A foaming method for SiO2 aerogel-modified TPEE

Abstract

This invention relates to the field of polymer material processing technology and discloses a foaming method for SiO2 aerogel-modified TPEE, comprising: S1, melting and molding a thermoplastic polyester elastomer raw material to obtain a preform with a preset geometric shape and size; S2, placing the preform into a sealable processing chamber, and introducing high-pressure foaming gas into the chamber under the condition of applying an external heat field to achieve gas permeation saturation; S3, performing a nonlinear pressure release program on the processing chamber under the saturation pressure to controllably expand and foam the preform. This invention, by dividing the pressure release process into a nucleation-dominant stage and a growth-dominant stage, and setting pressure drop rates that match the thermodynamic behavior of the material, achieves decoupled control of the two key sub-processes of bubble nucleation and growth, fundamentally solving the problem of poor controllability in the foaming process.

Description

Technical Field

[0001] This invention patent relates to the field of polymer material processing technology, specifically a foaming method for SiO2 aerogel-modified TPEE. Background Technology

[0002] Thermoplastic polyester elastomer (TPEE) is a block copolymer containing hard polyester segments and soft polyester segments (polyether or polyester). It combines the flexibility of rubber with the processability of thermoplastics, and exhibits excellent heat resistance, chemical resistance, fatigue resistance, and high elastic recovery. Foaming TPEE can further reduce its density and improve its specific strength, cushioning and energy absorption properties, as well as its thermal and sound insulation performance, thus demonstrating great application potential in the automotive industry (such as sealing strips and shock absorbers), sporting goods (such as shoe materials and equipment padding), electronic equipment cushioning packaging, and high-end sealing components.

[0003] Currently, the production of TPEE foam materials mainly relies on physical foaming methods, especially supercritical fluid foaming technology and high-pressure autoclave foaming processes. A typical existing technological process is as follows: First, TPEE granules or preforms are placed in a high-pressure reactor and heated to a specific temperature above the polymer's softening point, allowing the TPEE matrix to fully plasticize. Then, high-pressure gas (commonly carbon dioxide or nitrogen) is injected and maintained within the reactor at high pressure. Driven by pressure, the gas dissolves and permeates into the polymer melt, reaching thermodynamic dissolution equilibrium. Finally, rapid depressurization (usually instantaneously) creates a supersaturated state of the dissolved gas, inducing the nucleation and rapid growth of numerous bubbles, ultimately solidifying into a porous foam structure.

[0004] Although the above methods have some industrial applications, those skilled in the art recognize several significant technical drawbacks: First, the foaming process has poor controllability, leading to large fluctuations in product quality. While instantaneous rapid depressurization can induce foaming, this process is violent and uncontrollable. Bubble nucleation and growth occur simultaneously and disorderly within a very short time, easily resulting in excessively wide cell size distribution, cell merging or collapse, and even macroscopic defects such as cracking. This results in poor uniformity of cell structure between different batches and even within the same batch, leading to inconsistent mechanical and physical properties. Second, the dimensional stability of the product is poor, with severe post-shrinkage. The violent instantaneous foaming causes extremely uneven internal stress distribution in the polymer melt during expansion and shaping, and may lead to insufficient support of the cell structure due to excessively rapid gas escape. After molding, the foamed product will experience significant dimensional shrinkage (especially in the thickness direction) and shape distortion during storage or subsequent heating due to stress relaxation and continued gas diffusion, severely affecting the dimensional accuracy and assembly reliability of the final product. Third, the product's surface quality is defective. An unstable foaming process can easily form a rough skin, wrinkles, orange peel texture, or depressions on the surface of the product. This not only affects the appearance but can also act as stress concentration points, inducing crack propagation and reducing the product's fatigue life and service durability. Fourth, it negatively impacts subsequent processing efficiency. Due to poor dimensional stability and numerous surface defects, secondary processing steps such as trimming and shaping are often required, leading to a higher scrap rate, thereby reducing overall production efficiency and increasing production costs.

[0005] In view of this, we propose a foaming method for SiO2 aerogel-modified TPEE.

[0006] Invention Patent Content

[0007] The purpose of this invention is to provide a foaming method for SiO2 aerogel-modified TPEE to solve the problems existing in the background art.

[0008] To achieve the above objectives, this invention provides the following technical solution:

[0009] A foaming method for SiO2 aerogel-modified TPEE, comprising:

[0010] S1. Raw material pretreatment: The thermoplastic polyester elastomer raw material is melted, plasticized and molded to obtain a prefabricated profile with a preset geometric shape and size.

[0011] S2, Gas permeation saturation: The prefabricated profile is placed into a sealable processing chamber. Under the condition of applying an external heat field, high-pressure foaming gas is introduced into the chamber and a preset saturation pressure and saturation temperature are maintained for a set time, so that the foaming gas can be fully dissolved and permeate into the internal matrix of the prefabricated profile.

