Carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization method

Abstract

The invention relates to the technical field of thermoplastic elastomer preparation, and discloses a carboxyl-containing thermoplastic elastomer prepared by an emulsion polymerization method, which is prepared by the following steps: adding styrene, a part of a regulator and 50-70% of an emulsifier into a polymerization kettle, carrying out nitrogen pressurization-vacuum replacement, adding conjugated diene and 30-40% of an initiator, and starting a reaction at 40-50 DEG C; when the conversion rate reaches 20-35%, adding part of the emulsifier and 40-60% of acrylonitrile, heating to 55-65 DEG C, and continuing the reaction; when the conversion rate reaches 50%-60%, supplementing the remaining raw materials and 0.5-3 parts of unsaturated carboxylic acid or anhydride thereof, controlling the temperature at 65-75 DEG C until the conversion rate reaches 85%-89%, and terminating the reaction; and finally, carrying out flash evaporation degassing, antioxidant mixing, condensation, filtration dehydration and drying at 90-96 DEG C to finish post-treatment. By adopting a staged feeding and precise temperature control process, raw materials are reasonably added and the temperature is adjusted in each reaction stage, so that the molecular structure of the thermoplastic elastomer can be precisely regulated and controlled, the generation of gel is effectively reduced, and the gel content is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of thermoplastic elastomer preparation, in particular to a carboxyl-containing thermoplastic elastomer prepared by an emulsion polymerization method. Background Art

[0002] Thermoplastic elastomers (TPEs) are widely used in a wide range of fields, including automotive parts, medical devices, and electronic device casings, because they combine the processing characteristics of plastics with the elastic properties of rubber. The presence of carboxyl groups in TPEs can enhance the interaction between the material and other substances, further broadening their application range. For example, they excel in improving the interfacial compatibility of composite materials. Currently, there are various methods for preparing TPEs containing carboxyl groups, with emulsion polymerization being a more commonly used method. However, existing emulsion polymerization methods have many shortcomings in preparing TPEs containing carboxyl groups. TPEs containing carboxyl groups prepared by traditional methods often have uncontrollable molecular structures, resulting in unstable product performance. For example, during the polymerization process, the distribution of carboxyl groups on the molecular chain is relatively random, which results in large variations in the physical and mechanical properties of the material during processing, making it difficult to meet the strict performance consistency requirements of high-end products. Moreover, TPEs containing carboxyl groups prepared by existing technologies have a high gel content, which not only affects the processing fluidity of the material but also reduces the mechanical properties of the product, such as tensile strength and elongation at break.

[0003] In view of the broad application prospects of carboxyl-containing thermoplastic elastomers, it is particularly necessary to solve the above-mentioned deficiencies in the prior art. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and to propose a carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization is prepared by the following steps:

[0007] Initial polymerization: Styrene, part of the regulator and 50%-70% (based on the total weight of the emulsifier) of the emulsifier are added to the polymerization kettle. After nitrogen pressure-vacuum replacement, the conjugated diene is added. After stirring evenly, 30%-40% (based on the total weight of the initiator) of the initiator is added and the emulsion polymerization reaction is started at 40°C-50°C.

[0008] Mid-term feeding: When the reaction conversion rate reaches 20%-35%, add part of the emulsifier and 40%-60% (based on the total mass of acrylonitrile) of acrylonitrile, raise the temperature to 55℃-65℃ and continue the reaction;

[0009] Late crosslinking: When the reaction conversion rate reaches 50%-60%, add the remaining emulsifier, remaining initiator, remaining regulator and a mixture of remaining acrylonitrile and 0.5-3 parts (based on the total monomer mass) of unsaturated carboxylic acid or its anhydride, control the temperature at 65°C-75°C until the conversion rate reaches 85%-89%, and then add a terminator to terminate the reaction;

[0010] Post-treatment: Flash degas the product, mix the latex with 0.5%-1% (based on the mass of the latex) of an antioxidant emulsion, add a mixture of sodium chloride aqueous solution and dilute sulfuric acid solution to coagulate, filter and dehydrate, and then dry at 90°C-96°C to a moisture content of ≤0.5%.

[0011] Preferably, the emulsifier is one or more combinations of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, potassium stearate, potassium oleate, synthetic fatty acid potassium soap, and disproportionated rosin potassium soap.

[0012] Preferably, the conjugated diene is butadiene.

[0013] Preferably, the initiator is potassium persulfate, and the terminator is hydroquinone.

[0014] Preferably, the mass fraction of the sodium chloride aqueous solution is 5%-10%, the mass fraction of the dilute sulfuric acid solution is 3%-5%, and the volume ratio of the two is 1:1-2:1.

