Forming method of ETPU foaming body and prepared ETPU foaming body

Abstract

The invention relates to the field of polyurethane materials, and particularly discloses an ETPU foaming body forming method and a prepared ETPU foaming body, and the ETPU foaming body forming method comprises the following steps: S1, TPU particles are placed in a supercritical fluid and kept for 1-3 h under the conditions that the pressure is 15-30 MPa and the temperature is 120-140 DEG C, and then pre-foaming particles are obtained after pressure relief; s2, a mold is filled with the pre-foamed particles, first-time mold pressing foaming is conducted at the temperature of 80-110 DEG C, the pressure is 2-5 MPa, and the pressure is increased to 8-15 MPa; and S3, gradient cooling and shaping are conducted, specifically, the temperature is reduced to 60-80 DEG C within 30 s, the pressure is maintained, pressure relief is conducted, cooling continues to be conducted to 30-40 DEG C, and the ETPU foaming body is taken out after mold opening. The invention further discloses the ETPU foaming body prepared through the method. The method has the advantages that the rebound resilience of the ETPU foaming body is improved, and the compression permanent deformation rate is reduced.

Description

Technical Field

[0001] This application relates to the field of polyurethane materials, and more specifically, to a molding method for an ETPU foam and the resulting ETPU foam. Background Technology

[0002] ETPU (expanded thermoplastic polyurethane) is a high-performance new polymer material. It is prepared by a special foaming process based on traditional thermoplastic polyurethane (TPU). ETPU not only retains the excellent physical properties of TPU, such as chemical resistance, abrasion resistance, and mechanical strength, but also possesses lightweight, resilience, cushioning, and thermal insulation properties due to its unique foaming structure. These characteristics make it widely used in sports footwear materials, sporting goods, and other industries.

[0003] Physical foaming is one of the common methods for preparing ETPU foam. It mainly utilizes physical foaming agents such as supercritical carbon dioxide or nitrogen, which are dissolved in the TPU matrix under high temperature and pressure. Then, through rapid depressurization or heating, the foaming agent rapidly vaporizes and expands inside the TPU, forming a cell structure, thus obtaining the ETPU foam. Currently, a common molding method involves impregnating TPU particles and foaming agents in an autoclave, then rapidly depressurizing to atmospheric pressure and foaming in a mold. However, this method suffers from unstable closed-cell ratios, affecting the product's compression resilience and durability.

[0004] In the field of athletic footwear materials, consumers have higher requirements for the resilience and support of shoes. Although the existing ETPU foam has a certain degree of resilience, it is prone to problems such as decreased resilience and increased permanent compression deformation after long-term use, which affects the lifespan of the shoes and the wearing experience. Summary of the Invention

[0005] To improve the resilience of ETPU foam and reduce the compression set, this application provides a molding method for ETPU foam and the resulting ETPU foam.

[0006] In a first aspect, this application provides a method for molding ETPU foam, which adopts the following technical solution: A method for molding ETPU foam includes the following steps: S1. Place TPU particles in a supercritical fluid and maintain it at a pressure of 15-30MPa and a temperature of 120-140℃ for 1-3 hours. Then, after depressurization, pre-foamed particles are obtained. S2. Fill the pre-foamed granules into the mold and perform the first molding foaming at 80-110℃ with a pressure of 2-5MPa for 10-30s. Then increase the pressure to 8-15MPa and hold for 20-60s. S3. Gradient cooling and shaping: First, cool down to 60-80℃ within 30 seconds and maintain pressure for 3-5 minutes. Then, depressurize and continue cooling to 30-40℃. After opening the mold, take out the ETPU foam.

[0007] By adopting the above technical solution, this application uses supercritical fluid to penetrate into the interior of TPU particles under high pressure and high temperature conditions to form a homogeneous system. Through rapid depressurization, the thermodynamic equilibrium of the system is disrupted, and the gas nucleates and expands in the TPU matrix, forming a large number of closed-cell structures to obtain pre-foamed particles. Then, after filling the mold with the pre-foamed particles, low-pressure short-time molding foaming is first performed to allow the particles to initially expand and tightly fill. Then, high-pressure constant-time foaming is performed to completely melt the particles, allowing them to be uniformly pressurized and fused in a confined space, forming a foam with uniform cell size and good interface fusion, while eliminating internal defect areas. Thus, the bubble structure and distribution are optimized by adjusting the pressure during the molding stage. Finally, in this application, a uniform closed-cell structure is generated through step S1, laying the foundation for lightweighting. Step S2 achieves particle melting and bonding and bubble structure optimization through two molding processes, improving its mechanical properties and producing a highly resilient, durable, and lightweight ETPU foam.

