3D printing supercritical foaming high-supporting-performance foam sole material and preparation process thereof

Abstract

The invention discloses a 3D printing supercritical foaming high-supporting-performance foam sole material and a preparation process thereof, and belongs to the technical field of high polymer materials. The composite wire suitable for fused deposition modeling is prepared by introducing two functional modifiers, namely a mesoporous silica coated carbon nanotube hybrid and a phosphorus-nitrogen synergistic flame-retardant enhanced titanium dioxide nanorod, and carrying out melt blending. A fused deposition 3D printing technology is utilized to precisely print a small-size green body, and then supercritical nitrogen or carbon dioxide fluid is utilized to carry out saturated permeation and controlled foaming, so that the green body is uniformly expanded and shaped, and the foam shoe sole with a fine and dense foam hole structure is obtained. According to the invention, the defect that a personalized complex structure is difficult to realize by traditional mould pressing foaming is overcome, the obtained product has high supporting property, high rebound resilience and excellent flame retardant property and ultraviolet light stability while realizing remarkable light weight, and a brand new solution is provided for manufacturing high-performance personalized sports shoe soles.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a 3D-printed supercritical foam high-support foam shoe sole material and its preparation process. Background Technology

[0002] Ethylene-vinyl acetate copolymer (EVA) has long been widely used in the manufacture of athletic shoe midsoles and insoles due to its lightweight, softness, excellent cushioning properties, and relatively low cost. Currently, the mainstream processing method in the industry is compression molding with chemical foaming. This involves mixing EVA substrate with chemical foaming agents, crosslinking agents, and other additives, then placing the mixture in a mold for high-temperature, high-pressure vulcanization. This causes the foaming agent to decompose and generate gas, forming a cell structure inside the sole. However, this traditional process has several inherent drawbacks. First, compression molding is highly dependent on molds, resulting in long development cycles, high costs, and difficulty in manufacturing personalized soles with complex curved surfaces, hollow structures, or dot matrix structures, failing to meet the demands of modern consumers for personalized customization and functional structural optimization in sports equipment. Second, the decomposition of chemical foaming agents often leaves small-molecule byproducts, which may not only burden the environment but also make precise control of their uniform distribution in the finished product difficult, easily leading to uneven cell size and affecting the mechanical properties and durability of the sole. In addition, pure EVA foam material itself has relatively limited support, resistance to compression deformation and tear strength, making it difficult to provide sufficient anti-rollover support and long-term stability in high-intensity sports such as basketball, which restricts its further application in the field of high-performance sports shoes.

[0003] In recent years, the rapid development of fused deposition modeling (FDM) 3D printing technology has brought new possibilities to footwear manufacturing. This technology, which uses hot-melt filaments to form layers, offers significant advantages such as no need for molds, extremely high design freedom, and rapid transformation from design to physical product. In the footwear field, FDM technology has been explored for printing customized soles, insoles, and other components, enabling precise adaptation to individual foot shapes and movement habits. Meanwhile, supercritical fluid foaming technology, as a green physical foaming method, utilizes the high solubility of the polymer matrix in a supercritical state and the thermodynamic instability caused by rapid decompression of nitrogen or carbon dioxide. This allows for the preparation of foam materials with fine and uniform pores and excellent mechanical properties, offering advantages over traditional chemical foaming such as environmental friendliness, high efficiency, and adjustable pore structure. Currently, research has applied supercritical foaming technology to elastomers such as thermoplastic polyurethane (TPU) to prepare high-performance foam materials, providing a new technological path for upgrading the performance of athletic shoe soles.

[0004] While both FDM printing and supercritical foaming technologies exhibit significant advantages, effectively combining them to fabricate high-performance EVA foam soles still faces key technological challenges. First, FDM printing filaments are mostly pure polymers or simply modified fillers, lacking specialized composite materials designed for subsequent foaming processes. Directly printed preforms subjected to supercritical foaming often suffer from insufficient cell nucleation points, difficulty in controlling the foaming ratio, and large or uneven cell size. Second, soles printed using FDM alone are typically solid structures. While capable of achieving complex shapes, these products are heavy and lack the lightweight cushioning properties unique to foamed materials. Furthermore, how to introduce functional nano-reinforcing phases into the EVA matrix, while ensuring their good dispersion in the printing filaments and their role as heterogeneous nucleation points in the subsequent foaming process, to simultaneously achieve lightweight, high-support, and additional functions such as flame retardancy and UV resistance, remains a pressing problem for the industry. Therefore, developing a comprehensive technical solution that combines the personalized molding capabilities of FDM3D printing with the high-performance advantages of supercritical fluid foaming, while overcoming the inherent limitations of EVA materials, is of great significance for promoting technological advancements in the manufacturing of high-performance, personalized sports shoe soles. Summary of the Invention

[0005] The purpose of this invention is to provide a 3D printed supercritical foam high-support foam shoe sole material and its preparation process, which solves the technical problems of existing traditional EVA molding foam being unable to prepare complex and personalized structures, and FDM printed parts being solid and heavy with insufficient support from EVA foam material.

[0006] The present invention achieves the above objectives through the following technical solutions: A process for preparing a 3D-printed supercritical foam high-support foam shoe sole material includes the following steps: S1. By weight, 80-90 parts of ethylene-vinyl acetate copolymer, 5-8 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 1-2 parts of ethylene-bis-stearamide, 0.3-0.8 parts of antioxidant, 2-4 parts of mesoporous silica-coated carbon nanotube hybrid, and 3-5 parts of phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods are premixed to obtain a premix; the premix is ​​fed into a twin-screw extruder for melt blending, extrusion, water cooling, and pelletizing to obtain a composite masterbatch; the composite masterbatch is fed into a single-screw extruder for plasticizing and stretching through a sizing die to obtain a composite wire; the composite wire is printed on an FDM 3D printer to obtain a preform; S2. Place the preform into the high-pressure vessel of the supercritical fluid foaming device, seal it, inject nitrogen or carbon dioxide into the high-pressure vessel, heat it, pressurize it, depressurize it, and cool it to room temperature.

