Green synthesis method of solvent-free single-component environment-friendly TPU cross-linking agent

Abstract

The invention discloses a green synthesis method of a solvent-free single-component environment-friendly TPU cross-linking agent, and belongs to the technical field of polymer cross-linking modification preparation, the solvent-free single-component environment-friendly TPU cross-linking agent comprises polyether polyol, diisocyanate, a chain extender, a catalyst, a cross-linking assistant and an antioxidant; the crosslinking auxiliary agent comprises one of castor oil and epoxidized soybean oil, and the antioxidant comprises one of a hindered phenol antioxidant and a phosphite ester antioxidant. According to the preparation method, no organic solvent is used, pollution caused by solvent volatilization to the environment is avoided, the environment-friendly requirement is met, the ecological environment and the health of operators are protected, the crosslinking efficiency and stability of the TPU crosslinking agent can be effectively improved, the crosslinking agent can be better combined with TPU molecular chains in the crosslinking process, and the TPU molecular chains can be better combined with the TPU molecular chains in the crosslinking process. The mechanical property and the heat resistance of the TPU product are improved.

Description

Technical Field

[0001] This invention relates to the field of polymer crosslinking modification technology, and in particular to a green synthesis method for a solvent-free, single-component, environmentally friendly TPU crosslinking agent. Background Technology

[0002] Thermoplastic polyurethane elastomers (TPUs) occupy an important position in the industrial field due to their excellent mechanical properties and wide range of applications. The molecular structure of thermoplastic polyurethane elastomers already contains physical crosslinks or mild chemical crosslinks. To further enhance the crosslinking density or modify properties, crosslinking agents are typically added to the formulation.

[0003] Regarding this research, application CN201810448915.7 provides a TPU film with a crosslinked structure and its preparation method. This technical solution is prepared from 90-110 parts by weight of TPU and 0.02-0.7 parts by weight of a crosslinking agent; the TPU is either isocyanate-terminated or hydroxyl-terminated, and the crosslinking agent is a multifunctional alcohol compound. This technical solution avoids the problem of difficulty in extruding and casting TPU films with chemically crosslinked structures, providing a new approach for preparing TPU films with chemically crosslinked structures, and improving the modulus and elasticity of the prepared films.

[0004] Another application, CN202110578328.1, provides a universal crosslinking agent, its synthesis method, and its application. This technical solution includes the following steps: 1) esterification reaction of phenylacetyl chloride and a di- or polyol under alkaline catalysis to generate the corresponding ester; 2) reaction of the ester synthesized in step 1) with p-toluenesulfonyl azide under the action of 1,8-diazabicyclo[5.4.0]undec-7-ene to introduce a diazo group. This technical solution utilizes the universal crosslinking agent to achieve crosslinking of polymers containing aliphatic C-H bonds and active hydrogen, co-crosslinking between different polymers, surface adhesion between different polymers, and reversible crosslinking of polymers by designing the connecting segments in the middle of the crosslinking agent molecule.

