A high-resilience eTPU foam material and a process for its preparation

Abstract

The application discloses a kind of high resilience eTPU foamed materials and preparation process thereof, belong to foamed material technical field.The process includes: raw material premixing and TPU chain extension reaction, precursor system injection, in-situ phase change energy storage core-shell particle generation, supercritical two-fluid foaming, moulding post-processing.SiO2@TiO2Core-shell particles are made by non-hydrolytic sol-gel method, porous SiO2Core adsorbs fixed micro-crosslinking polyurethane-based phase change material, TiO2Shell provides sealing and support, particle is combined with TPU matrix by covalent bond, the micro-crosslinking polyurethane-based phase change material can effectively eliminate leakage hidden danger of phase change material in use process by its unique micro-crosslinking network structure, while synchronously strengthening interface bonding between inorganic particle and TPU matrix.The eTPU foamed material prepared by the application has the characteristics of high resilience, strong interface bonding, excellent energy storage stability and low compression permanent deformation, and is suitable for shoe material, automotive interior and other scenes.

Description

Technical Field

[0001] This invention relates to the field of foam materials technology, and in particular to a high-resilience eTPU foam material and its preparation process. Background Technology

[0002] Thermoplastic polyurethane elastomer (TPU) possesses excellent abrasion resistance, high elasticity, and good processability, making it widely used in footwear materials, automotive interiors, and other fields. Expanded thermoplastic polyurethane (eTPU), with its microporous structure reducing density and enhancing cushioning and rebound performance, is the preferred material for midsoles of high-end athletic shoes. As end-applications demand increasingly higher comprehensive material performance, phase change energy storage materials that endow eTPU with temperature regulation capabilities have become a research hotspot. However, existing phase change energy storage eTPU materials and their preparation processes still face many pressing technical challenges.

[0003] First, the leakage risk of phase change materials is incompatible with the encapsulation process. To endow materials with energy storage capabilities, paraffin-based phase change materials are often introduced, but their solid-liquid phase change characteristics easily lead to leakage. Existing technologies mostly use physical adsorption or hydrolytic sol-gel methods for preparation. However, physical adsorption results in poor coating and durability; while hydrolytic sol-gel methods require the introduction of a large amount of water, which seriously conflicts with TPU raw materials that are extremely sensitive to moisture, easily leading to side reactions, matrix degradation, or bubble defects. Furthermore, it is difficult to accurately control the regularity and density of the core-shell structure under continuous reactive extrusion conditions. Second, it is difficult to simultaneously achieve good dispersibility and interfacial compatibility of inorganic nanofillers. Whether it is the inorganic core-shell particles used as a carrier or other fillers added to improve resilience, their high surface energy makes them prone to agglomeration, and traditional physical blending processes cannot achieve uniform dispersion. Moreover, the large polarity difference between inorganic fillers and the organic TPU matrix results in weak interfacial bonding. During subsequent processing and dynamic fatigue use, the filler is prone to peeling and migration, leading to structural damage, leakage of phase change materials, and a significant decrease in mechanical properties, resulting in a trade-off between energy storage function and mechanical performance. Third, the uniformity and stability of the cell structure during foaming are difficult to balance. The viscoelastic properties of the system change after the introduction of functional core-shell particles. Single supercritical fluid foaming systems face the challenge of synergistic nucleation and growth; nucleation density and cell growth are mutually constrained, resulting in uneven cell size distribution, which becomes a weak point of stress concentration, significantly reducing the material's resilience and fatigue resistance. Fourth, the interfacial bonding strength is insufficient during the molding stage. In existing molding processes, eTPU foam beads rely on surface melting for physical bonding. This interface is prone to aging, delamination, or tearing under long-term dynamic loads or environmental changes, leading to product failure, especially after the introduction of phase change materials, this problem becomes more prominent.

[0004] In summary, the key technical bottlenecks that urgently need to be overcome are how to achieve efficient sealing and encapsulation of phase change materials while avoiding the introduction of moisture, construct a strong interface between inorganic fillers and TPU matrix, and synergistically optimize foaming and molding processes to obtain eTPU materials with high energy storage, high resilience, and high durability. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a high-resilience eTPU foam material and its preparation process.

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

[0007] A preparation process for a high-resilience eTPU foam material includes the following steps:

[0008] (1) Raw material premixing and TPU chain extension reaction: The polyether ester polyol, diisocyanate mixture, chain extender, TPU chain extension catalyst and additives are added to the co-rotating twin-screw reactive extruder. The temperature gradient is set along the screw axis to heat in stages to carry out the chain extension reaction until the TPU molecular weight increases stably.

[0009] (2) Precursor system injection: In the downstream section of the extruder after the chain extension reaction is completed, a non-hydrolyzable sol-gel precursor system is injected by a metering pump;

[0010] This step, injecting the precursor system downstream of the TPU chain extension reaction, is chosen to avoid interference from active substances in the precursor components with the main reaction process. The use of a non-hydrolyzable sol-gel route blocks the introduction of water, thus preventing side reactions between water and isocyanate groups that could lead to bubble formation or molecular weight loss in the matrix. The active groups carried by the functionalized silane coupling agent provide connection sites for subsequent chemical bonding with the TPU matrix at this stage.

[0011] (3) In-situ generation of core-shell particles for phase change energy storage: In the downstream micro-reaction zone of the extruder, the reaction conditions are controlled to cause the precursor system to undergo a condensation reaction, and SiO2@TiO2 core-shell nanoparticles loaded with micro-crosslinked polyurethane-based phase change material are generated in-situ. TPU masterbatch is obtained by underwater pelletizing.