[0007] In this invention, the preparation of the 3D-printed supercritical foamed high-support foam sole material utilizes physical foaming as its core mechanism. The composite material filament is premixed and melt-extruded from an ethylene-vinyl acetate copolymer matrix and various functional fillers, and then FDM-printed to form a dense preform. A supercritical fluid is injected into the preform in an autoclave, and precise temperature and pressure control ensures the fluid saturates and permeates the matrix. Rapid depressurization triggers thermodynamic instability, causing gas to instantly precipitate and form bubble nuclei. Phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods not only serve as efficient heterogeneous nucleation sites to optimize pore distribution but also impart synergistic flame-retardant properties through phytic acid grafted onto their surface. During combustion, a dense char layer is formed and inert gas is released, effectively suppressing flame propagation and significantly improving the fire safety of the sole material. After slow cooling and shaping, the material density is precisely controlled within a lightweight and high-strength range. The entire process is a physical phase transition without any chemical reaction. However, the synergistic effect of the fillers (including the nucleation guidance of mesoporous silica-coated carbon nanotube hybrids and the flame retardant enhancement of phosphorus and nitrogen synergistic flame retardant enhanced titanium dioxide nanorods) significantly optimizes the uniformity of the foam structure and mechanical properties, meeting the requirements for the preparation of high-performance shoe sole materials, while ensuring that the product has excellent flame retardant safety and structural support during use.

[0008] According to a preferred embodiment of the present invention, in step S1, the temperature of melt blending is 130-160°C; and the temperature of plasticizing is 140-155°C.

[0009] According to a preferred embodiment of the present invention, in step S2, the pressure is increased to 15-25 MPa.

[0010] According to a preferred embodiment of the present invention, the method for preparing the mesoporous silica-coated carbon nanotube hybrid includes: A1. By weight, 0.8-1.2 parts of multi-walled carbon nanotubes were added to a mixture of concentrated sulfuric acid and concentrated nitric acid, and sonicated at 58-62℃ to obtain the product. The product was diluted with deionized water, washed until neutral, and then vacuum dried to obtain acidified carbon nanotubes. 1.5-2.5 parts of hexadecyltrimethylammonium bromide were dissolved in a mixed solution of 300-500 parts of anhydrous ethanol and 300-500 parts of deionized water. The acidified carbon nanotubes were added and sonicated to disperse the mixture to obtain a suspension. Under stirring, 8-12 parts of tetraethyl orthosilicate were slowly added dropwise to the suspension to adjust the pH to 8.9-9.1. The mixture was stirred at 38-42℃ to obtain the reaction product. A2. Transfer the reaction product to a hydrothermal reactor and carry out a hydrothermal reaction at 98-102℃ to obtain a reaction mixture; separate the reaction mixture by centrifugation, wash with ethanol, and vacuum dry at 58-62℃ to obtain a dried solid; place the dried solid in a tube furnace and calcine at 545-555℃ under a nitrogen atmosphere.

[0011] In this invention, the preparation of the mesoporous silica-coated carbon nanotube hybrid is based on the synergistic effect of carbon nanotube surface functionalization and silicon source coating. Multi-walled carbon nanotubes undergo surface oxidation and acidification after treatment with a mixed acid of concentrated sulfuric acid and concentrated nitric acid, introducing hydrophilic functional groups such as carboxyl groups to enhance the adhesion of subsequent coatings. Subsequently, hexadecyltrimethylammonium bromide, as a template agent, is dissolved in a mixed solution of ethanol and water, and ultrasonically dispersed with the acidified carbon nanotubes to form a uniform suspension. Under alkaline conditions, tetraethyl orthosilicate hydrolyzes and condenses to form a silica precursor, which coats the carbon nanotube surface, constructing the coating layer through a sol-gel reaction. A hydrothermal reaction further promotes the crystallization of silica and the formation of mesoporous structures, increasing the specific surface area and porosity of the material. Finally, calcination removes the template agent, yielding a mesoporous silica-coated carbon nanotube hybrid with stable structure and excellent interfacial compatibility, providing efficient heterogeneous nucleation sites for subsequent composite materials.

[0012] According to a preferred embodiment of the present invention, in step A1, the ultrasonic treatment time at 58-62°C is 4-6 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the calcination time at 545-555°C is 5-10 hours.

[0014] According to a preferred embodiment of the present invention, the preparation method of the phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods includes: B1. By weight, 8-12 parts of tetrabutyl titanate are added dropwise to anhydrous ethanol and stirred to obtain solution A; 1.8-2.2 parts of glacial acetic acid, 4.5-5.5 parts of deionized water and 25-35 parts of anhydrous ethanol are mixed to obtain solution B; under stirring, solution B is added dropwise to solution A and stirring is continued to obtain a mixed solution; the mixed solution is transferred to a high-pressure reactor and hydrothermally reacted at 175-185℃ to obtain a reaction mixture; the reaction mixture is centrifuged, washed successively with anhydrous ethanol and deionized water, and vacuum dried at 78-82℃ to obtain titanium dioxide nanorods; the titanium dioxide nanorods are dispersed in a mixed solvent of 40-50 parts of ethanol and 2-5 parts of deionized water, 0.4-0.6 parts of γ-aminopropyltriethoxysilane are added, and the mixture is refluxed at 68-72℃. After the reaction is completed, the mixture is centrifuged to obtain a solid, which is washed with anhydrous ethanol and vacuum dried to obtain aminated titanium dioxide nanorods; B2. Aminated titanium dioxide nanorods were dispersed in 40-60 parts of 2-(N-morpholino)ethanesulfonic acid buffer at pH 5.4-5.6, and 0.15-0.25 parts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.08-0.12 parts of N-hydroxysuccinimide were added and activated at room temperature. 0.8-1.2 parts of phytic acid were added and reacted at room temperature to obtain the product. The product was separated by centrifugation, washed with deionized water, and dried under vacuum.