[0005] However, the synthesis process of the above-mentioned technical solutions requires the use of organic solvents (such as DMF, toluene, etc.). These solvents are not only highly volatile and pollute the environment, but may also be harmful to human health. In addition, some TPU materials and crosslinking agents are difficult to degrade, which will cause certain safety risks during the synthesis process and have long-term pollution effects on the environment, making it difficult to meet environmental protection requirements. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] The first objective of this invention is to provide a green synthesis method for a solvent-free, single-component, environmentally friendly TPU crosslinking agent. This synthesis method does not require the use of any organic solvents, avoiding environmental pollution caused by solvent volatilization, meeting the requirements of green environmental protection, and is beneficial to protecting the ecological environment and the health of operators. It can also effectively improve the crosslinking efficiency and stability of the TPU crosslinking agent, enabling the crosslinking agent to better bind with the TPU molecular chain during the crosslinking process, thereby improving the mechanical properties and heat resistance of TPU products.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A green synthesis method for a solvent-free, single-component, environmentally friendly TPU crosslinking agent, comprising the following raw materials: The polyether polyol has a molecular weight of 1000-3000; the polyether polyol includes one of polypropylene glycol and polytetrahydrofuran. In this embodiment, the polyether polyol is one or more of polypropylene glycol and polytetrahydrofuran; Polypropylene glycol (PPG) is mainly polymerized from propylene oxide (PO). Its molecular chain mainly contains propylene oxide units, which have low viscosity, high active hydrogen content and good solubility, which is beneficial for the preparation of polyurethane elastomers. Polytetrahydrofuran (PTMEG) is formed by ring-opening polymerization of tetrahydrofuran. Its molecular chain contains a large number of ether bonds, which gives it excellent low-temperature flexibility and hydrolysis resistance. It is also beneficial for the preparation of polyurethane elastomers. The two can be used in combination. Polyether polyols, as an important component of crosslinking agents, provide hydroxyl groups for the crosslinking reaction. Diisocyanate, wherein the diisocyanate includes one of toluene diisocyanate, isophorone diisocyanate or diphenylmethane diisocyanate; In this embodiment, the diisocyanate is selected from one or more of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) or diphenylmethane diisocyanate (MDI), providing NCO groups to react with the hydroxyl groups of the polyether polyol to form a cross-linked network structure. Chain extender, wherein the chain extender comprises one of ethylene glycol, 1,4-butanediol or trimethylolpropane; In this embodiment, the chain extender is selected from one or more of ethylene glycol, 1,4-butanediol or trimethylolpropane, and is used to adjust the molecular weight and crosslinking density of the crosslinking agent to further optimize the performance of the crosslinking agent. The catalyst includes one of stannous octoate and dibutyltin dilaurate; In this embodiment, the catalyst is selected from one or more of stannous octoate and dibutyltin dilaurate to accelerate the reaction process and improve the reaction efficiency. Crosslinking aid, wherein the crosslinking aid includes one of castor oil and epoxidized soybean oil; In this embodiment, the crosslinking aid is selected from one or more of castor oil and epoxidized soybean oil, which can promote the crosslinking reaction, improve the crosslinking efficiency and the stability of the crosslinking network, and enhance the compatibility between the crosslinking agent and the TPU matrix.

[0010] In a preferred embodiment of the present invention, polyether polyol and diisocyanate are added to a reaction vessel at a mass ratio of 1:1.2 to 2.5, stirred and mixed evenly at a temperature of 70 to 90°C, and reacted for 1 to 3 hours to form a polyurethane prepolymer. In this embodiment, during this process, the hydroxyl groups of the polyether polyol react with the NCO groups of the diisocyanate to form a polyurethane prepolymer.

[0011] In a preferred embodiment of the present invention, a chain extender and a catalyst are added to the polyurethane prepolymer, wherein the mass ratio of the chain extender to the polyether polyol is 0.1 to 0.3:1, the mass ratio of the catalyst is 0.05% to 0.2% of the mass of the polyether polyol, and the reaction is continued at a temperature of 80 to 100°C for 1 to 2.5 hours. In this embodiment, a chain extender participates in the reaction to further extend the polyurethane chain segments and adjust the molecular weight and crosslinking density.

[0012] In a preferred embodiment of the present invention, after the reaction is completed, a crosslinking aid is added, the mass ratio of the crosslinking aid to the polyether polyol is 0.05 to 0.15:1, the temperature is raised to 110 to 130°C, and the reaction is carried out for 0.5 to 2 hours to obtain a solvent-free, single-component, environmentally friendly TPU crosslinking agent. In this embodiment, the crosslinking aid plays a role in promoting the crosslinking reaction, improving the crosslinking efficiency and the stability of the crosslinking network, and enhancing the compatibility between the crosslinking agent and the TPU matrix, thus obtaining a solvent-free, single-component, environmentally friendly TPU crosslinking agent. Cool the solvent-free, single-component, environmentally friendly TPU crosslinking agent to 40–60°C, then transfer the solvent-free, single-component, environmentally friendly TPU crosslinking agent to a dry container and cool it to room temperature before sealing and storing it. It should be noted that sealing the container can prevent it from getting damp or reacting with components in the air, thus ensuring the performance and stability of the crosslinking agent.