[0012] The non-hydrolytic condensation reaction within the micro-reaction zone in this step promotes the in-situ generation of nanoparticles with a porous silica core and a dense titanium dioxide shell from the precursor. The porous silica core layer adsorbs and immobilizes the liquid micro-crosslinked polyurethane-based phase change material to address leakage issues, while the titanium dioxide shell provides mechanical support to withstand processing stress. Functionalized silane coupling agents act as molecular bridges in the reaction, enabling the inorganic particle surface to be tightly bound to the TPU molecular chains via covalent bonds. The micro-crosslinked polyurethane-based phase change material achieves solid-solid phase change characteristics through a chemical crosslinking network design. Its phase change mechanism is based on the reversible crystallization-melting behavior of polyurethane soft segments (formed by the reaction of 1,10-decanediol and diisocyanate) in the 25-40℃ temperature range, thereby efficiently absorbing or releasing latent heat. Compared with paraffin-based phase change materials, the micro-crosslinking network effectively restricts the macroscopic flow of polymer chains, overcomes the volume expansion and leakage problems during the phase change process, and significantly improves the encapsulation stability of the material. Regarding interfacial bonding, the dimethylolpropionic acid introduced into this phase change material provides a carboxyl polar group, which enhances its physical adsorption and chemical interaction with the porous SiO2 core and TiO2 shell surface. At the same time, the isocyanate group (-NCO) retained at the end of its molecule undergoes in-situ chemical bonding with the TPU matrix and functionalized silane coupling agent during extrusion, constructing a strong interfacial layer that runs through the "core-shell particles-phase change material-TPU matrix". This not only prevents the agglomeration of the phase change material, but also significantly improves the interfacial bonding strength and mechanical transport efficiency of the composite material.

[0013] (4) Supercritical two-fluid foaming: The dried TPU masterbatch is placed in a high-pressure reactor, and supercritical N2 and supercritical CO2 are introduced first. The reaction is carried out under certain temperature and pressure, and then the temperature is gradually reduced and the pressure is rapidly released to obtain foamed beads.

[0014] In this step, supercritical N2 can establish high-density bubble nuclei in the matrix, while supercritical carbon dioxide has excellent plasticizing effect and solubility on the TPU matrix. The graded impregnation process utilizes the mechanism of N2-dominated nucleation and carbon dioxide-dominated growth to achieve independent control of cell density and size. Combined with gradient cooling and rapid pressure relief processes, this mechanism significantly improves the uniformity of the cell structure.

[0015] (5) Post-molding treatment: The foamed beads are loaded into the mold, and high-pressure steam is introduced to melt the surface of the beads and achieve interface bonding; after heat preservation and pressure preservation, and cooling and demolding, high-resilience eTPU foam material is obtained.

[0016] This step, high-pressure steam heating, melts the surface of the beads, and water molecules initiate trace hydrolysis of the TPU molecular chains at the interface. The in-situ generated active end groups further react to form new chemical bonds, thereby significantly enhancing the interfacial bonding strength. The subsequent heat preservation and pressure holding process helps to eliminate internal stress in the product and stabilize the cell structure, ultimately improving the material's resilience.

[0017] Preferably, the eTPU foam material comprises a TPU matrix and in-situ generated SiO2@TiO2 core-shell nanoparticles loaded with micro-crosslinked polyurethane-based phase change material; the core-shell nanoparticles have a particle size of 40-100 nm, a core-shell ratio of SiO2:TiO2 of 1:1-3, a shell thickness of 5-15 nm, and the loading of micro-crosslinked polyurethane-based phase change material is 20-40% of the mass of the core-shell particles.

[0018] Preferably, in step (1), the temperature gradient gradually increases along the screw axis from the feed end to the die end, successively at 150-160℃, 170-180℃, 180-190℃, and 200-210℃; the number average molecular weight of the polyether ester polyol is 2000-4000; and the diisocyanate mixture is a mixture of hexamethylene diisocyanate and isophorone diisocyanate in a molar ratio of 1:0.3-0.7. Temperature control in separate temperature zones helps control the TPU chain extension reaction rate and molecular structure, avoiding reactions that are too fast or too slow. The molecular weight of the polyol and the type and ratio of diisocyanate together determine the ratio of soft and hard segments and the crystallization behavior of the TPU, thereby affecting the elasticity and mechanical strength of the matrix.

[0019] Preferably, in step (1), the chain extender is a mixture of 1,4-butanediol and trimethylolpropane in a molar ratio of 1:0.05-0.15; the TPU chain extender catalyst is dibutyltin dilaurate, added at 0.01-0.05% of the total mass of the TPU raw material; the additives are a mixture of antioxidant, lubricant, and nucleating agent, added at 0.1-1.0% of the total mass of the TPU raw material, wherein the antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1, the lubricant is zinc stearate, and the nucleating agent is talc or nano-calcium carbonate. The nucleating agent promotes the formation of bubble nuclei during the foaming stage, which is beneficial to improving the cell density and uniformity.

[0020] Preferably, in step (2), the precursor system comprises a metal halide, a metal alkoxide, a functionalized silane coupling agent, and a micro-crosslinked polyurethane-based phase change material; the metal halide is titanium tetrachloride, the metal alkoxide is tetraethyl orthosilicate, and the molar ratio of titanium tetrachloride to tetraethyl orthosilicate is 1:1-4; the functionalized silane coupling agent is propyltriethoxysilane isocyanate, and the amount added is 5-15% of the total mass of the precursor system.

[0021] Preferably, in step (2), the specific preparation steps of the micro-crosslinked polyurethane-based phase change material are as follows:

[0022] Add 1,10-decanediol, trimethylolpropane, and dimethylolpropionic acid to a four-necked reactor in a molar ratio of 1:0.03-0.10:0.05-0.15. Start stirring, heat to 80-90℃, and apply a vacuum of -0.095 to -0.100 MPa for 30-60 minutes to dehydrate. After dehydration, purge with nitrogen and cool to 60-70℃ for later use. Subsequently, under nitrogen protection, maintain the temperature at 60-70℃ and add hexamethylene diisocyanate dropwise to the reactor at 1-2 mL / min, controlling the NCO:OH molar ratio. The ratio of dibutyltin dilaurate to 1:1.1-1.3 was used. After the addition was complete, the mixture was stirred for 10-15 min. Then, 0.01-0.03% of the total mass of 1,10-decanediol, trimethylolpropane, dimethylolpropionic acid, and hexamethylene diisocyanate was added. The reaction was maintained at 60-70℃ for 1-2 h. After the reaction was completed, the temperature was lowered to 50-60℃, and n-dodecyl alcohol was added. The mixture was stirred for 20-30 min to ensure that the final NCO% was controlled at 1-3%. After the reaction was completed, the heating was turned off, the mixture was cooled to room temperature, dried, and granulated to obtain the micro-crosslinked polyurethane-based phase change material.