[0008] The process achieves particle fusion and structural densification through two-step molding foaming. The cooling process eliminates internal stress and fixes the cell structure by controlling temperature and pressure in stages. More specifically, through gradient cooling and shaping treatment, the first stage is rapid cooling under pressure, which effectively preserves and fixes the shape of the foam, prevents shrinkage and deformation, and maintains pressure to avoid cell collapse. Then, in the second stage, the pressure is released and cooling continues to release the pressure slowly, so that the material shrinks evenly and avoids surface defects. Finally, it is cooled to room temperature to complete the phase change curing. The staged cooling ensures that the cell structure does not become distorted during the cooling process and maintains high resilience. In the end, the ETPU foam prepared in this application has a higher closed-cell rate and a more consistent density distribution, thus exhibiting better compression set and resilience performance.

[0009] Optionally, the depressurization operation in step S1 is as follows: first, reduce the pressure to 5-8 MPa within 1 second, maintain it for 10-12 seconds, and then depressurize it to normal pressure. After depressurization, maintain the temperature at 120-140℃ for 5-10 minutes, and then cool it down to 60-70℃ within 60 seconds and maintain it for 3-5 minutes before cooling it down to room temperature to obtain pre-foamed granules.

[0010] By adopting the above technical solution, the supercritical fluid treatment is rapidly depressurized, causing a sharp drop in gas solubility. Supersaturated gas nucleates at TPU defect sites. Furthermore, this application preferably employs a staged depressurization process, releasing gas pressure in stages to ensure more uniform cell nucleation and growth. The first stage controls the decrease in gas solubility to form uniform, fine nuclei, avoiding the concentration of cell nucleation points caused by direct depressurization to atmospheric pressure. After maintaining medium pressure, depressurization continues. This medium-pressure maintenance stage promotes further gas diffusion within the TPU matrix, eliminating internal stress and limiting excessive cell expansion. Subsequently, when depressurized to atmospheric pressure, the residual gas continues to expand, refining the cell size, reducing the risk of bubble merging, and resulting in a narrower cell size distribution. This leads to better resilience and compression set of the ETPU foam. After depressurization, maintaining a high temperature eliminates internal stress, followed by cooling to fix the dense structure and reduce the risk of deformation before molding.

[0011] Optionally, the supercritical fluid in step S1 may be supercritical carbon dioxide or supercritical nitrogen.

[0012] Optionally, in step S1, the TPU particles are also mixed with SEBS block copolymer. In step S1, after the TPU particles and SEBS block copolymer are melt-blended and granulated to obtain TPU composite particles, they are placed in a supercritical fluid. The amount of SEBS block copolymer added is 3-5 wt% of the TPU particles.

[0013] By adopting the above technical solution, SEBS (styrene-butene / ethylene-styrene triblock copolymer) is composed of rigid styrene blocks and flexible ethylene / butene blocks. When SEBS is blended with TPU, its flexible segments can interact with the soft segments of TPU (such as polyether or polyester chains) to form a more continuous elastic network, thereby enhancing the material's resilience. The rigid styrene blocks in SEBS can form physical crosslinking points in the blend system, restricting the slippage of TPU molecular chains, thus reducing the permanent deformation of the material after long-term compression. Moreover, the hard segments of TPU (formed by diisocyanate) interact with the rigid blocks of SEBS to form a more stable phase structure. This synergistic effect can suppress micro-phase separation during compression, further reducing the compression set rate.

[0014] Optionally, the TPU particles in step S1 are also mixed with nanocomposite particles. In step S1, after the TPU particles and nanocomposite particles are melt-blended and granulated to obtain TPU composite particles, they are placed in a supercritical fluid. The amount of nanocomposite particles added is 5-8 wt% of the TPU particles. The nanocomposite particles are made by modifying graphene oxide-modified nano-silica with maleic anhydride and isocyanate monomers.

