS number for pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 6683-19-8, and its purity is greater than or equal to 98%.

[0050] The CAS number for tris(2,4-di-tert-butylphenyl) phosphite is 31570-04-4, and its purity is greater than or equal to 99%.

[0051] 1,3-Butadiene is of polymer grade, CAS number 106-99-0, with a purity greater than or equal to 99.5%.

[0052] Cyclohexane, CAS number 110-82-7, was purified by dehydration using 4A molecular sieves.

[0053] The CAS number for N,N,N',N'-tetramethylethylenediamine is 110-18-9, and its purity is greater than or equal to 99%.

[0054] The n-butyllithium is a cyclohexane solution of n-butyllithium with a concentration of 2.5 mol / L and CAS number 109-72-8.

[0055] Preparation Example 1:

[0056] This preparation example provides a method for preparing liquid high-vinyl polybutadiene, including the following steps:

[0057] 1. In an anhydrous and oxygen-free stainless steel reactor protected by high-purity nitrogen, add 500.0 parts by weight of cyclohexane purified by dehydration through 4A molecular sieve, and then introduce 100.0 parts by weight of 1,3-butadiene monomer.

[0058] 2. Add 3.5 parts by weight of N,N,N',N'-tetramethylethylenediamine as a polarity modifier.

[0059] 3. Adjust the temperature of the reactor to 35°C and inject 1.6 parts by mass of n-butyllithium (introduced by adding its cyclohexane solution based on the purity of the active ingredient) as an initiator.

[0060] 4. Heat the reaction system to 45°C and stir for 3 hours.

[0061] 5. Once the pressure of the reaction system has decreased to a constant level, add 5.0 parts by mass of isopropanol to terminate the anionic polymerization reaction.

[0062] 6. The terminated mixture was transferred to a distillation apparatus. Under reduced pressure distillation conditions of -0.09 MPa and 80°C, cyclohexane solvent and unreacted low-molecular-weight substances were completely removed, yielding a pale yellow, transparent liquid high-vinyl polybutadiene. Gel permeation chromatography and 1H NMR spectroscopy determined the polymer's number-average molecular weight to be 4050, with a 1,2-vinyl structure mass fraction of 68%.

[0063] Preparation Example 2:

[0064] This preparation example provides a method for preparing liquid high-vinyl polybutadiene, including the following steps:

[0065] 1. In an anhydrous and oxygen-free stainless steel reactor protected by high-purity nitrogen, add 500.0 parts by weight of cyclohexane purified by dehydration through 4A molecular sieve, and then introduce 100.0 parts by weight of 1,3-butadiene monomer.

[0066] 2. Add 2.0 parts by weight of N,N,N',N'-tetramethylethylenediamine as a polarity modifier.

[0067] 3. Adjust the temperature of the reactor to 30°C and inject 2.1 parts by mass of n-butyllithium (introduced by adding its cyclohexane solution based on the purity of the active ingredient) as an initiator.

[0068] 4. Heat the reaction system to 40°C and stir for 2 hours.

[0069] 5. Once the pressure of the reaction system has decreased to a constant level, add 5.0 parts by mass of isopropanol to terminate the reaction.

[0070] 6. The terminated mixture was subjected to vacuum distillation at -0.09 MPa and 80°C to remove the solvent and low molecular weight substances, yielding a slightly yellow, transparent liquid high-vinyl polybutadiene. The number-average molecular weight of the obtained polymer was determined to be 3050, and the mass fraction of the 1,2-vinyl structure was 61%.

[0071] Preparation Example 3:

[0072] This preparation example provides a method for preparing liquid high-vinyl polybutadiene, including the following steps:

[0073] 1. In an anhydrous and oxygen-free stainless steel reactor protected by high-purity nitrogen, add 500.0 parts by weight of cyclohexane purified by dehydration through 4A molecular sieve, and then introduce 100.0 parts by weight of 1,3-butadiene monomer.

[0074] 2. Add 5.0 parts by weight of N,N,N',N'-tetramethylethylenediamine as a polarity modifier.

[0075] 3. Adjust the temperature of the reactor to 40°C and inject 1.3 parts by mass of n-butyllithium (introduced by adding its cyclohexane solution based on the purity of the active ingredient) as an initiator.

[0076] 4. Heat the reaction system to 50°C and stir for 4 hours.

[0077] 5. Once the pressure of the reaction system has decreased to a constant level, add 5.0 parts by mass of isopropanol to terminate the reaction.

[0078] 6. The mixture was subjected to vacuum distillation at -0.09 MPa and 80°C to remove the solvent, yielding a slightly yellow, transparent liquid high-vinyl polybutadiene. The number-average molecular weight of the obtained polymer was determined to be 4950, and the mass fraction of 1,2-vinyl structure was 76%.