[0015] In this invention, the preparation of the phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods involves a chemical reaction of titanium dioxide surface functionalization and flame-retardant group grafting. The titanium dioxide nanorods are obtained through hydrothermal synthesis of tetrabutyl titanate in ethanol to achieve a rod-like structure. The nanorods are dispersed in a mixed solvent of ethanol and water, and an aminosilane coupling agent is added. After hydrolysis, the active groups condense with the hydroxyl groups on the titanium dioxide surface, forming an amino-functionalized surface. Subsequently, the amino-functionalized titanium dioxide reacts with phytic acid containing multiple phosphate groups in a weakly acidic buffer solution. The phosphate groups form phosphoramide bonds with the amino groups through nucleophilic substitution, or directly condense with the titanium dioxide surface to form titanium dioxide-phosphorus-oxygen bonds, achieving covalent grafting. This process does not rely on amidation reactions, but is based on the specific condensation of phosphate groups with amino groups or titanium dioxide hydroxyl groups, endowing the material with excellent flame retardancy and structural reinforcement properties.

[0016] According to a preferred embodiment of the present invention, in step B1, the reflux reaction time at 68-72°C is 6-8 hours.

[0017] According to a preferred embodiment of the present invention, in step B2, the reaction time at room temperature is 24-30 hours.

[0018] The present invention also provides a 3D printed supercritical foam high-support foam sole material prepared according to the preparation process of the 3D printed supercritical foam high-support foam sole material.

[0019] The beneficial effects of this invention are as follows: This invention innovatively combines fused deposition modeling (FDM) 3D printing technology with supercritical fluid foaming processes and introduces two self-designed functional nanomodifiers to construct a complete EVA-based composite material shoe sole manufacturing scheme. Compared with existing technologies, this scheme achieves significant technical advantages in manufacturing flexibility, material properties, and product functionality.

[0020] First, this process successfully unifies complex, personalized structures with lightweight foam materials. Traditional molding foaming processes are limited by molds, making it difficult to manufacture soles with complex curved surfaces, hollow structures, or lattice structures. This solution utilizes FDM 3D printing technology, allowing for flexible design and precise printing of small-sized blanks with arbitrarily complex geometries based on individual foot shape, movement habits, and functional needs. Subsequently, controlled foaming is achieved using supercritical nitrogen or carbon dioxide, causing the blank to expand uniformly to a preset ratio, ultimately resulting in a finished sole that combines a complex, personalized shape with a lightweight foam core. This process seamlessly integrates additive manufacturing, which offers extremely high design freedom, with green and efficient physical foaming technology, overcoming the dual limitations of traditional methods in terms of customization and lightweighting. It opens a new path for the personalized and rapid manufacturing of high-performance athletic shoes. The printed blanks are dimensionally precise and structurally dense, laying a solid foundation for subsequent uniform foaming. The final product density can be controlled within an extremely low range, achieving significant lightweighting while maintaining excellent dimensional stability.

[0021] Secondly, this invention fundamentally improves the microstructure and macroscopic mechanical properties of foam materials by introducing a mesoporous silica-coated carbon nanotube hybrid. This hybrid acts as a highly efficient heterogeneous nucleating agent during supercritical foaming. Its abundant mesoporous structure and nanoscale surface characteristics provide numerous uniform and stable nucleation sites for bubble formation, effectively avoiding problems such as coarse pores, merging, or collapse caused by insufficient or unevenly distributed nucleation sites in traditional foaming processes. The resulting pore structure is fine, uniformly distributed, and has a high closed-cell rate, significantly improving the compressive strength, resilience, and tear resistance of the foam material. This allows the sole to maintain its lightweight properties while possessing superior support and durability compared to traditional EVA foam materials, meeting the stringent requirements for support and cushioning in basketball due to frequent jumps, sudden stops, and changes of direction. Simultaneously, the coated mesoporous silica layer not only protects the carbon nanotubes but also enhances their interfacial bonding with the EVA matrix, forming an effective reinforcing network within the pore walls, further improving the overall stiffness and deformation resistance of the material.

[0022] Finally, the introduction of phosphorus and nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods endows the sole material with multiple additional functions, significantly expanding its application scenarios. These nanorods, with their rigid structure, synergistically reinforce the matrix, further enhancing the material's support. More importantly, the phosphorus and nitrogen elements introduced through phytic acid grafting give the composite material durable flame-retardant properties, effectively reducing the risk of combustion of the sole under accidental fire sources and improving product safety. Furthermore, the titanium dioxide nanorods themselves have excellent ultraviolet light absorption capabilities, which can significantly delay the aging, yellowing, and performance degradation of EVA materials caused by ultraviolet radiation during long-term outdoor use, extending the lifespan of the sole. The synergistic effect of the two functional modifiers not only does not sacrifice the original flexibility and processability of the EVA matrix, but also achieves good interfacial compatibility through the bridging effect of the compatibilizer, ensuring the stability and uniformity of the material system. In summary, this invention provides a comprehensive technical solution integrating personalized molding, lightweight and high strength, high support, flame retardancy, and weather resistance, offering a new design concept and reliable technical support for the manufacturing of high-performance sports equipment. Detailed Implementation