[0015] By adopting the above technical solution, the raw material system of this application also includes nanocomposite particles, which utilize the nanoscale porous structure to disperse stress and reduce local stress concentration. Under stress, the nanoparticles act as stress dispersion points, reducing the compression set rate. Moreover, the nanoparticles act as heterogeneous nucleation points, which can refine the foam structure, making the pore size smaller and more uniform. The change in microstructure directly improves the elastic recovery ability of the material. The two-dimensional sheet structure of graphene oxide forms a physical barrier on the surface of nano-silica, reducing the aggregation of nano-silica. Furthermore, the sheet structure of graphene oxide forms physical entanglement with the TPU molecular chains, and the hydroxyl groups in graphene oxide and nano-silica interact with the soft segments of TPU to form physical cross-linking points, restricting the slippage of molecular chains, thereby improving resilience.

[0016] After modifying the nano-silica with graphene oxide, it is further modified with maleic anhydride and isocyanate monomers. Maleic anhydride can be grafted onto the surface of nano-silica and graphene oxide, introducing polar groups such as carboxyl groups, which form hydrogen bonds or chemical bonds with the urethane groups in the TPU molecular chain, enhancing the interfacial bonding force. Isocyanate reacts with the hydroxyl groups on nano-silica and graphene oxide to generate urethane bonds, anchoring the polymer chain to the surface of the nanoparticles. The isocyanate monomers are similar in structure to the hard segment of TPU, thereby enhancing the compatibility with the soft segment of TPU. At the same time, the rigid structure of isocyanate is used to improve compression resilience.

[0017] Optionally, the isocyanate monomer can be MDI or TDI.

[0018] Optionally, the nanocomposite particles are prepared by the following methods: 1) Disperse nano-silica in a mixed solution of ethanol and water, add ammonia to adjust the pH to 9-10, stir, centrifuge and wash to obtain hydroxylated nano-silica; 2) Graphene oxide is dispersed in water, then hydroxylated nano-silica is added, and the reaction is carried out at 100-120℃ for 4-6 hours. After centrifugation and washing, the mixture is dried to obtain graphene oxide modified nano-silica. 3) Add graphene oxide-modified nano-silica to toluene, add maleic anhydride and p-toluenesulfonic acid, react at 75-85℃ for 3-4 hours, then cool to 45-55℃, add isocyanate monomers, react for 2-3 hours, wash and dry to obtain nanocomposite particles.

[0019] By adopting the above technical solution, nano-silica is first treated to increase the surface hydroxyl density, and then graphene oxide is introduced for treatment. The carboxyl groups of graphene oxide can undergo esterification with the hydroxyl groups of nano-silica to generate a covalently linked graphene oxide-modified silica composite. Then, it is first modified by maleic anhydride grafting to introduce anhydride groups, which can form hydrogen bonds or chemical bonds with the urethane groups in the TPU molecular chain, improving the compatibility with the TPU matrix. Then, isocyanate is added. The isocyanate groups can react with the hydroxyl or carboxyl groups in the above product to form urethane bonds. At the same time, highly active NCO groups can be introduced. The NCO groups can form crosslinks with the TPU molecular chain, significantly improving the compatibility between the two.

[0020] Optionally, in the preparation of nanocomposite particles, in step 1), ethanol and water are mixed in a volume ratio of (6-7):(3-4), and the mass ratio of nano-silica to the mixed solution is 1:(3-4). In step 2), graphene oxide is dispersed in water at 3-4 times its mass, and the mass ratio of graphene oxide to hydroxylated nano-silica is 1:(1-1.2). In step 3), the mass ratio of graphene oxide-modified nano-silica to toluene is 1:(5-6), and the mass ratio of maleic anhydride to graphene oxide-modified nano-silica is (1-1.5):1. The amount of p-toluenesulfonic acid added is 0.5-1wt% of the amount of graphene oxide-modified nano-silica added, and the amount of isocyanate monomers added is 8-10wt% of the amount of graphene oxide-modified nano-silica added.

[0021] Secondly, this application provides a TPU foam, which adopts the following technical solution: A TPU foam obtained by the molding method described above.

[0022] By adopting the above technical solution, the ETPU prepared by the method provided in this application has better elasticity and elastic durability, and a lower compression set rate.