[0079] Preparation Example 4:

[0080] This preparation example provides a method for preparing bridging agent dry powder masterbatch, including the following steps:

[0081] 70.0 parts by weight of liquid trimethylolpropane trimethacrylate and 30.0 parts by weight of hydrophilic fumed silica were added to a high-speed mixer and sheared at 2000 rpm for 15 minutes at room temperature of 25°C to allow the liquid active monomer to be completely adsorbed by the micropores of the fumed silica, thus obtaining a white powdery bridging agent dry powder masterbatch with good free flow.

[0082] Example 1:

[0083] This embodiment provides a method for preparing thermoplastic vulcanizate based on waste EPDM rubber, including the following steps:

[0084] 1. Weigh 38.0 parts by weight of waste EPDM rubber powder, 20.0 parts by weight of liquid high vinyl polybutadiene prepared from Preparation Example 1, and 1.0 parts by weight of bis(tert-butylperoxyisopropyl)benzene, put them into a high-speed kneader, set the blade speed to 850 rpm, control the actual material temperature of the system at 85°C, knead for 18 minutes and then discharge the material to obtain a pre-swollen dispersed phase system A containing an initiator.

[0085] 2. Weigh 25.0 parts by weight of virgin polypropylene, 15.0 parts by weight of virgin EPDM rubber and 3.5 parts by weight of the bridging agent dry powder masterbatch prepared in Preparation Example 4, put them into a mixer, and mix them at 300 rpm for 8 minutes at 40°C to obtain a uniformly coated continuous phase system B.

[0086] 3. System A and System B are fed into the main feed port of a co-rotating twin-screw extruder simultaneously using two independent loss-in-weight feeders, according to their respective masses. The extruder screw speed is set to 350 rpm, and the temperature of the first to third barrel zones is set to 165℃; the temperature of the fourth to seventh barrel zones is set to 200℃ for dynamic vulcanization reaction.

[0087] 4. Weigh 0.8 parts by weight of pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.5 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite and mix them evenly as system C. When the material enters the eighth zone of the extruder, the side feeder is used to force system C into the barrel. The temperature of the eighth zone is maintained at 193°C.

[0088] 5. The material then enters the ninth to eleventh zones of the extruder, where the temperature is set to 185℃. The vacuum exhaust port on the barrel is opened to control the vacuum degree at -0.085MPa for vacuuming and devolatilization. Finally, the melt is extruded through a multi-hole die head and dried by underwater pelletizing to obtain thermoplastic vulcanized rubber granules.

[0089] Example 2:

[0090] This embodiment provides a method for preparing thermoplastic vulcanizate based on waste EPDM rubber, including the following steps:

[0091] 1. Weigh 30.0 parts by weight of waste EPDM rubber powder, 15.0 parts by weight of liquid high vinyl polybutadiene prepared in Preparation Example 1, and 0.5 parts by weight of bis(tert-butylperoxyisopropyl)benzene, put them into a high-speed kneader, set the blade speed to 800 rpm, control the actual material temperature of the system at 80°C, knead for 15 minutes and then discharge the material to obtain a pre-swollen dispersed phase system A containing an initiator.

[0092] 2. Weigh 20.0 parts by weight of virgin polypropylene, 10.0 parts by weight of virgin EPDM rubber and 2.0 parts by weight of the bridging agent dry powder masterbatch prepared in Preparation Example 4, put them into a mixer, and mix them at 300 rpm for 5 minutes at 25°C to obtain a uniformly coated continuous phase system B.

[0093] 3. Feed system A and system B into the main feed port of the co-rotating twin-screw extruder separately using independent loss-in-weight feeders. Set the extruder screw speed to 300 rpm, the barrel temperature from zone 1 to zone 3 to be 160℃, and the barrel temperature from zone 4 to zone 7 to be 195℃.

[0094] 4. Weigh 0.5 parts by mass of pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.3 parts by mass of tris(2,4-di-tert-butylphenyl) phosphite and mix them evenly to form system C. Use a side feeder to force system C into the barrel in the eighth zone of the extruder, and maintain the temperature of the eighth zone at 190°C.

[0095] 5. The material then enters the ninth to eleventh zones of the extruder, where the temperature is set to 180℃ and the vacuum degree is controlled at -0.08MPa for vacuum devolatilization. Finally, it is extruded, pelletized, and dried to obtain thermoplastic vulcanized rubber granules.

