High-elastic supercritical foaming nylon elastomer foam and preparation method thereof

Abstract

The invention relates to the technical field of high polymer material processing, and discloses high-elastic supercritical foaming nylon elastomer foam and a preparation method thereof. 5.0 to 12.0 parts of an ionized modified precursor; 0.5 to 2.0 parts of a metal ion source; 0.5 to 3.0 parts of a sacrificial coordination sealing agent; 0.1 to 0.3 part of a heat stabilizer; the sacrificial coordination sealing agent is used for shielding the activity of metal ions in the melt extrusion stage, so that the low-viscosity processing fluidity is ensured; in the supercritical fluid dipping and foaming stage, a sealing agent is removed through extraction, metal ions are triggered in situ to construct a high-density physical cross-linked network, and the melt strength is greatly improved instantly. According to the technical scheme, the contradiction between the processing rheological property and the melt strength in the foaming process of the nylon elastomer is effectively solved, and the prepared foam material has the advantages that foam holes are fine and uniform, the rebound resilience is excellent, and the thermal reversible recovery characteristic is achieved.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, specifically to a high-elasticity supercritical foamed nylon elastomer foam and its preparation method. Background Technology

[0002] Polyether block polyamide (PEBA) elastomers, due to their unique soft and hard segment structure, possess excellent resilience, low-temperature flexibility, and good energy feedback characteristics, making them widely used in sports footwear materials, cushioning gear, and high-end packaging materials. With increasingly stringent environmental regulations and rising demands for lightweight materials, using supercritical fluids as foaming agents to prepare microporous foamed materials has become a mainstream industry trend. However, the linear molecular structure of PEBA resin results in low melt strength, and its viscoelastic behavior is sensitive to temperature and shear rate. During supercritical foaming, when cells nucleate and grow rapidly, the low-strength melt skeleton cannot effectively resist the tension within the bubbles, easily leading to cell wall rupture, merging, and collapse. This results in final products with large, uneven cell size, high density, and impaired resilience.

[0003] To improve the melt strength of PEBA and enhance its foaming properties, existing technologies often employ chemical crosslinking modification methods, such as adding organic peroxides or using high-energy radiation. While the covalent network constructed by chemical crosslinking can significantly increase melt viscosity and support the cell structure, this irreversible three-dimensional network structure causes the material to transition to a thermosetting state, losing its ability to be melt-processed. This results in scraps and waste products that cannot be recycled, leading to resource waste. Furthermore, the chemical crosslinking reaction is difficult to precisely control in terms of temperature during extrusion, easily causing scorching or gelation points within the processing equipment, affecting production stability.

[0004] Besides chemical crosslinking, introducing metal ions to construct a physical ionic crosslinking network is also an effective means to improve melt strength. However, traditional ionization modification techniques suffer from serious processing rheological contradictions. When metal salts are directly introduced into the polymer melt, strong electrostatic interactions and agglomeration occur between the metal ions and the polar groups on the polymer segments during the high-temperature mixing stage, leading to a sharp increase in melt viscosity. These prematurely formed ionic aggregates cause the material to exhibit extremely high shear resistance and torque during the extrusion granulation stage, easily leading to melt fracture, excessive die pressure, or even equipment blockage, making it difficult to obtain a uniformly dispersed and smooth latent foaming precursor. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-elasticity supercritical foamed nylon elastomer foam and its preparation method, solving the problem of cell collapse caused by low melt strength in existing polyether block polyamide resins during supercritical foaming.

[0006] A first aspect of the present invention provides a high-elasticity supercritical foamed nylon elastomer foam. This nylon elastomer foam is prepared from a raw material composition comprising the following components in parts by weight: 100 parts of a matrix resin polyether block polyamide; 5.0-12.0 parts of an ionized modified precursor; 0.5-2.0 parts of a metal ion source; 0.5-3.0 parts of a sacrificial coordination blocker; and 0.1-0.3 parts of a heat stabilizer.

[0007] The sacrificial coordination blocking agent is selected from alkanolamine compounds or β-diketone derivatives with a boiling point higher than 210℃ and a solubility in supercritical carbon dioxide greater than 1.5wt%. The matrix resin, polyether block polyamide, has a hard segment of polyamide 12 and a soft segment of polytetrahydrofuran, with a Shore hardness of 25D to 55D. The ionization modification precursor is a polyamide oligomer containing carboxylic acid groups or sulfonic acid groups at its ends or on its side chains, with a number-average molecular weight of 2000-5000 g / mol and an acid value of 30-80 mg KOH / g. The metal ion source is selected from one or more of anhydrous zinc acetate, zinc acetylacetonate, or magnesium stearate, and the molar ratio of the metal ion in the metal ion source to the carboxylic acid groups or sulfonic acid groups in the ionization modification precursor is 0.6:1 to 1.2:1. The sacrificial coordination blocking agent is specifically selected from N-methyldiethanolamine, N-ethyldiethanolamine, or benzoylacetone.