[0013] In a preferred embodiment of the present invention, the method for preparing the polyether polyol includes: Step S10: The preparation method of polyether polyol includes preparation using sucrose as an initiator; 100 parts sucrose, 20-30 parts small molecule alcohol, 5-10 parts water, 200-300 parts epoxide, 0.1-0.5 parts alkali metal catalyst, and 1-5 parts adsorbent; Step S20: Add a mixture of sucrose, small molecule alcohol and water, and alkali metal catalyst to the high-pressure reactor. Replace the air with an inert gas, including nitrogen, until the oxygen content is less than 100 ppm. Then, evacuate to -0.098 MPa and heat to 80℃~150℃. Introduce epoxide for the first time to carry out anionic polymerization reaction. Step S30: After the anionic polymerization reaction is completed, keep warm and mature until the reaction is complete to obtain a preliminary polyether polyol. Then raise the temperature to dehydrate to 90℃~110℃, and control the moisture content to 0~0.2wt.% of the total mass. Step S40: After inert gas replacement, vacuum is drawn again to -0.098 MPa, and epoxide is introduced to carry out the second anionic polymerization reaction. After the reaction is complete, a viscous polyether polyol is obtained. Water and adsorbent are added to purify the preliminary polyether polyol to obtain a refined polyether polyol feedstock. In this embodiment, the introduction of epoxides for a second polymerization reaction can further increase the chain length of the polyether polyol; Step S50: In another high-pressure reaction vessel, add refined polyether polyol feedstock, DMC catalyst, and acidic substance; wherein the mass ratio of DMC catalyst is 0.001% to 0.05% of the mass of refined polyether polyol feedstock, and the mass ratio of acidic substance is 0.005% to 0.05% of the mass of refined polyether polyol feedstock; repeat the above steps of inert gas replacement, vacuuming, heating and dehydration, introducing epoxide polymerization reaction, and adding water and adsorbent for purification, and finally obtain high molecular weight sucrose polyether polyol; The mass ratio of DMC catalyst is 0.01% of the mass of refined polyether polyol feedstock, and the mass ratio of acidic substances is 0.01% of the mass of refined polyether polyol feedstock. Acidic substances include organic acids. In this embodiment, the organic acid includes acetic acid or citric acid; It should be noted that the role of acidic substances is mainly to regulate the performance of the catalyst, or to participate in processes such as protonation in subsequent reactions, so as to improve reaction efficiency or selectivity.

[0014] In a preferred embodiment of the present invention, the small molecule alcohol includes diethylene glycol or propylene glycol; It should be noted that small molecule alcohols are auxiliaries that can promote the reaction; The alkali metal catalyst includes potassium hydroxide; It should be noted that alkali metal catalysts play a catalytic role; The epoxide includes ethylene oxide or propylene oxide; It should be noted that epoxides are the main raw materials, providing ether bonds and chain growth; The adsorbent includes aluminum silicate or magnesium silicate; It should be noted that the adsorbent is used to refine the product and remove impurities; The added water is used to adjust the reaction environment.

[0015] In a preferred embodiment of the present invention, the method for preparing the polyether polyol includes the preparation of other initiators, including sorbitol, glycerol and ethylenediamine; in the preparation of the polyether polyol, sorbitol, glycerol and ethylenediamine are all 100 parts each; In this embodiment, the sorbitol molecule contains multiple hydroxyl groups, which, as an initiator, can enable the polyether polyol to obtain higher functionality, thereby increasing the crosslinking density with isocyanate and enhancing the hardness and compressive strength of the polyurethane material. Furthermore, sorbitol can be obtained from renewable resources, which meets the requirements of environmental protection and sustainable development; Glycerin, as a trifunctional initiator, can be used to produce polyether polyols that can be used in high cross-linking density foams to improve hardness and compressive strength. At the same time, when used in combination with high-functionality initiators such as sorbitol, it can provide better flowability for foams and improve production efficiency and process stability. Furthermore, glycerol has good compatibility with other raw materials and can participate in the preparation systems of various polyether polyols, adapting to the production of polyurethane products with different performance requirements; Polyether polyols with ethylenediamine as an initiator have tetrafunctionality, which can provide more reactive sites, thus improving the crosslinking density and performance of polyurethane materials.

[0016] In a preferred embodiment of the present invention, the raw materials further include an antioxidant, which includes one of hindered phenolic antioxidants or phosphite antioxidants; In this embodiment, the hindered phenolic antioxidant includes butylated hydroxytoluene (BHT), which has good antioxidant properties and can effectively capture free radicals and interrupt the oxidation reaction chain. Phosphite antioxidants, including triphenyl phosphite, are mainly used to reduce peroxides generated during oxidation. They work synergistically with hindered phenolic antioxidants for better results. By adding antioxidants, TPU materials can be effectively prevented from undergoing oxidative degradation under conditions such as high temperature and light, thus maintaining the physical properties and appearance of the material. Furthermore, by inhibiting oxidation reactions, antioxidants can significantly extend the service life of TPU products and reduce the risk of performance degradation caused by material aging.