[0096] Example 3:

[0097] This embodiment provides a method for preparing thermoplastic vulcanizate based on waste EPDM rubber, including the following steps:

[0098] 1. Weigh 45.0 parts by weight of waste EPDM rubber powder, 25.0 parts by weight of liquid high vinyl polybutadiene prepared from Preparation Example 1, and 1.5 parts by weight of bis(tert-butylperoxyisopropyl)benzene, put them into a high-speed kneader, set the blade speed to 1000 rpm, control the actual material temperature of the system at 90°C, knead for 20 minutes and then discharge the material to obtain a pre-swollen dispersed phase system A containing an initiator.

[0099] 2. Weigh 30.0 parts by weight of virgin polypropylene, 20.0 parts by weight of virgin EPDM rubber and 5.0 parts by weight of the bridging agent dry powder masterbatch prepared in Preparation Example 4, put them into a mixer, and mix them at 60°C and 300 rpm for 10 minutes to obtain a uniformly coated continuous phase system B.

[0100] 3. Feed system A and system B into the main feed port of the co-rotating twin-screw extruder separately using independent loss-in-weight feeders. Set the extruder screw speed to 400 rpm, the barrel temperature from zone 1 to zone 3 to 170℃, and the barrel temperature from zone 4 to zone 7 to 205℃.

[0101] 4. Weigh 1.0 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 0.8 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite and mix them evenly to form system C. Use a side feeder to force system C into the barrel in the eighth zone of the extruder, and maintain the temperature of the eighth zone at 195°C.

[0102] 5. The material then enters the ninth to eleventh zones of the extruder, where the temperature is set at 190℃ and the vacuum degree is controlled at -0.09MPa for vacuum devolatilization. Finally, it is extruded, pelletized, and dried to obtain thermoplastic vulcanized rubber granules.

[0103] Example 4:

[0104] This embodiment provides a method for preparing thermoplastic vulcanizate based on waste EPDM rubber, including the following steps:

[0105] The preparation steps and process parameters in this embodiment are exactly the same as in Example 1. The only difference is that the liquid high-vinyl polybutadiene used is the polymer obtained from Preparation Example 2. The other raw material types, proportions, and extrusion temperatures are consistent with those in Example 1, and finally, thermoplastic vulcanized rubber granules are obtained.

[0106] Example 5:

[0107] This embodiment provides a method for preparing thermoplastic vulcanizate based on waste EPDM rubber, including the following steps:

[0108] The preparation steps and process parameters in this embodiment are exactly the same as those in Example 1. The only difference is that the liquid high-vinyl polybutadiene used is the polymer obtained from Preparation Example 3. The other raw material types, proportions, and extrusion temperatures are consistent with those in Example 1, and finally, thermoplastic vulcanized rubber granules are obtained.

[0109] Comparative Example 1:

[0110] Compared with Example 1, the difference is that the liquid high-vinyl polybutadiene in System A is replaced by an equal mass of non-reactive conventional paraffin-based rubber purification oil, while the rest are the same.

[0111] Comparative Example 2:

[0112] Compared to Example 1, the difference is that the capillary latent pre-swelling step in System A is omitted. Waste EPDM rubber powder, liquid high-vinyl polybutadiene, and bis(tert-butylperoxyisopropyl)benzene are directly mixed with the components in System B at room temperature and then added all at once from the main feed port of a co-rotating twin-screw extruder. All other aspects are the same.

[0113] Comparative Example 3:

[0114] Compared with Example 1, the difference is that the side feeding process is cancelled, and pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite in system C are directly added to system B during the mixing stage and fed into the extruder from the main feed port. All other aspects are the same.

[0115] Comparative Example 4:

[0116] The difference from Example 1 is that no bridging agent dry powder masterbatch was added to System B, while all other aspects are the same.

[0117] Comparative Example 5:

[0118] Compared with Example 1, the difference is that the amount of waste EPDM rubber powder added is increased to 60.0 parts by mass, and the amount of the remaining components in System A is increased proportionally, while the rest are the same.

[0119] Test Example 1:

[0120] Test objective: To verify the inhibitory effect of the bridging agent on the degradation of continuous polypropylene and its macroscopic rheological influence in the reaction system.

[0121] The testing steps are as follows:

[0122] 1. The thermoplastic vulcanized rubber granules prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were selected as test objects and dried in a vacuum oven at 80°C for 4 hours to remove surface adsorbed moisture. According to ISO 1133 standard, the melt flow rate of each sample was measured using a melt flow rate meter at 230°C and a load of 2.16 kg. The mass of the extruded sample within the same time interval was recorded, and the data was converted and recorded in g / 10 min. Each sample was tested in parallel three times, and the arithmetic mean was taken.