[0015] Preferably, the unsaturated carboxylic acid is one of acrylic acid, methacrylic acid and itaconic acid.

[0016] 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.

[0017] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0018] 1. The present invention adopts a process of staged feeding and precise control of reaction temperature. Raw materials are rationally added and the temperature is adjusted at different stages of the reaction, resulting in precise control of the molecular structure of the thermoplastic elastomer, effectively reducing gel formation and gel content, and significantly improving the processing fluidity and mechanical properties of the material, such as increasing the tensile strength by 20%-44%.

[0019] 2. The present invention introduces unsaturated carboxylic acid as the fourth monomer into the raw materials, and by rationally proportioning the amounts of the raw materials, carboxyl groups are introduced into the molecular chains of the thermoplastic elastomer, thereby enhancing the interaction between the molecular chains and the antioxidant and anti-degradation capabilities of the material, thereby greatly improving the aging resistance of the material. After 1000 hours of artificial accelerated aging, the tensile strength retention rate is increased by 10%-23%. DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0021] Example 1

[0022] Raw material preparation: 50 parts of styrene, 80 parts of butadiene, 30 parts of acrylonitrile, 1.5 parts of unsaturated carboxylic acid (acrylic acid), 5 parts of sodium lauryl sulfate (emulsifier), 0.5 parts of tert-dodecyl mercaptan (regulator), 0.8 parts of potassium persulfate (initiator), appropriate amount of hydroquinone (terminator), 1 part of antioxidant 1010 emulsion (antioxidant content is 10%), sodium chloride aqueous solution (mass fraction 8%), dilute sulfuric acid solution (mass fraction 4%).

[0023] Polymerization process:

[0024] Styrene, 0.3 parts tert-dodecyl mercaptan, and 3 parts sodium lauryl sulfate were added to a polymerization kettle. After nitrogen pressure and vacuum replacement three times, butadiene was added and stirred for 15 minutes. 0.3 parts potassium persulfate was added via a feed barrel, and emulsion polymerization was initiated at 45°C.

[0025] When the conversion rate reaches 25%, 1 part of sodium lauryl sulfate and 18 parts of acrylonitrile are added, and the temperature is raised to 60° C. to continue the reaction.

[0026] When the conversion rate reaches 55%, add the remaining 1 part of sodium lauryl sulfate, 0.5 parts of tert-dodecyl mercaptan, 0.5 parts of potassium persulfate, the remaining 12 parts of acrylonitrile and 1.5 parts of acrylic acid, control the temperature at 70°C, and react until the conversion rate reaches 87%. Add an appropriate amount of hydroquinone to terminate the reaction.

[0027] The reaction product was flash degassed, and the latex was mixed with 1 part of an antioxidant 1010 emulsion. Then, a sodium chloride aqueous solution and a dilute sulfuric acid solution were added in a volume ratio of 1.5:1 for coagulation. After filtration and dehydration, the mixture was dried at 93°C to a moisture content of 0.3% to obtain a carboxyl-containing thermoplastic elastomer.

[0028] Example 2

[0029] Raw material preparation: 40 parts of styrene, 90 parts of butadiene, 20 parts of acrylonitrile, 2 parts of unsaturated carboxylic acid (methacrylic acid), 6 parts of sodium dodecylbenzenesulfonate (emulsifier), 0.6 parts of tert-dodecyl mercaptan (regulator), 0.9 parts of potassium persulfate (initiator), appropriate amount of hydroquinone (terminator), 1.2 parts of antioxidant 1010 emulsion (antioxidant content is 10%), sodium chloride aqueous solution (mass fraction 7%), dilute sulfuric acid solution (mass fraction 3%).

[0030] Polymerization process:

[0031] Styrene, 0.4 parts of tert-dodecyl mercaptan, and 4 parts of sodium dodecylbenzenesulfonate were added to a polymerization kettle. After nitrogen pressure and vacuum replacement three times, butadiene was added and stirred for 15 minutes. 0.4 parts of potassium persulfate was added through the feed barrel, and emulsion polymerization was initiated at 42°C.

[0032] When the conversion rate reached 22%, 1.5 parts of sodium dodecylbenzenesulfonate and 12 parts of acrylonitrile were added, and the temperature was raised to 58° C. to continue the reaction.

[0033] When the conversion rate reaches 52%, the remaining 0.5 parts of sodium dodecylbenzenesulfonate, 0.6 parts of tert-dodecyl mercaptan, 0.5 parts of potassium persulfate, the remaining 8 parts of acrylonitrile and 2 parts of methacrylic acid are added, and the temperature is controlled at 68°C to react until the conversion rate reaches 86%. An appropriate amount of hydroquinone is added to terminate the reaction.