[0008] In the microstructure of the aforementioned high-elasticity supercritical foamed nylon elastomer, the nylon elastomer foam contains a physical ionic cross-linking network formed by metal ions and ionized modified precursors. This physical ionic cross-linking network is not formed during the raw material mixing stage, but rather formed in situ during the foaming process by removing the sacrificial coordination blocking agent.

[0009] A second aspect of the present invention provides a method for preparing the aforementioned high-elasticity supercritical foamed nylon elastomer. This method utilizes supercritical fluid extraction to regulate the coordination state of metal ions, thereby achieving a phased change in melt strength. The preparation method includes the following steps:

[0010] Step S1: The matrix resin polyether block polyamide, ionized modified precursor, metal ion source, sacrificial coordination blocker, and heat stabilizer are melt-blended in a twin-screw extruder. The extrusion temperature is set to 160℃-210℃. Under this temperature and shear conditions, the sacrificial coordination blocker preferentially binds to the metal ion source to form a coordination complex, occupying the coordination sites of the metal ions, thereby inhibiting the ionic interaction between the metal ions and the ionized modified precursor. After extrusion pelletizing and hot pressing, a latent preform is obtained. The screw speed of the twin-screw extruder is 200-450 rpm, and the average residence time of the material in the barrel is 1.5-3.0 minutes.

[0011] Step S2: Place the latent preform in an autoclave, heat to a saturation temperature of 130℃-165℃, and introduce carbon dioxide to a saturation pressure of 15.0-28.0 MPa. Maintain constant temperature and pressure treatment under these conditions for 2.0-6.0 hours. The saturation temperature is set within the range of 5℃ to 20℃ below the melting point of the matrix resin polyether block polyamide. During this process, utilizing the solubility difference of the sacrificial coordination blocker between the supercritical carbon dioxide phase and the polymer phase, the supercritical carbon dioxide extracts the sacrificial coordination blocker from the latent preform and migrates it into the fluid phase, thereby re-exposing the coordination sites of metal ions.

[0012] Step S3: Open the pressure relief valve and reduce the pressure to atmospheric pressure at a rate of 10-60 MPa / s. The pressure reduction causes the carbon dioxide dissolved in the polymer matrix to instantly vaporize, nucleate, and grow into cells. Simultaneously, since the sacrificial coordinating blocker has been removed, the exposed metal ions rapidly combine with carboxylic acid or sulfonic acid groups in the ionized modified precursor, forming an ionic crosslinking network in situ. This ionic crosslinking network improves the melt strength of the polymer matrix under tensile conditions, thereby stabilizing the cell structure.

[0013] In addition, the preparation method may also include step S4: foaming the particles obtained after extrusion and pelletizing in step S1 into foamed beads through the process in step S2, and curing the foamed beads in an oven at 40℃-60℃ for 12-24 hours; and using steam molding to prepare the foamed beads into molded parts, wherein the mold filling pressure is 0.2-0.4MPa and the steam pressure is 0.3-0.6MPa.

[0014] This invention provides a high-elasticity supercritical foamed nylon elastomer foam and its preparation method. It has the following beneficial effects:

[0015] 1. This invention introduces a sacrificial coordination blocker during the melt blending stage, utilizing its preferential coordination with metal ions to temporarily shield the electrostatic aggregation between ions under high-temperature shear conditions. This feature allows the high melt strength ionized system to exhibit low-viscosity thermoplastic fluid behavior during extrusion granulation, effectively avoiding the high torque, high heat generation, and melt fracture phenomena commonly found in traditional ionomer processing. This ensures uniform dispersion of the matrix resin and modifier under low-energy conditions, resulting in a uniform latent preform after hot pressing.

[0016] 2. This invention utilizes the extraction mechanism of supercritical carbon dioxide on sacrificial coordination blockers, synchronizing the melt strength development with the bubble growth process. Upon depressurization, as the blocker is removed, metal ion sites are exposed and rapidly form an ionic cross-linking network. This in-situ generated physical network can withstand the bidirectional tensile force generated by the rapid expansion of bubbles, effectively preventing the rupture and merging of the bubble walls. This mechanism ensures the preparation of nylon elastomer foams with high closed-cell ratio and microporous structure without the need for adding a high proportion of inorganic nucleating agents.

[0017] 3. This invention constructs a thermally sensitive ion cluster physical cross-linked network through irreversible covalent bond cross-linking induced by peroxides or radiation. Scrap materials or waste products generated during the production process can dissociate their ion cluster aggregates upon reheating and melting, thereby restoring their thermoplastic flow behavior. This allows the material to be 100% recycled through conventional melt granulation processes, solving the industry problem that traditional cross-linked foam materials become thermosetting wastes and are difficult to degrade and regenerate through physical methods. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation steps of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described 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.

