A high-strength elastomer composite material and its supercritical CO2 foaming molding process

Abstract

This invention relates to the field of polymer foaming materials technology, and discloses a high-strength elastomer composite material and its supercritical CO2 foaming molding process. The process includes preparing a composite precursor using ethylene-1-octene copolymer, ethylene-methacrylic acid copolymer zinc salt, maleic anhydride graft, and antioxidant; placing it in an autoclave, simultaneously injecting liquid carbon dioxide and anhydrous ethanol as a co-solvent; after constant temperature and pressure permeation equilibrium, cooling and step-depressurization foaming are performed, followed by curing to obtain the final product. This invention improves matrix compatibility through a dynamic physical cross-linking network formed by polar groups and zinc ions; during the permeation stage, anhydrous ethanol induces network dissociation, reducing gas permeation resistance and promoting diffusion; during the foaming stage, the vaporization and extraction of anhydrous ethanol causes instantaneous reconstruction of the cross-linking network, forming a strain hardening effect to support cell expansion, preventing gas escape and cell collapse, ultimately obtaining a high-strength foamed material with intact cell structure and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polymer foaming materials technology, specifically to a high-strength elastomer composite material and its supercritical CO2 foaming molding process. Background Technology

[0002] Polyolefin elastomers possess excellent flexibility, resilience, and weather resistance, making them widely used in athletic footwear materials, automotive interiors, and cushioning packaging. To reduce material density and increase specific strength, foaming is typically required. Traditional foaming processes often rely on chemical crosslinking agents such as peroxides and chemical foaming agents such as azodicarbonamide. This process not only generates irritating odors and harmful byproducts, but also results in chemically crosslinked materials exhibiting thermosetting characteristics, making them unsuitable for melt-down recycling and reuse, thus failing to meet current environmental recycling requirements.

[0003] Molding technology using supercritical carbon dioxide as a physical foaming agent is currently an effective alternative to traditional chemical foaming. However, polyolefin elastomers are linear macromolecules with relatively little entanglement between molecular chains, resulting in low melt strength and viscosity. During the supercritical fluid depressurization foaming stage, the low melt strength cannot effectively resist the tensile stress generated during bubble growth, making it prone to gas escape, cell rupture, and collapse, leading to an uneven cell structure and poor mechanical strength in the final foamed material. To improve this problem, existing technologies typically introduce ionomers (such as zinc salts of ethylene-methacrylic acid copolymer) into the system for blending, relying on the physical cross-linking network formed by metal ions and polar groups to improve the melt strength of the matrix. However, in actual processes, this strong physical cross-linking effect causes a sharp increase in matrix viscosity, leading to increased diffusion resistance of the supercritical fluid within the polymer and a slow permeation process. Often, it is necessary to extend the holding time or increase the working pressure to achieve permeation equilibrium, increasing energy consumption and production costs. Furthermore, the fixed and unchanging strong physical cross-linked network will excessively restrict the growth of cells during depressurization expansion, making it difficult to further increase the foaming ratio of the material; if the viscosity is reduced simply by increasing the temperature, the physical cross-linked network will completely disintegrate, the melt strength will drop sharply, and cell collapse will occur again.

[0004] Therefore, how to effectively reduce the matrix viscosity during the supercritical gas permeation stage to promote rapid gas diffusion, while simultaneously restoring the melt strength of the matrix instantaneously during the depressurization foaming stage to support stable cell formation, is a technical problem that urgently needs to be solved in the field of polymer supercritical foaming. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-strength elastomer composite material and its supercritical CO2 foaming molding process. This solves the problem that polyolefin elastomers are linear macromolecules with less entanglement between molecular chains and lower melt strength. As a result, they cannot effectively resist the tensile stress generated by bubble growth during the supercritical fluid depressurization foaming stage, which easily leads to gas escape and cell collapse.

[0006] To achieve the above objectives, the present invention provides a high-strength elastomer composite material, which adopts the following technical solution: Firstly, the present invention provides a high-strength elastomer composite material, which adopts the following technical solution: A high-strength elastomer composite material is prepared by supercritical carbon dioxide foaming of a composite precursor material containing the following parts by weight: 70.0-85.0 parts of ethylene-1-octene copolymer; 10.0-20.0 parts of zinc salt of ethylene-methacrylic acid copolymer; 5.0-10.0 parts of maleic anhydride-grafted ethylene-1-octene copolymer; and 0.1-0.5 parts of antioxidant. The polar anhydride groups of the maleic anhydride-grafted ethylene-1-octene copolymer have coordination bonds and hydrogen bonds with the zinc ions or free carboxyl groups in the zinc salt of the ethylene-methacrylic acid copolymer, forming polar ion clusters microdomains bonded within the nonpolar ethylene-1-octene copolymer continuous phase.

[0007] By adopting the above technical solution, the present invention constructs a specific structure of microscopic phase separation and interfacial bonding within the material. The specific innovative mechanism is as follows: Step 1: Construction of interfacial compatibility. Ethylene-1-octene copolymers are nonpolar and thermodynamically incompatible with zinc salts of ethylene-methacrylic acid copolymers containing polar groups. The main chain structure of maleic anhydride-grafted ethylene-1-octene copolymers is identical to that of the continuous phase matrix, allowing for uniform dispersion within the continuous phase through molecular chain entanglement. The polar anhydride groups they carry are enriched at the phase interface.

[0008] Step two: Dynamic physical cross-linking network formation. Under the mechanical shear and thermal action of melt blending, polar anhydride groups undergo ring-opening to generate carboxyl groups, or directly react with zinc ions and incompletely neutralized free carboxyl groups within the ethylene-methacrylic acid copolymer zinc salt system. Hydrogen bonds form between polar groups, while zinc ions coordinate with multiple carboxyl groups and anhydride units to form coordinate bonds.