[0023] Preferably, in step (2), the precursor system is diluted with an inert high-boiling-point solvent before injection. The inert high-boiling-point solvent is one of liquid polyester polyol, dioctyl phthalate, or dioctyl terephthalate, and the mass ratio of the precursor system to the inert high-boiling-point solvent is 1:0.5-1.2. The inert high-boiling-point solvent can reduce the viscosity of the precursor system and improve its dispersion in the TPU melt, while not volatilizing or decomposing at the extrusion temperature, thus avoiding the generation of bubbles or interference with the main reaction.

[0024] Preferably, in step (3), the micro-reaction zone is constructed using a screw element assembly, which includes a forward conveying block, a kneading block, and a reverse threaded element. The number of kneading blocks is 2-4 sets, and the reverse threaded element is located downstream of the kneading blocks to extend the precursor reaction residence time and ensure the dense sealing of the TiO2 shell. The forward conveying block is used for material propulsion, the kneading block provides shearing and mixing, and the reverse threaded element forms a localized filling zone, extending the reaction residence time and facilitating the full non-hydrolytic condensation process to form a dense TiO2 shell.

[0025] Preferably, in step (5), the pressure of the high-pressure steam is 0.3-0.5 MPa; the interfacial bonding is achieved by the steam initiating a trace amount of TPU ester bond hydrolysis at the bead contact interface, generating urethane bonds in situ to enhance the interface. The high-pressure steam heating melts the surface layer of the beads, and at the same time, water molecules initiate a trace amount of TPU ester bond hydrolysis at the interface. The generated end groups then react with neighboring molecules to form new urethane bonds, thereby establishing chemical bonds at the bead interface, improving the interfacial bonding strength and product durability.

[0026] High-resilience eTPU foam material prepared according to the above-described preparation process.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. This invention employs a non-hydrolyzable sol-gel route to generate SiO2@TiO2 core-shell nanoparticles in situ within the micro-reaction zone of a reactive extruder. This, combined with the mechanism of porous SiO2 core adsorption and fixation of micro-crosslinked polyurethane-based phase change material and the sealing mechanism of a dense TiO2 shell, solves the problems of easy destruction of the core-shell structure, particle agglomeration in physical blending, and easy leakage of the phase change material in traditional hydrolysis systems. Furthermore, this invention uses a micro-crosslinked polyurethane-based phase change material instead of traditional paraffin-based materials. This material possesses solid-solid phase change characteristics, effectively limiting volume expansion during the phase change process and preventing damage to the core-shell sealing layer. Moreover, the carboxyl polar groups introduced into its molecular chain and the isocyanate groups retained at the ends form chemical bonds with the core-shell particles and the TPU matrix. Compared to traditional paraffin-based materials, the micro-crosslinked polyurethane phase change material of this invention has better compatibility and stronger bonding with the matrix, achieving extremely low leakage and high energy storage stability of the phase change material without sacrificing the mechanical properties of the matrix.

[0029] 2. This invention adds a functionalized silane coupling agent containing isocyanate active groups to the precursor system. Combined with the interfacial bonding mechanism of the coupling agent forming covalent bonds with the TPU molecular chain, it solves the problems of poor interfacial compatibility and weak bonding force between inorganic nanofillers and organic TPU matrix, and achieves the effects of improving the mechanical properties of materials and optimizing energy storage stability.

[0030] 3. This invention employs a supercritical N2 and CO2 staged impregnation foaming process, combined with the synergistic mechanism of N2-dominated nucleation, CO2-dominated cell growth, and gradient cooling and rapid depressurization, which solves the problems of uneven cell size and poor synergy between nucleation and growth in a single supercritical fluid foaming system, and achieves the effect of high resilience and low compression set of the material.

[0031] 4. This invention employs high-pressure steam molding and dynamic post-processing, combined with the interface enhancement mechanism of steam-induced micro-hydrolysis of TPU ester bonds and in-situ generation of urethane bonds. This solves the problem of low bonding strength and easy aging and delamination of foamed beads in traditional hot pressing, which rely solely on physical melting and bonding. This invention achieves strong bonding of the product interface and excellent dynamic fatigue durability.

[0032] 5. This invention overcomes the technical bottlenecks faced by traditional paraffin-based phase change materials after encapsulation by in-situ synthesis of micro-crosslinked polyurethane-based phase change materials and in-situ loading of core-shell particles, and by precisely controlling process parameters such as non-hydrolyzable sol-gel, functionalized silane coupling agent, two-fluid foaming and water vapor chemical bonding. It successfully solves the problem of mutual constraint between energy storage function and mechanical properties in functional foamed materials, and achieves the effect of synergistic balance between phase change energy storage function and high mechanical properties. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] Example 1: Preparation of high-resilience eTPU foam material:

[0035] (1) Raw material premixing and TPU chain extension reaction: 100g of polyether ester polyol with a number average molecular weight of 2000, hexamethylene diisocyanate (3mol, 504.54g) and isophorone diisocyanate (0.9mol, 200.06g) mixed in a molar ratio of 1:0.3, 1,4-butanediol (1mol, 9.01g) and trimethylolpropane (0.05mol, 6.71g) A chain extender mixed in a molar ratio of 1:0.05, 0.01% of dibutyltin dilaurate (0.0081g) by mass of the total TPU raw material, and 0.1% of additives by mass of the total TPU raw material (0.0203g each of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a 1:1 mass ratio, 0.0203g of zinc stearate, and 0.0203g of talc mixed in proportion) are added to a co-rotating twin-screw reactive extruder. A temperature gradient of 150℃, 170℃, 180℃, and 200℃ is set along the screw axis from the feed end to the die end to carry out the chain extension reaction in stages until the TPU molecular weight increases stably.