[0020] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0021] This invention provides a high-elasticity supercritical foamed nylon elastomer foam and its preparation method, comprising the following materials:

[0022] Matrix resin: polyether block polyamide resin, hard segment is polyamide 12 (PA12), soft segment is polytetrahydrofuran, Shore hardness 40D, melting point 147℃, CAS number: 77402-38-1.

[0023] Metal ion sources: Anhydrous zinc acetate: purity ≥99.5%, CAS No.: 557-34-6. Zinc acetylacetone: purity ≥99%, CAS No.: 14024-63-6. Magnesium stearate: purity ≥98%, CAS No.: 557-04-0.

[0024] Sacrificial coordination blocking agents: N-methyldiethanolamine: boiling point 247℃, purity ≥99%, CAS No.: 105-59-9. N-ethyldiethanolamine: boiling point 251℃, purity ≥98%, CAS No.: 139-87-7. Benzoylacetone: boiling point 260-262℃, purity ≥99%, CAS No.: 93-91-4.

[0025] Heat stabilizer: Antioxidant 1010: Chemical name is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid], CAS number: 6683-19-8.

[0026] Foaming agent / extractant: Carbon dioxide: purity ≥99.9%, CAS No.: 124-38-9.

[0027] Monomers for synthesis, used to prepare ionization-modified precursors: Dodecyl lactam: purity ≥99%, CAS No.: 947-04-6; Sodium 5-sulfoisophthalate: purity ≥98%, CAS No.: 6362-79-4; Adipic acid: purity ≥99.5%, CAS No.: 124-04-9.

[0028] The ionization-modified precursor described in this invention was prepared by the following synthesis example;

[0029] Synthesis Example 1: Preparation of Ionization-Modified Precursor A (Containing Sulfonic Acid Groups)

[0030] In a 5L stainless steel high-pressure reactor equipped with a mechanical stirrer, nitrogen inlet pipe, thermometer and condenser, add 1500.0g dodecyl lactam, 180.0g 5-sulfoisophthalic acid monosodium salt (5-SSIPA) and 60.0g adipic acid.

[0031] The air inside the reactor was replaced three times with high-purity nitrogen, and then the reactor was sealed.

[0032] Start the stirrer at 50 rpm and heat to 260°C. At this temperature, maintain the pressure inside the reactor between 1.5 MPa and 2.0 MPa and continue the reaction for 3.0 hours to carry out ring-opening polymerization.

[0033] Subsequently, the pressure relief valve was slowly opened over 1.0 hour to reduce the pressure inside the reactor to atmospheric pressure, and the polycondensation reaction was continued for 2.0 hours at 260°C under atmospheric pressure nitrogen gas protection to adjust the molecular weight and remove small molecule byproducts.

[0034] After the reaction was completed, the melt was extruded through the outlet, water-cooled and stretched into strips, granulated, and dried in a vacuum oven at 80°C for 12 hours to obtain a light yellow granular ionized modified precursor A.

[0035] Analysis results: The acid value of the precursor was 52 mg KOH / g by end-group titration; the number-average molecular weight Mn was 3200 g / mol by gel permeation chromatography.

[0036] Synthesis Example 2: Preparation of Ionization-Modified Precursor B (containing a carboxylic acid group)

[0037] In a 5L stainless steel high-pressure reactor equipped with a mechanical stirrer, nitrogen inlet pipe, thermometer and condenser, add 1500.0g dodecyl lactam and 250.0g adipic acid.

[0038] The air inside the reactor was replaced three times with high-purity nitrogen, and then the reactor was sealed.

[0039] Turn on the stirrer, set the speed to 50 rpm, and heat to 250°C. At this temperature, maintain the pressure inside the reactor at 2.0 MPa and continue the reaction for 3.5 hours.

[0040] Subsequently, the pressure was slowly released to atmospheric pressure over 1.0 hour, and the polycondensation reaction continued for 1.5 hours under the protection of nitrogen flow at atmospheric pressure and 250°C.

[0041] After the reaction was completed, the melt was extruded through the outlet, water-cooled into strips, granulated, and dried in a vacuum oven at 80°C for 12 hours to obtain white granular ionized modified precursor B.

[0042] Analysis results: The acid value of the precursor was 75 mg KOH / g, as determined by end-group titration; and its number-average molecular weight (Mn) was 2400 g / mol, as determined by gel permeation chromatography.

[0043] Please see the appendix Figure 1 In Examples 1-5 and Comparative Examples 1-2 below, unless otherwise specified, the following general process flow was used for preparation:

[0044] Melt blending and granulation: The weighed matrix resin, ionized modification precursor, metal ion source, sacrificial coordination blocker, and heat stabilizer are added to a high-speed mixer and mixed for 3 minutes. The mixed material is then fed into the main feed port of a co-rotating twin-screw extruder.

[0045] The extruder has a length-to-diameter ratio (L / D) of 44:1 and the screw speed is set to 300 rpm.