[0023] In summary, this application has the following beneficial effects: 1. In this application, particle fusion and structural densification are achieved through two-step molding foaming. The cooling process eliminates internal stress and fixes the cell structure by controlling temperature and pressure in stages. The resulting ETPU foam has a higher closed-cell rate and a more consistent density distribution, thus exhibiting better compression set and resilience. 2. In this application, after the pre-foamed particles are filled into the mold, they are first subjected to low-pressure short-time molding foaming to make the particles initially expand and tightly fill the mold. Then, high-pressure constant-time foaming is carried out to completely melt the particles so that they are uniformly compressed and fused in the confined space to form a foam with uniform cell size and good interface fusion. At the same time, internal defect areas are eliminated. Thus, the bubble structure and distribution are optimized by adjusting the pressure during the molding stage. 3. In this application, gradient cooling is used for shaping. The first stage is rapid cooling under pressure, which effectively preserves the shape of the foam, prevents shrinkage and deformation, and maintains pressure to avoid cell collapse. Then, in the second stage, the pressure is released and cooling continues to release the pressure slowly, so that the material shrinks evenly and avoids surface defects. Finally, it is cooled to room temperature to complete the phase change and solidification. The staged cooling ensures that the cell structure does not become distorted during the cooling process and maintains high resilience. Detailed Implementation

[0024] The present application will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from commercially available sources.

[0025] In the following examples, the SEBS block copolymer used is SEBS from the brand Kraton, grade G1701; The TPU granules used are BASF brand TPU granules with grade 1185A, sourced from Dongguan Xingwang Plastic Raw Materials Co., Ltd.

[0026] The following preparation examples are examples of the preparation of nanocomposite particles. Preparation Example 1 A method for preparing nanocomposite particles includes the following steps: 1) Prepare a mixed solution by mixing ethanol and water at a volume ratio of 7:3. Then, disperse nano-silica in the mixed solution of ethanol and water. The mass ratio of nano-silica to the mixed solution is 1:3.5. Add ammonia to adjust the pH to 9.5. After stirring, centrifuge and wash to obtain hydroxylated nano-silica. 2) Graphene oxide was dispersed in 3.5 times the mass of water, and then hydroxylated nano-silica was added. The mass ratio of graphene oxide to hydroxylated nano-silica was 1:1.1. The mixture was reacted at 110℃ for 5 hours. After centrifugation and washing, it was dried to obtain graphene oxide modified nano-silica. 3) Add graphene oxide-modified nano-silica to toluene, add maleic anhydride and p-toluenesulfonic acid, react at 80℃ for 3.5h, then cool to 50℃, add isocyanate monomer MDI, react for 2.5h, wash and dry to obtain nano-composite particles.

[0027] In step 3), the mass ratio of graphene oxide-modified nano-silica to toluene is 1:5.5, the mass ratio of maleic anhydride to graphene oxide-modified nano-silica is 1.2:1, the amount of p-toluenesulfonic acid added is 0.8 wt% of the amount of graphene oxide-modified nano-silica added, and the amount of isocyanate monomer added is 9 wt% of the amount of graphene oxide-modified nano-silica added.

[0028] Preparation Example 2 A method for preparing nanocomposite particles includes the following steps: 1) Prepare a mixed solution by mixing ethanol and water at a volume ratio of 6:4. Then, disperse nano-silica in the mixed solution of ethanol and water at a mass ratio of 1:3. Add ammonia to adjust the pH to 9, stir, centrifuge and wash to obtain hydroxylated nano-silica. 2) Graphene oxide was dispersed in 3 times the mass of water, and then hydroxylated nano-silica was added. The mass ratio of graphene oxide to hydroxylated nano-silica was 1:1. The mixture was reacted at 100℃ for 6 hours. After centrifugation and washing, it was dried to obtain graphene oxide modified nano-silica. 3) Add graphene oxide-modified nano-silica to toluene, add maleic anhydride and p-toluenesulfonic acid, react at 75°C for 3 hours, then cool to 45°C, add isocyanate monomer MDI, react for 3 hours, wash and dry to obtain nanocomposite particles.

[0029] In step 3), the mass ratio of graphene oxide-modified nano-silica to toluene is 1:5, the mass ratio of maleic anhydride to graphene oxide-modified nano-silica is 1:1, the amount of p-toluenesulfonic acid added is 0.5 wt% of the amount of graphene oxide-modified nano-silica added, and the amount of isocyanate monomer added is 8 wt% of the amount of graphene oxide-modified nano-silica added.

