High-performance recycled EVA composite material and preparation method thereof

Abstract

The application discloses a kind of high-performance recycling EVA composite material and preparation method thereof, belong to polymer material recycling technical field.The composite material uses ethylene-vinyl acetate copolymer and EVA foaming recycled material as matrix, adds zinc oxide / procyanidin composite antioxidant and foaming, crosslinking and processing aid, is prepared by closed mixing, open mill and mould pressing.Compound antioxidant is prepared under argon protection by coprecipitation method, procyanidin phenolic hydroxyl group and zinc oxide surface hydroxyl group form hydrogen bond and coordination bond, construct inorganic-organic bridging structure, with excellent dispersibility and compatibility in EVA matrix.Procyanidin radical scavenging capacity and zinc oxide ultraviolet shielding effect synergistic inhibition thermal oxygen aging, zinc oxide nanoparticles as heterogeneous nucleating agent refine cell, enhance mechanical properties and wear resistance.The high-performance recycling EVA composite material made of recycled EVA foaming material has good mechanical properties by adding only a small amount of compound antioxidant in the present application.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite foam materials, specifically relating to a high-performance recyclable EVA composite material and its preparation method. Background Technology

[0002] EVA (ethylene-vinyl acetate copolymer) foam composites possess advantages such as low density, strong cushioning and shock absorption, and low-temperature resistance, making them widely used in footwear, construction, and packaging. However, like most polymer plastics, EVA foam composites undergo chemical cross-linking after foaming, resulting in poor abrasion resistance. Extremely high abrasion levels severely limit their application in footwear materials requiring high abrasion resistance, and may even lead to product failure. Therefore, developing EVA foam composites that combine high mechanical properties and abrasion resistance is of significant value for their application in the footwear industry. However, due to the irreversible chemical cross-linking of post-consumer EVA foam composites, performance degradation becomes a bottleneck during recycling, leading to the disposal of large quantities of post-consumer foamed products and causing environmental pollution.

[0003] Proanthocyanidins are a class of polyphenolic compounds widely found in plants, possessing strong antioxidant activity and free radical scavenging capabilities. Their unique molecular structure gives them excellent application potential in the field of materials modification. Zinc oxide, as an important inorganic functional material, has good thermal stability and mechanical properties, and its nanoscale particle structure can effectively improve the overall performance of composite materials. Proanthocyanidins and zinc oxide form a stable composite system through hydrogen bonds and coordination bonds. This not only retains the antioxidant properties of proanthocyanidins but also leverages the physicochemical properties of zinc oxide to synergistically enhance the weather resistance, mechanical strength, and dispersion stability of materials, demonstrating significant research value and application prospects in the field of polymer composites.

[0004] Chinese patent CN122103737A discloses a recycled EVA shoe material and a foamed shoe material. The formula, by weight, includes the following components: 60 parts pure EVA, 30-60 parts recycled EVA, 1-2 parts crosslinking agent, 0.6-5 parts oxidized multi-walled carbon nanotubes (MWNTs), 10-30 parts SEBS, 3-5 parts polyolefin elastomer (POE), and 5-12 parts maleic anhydride-grafted EVA. This invention recycles waste EVA through a pyrolysis polymerization method and uses oxidized multi-walled carbon nanotubes as a reinforcing filler to construct a ternary synergistic improvement system of oxidized MWNTs, SEBS, and maleic anhydride-grafted EVA, thus optimizing the performance of the recycled EVA shoe material.

