Thermoplastic elastomer prepared by supercritical fluid assisted dynamic vulcanization

Abstract

The invention relates to the technical field of preparation of high polymer materials, and discloses a method for preparing a carboxyl-containing thermoplastic elastomer by an emulsion polymerization method, which comprises the following steps: initial polymerization, middle-stage material supplementation, later-stage crosslinking and post-treatment: during initial polymerization, adding styrene, part of a regulator and part of an emulsifier into a polymerization kettle; after nitrogen displacement, adding conjugated diene and part of the initiator, and controlling the temperature to react; in the middle-stage material supplementing stage, adding part of the emulsifier and acrylonitrile under a specific conversion rate, and heating to continue the reaction; during later crosslinking, supplementing the residual raw materials and unsaturated carboxylic acid or anhydride thereof under the corresponding conversion rate, and adding a terminating agent after the temperature is controlled to react to the end point; and finally, carrying out flash evaporation degassing, antioxidant mixing, condensation, filtration dehydration and drying to obtain the product. A vulcanization system is added in stages, and the reaction environment is adjusted by virtue of supercritical fluid, so that the product performance is more stable, the compression permanent deformation rate is reduced, and the rebound resilience is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material preparation, and in particular to a thermoplastic elastomer prepared by supercritical fluid-assisted dynamic vulcanization. Background Art

[0002] Thermoplastic elastomers (TPEs), an important class of polymer materials, combine the processing characteristics of plastics with the elastic properties of rubber. They are widely used in a wide range of fields, including automotive, electrical, electronic, construction, and daily life. For example, in automotive manufacturing, they are used to manufacture seals and interior trims; in the electronic equipment sector, they are used to produce mobile phone casings and wire and cable sheaths. However, traditional methods for preparing thermoplastic elastomers have limitations in terms of performance and production efficiency.

[0003] In the traditional dynamic vulcanization process for preparing thermoplastic elastomers, achieving ideal uniformity in the dispersion of the rubber and plastic phases is difficult, resulting in limited mechanical properties of the product, such as insufficient tensile strength and tear strength. Furthermore, the vulcanization reaction is difficult to control, and over- or under-vulcanization is prone to occur, which not only affects the stability of product performance but also increases the scrap rate during production. Furthermore, traditional preparation methods typically require high processing temperatures and long processing times, resulting in high energy consumption and low production efficiency.

[0004] Therefore, developing a method for preparing thermoplastic elastomers that can overcome the above-mentioned shortcomings has important practical significance. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems and to propose a thermoplastic elastomer prepared by supercritical fluid assisted dynamic vulcanization.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization, the preparation steps including initial polymerization, mid-term feeding, late cross-linking and post-treatment, are specifically as follows:

[0008] Initial polymerization: Add styrene, part of the regulator and 50%-70% of the emulsifier into the polymerization kettle. After nitrogen pressure and vacuum replacement, add the conjugated diene. After stirring evenly, add 30%-40% of the initiator and start the emulsion polymerization reaction at 40℃-50℃.

[0009] Mid-stage feeding: When the reaction conversion rate reaches 20%-35%, add part of the emulsifier and 40%-60% of acrylonitrile, raise the temperature to 55℃-65℃ and continue the reaction;

[0010] Late crosslinking: When the reaction conversion rate reaches 50%-60%, add the remaining emulsifier, the remaining initiator, the remaining regulator, the remaining acrylonitrile and 0.5-3 parts (based on the total monomer weight) of an unsaturated carboxylic acid or its anhydride. Control the temperature at 65°C-75°C until the conversion rate reaches 85%-89%. Then add a terminator to terminate the reaction.

[0011] Post-treatment: the product is flash-evaporated and degassed, mixed with an antioxidant emulsion, and subjected to coagulation, filtration, dehydration, and drying to obtain a carboxyl-containing thermoplastic elastomer.

[0012] Preferably, the emulsifier is one or more combinations of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, potassium stearate, potassium oleate, synthetic fatty acid potassium soap, and disproportionated rosin potassium soap, and the emulsifier contains at least a compound system of sodium lauryl sulfate and disproportionated rosin potassium soap, with a compound mass ratio of 3:1.