[0009] Step 3: Construction of the stress transfer network. The combination of hydrogen bonds and coordination bonds causes local polar groups to aggregate, forming nanoscale ion clusters. These ion clusters serve as physical cross-linking points, firmly bound to the continuous phase of the ethylene-1-octene copolymer through coordination bonds. At room temperature or under stress, this dynamic physical cross-linking network can effectively transfer external stress and restrict the slippage of molecular chains, improving the basic mechanical strength of the material. During high-temperature processing, the coordination bonds and hydrogen bonds undergo reversible dissociation, endowing the material with thermoplastic processing capabilities.

[0010] Preferably, the antioxidant is a mixture of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite.

[0011] By adopting the above technical solution, the composite antioxidant system can provide dual antioxidant protection of free radical capture and peroxide decomposition during the high-temperature reactive melt blending stage, preventing the polymer chain segments from undergoing thermo-oxidative degradation and chain breakage, and maintaining the molecular weight and initial mechanical properties of the system.

[0012] Preferably, the preparation method of the composite precursor material includes: adding ethylene-1-octene copolymer, ethylene-methacrylic acid copolymer zinc salt, maleic anhydride-grafted ethylene-1-octene copolymer and antioxidant into a high-speed mixer, and premixing at room temperature to obtain a dry mixture; feeding the dry mixture into a co-rotating twin-screw extruder for reactive melt blending; granulating and drying the extruded material and then adding it into an injection molding machine, injecting it into a mold and cooling and shaping it to obtain the composite precursor material.

[0013] By adopting the above technical solution, solid-phase dry mixing is performed first, followed by melt blending. The high shear force provided by the co-rotating twin-screw extruder promotes the mutual movement between macromolecular chain segments and the full contact of polar groups, improves the conversion rate of interfacial coordination reaction, and ensures that the ion cluster micro-regions are evenly distributed in the matrix.

[0014] Preferably, the high-speed mixer during premixing has a rotation speed of 300-500 rpm and a premixing time of 3-5 min.

[0015] By adopting the above technical solution, a suitable mechanical mixing intensity is provided to prevent the material from agglomerating prematurely due to frictional heating caused by prolonged high speed.

[0016] Preferably, the feeding section temperature of the co-rotating twin-screw extruder is 135–145°C, the melting section temperature is 155–165°C, the reaction section temperature is 175–185°C, the homogenization section temperature is 170–180°C, the die head temperature is 165–175°C, and the screw speed is 150–250 rpm; in the injection molding machine, the barrel temperature is 165–180°C, and the injection pressure is 50–80 MPa.

[0017] By adopting the above technical solution, the stepped heating and cooling settings enable the raw materials to melt smoothly and obtain the highest thermal activation energy in the reaction section, promoting the formation of coordination bonds; the subsequent homogenization and extrusion sections are appropriately cooled to avoid thermal degradation of the polymer or irreversible damage to the cross-linking network due to overheating. The injection molding and shaping steps with specific parameters allow the melt to cool and crystallize in the mold cavity, locking in the pre-formed microscopic physical cross-linking network.

[0018] Secondly, the present invention provides a supercritical CO2 foaming molding process for high-strength elastomer composite materials, employing the following technical solution: A supercritical CO2 foaming molding process for a high-strength elastomer composite material includes the following steps: The composite precursor material is placed in an autoclave and sealed. Liquid carbon dioxide is injected into the autoclave, and anhydrous ethanol is injected simultaneously as a co-solvent to raise the temperature and pressure inside the autoclave and stabilize it. Under these conditions, the pressure is maintained at a constant temperature and pressure, allowing the fluid to diffuse into the composite precursor material until it reaches osmotic equilibrium. The pressure inside the autoclave is kept constant, and the autoclave is cooled to a stable temperature at the foaming window temperature, and then held at this temperature until equilibrium is reached. The pressure relief valve of the autoclave is opened to perform a step-wise pressure reduction, reducing the pressure inside the autoclave to atmospheric pressure, causing the composite precursor material to expand and foam instantly inside the autoclave. The foamed material is removed from the autoclave and allowed to mature at room temperature to obtain the high-strength elastomer composite material.

[0019] By adopting the above technical solution, this process achieves dynamic rheological control by reducing the system viscosity during the penetration and diffusion stage and instantly increasing the melt strength during the foaming and molding stage. The specific innovative mechanism is as follows: During the isothermal and pressure-holding stage, supercritical carbon dioxide carries anhydrous ethanol molecules into the polymer matrix. Anhydrous ethanol molecules are small and contain highly polar hydroxyl groups, which compete for coordination with zinc ions in the system. The ethanol hydroxyl groups seize coordination vacancies on the zinc ions, replacing the carboxyl groups on the original polymer macromolecular chains, forming relatively unstable zinc-ethanol complexes. The original physical cross-linking network of zinc-carboxyl groups disintegrates, leading to the release of the macromolecular chains.

[0020] The dissociation of the physical cross-linking network significantly reduces the melt viscosity and interfacial tension of the polymer matrix. The homogeneous fluid composed of supercritical carbon dioxide and ethanol can diffuse rapidly within the low-permeability matrix, shortening the time required to reach osmotic equilibrium and improving the uniformity and solubility of gas dissolution within the polymer.

[0021] During the step-depressurization foaming stage, the system pressure drops rapidly to ambient atmospheric pressure within a very short time. This pressure drop causes the anhydrous ethanol, which is at a high temperature, to undergo a flash phase transition, transforming into a gas and quickly escaping from the matrix. The extraction of anhydrous ethanol leads to the decomposition of the zinc-ethanol complex. The zinc ions, having lost their ethanol coordination, rapidly seek out free carboxyl groups and polar anhydride groups within the system, reforming stable zinc-carboxyl coordination bonds.