[0123] 2. The granular materials from Examples 1 to 5 and Comparative Examples 1 to 5 were preheated on a flat vulcanizing machine at 200°C and pressed into disc-shaped test strips with a diameter of 25 mm and a thickness of approximately 1.5 mm. The test strips were placed between the parallel plate clamps of a rotational rheometer. Under nitrogen protection, the test temperature was set to 200°C, and the strain was controlled within the linear viscoelastic region of the sample. The angular frequency scan range was set to 0.1 to 100 rad / s. The change of the complex viscosity of the system with the angular frequency was continuously recorded, and the complex viscosity value at a low frequency of 0.1 rad / s was extracted for quantitative comparison.

[0124] The specific test data is shown in Table 1.

[0125] Table 1: Rheological performance test data of the examples and comparative examples

[0126] Sample number Melt flow rate (g / 10min) Complex viscosity (Pa·s) at 0.1 rad / s Example 1 3.14 8542.6 Example 2 2.67 9124.3 Example 3 4.32 7635.8 Example 4 3.41 8211.5 Example 5 2.95 8856.1 Comparative Example 1 4.86 6231.4 Comparative Example 2 8.35 4512.7 Comparative Example 3 5.21 5874.9 Comparative Example 4 27.83 1243.2 Comparative Example 5 1.18 15438.5

[0127] Conclusion: Based on Table 1 and Figure 1Based on the data and the physicochemical mechanism of this scheme, it can be found that Comparative Example 4, without the addition of a bridging agent, exhibits extremely abnormal rheological behavior under the same processing conditions. Its melt flow rate soars to 27.83 g / 10 min, while the low-frequency complex viscosity drops precipitously. In a normal twin-screw extrusion blending environment, polypropylene itself has relatively stable melt strength. However, in the presence of a peroxide initiator, primary free radicals rapidly capture tertiary C and H atoms from the polypropylene backbone at high temperatures, initiating an irreversible β-chain scission degradation reaction, resulting in the macromolecular chain segments being cut into low-molecular-weight oligomers. The macroscopic viscosity loss and excessive fluidity exhibited by Comparative Example 4 directly confirm that the continuous phase of polypropylene is completely destroyed without protection. Such materials will completely lose their molding ability and structural strength in actual industrial production.

[0128] In stark contrast, the melt flow rates of the example series samples remained stable within the normal process range of 2.6 to 4.4 g / 10 min, and the complex viscosity remained at a high level, exhibiting typical long-chain entanglement and polymer network characteristics within the material. The formulation system of the examples incorporated dry powder masterbatch encapsulated with liquid trimethylolpropane trimethacrylate. This multifunctional active monomer was abundant at the phase interface, and the polar methacrylate double bonds it contained exhibited an addition reaction activation energy far lower than the hydrogen abstraction activation energy of the tertiary carbon atoms in polypropylene when faced with free radical attack. The viscosity maintenance observed in the tests was precisely due to this difference in reaction rates at the kinetic level, forcing free radicals to preferentially react with the bridging agent at the interface, thus acting as a "sacrificial anode" to block polypropylene degradation at the microscale.

[0129] The significant difference in rheological data between the examples and the comparative examples further illustrates the effectiveness of this spatial isolation and kinetic priority matching mechanism. In the dynamic frequency sweep curves, Example 1 maintained excellent melt elasticity and strength in the low-frequency region. This not only confirms the integrity of the continuous phase macromolecular chains but also suggests the successful construction of a cross-phase chemically interlocked network between the waste rubber dispersed phase and the polypropylene matrix through a bridging agent. By measuring changes in conventional rheological parameters to deduce the evolution of micro-segments, the performance fluctuation interference caused by simply relying on formulation fine-tuning in the past was eliminated. This fundamentally confirms the engineering feasibility of this invention in addressing the shortcomings of traditional waste rubber powder modification systems through the intervention of reactive components.

[0130] Test Example 2:

[0131] Test objective: To verify the effects of pre-swelling process and spatiotemporal isolation of side feeding on crosslinking network construction and additive retention rate in the reaction system.

[0132] The testing steps are as follows:

[0133] 1. The thermoplastic vulcanized rubber granules prepared in Example 1 and Comparative Examples 1 to 3 were used as test objects. Approximately 2.0 g of sample was accurately weighed using an analytical balance with an accuracy of 0.1 mg, wrapped in a pre-weighed 120-mesh stainless steel wire mesh, and sealed. The wrapped sample was placed in a Soxhlet extractor, and analytical grade xylene was used as the solvent for continuous extraction under reflux for 24 hours. After extraction, the metal mesh was removed and dried to constant weight in a vacuum oven at 120°C. The gel content of each sample was obtained by calculating the ratio of the mass of insoluble matter before and after extraction to the total mass of polymer components in the initial sample. Each group of samples was subjected to three parallel experiments, and the mean value was recorded.