[0012] S3. Controlled Expansion Foaming: A nonlinear pressure release procedure is performed on the processing chamber under the saturation pressure. This procedure includes at least an early pressure release stage with a first pressure change characteristic and a late pressure release stage with a second pressure change characteristic, the second pressure change characteristic being different from the first pressure change characteristic. Specifically, the pressure drop rate in the early pressure release stage is set to reduce the gas supersaturation growth rate inside the preformed profile to below a critical nucleation rate threshold, thereby forming uniformly distributed bubble nuclei primarily through homogeneous nucleation in this stage. The pressure drop rate in the late pressure release stage is set to increase the gas supersaturation growth rate inside the preformed profile to above a critical growth rate threshold, thereby driving the bubble nuclei to expand and grow synchronously in this stage, obtaining TPEE foam material.

[0013] Preferably, the raw material pretreatment step specifically includes: placing thermoplastic polyester elastomer granules or powder in an extrusion device, heating and shearing it with a screw to uniformly plasticize it into a molten state, and then guiding the molten material through a molding die with a constant cross-sectional shape. After traction and cooling, a sheet-like, film-like, or profile with a specific cross-section is obtained as the preformed profile.

[0014] Preferably, in the gas permeation saturation step, the high-pressure foaming gas contains two or more physical foaming agents with different dissolution and diffusion properties, and the physical foaming agents are selected from carbon dioxide and nitrogen.

[0015] Preferably, the high-pressure foaming gas is a binary composite gas system formed by mixing carbon dioxide and nitrogen in a specific volume ratio; wherein, the carbon dioxide acts as a nucleation promoter, utilizing its high solubility to pre-create a dense gas enrichment zone in the prefabricated profile matrix, providing nucleation sites for subsequent bubble nucleus formation; the nitrogen acts as a structural stabilizer, utilizing its low diffusion coefficient to suppress excessive expansion and collapse of the bubbles during the nonlinear pressure release process.

[0016] Preferably, the volume ratio of carbon dioxide to nitrogen is determined based on the target average pore diameter D and pore density ρ using the following empirical formula:

[0017] ;

[0018] Wherein, k, a, and b are constants determined through experiments, and the volume ratio ranges from 1:2 to 2:1.

[0019] Preferably, in the controlled expansion foaming step, the nonlinear pressure release procedure is implemented by actively controlling the pressure drop process in the processing chamber according to a preset time sequence and pressure change curve through a pressure control system connected to the processing chamber.

[0020] Preferably, the first pressure change characteristic corresponding to the initial decompression stage is: the pressure in the processing chamber decreases from the initial saturation pressure at a first average rate, the first average rate being 3 MPa / s to 10 MPa / s; the second pressure change characteristic corresponding to the later decompression stage is: the pressure in the processing chamber decreases to ambient atmospheric pressure at a second average rate, wherein the second average rate is greater than the first average rate.

[0021] Preferably, the initial pressure release stage and the later pressure release stage are connected by a pressure switching point; the pressure switching point is determined based on whether the real-time pressure value in the processing chamber reaches a preset critical pressure threshold; when the pressure drops to the critical pressure threshold, the pressure release procedure switches from the initial pressure release stage to the later pressure release stage; the critical pressure threshold is determined based on the crystallization temperature-pressure relationship of the thermoplastic polyester elastomer at the saturation temperature, specifically: the crystallization temperature of the thermoplastic polyester elastomer at different pressures is determined by differential scanning calorimetry, and the critical pressure threshold is set such that when the pressure drops to the threshold, the matrix temperature of the preformed profile is still higher than its crystallization temperature at that pressure, so as to maintain the matrix in a highly elastic state.

[0022] Preferably, after the controlled expansion foaming step, a shaping and curing step is further included: cooling the TPEE nascent foam body with formed cell structure obtained after the nonlinear pressure release procedure. The cooling process adopts a segmented cooling method to form a crystallinity gradient distribution from the outside to the inside of the cell wall of the TPEE nascent foam body, thereby fixing the porous cell structure and obtaining a dimensionally stable TPEE foam material product.

[0023] Preferably, in the controlled expansion foaming step, the nonlinear pressure release procedure includes two or more pressure release sub-stages, each sub-stage having a different pressure change rate, and the pressure change rate exhibits an increasing, decreasing, or first increasing and then decreasing pattern along the release sequence.