[0022] Due to the re-occurrence of coordination reactions, the dynamic physical cross-linking network between macromolecular chains is reconstructed instantaneously upon depressurization. The matrix melt strength and tensile viscosity increase exponentially, resulting in a strain hardening effect. This high-strength melt network can encapsulate and support the supercritical carbon dioxide bubbles that expand rapidly due to depressurization, effectively resisting the tensile stress caused by bubble growth, preventing gas film rupture and cell collapse, and ultimately forming a high-strength foamed material with uniform cell size, high closed-cell ratio, and excellent mechanical properties.

[0023] Preferably, the amount of anhydrous ethanol injected accounts for 1.0% to 3.0% of the total mass of carbon dioxide injected into the autoclave, the temperature inside the autoclave is raised to 110 to 120°C, the pressure is increased and stabilized to 15 to 18 MPa, and the pressure is maintained at constant temperature and pressure for 60 to 120 minutes.

[0024] By employing the above technical solution, controlling the mass ratio of anhydrous ethanol ensures a sufficient number of hydroxyl groups to dissociate the physical cross-linking network, while avoiding excessive polar solvents that could cause macroscopic swelling and deformation of the polymer matrix. The aforementioned temperature and pressure range keeps carbon dioxide and ethanol in a supercritical or near-critical homogeneous state, providing sufficient diffusion driving force to complete saturated gas permeation within a limited time.

[0025] Preferably, the cooling rate is controlled at 1.0 to 2.0 °C / min to stably cool the environment inside the autoclave to the foaming window temperature of 95 to 100 °C, and then maintain the temperature at this temperature for 15 to 30 minutes.

[0026] By adopting the above technical solution, a smooth and slow cooling rate avoids the generation of temperature gradients and thermal stress within the polymer. The foaming window temperature of 95–100°C is higher than the crystallization temperature of the polymer continuous phase but lower than its melting temperature. At this temperature, the system is in a highly elastic state and possesses suitable ductility for cell nucleation and initial growth.

[0027] Preferably, the pressure relief valve of the autoclave is opened, and the pressure relief rate is controlled at 5-15 MPa / s to perform a step-by-step pressure reduction.

[0028] By employing the above technical solution, the high depressurization rate generates significant thermodynamic instability, inducing extremely high-density homogeneous nucleation. Simultaneously, this rate ensures that the pressure drop is much faster than the ethanol vapor pressure, prompting a dramatic flash phase transition in ethanol to trigger the rapid reconstruction of the physical cross-linked network, providing structural support for high-ratio foaming.

[0029] This invention provides a high-strength elastomer composite material and its supercritical CO2 foaming molding process. It has the following beneficial effects: 1. This invention introduces zinc salt of ethylene-methacrylic acid copolymer and maleic anhydride-grafted ethylene-1-octene copolymer into the continuous phase of ethylene-1-octene copolymer. The polar anhydride groups on the graft copolymer form coordination bonds and hydrogen bonds with zinc ions or free carboxyl groups in the zinc salt, constructing a reversible dynamic physical cross-linking network within the composite material. This microstructure promotes the uniform distribution of polar ion clusters in the non-polar matrix, improving the interfacial compatibility between different components. This provides a good matrix structure for the subsequent foaming process and effectively enhances the structural strength and mechanical properties of the molded foamed material.

[0030] 2. This invention involves simultaneously injecting anhydrous ethanol as a co-solvent during the isothermal and isobaric permeation stage of supercritical carbon dioxide. The polar hydroxyl groups in the anhydrous ethanol molecules form complexes with zinc ions, temporarily replacing the carboxyl groups on the polymer chains and inducing solvation dissociation of the dynamic physical cross-linking network within the polymer. This step can moderately reduce the melt viscosity and interfacial tension of the material matrix, lower gas permeation resistance, and allow the homogeneous fluid of supercritical carbon dioxide and ethanol to diffuse more rapidly and uniformly into the composite precursor material to achieve permeation equilibrium.

[0031] 3. This invention employs a step-depressurization process during the foaming stage, causing the anhydrous ethanol in the system to undergo a flash phase change and vaporize upon depressurization, eliminating solvation dissociation and forcing zinc ions in the polymer matrix to instantly reassociate with free carboxyl groups. This rapid reconstruction of the physical cross-linked network creates a strain hardening effect during the cell expansion stage, providing sufficiently high melt strength to support the cell walls, effectively preventing gas escape and cell collapse, ultimately resulting in a high-strength foamed material with intact cell structure, high compressive fatigue life, and low energy absorption decay rate. Attached Figure Description

[0032] Figure 1 This is a comparison chart of the test results of apparent density, volume shrinkage rate and foaming expansion ratio of the foamed materials in various embodiments and comparative examples of the present invention. Figure 2 This is a comparison chart of the test results of right-angle tear strength, Shore hardness and drop ball rebound rate of foamed materials in various embodiments and comparative examples of the present invention; Figure 3The graphs show the thickness retention rate and energy absorption attenuation rate of the foamed materials after undergoing high-frequency dynamic compression tests in the various embodiments and comparative examples of this invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a custom composite precursor material, including the following steps: 70.0 parts by weight of ethylene-1-octene copolymer, 10.0 parts by weight of zinc salt of ethylene-methacrylic acid copolymer, 5.0 parts by weight of maleic anhydride-grafted ethylene-1-octene copolymer, and 0.1 parts by weight of antioxidant (composed of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite in a mass ratio of 1:1) were added to a high-speed mixer and premixed at room temperature for 3 minutes at 300 rpm to obtain a dry mixture. The dry mixture was then fed into a co-rotating twin-screw extruder for reactive melt blending. The temperature of the feeding section of the co-rotating twin-screw extruder was 135°C, the melting section temperature was 155°C, the reaction section temperature was 175°C, the homogenization section temperature was 170°C, the die temperature was 165°C, and the screw speed was 150 rpm. After underwater pelletizing and centrifugal dehydration, the extruded material is dried in a 60℃ forced-air oven for 4 hours to obtain composite material particles. The composite material particles are added to an injection molding machine and injected into a mold at a barrel temperature of 165℃ and an injection pressure of 50MPa. After cooling and solidification, the material is demolded to obtain the first composite precursor material preform.