[0013] Preferably, the conjugated diene is butadiene, the initiator is potassium persulfate, the terminator is hydroquinone, and the regulator is tert-dodecyl mercaptan, and the amount thereof is 0.3-0.6 parts (based on the total monomer mass).

[0014] Preferably, the unsaturated carboxylic acid is one of acrylic acid, methacrylic acid and itaconic acid, and the unsaturated carboxylic acid is evenly grafted onto the rubber segment molecular chain in the form of side groups in the later crosslinking stage, with a grafting rate of ≥75%.

[0015] Preferably, the amount of antioxidant emulsion used in the post-treatment is 0.5%-1% of the mass of the latex, and the coagulation step uses a mixture of 5%-10% sodium chloride aqueous solution and 3%-5% dilute sulfuric acid solution, with a volume ratio of 1:1-2:1.

[0016] Preferably, the preparation process forms a "core-shell" structure of the thermoplastic elastomer molecular chain by controlling the temperature and feeding in stages, wherein the soft segment is a butadiene segment, the hard segment is a styrene-acrylonitrile copolymer segment, and the carboxyl groups are mainly distributed in the interface area between the soft segment and the hard segment.

[0017] Preferably, the thermoplastic elastomer has a gel content of ≤4%, a tensile strength of ≥23 MPa, and a tensile strength retention rate of ≥83% after 1000 hours of artificial accelerated aging.

[0018] Preferably, the amount of the composite emulsifier of sodium lauryl sulfate and disproportionated rosin potassium soap is 3-5 parts (based on the total monomer mass), which can control the particle size of the latex particles to be 80-120 nm.

[0019] Preferably, the relationship between the amount of tert-dodecyl mercaptan used and the molecular weight distribution index (Mw / Mn) is: when the amount is 0.3-0.6 parts, Mw / Mn≤1.8.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] 1. The present invention significantly improves the dispersion of the rubber phase within the plastic matrix by introducing a supercritical fluid. Scanning electron microscopy revealed that the average particle size of the rubber particles in the thermoplastic elastomer prepared by the present invention is smaller than that prepared by conventional methods, and the particle size distribution range is narrower. This significantly enhances the mechanical properties of the product.

[0022] 2. This invention uses a phased addition of the vulcanization system and utilizes supercritical fluid to regulate the reaction environment, enabling precise control of the vulcanization reaction process. This avoids the problems of over- or under-vulcanization found in traditional methods, resulting in more stable product performance, reduced compression set, and improved rebound performance. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] Example 1

[0025] Raw materials preparation:

[0026] Plastic: Polypropylene (PP), melt flow rate 15 g / 10 min (230° C., 2.16 kg).

[0027] Rubber: EPDM, Mooney viscosity 65ML1+4 (125℃).

[0028] Curing system: dicumyl peroxide (DCP), the amount of which is 0.8% of the total mass of the material; N,N-diisopropyl-2-benzothiazolesulfenamide (DZ), the amount of which is 0.3% of the total mass of the material.

[0029] Supercritical fluid: carbon dioxide.

[0030] Preparation process:

[0031] Premixing: Add PP, EPDM and 30% of the vulcanization system in a mass ratio of 7:3:0.33 into a high-speed mixer and mix at 80°C and 500 r / min for 10 minutes.

[0032] Supercritical fluid injection and dynamic vulcanization: The premix is added to a twin-screw extruder. Supercritical carbon dioxide is injected into the barrel at a supercritical temperature of 32°C and a pressure of 8 MPa. The extruder processing temperature is controlled at 160°C and the screw speed is 300 r / min. The remaining 70% of the vulcanization system is added at a point one-third the screw length from the feed port.

[0033] Molding: After the material is extruded from the extruder, it is hot-pressed at 180°C and 10 MPa on a flat vulcanizer to obtain a thermoplastic elastomer sheet.

[0034] Performance testing:

[0035] Tensile strength test: According to GB / T528-2009 standard, the test was carried out using a universal material testing machine with a tensile speed of 500 mm / min, and the test result was 28 MPa.

[0036] Tear strength test: According to GB / T529-2008 standard, using right-angle tearing specimen, the test result is 22N / mm.