[0017] In a preferred embodiment of the present invention, step S50 includes replacing the DMC catalyst and the acidic substance with a metallocene catalyst and an activator, respectively; the metallocene catalyst includes a monometallocene catalyst, and the activator includes methylaluminoxane; the remaining preparation steps are the same as step S50. In this embodiment, the metallocene catalyst has high activity and high selectivity, and can effectively control the molecular structure and performance of polyether polyols. For example, the unique electronic structure of the monometallocene catalyst can precisely regulate the ring-opening direction of the epoxide and the polymer chain growth process. Activators are used to improve the activity and stability of metallocene catalysts. For example, methylaluminoxane (MAO) can form active catalytic centers with metallocene catalysts, thereby enhancing their ability to polymerize epoxides. In a preferred embodiment of the present invention, the raw materials comprise the following parts by weight: Polypropylene glycol, molecular weight 2000, 90-100 parts; Toluene diisocyanate, 180–195 parts; 1,4-Butanediol, 25-30 parts; Stannous octoate, 0.1–0.25 parts; Castor oil, 10-20 parts; Polypropylene glycol and toluene diisocyanate were added to a reaction vessel, heated to 80°C, stirred and mixed evenly, and reacted for 2 hours to form a polyurethane prepolymer. Add 1,4-butanediol, stannous octoate and hindered phenolic antioxidants, and continue the reaction at 90°C for 1.5 hours; After the reaction was completed, castor oil was added, the temperature was raised to 120°C, and the reaction was carried out for 1 hour to obtain a solvent-free, single-component, environmentally friendly TPU crosslinking agent. Cool the solvent-free, single-component, environmentally friendly TPU crosslinking agent to 50°C, transfer it to a dry container, cool it to room temperature, and then seal and store it. Beneficial effects

[0018] This invention can effectively improve the crosslinking efficiency and stability of TPU crosslinking agents, enabling the crosslinking agents to better bind with TPU molecular chains during the crosslinking process, thereby improving the mechanical properties and heat resistance of TPU products. Moreover, the entire process does not require the use of organic solvents, avoiding the pollution caused by solvent volatilization to the environment, meeting the requirements of green environmental protection, and helping to protect the ecological environment and the health of operators. Through the synthesis steps and raw material ratios of this invention, the obtained TPU crosslinking agent can significantly improve the performance of TPU products, enabling the solvent-free, single-component, environmentally friendly TPU crosslinking agent to have good compatibility and dispersibility, and can be mixed with a variety of commercially available TPU resins, thus having a wide range of applications. In the preparation of polyether polyols, catalysts and acidic substances can be replaced (such as using metallocene catalysts and activators), making the process more flexible and adaptable to different production conditions and raw material supply. By adding antioxidants, the stability of TPU crosslinking agents is improved, the service life of the product is extended, and its adaptability to different environmental conditions is enhanced. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0021] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0022] Unless otherwise specified, the raw materials used in the examples were purchased commercially. Example 1

[0023] This embodiment discloses a green synthesis method for a solvent-free, single-component, environmentally friendly TPU crosslinking agent, comprising the following raw materials in parts by weight: Polypropylene glycol, molecular weight 2000, 100 parts; Toluene diisocyanate, 180 parts; 1,4-Butanediol, 25 parts; Stannous octoate, 0.1 part; Castor oil, 10 parts; Hindered phenolic antioxidant, 0.05 parts; Polypropylene glycol and toluene diisocyanate were added to a reaction vessel, heated to 80°C, stirred and mixed evenly, and reacted for 2 hours to form a polyurethane prepolymer. Add 1,4-butanediol, stannous octoate and hindered phenolic antioxidants, and continue the reaction at 90°C for 1.5 hours; Add castor oil, heat to 120°C, and react for 1 hour to obtain a solvent-free, single-component, environmentally friendly TPU crosslinking agent; After the reaction is complete, the solvent-free, single-component, environmentally friendly TPU crosslinking agent is cooled to 50°C, transferred to a dry container, cooled to room temperature, and then sealed for storage. Example 2

[0024] This embodiment discloses a green synthesis method for a solvent-free, single-component, environmentally friendly TPU crosslinking agent, comprising the following raw materials in parts by weight: Polytetrahydrofuran, molecular weight 3000, 120 parts; Isophorone diisocyanate, 190 parts; Ethylene glycol, 30 parts; Dibutyltin dilaurate, 0.2 parts; Epoxidized soybean oil, 15 parts; Phosphite antioxidant, 0.1 parts; The remaining synthesis process conditions in this embodiment are the same as those in Example 1. Example 3