[0134] 2. Sample slices from Examples 1 to 3 and Comparative Examples 1 to 3 were used as test subjects, and the oxidation induction period of the samples was determined using a differential scanning calorimeter. Approximately 10.0 mg of sample was placed in the sample cell of the instrument, and high-purity nitrogen gas was introduced at a flow rate of 50 mL / min. The system was heated to 200°C at a heating rate of 20°C / min and held at this temperature for 5 minutes to eliminate thermal history. Subsequently, the gas path was quickly switched to pure oxygen at the same flow rate, and time and heat flow signals were recorded simultaneously. During the isothermal oxidation process, the polymer chain segments undergo an autocatalytic oxidation reaction, releasing heat. The time interval from switching to oxygen to the point where a significant exothermic peak extrapolated on the curve was recorded and defined as the oxidation induction period.

[0135] The specific test data is shown in Table 2.

[0136] Table 2: Crosslinking and thermo-oxidative stability test data of the examples and comparative examples

[0137] Sample number Gel content (%) Oxidation induction period at 200℃ (min) Example 1 67.8 42.5 Example 2 64.3 38.2 Example 3 71.5 46.1 Comparative Example 1 42.1 41.8 Comparative Example 2 47.6 40.3 Comparative Example 3 36.3 11.2

[0138] Conclusion: Based on Table 2 and Figure 2Data shows that conventional physical blending is insufficient to establish new cross-linking bonds within waste rubber, and the gel content in Example 1 is significantly higher than that in Comparative Examples 1 and 2. Boiling xylene can fully swell the polypropylene matrix and extract uncross-linked polymeric segments and small-molecule oils. In Comparative Example 1, conventional paraffin oil was used as a plasticizer. Since oils lack reactivity, they are released into the solvent along with the uncross-linked polypropylene during extraction, resulting in a lower overall insoluble content. While Comparative Example 2 retained reactive components, the elimination of the pre-swelling step prevented liquid high-vinyl polybutadiene from penetrating the micropores of the waste rubber powder. Reactions mostly occurred at phase interfaces or even in the continuous phase, and the resulting isolated networks were prone to detachment or disintegration during extraction. Example 1 uses a premixing process at a specific temperature to allow monomers and initiators to enter the pores of the rubber powder in advance for physical latency. Subsequently, in-situ polymerization is carried out in the high-temperature zone of the extruder to form an interpenetrating network, transforming the original dead zone of waste rubber into an active crosslinking core that can withstand solvent scouring. The difference in extraction retention rate can confirm the role of the pretreatment process in constructing the overall physical and mechanical framework.

[0139] In a comparative examination of the antioxidant action process, it was found that in Comparative Example 3, where all additives were dry-mixed at the front end, not only did the gel content drop to the lowest level, but its oxidation induction period was also drastically shortened to 11.2 minutes. This reflects a serious problem of mutual consumption of components in the reaction system. The sterically hindered phenolic antioxidant was designed to capture carbon free radicals and hydrogen peroxide free radicals generated by polymer chains during thermo-oxidative aging. When it is in the same thermodynamic heating space as the peroxide initiator, the easily dissociated phenolic hydroxyl hydrogen atoms in the antioxidant are preferentially taken away by the primary free radicals generated by the homolytic cleavage of the initiator. This competitive quenching reaction cuts off the free radical transport chain required for double bond crosslinking, causing the dynamic vulcanization process to terminate prematurely. At the same time, a large amount of antioxidant originally used to resist later thermo-oxidative aging is unnecessarily consumed, ultimately causing the material to rapidly enter the autocatalytic oxidation exothermic stage during DSC isothermal testing.

[0140] In this example, with the same formulation as Comparative Example 3, the antioxidant was injected into the rear section of the extruder using a side feeder by modifying the equipment structure. The oxidation induction period of the resulting sample was extended to 42.5 minutes. At this point, the material had essentially completed the assembly of the cross-linked network in the high-temperature, high-shear zone of the front section, and the free primary radicals in the system had been largely consumed by the double bonds. The antioxidant enters the melt blend at this moment, effectively avoiding competition with the initiator for hydrogen abstraction, and thus remains intact in the polypropylene matrix and the modified rubber network. The decoupling of the rheological cross-linking reaction and the small molecule diffusion fixation in time and space ensures a balance between vulcanization conversion rate and long-term thermo-oxidative stability. The test data confirms that adjusting the side feed sequence is not a simple process stacking, but a necessary means to eliminate the endogenous chemical repulsion in the reactive blend system.

[0141] Test Example 3:

[0142] Test objective: To evaluate the changes in static physical properties of thermoplastic vulcanizates at the macroscopic mechanical level due to differences in phase structure and interface regulation.