[0036] (2) Precursor system injection: In the downstream section of the reactive extruder after the TPU chain extension reaction in step (1), a non-hydrolyzable sol-gel precursor system diluted with liquid polyester polyol (precursor system to liquid polyester polyol mass ratio 1:0.5) is injected through a high-precision metering pump. The precursor system contains a mixture of 94.84g of titanium tetrachloride and 104.12g of tetraethyl orthosilicate in a molar ratio of 1:1, 2.5g of propyltriethoxysilane isocyanate accounting for 5% of the total mass of the precursor system, and 5g of micro-crosslinked polyurethane-based phase change material accounting for 10% of the total mass of the precursor system; and 25g of liquid polyester polyol for dilution.

[0037] (3) In-situ generation of core-shell particles for phase change energy storage: Downstream of the injection point of the reactive extruder, in a micro-reaction zone constructed by a forward conveying block, two sets of kneading blocks, and a downstream reverse threaded element, the temperature is controlled at 170℃, the screw speed at 100rpm, and the residence time at 0.5min, causing the precursor system to undergo a condensation reaction, thus generating SiO2@TiO2 core-shell nanoparticles loaded with micro-crosslinked polyurethane-based phase change material in situ. The core-shell particles have a particle size of 40nm, a core-shell ratio of SiO2:TiO2 of 1:1, a shell thickness of 5nm, and a micro-crosslinked polyurethane-based phase change material loading of 20% of the core-shell particle mass. The particle surface is covalently bonded to the TPU molecular chain, and the nano-reinforced phase change energy storage TPU masterbatch is obtained by underwater pelletizing.

[0038] (4) Supercritical two-fluid foaming: The dried nano-reinforced phase change energy storage TPU masterbatch was placed in a high-pressure reactor. First, supercritical N2 was introduced and kept at 20 MPa and 80 °C for 2 hours. Then, supercritical CO2 was introduced and the total pressure was adjusted to 25 MPa and the CO2 partial pressure to 15 MPa. The temperature was kept at 1 hour. Then, the temperature was gradually reduced to room temperature at a rate of 2 °C / min while maintaining the pressure. The pressure was then rapidly released at a rate of 5 MPa / s to release the gas and obtain foamed beads.

[0039] (5) Post-molding treatment: The foamed beads are loaded into the mold and high-pressure steam at 140℃ and 0.3MPa is introduced to melt the surface of the beads and achieve interfacial bonding; dynamic stress relaxation is carried out by keeping the temperature and pressure for 5 minutes, and the mold is slowly cooled down to obtain high-resilience eTPU foam material.

[0040] The preparation method of the micro-crosslinked polyurethane-based phase change material is as follows:

[0041] 174.3 g of 1,10-decanediol, 4.03 g of trimethylolpropane, and 6.71 g of dimethylolpropionic acid were added to a four-necked reactor. Stirring was started, the temperature was raised to 80°C, and a vacuum was applied to -0.095 MPa for dehydration for 30 min. After dehydration, nitrogen gas was introduced, and the temperature was lowered to 60°C for later use. Subsequently, under nitrogen protection, the temperature was maintained at 60°C, and 224.2 g of hexamethylene diisocyanate was added dropwise to the reactor at a rate of 1 mL / min, controlling the NCO:OH molar ratio at 1:1.1. After the addition was complete, the mixture was stirred for 10 min, and 0.0405 g of dibutyltin dilaurate was added. The reaction was maintained at 60°C for 1 h. After the reaction was completed, the temperature was lowered to 50°C, and 1.5 g of n-dodecyl alcohol was added. The mixture was stirred for 20 min, and the final NCO% was controlled at 1% by chemical titration. After the reaction was completed, the heating was turned off, the mixture was cooled to room temperature, and granulated using a granulator to obtain a micro-crosslinked polyurethane-based phase change material.

[0042] Example 2: Preparation of high-resilience eTPU foam material:

[0043] (1) Raw material premixing and TPU chain extension reaction: 100g of polyether ester polyol with a number average molecular weight of 3000, 504.54g of hexamethylene diisocyanate and 333.44g of isophorone diisocyanate mixed in a molar ratio of 1:0.5, 9.01g of 1,4-butanediol and 13.42g of trimethylolpropane mixed in a molar ratio of 1:0.1, 0.03% of the total mass of TPU raw materials, 0.0285g of dibutyltin dilaurate, and 0.55% of the total mass of TPU raw materials (0.1308g of hindered phenolic antioxidant 1010, 0.1308g of phosphite antioxidant 168 compounded in a mass ratio of 1:1, 0.1308g of zinc stearate and 0.1308g of nano calcium carbonate mixed in proportion) were added to a co-rotating twin-screw reactive extruder. A temperature gradient of 155℃, 175℃, 185℃, and 205℃ is set along the screw axis from the feed end to the die end to carry out the chain extension reaction in stages until the TPU molecular weight increases stably.

[0044] (2) Precursor system injection: In the downstream section of the reaction extruder after the TPU chain extension reaction in step (1), a non-hydrolyzable sol-gel precursor system diluted with dioctyl phthalate (mass ratio of precursor system to dioctyl phthalate 1:1.25) is injected through a high-precision metering pump; the precursor system contains a mixture of 75.87g titanium tetrachloride and 208.24g tetraethyl orthosilicate mixed at a molar ratio of 1:2.5, 5g propyltriethoxysilane isocyanate accounting for 10% of the total mass of the precursor system, and 10g micro-crosslinked polyurethane-based phase change material accounting for 20% of the total mass of the precursor system; 60g dioctyl phthalate is used for dilution.