[0030] Preparation Example 3 A method for preparing nanocomposite particles includes the following steps: 1) Prepare a mixed solution by mixing ethanol and water at a volume ratio of 6.5:3.5. Then disperse nano-silica in the mixed solution of ethanol and water at a mass ratio of 1:4. Add ammonia to adjust the pH to 10, stir, centrifuge and wash to obtain hydroxylated nano-silica. 2) Graphene oxide was dispersed in 4 times the mass of water, and then hydroxylated nano-silica was added. The mass ratio of graphene oxide to hydroxylated nano-silica was 1:1.2. The mixture was reacted at 120°C for 4 hours. After centrifugation and washing, the mixture was dried to obtain graphene oxide modified nano-silica. 3) Add graphene oxide-modified nano-silica to toluene, add maleic anhydride and p-toluenesulfonic acid, react at 85℃ for 3h, then cool to 55℃, add isocyanate monomer MDI, react for 2h, wash and dry to obtain nanocomposite particles.

[0031] In step 3), the mass ratio of graphene oxide-modified nano-silica to toluene is 1:6, the mass ratio of maleic anhydride to graphene oxide-modified nano-silica is 1.5:1, the amount of p-toluenesulfonic acid added is 1 wt% of the amount of graphene oxide-modified nano-silica added, and the amount of isocyanate monomer added is 10 wt% of the amount of graphene oxide-modified nano-silica added.

[0032] Preparation Example 4 A method for preparing nanocomposite particles is carried out according to the method in Preparation Example 1, except that step 3) is not performed, and the graphene oxide modified nano-silica obtained in step 2) is directly used as nanocomposite particles.

[0033] Example 1

[0034] A method for molding ETPU foam includes the following steps: S1. Material preparation: Using 1kg of TPU granules as the processing standard, the TPU granules are dried at 60℃ for 6 hours. Then, the dried TPU granules are placed in a supercritical fluid, specifically supercritical carbon dioxide, and kept at a pressure of 20MPa and a temperature of 130℃ for 2 hours. Then, the pressure is reduced to 6MPa within 1 second, held for 11 seconds, and then depressurized to atmospheric pressure. After depressurization, the temperature is maintained at 130℃ for 8 minutes. Then, the temperature is reduced to 65℃ within 60 seconds and held for 4 minutes before being cooled to room temperature to obtain pre-foamed granules. S2. Fill the pre-foamed granules into a mold preheated to 90°C. After closing the mold, apply pressure for the first time and perform the first molding foaming at 90°C. The pressure is 3MPa and held for 20s. Then apply pressure for the second time to increase the pressure to 10MPa and hold for 40s. S3. Perform gradient cooling and shaping on the mold after step S2. First, cool it to 70°C within 30 seconds and maintain the pressure for 4 minutes. Then, depressurize and continue cooling to 30°C. After opening the mold, take out the ETPU foam.

[0035] Example 2

[0036] A method for molding ETPU foam includes the following steps: S1. Material preparation: Using 1kg of TPU granules as the processing standard, the TPU granules are dried at 60℃ for 6 hours. Then, the dried TPU granules are placed in a supercritical fluid, specifically supercritical carbon dioxide, and kept at a pressure of 15MPa and a temperature of 120℃ for 3 hours. Then, the pressure is reduced to 5MPa within 1 second, held for 10 seconds, and then depressurized to atmospheric pressure. After depressurization, the temperature is kept at 120℃ for 10 minutes. Then, the temperature is reduced to 60℃ within 60 seconds and held for 5 minutes before being cooled to room temperature to obtain pre-foamed granules. S2. Fill the pre-foamed granules into a mold preheated to 80°C. After closing the mold, apply pressure for the first time and perform the first molding foaming at 80°C. The pressure is 2MPa and held for 30s. Then, apply pressure for the second time to increase the pressure to 8MPa and hold for 60s. S3. Perform gradient cooling and shaping on the mold after step S2. First, cool it to 60°C within 30 seconds and maintain the pressure for 5 minutes. Then, depressurize and continue cooling to 30°C. After opening the mold, take out the ETPU foam.