[0024] By employing the above technical solution, this invention patent provides a foaming method for SiO2 aerogel-modified TPEE. It possesses at least the following beneficial effects:

[0025] This invention patent divides the decompression process into a nucleation-dominant stage and a growth-dominant stage, and sets pressure drop rates that match the thermodynamic behavior of the material for each stage. In the nucleation-dominant stage, by controlling the supersaturation growth rate below the critical nucleation rate threshold, the system is forced to primarily undergo homogeneous nucleation, avoiding premature local foaming caused by heterogeneous nucleation at impurities or interfaces. This results in a large number of bubble nuclei (density up to 10^9-10^12 nuclei / cm³) with highly uniform size (coefficient of variation <15%). In the subsequent growth-dominant stage, by allowing the supersaturation growth rate to exceed the critical growth rate threshold, a synchronous and strong expansion driving force is provided for all bubble nuclei, ensuring the uniformity and integrity of bubble growth and effectively suppressing bubble merging or collapse caused by differences in growth rates. This achieves decoupled control of the two key sub-processes of bubble nucleation and growth, fundamentally solving the problem of poor controllability in the foaming process.

[0026] By correlating the critical pressure threshold with the crystallization temperature-pressure relationship of TPEE, the precise matching of the pressure relief switching timing with the material's own physical state is ensured. When the pressure drops to the critical pressure threshold, the TPEE matrix is ​​precisely in a highly elastic state, with sufficient mobility of molecular chain segments to respond to cell expansion, while simultaneously avoiding entering a viscous flow state that would cause cell wall rupture. This method of determining the switching point based on material thermodynamic parameters frees the foaming method of this invention from dependence on operator experience, possessing universality and portability across material grades and specifications, and solving the industry-wide common problem of difficulty in replicating process parameters across materials.

[0027] By revealing the differentiated dissolution-diffusion synergistic mechanism of CO2 and N2 in TPEE and establishing an empirical formula for the gas ratio and target pore parameters, CO2, as a nucleation promoter, with its high solubility, helps to pre-establish dense gas-rich regions in the matrix, laying the foundation for subsequent pore nucleus formation; N2, as a structural stabilizer, with its low diffusion coefficient, plays a buffering role during pressure relief, preventing excessive pore expansion or collapse. The synergistic use of the two gases enables this invention to flexibly control the pore diameter from 10 μm to 200 μm and the pore density from 10^8 to 10^12 pores / cm³ within a wide ratio range of 1:2 to 2:1, realizing the active design and precise control of the microstructure of the foamed material.

[0028] By employing a segmented cooling curing method, TPEE foam develops a gradient crystalline structure from the outside in, characterized by a dense outer layer and a loose core. The dense outer layer provides excellent surface quality and abrasion resistance, while the loose core maintains low density and high elasticity. This gradient structure effectively balances the rigidity and toughness of the product and significantly reduces post-shrinkage, creating a gradient distribution of crystallinity on the cell walls, further enhancing the dimensional stability and overall mechanical properties of the foamed product. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the invention, form part of this application:

[0030] Figure 1 This is a schematic diagram of the overall process of this invention patent. Detailed Implementation

[0031] The technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] Please see Figure 1 The foaming method of SiO2 aerogel modified TPEE according to the present invention includes:

[0033] Step S1, Raw material pretreatment: The thermoplastic polyester elastomer raw material is melt-plasticized and molded to obtain a preform with a preset geometric shape and size;

[0034] It should be noted that step S1 provides a material base with a regular shape and uniform structure for subsequent foaming. In actual operation, the TPEE material blended with SiO2 can be fed into a twin-screw extruder; inside the extruder, the modified TPEE is heated to above its melting temperature (e.g., 180℃-220℃) by the heat generated by the heating sleeve and screw shearing, so that it is fully plasticized into a uniform melt; then, the melt is extruded through a T-die with a flat slit to form an initial sheet melt; this sheet melt is calendered, drawn, and cooled by a set of cooling rollers to finally produce a modified TPEE sheet with uniform thickness, smooth surface, and dense interior, which serves as a preform for subsequent foaming. Step S1 ensures the uniformity of material heating and gas adsorption in subsequent steps.

[0035] Step S2, Gas Permeation Saturation: The prefabricated profile is placed into a sealable processing chamber. Under the condition of applying an external heat field, high-pressure foaming gas is introduced into the chamber and a preset saturation pressure and saturation temperature are maintained for a set time to allow the foaming gas to fully dissolve and permeate into the internal matrix of the prefabricated profile.

[0036] It should be noted that the purpose of step S2 is to allow the foaming gas to fully penetrate and dissolve in the TPEE matrix under high temperature and pressure, forming a gas-polymer saturated system. During operation, the TPEE sheet obtained in step S1 is placed in a high-pressure reactor; after sealing, the reactor is heated to raise the internal temperature to the suitable foaming temperature of the TPEE, for example, controlled between 100℃ and 130℃; after the temperature stabilizes, high-pressure foaming gas is injected into the reactor; the high-pressure foaming gas is preferably a mixture of carbon dioxide and nitrogen, which can be mixed in a specific volume ratio; the pressure inside the reactor is raised to and maintained at a high pressure of 20MPa to 25MPa; at this temperature and pressure, the pressure is maintained for a period of time (e.g., 1-4 hours) to allow the mixed gas to fully dissolve and diffuse throughout the entire cross-section of the modified TPEE sheet, reaching a saturated state, thus reserving a uniform physical foaming agent for foaming.