[0035] Preparation Example 2: This preparation example provides a method for preparing a custom composite precursor material, including the following steps: 78.0 parts by weight of ethylene-1-octene copolymer, 15.0 parts by weight of zinc salt of ethylene-methacrylic acid copolymer, 8.0 parts by weight of maleic anhydride-grafted ethylene-1-octene copolymer, and 0.3 parts by weight of antioxidant (composed of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite in a mass ratio of 1:1) were added to a high-speed mixer and premixed at room temperature for 4 minutes at 400 rpm to obtain a dry mixture. The dry mixture was then fed into a co-rotating twin-screw extruder for reactive melt blending. The temperature of the feeding section of the co-rotating twin-screw extruder was 140°C, the melting section temperature was 160°C, the reaction section temperature was 180°C, the homogenization section temperature was 175°C, the die temperature was 170°C, and the screw speed was 200 rpm. After underwater pelletizing and centrifugal dehydration, the extruded material is dried in a 60℃ forced-air oven for 5 hours to obtain composite material particles. The composite material particles are added to an injection molding machine and injected into a mold at a barrel temperature of 175℃ and an injection pressure of 65MPa. After cooling and solidification, the material is demolded to obtain the second composite precursor material preform.

[0036] Preparation Example 3: This preparation example provides a method for preparing a custom composite precursor material, including the following steps: 85.0 parts by weight of ethylene-1-octene copolymer, 20.0 parts by weight of zinc salt of ethylene-methacrylic acid copolymer, 10.0 parts by weight of maleic anhydride-grafted ethylene-1-octene copolymer, and 0.5 parts by weight of antioxidant (composed of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite in a mass ratio of 1:1) were added to a high-speed mixer and premixed at room temperature for 5 minutes at 500 rpm to obtain a dry mixture. The dry mixture was then fed into a co-rotating twin-screw extruder for reactive melt blending. The temperature of the feeding section of the co-rotating twin-screw extruder was 145°C, the melting section temperature was 165°C, the reaction section temperature was 185°C, the homogenization section temperature was 180°C, the die temperature was 175°C, and the screw speed was 250 rpm. After underwater pelletizing and centrifugal dehydration, the extruded material is dried in a 60℃ forced-air oven for 6 hours to obtain composite material particles. The composite material particles are added to an injection molding machine and injected into a mold at a barrel temperature of 180℃ and an injection pressure of 80MPa. After cooling and solidification, the material is demolded to obtain the composite precursor material preform.

[0037] Examples 1-3: Example 1: This embodiment provides a high-strength elastomer composite material and its supercritical CO2 foaming molding process, including the following steps: The composite precursor material preform obtained in Example 1 was placed in a clamp-type static autoclave and sealed. Liquid carbon dioxide was injected into the autoclave using a high-pressure horizontal flow pump, while anhydrous ethanol was simultaneously injected in proportion using a co-solvent pump. The amount of anhydrous ethanol injected was 1.0% of the total mass of carbon dioxide injected into the autoclave. The heating jacket of the autoclave was turned on, raising the temperature inside the autoclave to 110°C and increasing the pressure to 15 MPa. Under these conditions, the pressure was maintained at constant temperature and pressure for 60 min, allowing the homogeneous fluid of supercritical carbon dioxide and anhydrous ethanol to diffuse into the preform until osmotic equilibrium was reached. After the pressure holding time was completed, the pressure inside the autoclave was kept constant at 15 MPa. The jacket circulating cooling water was switched, and the system inside the autoclave was cooled steadily to the foaming window temperature of 95°C at a cooling rate of 1.0°C / min. The system was then held at this temperature for 15 min to achieve equilibrium. The rapid pneumatic pressure relief valve of the autoclave is opened, and the pressure is reduced in a stepwise manner at a pressure relief rate of 5 MPa / s to reduce the pressure inside the autoclave to ambient atmospheric pressure, causing the preform to expand and foam instantly inside the autoclave. The foamed material is then removed from the autoclave and allowed to stand and mature at room temperature for 24 hours to obtain a high-strength elastomer composite material.

[0038] Example 2: This embodiment provides a high-strength elastomer composite material and its supercritical CO2 foaming molding process, including the following steps: The composite precursor material preform obtained in Preparation Example 2 was placed in a clamp-type static autoclave and sealed. Liquid carbon dioxide was injected into the autoclave using a high-pressure horizontal flow pump, while anhydrous ethanol was simultaneously injected in proportion using a co-solvent pump. The amount of anhydrous ethanol injected accounted for 2.0% of the total mass of carbon dioxide injected into the autoclave. The heating jacket of the autoclave was turned on, raising the temperature inside the autoclave to 115°C and increasing the pressure to 16.5 MPa. Under these conditions, the pressure was maintained at constant temperature and pressure for 90 minutes, allowing the homogeneous fluid of supercritical carbon dioxide and anhydrous ethanol to diffuse into the preform until osmotic equilibrium was reached. After the pressure holding time was completed, the pressure inside the autoclave was kept constant at 16.5 MPa, and the jacket circulating cooling water was switched to cool the system inside the autoclave steadily to the foaming window temperature of 98°C at a cooling rate of 1.5°C / min. The system was then held at this temperature for 20 minutes to achieve equilibrium. The rapid pneumatic pressure relief valve of the autoclave was opened, and the pressure was reduced in a stepwise manner at a pressure relief rate of 10 MPa / s to reduce the pressure inside the autoclave to ambient atmospheric pressure, causing the second mold to expand and foam instantly inside the autoclave. The foamed material was then removed from the autoclave and allowed to stand and mature at room temperature for 36 hours to obtain a high-strength elastomer composite material.