[0045] (3) In-situ generation of core-shell particles for phase change energy storage: Downstream of the injection point of the reactive extruder, in the micro-reaction zone constructed by the forward conveying block, 3 sets of kneading blocks and downstream reverse threaded elements, the temperature is controlled at 180℃, the screw speed at 200rpm and the residence time at 1.25min, so that the precursor system undergoes a condensation reaction, and SiO2@TiO2 core-shell nanoparticles loaded with micro-crosslinked polyurethane-based phase change material are generated in situ; the core-shell particles have a particle size of 70nm, a core-shell ratio of SiO2:TiO2 of 1:2, a shell thickness of 10nm, and the loading of micro-crosslinked polyurethane-based phase change material is 30% of the mass of the core-shell particles. The particle surface is bonded to the TPU molecular chain through covalent bonds, and nano-reinforced phase change energy storage TPU masterbatch is obtained by underwater pelletizing.

[0046] (4) Supercritical two-fluid foaming: The dried nano-reinforced phase change energy storage TPU masterbatch was placed in a high-pressure reactor. First, supercritical N2 was introduced and kept at 22.5 MPa and 85 °C for 2.5 h. Then, supercritical CO2 was introduced and the total pressure was adjusted to 27.5 MPa and the CO2 partial pressure to 17.5 MPa. The temperature was kept at 1.5 h. Then, the temperature was gradually reduced to room temperature at a rate of 3.5 °C / min while maintaining the pressure. The pressure was then rapidly released at a rate of 7.5 MPa / s to release the gas and obtain foamed beads.

[0047] (5) Post-molding treatment: The foamed beads are loaded into the mold and high-pressure steam at 150℃ and 0.4MPa is introduced to melt the surface of the beads and achieve interfacial bonding; the temperature and pressure are maintained for 7.5 minutes to relax the dynamic stress, and the temperature is slowly reduced to demold the high-resilience eTPU foam material.

[0048] The preparation method of the micro-crosslinked polyurethane-based phase change material is as follows:

[0049] 174.3 g of 1,10-decanediol, 8.72 g of trimethylolpropane, and 13.41 g of dimethylolpropionic acid were added to a four-necked reactor. Stirring was started, the temperature was raised to 85°C, and a vacuum was applied to -0.098 MPa for 45 min to dehydrate. After dehydration, nitrogen gas was introduced, and the temperature was lowered to 65°C for later use. Subsequently, under nitrogen protection, the temperature was maintained at 65°C, and 241.7 g of hexamethylene diisocyanate was added dropwise to the reactor at a rate of 1.5 mL / min, controlling the NCO:OH molar ratio at 1:1.2. After the addition was complete, the mixture was stirred for 12 min, and 0.088 g of dibutyltin dilaurate was added. The reaction was maintained at 65°C for 1.5 h. After the reaction was completed, the temperature was lowered to 55°C, and 2.25 g of n-dodecyl alcohol was added. The mixture was stirred for 25 min, and the final NCO% was controlled at 2% by chemical titration. After the reaction was completed, the heating was turned off, the mixture was cooled to room temperature, and granulated using a granulator to obtain a micro-crosslinked polyurethane-based phase change material.

[0050] Example 3: Preparation of high-resilience eTPU foam material:

[0051] (1) Raw material premixing and TPU chain extension reaction: 100g of polyether ester polyol with a number average molecular weight of 4000, 504.54g of hexamethylene diisocyanate and 466.81g of isophorone diisocyanate mixed in a molar ratio of 1:0.7, 9.01g of 1,4-butanediol and 20.12g of trimethylolpropane mixed in a molar ratio of 1:0.15, 0.05% of the total mass of TPU raw materials, 0.0496g of dibutyltin dilaurate, and 1.0% of the total mass of TPU raw materials, including 0.248g of hindered phenolic antioxidant 1010 and 0.248g of phosphite antioxidant 168 mixed in a mass ratio of 1:1, 0.248g of zinc stearate and 0.248g of nano calcium carbonate mixed in equal mass, were added to a co-rotating twin-screw reactive extruder. A temperature gradient of 160℃, 180℃, 190℃, and 210℃ is set along the screw axis from the feed end to the die end to carry out the chain extension reaction in stages until the TPU molecular weight increases stably.

[0052] (2) Precursor system injection: In the downstream section of the reaction extruder after the TPU chain extension reaction in step (1), a non-hydrolyzable sol-gel precursor system diluted with dioctyl terephthalate (mass ratio of precursor system to dioctyl terephthalate is 1:2) is injected through a high-precision metering pump; the precursor system contains a mixture of 56.90g of titanium tetrachloride and 249.89g of tetraethyl orthosilicate mixed in a molar ratio of 1:4, 7.5g of propyltriethoxysilane isocyanate accounting for 15% of the total mass of the precursor system, and 15g of micro-crosslinked polyurethane-based phase change material accounting for 30% of the total mass of the precursor system; 60g of dioctyl terephthalate is used for dilution.

[0053] (3) In-situ generation of core-shell particles for phase change energy storage: Downstream of the injection point of the reactive extruder, in the micro-reaction zone constructed by the forward conveying block, 4 sets of kneading blocks and downstream reverse threaded elements, the temperature is controlled at 190℃, the screw speed at 300rpm and the residence time at 2min, so that the precursor system undergoes a condensation reaction and SiO2@TiO2 core-shell nanoparticles loaded with micro-crosslinked polyurethane-based phase change material are generated in situ; the core-shell particles have a particle size of 100nm, a core-shell ratio of SiO2:TiO2 of 1:3, a shell thickness of 15nm, and a loading of micro-crosslinked polyurethane-based phase change material of 40% of the mass of the core-shell particles. The particle surface is bonded to the TPU molecular chain through covalent bonds, and nano-reinforced phase change energy storage TPU masterbatch is obtained by underwater pelletizing.