[0005] Existing EVA recycling processes often face problems such as severe material performance degradation and limited recycling cycles. This invention, through a zinc oxide / proanthocyanidin composite system, successfully achieves efficient recycling of waste EVA foam materials, preparing recycled EVA foam materials with high mechanical properties, good recyclability, and wear resistance. This provides a new technical path for the green circular economy of polymer materials, with significant environmental benefits and economic value. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance recyclable EVA composite material. This invention combines proanthocyanidins with zinc oxide, utilizing the polyhydroxy structure on the surface of proanthocyanidins. Through a co-precipitation composite method, proanthocyanidins are loaded onto the surface of zinc oxide via hydrogen bonds and coordination bonds, resulting in a zinc oxide / proanthocyanidin composite antioxidant. Zinc oxide serves as the carrier for loading proanthocyanidins. The presence of hydroxyl groups on the proanthocyanidin surface significantly improves the dispersibility of zinc oxide, ensuring uniform dispersion within the EVA matrix. This effectively enhances the mechanical and wear-resistant properties of the EVA composite material. Simultaneously, the uniform dispersion of zinc oxide / proanthocyanidins effectively expands the range of proanthocyanidins' resistance to thermal aging, significantly reducing the performance degradation of the EVA composite material during recycling. This invention solves the problems of EVA's inability to de-crosslink and degrade after chemical crosslinking, preventing material recycling, and poor dispersibility during physical recycling, which leads to poor mechanical and wear-resistant properties in recyclable composite materials. The invention successfully produces an EVA composite foam material with excellent mechanical properties and good wear resistance, possessing great application prospects and generating significant social and economic benefits.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: A high-performance recyclable EVA composite material, by weight, comprises 46 parts ethylene-vinyl acetate copolymer, 3 parts azodicarbonamide, 1 part dicumyl peroxide, 0.5 parts stearic acid, 0.5 parts zinc stearate, 1 part zinc oxide, 45-49 parts recycled EVA foam material, and 1-5 parts composite antioxidant. The vinyl acetate content in the ethylene-vinyl acetate copolymer is 18wt%-26wt%. The EVA foam recycled material is waste generated during the shoe material foaming process, with a hardness of 30-40HC and a density of 0.1-0.15 g / cm³. 3 The tensile strength is 0.6-0.8 MPa, the elongation at break is 340-360%, and the resilience is 30-35%. The composite antioxidant is obtained by linking proanthocyanidins and zinc oxide through hydrogen bonds and coordination bonds. The zinc oxide / proanthocyanidin composite antioxidant, with zinc oxide as the carrier and proanthocyanidins as the loading material, is prepared using the following steps: T1. Add proanthocyanidins and deionized water to a flask at a ratio of 0.6-1.0 g / 100 ml, and sonicate to dissolve completely. Then, add zinc salt to the flask at a ratio of 2.0-2.4 g / 100 ml while stirring at 6-8℃ and 800-1000 rpm, and stir until completely dissolved. Then, stir and react for 20-40 min under argon protection. Then, while stirring at 800-1000 rpm, add alkaline solution dropwise to the flask until the pH reaches 7.5-8.5 and no new precipitate forms. After the addition is complete, continue stirring at 6-8℃ for 1-3 hours to allow the reaction to proceed fully. After the reaction is complete, centrifuge to collect the precipitate and obtain the composite precipitate. T2. Filter and wash the composite precipitate obtained in T1 until neutral to fully remove acetate ions, free zinc ions, and other impurities. Dry the washed and filtered composite precipitate at 80°C for 8 hours to fully remove free water and adsorbed water. After drying, remove the sample to obtain the zinc oxide / proanthocyanidin composite antioxidant. The zinc salt in step T1 is at least one of zinc acetate, zinc nitrate, zinc chloride, or zinc sulfate. In step T1, the alkaline solution is at least one of ammonia, sodium hydroxide solution, or potassium hydroxide solution.

[0008] A method for preparing the above-mentioned high-performance recyclable EVA composite material specifically includes the following steps: S1. Mix ethylene-vinyl acetate copolymer, treated EVA foam recycled material, stearic acid, crosslinking agent dicumyl peroxide, foaming agent azodicarbonamide, zinc stearate and zinc oxide evenly according to the proportion, and then use a preheated two-roll mill to mix evenly for 5 minutes at a heating temperature of 80°C. After the rubber compound is completely mixed evenly, pass it through a thin mill 4-6 times to obtain a 2-4 mm rubber compound sheet. Among them, the treated EVA foam recycled material is obtained by mixing 45-49 parts of EVA foam recycled material with 1-5 parts of zinc oxide / proanthocyanidin composite antioxidant, and then mixing it evenly for 10-20 minutes using a two-roll open mill. After the rubber compound is completely mixed evenly, it is passed through a thin sheet 4-6 times to obtain a rubber compound sheet with a thickness of 2-4 mm. S2. Place the mixture obtained in step S1 into the preheated mold cavity of the flat vulcanizing machine for molding and foaming. After molding and foaming for 300s at 165℃ and 12MPa, a high-performance recyclable EVA composite material is obtained.