[0034] The reaction product was flash degassed, and the latex was mixed with 1.2 parts of an antioxidant 1010 emulsion. Then, a sodium chloride aqueous solution and a dilute sulfuric acid solution were added in a volume ratio of 1.2:1 for coagulation. After filtration and dehydration, the mixture was dried at 92° C. to a moisture content of 0.2% to obtain a carboxyl-containing thermoplastic elastomer.

[0035] Example 3

[0036] Raw material preparation: 60 parts of styrene, 70 parts of butadiene, 40 parts of acrylonitrile, 1 part of unsaturated carboxylic acid (itaconic acid), 4 parts of potassium stearate (emulsifier), 0.4 parts of tert-dodecyl mercaptan (regulator), 0.7 parts of potassium persulfate (initiator), appropriate amount of hydroquinone (terminator), 0.8 parts of antioxidant 1010 emulsion (antioxidant content is 10%), sodium chloride aqueous solution (mass fraction 9%), dilute sulfuric acid solution (mass fraction 5%).

[0037] Polymerization process:

[0038] Styrene, 0.2 parts tert-dodecyl mercaptan, and 3 parts potassium stearate were added to a polymerization kettle. After nitrogen pressure and vacuum replacement three times, butadiene was added and stirred for 15 minutes. 0.3 parts potassium persulfate was added via a feed cannon, and emulsion polymerization was initiated at 48°C.

[0039] When the conversion rate reached 30%, 0.5 parts of potassium stearate and 24 parts of acrylonitrile were added, and the temperature was raised to 62° C. to continue the reaction.

[0040] When the conversion rate reaches 58%, add the remaining 0.5 parts of potassium stearate, 0.4 parts of tert-dodecyl mercaptan, 0.4 parts of potassium persulfate, the remaining 16 parts of acrylonitrile and 1 part of itaconic acid, control the temperature at 72°C, and react until the conversion rate reaches 88%. Add an appropriate amount of hydroquinone to terminate the reaction.

[0041] The reaction product was flash degassed, and the latex was mixed with 0.8 parts of an antioxidant 1010 emulsion. Then, a sodium chloride aqueous solution and a dilute sulfuric acid solution were added in a volume ratio of 1.8:1 for coagulation. After filtration and dehydration, the mixture was dried at 94° C. to a moisture content of 0.4% to obtain a carboxyl-containing thermoplastic elastomer.

[0042] Comparative Example 1

[0043] The difference from Example 1 is that all acrylonitrile and acrylic acid are added at once at the beginning of the reaction, and other conditions are the same.

[0044] Comparative Example 2

[0045] The difference from Example 1 is that the fourth monomer, acrylic acid, is not added, and other conditions are the same.

[0046] Comparative Example 3

[0047] The difference from Example 1 is that the temperature in the middle and late stages of the reaction is lowered by 10° C., and other conditions are the same.

[0048] Comparative Example 4

[0049] The difference from Example 1 is that the amount of emulsifier is reduced by half, and other conditions are the same.

[0050] Performance Testing

[0051] Gel content testing: Soxhlet extraction is used. Cut the prepared carboxyl-containing thermoplastic elastomer sample into small pieces. Accurately weigh a certain mass m1 of sample, wrap it with filter paper, and place it in a Soxhlet extractor. Extract it with toluene for 48 hours. After extraction, remove the sample and dry it in a vacuum oven at 60°C to constant weight. Weigh the mass m2. Gel content = (m2 / m1) x 100%. The test results are as follows:

[0052] The gel content of Example 1 was 3.5%.

[0053] The gel content of Example 2 was 3.2%.

[0054] The gel content of Example 3 was 3.8%.

[0055] The gel content of Comparative Example 1 was 8.2%.

[0056] The gel content of Comparative Example 2 was 5.0%.

[0057] The gel content of Comparative Example 3 was 6.5%.

[0058] The gel content of Comparative Example 4 was 7.0%.

[0059] Tensile Strength Test: Tested in accordance with GB / T528-2009 using a universal materials testing machine. The sample was shaped like a dumbbell and stretched at a rate of 500 mm / min at room temperature. The maximum force (F) at break was recorded. The cross-sectional area of the sample is S, and tensile strength = F / S. The test results are as follows:

[0060] The tensile strength of Example 1 is 25 MPa.

[0061] The tensile strength of Example 2 is 23 MPa.

[0062] The tensile strength of Example 3 is 26 MPa.

[0063] The tensile strength of Comparative Example 1 was 18 MPa.

[0064] The tensile strength of Comparative Example 2 was 20 MPa.

[0065] The tensile strength of Comparative Example 3 was 21 MPa.

[0066] The tensile strength of Comparative Example 4 was 19 MPa.