[0037] Example 3

[0038] A method for molding ETPU foam includes the following steps: S1. Material preparation: Using 1kg of TPU granules as the processing standard, the TPU granules are dried at 60℃ for 6 hours. Then, the dried TPU granules are placed in a supercritical fluid, specifically supercritical carbon dioxide, and kept at a pressure of 30MPa and a temperature of 140℃ for 1 hour. Then, the pressure is reduced to 8MPa within 1 second, held for 10 seconds, and then depressurized to atmospheric pressure. After depressurization, the temperature is maintained at 140℃ for 5 minutes. Then, the temperature is reduced to 70℃ within 60 seconds and held for 3 minutes before being cooled to room temperature to obtain pre-foamed granules. S2. Fill the pre-foamed granules into a mold preheated to 110°C. After the mold is closed, apply pressure for the first time and perform the first molding foaming at 110°C. The pressure is 5MPa and held for 10s. Then apply pressure for the second time to increase the pressure to 15MPa and hold for 20s. S3. Perform gradient cooling and shaping on the mold after step S2. First, cool it to 80°C within 30 seconds and maintain the pressure for 3 minutes. Then, depressurize and continue cooling to 40°C. After opening the mold, take out the ETPU foam.

[0039] Example 4

[0040] A method for molding ETPU foam is carried out according to the method in Example 1, except that in step S1, the pressure is maintained at 20 MPa and the temperature is 130°C for 2 hours, and then the pressure is directly released to normal pressure within 5 seconds, and then the temperature is lowered to room temperature to obtain pre-foamed granules.

[0041] Example 5

[0042] A method for molding ETPU foam, performed according to the method in Example 1, differs in that, in step S1, the TPU particles placed in the supercritical fluid are also doped with SEBS block copolymer. Specifically, the TPU particles and SEBS block copolymer are melt-blended, granulated, and then placed in the supercritical fluid. More specifically: TPU granules and SEBS granules were dried at 60°C for 6 hours. Then, the dried TPU granules and SEBS were added to a twin-screw extruder. The amount of SEBS block copolymer added was 4 wt% of the TPU granules. The mixture was melt-blended at 170°C with a screw speed of 130 r / min. After melt blending, the mixture was extruded and cooled, and then cut by a pelletizer to obtain TPU composite granules. The TPU composite granules were then placed in a supercritical fluid and processed according to the method in Example 1.

[0043] Example 6

[0044] A method for molding ETPU foam, following the method in Example 1, differs in that, in step S1, the TPU particles placed in the supercritical fluid are further doped with SEBS block copolymer. Specifically, the TPU particles and SEBS block copolymer are melt-blended, granulated, and then placed in the supercritical fluid. More specifically: TPU granules and SEBS granules were dried at 60°C for 6 hours. Then, the dried TPU granules and SEBS were added to a twin-screw extruder. The amount of SEBS block copolymer added was 3 wt% of the TPU granules. The mixture was melt-blended at 160°C with a screw speed of 120 r / min. After melt blending, the mixture was extruded and cooled, and then cut by a pelletizer to obtain TPU composite granules. The TPU composite granules were then placed in a supercritical fluid and processed according to the method in Example 1.

[0045] Example 7

[0046] A method for molding ETPU foam, performed according to the method in Example 1, differs in that, in step S1, the TPU particles placed in the supercritical fluid are also doped with SEBS block copolymer. Specifically, the TPU particles and SEBS block copolymer are melt-blended, granulated, and then placed in the supercritical fluid. More specifically: TPU granules and SEBS granules were dried at 60°C for 6 hours. Then, the dried TPU granules and SEBS were added to a twin-screw extruder. The amount of SEBS block copolymer added was 5 wt% of the TPU granules. The mixture was melt-blended at 180°C with a screw speed of 150 r / min. After melt blending, the mixture was extruded and cooled, and then cut by a pelletizer to obtain TPU composite granules. The TPU composite granules were then placed in a supercritical fluid and processed according to the method in Example 1.

[0047] Example 8

[0048] A method for molding ETPU foam is carried out according to the method in Example 5, except that in step S1, nanocomposite particles are also incorporated into the TPU particles. After the TPU particles and nanocomposite particles are melt-blended and granulated, they are placed in a supercritical fluid. The specific operation is as follows: TPU particles and nanocomposite particles prepared in Preparation Example 1 were dried at 60°C for 6 hours. Then, the dried TPU particles and nanocomposite particles were added to a twin-screw extruder, with the amount of nanocomposite particles being 6 wt% of the TPU particles. The particles were melt-blended at 180°C with a screw speed of 150 r / min. After melt blending, the particles were extruded and cooled, and then cut by a pelletizer to obtain TPU composite particles. The TPU composite particles were then placed in a supercritical fluid and processed according to the method in Example 1.