[0046] The barrel temperature zones are set as follows, from the feed port to the die head: Zone 1 160℃, Zone 2 180℃, Zone 3 190℃, Zone 4 200℃, Zone 5 200℃, Zone 6 200℃, Zone 7 195℃, and Die Head 190℃.

[0047] After the material is extruded through the die, it enters a water tank for cooling, is dehydrated by an air knife, and is then pelletized. Finally, it is dried in a vacuum oven at 80°C for 6 hours to obtain latent preformed particles.

[0048] The dried latent pre-formed particles, or the comparative particles, are formed into pre-formed sheets using a hot press, and then placed into a stainless steel autoclave equipped with a heating and pressurizing system. The autoclave is sealed, and low-pressure carbon dioxide gas is introduced to replace the air inside the autoclave three times.

[0049] Turn on the heating system to raise the temperature inside the vessel to the set saturation temperature. Once the temperature is reached, inject carbon dioxide using a high-pressure metering pump until the set saturation pressure is reached.

[0050] Under constant temperature and pressure conditions for a certain period of time, saturated impregnation and extraction are carried out using supercritical carbon dioxide fluid.

[0051] After the processing time is over, the pneumatic pressure relief valve is opened to control the pressure relief rate, so that the pressure inside the reactor drops to atmospheric pressure. The sheet expands and foams instantly during the pressure relief process.

[0052] After foaming, the sheet is removed from the autoclave and placed in a 50°C forced-air oven for 24 hours to eliminate internal stress and stabilize dimensions.

[0053] Example 1

[0054] This embodiment prepares a high-elasticity supercritical foamed nylon elastomer foam as a preferred formulation. The raw material composition includes the following components by weight: 100 parts of matrix resin; 8.0 parts of ionized modified precursor A (prepared from Synthesis Example 1); 1.2 parts of anhydrous zinc acetate; 1.5 parts of N-methyldiethanolamine; and 0.2 parts of antioxidant 1010. Extrusion granulation and hot pressing processes are carried out according to the above-described general process. The foaming process parameters are set as follows: saturation temperature 140℃, saturation pressure 20.0 MPa, and impregnation time 4.0 hours. The average depressurization rate is approximately 25 MPa / s.

[0055] Example 2

[0056] This embodiment prepares a high-elasticity supercritical foamed nylon elastomer foam by changing the type of sacrificial coordination blocker. The raw material composition includes the following components by weight: 100 parts of matrix resin; 8.0 parts of ionized modified precursor A (prepared from Synthesis Example 1); 1.2 parts of anhydrous zinc acetate; 1.8 parts of benzoyl acetone; and 0.2 parts of antioxidant 1010. The extrusion granulation process and hot pressing are carried out according to the above-mentioned general process. The foaming process parameters are set as follows: saturation temperature 140°C, saturation pressure 20.0 MPa, and impregnation time 4.0 hours.

[0057] Example 3

[0058] This embodiment prepares a high-elasticity supercritical foamed nylon elastomer foam by changing the metal ion source to magnesium salt and incorporating a carboxyl-containing ionized modified precursor. The raw material composition includes the following components by weight: 100 parts of matrix resin; 10.0 parts of ionized modified precursor B (prepared from Synthesis Example 2); 1.5 parts of magnesium stearate; 2.0 parts of N-ethyldiethanolamine; and 0.2 parts of antioxidant 1010. The extrusion granulation process and hot pressing are carried out according to the above-mentioned general process. The foaming process parameters are set as follows: saturation temperature 138°C, saturation pressure 22.0 MPa, and impregnation time 4.0 hours.

[0059] Example 4

[0060] This embodiment aims to verify the preparation effect under the lower limit conditions of the component content described in the claims. The raw material composition includes the following components in parts by weight: 100 parts of matrix resin; 5.0 parts of ionized modified precursor A (prepared from Synthesis Example 1); 0.5 parts of anhydrous zinc acetate; 0.5 parts of N-methyldiethanolamine; and 0.1 parts of antioxidant 1010. The extrusion granulation process and hot pressing molding were carried out according to the above general process. The foaming process parameters were set as follows: saturation temperature 142°C, saturation pressure 18.0 MPa, and impregnation time 3.0 hours. Due to the low content of the ion-crosslinked component, the foaming temperature was appropriately increased and the saturation pressure was reduced to adapt to the change in melt strength.

[0061] Example 5

[0062] This embodiment aims to verify the preparation effect under the maximum content conditions of the components described in the claims. The raw material composition includes the following components in parts by weight: 100 parts of matrix resin; 12.0 parts of ionized modified precursor A (prepared from Synthesis Example 1); 2.0 parts of anhydrous zinc acetate; 3.0 parts of N-methyldiethanolamine; and 0.3 parts of antioxidant 1010. In the extrusion granulation process, to ensure that the high content of ionized modified precursor and metal ion source are uniformly dispersed and do not undergo premature crosslinking, the temperature of each zone of the extruder is increased by 5°C based on the general process. The foaming process parameters are set as follows: saturation temperature 135°C, saturation pressure 26.0 MPa, and impregnation time 5.0 hours. A lower foaming temperature and higher pressure, and an extended impregnation time are used to ensure that the high content of sacrificial coordination blocking agent is fully extracted and to take advantage of the high melt strength of the high-density ion crosslinking network.