[0037] Compression set test: According to GB / T7759.1-2015 standard, under the conditions of 70℃ and 25% compression rate, the compression set rate is 12% after 24 hours of compression.

[0038] Chemical corrosion resistance test: The prepared thermoplastic elastomer sheet was immersed in a 10% sulfuric acid solution at 50° C. for 72 hours. The mass loss rate of the sheet was measured to be 3%.

[0039] Example 2

[0040] Raw materials preparation:

[0041] Plastic: Polypropylene (PP), melt flow rate 12 g / 10 min (230° C., 2.16 kg).

[0042] Rubber: EPDM, Mooney viscosity 70ML1+4 (125℃).

[0043] Curing system: dicumyl peroxide (DCP), the amount of which is 0.7% of the total mass of the material; N,N-diisopropyl-2-benzothiazolesulfenamide (DZ), the amount of which is 0.25% of the total mass of the material.

[0044] Supercritical fluid: carbon dioxide.

[0045] Preparation process:

[0046] Premixing: Add PP, EPDM and 40% vulcanization system in a mass ratio of 6:4:0.3 into a high-speed mixer and mix at 75°C and 450 r / min for 12 minutes.

[0047] Supercritical fluid injection and dynamic vulcanization: The premix is added to a twin-screw extruder. Supercritical carbon dioxide is injected into the barrel at a supercritical temperature of 33°C and a pressure of 8.5 MPa. The extruder processing temperature is controlled at 155°C and the screw speed is 280 r / min. The remaining 60% of the vulcanization system is added at a point one-quarter the screw length from the feed port.

[0048] Molding: After the material is extruded from the extruder, it is hot-pressed at 175°C and 9 MPa on a flat vulcanizer to obtain a thermoplastic elastomer sheet.

[0049] Performance testing:

[0050] Tensile strength test: According to GB / T528-2009 standard, the test was carried out using a universal material testing machine with a tensile speed of 500 mm / min, and the test result was 26 MPa.

[0051] Tear strength test: According to GB / T529-2008 standard, using right-angle tearing specimen, the test result is 20N / mm.

[0052] Compression set test: According to GB / T7759.1-2015 standard, under the conditions of 70℃ and 25% compression rate, the compression set rate is 13% after 24 hours of compression.

[0053] Chemical corrosion resistance test: The prepared thermoplastic elastomer sheet was immersed in a 10% sulfuric acid solution at 50° C. for 72 hours. The mass loss rate of the sheet was measured to be 3.5%.

[0054] Example 3

[0055] Raw materials preparation:

[0056] Plastic: Polypropylene (PP), melt flow rate 18 g / 10 min (230° C., 2.16 kg).

[0057] Rubber: EPDM, Mooney viscosity 60ML1+4 (125℃).

[0058] Curing system: dicumyl peroxide (DCP), the amount of which is 0.9% of the total mass of the material; N,N-diisopropyl-2-benzothiazolesulfenamide (DZ), the amount of which is 0.35% of the total mass of the material.

[0059] Supercritical fluid: carbon dioxide.

[0060] Preparation process:

[0061] Premixing: Add PP, EPDM and 25% vulcanization system in a mass ratio of 8:2:0.35 into a high-speed mixer and mix at 85°C and 550 r / min for 8 minutes.

[0062] Supercritical fluid injection and dynamic vulcanization: The premix is fed into a twin-screw extruder, and supercritical carbon dioxide is injected into the barrel at a supercritical temperature of 31.5°C and a pressure of 7.8 MPa. The extruder processing temperature is controlled at 165°C and the screw speed is 320 r / min. The remaining 75% of the vulcanization system is added at a point one-third the screw length from the feed port.

[0063] Molding: After the material is extruded from the extruder, it is hot-pressed at 185°C and 11 MPa on a flat vulcanizer to obtain a thermoplastic elastomer sheet.

[0064] Performance testing:

[0065] Tensile strength test: According to GB / T528-2009 standard, the test was carried out using a universal material testing machine with a tensile speed of 500 mm / min. The test result was 29 MPa.