[0023] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0024] Example 1 This embodiment provides a process for preparing a 3D-printed supercritical foam high-support foam shoe sole material, the steps of which include: The preparation method of mesoporous silica-coated carbon nanotube hybrids includes the following steps: A1. 1.0 g of multi-walled carbon nanotubes (outer diameter 10-20 nm, length 10-30 μm, purity greater than 95%) were added to a mixture of concentrated sulfuric acid (98% by mass) and concentrated nitric acid (68% by mass) in a volume ratio of 3:1. The mixture was ultrasonically treated for 5 hours in a 60℃ water bath (ultrasonic power 200 W, frequency 40 kHz) to obtain a reaction mixture. The reaction mixture was diluted 10 times with deionized water and then vacuum filtered using a 0.22 μm polytetrafluoroethylene microporous membrane. The filter cake was repeatedly washed with deionized water until the pH of the filtrate reached 7.0. The filter cake was collected and dried in a 60℃ vacuum drying oven for 24 hours to obtain the desired product. Acidified carbon nanotubes: 2.0 g of hexadecyltrimethylammonium bromide (CTAB) was dissolved in a mixed solution of 400 g anhydrous ethanol and 400 g deionized water. All the acidified carbon nanotubes were added, and the mixture was ultrasonically dispersed at room temperature for 30 minutes (ultrasonic power 200 W, frequency 40 kHz) to obtain a uniform suspension. 10 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise to the suspension under magnetic stirring (500 rpm) at a rate of 1 mL / min. Then, ammonia water (25% by mass) was added to adjust the pH to 9.0. The reaction was continued to be stirred in a 40°C water bath for 24 hours to obtain the reaction product. A2. Transfer the above reaction product to a 1000 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene, seal it, and place it in an oven. React it hydrothermally at 100°C for 48 hours. After naturally cooling to room temperature, remove it to obtain the reaction mixture. Centrifuge the reaction mixture at 8000 rpm for 10 minutes, discard the supernatant, and wash the precipitate three times with anhydrous ethanol (200 mL of anhydrous ethanol each time, ultrasonically disperse for 5 minutes, and then centrifuge). Collect the precipitate and dry it in a vacuum drying oven at 60°C for 12 hours to obtain the dried solid. Place the dried solid in a tube furnace, first introduce nitrogen gas (flow rate 200 mL / min) for 30 minutes to remove air, and then heat it to 550°C at a heating rate of 2°C / min under nitrogen atmosphere protection. Calcinate it at 550°C for 6 hours, and after naturally cooling to room temperature, remove it and grind it evenly to obtain the mesoporous silica-coated carbon nanotube hybrid.

[0025] The preparation method of phosphorus and nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods includes the following steps: B1. Slowly add 10g of tetrabutyl titanate to 40g of anhydrous ethanol and stir magnetically (300rpm) for 30 minutes at room temperature to obtain solution A. Mix 2.0g of glacial acetic acid, 5.0g of deionized water, and 30g of anhydrous ethanol evenly and stir magnetically (300rpm) for 10 minutes to obtain solution B. Under vigorous stirring (600rpm), slowly add solution B to solution A through a constant pressure dropping funnel at a dropping rate of 2mL / min. After the addition is complete, continue stirring for 30 minutes to obtain a clear and transparent mixed solution. Transfer the mixed solution to a 100mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven for hydrothermal reaction at 180℃ for 24 hours. After naturally cooling to room temperature, remove it to obtain the reaction mixture. Centrifuge the reaction mixture at 8000rpm for 10 minutes, discard the supernatant, and precipitate successively with anhydrous ethanol and deionized water. Wash the nanorods three times with water (50 mL solvent each time, ultrasonically dispersed for 5 minutes and then centrifuged), collect the precipitate and dry it in a vacuum drying oven at 80℃ for 12 hours to obtain white titanium dioxide nanorod powder; take 1.0 g of the above titanium dioxide nanorod powder, disperse it in a mixed solvent of 45 g ethanol and 3 g deionized water, ultrasonically disperse it for 15 minutes (ultrasonic power 200 W, frequency 40 kHz), transfer it to a 250 mL round bottom flask, add 0.5 g γ-aminopropyltriethoxysilane (KH550), reflux it in an oil bath at 70℃ for 7 hours (magnetic stirring speed 300 rpm), after the reaction is completed, cool it naturally to room temperature, centrifuge the reaction solution at 8000 rpm for 10 minutes, collect the precipitate, wash it three times with anhydrous ethanol (50 mL anhydrous ethanol each time, ultrasonically dispersed for 5 minutes and then centrifuged), and dry it in a vacuum drying oven at 60℃ for 12 hours to obtain aminated titanium dioxide nanorods; B2. Take 0.5 g of the above-mentioned aminated titanium dioxide nanorods and disperse them in 50 g of 0.1 M 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution at pH 5.5. Sonicate for 15 minutes (200 W, 40 kHz). Transfer to a 250 mL Erlenmeyer flask, add 0.2 g of 1-ethyl-3-3-dimethylaminopropylcarbodiimide hydrochloride (EDC·HCl) and 0.1 g of N-hydroxysuccinimide (NHS), and magnetically stir at room temperature (200 rpm). Activate for 30 minutes at 100 rpm; then add 1.0 g of 50% phytic acid aqueous solution and continue to react at room temperature with magnetic stirring (200 rpm) for 27 hours to obtain the reaction product; centrifuge the reaction product at 8000 rpm for 10 minutes, discard the supernatant, wash the precipitate three times with deionized water (50 mL of deionized water each time, ultrasonically disperse for 5 minutes and then centrifuge), collect the precipitate and dry it in a vacuum drying oven at 50℃ for 24 hours to obtain phosphorus and nitrogen synergistic flame retardant enhanced titanium dioxide nanorods.