[0063] Comparative Example 1

[0064] This comparative example was used to verify the effect of the sacrificial coordination blocker. The raw material composition included the following components by weight: 100 parts of matrix resin; 8.0 parts of ionized modified precursor A; 1.2 parts of anhydrous zinc acetate; and 0.2 parts of antioxidant 1010. No sacrificial coordination blocker was added in this comparative example. During extrusion granulation according to the general preparation process, due to the lack of shielding effect from the coordination blocker, the material exhibited significant thickening within the barrel, resulting in large fluctuations in the main machine current load, with an average value exceeding 85% of the rated current. Melt fracture also occurred at the die, and the collected particles had a rough surface and irregular shape. Subsequently, the collected particles were formed in a hot press and treated in an autoclave according to the same foaming process parameters as in Example 1.

[0065] Comparative Example 2

[0066] This comparative example was used to verify the effect of physical foaming with pure resin. The raw material composition included the following components by weight: 100 parts of matrix resin; 0.2 parts of antioxidant 1010. No ionization modification precursor or metal ion source was added to this comparative example. The extrusion granulation and hot pressing processes were successful. The foaming process parameters were the same as in Example 1, set at a saturation temperature of 140°C and a saturation pressure of 20.0 MPa.

[0067] Comparative Example 3

[0068] This comparative example was prepared using a peroxide chemical crosslinking system to compare recyclability. The raw material composition included the following components by weight: 100 parts matrix resin; 0.8 parts dicumyl peroxide; 0.5 parts triallyl isocyanurate; and 0.2 parts antioxidant 1010. Its preparation process differed from the examples, consisting of three stages: reactive extrusion, curing crosslinking, and foaming. First, reactive extrusion was performed. To prevent premature decomposition of the peroxide during extrusion, which could lead to crosslinking, the barrel temperature of the twin-screw extruder was set relatively low, with a maximum temperature controlled at 125°C, resulting in a masterbatch containing the crosslinking agent. Subsequently, curing crosslinking was performed. The masterbatch was placed in an autoclave, heated to 165°C, and maintained at atmospheric pressure for 2.0 hours to decompose the peroxide and initiate chemical crosslinking. Finally, foaming was performed. After crosslinking was completed, the temperature inside the autoclave was lowered to 140°C, carbon dioxide was introduced to 20.0 MPa, and maintained for 3.0 hours before depressurization and foaming.

[0069] Performance testing methods: The following methods were used to test the performance of the samples prepared in the above embodiments and comparative examples:

[0070] (1) Processing rheology assessment: Record the percentage of torque during stable operation of the twin-screw extruder to characterize the melt viscosity and processing ease of the material. The lower the value, the better the processing fluidity.

[0071] (2) Foaming density: The apparent density of foamed nylon elastomer was measured by the water displacement method according to ASTM D792 standard.

[0072] (3) Falling ball rebound rate: According to ASTM D2632 standard, foamed nylon elastomer was prepared into standard test blocks and its vertical rebound rate was tested using a falling ball rebound tester.

[0073] (4) Compression set: The compression set of the specimen was tested according to ASTM D395 Method B at 50°C for 22 hours under 25% compression. This indicator reflects the stability of the cell structure and the fatigue resistance of the material. The lower the value, the better the performance.

[0074] (5) Recyclability Melt Flow Rate Retention Rate: Tested according to ASTM D1238 standard (230℃, 2.16kg). First, the MFR value of the masterbatch before foaming was tested and recorded as the initial MFR. The foamed material was crushed, and 0.5wt% of the original sacrificial coordination blocker was added to the extruder for the example or directly remelted for the comparative example. After extrusion and granulation, the MFR value was tested and recorded as the recycled MFR. The calculation formula is: Retention Rate = Recycled MFR / Initial MFR × 100%.

[0075] The performance test results of the embodiments and comparative examples are summarized in the following table: Table 1 Performance test results of the embodiments and comparative examples.

[0076] Table 1

[0077] project Extrusion torque (%) Foaming density (g / cm³) Ball bounce rate (%) Compression set (%) MFR retention rate of recycled materials (%) Example 1 32 0.16 68 12 95 Example 2 30 0.17 66 13 92 Example 3 35 0.18 65 14 94 Example 4 27 0.20 60 18 97 Example 5 38 0.13 72 10 90 Comparative Example 1 88 0.28 52 35 30 Comparative Example 2 26 0.35 48 42 98 Comparative Example 3 45 0.18 64 15 <2

[0078] In terms of processing performance, the extrusion torque of Examples 1-5 remained within a controllable range of 27%-38%. Among them, Example 4 had the lowest viscosity due to its low addition amount; Example 5 had a slightly higher viscosity due to its high addition amount, but it was still much lower than that of Comparative Example 1 without the addition of sacrificial coordination blocker, demonstrating the key role of the blocker in improving processing flowability.