[0039] Example 3: This embodiment provides a high-strength elastomer composite material and its supercritical CO2 foaming molding process, including the following steps: The composite precursor material preform obtained in Preparation Example 3 was placed in a clamp-type static autoclave and sealed. Liquid carbon dioxide was injected into the autoclave using a high-pressure horizontal flow pump, while anhydrous ethanol was simultaneously injected in proportion using a co-solvent pump. The amount of anhydrous ethanol injected accounted for 3.0% of the total mass of carbon dioxide injected into the autoclave. The heating jacket of the autoclave was turned on, raising the temperature inside the autoclave to 120°C and increasing the pressure to 18 MPa. Under these conditions, the pressure was maintained at constant temperature and pressure for 120 min, allowing the homogeneous fluid of supercritical carbon dioxide and anhydrous ethanol to diffuse into the preform until osmotic equilibrium was reached. After the pressure holding time was completed, the pressure inside the autoclave was kept constant at 18 MPa. The jacket circulating cooling water was switched, and the system inside the autoclave was steadily cooled to the foaming window temperature of 100°C at a cooling rate of 2.0°C / min. The system was then held at this temperature for 30 min to achieve equilibrium. The rapid pneumatic pressure relief valve of the autoclave was opened, and the pressure was reduced in a stepwise manner at a rate of 15 MPa / s to reduce the pressure inside the autoclave to ambient atmospheric pressure, causing the preform three to expand and foam instantly inside the autoclave. The foamed material was then removed from the autoclave and allowed to stand and mature at room temperature for 48 hours to obtain a high-strength elastomer composite material.

[0040] Comparative Examples 1-4: Comparative Example 1: Compared with Example 2, the difference is that when preparing the composite precursor material, maleic anhydride-grafted ethylene-1-octene copolymer was not added, and its 8.0 parts by mass were replaced with ethylene-1-octene copolymer (i.e., the total amount of ethylene-1-octene copolymer added was 86.0 parts by mass), and the rest were the same.

[0041] Comparative Example 2: Compared with Example 2, the difference is that when preparing the composite precursor material, ethylene-methacrylic acid copolymer zinc salt and maleic anhydride-grafted ethylene-1-octene copolymer were not added, but 0.8 parts by weight of dicumyl peroxide and 2.0 parts by weight of talc were added; and in the supercritical foaming permeation stage, the temperature in the autoclave was raised to 160°C and kept at constant temperature and pressure for 90 minutes, and the rest were the same.

[0042] Comparative Example 3: Compared with Example 2, the difference is that in the permeation stage of supercritical foaming, anhydrous ethanol was not injected into the autoclave through a co-solvent pump, but only liquid carbon dioxide was injected, and the rest were the same.

[0043] Comparative Example 4: Compared with Example 2, the difference is that in the step depressurization stage of supercritical foaming, the pressure relief rate of the pressure relief valve of the high-pressure vessel was changed to 0.5 MPa / s, and the rest were the same.

[0044] Test Example 1-3: Test Example 1: Macroscopic Foaming Indicators and Density Test Sample preparation: The foamed materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were cut off with a band saw, and then core standard test blocks with a size of 30mm×30mm×10mm were cut on a sample cutting machine. Five parallel samples were taken for each formulation.

[0045] Apparent density test: Conducted according to ASTM D1622 standard at 23°C and 50% relative humidity. The mass of the test block in air was measured using an analytical balance with an accuracy of 0.0001 g. The length, width, and thickness of the test block were measured using a digital vernier caliper with an accuracy of 0.01 mm, and the volume was calculated. The apparent density was obtained by dividing the mass by the volume, and the arithmetic mean of five parallel samples was taken.

[0046] Expansion ratio test: The displacement method (Archimedes' principle) was used for determination. The volume of the solid composite precursor material preform before foaming and the volume of the sample after foaming were measured respectively. The expansion ratio was calculated as the ratio of the volume after foaming to the volume before foaming.

[0047] Volume shrinkage test: After the sample was demolded from the autoclave and left at room temperature for 1 hour, its initial foaming volume was measured using the displacement method. The sample was then placed in a standard environmental chamber at 25°C and 50% relative humidity for 72 hours, and its volume was measured again. The volume shrinkage rate was calculated as a percentage of the difference between the initial volume and the volume after standing, divided by the initial volume.

[0048] Table 1. Macroscopic foaming indices and density test data of foamed materials in each embodiment and comparative example. See attached document Figure 1 , attached Figure 1 This paper demonstrates the influence of different component ratios and supercritical molding processes on the macroscopic foaming properties of elastomeric composites. The horizontal axis corresponds to the test samples of Examples 1 to 3 and Comparative Examples 1 to 4 of this invention. The graph includes two vertical axes: the left primary axis reflects the apparent density of the material, and the right secondary axis reflects the volume shrinkage rate of the material after standing for 72 hours under standard conditions. Furthermore, the specific values ​​at the top of the apparent density histogram represent the foaming expansion ratio of the sample. By comparing the height of the apparent density histogram and the values ​​above it, it can be seen that the example group is significantly better than the comparative example group in terms of foaming density and expansion ratio. Combined with the height variation of the volume shrinkage rate histogram, this proves that the present invention can achieve a lightweight structure while stably controlling the macroscopic dimensional shrinkage rate of the product at an extremely low level, verifying the supporting role of the crosslinking network on the cell structure.

[0049] According to the data in Table 1, the apparent density distribution of Examples 1 to 3 is 0.082 g / cm³. 3 Up to 0.114 g / cm 3Between these values, the expansion ratio reached 7.62 to 10.51, and the volume shrinkage rate after 72 hours was controlled below 2.5%, indicating that the foamed material maintained a stable cell structure while achieving low density.