[0066] Tear strength test: According to GB / T529-2008 standard, using right-angle tearing specimen, the test result is 23N / mm.

[0067] Compression set test: According to GB / T7759.1-2015 standard, under the conditions of 70℃ and 25% compression rate, the compression set rate is 11% after 24 hours of compression.

[0068] Chemical corrosion resistance test: The prepared thermoplastic elastomer sheet was immersed in a 10% sulfuric acid solution at 50° C. for 72 hours. The mass loss rate of the sheet was measured to be 2.8%.

[0069] Comparative Example 1

[0070] Raw material preparation: same as Example 1.

[0071] Preparation process:

[0072] Traditional dynamic vulcanization: PP, EPDM and the entire vulcanization system are directly added to the twin-screw extruder, and dynamic vulcanization is carried out at a temperature of 180°C and a screw speed of 300r / min without introducing supercritical fluid.

[0073] Molding: Same as Example 1.

[0074] Performance testing:

[0075] Tensile strength: 17MPa.

[0076] Tear strength: 14N / mm.

[0077] Compression set rate: 18%.

[0078] Chemical corrosion resistance test: mass loss rate is 8%.

[0079] Comparative Example 2

[0080] Raw material preparation: same as Example 2.

[0081] Preparation process:

[0082] Traditional dynamic vulcanization: PP, EPDM and the entire vulcanization system are directly added to the twin-screw extruder, and dynamic vulcanization is carried out at a temperature of 175°C and a screw speed of 280r / min without introducing supercritical fluid.

[0083] Molding: Same as Example 2.

[0084] Performance testing:

[0085] Tensile strength: 15MPa.

[0086] Tear strength: 13N / mm.

[0087] Compression set rate: 20%.

[0088] Chemical corrosion resistance test: mass loss rate is 8.5%.

[0089] Comparative Example 3

[0090] Raw material preparation: same as Example 3.

[0091] Preparation process:

[0092] Traditional dynamic vulcanization: PP, EPDM and the entire vulcanization system are directly added to the twin-screw extruder, and dynamic vulcanization is carried out at a temperature of 185°C and a screw speed of 320r / min without introducing supercritical fluid.

[0093] Molding: Same as Example 3.

[0094] Performance testing:

[0095] Tensile strength: 16MPa.

[0096] Tear strength: 13.5N / mm.

[0097] Compression set rate: 19%.

[0098] Chemical corrosion resistance test: mass loss rate is 8.2%.

[0099] Comparative Example 4

[0100] Raw material preparation: same as Example 1.

[0101] Preparation process:

[0102] The premixing step is the same as in Example 1; the premixed material is added to a twin-screw extruder and dynamically vulcanized at a temperature of 160°C and a screw speed of 300 r / min. Supercritical carbon dioxide is not injected during the whole process, and the vulcanization system is added all at once.

[0103] Molding: Same as Example 1.

[0104] Performance testing:

[0105] Tensile strength: 18MPa.

[0106] Tear strength: 15N / mm.

[0107] Compression set rate: 17%.

[0108] Chemical corrosion resistance test: mass loss rate is 7.5%.

[0109] Result Analysis

[0110] Comparison between Examples: Examples 1-3 demonstrate that, under the process of the present invention, by adjusting the raw material ratios, premixing conditions, and vulcanization parameters, thermoplastic elastomers with superior performance to those obtained using conventional methods can be obtained. For example, in Example 3, by increasing the amount of vulcanizing agent and adjusting the screw speed, the tensile strength reached 29 MPa, further demonstrating that the process parameters of the present invention can be flexibly adjusted to optimize product performance.

[0111] Comparison of the examples with the comparative examples reveals that all examples exhibit significantly higher tensile and tear strength than their comparative counterparts, with an average improvement exceeding 50%. Compression set is reduced by over 30%, and mass loss in chemical resistance testing is reduced by over 50%. This demonstrates that the supercritical fluid-assisted dynamic vulcanization process and the phased addition of the vulcanization system effectively improve the dispersion of rubber and plastic, precisely control the vulcanization reaction, and thus enhance the overall performance of the product.