[0079] Regarding foaming performance, Example 5 achieved the lowest density, highest resilience, and lowest compression set due to the highest content of ionic crosslinking components and the strongest physical network formed. Although Example 4 had a lower crosslinking density, resulting in a slightly higher density, it was still superior to the purely physical foaming of Comparative Example 2, demonstrating that the technical solution remains effective even at low addition levels.

[0080] Regarding recyclability, the MFR retention rate of all embodiments was above 90%, confirming the thermal reversibility of the physically ionicly crosslinked network. In contrast, Comparative Example 3, which used chemical crosslinking, completely lost its thermoplastic processing capability.

[0081] Experimental Example 2: Microstructure and tensile mechanical properties test.

[0082] For the foamed materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3, the microstructure morphology and tensile mechanical properties were further statistically analyzed. The specific operation steps are as follows:

[0083] Samples of foamed nylon elastomer from each group were immersed in liquid nitrogen for 30 minutes for freezing. After complete freezing, the samples were rapidly fractured in liquid nitrogen to expose fresh cross-sections. The fractured samples were fixed onto conductive tape and subjected to surface gold sputtering in a vacuum sputtering instrument for 60 seconds. Subsequently, the samples were placed on a scanning electron microscope stage, and the morphology of the cell cross-sections was observed under an accelerating voltage of 5.0 kV. Electron micrographs were taken from three different regions. The cells in the images were statistically analyzed using image analysis software. At least 100 cells were selected from each sample, and their diameters were measured and the arithmetic mean was calculated as the average cell diameter. Based on the number of cells and the actual area of ​​the images, the cell density was calculated using the volume conversion formula.

[0084] Foamed nylon elastomer was prepared into standard sheets. Following ISO 37 standards, the sheets were punched into dumbbell-shaped specimens using a cutter. The specimens were placed in the fixture of a universal testing machine with a gauge length set to 25 mm. Uniaxial tensile testing was conducted at room temperature (23±2℃) and a tensile rate of 500 mm / min until the specimen fractured. The instrument automatically recorded the stress-strain curve and output the tensile strength, breaking strength, and elongation at break values. Five parallel samples were tested for each group of samples, and the average value was recorded.

[0085] The microstructure parameters and mechanical properties of each group of samples are recorded in Table 2.

[0086] Table 2 Summary of Microcellular Structure and Tensile Property Test Data

[0087] Group Average cell diameter (μm) <![CDATA[Cell density (10 6 cells / cm³)]]> Tensile strength (MPa) Elongation at break (%) Example 1 42.3 8.52 5.84 412.5 Example 2 45.7 7.93 5.62 405.3 Example 3 38.4 9.15 6.13 396.8 Example 4 68.9 3.24 4.35 445.2 Example 5 24.1 18.67 7.42 328.6 Comparative Example 1 182.5 0.46 1.83 125.4 Comparative Example 2 156.8 0.68 2.15 288.7 Comparative Example 3 48.2 7.45 5.91 185.3

[0088] Experimental data show that the content of metal ion source and ionized modified precursor in the system directly determines the density of the physical cross-linking network, thus affecting the final cell morphology. In Example 5, the high concentration of ionic components formed a high-density ion cluster aggregate the instant the sacrificial coordination blocker was removed by supercritical carbon dioxide extraction. This high-strength physical network limited the excessive growth and merging of bubbles during expansion, thus achieving the smallest average cell diameter and the highest cell density. In contrast, in Example 4, the ionic component content was at the critical lower limit, resulting in a larger spacing between cross-linking points and a weakened constraint on polymer chain slippage. This led to significant bubble growth after nucleation, with the average cell diameter increasing to 68.9 μm. However, under the control of the sacrificial coordination blocker, the integrity of the cell structure was maintained, and the severe cell breakage and collapse phenomena observed in Comparative Examples 1 and 2 did not occur.

[0089] The differences in tensile mechanical properties stem from the binding effect of the ionic crosslinking network in the matrix resin on the movement of molecular chains. Under tensile load, the in-situ formed ionic cluster microregions act as physical crosslinking points and nano-reinforcing phases, hindering the deentanglement and slippage of molecular chains, thereby significantly improving the tensile strength of the material. With the increase of metal ion and modified precursor content in the system, the tensile strength exhibits a non-linear growth trend. At the same time, due to the high-density network limiting the extension ability of chain segments, the elongation at break decreases accordingly. Comparative Example 1, due to the lack of a sacrificial coordinating blocker, causes premature aggregation of metal ions during processing, resulting in phase separation. It is unable to form a uniform stress-bearing network during foaming, therefore its tensile strength and elongation are the lowest.