[0009] The beneficial effects of this invention are as follows: (1) The proanthocyanidin molecule is rich in ortho-phenolic hydroxyl groups. In this invention, through a co-precipitation composite process, the phenolic hydroxyl groups of proanthocyanidins form a high-density hydrogen bond network and stable coordination bonds with the active hydroxyl groups on the surface of zinc oxide. This is equivalent to coating the surface of zinc oxide with an organic shell, which significantly reduces the surface energy of zinc oxide. The zinc oxide / proanthocyanidin composite antioxidant prepared by this method has excellent compatibility and can be uniformly dispersed in the EVA matrix, which greatly eliminates the stress concentration and performance shortcomings caused by the aggregation of inorganic particles. In addition, the proanthocyanidin coating layer not only improves the dispersion, but its molecular chains can also entangle and physically crosslink with the EVA molecular chains during processing to form a strong interfacial transition layer, which greatly improves the tensile strength and wear resistance of the composite material. At the same time, the highly dispersed zinc oxide nanonuclei act as efficient heterogeneous nucleating agents, inducing a large number of uniform cell nuclei during the foaming process, significantly refining the cell diameter, improving the cell density and uniformity, and further improving the comprehensive mechanical properties.

[0010] (2) As a highly efficient free radical scavenger, proanthocyanidins can quickly terminate the alkyl free radicals and peroxy free radicals generated by the EVA molecular chain during the processing heat history, blocking the chain degradation reaction. At the same time, the present invention uses a nitrogen atmosphere for protection during the preparation process, which avoids the polyphenol structure of proanthocyanidins being oxidized and destroyed by oxygen in the air at high temperature, thereby maximizing the preservation of its free radical scavenging activity. It can effectively inhibit the thermo-oxidative aging of EVA foam recycled material during secondary processing. The uniformly dispersed zinc oxide nanoparticles, as carrier particles of proanthocyanidins, can be fully dispersed in the matrix under the action of proanthocyanidins, improving the range of proanthocyanidins' resistance to thermal aging. The two work together to construct a multi-level protection system, improving the performance of the recycled material. The zinc oxide / proanthocyanidin composite antioxidant prepared by the present invention is uniformly dispersed in EVA foam recycled material, which can effectively inhibit the thermo-oxidative degradation during secondary processing and significantly improve the mechanical properties, recycling performance and wear resistance of recycled EVA material.

[0011] (3) The zinc oxide / proanthocyanidin composite antioxidant developed in this invention and its application in EVA recycling are characterized by a scientifically sound formula and a simple and controllable process. A highly efficient and stable EVA foam material recycling system was constructed using green chemistry methods. Based on the aforementioned advantages of dispersibility and synergistic anti-aging, the composite antioxidant developed in this invention only needs to be added in 1-3 parts to exert a significant effect in a 50wt.% high-proportion EVA foam recycled material system. This successfully solves the problems of high dosage, easy precipitation, and deterioration of processing performance associated with traditional antioxidants. After multiple cycles, the mechanical properties have been well maintained, truly giving EVA foam waste the ability to "regenerate." This technology has a scientifically sound formula and a green and controllable process, breaking through the bottleneck of severe material performance deterioration in traditional EVA foam recycling processes. It provides an innovative solution for the high-value recycling of EVA foam materials, and is of great significance in reducing plastic waste pollution and resource consumption, with broad application prospects. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the preparation process of the zinc oxide / proanthocyanidin composite antioxidant in Example 1.

[0013] Figure 2 This is a schematic diagram of the molecular structure of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1.

[0014] Figure 3 The image shows the X-ray diffraction pattern of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1.

[0015] Figure 4 The infrared characteristic spectrum of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1 is shown.

[0016] Figure 5 SEM and EDS images of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1.

[0017] Figure 6 The image shows the melt crystallization curve of the EVA recyclable composite material prepared in this invention. Where a) is Example 1; b) is Example 4; c) is Example 5; and d) is Comparative Example 1. Detailed Implementation

[0018] To further explain the technical solution of the present invention, specific embodiments are described below. These embodiments are used to illustrate the content of the present invention, but should not be construed as limiting the scope of the invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 This embodiment discloses a high-performance recyclable EVA composite material, the components of which, by weight, include: Ethylene-vinyl acetate copolymer: 46 parts; EVA foam recycled material: 47 parts; Zinc oxide / proanthocyanidin complex antioxidant: 3 parts; Azodicarbonamide: 3 parts; Dicumyl peroxide: 1 part; Stearic acid: 0.5 parts; Zinc stearate: 0.5 parts; Zinc oxide: 1 part.