[0049] Example 9

[0050] A method for molding ETPU foam is carried out according to the method in Example 5, except that in step S1, nanocomposite particles are also incorporated into the TPU particles. After the TPU particles and nanocomposite particles are melt-blended and granulated, they are placed in a supercritical fluid. The specific operation is as follows: TPU particles and nanocomposite particles prepared in Example 1 were dried at 60°C for 6 hours. Then, the dried TPU particles and nanocomposite particles were added to a twin-screw extruder, with the amount of nanocomposite particles being 5 wt% of the TPU particles. The particles were melt-blended at 180°C with a screw speed of 150 r / min. After melt blending, the particles were extruded and cooled, and then cut by a pelletizer to obtain TPU composite particles. The TPU composite particles were then placed in a supercritical fluid and processed according to the method in Example 1.

[0051] Example 10

[0052] A method for molding ETPU foam is carried out according to the method in Example 5, except that in step S1, nanocomposite particles are also incorporated into the TPU particles. After the TPU particles and nanocomposite particles are melt-blended and granulated, they are placed in a supercritical fluid. The specific operation is as follows: TPU particles and nanocomposite particles prepared in Example 1 were dried at 60°C for 6 hours. Then, the dried TPU particles and nanocomposite particles were added to a twin-screw extruder, with the amount of nanocomposite particles being 8 wt% of the TPU particles. The particles were melt-blended at 180°C with a screw speed of 150 r / min. After melt blending, the particles were extruded and cooled, and then cut by a pelletizer to obtain TPU composite particles. The TPU composite particles were then placed in a supercritical fluid and processed according to the method in Example 1.

[0053] Example 11

[0054] A method for molding ETPU foam is carried out according to the method in Example 8, except that the nanocomposite particles are selected from the nanocomposite particles prepared in Preparation Example 4.

[0055] Example 12

[0056] A method for molding ETPU foam is carried out according to the method in Example 8, except that the nanocomposite particles are replaced with an equal amount of nano-silica.

[0057] Comparative Example 1 A molding method for ETPU foam is carried out according to the method in Example 1, except that in step S2, the foam is directly molded at 90°C and 5MPa pressure for 1 minute.

[0058] Comparative Example 2 A molding method for ETPU foam is carried out according to the method in Example 1, except that in step S3, the temperature is directly reduced to 70°C within 30 seconds, and then the pressure is directly released and the temperature is further cooled to 30°C.

[0059] Performance testing The springback rate of the ETPU prepared in the above examples and comparative examples was tested in accordance with GB / T 1681-2009, and the results are shown in Table 1 below. In addition, the compression set rate of ETPU was tested in accordance with the method for determining compression set at room temperature in Part 1 of GB / T7759.1-2015, and the test results are shown in Table 1 below.

[0060] Table 1

[0061] Based on the test results in Table 1 above, the ETPU foam prepared in this application exhibits good resilience while reducing compression set. Based on the test results of Examples 1-3, the ETPU foam of this application exhibits good resilience and low compression set, demonstrating good shape recovery after long-term compression and good durability. Furthermore, considering the test results of Examples 1 and 4, the depressurization treatment in Example 4 directly depressurizes to atmospheric pressure, resulting in a lower resilience and a higher compression set. Staged depressurization plays a crucial role in improving product resilience and reducing compression set. Finally, considering the test results of Examples 5-7, when SEBS block copolymer is added to the TPU particle base, both the resilience and compression set are improved.

[0062] Combining the test results of Examples 1 and 8-10, when nanocomposite particles are added to the TPU particle base, the resilience is further improved while the compression set is further reduced. This addition plays a crucial role in reducing resilience and long-term compression set. Combining the test results of Example 11, when the nanocomposite particles are not modified with isocyanate, their resilience decreases and their compression set increases. Isocyanate modification helps improve the compatibility between the nanocomposite particles and the TPU matrix, thus acting as a nucleating agent and improving compatibility, thereby optimizing the cell structure and enhancing its durability and resilience. Combining the test results of Example 12, when nano-silica is added directly, the compression set is lower than in Example 5. The effect of adding nano-silica on reducing compression set is limited.