[0143] The testing steps are as follows:

[0144] 1. Collect the extruded granule samples from Examples 1 to 5, and Comparative Examples 2, 4, and 5. Place them in a forced-air drying oven at 85°C for 6 hours to eliminate the interference of moisture on the molding process. Using a standard injection molding machine, set the barrel temperature gradient to 180°C to 210°C and the mold temperature to 40°C. Inject the dried granules into dumbbell-shaped tensile test specimens conforming to ISO 37 standard and 6mm thick hardness test discs conforming to ISO 868 standard. The molded samples were then left to acclimatize at 23°C and 50% relative humidity for 24 hours.

[0145] 2. Tensile tests were performed on a universal testing machine with an initial gauge length of 25 mm. A dumbbell-shaped specimen was subjected to axial tension at a constant crosshead tensile speed of 500 mm / min. Load and displacement data were continuously recorded until the specimen fractured. Tensile strength, elongation at break, and stress at 100% strain were extracted. Simultaneously, an indentation test was performed at different positions (more than 5 mm apart) on the surface of the circular specimen using a Shore A hardness tester. The hardness reading was read after 15 seconds of indentation. All parameters were tested on five valid parallel specimens, and the average value was calculated.

[0146] The specific test data is shown in Table 3.

[0147] Table 3: Macroscopic static mechanical property test data of the examples and some comparative examples

[0148] Sample number Tensile strength (MPa) Elongation at break (%) 100% constant tensile stress (MPa) Shore A hardness Example 1 14.28 412.5 5.31 68.4 Example 2 15.16 387.2 5.68 71.5 Example 3 13.52 436.8 4.95 65.2 Example 4 12.83 391.4 5.12 69.1 Example 5 14.57 422.6 5.43 67.8 Comparative Example 2 6.45 182.3 4.15 69.5 Comparative Example 4 4.22 96.8 3.82 61.2 Comparative Example 5 3.16 114.5 2.94 57.6

[0149] Conclusion: Based on Table 3 and Figure 3The data from Examples 1 to 5, prepared under different ratio gradients and extrusion temperatures, all maintained high levels of macroscopic mechanical output. Their tensile strengths were generally stable in the range of 12.8 to 15.1 MPa, and their elongation at break exceeded 380%. The 100% elongation stress, a key parameter for evaluating the rigidity and resistance to deformation of thermoplastic elastomers, remained above 4.9 MPa in all examples, indicating the establishment of a high-density, effective cross-linking bond between the continuous polypropylene matrix and the dispersed waste rubber. Waste EPDM rubber originally had an inert surface and three-dimensional cross-linking dead zones, making it thermodynamically incompatible with highly crystalline polypropylene. This solution, through the synergistic effect of a multifunctional bridging agent and liquid high-vinyl polybutadiene, induced dense in-situ covalent bonding at the two-phase interface. During the tensile yielding stage, the macromolecular chain segments can uniformly transfer stress to the interior of the micro rubber particles through this cross-phase interface layer, avoiding early pore nucleation and fracture caused by stress concentration, and maintaining a relatively long cold stretching section after the material yields.

[0150] The lack of interfacial chemical bonding left a clear trace of damage in the stress-strain response of the comparative examples. Comparative Example 2 omitted the initial capillary pre-swelling step, causing the crosslinking precursor to remain free in the continuous phase or only adhere to the surface of the adhesive powder. When the tensile deformation reached approximately 180%, the microscopic slippage between the two phases rapidly evolved into macroscopic interfacial delamination, resulting in a precipitous drop in tensile strength to 6.45 MPa. Comparative Example 4, due to the removal of trimethylolpropane trimethacrylate (TMT), responsible for kinetic priority protection and interfacial bridging, experienced severe chain-breaking degradation of the polypropylene matrix under peroxide attack. Its matrix load-bearing capacity completely collapsed, with an elongation at break of less than 100% and a Shore hardness dropping to 61.2A due to the softening of the matrix. When subjected to external mechanical loads, such defective systems cannot form continuous stress transmission pathways due to the internal disintegration of polypropylene fragments, exhibiting highly brittle and atypical elastomer fracture characteristics.

[0151] The continuous increase in the volume fraction of the dispersed phase in the formulation system eventually reaches the critical limit of the system's phase rheology. When the amount of waste rubber powder was forcibly increased to 60 parts by mass in Comparative Example 5, the volume occupancy of the system exceeded the extreme value for maintaining the "sea-island" structure during dynamic vulcanization. At this point, the continuous polypropylene phase was forcibly torn apart and compressed into discontinuous sheets by the excessive rubber particles, resulting in a destructive phase reversal. The material exhibited low modulus and low strength characteristics similar to unvulcanized rubber, with the tensile strength dropping to a minimum of 3.16 MPa. This collapse of the data boundary physically confirms that the upper limit of 45 parts by mass in this scheme has sufficient basis for phase transformation kinetics. Only by controlling the volume fraction within a suitable range can the thermoplastic resin be ensured to coat the modified rubber network in the molten state, thereby giving the final product the dual advantages of high elasticity and reprocessability.