[0020] Its preparation method includes the following steps: S1. Mix 46 parts of ethylene-vinyl acetate copolymer, treated EVA foam recycled material, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly, and then mix evenly for 5 minutes using a preheated two-roll mill at a heating temperature of 80°C. After the rubber compound is completely mixed evenly, pass it through a thin sheet 5 times to obtain a 2mm rubber compound sheet. Among them, the treated EVA foam recycled material is obtained by mixing 47 parts of EVA foam recycled material with 3 parts of zinc oxide / proanthocyanidin composite antioxidant, mixing evenly for 10 minutes using a two-roll open mill, and then passing the mixture through a thin sheet with a thickness of 2mm after the rubber material is completely mixed evenly 5 times. S2. Place the mixture obtained in step S1 into the preheated mold cavity of the flat vulcanizing machine for molding and foaming. After molding and foaming for 300s at 165℃ and 12MPa, a high-performance recyclable EVA composite material is obtained.

[0021] To control the performance differences between different recycled EVA foam materials, the recycled EVA foam material used in step S1 of this embodiment is prepared according to the EVA foam material formulation for shoe materials, and its preparation method is as follows: S01. Mix 89 parts of ethylene-vinyl acetate copolymer, 5 parts of talc, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly, and then mix evenly for 5 minutes using a preheated two-roll mill at 80°C. After the rubber compound is completely mixed evenly, pass it through a thin sheet 5 times to obtain a 2mm rubber compound sheet. S02. Place the sheet obtained in step S01 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 175℃ for 300s to obtain EVA foamed recycled material. The density of the recycled EVA foam prepared in this embodiment was measured to be 0.13 g / cm³. 3The tensile strength is 0.71 MPa and the elongation at break is 348.74%.

[0022] The preparation method of the zinc oxide / proanthocyanidin composite antioxidant includes the following steps: T1. Add 2.4g of proanthocyanidins and 300ml of deionized water to a 500ml flask and sonicate for 3min to dissolve them completely. Then, add 6.6g of zinc acetate to the flask at 0.2g / min while stirring at 6℃ and 800rpm. Stir until the zinc acetate is completely dissolved, and then stir and react for 30min under argon protection. Then, while stirring continuously at 800 rpm at room temperature, 0.1 mol / L ammonia solution was added dropwise to the flask at a rate of 1 ml / min until the pH reached 7.5-8.5 and no new precipitate was formed. After the addition was complete, the mixture was stirred at 6 °C for 2 h. After the reaction was completed, the precipitate was collected by centrifugation to obtain a composite precipitate. T2. Filter and wash the composite precipitate obtained in T1 until neutral to fully remove acetate ions, free zinc ions and other impurities. Dry the washed and filtered composite precipitate at 80℃ for 8 hours to fully remove free water and adsorbed water from the composite precipitate. After drying, take out the sample to obtain the zinc oxide / proanthocyanidin composite antioxidant.

[0023] Example 2 This embodiment discloses a high-performance recyclable EVA composite material. Compared with Example 1, the difference lies in the amount of recycled EVA foam and zinc oxide / proanthocyanidin composite antioxidant used in step S1. The components of this embodiment include: Ethylene-vinyl acetate copolymer: 46 parts; EVA foam recycled material: 49 parts; Zinc oxide / proanthocyanidin complex antioxidant: 1 part; Azodicarbonamide: 3 parts; Dicumyl peroxide: 1 part; Stearic acid: 0.5 parts; Zinc stearate: 0.5 parts; Zinc oxide: 1 part.

[0024] The density of the recycled EVA foam prepared in this embodiment is 0.12 g / cm³. 3 The tensile strength was 0.73 MPa and the elongation at break was 346.25%; the rest of the preparation method was the same as in Example 1.

[0025] Example 3 This embodiment discloses a high-performance recyclable EVA composite material. Compared with Example 1, the difference lies in the amount of recycled EVA foam and zinc oxide / proanthocyanidin composite antioxidant used in step S1. The components of this embodiment include: Ethylene-vinyl acetate copolymer: 46 parts; EVA foam recycled material: 45 parts; Zinc oxide / proanthocyanidin complex antioxidant: 5 parts; Azodicarbonamide: 3 parts; Dicumyl peroxide: 1 part; Stearic acid: 0.5 parts; Zinc stearate: 0.5 parts; Zinc oxide: 1 part.