[0090] This technical solution utilizes the extraction and depressurization process of supercritical fluids to achieve simultaneous removal of sacrificial coordinating blockers and construction of ionic crosslinking networks over time. Data comparison shows that pure resin physical foaming, due to insufficient melt strength, is prone to cell wall rupture under biaxial stretching, resulting in large cells and poor mechanical properties. While chemical crosslinking systems can achieve smaller cell sizes and higher strength, their covalent bond network restricts molecular chain orientation under high-ratio stretching, leading to a significantly lower elongation at break compared to the physical ionic crosslinking system of this invention. This confirms that the reversible ionic crosslinking network triggered by supercritical extraction can impart excellent large deformation resilience to the material while ensuring high melt strength to stabilize the microporous structure.

[0091] Experimental Example 3: Characterization of Thermally Reversible Rheological Behavior and Solubility Properties

[0092] This experiment tested the thermally reversible processing performance and solvent solubility of the foamed materials prepared in each embodiment and comparative example to verify the thermosensitive properties and physicochemical nature of the internal cross-linked network of the material.

[0093] The foamed nylon elastomers prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were placed in a liquid nitrogen cryogenic pulverizer and pulverized into powders with an average particle size of 2 mm to 3 mm. For the powder samples of Examples 1 to 5, 0.5 wt% of the corresponding type of sacrificial coordination blocker relative to the powder weight was added to a high-speed mixer, i.e., N-methyldiethanolamine was added in Example 1, benzoylacetone was added in Example 2, and so on, and the mixture was stirred at a low speed until homogeneous; no blocker was added to the comparative sample. The mixed powder was fed into a single-screw extruder for remelting and granulation, and the extrusion temperature was set to 230°C.

[0094] After secondary granulation, the particles were tested for melt mass flow rate (MFR) at 230℃ and 2.16kg load according to ASTM D1238 standard, and denoted as MFR_recycle. The MFR retention rate was calculated by combining the initial melt flow rate of the masterbatch before foaming.

[0095] Take approximately 0.5 g of each group of foamed nylon elastomer and place it in an Erlenmeyer flask containing 50 mL of m-cresol. Heat the flask in an oil bath at 100°C and stir magnetically for 4.0 hours. Observe the dissolution state of the sample in the solvent. If the sample completely disappears to form a transparent or translucent solution, record it as "completely dissolved"; if the sample swells but maintains its blocky or granular integrity under stirring, record it as "insoluble / swelling". This test is used to distinguish between physical ionic crosslinking and chemical covalent crosslinking.

[0096] The rheological data retention rate and solubility test results of each group of samples are summarized in Table 3.

[0097] Table 3 Test data on thermal reversible recovery performance and dissolution characteristics

[0098] Group Initial MFR (g / 10min) MFR recovery (g / 10min) MFR retention rate (%) Soluble state in m-cresol Example 1 18.4 17.3 94.0 Completely dissolved Example 2 19.2 17.5 91.1 Completely dissolved Example 3 17.8 16.6 93.3 Completely dissolved Example 4 22.5 21.7 96.4 Completely dissolved Example 5 14.1 12.6 89.4 Completely dissolved Comparative Example 1 3.2 1.1 34.4 Slow dissolve Comparative Example 2 24.6 23.9 97.2 Completely dissolved Comparative Example 3 16.5 0.0 0.0 Insoluble / swelling

[0099] Rheological property test data revealed the thermosensitive mechanism of the ion cluster crosslinked network in this technical solution. After undergoing a supercritical foaming process and forming a high-strength ion crosslinked network, the samples from Examples 1 to 5, upon supplementation with a trace amount of sacrificial coordination blocker and reheating to the melting temperature, all maintained a MFR retention rate above 89%. This indicates that under high temperature and in the presence of the blocker, the electrostatic interaction between metal ions and ionic groups on the polymer chain segments is effectively weakened or shielded, causing the ion cluster aggregates to dissociate, releasing the bound molecular chains, and restoring the material to thermoplastic-like flow behavior. Example 5, due to its higher metal ion content and higher initial network density, required higher energy for dissociation or higher blocker concentration, resulting in a slightly higher viscosity and relatively lower retention rate under the same test conditions, but still possessing complete reprocessability.

[0100] Solubility experiments further confirmed the physical nature of the cross-linked network. All samples from the examples were completely soluble in the polar solvent m-cresol, indicating the absence of permanent covalent bonds between the molecular chains. The physical cross-linking points formed by metal ions disintegrated under the solvation effect of a good solvent, allowing polymer segments to disperse into the solvent phase. In contrast, the sample of Comparative Example 3, which used peroxide-induced cross-linking, only swelled in hot solvent and failed to dissolve, and no melt flowed out during the MFR test, confirming the formation of an irreversible three-dimensional network covalent bond structure. This structure makes the material unrecyclable by physical methods.