[0026] The preparation steps for 3D printing supercritical foam high-support foam shoe sole materials include: S1. Weigh out 85g of ethylene-vinyl acetate copolymer (EVA), 6.5g of maleic anhydride-grafted ethylene-vinyl acetate copolymer (EVA-g-MAH), 1.5g of ethylene-bis-stearamide (EBS), 0.5g of antioxidant (primary antioxidant 1010 and secondary antioxidant 168 in a 1:1 mass ratio), 3.0g of the mesoporous silica-coated carbon nanotube hybrid prepared above, and 4.0g of the phosphorus-nitrogen synergistic flame-retardant reinforced silica prepared above. Titanium nanorods were prepared by adding the above materials to a high-speed mixer and premixing at 1500 rpm for 12 minutes at room temperature to obtain a homogeneous premix. The premix was then fed into a twin-screw extruder (L / D ratio 40:1, screw diameter 35 mm). The extruder temperatures were set at 130°C, 140°C, 145°C, 145°C, and 140°C respectively from the feed port to the die head, with the main extruder speed at 150 rpm. Melt-blending extrusion was performed, and the extruded strip was cooled by a cold water bath. The material is then pelletized in a pelletizer to obtain composite masterbatch with a diameter of approximately 3 mm. The composite masterbatch is dried in a vacuum drying oven at 60°C for 4 hours, and then fed into a single-screw wire extruder (screw diameter 30 mm, length-to-diameter ratio 25:1). The temperatures of each section of the extruder are set to 140°C, 145°C, 150°C, and 148°C from the feed port to the die head, with the main motor speed at 30 rpm. The material is stretched through a 1.75 mm diameter sizing die and monitored online by air cooling and a laser diameter gauge. The material is then wound to obtain composite wire with a diameter of 1.75 ± 0.05 mm. The composite wire is then printed on an FDM 3D printer. A 3D model is designed proportionally based on a preset foaming ratio of 5 times. The print file is imported, and the nozzle temperature is set to 160°C, the heated bed temperature to 50°C, the printing speed to 40 mm / s, the layer height to 0.15 mm, the extrusion ratio to 1.05, and a 100% solid fill mode is used to print a small-sized blank with precise dimensions. S2. Place the printed blank into the autoclave (500mL volume) of the supercritical fluid foaming device, seal it, inject carbon dioxide gas into the autoclave, start the heating and pressurization program, heat to 100℃, pressurize to 20MPa, maintain this temperature and pressure for 120 minutes to allow the supercritical carbon dioxide to fully penetrate and dissolve in the EVA composite matrix to reach saturation; then quickly open the pressure relief valve to rapidly depressurize to atmospheric pressure at a rate of 15MPa / s, and naturally cool to room temperature in room temperature air at a cooling rate of 8℃ / min to complete the final shaping of the foam structure and obtain the 3D printed supercritical foamed high-support foam shoe sole material.

[0027] Example 2 The specific implementation method is the same as in Example 1, except that the preparation method of the mesoporous silica-coated carbon nanotube hybrid includes: A1. 1.2 g of multi-walled carbon nanotubes were added to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. The mixture was sonicated at 62 °C for 4 hours to obtain the product. The product was diluted with deionized water, washed until neutral, and then vacuum dried to obtain acidified carbon nanotubes. 2.5 g of hexadecyltrimethylammonium bromide was dissolved in a mixed solution of 500 g of anhydrous ethanol and 300 g of deionized water. The acidified carbon nanotubes were added and sonicated at room temperature for 30 minutes to obtain a uniform suspension. 12 g of tetraethyl orthosilicate was slowly added dropwise to the suspension under magnetic stirring. Then, ammonia was added dropwise to adjust the pH to 9.1. The mixture was stirred at 38 °C for 24 hours to obtain the reaction product. A2. The reaction product was transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 102°C for 48 hours to obtain a reaction mixture. The reaction mixture was centrifuged, washed three times with ethanol, and vacuum dried at 58°C for 12 hours to obtain a dried solid. The dried solid was placed in a tube furnace and heated to 545°C at a heating rate of 2°C / min under a nitrogen atmosphere. It was then calcined at 545°C for 10 hours to obtain a mesoporous silica-coated carbon nanotube hybrid.

[0028] The preparation methods of phosphorus and nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods include: B1. 8g of tetrabutyl titanate was slowly added dropwise to 35g of anhydrous ethanol and stirred for 30 minutes to obtain solution A. 1.8g of glacial acetic acid, 4.5g of deionized water, and 25g of anhydrous ethanol were mixed evenly to obtain solution B. Solution B was slowly added dropwise to solution A under vigorous stirring and stirred for another 30 minutes to obtain a mixed solution. The mixed solution was transferred to a 100mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and hydrothermally reacted at 175℃ for 24 hours to obtain a reaction mixture. The reaction mixture was centrifuged, washed three times each with anhydrous ethanol and deionized water, and vacuum dried at 78℃ for 12 hours to obtain titanium dioxide nanorods. 1.0g of titanium dioxide nanorods were dispersed in a mixed solvent of 40g of ethanol and 2g of deionized water, and 0.4g of γ-aminopropyltriethoxysilane was added. The mixture was refluxed at 68℃ for 8 hours. After the reaction was completed, the solid was centrifuged and washed three times with anhydrous ethanol and vacuum dried to obtain aminated titanium dioxide nanorods. B2. 0.5 g of aminated titanium dioxide nanorods were dispersed in 40 g of 2-(N-morpholino)ethanesulfonic acid buffer solution at pH 5.4. 0.15 g of 1-ethyl-3-3-dimethylaminopropylcarbodiimide hydrochloride and 0.08 g of N-hydroxysuccinimide were added, and the mixture was activated at room temperature for 30 minutes. Then, 0.8 g of 50% phytic acid aqueous solution was added, and the mixture was reacted at room temperature for 30 hours to obtain the product. The product was separated by centrifugation, washed three times with deionized water, and vacuum dried at 50 °C for 24 hours to obtain phosphorus and nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods.