[0026] The density of the recycled EVA foam prepared in this embodiment is 0.13 g / cm³. 3 The tensile strength was 0.72 MPa and the elongation at break was 349.66%; the rest of the preparation method was the same as in Example 1.

[0027] Example 4 This embodiment discloses a high-performance recyclable EVA composite material. Compared with Example 1, the difference lies in the preparation method of the EVA foamed recycled material. The preparation method of the EVA foamed recycled material in this embodiment is as follows: S01. Mix 89 parts of ethylene-vinyl acetate copolymer, 5 parts of talc, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes. Then transfer the mixture to an open mill and mix for 10 minutes. Press the material into 2 mm sheets. S02. Place the sheet obtained in step S01 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 175℃ for 300s to obtain EVA primary recycled material. The density of the primary recycled EVA material prepared in this embodiment was measured to be 0.13 g / cm³. 3 The tensile strength is 0.71 MPa and the elongation at break is 348.13%.

[0028] S03. Place 47 parts of the EVA primary recycled material obtained from S02 into a two-roll mill and mix for 10 minutes. Press the material into 2mm thin sheets, add 3 parts of zinc oxide / proanthocyanidin composite antioxidant and mix evenly for 10 minutes, then press into 2mm thin sheets. S04. Mix 46 parts of ethylene-vinyl acetate copolymer, the EVA foam recycled material obtained in step S03, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes and then press the material into 2 mm sheets using an open mill. S05. Place the sheet obtained in step S04 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 165℃ for 300s to obtain EVA foamed recycled material.

[0029] Example 5 This embodiment discloses a high-performance recyclable EVA composite material. Compared with Example 1, the difference lies in the preparation method of the EVA foamed recycled material. The preparation method of the EVA foamed recycled material in this embodiment is as follows: S01. Mix 89 parts of ethylene-vinyl acetate copolymer, 5 parts of talc, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes. Then transfer the mixture to an open mill and mix for 10 minutes. Press the material into 2 mm sheets. S02. Place the sheet obtained in step S01 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 175℃ for 300s to obtain EVA primary recycled material. The density of the primary recycled EVA material prepared in this embodiment was measured to be 0.12 g / cm³. 3 The tensile strength is 0.69 MPa and the elongation at break is 347.54%.

[0030] S03. Place 47 parts of the EVA primary recycled material obtained from S02 into a two-roll mill and mix for 10 minutes. Press the material into 2mm thin sheets, add 3 parts of zinc oxide / proanthocyanidin composite antioxidant and mix evenly for 10 minutes, then press into 2mm thin sheets. S04. Mix 46 parts of ethylene-vinyl acetate copolymer, the EVA foam recycled material obtained in step S03, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes and then press the material into 2 mm sheets using an open mill. S05. Place the sheet obtained in step S04 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 165℃ for 300s to obtain the secondary recycled EVA material.

[0031] S06. Place 47 parts of the secondary recycled EVA material obtained from S05 into a two-roll mill and mix for 10 minutes. Press the material into 2mm thin sheets, add 3 parts of zinc oxide / proanthocyanidin composite antioxidant and mix evenly for 10 minutes, then press into 2mm thin sheets. S07. Mix 46 parts of ethylene-vinyl acetate copolymer, the secondary recycled EVA material obtained in step S06, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes and then press the material into 2 mm sheets using an open mill. S08. Place the sheet obtained in step S07 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 165℃ for 300s to obtain EVA foamed recycled material.

[0032] Comparative Example 1 This comparative example discloses a recyclable EVA composite material, the components of which, by weight, include: Ethylene-vinyl acetate copolymer: 46 parts; EVA foam recycled material: 50 parts; Azodicarbonamide: 3 parts; Dicumyl peroxide: 1 part; Stearic acid: 0.5 parts; Zinc stearate: 0.5 parts; Zinc oxide: 1 part.

[0033] Its preparation method includes the following steps: S1. Place 50 parts of recycled EVA foam in a two-roll mill and mix for 10 minutes. Then press the material into 2mm thin sheets. S2. Mix 46 parts of ethylene-vinyl acetate copolymer, the EVA foam recycled material obtained in step S1, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix for 5 minutes at a set temperature of 80℃ and a speed of 20 rpm and then press the material into 2 mm thin sheets using an open mill. S3. Place the sheet obtained in step S2 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 165℃ for 300s to obtain the recyclable EVA composite material.