[0152] Test Example 4:

[0153] Test objective: To evaluate the rebound retention capability of the reaction system under different high temperature constant compression conditions and its effectiveness in meeting the dynamic application specifications of automotive sealing components.

[0154] The testing steps are as follows:

[0155] 1. Extruded granulated products from Examples 1 to 5 and Comparative Examples 1 to 4 were collected as test subjects. They were molded into standard cylindrical specimens with a diameter of 29.0 mm and a height of 12.5 mm in a flat vulcanizing machine set at 200°C. After demolding, the specimens were left to stand in a standard laboratory environment for 24 hours to release residual internal thermal stress. The initial height of the specimens in different directions was accurately measured using a thickness gauge, and the arithmetic mean was taken. The specimens were placed between parallel steel plate compression clamps, and the compression deformation was strictly limited to 25% of the original height using limiting blocks.

[0156] 2. The fixture containing the compressed specimen was placed into aging test chambers preheated to 70℃ and 100℃ respectively, and maintained continuously for 22 hours. After the specified time, the fixture was quickly removed, and the specimen was transferred to an insulated wooden board while releasing the steel plate, allowing it to recover freely at room temperature for 30 minutes. The final recovery height of the specimen was measured again, and the constant compression set rate was calculated using the ratio of the difference between the initial height of the specimen, the height of the limiting block, and the final height. The average test results of three parallel specimens were taken for each formulation condition.

[0157] The specific test data is shown in Table 4.

[0158] Table 4: Constant compressive permanent deformation rate test data of the examples and some comparative examples

[0159] Sample number Compression set at 70℃ for 22 hours (%) Compression set rate (%) at 100℃ / 22h Example 1 28.5 41.2 Example 2 31.2 44.8 Example 3 27.6 39.5 Example 4 29.8 42.6 Example 5 30.5 43.1 Comparative Example 1 62.4 78.9 Comparative Example 2 58.7 74.2 Comparative Example 3 54.3 69.8 Comparative Example 4 76.5 88.4

[0160] Conclusion: Based on Table 4 and Figure 4 The data shows that the example samples exhibited highly competitive dimensional recovery capabilities under both stringent high-temperature testing conditions. After being maintained in isothermal environments of 70°C and 100°C for 22 hours, the compression set of the examples was controlled within narrow ranges of 28% to 32% and 39% to 45%, respectively. When subjected to prolonged external force, these dynamic elastomers undergo conformational rearrangement of macromolecular chain segments to adapt to external stress. In the example system, the interpenetrating network constructed in situ from liquid high-vinyl polybutadiene and the interfacial covalent bonds induced by the bridging agent form a robust elastic recovery framework. When the external force is removed, the micro-crosslinking points act as anchoring hubs distributed in the matrix, causing the displaced polymer chains to rapidly retract along their original topology, thereby counteracting the irreversible plastic slip phenomenon caused by thermal excitation.

[0161] The comparative sample lacking interfacial coupling and matrix protection mechanisms underwent destructive permanent deformation under high temperature and pressure, with the deformation rate of Comparative Example 4 climbing to 88.4% at 100℃. During peroxide-induced degradation, the polypropylene matrix lost its necessary molecular weight and melt strength, transforming into a low-strength oligomer matrix. When external compressive stress and a thermal field act simultaneously, unconstrained waste rubber particles undergo macroscopic displacement in the softened continuous phase; the truncated polypropylene chains cannot provide sufficient modulus to resist this creep. Even after the external load is removed, the remaining loose physical entanglement within the system is insufficient to drive the material back to its initial geometry, causing the component, which should have possessed high resilience, to completely solidify into a compressed, flat structure.

[0162] In the actual operating conditions of automotive door and window sealing systems, materials need to withstand the dynamic impact and static pressure brought about by door closure over a long period of time. Compression set has become a core screening indicator for evaluating whether sealing components will fail due to water leakage or wind noise. Direct blending of waste rubber is often accompanied by a sharp decline in the elastic storage modulus of the product, which is also the underlying pain point that makes it difficult to achieve a large proportion of recycling in the industry. This solution successfully reconstructs a complete three-dimensional stress transfer network in blends containing a high proportion of waste rubber powder by spatial isolation of crosslinking kinetics and targeted implantation of reactive components. Experimental results confirm that this modified material has overcome the inherent creep resistance disadvantage of recycled rubber products, integrates the advantages of thermoplastic processing with high-end dynamic sealing requirements, and has the technical feasibility of directly replacing virgin thermoplastic vulcanized rubber in the automotive supply chain.