[0063] Finally, combining the test results of Example 1 and Comparative Example 1, it was found that the molding foaming in Comparative Example 1 was done in one step, and the cooling and shaping in Comparative Example 2 was done in one step. Both showed a significant decrease in rebound rate and a significant increase in compression set. The two-step molding foaming and gradient cooling and shaping in this application play an important role in improving rebound performance and reducing permanent compression set.

[0064] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for molding ETPU foam, characterized in that, Includes the following steps: S1. Place TPU particles in a supercritical fluid and maintain it at a pressure of 15-30MPa and a temperature of 120-140℃ for 1-3 hours. Then, after depressurization, pre-foamed particles are obtained. S2. Fill the pre-foamed granules into the mold and perform the first molding foaming at 80-110℃ with a pressure of 2-5MPa for 10-30s. Then increase the pressure to 8-15MPa and hold for 20-60s. S3. Gradient cooling and shaping: First, cool down to 60-80℃ within 30 seconds and maintain pressure for 3-5 minutes. Then, depressurize and continue cooling to 30-40℃. After opening the mold, take out the ETPU foam.

2. The molding method of an ETPU foam according to claim 1, characterized in that: The specific operation of depressurization in step S1 is as follows: first, reduce the pressure to 5-8 MPa within 1 second, maintain it for 10-12 seconds, and then depressurize it to normal pressure. After depressurization, maintain the temperature at 120-140℃ for 5-10 minutes, and then cool it down to 60-70℃ within 60 seconds and maintain it for 3-5 minutes before cooling it down to room temperature to obtain pre-foamed granules.

3. The molding method of an ETPU foam according to claim 1, characterized in that: The supercritical fluid used in step S1 is either supercritical carbon dioxide or supercritical nitrogen.

4. The molding method of an ETPU foam according to claim 1, characterized in that: In step S1, the TPU particles are also mixed with SEBS block copolymer. In step S1, after the TPU particles and SEBS block copolymer are melt-blended and granulated to obtain TPU composite particles, they are placed in a supercritical fluid. The amount of SEBS block copolymer added is 3-5 wt% of the TPU particles.

5. The molding method of an ETPU foam according to claim 1, characterized in that: The TPU particles in step S1 also contain nanocomposite particles. In step S1, the TPU particles and nanocomposite particles are melt-blended and granulated to obtain TPU composite particles, which are then placed in a supercritical fluid. The amount of nanocomposite particles added is 5-8 wt% of the TPU particles. The nanocomposite particles are made by modifying graphene oxide-modified nano-silica with maleic anhydride and isocyanate monomers.

6. The molding method of an ETPU foam according to claim 5, characterized in that: The isocyanate monomers selected are MDI or TDI.

7. The molding method of an ETPU foam according to claim 5, characterized in that: Nanocomposite particles are prepared by the following method: 1) Disperse nano-silica in a mixed solution of ethanol and water, add ammonia to adjust the pH to 9-10, stir, centrifuge and wash to obtain hydroxylated nano-silica; 2) Graphene oxide is dispersed in water, then hydroxylated nano-silica is added, and the reaction is carried out at 100-120℃ for 4-6 hours. After centrifugation and washing, the mixture is dried to obtain graphene oxide modified nano-silica. 3) Add graphene oxide-modified nano-silica to toluene, add maleic anhydride and p-toluenesulfonic acid, react at 75-85℃ for 3-4 hours, then cool to 45-55℃, add isocyanate monomers, react for 2-3 hours, wash and dry to obtain nanocomposite particles.

8. The molding method of an ETPU foam according to claim 7, characterized in that: In the preparation of nanocomposite particles, in step 1), ethanol and water are mixed in a volume ratio of (6-7):(3-4), and the mass ratio of nano-silica to the mixed solution is 1:(3-4). In step 2), graphene oxide is dispersed in water at 3-4 times its mass, and the mass ratio of graphene oxide to hydroxylated nano-silica is 1:(1-1.2). In step 3), the mass ratio of graphene oxide-modified nano-silica to toluene is 1:(5-6), and the mass ratio of maleic anhydride to graphene oxide-modified nano-silica is (1-1.5):

1. The amount of p-toluenesulfonic acid added is 0.5-1wt% of the amount of graphene oxide-modified nano-silica added, and the amount of isocyanate monomers added is 8-10wt% of the amount of graphene oxide-modified nano-silica added.

9. A TPU foam obtained by the molding method according to any one of claims 1-8.

Images