[0050] The comparison revealed that, in Comparative Example 3, no anhydrous ethanol was injected during the supercritical foaming and permeation stage, and its apparent density increased to 0.179 g / cm³. 3 The expansion ratio is only 4.81. Due to the lack of coordination competition from the polar hydroxyl groups of anhydrous ethanol, the physical cross-linking network of ion clusters did not undergo solvent-induced dissociation, resulting in excessively high polymer melt viscosity. This hindered the permeation of supercritical carbon dioxide, made fluid mass transfer difficult, and limited the foaming ratio.

[0051] Comparative Example 4 reduced the pressure relief rate during the step depressurization stage to 0.5 MPa / s, and its apparent density reached 0.224 g / cm³. 3 The volume shrinkage rate was as high as 9.05%. The slow depressurization process failed to induce a violent flash phase transition of the ethanol dissolved in the matrix. Because the ethanol ligands failed to vaporize and be extracted instantaneously, the dynamic cross-linking network of zinc ions and carboxyl groups could not achieve instantaneous forced association. The foaming system failed to produce strain hardening effect during the cell expansion stage, the melt tensile viscosity was insufficient, and the cell walls ruptured and merged during biaxial tension, ultimately causing severe collapse and shrinkage of the macrostructure.

[0052] In Comparative Example 1, without the addition of maleic anhydride grafts, the volume shrinkage rate of the foamed material was 7.12%. Due to the lack of anhydride groups as anchoring nodes in the system, the spontaneously formed polar microdomains of the ethylene-methacrylic acid copolymer zinc salt could not effectively anchor the non-polar continuous phase segments. During the foaming expansion process, the slip resistance at the phase interface was insufficient to support the expansion stress of the phase change gas, leading to gas escape and product shrinkage.

[0053] Comparative Example 2 used a traditional peroxide chemical crosslinking and talc nucleation system, with an apparent density of 0.137 g / cm³. 3 The expansion ratio is 6.32. The covalent cross-linked network is irreversible, which restricts the free volume expansion of the matrix macromolecular chains at the foaming window temperature. Its foaming capacity and weight reduction are lower than the scheme of this invention based on dynamic coordination cross-linking and supercritical fluid phase change control.

[0054] Test Example 2: Static Mechanical Properties and Rebound Test According to ASTM D624, the foam material was cut into C-shaped right-angle tear test specimens along its thickness using a standard cutter. The specimens were clamped in the upper and lower grips of a universal testing machine, and the tensile speed was set to 500 mm / min. The machine was started to stretch the specimens until they broke. The maximum tensile force during the test was recorded. The right-angle tear strength was calculated by dividing the maximum tensile force by the initial thickness at the point of fracture. Five parallel specimens were tested for each formulation, and the arithmetic mean was taken.

[0055] Cut a foamed material sample with a thickness greater than 6 mm, a smooth surface, and parallel top and bottom, and place it on a horizontal and rigid substrate. Press a Shore C hardness tester vertically onto the sample surface, applying a constant load to ensure full contact between the indenter tip and the sample. Read the value after 1 second of contact. Take measurements at five different locations on each sample surface, at least 12 mm from the edge, with a spacing of more than 6 mm between the measurement points. Take the arithmetic mean of the five readings as the hardness value.

[0056] Cut foamed test blocks to standard dimensions of 50mm × 50mm × 20mm. Place the test blocks on the rigid support platform at the bottom of the drop ball rebound tester and fix them in place. Release a standard steel ball with a mass of 16g ​​and a diameter of 16mm, allowing it to fall freely from an initial height of 400mm, impacting the center of the test block surface. Read the scale at the highest point of the steel ball's rebound. The rebound rate is calculated by multiplying the ratio of the rebound height to the initial drop height by 100%. Test 5 parallel samples for each formulation and take the arithmetic mean.

[0057] Table 2. Static mechanical properties and rebound test data of foamed materials in each embodiment and comparative example See attached document Figure 2 , attached Figure 2This paper demonstrates the comprehensive impact of different material formulations and molding processes on the static mechanical properties of the final foamed products. The horizontal axis represents the test samples of Examples 1 to 3 and Comparative Examples 1 to 4 of this invention. The vertical axis represents the test index values ​​after unification of dimensions. Three different bar charts are used in the figure for data comparison, representing right-angle tear strength, Shore hardness, and drop ball rebound rate, respectively. The precise test measurement value is marked above each bar. It can be seen from the height distribution of each bar in the examples and comparative examples that, under the condition that the Shore hardness is kept at a low level, the right-angle tear strength and rebound rate of the example group are at a high level globally, indicating that the material has both high elasticity and flexibility and high mechanical strength. In the comparative examples, the tear strength and rebound rate of Comparative Examples 1 and 2 decreased, reflecting the weakening of mechanical properties due to conventional crosslinking systems or lack of effective interface anchoring; the Shore hardness of Comparative Examples 3 and 4 increased abnormally and the rebound rate decreased, indicating that the failure of the foam structure led to the solidification and rigidity of the material, losing the buffering and rebound characteristics required for elastomeric foam materials. This attached figure visually demonstrates the decisive role of the dynamic coordination crosslinking network in the macroscopic mechanical equilibrium of this invention.

[0058] According to the data in Table 2, the right-angle tear strength of Examples 1 to 3 ranged from 16.9 N / mm to 21.7 N / mm, the Shore C hardness was controlled between 36.5 and 42.2, and the resilience reached 67.4% to 71.8%. The foamed material exhibited a combination of high tensile strength and high elastic recovery under low density conditions. The instantaneous forced association between zinc ions and free carboxyl groups during the flash phase transition constructed a dense physical cross-linked network within the cell walls, enhancing the mechanical strength of the matrix.