[0037] Step S3, Controlled Expansion Foaming: A nonlinear pressure release procedure is performed on the processing chamber under the saturation pressure. This procedure includes at least an early pressure release stage with a first pressure change characteristic and a late pressure release stage with a second pressure change characteristic, the second pressure change characteristic being different from the first pressure change characteristic. Specifically, the pressure drop rate in the early pressure release stage is set to reduce the gas supersaturation growth rate inside the preform to below a critical nucleation rate threshold, thereby forming uniformly distributed bubble nuclei primarily through homogeneous nucleation in this stage. The pressure drop rate in the late pressure release stage is set to increase the gas supersaturation growth rate inside the preform to above a critical growth rate threshold, thereby driving the bubble nuclei to expand and grow synchronously in this stage, obtaining TPEE foam material.

[0038] It should be noted that step S3 achieves decoupled control of bubble nucleation and growth by deeply coupling the macroscopic pressure relief process with the microscopic physical mechanism of the material. During operation, a preset pressure release curve is executed through a precision pressure control system (such as an electronically controlled proportional valve, a back pressure valve, and a control system) connected to the high-pressure reactor.

[0039] Early depressurization stage (nucleation-dominated stage): The control system releases the pressure inside the vessel at a relatively slow rate, for example, controlling the depressurization rate within the range of 3 MPa / s to 10 MPa / s. During this stage, the system pressure decreases gradually, and the gas supersaturation increases slowly. By controlling the supersaturation rate growth rate below the critical nucleation rate threshold, homogeneous nucleation is forced into the system, i.e., a large number of uniform and fine bubble nuclei spontaneously form in the TPEE matrix, avoiding premature local foaming caused by heterogeneous nucleation at impurities or interfaces. This stage is crucial in determining the final cell density.

[0040] Late-stage depressurization (growth-dominant stage): When the pressure inside the vessel drops to a preset critical pressure threshold due to the initial depressurization, the control system immediately switches to rapid depressurization mode, quickly releasing the remaining pressure inside the vessel to atmospheric pressure at a depressurization rate much higher than the initial rate (e.g., much greater than 10 MPa / s). During this stage, the gas supersaturation rate exceeds the critical growth rate threshold, providing a strong and synchronized expansion driving force for the already formed uniform bubble nuclei, causing them to grow into uniform bubbles and completing the foaming process.

[0041] Determination of the critical pressure threshold: The critical pressure threshold is a key control parameter for staged pressure relief. This invention correlates it with the crystallization temperature-pressure relationship of TPEE material. Specifically, the crystallization temperature of TPEE under different pressures is determined by differential scanning calorimetry, and the critical pressure threshold is set such that when the pressure of the preformed profile drops to this threshold, its matrix temperature is still higher than its crystallization temperature at that pressure. This ensures that the TPEE matrix remains in a highly elastic state during switching, and that the molecular chain segments have sufficient mobility to respond to cell expansion, while not entering a viscous flow state that would cause cell wall rupture.

[0042] Synergistic effect of composite gases: This invention preferably uses a mixture of carbon dioxide and nitrogen as the foaming agent. Carbon dioxide has high solubility in TPEE, enabling the creation of dense gas-rich zones in the matrix, acting as "seeds" for subsequent bubble nucleus formation; nitrogen has low solubility in TPEE but also a low diffusion coefficient, playing a "slow-release" role during pressure relief, preventing excessive expansion or collapse of the bubbles. The volume ratio of the two gases can be determined using empirical formulas based on the target bubble parameters.

[0043] The raw material pretreatment step specifically includes: placing thermoplastic polyester elastomer granules or powder in an extrusion device, heating and shearing the screw to uniformly plasticize it into a molten state, and then guiding the molten material through a molding die with a constant cross-sectional shape. After traction and cooling, sheet-like, film-like or profiles with specific cross-sections are obtained as the preformed profiles.

[0044] It should be noted that the core advantage of using extrusion molding to prepare preformed profiles lies in its ability to precisely control the cross-sectional shape and dimensional tolerances of the profiles. By changing the molding dies with different cross-sections (such as T-die, round bar die, and profile die), sheets, films, bars, or profiles with complex cross-sections can be obtained to meet the geometric requirements of foamed products in different application scenarios. In addition, the high-temperature shearing action during the extrusion process helps to eliminate microcrystal nuclei and stress concentration points inside the TPEE raw material, making the matrix more uniform and facilitating the formation of a uniform dissolution distribution during subsequent gas permeation saturation, thus creating favorable conditions for uniform nucleation. The calendering and cooling rate of the cooling rollers also need to be properly controlled to avoid internal stress or warping deformation caused by uneven cooling.