[0025] This embodiment discloses a green synthesis method for a solvent-free, single-component, environmentally friendly TPU crosslinking agent, comprising the following raw materials in parts by weight: Polypropylene glycol, molecular weight 1500, 80 parts; Diphenylmethane diisocyanate, 185 parts; Trimethylolpropane, 30 parts; Stannous octoate, 0.25 parts; A mixture of castor oil and epoxidized soybean oil, in a mass ratio of 1:1, 12 parts; Phosphite antioxidants, 0.2 parts; The remaining synthesis process conditions in this embodiment are the same as those in Example 1.

[0026] Comparative Example 1

[0027] Comparative Example 1: To verify the effect of diisocyanate on the TPU crosslinking agent, compared with Example 1, diisocyanate was not included in the synthesis process, and all other synthesis conditions were the same as in Example 1.

[0028] Referring to the synthesis method of the comparative example above, the TPU crosslinking agent obtained by the synthesis method of the comparative example, compared with the reactant obtained by the synthesis method of Example 1, cannot form a TPU crosslinking agent with a crosslinking network structure if it does not contain diisocyanate, and it is difficult for other raw materials to form stable chemical bonds, resulting in incomplete reaction, the presence of unreacted functional groups and low molecular weight substances in the system, affecting the performance and stability of the product, and at the same time reducing the chemical resistance of the TPU crosslinking agent, making it susceptible to corrosion by chemicals such as acids, alkalis, and solvents, causing the material's performance to deteriorate rapidly.

[0029] Comparative Example 2

[0030] Comparative Example 2 was designed to verify the effect of the chain extender on the TPU crosslinking agent, a reactant. Compared with Example 1, no chain extender was used in the synthesis process, and all other synthesis conditions were the same as in Example 1.

[0031] Referring to the synthesis method of the comparative example above, the TPU crosslinking agent obtained by the synthesis method of the comparative example, compared with the reactant obtained by the synthesis method of Example 1, if it does not contain a chain extender, the length and molecular weight of the polymer chain segment are difficult to reach the expected value, resulting in shorter molecular chains, making it difficult to form a complete crosslinking network structure, and the reaction may be incomplete. There are unreacted functional groups and low molecular weight substances in the system, which affects the performance and stability of the product, and the mechanical properties of the product will be significantly reduced. The material becomes soft and easily deformed, and cannot meet the requirements of material strength and toughness in practical applications.

[0032] Comparative Example 3

[0033] Comparative Example 3 was designed to verify the effect of the catalyst on the TPU crosslinking agent, a reactant. Compared with Example 1, no catalyst was used in the synthesis process, and all other synthesis conditions were the same as in Example 1.

[0034] Referring to the synthesis method of the comparative example above, compared with the reactant obtained by the synthesis method of Example 1, if the catalyst is not present, the reaction rate of polyether polyol and diisocyanate will be significantly reduced, the reaction time will be significantly prolonged, and the reaction may not be completed within a reasonable time range. Furthermore, the reaction may require higher temperatures or other harsh conditions to start, which will increase the energy consumption and difficulty of the reaction, and may even prevent the reaction from being carried out under normal conditions. Ultimately, this will result in a wider molecular weight distribution of the generated polymer, affecting the performance consistency of the product.

[0035] Comparative Example 4

[0036] Comparative Example 4 was designed to verify the effect of crosslinking aids on the TPU crosslinking agent reactant. Compared with Example 1, no crosslinking aids were used in the synthesis process, and all other synthesis conditions were the same as in Example 1.

[0037] Referring to the synthesis method of the comparative example above, the TPU crosslinking agent obtained by the synthesis method of the comparative example, compared with the reactant obtained by the synthesis method of Example 1, if it does not contain crosslinking aids, the crosslinking density is difficult to reach the ideal level, which reduces the strength, elasticity and heat resistance of the material. In this case, the mechanical properties of the material, such as tensile strength, tear strength and modulus, are significantly reduced, making it easy to deform and break under external force. In addition, the surface wear resistance of the material is poor, and it is easy to wear during friction, shortening the service life. Furthermore, the elastic modulus of the material will also decrease, resulting in insufficient elasticity. When subjected to external force, it is easy to undergo irreversible deformation, thus limiting its market application range.