[0029] The preparation steps for 3D printing supercritical foam high-support foam shoe sole materials include: S1. Weigh 80g of ethylene-vinyl acetate copolymer, 5g of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 1g of ethylene-bis-stearamide, 0.3g of antioxidant (main antioxidant 1010 and auxiliary antioxidant 168 in a 1:1 mass ratio), 2g of mesoporous silica-coated carbon nanotube hybrid, and 3g of phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods. Premix them in a high-speed mixer for 10 minutes to obtain a premix. Feed the premix into a twin-screw extruder. The composite masterbatch is obtained by melt blending, extrusion, water cooling, and pelletizing at 130℃. The composite masterbatch is fed into a single-screw wire extruder and plasticized at 140℃. The composite wire with a diameter of 1.75mm is stretched through a sizing die. The composite wire is then printed on an FDM 3D printer with the nozzle temperature set to 150℃, the heated bed temperature to 40℃, the printing speed to 30mm / s, the layer height to 0.1mm, and a 100% solid fill mode to produce a small-sized preform. S2. Place the printed blank into the autoclave of the supercritical fluid foaming device, seal it, inject nitrogen into the autoclave, heat it to 115°C, pressurize it to 15MPa, and maintain it for 150 minutes to allow the supercritical nitrogen to fully penetrate; then depressurize it to atmospheric pressure at a rate of 12MPa / s; finally cool it to room temperature at a cooling rate of 5°C / min to obtain the 3D printed supercritical foamed high-support foam shoe sole material.

[0030] Example 3 The specific implementation method is the same as in Example 1, except that the preparation method of the mesoporous silica-coated carbon nanotube hybrid includes: A1. 0.8 g of multi-walled carbon nanotubes were added to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. The mixture was sonicated at 58 °C for 6 hours to obtain the product. The product was diluted with deionized water, washed until neutral, and then vacuum dried to obtain acidified carbon nanotubes. 1.5 g of hexadecyltrimethylammonium bromide was dissolved in a mixed solution of 300 g of anhydrous ethanol and 500 g of deionized water. The acidified carbon nanotubes were added and sonicated at room temperature for 30 minutes to obtain a uniform suspension. 8 g of tetraethyl orthosilicate was slowly added dropwise to the suspension under magnetic stirring. Then, ammonia was added dropwise to adjust the pH to 8.9. The mixture was stirred at 42 °C for 24 hours to obtain the reaction product. A2. The reaction product was transferred to a hydrothermal reactor and subjected to hydrothermal reaction at 98°C for 48 hours to obtain a reaction mixture. The reaction mixture was centrifuged, washed three times with ethanol, and vacuum dried at 62°C for 12 hours to obtain a dried solid. The dried solid was placed in a tube furnace and heated to 555°C at a heating rate of 2°C / min under nitrogen atmosphere protection. It was then calcined at 555°C for 5 hours to obtain a mesoporous silica-coated carbon nanotube hybrid.

[0031] The preparation methods of phosphorus and nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods include: B1. 12g of tetrabutyl titanate was slowly added dropwise to 45g of anhydrous ethanol and stirred for 30 minutes to obtain solution A; 2.2g of glacial acetic acid, 5.5g of deionized water and 35g of anhydrous ethanol were mixed evenly to obtain solution B; solution B was slowly added dropwise to solution A under vigorous stirring and stirred for another 30 minutes to obtain a mixed solution; the mixed solution was transferred to a 100mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and hydrothermally reacted at 185℃ for 24 hours to obtain a reaction mixture; the reaction mixture was centrifuged, washed three times each with anhydrous ethanol and deionized water, and vacuum dried at 82℃ for 12 hours to obtain titanium dioxide nanorods; 1.0g of titanium dioxide nanorods were dispersed in a mixed solvent of 50g of ethanol and 5g of deionized water, and 0.6g of γ-aminopropyltriethoxysilane was added, and the mixture was refluxed at 72℃ for 6 hours. After the reaction was completed, the solid was centrifuged and washed three times with anhydrous ethanol and vacuum dried to obtain aminated titanium dioxide nanorods; B2. 0.5 g of aminated titanium dioxide nanorods were dispersed in 60 g of 2-(N-morpholino)ethanesulfonic acid buffer solution at pH 5.6. 0.25 g of 1-ethyl-3-3-dimethylaminopropylcarbodiimide hydrochloride and 0.12 g of N-hydroxysuccinimide were added, and the mixture was activated at room temperature for 30 minutes. Then, 1.2 g of 50% phytic acid aqueous solution was added, and the mixture was reacted at room temperature for 24 hours to obtain the product. The product was separated by centrifugation, washed three times with deionized water, and vacuum dried at 50 °C for 24 hours to obtain phosphorus and nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods.

[0032] The preparation steps for 3D printing supercritical foam high-support foam shoe sole materials include: S1. Weigh 90g of ethylene-vinyl acetate copolymer, 8g of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 2g of ethylene-bis-stearamide, 0.8g of antioxidant (primary antioxidant 1010 and secondary antioxidant 168 in a 1:1 mass ratio), 4g of mesoporous silica-coated carbon nanotube hybrid, and 5g of phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods. Premix them in a high-speed mixer for 15 minutes to obtain a premix. Feed the premix into a twin-screw extruder. The composite masterbatch is obtained by melt blending, extrusion, water cooling, and pelletizing at 160℃. The composite masterbatch is fed into a single-screw wire extruder and plasticized at 155℃. The composite wire with a diameter of 1.75mm is stretched through a sizing die. The composite wire is then printed on an FDM 3D printer with the nozzle temperature set to 170℃, the heated bed temperature to 60℃, the printing speed to 50mm / s, the layer height to 0.2mm, and the 100% solid fill mode to produce a small-sized preform. S2. Place the printed blank into the autoclave of the supercritical fluid foaming device, seal it, inject carbon dioxide into the autoclave, heat it to 110°C, pressurize it to 25MPa, and maintain it for 60 minutes to allow the supercritical carbon dioxide to fully penetrate; then depressurize it to atmospheric pressure at a rate of 18MPa / s; finally cool it to room temperature at a cooling rate of 10°C / min to obtain the 3D printed supercritical foamed high-support foam shoe sole material.

[0033] Comparative Example 1 The specific implementation method is the same as in Example 1, except that mesoporous silica-coated carbon nanotube hybrids are not added. The remaining steps are the same as in Example 1.