[0045] In the gas permeation saturation step, the high-pressure foaming gas contains two or more physical foaming agents with different dissolution and diffusion properties, and the physical foaming agents are selected from carbon dioxide and nitrogen.

[0046] It is worth noting that selecting two or more physical foaming agents with different solubility and diffusion properties for mixed use is one of the key points of this invention. Different gases exhibit significant differences in solubility (Henry's constant) and diffusion coefficient in modified TPEE. For example, carbon dioxide has a much higher solubility than nitrogen, but its diffusion coefficient is also larger; conversely, nitrogen has low solubility but slow diffusion. By mixing high-solubility gases with low-diffusion-coefficient gases in a specific ratio, the foaming process can be synergistically controlled: the high-solubility gas dissolves extensively in the matrix during the saturation stage, providing a sufficient nucleation material basis; the low-diffusion-coefficient gas acts as an "anchor" during the depressurization stage, slowing the rate at which gas escapes from the matrix, thereby prolonging cell growth time and inhibiting cell merging and collapse. Furthermore, other gases (such as argon, pentane, etc.) can be introduced as needed to adjust the plasticizing effect or cell morphology of the system.

[0047] The high-pressure foaming gas is a binary composite gas system formed by mixing carbon dioxide and nitrogen in a specific volume ratio; wherein, the carbon dioxide acts as a nucleation promoter, and its high solubility creates a dense gas enrichment zone in the prefabricated profile matrix, providing nucleation sites for subsequent bubble nucleus formation; the nitrogen acts as a structural stabilizer, and its low diffusion coefficient inhibits excessive expansion and collapse of the bubbles in the nonlinear pressure release process.

[0048] It is worth noting that the roles of CO2 and N2 in the binary composite gas system have been further clarified. The high solubility of CO2 allows it to form numerous tiny gas-rich regions (or "gas clusters") in the modified TPEE matrix. These regions preferentially become the starting point for bubble nucleus formation during subsequent depressurization, thus significantly increasing the bubble nucleus density. Meanwhile, the low diffusion coefficient of N2 means that its migration rate in the matrix is ​​slow. When depressurization occurs, N2 tends to remain inside the bubble pores, acting as an "internal support" to prevent the bubble walls from expanding too rapidly due to a sudden drop in external pressure, which could lead to rupture. It also slows down the outward diffusion of gas within the bubble pores, resulting in more stable bubble growth and a more complete structure. This synergistic mechanism of "one promoting growth and the other stabilizing" is key to achieving uniform bubble size and controllable density.

[0049] The volume ratio of carbon dioxide to nitrogen is determined based on the target average bubble diameter D and bubble density ρ using the following empirical formula:

[0050] ;

[0051] Wherein, k, a, and b are constants determined through experiments, and the volume ratio ranges from 1:2 to 2:1;

[0052] It is worth noting that the formula shows that to obtain a smaller bubble diameter D, the proportion of CO2 needs to be increased (because the exponent of D is negative, the smaller D is, the more CO2 is required). (The larger the cell size), to obtain a higher cell density Similarly, it is necessary to increase the proportion of CO2 ( The exponents are positive. The constants k, a, and b need to be calibrated through a small number of preliminary experiments for specific grades of TPEE material and specific process conditions. For example, by designing 3-5 sets of experiments with different gas ratios, the corresponding D and... The parameters are then fitted to obtain the values. This formula allows operators to quickly determine the optimal gas ratio without extensive trial and error, significantly improving process development efficiency. It is important to note that the gas ratio should not exceed the range of 1:2 to 2:1, otherwise it may lead to a deterioration in the foaming effect: too much CO2 will cause the cells to grow too quickly and become thin and easily broken; too much N2 will result in insufficient nucleation and excessively low cell density.

[0053] In the controlled expansion and foaming step, the nonlinear pressure release procedure is implemented by actively controlling the pressure drop process inside the processing chamber according to a preset time sequence and pressure change curve through a pressure control system connected to the processing chamber.

[0054] It is worth noting that traditional rapid pressure relief often relies on manually opening valves, resulting in uncontrollable and poorly repeatable pressure relief rates. The pressure control system employed in this invention (such as an electro-proportional valve coupled with a PID controller or servo valve) can monitor the pressure inside the reactor in real time and precisely adjust the valve opening according to a pre-programmed pressure relief curve (e.g., piecewise linear, exponential decay, or multi-stage stepped), thereby achieving millisecond-level response and closed-loop control of the pressure relief rate. This active control method not only ensures the consistency of the process for each batch but also provides the hardware foundation for exploring more complex nonlinear pressure relief modes (such as slow-then-fast-then-slow, pulsed pressure relief, etc.), which is a crucial technical guarantee for achieving "nucleation-growth separation control" in this invention.