[0054] (4) Supercritical two-fluid foaming: The dried nano-reinforced phase change energy storage TPU masterbatch was placed in a high-pressure reactor. First, supercritical N2 was introduced and kept at 25 MPa and 90 °C for 3 hours. Then, supercritical CO2 was introduced and the total pressure was adjusted to 30 MPa and the CO2 partial pressure to 20 MPa. The temperature was kept at 2 hours. Then, the temperature was gradually reduced to room temperature at a rate of 5 °C / min while maintaining the pressure. The pressure was then rapidly released at a rate of 10 MPa / s to release the gas and obtain foamed beads.

[0055] (5) Post-molding treatment: The foamed beads are loaded into the mold and high-pressure steam at 160℃ and 0.5MPa is introduced to melt the surface of the beads and achieve interfacial bonding; the temperature and pressure are maintained for 10 minutes to relax the dynamic stress, and the temperature is slowly reduced to demold the high-resilience eTPU foam material.

[0056] The preparation method of the micro-crosslinked polyurethane-based phase change material is as follows:

[0057] 174.3 g of 1,10-decanediol, 13.42 g of trimethylolpropane, and 20.12 g of dimethylolpropionic acid were added to a four-necked reactor. Stirring was started, the temperature was raised to 90°C, and a vacuum was applied to -0.100 MPa for 60 min to dehydrate. After dehydration, nitrogen gas was introduced, and the temperature was lowered to 70°C for later use. Subsequently, under nitrogen protection, the temperature was maintained at 70°C, and 269.1 g of hexamethylene diisocyanate was added dropwise to the reactor at a rate of 2 mL / min, controlling the NCO:OH molar ratio at 1:1.3. After the addition was complete, the mixture was stirred for 15 min, and 0.1214 g of dibutyltin dilaurate was added. The reaction was maintained at 70°C for 2 h. After the reaction was completed, the temperature was lowered to 60°C, and 3.0 g of n-dodecyl alcohol was added. The mixture was stirred for 30 min, and the final NCO% was controlled at 3% by chemical titration. After the reaction was completed, the heating was turned off, the mixture was cooled to room temperature, and granulated using a granulator to obtain a micro-crosslinked polyurethane-based phase change material.

[0058] Comparative Example 1: Based on Example 2, the difference is that: inorganic particles containing micro-crosslinked polyurethane-based phase change materials are prepared using the traditional hydrolytic sol-gel route. Water is introduced into the precursor system and a hydrolysis-condensation reaction occurs during the reactive extrusion process. The specific preparation method is as follows: 0.4 mol (75.87 g) of titanium tetrachloride and 1 mol (208.24 g) of tetraethyl orthosilicate (molar ratio 1:2.5) of metal alkoxide / halide mixture are dissolved in 60 g of dioctyl phthalate in an inert high-boiling-point solvent. 30.24 mL of water equivalent to 1.2 times the amount of metal salt and 1 mL of hydrochloric acid catalyst with a molar concentration of 0.1 mol / L are added and stirred evenly to obtain a hydrolytic precursor system. In step (2), the hydrolytic precursor system is mixed with 10 g of micro-crosslinked polyurethane-based phase change material and then injected into the reactive extruder. The rest is the same as in Example 2.

[0059] Comparative Example 2: Based on Example 2, the difference is that no functionalized silane coupling agent is added to the precursor system in step (2). A mixture of titanium tetrachloride (75.87 g) and tetraethyl orthosilicate (208.24 g) (molar ratio 1:2.5) and 10 g of micro-crosslinked polyurethane-based phase change material were mixed according to the formula, diluted with 60 g of dioctyl phthalate, and injected into a reactive extruder. The rest was the same as in Example 2.

[0060] Comparative Example 3: Based on Example 2, the difference is that: instead of using in-situ sol-gel to generate SiO2@TiO2 core-shell nanoparticles, commercially available nano-SiO2 and TiO2 were directly physically blended and added, and the core-shell structure design of the micro-crosslinked polyurethane-based phase change material was not performed. The specific preparation method is as follows: after the TPU chain extension reaction in step (1) is completed, 5g of commercially available nano-SiO2, 10g of nano-TiO2 and 10g of micro-crosslinked polyurethane-based phase change material are directly added to the reaction extruder through the side feed port, and granulated after melt mixing; the rest is the same as in Example 2.

[0061] Comparative Example 4: Based on Example 2, the difference is that in step (4), only supercritical CO2 is used for impregnation and foaming, supercritical N2 is not used, and graded impregnation is not performed. The specific operation is as follows: the dried nano-reinforced phase change energy storage TPU masterbatch is placed in a high-pressure autoclave, and supercritical CO2 is introduced at a pressure of 22.5 MPa and a temperature of 85 °C for 3 hours to keep it warm and pressurized. Then, the temperature is gradually reduced to room temperature at a gradient of 3.5 °C / min while maintaining the pressure. The pressure is then rapidly released at 7.5 MPa / s to obtain foamed beads. The rest is the same as in Example 2.

[0062] Comparative Example 5: Based on Example 2, the difference is that the precursor system is adjusted to retain only metal halide, metal alkoxide and functionalized silane coupling agent, and the micro-crosslinked polyurethane-based phase change material is removed, while the other proportions remain unchanged, and the rest is the same as in Example 2.

[0063] Comparative Example 6: Based on Example 2, the difference is that step (5) is changed to not using high-pressure steam, but only conventional hot pressing at the same temperature of 150°C, and the rest is the same as Example 2.

[0064] Comparative Example 7: Based on Example 2, the difference is that the micro-crosslinked polyurethane-based phase change material is replaced with an equal amount of traditional paraffin-based phase change material, specifically a mixture of 5g n-octadecane and 5g n-eicosane. The rest is the same as in Example 2.

[0065] Performance testing: The materials prepared in Examples 1-3 and Comparative Examples 1-7 were subjected to performance testing, and the testing methods are as follows.

[0066] (1) The melting enthalpy (ΔHm) of the material was tested using a differential scanning calorimeter (DSC) at a heating rate of 10℃ / min and a temperature range of 0-80℃. The phase transition enthalpy (J / g) was recorded. The sample was subjected to 50 heating-cooling cycles, and the enthalpy value was tested again. The enthalpy retention rate was calculated.