[0101] Although Comparative Example 1 also contained metal ions and did not undergo chemical cross-linking, the lack of a sacrificial coordination blocker during preparation led to uneven dispersion of metal ions in the matrix and uncontrollable early agglomeration. This non-uniform phase structure exhibited extremely high shear viscosity and poor flow stability during secondary processing, making effective melt plasticization difficult to achieve. This underscores the necessity of sacrificial coordination blockers in regulating the metal ion coordination environment to achieve a reversible cycle of plasticization during processing, strengthening during foaming, and reduction during recycling.

[0102] Although embodiments of the 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 invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-elasticity supercritical foamed nylon elastomer foam, characterized in that, It comprises the following components by weight: 100 parts of matrix resin polyether block polyamide; 5.0-12.0 parts of ionization modified precursor; 0.5-2.0 parts of metal ion source; 0.5-3.0 parts of sacrificial coordination blocker; and 0.1-0.3 parts of heat stabilizer. The sacrificial coordination blocking agent is selected from alcohol amine compounds or β-diketone derivatives with a boiling point higher than 210°C and a solubility in supercritical carbon dioxide greater than 1.5 wt%.

2. The high-elasticity supercritical foamed nylon elastomer foam according to claim 1, characterized in that: The hard segment of the matrix resin polyether block polyamide is polyamide 12, the soft segment is polytetrahydrofuran, and the Shore hardness is 25D to 55D; the ionization modification precursor is a polyamide oligomer with carboxylic acid groups or sulfonic acid groups at the end or on the side chain, with a number average molecular weight of 2000-5000 g / mol and an acid value of 30-80 mg KOH / g.

3. The high-elasticity supercritical foamed nylon elastomer foam according to claim 2, characterized in that: The metal ion source is selected from one or more of anhydrous zinc acetate, zinc acetylacetonate, or magnesium stearate. Furthermore, the molar ratio of the metal ion molar amount in the metal ion source to the acid radical group in the ionization modification precursor is 0.6:1 to 1.2:

1.

4. The high-elasticity supercritical foamed nylon elastomer foam according to claim 1, characterized in that: The sacrificial coordination blocker is selected from N-methyldiethanolamine, N-ethyldiethanolamine, or benzoylacetone.

5. The high-elasticity supercritical foamed nylon elastomer foam according to claim 1, characterized in that: The nylon elastomer foam has a physical ionic cross-linked network formed by metal ions and ionized modified precursors, and the network is formed in situ by removing the sacrificial coordination blocker during the foaming process.

6. A method for preparing a high-elasticity supercritical foamed nylon elastomer foam as described in any one of claims 1-5, characterized in that, Includes the following steps: Step S1: The matrix resin polyether block polyamide, ionized modified precursor, metal ion source, sacrificial coordination blocker and heat stabilizer are melt-blended in a twin-screw extruder at an extrusion temperature of 160℃-210℃, so that the sacrificial coordination blocker and the metal ion source form a coordination complex. The mixture is then extruded and pelletized, and hot-pressed in a hot press to obtain a latent preformed sheet. Step S2: Place the latent preform in an autoclave, heat it to a saturation temperature of 130℃-165℃, and introduce carbon dioxide to a saturation pressure of 15.0-28.0MPa. Maintain constant temperature and pressure for 2.0-6.0 hours, and use supercritical carbon dioxide to extract and remove the sacrificial coordination blocking agent from the latent preform. Step S3: Open the pressure relief valve and reduce the pressure to normal pressure at a pressure relief rate of 10-60 MPa / s, so that carbon dioxide is vaporized and nucleated. At the same time, the exposed metal ions form an ion crosslinking network with the ionized modified precursor in situ, and the foamed sheet is obtained.

7. The method for preparing a high-elasticity supercritical foamed nylon elastomer foam according to claim 6, characterized in that: In step S1, the screw speed of the twin-screw extruder is 200-450 rpm, and the average residence time of the material in the barrel is 1.5-3.0 minutes.

8. The method for preparing a high-elasticity supercritical foamed nylon elastomer foam according to claim 6, characterized in that: In step S2, the saturation temperature is set in the range of 5°C to 20°C below the melting point of the matrix resin polyether block polyamide.

9. The method for preparing a high-elasticity supercritical foamed nylon elastomer foam according to claim 6, characterized in that: The particles extruded and granulated in step S1 can also be processed using the same foaming process to obtain foamed beads.

10. The method for preparing a high-elasticity supercritical foamed nylon elastomer according to claim 9, characterized in that: It also includes the step of preparing the foamed beads into molded parts by steam molding, wherein the foamed beads are placed in an oven at 40℃-60℃ for 12-24 hours, the mold filling pressure is 0.2-0.4MPa, and the steam pressure is 0.3-0.6MPa.

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