[0055] The first pressure change characteristic corresponding to the initial decompression stage is that the pressure in the processing chamber decreases from the initial saturation pressure at a first average rate, which is 3 MPa / s to 10 MPa / s; the second pressure change characteristic corresponding to the later decompression stage is that the pressure in the processing chamber decreases to ambient atmospheric pressure at a second average rate, wherein the second average rate is greater than the first average rate.

[0056] It is worth noting that the first average rate of 3-10 MPa / s is a relatively slow depressurization rate. At this rate, the growth rate of gas supersaturation is limited to below the critical nucleation rate threshold, thus ensuring that the nucleation process is mainly homogeneous and avoiding explosive, uncontrollable nucleation caused by a surge in supersaturation. The second average rate is much greater than 10 MPa / s (e.g., 50 MPa / s in the example), which is a rapid depressurization process. At this time, the supersaturation growth rate rapidly exceeds the critical growth rate threshold, providing a strong expansion driving force for the formed bubble nuclei, enabling them to grow synchronously to the target size in a short period of time. The rate difference between the two stages must be at least one order of magnitude to achieve the effect of "separation of nucleation and growth". If the rate in the early stage is too fast, nucleation and growth overlap, and uniform pores cannot be obtained; if the rate in the later stage is too slow, the driving force for bubble nuclei growth is insufficient, and the pores are small or cannot expand sufficiently.

[0057] The initial pressure release stage and the later pressure release stage are connected by a pressure switching point. The pressure switching point is determined based on whether the real-time pressure value in the processing chamber reaches a preset critical pressure threshold. When the pressure drops to the critical pressure threshold, the pressure release procedure switches from the initial pressure release stage to the later pressure release stage. The critical pressure threshold is determined based on the crystallization temperature-pressure relationship of the thermoplastic polyester elastomer at the saturation temperature. Specifically, the crystallization temperature of the thermoplastic polyester elastomer at different pressures is determined by differential scanning calorimetry, and the critical pressure threshold is set such that when the pressure drops to the threshold, the matrix temperature of the preformed profile is still higher than its crystallization temperature at that pressure, so as to maintain the matrix in a highly elastic state.

[0058] It is worth noting that the method for determining the critical pressure threshold is another key aspect of this invention. In traditional methods, the pressure relief switching point is often set empirically, lacking a physical basis. This invention links the switching point to the crystallization behavior of TPEE materials: at saturation temperature, the TPEE matrix is ​​in a molten or elastic state; as the pressure decreases, its crystallization temperature changes (usually, as pressure decreases, the crystallization temperature increases). By measuring the crystallization temperature of TPEE at different pressures using DSC, a crystallization temperature-pressure curve can be plotted. The critical pressure threshold should be selected near the point corresponding to the saturation temperature on this curve, but slightly higher (i.e., slightly higher pressure), to ensure that the matrix temperature remains above the crystallization temperature when the switching occurs, and the matrix remains in an elastic state rather than entering a crystalline state. If the switching point pressure is too low (the matrix has already crystallized), the molecular chain mobility is insufficient, and the cells cannot grow effectively; if the switching point pressure is too high (the matrix is ​​still in a viscous flow state), the cell wall strength is insufficient, and it is prone to collapse. Therefore, the scientific determination of this threshold is crucial to ensuring successful foaming.

[0059] The controlled expansion foaming step is followed by a shaping and curing step: the TPEE nascent foam body with a formed cell structure obtained after the nonlinear pressure release procedure is cooled. The cooling process adopts a segmented cooling method to form a crystallinity gradient distribution from the outside to the inside of the cell wall of the TPEE nascent foam body, thereby fixing the porous cell structure and obtaining a dimensionally stable TPEE foam material product.

[0060] It is worth noting that the shaping and curing step is the final key step in locking the cell structure and giving the product dimensional stability. Using a segmented cooling method (such as rapid cooling to 60°C followed by slow cooling to room temperature in Example 1) allows for differentiated control of the cell wall crystallization behavior: the first stage of rapid cooling quickly lowers the surface layer to below the glass transition temperature, forming a dense skin layer that prevents further gas escape from the cells and imparts good surface quality and wear resistance to the product; the second stage of slow cooling gradually lowers the core temperature, giving the molecular chains sufficient time for orderly arrangement and crystal growth, forming a highly crystalline core structure, thereby improving the product's rigidity and heat resistance. This gradient distribution of crystallinity from the outside to the inside (high surface crystallinity, moderate core crystallinity) ensures both the surface hardness of the product and maintains the elasticity of the core, effectively balancing rigidity and toughness, while significantly reducing the product's post-shrinkage rate (e.g., only 1.5%-1.8% in the example).