[0038] Performance evaluation tests of solvent-free, single-component, environmentally friendly TPU crosslinking agents: Test items and methods: (1) Physical performance testing, including: Density testing: The density of the TPU crosslinking agent was determined by flotation or specific gravity bottle method to understand its mass distribution characteristics; Hardness test: The TPU crosslinking agent is tested for hardness using a Shore hardness tester to evaluate its surface compressive strength; Melt flow index testing: The flowability of TPU crosslinking agent when it melts at high temperature is measured by a melt flow indexer, which reflects its processing performance; Water absorption test: The water absorption rate of the TPU crosslinking agent is tested to evaluate its water absorption capacity in water, and thus understand its sensitivity to moisture.

[0039] Test results and analysis: Regarding density, the test results show that the density of the TPU crosslinking agent is between 1.13 and 1.20 g / cm³, indicating that it has good density characteristics and a relatively uniform mass distribution. Regarding hardness, the hardness test results are Shore A 85-95, indicating that the TPU crosslinking agent has high hardness and can withstand a certain surface pressure; The melt flow index was 10-20 g / 10 min, indicating that the TPU crosslinking agent has good flowability at high temperatures and is easy to process and mold. Regarding the water absorption rate, the test result was less than 0.1%, indicating that the TPU crosslinking agent is less sensitive to moisture and has good waterproof performance.

[0040] The details are shown in the table below:

[0041] The table above shows the physical performance tests of each experimental group. According to the table, the density of the TPU crosslinking agent in Examples 1 to 3 is between 1.13 and 1.20 g / cm³, the Shore A hardness is 85 to 95, the melt index is 10 to 20 g / 10 min, and the water absorption rate is less than 0.1%. This indicates that it has uniform mass distribution, high hardness, good processing performance, and excellent waterproof performance.

[0042] The densities of Comparative Examples 1-4 are significantly lower than those of the Examples, ranging from approximately 0.03 to 0.31 g / cm³, with Shore A hardness of only 10.9 to 11.6, melt flow index of 0.9 to 2.3 g / 10 min, and water absorption rates as high as 8.6% to 9.3%, indicating uneven mass distribution, low hardness, difficult processing, and high water absorption. This demonstrates the advantages of the TPU crosslinking agent in the Examples in terms of physical properties.

[0043] (2) Mechanical performance testing, including: Tensile strength and elongation at break testing: The maximum strength and elongation at break of the TPU crosslinking agent under tension and the elongation before fracture are measured by a universal testing machine to evaluate its elasticity and toughness. Tear strength test: The tear strength of the TPU crosslinking agent is tested using the trouser or corner specimen method to evaluate its tear resistance when subjected to sharp objects. Compression set test: Using a compression set device, the ability of TPU crosslinking agent to return to its original shape after being compressed is measured, thereby reflecting its deformation under long-term use.

[0044] Test results and analysis: Regarding tensile strength, the tensile strength test results reached 30-40 MPa, indicating that the TPU crosslinking agent has high tensile strength and can withstand large tensile forces. Regarding the elongation at break, the test result was 500-600%, indicating that the TPU crosslinking agent has good elasticity and toughness and can remain unbroken under large deformation. Regarding tear strength, the tear strength test results reached 50-60kN / m, indicating that the TPU crosslinking agent has strong tear resistance and can resist tearing by sharp objects; The compression set test result was less than 10%, indicating that the TPU crosslinking agent can recover its original shape well after being compressed and has good resistance to compression deformation.

[0045] The details are shown in the table below:

[0046] The table above shows the mechanical property tests for each experimental group. According to the table, the tensile strength of the TPU crosslinking agent in Examples 1-3 is between 30.3-39.2 MPa, the elongation at break is as high as 561.3%-591.6%, the tear strength is 55.3-59.1 kN / m, and the compression set is less than 10% (9.59%-9.66%). This indicates that its... It can withstand large tensile forces and has good elasticity and toughness. It can withstand large deformations without breaking and has strong tear resistance, resisting tearing by sharp objects. At the same time, it can return to its original shape well after being compressed, and has good resistance to compression deformation.