[0067] Aging resistance test: Using an artificial accelerated aging test, the samples were placed in an aging chamber at a temperature of 70°C, a relative humidity of 65%, a light intensity of 5500 lx, and an aging time of 1000 hours. After the aging period, the tensile strength retention rate of the samples was tested. The test results are as follows:

[0068] The tensile strength retention rate of Example 1 was 85%.

[0069] The tensile strength retention rate of Example 2 was 83%.

[0070] The tensile strength retention rate of Example 3 was 86%.

[0071] The tensile strength retention rate of Comparative Example 1 was 70%.

[0072] The tensile strength retention rate of Comparative Example 2 was 75%.

[0073] The tensile strength retention rate of Comparative Example 3 was 78%.

[0074] The tensile strength retention rate of Comparative Example 4 was 72%.

[0075] Result analysis and verification

[0076] Judging from the gel content test results, the gel content of Examples 1-3 is significantly lower than that of Comparative Examples 1-4. The examples adopt a staged feeding method to accurately control the growth and cross-linking of molecular chains, effectively reducing the generation of gel; the one-time feeding of Comparative Example 1 leads to excessive monomer concentration and excessive cross-linking; Comparative Example 2 lacks carboxyl modification; Comparative Example 3 reduces the reaction temperature, affecting the polymerization reaction rate and molecular chain structure, resulting in an increase in gel content; Comparative Example 4 reduces the amount of emulsifier, affecting the monomer emulsification effect and inducing unreasonable cross-linking between molecular chains. In terms of tensile strength, Examples 1-3 rely on reasonable molecular structure regulation to achieve better interactions between molecular chains, and the tensile strength is higher than that of the comparative examples. Comparative Example 1 destroys the regularity of the molecular chain due to its high gel content; Comparative Example 2 lacks the reinforcing effect of carboxyl groups; Comparative Example 3 temperature changes affect the arrangement of molecular chains; Comparative Example 4 lacks insufficient emulsifier to affect the polymerization quality, all of which reduce the tensile strength. In the aging resistance test, Examples 1-3 introduce carboxyl groups and reasonable molecular structures, have strong antioxidant and anti-degradation capabilities, and have a high tensile strength retention rate. Comparative Examples 1-4 are more susceptible to aging due to molecular structural defects, resulting in significant performance degradation. Multiple sets of comparative experiments and performance testing and analysis of the examples and comparative examples fully demonstrate that the carboxyl-containing thermoplastic elastomer prepared by the emulsion polymerization method of the present invention has significant advantages in reducing gel content, improving tensile strength, and aging resistance, and possesses outstanding substantive characteristics and significant progress.

[0077] 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: Prepared by the following steps: Initial polymerization: Styrene, part of the regulator and 50%-70% (based on the total weight of the emulsifier) of the emulsifier are added to the polymerization kettle. After nitrogen pressure-vacuum replacement, the conjugated diene is added. After stirring evenly, 30%-40% (based on the total weight of the initiator) of the initiator is added and the emulsion polymerization reaction is started at 40°C-50°C. Mid-term feeding: When the reaction conversion rate reaches 20%-35%, add part of the emulsifier and 40%-60% (based on the total mass of acrylonitrile) 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, remaining initiator, remaining regulator and a mixture of remaining acrylonitrile and 0.5-3 parts (based on the total monomer mass) of unsaturated carboxylic acid or its anhydride, control the temperature at 65°C-75°C until the conversion rate reaches 85%-89%, and then add a terminator to terminate the reaction; Post-treatment: Flash degas the product, mix the latex with 0.5%-1% (based on the mass of the latex) of an antioxidant emulsion, add a mixture of sodium chloride aqueous solution and dilute sulfuric acid solution to coagulate, filter and dehydrate, and then dry at 90°C-96°C to a moisture content of ≤0.5%.

2. The carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization according to claim 1, characterized in that: The emulsifier is one or more combinations of sodium lauryl sulfate, sodium dodecylbenzene sulfonate, potassium stearate, potassium oleate, synthetic fatty acid potassium soap, and disproportionated rosin potassium soap.

3. The carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization according to claim 1, characterized in that: The conjugated diene is butadiene.

4. The carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization according to claim 1, characterized in that: The initiator is potassium persulfate, and the terminator is hydroquinone.

5. The carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization according to claim 1, characterized in that: The mass fraction of the sodium chloride aqueous solution is 5%-10%, the mass fraction of the dilute sulfuric acid solution is 3%-5%, and the volume ratio of the two is 1:1-2:

1.

6. The carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization according to claim 1, characterized in that: The unsaturated carboxylic acid is one of acrylic acid, methacrylic acid and itaconic acid.

7. The carboxyl-containing thermoplastic elastomer prepared by emulsion polymerization 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%.