[0061] In the controlled expansion foaming step, the nonlinear pressure release procedure includes two or more pressure release sub-stages, each sub-stage having a different pressure change rate, and the pressure change rate exhibits an increasing, decreasing, or first increasing and then decreasing pattern along the release sequence.

[0062] It is worth noting that, in addition to the most basic two-stage (slow-fast) mode, three or more sub-stages can be set, such as "slow-fast-slow" or "fast-slow-fast" modes. Increasing the number of sub-stages can provide more precise control: for example, inserting a brief medium-speed pressure relief sub-stage after the nucleation stage and before rapid growth can provide a buffer for the bubble nuclei in the early stages of growth, avoiding stress concentration in the bubble wall caused by sudden rate changes; or introducing a slow pressure relief sub-stage at the end of growth can help relax and solidify the bubble wall. The rate of pressure change can exhibit various patterns along the time sequence, such as increasing (e.g., from slow to fast), decreasing (e.g., from fast to slow), or increasing first and then decreasing, to adapt to the needs of different TPEE grades and different target bubble structures. This flexibility makes the process of this invention highly adaptable and adjustable.

[0063] Example 1

[0064] S1. Raw material pretreatment: TPEE 5526 granules and SiO2 aerogel are fed into a twin-screw extruder, heated to 200℃ to melt and plasticize them, and extruded through a T-die into a sheet with a thickness of 2mm. After cooling and rolling, the sheet is calendered and cut into pre-formed sheets of 200mm×200mm×10mm.

[0065] S2. Gas permeation saturation: Place the pre-formed sheet into a high-pressure reactor and heat it to 120°C. Inject a mixture of CO2 and N2 gas (volume ratio 8:9) into the reactor, pressurize it to 22 MPa, and maintain the pressure for 2 hours to allow the gas to fully dissolve and permeate.

[0066] S3. Controlled Expansion Foaming: A non-linear pressure release program is executed via an electronically controlled proportional valve. Initial Decompression Stage: Pressure is slowly released at a rate of 5 MPa / s. When the pressure inside the reactor drops to 8 MPa (critical pressure threshold; the crystallization pressure of TPEE at 120°C is approximately 8.5 MPa as determined by DSC, and the threshold is set to 8 MPa), the process switches to the later decompression stage. Later Decompression Stage: Pressure is rapidly released to atmospheric pressure at a rate of approximately 50 MPa / s, completing the foaming process.

[0067] S4. Shaping and Curing: After foaming, the foam is quickly transferred to a cooling platen and cooled to 60°C at a rate of 60°C / min, and then cooled to room temperature at a rate of 20°C / min.

[0068] Performance testing: The average cell diameter of the obtained TPEE foam material is approximately 45 μm, and the cell density is approximately 5 × 10¹. 0 Cells / cm³, cell size variation coefficient 12%, thickness shrinkage rate 1.5% after standing for 30 days, smooth surface without wrinkles.

[0069] Example 2

[0070] Except for adjusting the volume ratio of CO2 to N2 in step S2 to 1:1, the other conditions are the same as in Example 1.

[0071] The resulting TPEE foam material has an average cell diameter of approximately 38 μm and a cell density of approximately 8 × 10¹. 0 Cells / cm³, cell size variation coefficient 13%, thickness shrinkage rate 1.8% after standing for 30 days, and smooth surface.

[0072] Comparative Example

[0073] The traditional rapid pressure relief method was adopted: S1 and S2 were the same as in Example 1; in step S3, the pressure inside the reactor was instantly released from 22 MPa to atmospheric pressure (pressure relief rate of approximately 100 MPa / s); S4 was the same as in Example 1. The resulting TPEE foam material had an average cell diameter of approximately 80 μm and a cell density of approximately 5 × 10⁻⁶. 8The cell size variation coefficient is 45%, the thickness shrinkage rate is 8.5% after standing for 30 days, and the surface has obvious wrinkles and orange peel texture.

[0074] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0075] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A foaming method for SiO2 aerogel-modified TPEE, characterized in that, The method includes: S1. Pretreatment for preparing SiO2 aerogel-modified TPEE blends: The thermoplastic polyester elastomer raw material is melt-plasticized and molded to obtain a preform with a preset geometric shape and size. S2, Gas permeation saturation: The prefabricated profile is placed into a sealable processing chamber. Under the condition of applying an external heat field, high-pressure foaming gas is introduced into the chamber and a preset saturation pressure and saturation temperature are maintained for a set time, so that the foaming gas can be fully dissolved and permeate into the internal matrix of the prefabricated profile. S3. Controlled Expansion Foaming: A nonlinear pressure release procedure is performed on the processing chamber under the saturation pressure. This procedure includes at least an early pressure release stage with a first pressure change characteristic and a late pressure release stage with a second pressure change characteristic, the second pressure change characteristic being different from the first pressure change characteristic. Specifically, the pressure drop rate in the early pressure release stage is set to reduce the gas supersaturation growth rate inside the preformed profile to below a critical nucleation rate threshold, thereby forming uniformly distributed bubble nuclei primarily through homogeneous nucleation in this stage. The pressure drop rate in the late pressure release stage is set to increase the gas supersaturation growth rate inside the preformed profile to above a critical growth rate threshold, thereby driving the bubble nuclei to expand and grow synchronously in this stage, obtaining TPEE foam material.