[0034] The preparation method of the EVA foam recycled material used in step S1 of this comparative example is as follows: S01. Mix 89 parts of ethylene-vinyl acetate copolymer, 5 parts of talc, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes. Then transfer the mixture to an open mill and mix for 10 minutes. Press the material into 2 mm sheets. S02. Place the sheet obtained in step S01 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 175℃ for 300s to obtain EVA foamed recycled material.

[0035] The density of the EVA foam recycled material prepared in this comparative example was measured to be 0.13 g / cm³. 3 The tensile strength is 0.72 MPa and the elongation at break is 349.12%.

[0036] Comparative Example 2 This comparative example discloses a recyclable EVA composite material. Compared with Comparative Example 1, the difference lies in the preparation method of the EVA foamed recycled material. The preparation method of the EVA foamed recycled material in this comparative example is as follows: S01. Mix 89 parts of ethylene-vinyl acetate copolymer, 5 parts of talc, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes. Then transfer the mixture to an open mill and mix for 10 minutes. Press the material into 2 mm sheets. S02. Place the sheet obtained in step S01 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 175℃ for 300s to obtain EVA primary recycled material. The density of the primary recycled EVA material prepared in this comparative example was measured to be 0.12 g / cm³. 3 The tensile strength is 0.71 MPa and the elongation at break is 348.87%.

[0037] S03. Place 50 parts of the EVA primary recycled material obtained from S02 into a two-roll mill and mix for 10 minutes. Then press the material into 2mm thin sheets. S04. Mix 46 parts of ethylene-vinyl acetate copolymer, the EVA foam recycled material obtained in step S03, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes and then press the material into 2 mm sheets using an open mill. S05. Place the sheet obtained in step S04 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 165℃ for 300s to obtain EVA foamed recycled material.

[0038] Comparative Example 3 This comparative example discloses a recyclable EVA composite material. Compared with Comparative Example 1, the difference lies in the preparation method of the EVA foamed recycled material. The preparation method of the EVA foamed recycled material in this comparative example is as follows: S01. Mix 89 parts of ethylene-vinyl acetate copolymer, 5 parts of talc, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes. Then transfer the mixture to an open mill and mix for 10 minutes. Press the material into 2 mm sheets. S02. Place the sheet obtained in step S01 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 175℃ for 300s to obtain EVA primary recycled material. The density of the primary recycled EVA material prepared in this comparative example was measured to be 0.13 g / cm³. 3 The tensile strength is 0.69 MPa and the elongation at break is 346.67%.

[0039] S03. Place 50 parts of the EVA primary recycled material obtained from S02 into a two-roll mill and mix for 10 minutes. Then press the material into 2mm thin sheets. S04. Mix 46 parts of ethylene-vinyl acetate copolymer, the EVA foam recycled material obtained in step S03, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes and then press the material into 2 mm sheets using an open mill. S05. Place the sheet obtained in step S04 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 165℃ for 300s to obtain the secondary recycled EVA material.

[0040] S06. Place 50 parts of the secondary recycled EVA material obtained from S05 into a two-roll mill and mix for 10 minutes. Then press the material into 2mm thin sheets. S07. Mix 46 parts of ethylene-vinyl acetate copolymer, the secondary recycled EVA material obtained in step S06, 0.5 parts of stearic acid, 1 part of crosslinking agent dicumyl peroxide, 3 parts of foaming agent azodicarbonamide, 0.5 parts of zinc stearate and 1 part of zinc oxide evenly and place them in a preheated internal mixer. Mix at 80°C and 20 rpm for 5 minutes and then press the material into 2 mm sheets using an open mill. S08. Place the sheet obtained in step S07 into the preheated mold cavity of the flat vulcanizing machine, and mold and foam it at 12MPa and 165℃ for 300s to obtain EVA foamed recycled material.

[0041] Comparative Example 4 This comparative example discloses a recyclable EVA composite material. The difference from Example 5 is that the zinc oxide / proanthocyanidin composite antioxidant is adjusted to a mixture of zinc oxide and proanthocyanidins in a 1:1 mass ratio. The components of this comparative example include: Ethylene-vinyl acetate copolymer: 46 parts; EVA foam recycled material: 47 parts; Zinc oxide-proanthocyanidin mixture: 3 parts; Azodicarbonamide: 3 parts; Dicumyl peroxide: 1 part; Stearic acid: 0.5 parts; Zinc stearate: 0.5 parts; Zinc oxide: 1 part; The zinc oxide-proanthocyanidin mixture is obtained by mixing zinc oxide and proanthocyanidins in a mass ratio of 1:1.