[0059] In Comparative Example 1, without the introduction of maleic anhydride grafts, the right-angle tear strength decreased to 10.4 N / mm. The polar microregions formed by the zinc salt of the ethylene-methacrylic acid copolymer lack anchoring groups and cannot form effective bonds with the non-polar ethylene-1-octene copolymer continuous phase. Under external tear stress, the phase interface is prone to slippage and detachment, and the stress cannot be uniformly transmitted between molecular chains, resulting in a decrease in the material's tear resistance.

[0060] Comparative Example 2, using peroxide crosslinking and inorganic talc nucleation, showed a decrease in resilience to 53.7% and a tear strength of 12.6 N / mm. The irreversible covalent crosslinking network constrained the mobility and conformational freedom of the polymer molecular chains, resulting in hysteresis in conformational recovery under pressure. Inorganic talc particles, acting as heterogeneous nucleating agents, exhibited interfacial compatibility differences with the polymer matrix, leading to microscopic stress concentration points under stress and inducing microcrack propagation.

[0061] Comparative Example 3 did not contain anhydrous ethanol as an entrainer, and Comparative Example 4 had an excessively low decompression rate, resulting in hardnesses of 57.2 and 64.1 for the test pieces, respectively, and significantly reduced resilience. Impaired supercritical fluid mass transfer and failure to trigger ethanol flash evaporation during the decompression stage led to cell expansion and rupture, and macroscopic volume shrinkage. The increased proportion of densified solid polymer resulted in higher overall material rigidity, manifesting as higher hardness and a loss of the buffering and resilience provided by the porous structure. Comparative Example 4, due to extremely uneven cell wall thickness, even exhibited a high fracture force (19.8 N / mm), but this is a characteristic of incompletely foamed solid materials and deviates from the design requirements of lightweight, highly elastic foamed materials.

[0062] Test Example 3: MTS Dynamic Compression Fatigue Life Test According to relevant testing standards, a cylindrical standard specimen with a diameter of 50 mm and a thickness of 20 mm was cut from the center area of ​​the foam material using a precision band saw. The initial center thickness of the specimen was measured before testing, accurate to 0.01 mm. Three parallel specimens were prepared for each formulation.

[0063] Place the sample at the center of the vertically parallel dynamic compression fixture of the MTS elastomer servo testing system. Adjust the servo hydraulic cylinder to make the upper fixture rigidly contact the upper surface of the sample, set the contact preload to 5N, and set this position as the zero point of compression displacement.

[0064] The system was configured to operate in load-controlled mode using dynamic compression cycles. A single cycle period was set to 900ms. The loading procedure was as follows: within the initial 100ms, the load linearly increased from 0N to 1500N; within the following 100ms, the load linearly unloaded from 1500N to 0N; then held at 0N for 700ms. The system ran continuously for 100,000 cycles, synchronously recording the load displacement hysteresis loop data for each cycle.

[0065] After 100,000 cycles, the sample was removed and placed in a standard environment at 23°C and 50% relative humidity for 24 hours to recover freely. The center thickness of the recovered sample was measured. The thickness retention rate was calculated by multiplying the recovered thickness by 100%. The area integral of the load-displacement hysteresis loop from the first cycle and the 100,000th cycle was extracted as the energy absorption value. The energy absorption attenuation rate was calculated as the difference between the two values ​​divided by the energy absorption value of the first cycle. The arithmetic mean of three parallel samples was taken.

[0066] Table 3. MTS dynamic compression fatigue test data of foamed materials in each embodiment and comparative example See attached document Figure 3 , attached Figure 3This demonstrates the microstructural stability of different material formulations after undergoing high-frequency dynamic compression loading. The horizontal axis represents the test sample names of Examples 1 to 3 and Comparative Examples 1 to 4. The left main vertical axis corresponds to the thickness retention rate, represented by solid lines connecting square data points; the right secondary vertical axis corresponds to the energy absorption attenuation rate, represented by dashed lines connecting circular data points. The curve trends show that the thickness retention rate curves for Examples 1 to 3 are at a high top, while the corresponding energy absorption attenuation rate curves are at a low bottom, indicating that these three materials experienced almost no permanent deformation after 100,000 cycles of compression, and their energy absorption buffering effect remained stable. This is due to the construction of a dynamically reversible coordination cross-linking network within the materials, achieving molecular-level energy dissipation and network self-healing during deformation and recovery. Conversely, the curves of the comparative examples show a clear deterioration trend, especially for Comparative Examples 2 and 4, where the thickness retention rate decreases and the energy absorption attenuation rate increases sharply. This confirms that irreversible covalent crosslinking, the addition of inorganic nucleating agents, and improper control of foaming parameters can all lead to phase interface cracking, molecular chain breakage, and cell wall collapse under repeated stress, thereby causing the foamed material to lose its fatigue resistance.

[0067] According to the data in Table 3, after 100,000 high-frequency dynamic high-load compression cycles, Examples 1 to 3 maintained a thickness retention rate between 95.4% and 98.2%, and an energy absorption attenuation rate between 4.6% and 7.9%. The foamed material did not experience macroscopic structural collapse or large-area rupture of microcellular walls under long-term reciprocating deformation. During dynamic compression, the coordination crosslinking network formed by the zinc salt of the ethylene-methacrylic acid copolymer and free carboxyl groups exhibited dynamic reversible supramolecular chemical properties. When the local stress caused by external force exceeds the bond energy of the coordination bonds, the zinc ion coordination bonds dissociate to dissipate the compression mechanical energy; during the unloading and static recovery stages, the dissociated ion clusters recombine under thermodynamic drive, repairing the crosslinking network. This molecular-level energy dissipation and network self-healing mechanism endows the matrix with excellent resistance to fatigue failure.