[0034] Comparative Example 2 The specific implementation method is the same as in Example 1, except that phosphorus and nitrogen synergistic flame-retardant enhanced titanium dioxide nanorods are not added, and the remaining steps are the same as in Example 1.

[0035] Comparative Example 3 The specific implementation method is the same as in Example 1, except that neither mesoporous silica-coated carbon nanotube hybrid nor phosphorus-nitrogen synergistic flame-retardant enhanced titanium dioxide nanorods are added. The remaining steps are the same as in Example 1.

[0036] Performance testing The 3D-printed supercritical foamed high-support foam shoe sole materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following method, which includes the following steps: Density testing method: Five 50mm × 50mm × 25mm square specimens were cut from the center of the foam shoe sole material prepared in each embodiment and comparative example, ensuring that the specimen surface was flat and free of defects. The specimens were placed in a constant temperature and humidity environment of 23℃ ± 2℃ and 50% ± 5% for 24 hours. The mass of each specimen was weighed using an electronic analytical balance with an accuracy of 0.1mg and recorded as m (g). The length, width, and height of the specimen were measured using a vernier caliper with an accuracy of 0.02mm. Each dimension was measured three times at different locations on the specimen, and the arithmetic mean was recorded as L, W, and H (cm). The apparent density of each specimen was calculated using the formula ρ = m / (L × W × H) and the unit was g / cm³. 3 The arithmetic mean of the five samples is taken as the final test result, and two decimal places are retained.

[0037] Compressive strength test method: Five 50mm×50mm×25mm square specimens were cut from the center of the foam shoe sole material prepared in each embodiment and comparative example, ensuring that the upper and lower surfaces of the specimens were parallel and free of defects. The specimens were placed in a constant temperature and humidity environment of 23℃±2℃ and 50%±5% relative humidity for 24 hours. A universal testing machine was used for compression testing, equipped with a circular compression plate with a diameter of not less than 100mm. The load sensor of the testing machine had a range of 5kN and an accuracy of 0.5%. The specimen was placed in the center of the compression plate, and a compressive load was applied to the specimen at a constant speed of 2.5mm / min. The load-displacement curve was continuously recorded until the strain reached more than 30%. The strain was calculated based on the original thickness of the specimen (25mm). The compressive load at 25% strain was read from the load-displacement curve and recorded as F, in N. The compressive strength was calculated according to the formula σ=F / (L×W), where L and W are the original length and width of the specimen in mm, and the compressive strength σ is in MPa. Each sample was tested once, and the arithmetic mean of the five samples was taken as the final test result, which was retained to two decimal places.

[0038] Rebound Test Method: Five cylindrical specimens, each 30 mm in diameter and 25 mm thick, were cut from the center of the foam shoe sole material prepared in each embodiment and comparative example, ensuring that the upper and lower surfaces of the specimens were parallel and free of defects. The specimens were placed in a constant temperature and humidity environment of 23℃±2℃ and 50%±5% relative humidity for 24 hours. A falling ball rebound tester was used. The instrument was equipped with a 16 mm diameter, 16.8 g steel ball, with a release height of 500 mm. The release device ensured that the steel ball fell freely without rotation. The specimen was placed in the center of the rebound tester base, and the release device was adjusted so that the bottom of the steel ball was 500 mm from the specimen surface. The steel ball was released to fall freely and impact the specimen surface. The maximum height of the first rebound was recorded as h, in mm. The rebound rate was calculated using the formula R=(h / 500)×100%, in %. Each sample was tested 5 times, with an interval of no less than 30 seconds between each test. The arithmetic mean of the 5 tests was taken as the result of the sample. The arithmetic mean of the 5 samples was then taken as the final test result, and one decimal place was retained.

[0039] Limiting Oxygen Index (LOI) Test Method: Twenty 100mm × 10mm × 10mm strip samples were cut from the center of the foam shoe sole materials prepared in each embodiment and comparative example, ensuring the sample surface was smooth and crack-free. The samples were placed in a constant temperature and humidity environment of 23℃ ± 2℃ and 50% ± 5% relative humidity for 24 hours. An oxygen index meter was used for testing. The instrument was equipped with a transparent combustion cylinder with an inner diameter of 75mm and a height of 450mm, and the oxygen and nitrogen flow control accuracy was ±0.5%. The sample was vertically clamped in the center of the combustion cylinder, and the total flow rate of the oxygen-nitrogen mixture was adjusted to 10L / min. The top-ignition method was used, with an ignition flame length of 15mm. The flame was in contact with the top of the sample for 30 seconds, then removed every 5 seconds, and the combustion behavior of the sample was observed. The lowest oxygen concentration required for the sample to extinguish after 180 seconds of combustion or when the combustion length reached 50mm was taken as the limiting oxygen index. A series of tests were conducted by adjusting the oxygen concentration, and the arithmetic mean of the valid tests was taken as the final test result, rounded to one decimal place.

[0040] Test results: Table 1: Test results of each embodiment and comparative example ; As can be seen from Table 1, the compressive strength of Examples 1-3 reached 0.28-0.42 MPa, which is significantly higher than that of Comparative Example 3 without any modifier (0.16 MPa). This demonstrates that the synergistic effect of the mesoporous silica-coated carbon nanotube hybrid and the phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods greatly improves the support of EVA foam materials and solves the defect of insufficient support in traditional EVA foam materials. The rebound rates of Examples 1-3 reached 58-65%, significantly higher than the 48% of Comparative Example 3, indicating that the material has better cushioning performance; the densities of Examples 1-3 were controlled between 0.18-0.24 g / cm³. 3 It is comparable to or even lighter than traditional EVA foam materials, but it achieves the free molding of complex and personalized structures through FDM 3D printing technology. Then, it obtains lightweight foam through supercritical foaming, which solves the defects of solid and heavy FDM printed parts. Comparative Examples 1 and 2, lacking one modifier respectively, exhibited lower compressive strength and resilience than the Example but higher than Comparative Example 3, confirming the synergistic reinforcing effect of the two modifiers. Comparative Example 3 showed the lowest performance across all aspects, further highlighting how the present invention, through the combination of FDM printing and supercritical foaming processes and the introduction of a dual-functional modifier, simultaneously solves the three major technical challenges of complex structure molding, lightweighting, and high support.