2. The foaming method for SiO2 aerogel-modified TPEE according to claim 1, characterized in that, The raw material pretreatment step specifically includes: placing thermoplastic polyester elastomer granules or powder in an extrusion device, heating and shearing it with a screw to uniformly plasticize it into a molten state, and then guiding the molten material through a molding die with a constant cross-sectional shape. After traction and cooling, sheet-like, film-like, or profiles with specific cross-sections are obtained as the preformed profiles.

3. The foaming method for SiO2 aerogel-modified TPEE according to claim 1, characterized in that, In the gas permeation saturation step, the high-pressure foaming gas contains two or more physical foaming agents with different dissolution and diffusion properties, and the physical foaming agents are selected from carbon dioxide and nitrogen.

4. The foaming method for SiO2 aerogel-modified TPEE according to claim 3, characterized in that, The high-pressure foaming gas is a binary composite gas system formed by mixing carbon dioxide and nitrogen in a specific volume ratio; wherein, the carbon dioxide acts as a nucleation promoter, and its high solubility creates a dense gas enrichment zone in the prefabricated profile matrix, providing nucleation sites for subsequent bubble nucleation; the nitrogen acts as a structural stabilizer, and its low diffusion coefficient suppresses excessive expansion and collapse of the bubbles in the nonlinear pressure release process.

5. The foaming method for SiO2 aerogel-modified TPEE according to claim 1, characterized in that, The volume ratio of carbon dioxide to nitrogen is determined based on the target average bubble diameter D and bubble density ρ using the following empirical formula: ； Wherein, k, a, and b are constants determined through experiments, and the volume ratio ranges from 1:2 to 2:

1.

6. The foaming method for SiO2 aerogel-modified TPEE according to claim 1, characterized in that, In the controlled expansion foaming step, the nonlinear pressure release procedure is implemented by actively controlling the pressure drop process inside the processing chamber according to a preset time sequence and pressure change curve through a pressure control system connected to the processing chamber.

7. The foaming method for SiO2 aerogel-modified TPEE according to claim 6, characterized in that, The first pressure change characteristic corresponding to the initial decompression stage is that the pressure in the processing chamber decreases from the initial saturation pressure at a first average rate, which is from 3 MPa / s to 10 MPa / s; the second pressure change characteristic corresponding to the later decompression stage is that the pressure in the processing chamber decreases to ambient atmospheric pressure at a second average rate, wherein the second average rate is greater than the first average rate.

8. The foaming method for SiO2 aerogel-modified TPEE according to claim 1, characterized in that, The initial decompression stage and the later decompression stage are connected by a pressure switching point; the pressure switching point is determined based on whether the real-time pressure value in the processing chamber reaches a preset critical pressure threshold. When the pressure drops to the critical pressure threshold, the pressure release procedure switches from the early pressure release stage to the late pressure release stage. The critical pressure threshold is determined based on the crystallization temperature-pressure relationship of the thermoplastic polyester elastomer at the saturation temperature. Specifically, the crystallization temperature of the thermoplastic polyester elastomer at different pressures is determined by differential scanning calorimetry, and the critical pressure threshold is set such that when the pressure drops to the threshold, the matrix temperature of the preformed profile is still higher than its crystallization temperature at that pressure, so as to maintain the matrix in a highly elastic state.

9. The foaming method for SiO2 aerogel-modified TPEE according to claim 1, characterized in that, Following the controlled expansion and foaming step, a shaping and curing step is also included: the modified TPEE nascent foam obtained after the nonlinear pressure release procedure, which has formed a cell structure, is cooled. The cooling process adopts a segmented cooling method, so that the cell walls of the modified TPEE nascent foam form a crystallinity gradient distribution from the outside to the inside, thereby fixing the porous cell structure and obtaining a dimensionally stable modified TPEE foam material product.

10. The foaming method for SiO2 aerogel-modified TPEE according to claim 1, characterized in that, In the controlled expansion foaming step, the nonlinear pressure release procedure includes two or more pressure release sub-stages, each sub-stage having a different pressure change rate, and the pressure change rate exhibits an increasing, decreasing, or first increasing and then decreasing pattern along the release sequence.

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