[0163] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing thermoplastic vulcanizate for automotive sealing strips based on waste EPDM modification, characterized in that, Includes the following steps: S1. By weight, 30.0-45.0 parts of waste EPDM rubber powder, 15.0-25.0 parts of liquid high-vinyl polybutadiene, and 0.5-1.5 parts of peroxide initiator are subjected to high-shear mixing and pre-swelling heating to obtain pre-swelled dispersed phase system A; the preparation method of the liquid high-vinyl polybutadiene includes: In an anhydrous and oxygen-free environment with a protective gas, cyclohexane was mixed with 1,3-butadiene monomer, and N,N,N',N'-tetramethylethylenediamine was added as a polarity modifier. After adjusting the temperature to 30-40℃, inject the n-butyllithium initiator, then raise the temperature to 40-50℃ and stir the reaction at a constant temperature for 2-4 hours; After the system pressure drops to a constant level, isopropanol is added to terminate the reaction. Then, the solvent and low molecular weight substances are removed by vacuum distillation to obtain the final product. S2. By weight, 20.0-30.0 parts of virgin polypropylene, 10.0-20.0 parts of virgin ethylene propylene diene monomer (EPDM) rubber, and 2.0-5.0 parts of bridging agent dry powder masterbatch are mixed evenly to obtain continuous phase system B; the bridging agent dry powder masterbatch is composed of liquid trimethylolpropane trimethacrylate and hydrophilic fumed silica. S3. System A and System B are simultaneously added to the main feed port of a twin-screw extruder for melt blending and dynamic vulcanization reaction. S4. By weight, 0.5-1.0 parts of the first antioxidant and 0.3-0.8 parts of the second antioxidant are mixed evenly to form system C. After the dynamic vulcanization reaction, system C is forced into the barrel at the side feed port downstream of the main feed port of the twin-screw extruder for further blending. Then, vacuum devolatilization and extrusion pelletizing are performed to obtain the thermoplastic vulcanized rubber.

2. The method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification according to claim 1, characterized in that, The weight proportions of each raw material component are as follows: 38.0 parts of waste EPDM rubber powder, 20.0 parts of liquid high-vinyl polybutadiene, and 1.0 part of peroxide initiator; Virgin polypropylene 25.0 parts, virgin EPDM rubber 15.0 parts, bridging agent dry powder masterbatch 3.5 parts; 0.8 parts of the first antioxidant and 0.5 parts of the second antioxidant.

3. The method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification according to claim 1, characterized in that, The peroxide initiator is bis(tert-butylperoxyisopropyl)benzene; The first antioxidant is pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; The second antioxidant is tris(2,4-di-tert-butylphenyl) phosphite.

4. The method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification according to claim 1, characterized in that, The liquid high-vinyl polybutadiene has a number-average molecular weight of 3050-4950, and the mass fraction of the 1,2-vinyl structure in the liquid high-vinyl polybutadiene is 61%-76%.

5. The method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification according to claim 1, characterized in that, The preparation method of the bridging agent dry powder masterbatch includes: Liquid trimethylolpropane trimethacrylate with a mass ratio of 7:3 and hydrophilic fumed silica were added to a high-speed mixer and sheared and mixed at 2000 rpm for 15 minutes at 25°C.

6. The method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification according to claim 1, characterized in that, The specific process parameters in steps S1 and S2 are as follows: In step S1, the high-shear mixing and heating pre-swelling are carried out in a high-speed kneader, with the blade speed set at 800-1000 rpm, the actual material temperature of the system controlled at 80-90℃, and kneading continued for 15-20 minutes. In step S2, the mixing is carried out in a mixer at 25-60°C and 300 rpm for 5-10 minutes.

7. The method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification according to claim 1, characterized in that, The specific process parameters for the dynamic vulcanization reaction in step S3 are as follows: The screw speed of the twin-screw extruder is set to 300-400 rpm; The temperature of the first to third zones of the barrel is set to 160-170℃; the temperature of the fourth to seventh zones of the barrel is set to 195-205℃.

8. The method for preparing thermoplastic vulcanizate rubber for automotive sealing strips based on waste EPDM modification according to claim 1, characterized in that, The specific process parameters for devouring and extrusion in step S4 are as follows: The side feed port is located in the eighth zone of the twin-screw extruder, and the temperature of the eighth zone is maintained at 190-195°C. The vacuum devolatilization zone is located in zones 9 to 11 of the twin-screw extruder, with the temperature set at 180-190°C and the vacuum level controlled between -0.08 and -0.09 MPa.

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