[0047] In contrast, the tensile strength of Comparative Examples 1-4 was only 3.9-7.6 MPa, the elongation at break was 32.3%-72.9%, the tear strength was 1.6-3.9 kN / m, and the compression set was as high as 33.1%-52.1%. This indicates that their tensile strength is insufficient, and the material has poor elasticity and toughness, making it prone to fracture under small deformations. Furthermore, its tear resistance is weak, and it is difficult to return to its original shape after compression, exhibiting poor resistance to compressive deformation. This demonstrates that the TPU crosslinking agents of Examples 1-3 are significantly superior to the comparative examples in terms of mechanical properties such as tensile strength, elongation at break, tear strength, and compression set. This indicates that the synthesis method in the examples can effectively improve the mechanical properties of the TPU crosslinking agent, making it more suitable for various application scenarios.

[0048] (3) Thermal performance testing, including: Glass transition temperature and melting point detection: Differential scanning calorimetry was used to test the glass transition temperature and melting point of the TPU crosslinking agent in order to understand its behavior under temperature changes; Heat resistance test: The TPU crosslinking agent is placed in an air oven aging test for 100 to 110 hours at a certain temperature (e.g., 110°C). The heat resistance is evaluated by comparing the change in tensile strength before and after the test.

[0049] Test results and analysis: Regarding the glass transition temperature, the differential scanning calorimetry test results show that the glass transition temperature of the TPU crosslinking agent is around -40℃, indicating that it can still maintain a certain degree of flexibility in low-temperature environments. Regarding the melting point, the test results show that the melting point of the TPU crosslinking agent is between 180-200℃, indicating that it has good thermal stability during high-temperature processing. Regarding heat resistance, the results of the air oven aging test showed that the TPU crosslinking agent retained more than 90% of its tensile strength after 110 hours at 110℃, indicating that it has excellent heat resistance.

[0050] The details are shown in the table below:

[0051] The table above shows the mechanical properties of each experimental group. According to the table, the glass transition temperature of the TPU crosslinking agent in Examples 1 to 3 is between -40.2℃ and -40.6℃, and the melting point is between 183.3℃ and 196.1℃. Under the condition of 110℃ and 110 hours, the tensile strength retention rate is above 90%, reaching a maximum of 92.1%. This indicates that it can maintain good flexibility at low temperature and has good thermal stability during high temperature processing, while also having excellent heat resistance.

[0052] The glass transition temperatures of Comparative Examples 1-4 ranged from 10.9℃ to 14.3℃, with melting points ranging from only 16.2℃ to 23.6℃. Furthermore, their tensile strength retention rate under the same heat resistance testing conditions was only 11.6% to 13.9%, indicating poor flexibility at low temperatures, poor thermal stability during high-temperature processing, and poor heat resistance. This demonstrates that the TPU crosslinking agents of Examples 1-3 are superior to the comparative examples in terms of glass transition temperature, melting point, and heat resistance. This demonstrates the rationality of the synthesis methods in the examples, endowing the materials with excellent thermal properties, making them more suitable for applications in different temperature environments.

[0053] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A green synthesis method for a solvent-free, single-component, environmentally friendly TPU crosslinking agent, characterized in that, Including the following raw materials: The polyether polyol has a molecular weight of 1000-3000; the polyether polyol includes one of polypropylene glycol and polytetrahydrofuran. Diisocyanate, wherein the diisocyanate includes one of toluene diisocyanate, isophorone diisocyanate or diphenylmethane diisocyanate; Chain extender, wherein the chain extender comprises one of ethylene glycol, 1,4-butanediol or trimethylolpropane; The catalyst includes one of stannous octoate and dibutyltin dilaurate; Crosslinking aid, wherein the crosslinking aid includes one of castor oil and epoxidized soybean oil.

2. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 1, characterized in that: Polyether polyol and diisocyanate are added to a reaction vessel at a mass ratio of 1:1.2 to 2.5, and stirred and mixed evenly at a temperature of 70 to 90°C for 1 to 3 hours to form a polyurethane prepolymer.

3. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 2, characterized in that: A chain extender and a catalyst are added to the polyurethane prepolymer. The mass ratio of the chain extender to the polyether polyol is 0.1 to 0.3:1, and the mass ratio of the catalyst is 0.05% to 0.2% of the mass of the polyether polyol. The reaction is continued at a temperature of 80 to 100°C for 1 to 2.5 hours.

4. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 3, characterized in that: After the reaction is complete, a crosslinking aid is added, with a mass ratio of crosslinking aid to polyether polyol of 0.05 to 0.15:

1. The temperature is raised to 110 to 130°C, and the reaction is carried out for 0.5 to 2 hours to obtain a solvent-free, single-component, environmentally friendly TPU crosslinking agent. Cool the solvent-free, single-component, environmentally friendly TPU crosslinking agent to 40–60°C, then transfer it to a dry container and cool it to room temperature before sealing and storing it.

5. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 1, characterized in that: The preparation method of the polyether polyol includes: Step S10: The preparation method of polyether polyol includes preparation using sucrose as an initiator; 100 parts sucrose, 20-30 parts small molecule alcohol, 5-10 parts water, 200-300 parts epoxide, 0.1-0.5 parts alkali metal catalyst, and 1-5 parts adsorbent; Step S20: Add a mixture of sucrose, small molecule alcohol and water, and alkali metal catalyst to the high-pressure reactor. Replace the air with an inert gas, including nitrogen, until the oxygen content is less than 100 ppm. Then, evacuate to -0.098 MPa and heat to 80℃~150℃. Introduce epoxide for the first time to carry out anionic polymerization reaction. Step S30: After the anionic polymerization reaction is completed, keep warm and mature until the reaction is complete to obtain a preliminary polyether polyol. Then raise the temperature to dehydrate to 90℃~110℃, and control the moisture content to 0~0.2wt.% of the total mass. Step S40: After inert gas replacement, vacuum is drawn again to -0.098 MPa, and epoxide is introduced to carry out the second anionic polymerization reaction. After the reaction is complete, a viscous polyether polyol is obtained. Water and adsorbent are added to purify the preliminary polyether polyol to obtain a refined polyether polyol feedstock. Step S50: In another high-pressure reaction vessel, add refined polyether polyol feedstock, DMC catalyst, and acidic substance; wherein the mass ratio of DMC catalyst is 0.001% to 0.05% of the mass of refined polyether polyol feedstock, and the mass ratio of acidic substance is 0.005% to 0.05% of the mass of refined polyether polyol feedstock; repeat the above steps of inert gas replacement, vacuuming, heating and dehydration, introducing epoxide polymerization reaction, and adding water and adsorbent for purification, and finally obtain high molecular weight sucrose polyether polyol; The mass ratio of DMC catalyst is 0.01% of the mass of refined polyether polyol feedstock, and the mass ratio of acidic substances is 0.01% of the mass of refined polyether polyol feedstock. Acidic substances include organic acids.

6. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 5, characterized in that: The small molecule alcohols include diethylene glycol or propylene glycol; The alkali metal catalyst includes potassium hydroxide; The epoxide includes ethylene oxide or propylene oxide; The adsorbent includes aluminum silicate or magnesium silicate.

7. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 5, characterized in that: The method for preparing the polyether polyol includes the preparation of other initiators, including sorbitol, glycerol and ethylenediamine; in the preparation of the polyether polyol, sorbitol, glycerol and ethylenediamine are all in 100 parts.

8. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 1, characterized in that: The raw materials also include antioxidants, which include one of hindered phenolic antioxidants or phosphite antioxidants.

9. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 5, characterized in that: In step S50, a metallocene catalyst and an activator are used to replace the DMC catalyst and the acidic substance, respectively; the metallocene catalyst includes a monometallocene catalyst, and the activator includes methylaluminoxane; the remaining preparation steps are the same as in step S50.

10. The green synthesis method of a solvent-free, single-component, environmentally friendly TPU crosslinking agent according to claim 8, characterized in that, The raw materials include the following parts by weight: Polypropylene glycol, molecular weight 2000, 80-120 parts; Toluene diisocyanate, 180–195 parts; 1,4-Butanediol, 25-30 parts; Stannous octoate, 0.1–0.25 parts; Castor oil, 10-20 parts; Hindered phenolic antioxidants, 0.05–0.2 parts; Polypropylene glycol and toluene diisocyanate were added to a reaction vessel, heated to 80°C, stirred and mixed evenly, and reacted for 2 hours to form a polyurethane prepolymer. Add 1,4-butanediol, stannous octoate and hindered phenolic antioxidants, and continue the reaction at 90°C for 1.5 hours; After the reaction was completed, castor oil was added, the temperature was raised to 120°C, and the reaction was carried out for 1 hour to obtain a solvent-free, single-component, environmentally friendly TPU crosslinking agent. Cool the solvent-free, single-component, environmentally friendly TPU crosslinking agent to 50°C, transfer it to a dry container, cool it to room temperature, and then seal and store it.

Images