[0068] Comparative Example 2, using a peroxide crosslinking system and a talc nucleation system, showed a thickness retention rate reduced to 74.1% and an energy absorption attenuation rate as high as 39.8%. Under repeated high-intensity strain, covalent bonds underwent irreversible homogeneous chain breakage, resulting in permanent damage to the polymer network. Inorganic rigid particles such as talc formed significant interfacial defects in the flexible matrix. Under cyclic compressive stress, extremely high stress concentration occurred at the sharp corners of the inorganic particles, inducing the generation of microcracks that rapidly propagated along the interfacial, leading to fatigue fracture of the cell walls. Macroscopically, this manifested as severe thinning and hardening of the material, as well as a sharp loss of its buffering and energy absorption properties.

[0069] Comparative Example 1, lacking maleic anhydride grafts as compatibility and anchoring nodes, exhibited a thickness retention of 82.5%. Dynamically coordinated ion clusters failed to stably anchor to the main chain of the ethylene-1-octene copolymer continuous phase. During repeated tensile and compressive deformation, relative slippage occurred between the polar microregions and the non-polar matrix, leading to irreversible plastic deformation of the macromolecular chains and an increase in accumulated residual strain.

[0070] Comparative Examples 3 and 4 exhibited low expansion ratios and severely uneven cell structures due to failure in foaming rheological control. Some extremely thin cell walls buckled and collapsed during the initial few compression cycles, while the thicker polymer sections subsequently bore uneven localized high pressure, leading to accelerated fatigue degradation. Their energy absorption attenuation rates reached 18.2% and 31.5%, respectively, demonstrating that the irregular physical structure directly weakened the overall load-bearing and energy absorption performance.

Claims

1. A high-strength elastomer composite material, characterized in that, A composite precursor material prepared from raw materials comprising the following parts by weight is produced by supercritical carbon dioxide foaming: Ethylene-1-octene copolymer: 70.0–85.0 parts; Zinc salt of ethylene-methacrylic acid copolymer: 10.0–20.0 parts; Maleic anhydride-grafted ethylene-1-octene copolymer: 5.0–10.0 parts; Antioxidant: 0.1–0.5 parts; The polar anhydride groups of the maleic anhydride-grafted ethylene-1-octene copolymer have coordination bonds and hydrogen bonds with the zinc ions or free carboxyl groups in the zinc salt of the ethylene-methacrylic acid copolymer, and the polar ion cluster microregions are combined in the nonpolar ethylene-1-octene copolymer continuous phase.

2. The high-strength elastomer composite material according to claim 1, characterized in that, The antioxidant is a mixture of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite.

3. The high-strength elastomer composite material according to claim 1, characterized in that, The composite precursor material is obtained by the following preparation method: Ethylene-1-octene copolymer, zinc salt of ethylene-methacrylic acid copolymer, maleic anhydride-grafted ethylene-1-octene copolymer and antioxidant are added to a high-speed mixer and premixed at room temperature to obtain a dry mixture; The dry mixture is fed into a co-rotating twin-screw extruder for reactive melt blending; The extruded material is granulated and dried before being added to an injection molding machine, injected into a mold, and cooled and shaped to obtain the composite precursor material.

4. The high-strength elastomer composite material according to claim 3, characterized in that, The premixing time is 300-500 rpm and the premixing time is 3-5 min.

5. A high-strength elastomer composite material according to claim 3, characterized in that, The temperature of the feeding section of the co-rotating twin-screw extruder is 135-145℃, the temperature of the melting section is 155-165℃, the temperature of the reaction section is 175-185℃, the temperature of the homogenization section is 170-180℃, the temperature of the die head is 165-175℃, and the screw speed is 150-250 rpm.

6. A high-strength elastomer composite material according to claim 3, characterized in that, In the injection molding machine, the barrel temperature is 165-180℃ and the injection pressure is 50-80MPa.

7. A supercritical CO2 foaming molding process for a high-strength elastomer composite material, characterized in that, The method for preparing a high-strength elastomeric composite material as described in any one of claims 1-6 comprises the following steps: The composite precursor material is placed in an autoclave and sealed. Liquid carbon dioxide is injected into the autoclave, and anhydrous ethanol is injected simultaneously as a co-solvent to raise the temperature and pressure inside the autoclave and stabilize it. Under these conditions, the temperature and pressure are kept constant to allow the fluid to diffuse into the interior of the composite precursor material until it reaches osmotic equilibrium. Maintain a constant pressure inside the autoclave, cool it down to a stable temperature at the foaming window, and maintain a constant temperature equilibrium at this temperature. Open the pressure relief valve of the autoclave to perform a step-by-step pressure reduction, reducing the pressure inside the autoclave to ambient atmospheric pressure, which causes the composite precursor material to expand and foam instantly inside the autoclave. The foamed material is removed from the autoclave and allowed to stand and mature at room temperature to obtain the high-strength elastomer composite material.

8. The supercritical CO2 foaming molding process for a high-strength elastomer composite material according to claim 7, characterized in that, The amount of anhydrous ethanol injected accounts for 1.0% to 3.0% of the total mass of carbon dioxide injected into the autoclave. The temperature inside the autoclave is raised to 110 to 120°C, and the pressure is increased and stabilized to 15 to 18 MPa. At the same time, the pressure is maintained at constant temperature and pressure for 60 to 120 minutes.

9. The supercritical CO2 foaming molding process for a high-strength elastomer composite material according to claim 7, characterized in that, The cooling rate is controlled at 1.0 to 2.0 °C / min to stably cool the environment inside the autoclave to the foaming window temperature of 95 to 100 °C, and then maintain the temperature at this temperature for 15 to 30 minutes.

10. The supercritical CO2 foaming molding process for a high-strength elastomer composite material according to claim 7, characterized in that, Open the pressure relief valve of the autoclave and control the pressure relief rate to 5-15 MPa / s for step-by-step pressure reduction.

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