[0067] (2) High-temperature leakage resistance (accelerated aging test): The sample was placed in an 80℃ forced-air drying oven and baked continuously for 72 hours. After removal, it was cooled to room temperature, and the sample surface was wiped with anhydrous ethanol to remove any possible oil stains. It was then weighed again. The leakage rate of the phase change material was tested, i.e., the mass loss rate after aging. The calculation formula is: mass loss rate after aging (%) = [(m0-m1) / m0] × 100%; where m0 is the mass before aging, and m1 is the mass after wiping after aging. The lower the loss rate, the more tightly the phase change material is packaged, and the better its leakage resistance.

[0068] The better.

[0069] (3) Tensile strength: tested according to GB / T 6344-2008 standard.

[0070] (4) Rebound rate: Tested according to GB / T 6670-2008 standard.

[0071] (5) Compression permanent deformation: Tested according to GB / T 10653-2001 standard, temperature 70℃, heat preservation for 22h, unload and restore for 30min before measurement.

[0072] (6) Interface bonding strength: For the molded product, the interface peel strength is tested by a universal testing machine (sample size 100mm×25mm×5mm, peel rate 50mm / min); the interface is observed to delaminate or tear by dynamic fatigue test (100,000 compression cycles, compression rate 30%, frequency 2Hz).

[0073] The test results are as follows:

[0074] Performance test results of Examples 1-3 and Comparative Examples 1-7

[0075] Data Analysis:

[0076] Analysis of the above data shows that Examples 1-3 overcome existing technological bottlenecks through the synergistic design of four major technologies: non-hydrolyzed in-situ core-shell particles, functionalized coupling agents, two-fluid foaming, and steam chemical bonding synthesis. Among them, Example 2 achieved peak performance due to optimal process parameter adaptability. Although Examples 1 and 3 showed slight differences in performance, their overall performance was excellent, far exceeding that of the comparative examples, fully demonstrating the core value of this technology in improving the mechanical properties, energy storage stability, and durability of materials.

[0077] Comparative Example 1 used a water-containing hydrolysis system. The side reactions generated by hydrolysis damaged the integrity of the core-shell structure, leading to a significant decrease in phase change energy storage performance and stability, and leakage of the micro-crosslinked polyurethane-based phase change material. Examples 1-3, through non-hydrolysis condensation reactions, precisely formed a structure with porous SiO2 as the core and dense TiO2 as the shell within the micro-reaction zone. The SiO2 core can stably adsorb and fix the micro-crosslinked polyurethane-based phase change material, and the TiO2 shell can effectively block the leakage of the phase change material, significantly improving energy storage stability and aging resistance.

[0078] In Comparative Example 2, without the addition of a functionalized silane coupling agent, the inorganic particles only have physical contact with the TPU matrix, resulting in weak interfacial bonding and a tendency for particle aggregation and interfacial delamination, thus limiting mechanical properties and energy storage stability. In the example, the added isocyanate-containing silane coupling agent can form covalent bonds with the TPU molecular chains, promoting uniform particle dispersion within the matrix. This improves interfacial bonding strength and mechanical properties, reduces energy storage failures caused by particle migration, and further optimizes overall performance stability.

[0079] In Comparative Example 3, the direct blending of SiO2 and TiO2 particles easily leads to particle agglomeration and fails to form a sealed structure. The micro-crosslinked polyurethane-based phase change material is prone to leakage, exhibiting poor mechanical and energy storage properties. Examples 1-3, through in-situ condensation reactions, generate core-shell particles with uniform particle size. These particles are tightly bonded to the TPU matrix via covalent bonds, effectively avoiding particle agglomeration and stress concentration problems, achieving a synergistic improvement in both mechanical properties and energy storage function.

[0080] Comparative Example 4 used a single supercritical CO2 foaming process, which lacked a high-density bubble nucleus construction process, resulting in uneven cell size, an imbalance between nucleation and growth, and poor resilience and fatigue resistance. The embodiment first constructed a high-density bubble nucleus using supercritical N2, and then used supercritical CO2 to regulate cell growth. The hierarchical mechanism made the cell structure more uniform, significantly improving the material's resilience and fatigue stability.

[0081] Comparative Example 5, a polyurethane-based phase change material without micro-crosslinking, has mechanical properties similar to those of the examples, but its phase change enthalpy is 0. This proves that while retaining high mechanical properties, the present invention successfully integrates phase change energy storage function through a core-shell structure, achieving a synergistic improvement in performance and function.

[0082] Comparative Example 6 uses conventional hot pressing molding, where the bead interface relies solely on physical melting for bonding, resulting in low interfacial strength and a tendency to delamination and cracking under long-term dynamic loads. Examples 1-3 introduce high-pressure steam, which causes water molecules to initiate trace hydrolysis of TPU ester bonds, generating in-situ urethane bonds to achieve interfacial chemical bonding. This significantly improves interfacial bonding strength and product durability, and substantially optimizes dynamic fatigue performance.