[0041] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A preparation process for a 3D-printed supercritical foam high-support foam shoe sole material, characterized by the following steps: include: S1. By weight, 80-90 parts of ethylene-vinyl acetate copolymer, 5-8 parts of maleic anhydride-grafted ethylene-vinyl acetate copolymer, 1-2 parts of ethylene-bis-stearamide, 0.3-0.8 parts of antioxidant, 2-4 parts of mesoporous silica-coated carbon nanotube hybrid, and 3-5 parts of phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods are premixed to obtain a premix; the premix is ​​fed into a twin-screw extruder for melt blending, extrusion, water cooling, and pelletizing to obtain a composite masterbatch; the composite masterbatch is fed into a single-screw extruder for plasticizing and stretching through a sizing die to obtain a composite wire; the composite wire is printed on an FDM 3D printer to obtain a preform; S2. Place the preform into the high-pressure vessel of the supercritical fluid foaming device, seal it, inject nitrogen or carbon dioxide into the high-pressure vessel, heat it, pressurize it, depressurize it, and cool it to room temperature.

2. The preparation process of the 3D printed supercritical foam high-support foam shoe sole material according to claim 1, characterized in that, In step S1, the melt blending temperature is 130-160℃; the plasticizing temperature is 140-155℃.

3. The preparation process of the 3D printed supercritical foam high-support foam shoe sole material according to claim 1, characterized in that, In step S2, the pressure is increased to 15-25 MPa.

4. The preparation process of the 3D printed supercritical foam high-support foam shoe sole material according to claim 1, characterized in that, The method for preparing the mesoporous silica-coated carbon nanotube hybrid includes: A1. By weight, 0.8-1.2 parts of multi-walled carbon nanotubes were added to a mixture of concentrated sulfuric acid and concentrated nitric acid, and sonicated at 58-62℃ to obtain the product. The product was diluted with deionized water, washed until neutral, and then vacuum dried to obtain acidified carbon nanotubes. 1.5-2.5 parts of hexadecyltrimethylammonium bromide were dissolved in a mixed solution of 300-500 parts of anhydrous ethanol and 300-500 parts of deionized water. The acidified carbon nanotubes were added and sonicated to disperse the mixture to obtain a suspension. Under stirring, 8-12 parts of tetraethyl orthosilicate were slowly added dropwise to the suspension to adjust the pH to 8.9-9.

1. The mixture was stirred at 38-42℃ to obtain the reaction product. A2. Transfer the reaction product to a hydrothermal reactor and carry out a hydrothermal reaction at 98-102℃ to obtain a reaction mixture; separate the reaction mixture by centrifugation, wash with ethanol, and vacuum dry at 58-62℃ to obtain a dried solid; place the dried solid in a tube furnace and calcine at 545-555℃ under a nitrogen atmosphere.

5. The preparation process of the 3D printed supercritical foam high-support foam shoe sole material according to claim 4, characterized in that, In step A1, the ultrasonic treatment at 58-62℃ takes 4-6 hours.

6. The preparation process of the 3D printed supercritical foam high-support foam shoe sole material according to claim 4, characterized in that, In step A2, the calcination time at 545-555℃ is 5-10 hours.

7. The preparation process of the 3D printed supercritical foam high-support foam shoe sole material according to claim 1, characterized in that, The preparation method of the phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods includes: B1. By weight, 8-12 parts of tetrabutyl titanate are added dropwise to anhydrous ethanol and stirred to obtain solution A; 1.8-2.2 parts of glacial acetic acid, 4.5-5.5 parts of deionized water and 25-35 parts of anhydrous ethanol are mixed to obtain solution B; under stirring, solution B is added dropwise to solution A and stirring is continued to obtain a mixed solution; the mixed solution is transferred to a high-pressure reactor and hydrothermally reacted at 175-185℃ to obtain a reaction mixture; the reaction mixture is centrifuged, washed successively with anhydrous ethanol and deionized water, and vacuum dried at 78-82℃ to obtain titanium dioxide nanorods; the titanium dioxide nanorods are dispersed in a mixed solvent of 40-50 parts of ethanol and 2-5 parts of deionized water, 0.4-0.6 parts of γ-aminopropyltriethoxysilane are added, and the mixture is refluxed at 68-72℃. After the reaction is completed, the mixture is centrifuged to obtain a solid, which is washed with anhydrous ethanol and vacuum dried to obtain aminated titanium dioxide nanorods; B2. Aminated titanium dioxide nanorods were dispersed in 40-60 parts of 2-(N-morpholino)ethanesulfonic acid buffer at pH 5.4-5.6, and 0.15-0.25 parts of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.08-0.12 parts of N-hydroxysuccinimide were added and activated at room temperature. 0.8-1.2 parts of phytic acid were added and reacted at room temperature to obtain the product. The product was separated by centrifugation, washed with deionized water, and dried under vacuum.

8. The preparation process of the 3D printed supercritical foamed high-support foam shoe sole material according to claim 7, characterized in that, In step B1, the reflux reaction is carried out at 68-72℃ for 6-8 hours.

9. The preparation process of the 3D printed supercritical foam high-support foam shoe sole material according to claim 7, characterized in that, In step B2, the reaction time at room temperature is 24-30 hours.

10. A 3D-printed supercritical foam high-support foam sole material, characterized in that, The 3D-printed supercritical foam high-support foam sole material is prepared according to the preparation process of the 3D-printed supercritical foam high-support foam sole material according to any one of claims 1-9.