[0112] The above description of the embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization, characterized in that: The preparation steps include initial polymerization, mid-term feeding, late cross-linking and post-processing, as follows: Initial polymerization: Add styrene, part of the regulator and 50%-70% of the emulsifier into the polymerization kettle. After nitrogen pressure and vacuum replacement, add the conjugated diene. After stirring evenly, add 30%-40% of the initiator and start the emulsion polymerization reaction at 40℃-50℃. Mid-stage feeding: When the reaction conversion rate reaches 20%-35%, add part of the emulsifier and 40%-60% of acrylonitrile, raise the temperature to 55℃-65℃ and continue the reaction; Late crosslinking: When the reaction conversion rate reaches 50%-60%, add the remaining emulsifier, the remaining initiator, the remaining regulator, the remaining acrylonitrile and 0.5-3 parts (based on the total monomer weight) of an unsaturated carboxylic acid or its anhydride. Control the temperature at 65°C-75°C until the conversion rate reaches 85%-89%. Then add a terminator to terminate the reaction. Post-treatment: the product is flash-evaporated and degassed, mixed with an antioxidant emulsion, and subjected to coagulation, filtration, dehydration, and drying to obtain a carboxyl-containing thermoplastic elastomer.

2. The thermoplastic elastomer prepared by supercritical fluid-assisted dynamic vulcanization according to claim 1, characterized in that: The emulsifier is one or more combinations of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, potassium stearate, potassium oleate, synthetic fatty acid potassium soap, and disproportionated rosin potassium soap, and the emulsifier contains at least a compound system of sodium lauryl sulfate and disproportionated rosin potassium soap, with a compound mass ratio of 3:

1.

3. The thermoplastic elastomer prepared by supercritical fluid-assisted dynamic vulcanization according to claim 1, characterized in that: The conjugated diene is butadiene, the initiator is potassium persulfate, the terminator is hydroquinone, and the regulator is tert-dodecyl mercaptan, and the amount thereof is 0.3-0.6 parts (based on the total monomer mass).

4. The thermoplastic elastomer prepared by supercritical fluid-assisted dynamic vulcanization according to claim 1, characterized in that: The unsaturated carboxylic acid is one of acrylic acid, methacrylic acid and itaconic acid, and the unsaturated carboxylic acid is evenly grafted onto the rubber segment molecular chain in the form of side groups in the later cross-linking stage, with a grafting rate of ≥75%.

5. The thermoplastic elastomer prepared by supercritical fluid assisted dynamic vulcanization according to claim 1, characterized in that: The amount of the antioxidant emulsion used in the post-treatment is 0.5%-1% of the mass of the latex. The coagulation step uses a mixture of a 5%-10% sodium chloride aqueous solution and a 3%-5% dilute sulfuric acid solution in a volume ratio of 1:1-2:

1.

6. The thermoplastic elastomer prepared by supercritical fluid-assisted dynamic vulcanization according to claim 1, characterized in that: The preparation process uses staged temperature control and material feeding to form a "core-shell" structure in the thermoplastic elastomer molecular chain, in which the soft segment is a butadiene segment, the hard segment is a styrene-acrylonitrile copolymer segment, and the carboxyl groups are mainly distributed in the interface area between the soft segment and the hard segment.

7. The thermoplastic elastomer prepared by supercritical fluid-assisted dynamic vulcanization according to claim 1, characterized in that: The gel content of the thermoplastic elastomer is ≤4%, the tensile strength is ≥23MPa, and the tensile strength retention rate after 1000 hours of artificial accelerated aging is ≥83%.

8. The thermoplastic elastomer prepared by supercritical fluid-assisted dynamic vulcanization according to claim 1, characterized in that: The dosage of the composite emulsifier of sodium lauryl sulfate and disproportionated rosin potassium soap is 3-5 parts (based on the total monomer mass), which can control the particle size of the latex particles to be 80-120 nm.

9. The thermoplastic elastomer prepared by supercritical fluid assisted dynamic vulcanization according to claim 1, characterized in that: The relationship between the amount of tert-dodecyl mercaptan used and the molecular weight distribution index (Mw / Mn) is: when the amount is 0.3-0.6 parts, Mw / Mn≤1.8.