[0083] Comparative Example 7 uses a traditional paraffin-based phase change material. Although its initial phase change enthalpy is slightly higher, its leakage rate and mechanical properties under core-shell encapsulation are inferior to those of Example 2. Paraffin-based materials belong to solid-liquid phase change. The stress generated by volume expansion during the phase change process easily damages the TiO2 shell structure. Furthermore, paraffin has poor compatibility with the TPU matrix and lacks chemical bonding. Relying solely on silane coupling agents makes it difficult to achieve perfect interfacial bonding, resulting in a decrease in the tensile strength, resilience, and interfacial peel strength of the composite material. The phase change enthalpy retention rate after aging is also low. This fully demonstrates that the present invention uses a micro-crosslinked polyurethane-based phase change material, utilizing its solid-solid phase change characteristics to reduce volume change and achieving chemical bonding with the matrix through the -NCO groups at the molecular chain ends. This solves the leakage problem of phase change materials while synergistically improving the mechanical properties and durability of the material.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A preparation process for a high-resilience eTPU foam material, characterized in that, Includes the following steps: (1) Raw material premixing and TPU chain extension reaction: The polyether ester polyol, diisocyanate mixture, chain extender, TPU chain extension catalyst and additives are added to the co-rotating twin-screw reactive extruder. The temperature gradient is set along the screw axis to heat in stages to carry out the chain extension reaction until the TPU molecular weight increases stably. (2) Precursor system injection: In the downstream section of the extruder after the chain extension reaction is completed, a non-hydrolyzable sol-gel precursor system is injected by a metering pump; (3) In-situ generation of core-shell particles for phase change energy storage: In the downstream micro-reaction zone of the extruder, the reaction conditions are controlled to cause the precursor system to undergo a condensation reaction, and SiO2@TiO2 core-shell nanoparticles loaded with micro-crosslinked polyurethane-based phase change material are generated in-situ. TPU masterbatch is obtained by underwater pelletizing. (4) Supercritical two-fluid foaming: The dried TPU masterbatch is placed in a high-pressure reactor, and supercritical N2 and supercritical CO2 are introduced first. The reaction is carried out under certain temperature and pressure, and then the temperature is gradually reduced and the pressure is rapidly released to obtain foamed beads. (5) Post-molding treatment: The foamed beads are loaded into the mold, and high-pressure steam is introduced to melt the surface of the beads and achieve interfacial bonding; after heat preservation and pressure preservation, and cooling and demolding, high-resilience eTPU foam material is obtained. In step (2), the precursor system comprises a metal halide, a metal alkoxide, a functionalized silane coupling agent, and a micro-crosslinked polyurethane-based phase change material; the metal halide is titanium tetrachloride, the metal alkoxide is tetraethyl orthosilicate, and the molar ratio of titanium tetrachloride to tetraethyl orthosilicate is 1:1-4; the functionalized silane coupling agent is propyltriethoxysilane isocyanate, and the amount added is 5-15% of the total mass of the precursor system; The specific preparation steps for the micro-crosslinked polyurethane-based phase change material are as follows: Add 1,10-decanediol, trimethylolpropane, and dimethylolpropionic acid to a four-necked reactor in a molar ratio of 1:0.03-0.10:0.05-0.

15. Start stirring, heat to 80-90℃, and apply a vacuum of -0.095 to -0.100 MPa for 30-60 minutes to dehydrate. After dehydration, purge with nitrogen and cool to 60-70℃ for later use. Subsequently, under nitrogen protection, maintain the temperature at 60-70℃ and add hexamethylene diisocyanate dropwise to the reactor at 1-2 mL / min, controlling the NCO:OH molar ratio. The ratio of dibutyltin dilaurate to 1:1.1-1.3 was used. After the addition was complete, the mixture was stirred for 10-15 min. Then, 0.01-0.03% of the total mass of 1,10-decanediol, trimethylolpropane, dimethylolpropionic acid, and hexamethylene diisocyanate was added. The reaction was maintained at 60-70℃ for 1-2 h. After the reaction was completed, the temperature was lowered to 50-60℃, and n-dodecyl alcohol was added. The mixture was stirred for 20-30 min to ensure that the final NCO% was controlled at 1-3%. After the reaction was completed, the heating was turned off, the mixture was cooled to room temperature, dried, and granulated to obtain the micro-crosslinked polyurethane-based phase change material.

2. The preparation process according to claim 1, characterized in that, The eTPU foam material comprises a TPU matrix and in-situ generated SiO2@TiO2 core-shell nanoparticles loaded with micro-crosslinked polyurethane-based phase change material; the core-shell nanoparticles have a particle size of 40-100 nm, a core-shell ratio of SiO2:TiO2 of 1:1-3, a shell thickness of 5-15 nm, and the loading of micro-crosslinked polyurethane-based phase change material is 20-40% of the mass of the core-shell particles.

3. The preparation process according to claim 1, characterized in that, In step (1), the temperature gradient gradually increases along the screw axis from the feed end to the die end, and is successively 150-160℃, 170-180℃, 180-190℃, and 200-210℃; the number average molecular weight of the polyether ester polyol is 2000-4000; the diisocyanate mixture is a mixture of hexamethylene diisocyanate and isophorone diisocyanate in a molar ratio of 1:0.3-0.

7.

4. The preparation process according to claim 1, characterized in that, In step (1), the chain extender is a mixture of 1,4-butanediol and trimethylolpropane in a molar ratio of 1:0.05-0.15; the TPU chain extender catalyst is dibutyltin dilaurate, and the amount added is 0.01-0.05% of the total mass of the TPU raw material; the additive is a mixture of antioxidant, lubricant and nucleating agent, and the total amount added is 0.1-1.0% of the total mass of the TPU raw material, wherein the antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1, the lubricant is zinc stearate, and the nucleating agent is talc or nano calcium carbonate.

5. The preparation process according to claim 1, characterized in that, In step (2), the precursor system is injected after being diluted with an inert high-boiling-point solvent. The inert high-boiling-point solvent is one of liquid polyester polyol, dioctyl phthalate or dioctyl terephthalate, and the mass ratio of the precursor system to the inert high-boiling-point solvent is 1:0.5-1.

2.

6. The preparation process according to claim 1, characterized in that, In step (3), the micro-reaction zone is constructed by a screw element assembly, which includes a forward conveying block, a kneading block, and a reverse thread element. The number of kneading blocks is 2-4 sets, and the reverse thread element is set downstream of the kneading block to extend the reaction residence time of the precursor to ensure the tight sealing of the TiO2 shell.

7. The preparation process according to claim 1, characterized in that, In step (5), the pressure of the high-pressure steam is 0.3-0.5 MPa; the interface bonding is achieved by the steam initiating the hydrolysis of trace TPU ester bonds at the contact interface of the beads, generating urethane bonds in situ to achieve interface enhancement.

8. The high-resilience eTPU foam material prepared according to any one of the preparation processes described in claims 1-7.

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