[0042] The density of the primary recycled EVA material prepared in this comparative example is 0.13 g / cm³. 3 The tensile strength was 0.7 MPa and the elongation at break was 347.53%; the rest of the preparation method was the same as in Example 5.

[0043] Performance testing like Figure 2The diagram shows the molecular structure of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1. Proanthocyanidins are responsible for surface stabilization and organic shell formation, forming a "Zn-proanthocyanidin" bridging structure. This composite achieves stable binding through hydrogen bonding between zinc oxide and proanthocyanidin polyphenols, as well as coordination bonds formed between zinc ions and proanthocyanidin polyphenols during precipitation. Proanthocyanidins improve organic coating efficiency and dispersion stability, resulting in smaller and more uniform nanoparticles. Compared to unmodified simple compounding, proanthocyanidins solve the problems of easy aggregation, poor compatibility, and weak antioxidant capacity of traditional ZnO, achieving multifunctional integration. Zinc oxide / proanthocyanidin composite antioxidant is mixed with EVA foamed material in 1, 3, and 5 parts on a two-roll mill. Through multiple rolling processes, EVA foamed recycled material is formed. In this process, the zinc oxide / proanthocyanidin composite antioxidant mixed in the EVA foamed recycled material plays a role in improving the thermal and mechanical stability of the recycled material during repeated processing, thereby improving the wear resistance and mechanical properties of the EVA recycled foamed material.

[0044] like Figure 3 The XRD pattern of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1 is shown. Characteristic peaks appear at 31.8°, 34.4°, 36.3°, 47.5°, and 56.6° in the XRD patterns of both zinc oxide and the zinc oxide / proanthocyanidin composite antioxidant, corresponding to the (100), (002), (101), (102), and (110) crystal planes, respectively. This indicates that both zinc oxide and the zinc oxide / proanthocyanidin composite antioxidant have a hexagonal wurtzite structure. Simultaneously, a broad diffraction peak appears near 21.1° in the XRD pattern of the zinc oxide / proanthocyanidin composite antioxidant, corresponding to the amorphous structure in proanthocyanidins.

[0045] like Figure 4 The image shown is the FT-IR spectrum of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1. The spectrum can be seen at 3200–3450 cm⁻¹. -1 and 3450–3580cm -1 The presence of a characteristic OH peak at 1600–1630 cm⁻¹ corresponds to the phenolic hydroxyl structure of proanthocyanidins and the surface hydroxyl groups of zinc oxide. The OH peak of the zinc oxide / proanthocyanidin composite antioxidant shows a red shift and broadens, indicating a hydrogen bonding interaction between zinc oxide and proanthocyanidins. -1 and 1510–1530cm -1 The presence of a C=C characteristic peak at 1340–1360 cm⁻¹ indicates that proanthocyanidins have combined with zinc oxide; -1 1200–1220cm -1 and 1060–1080cm -1 A C–O characteristic peak appears at 1200–1220 cm⁻¹. -1 The characteristic C–O–C peaks appear at 480–520 cm⁻¹.-1 400–430cm -1 and 600–700cm -1 Characteristic Zn–O peaks appear at [value], corresponding to the zinc oxide structure; notably, the composite material exhibits peaks at 480–520 cm⁻¹. -1 The peak broadening and slight red shift are attributed to lattice distortion and surface coordination in the zinc oxide / proanthocyanidin composite antioxidant.

[0046] like Figure 5 The images shown are SEM and EDS images of the zinc oxide / proanthocyanidin composite antioxidant prepared in Example 1. The results show that the synthesized zinc oxide / proanthocyanidin composite antioxidant has a microsphere structure with a size of about 200 nm. This is because proanthocyanidins have a strong effect on the oxidation of zinc oxide (ZnO2). 2+ The coordination of ions alters the crystal growth pattern of zinc oxide, resulting in larger particles appearing in regions lacking proanthocyanidin binding. Simultaneously, the elemental distribution spectra of O, C, and Zn reflect the binding of proanthocyanidins with ZnO, indirectly confirming the "Zn-proanthocyanidin" bridging structure and demonstrating the successful preparation of the zinc oxide / proanthocyanidin composite antioxidant.

[0047] like Figure 6 The figure shows the melt crystallization curve of the EVA recyclable composite material prepared according to the present invention, where a) is Example 1; b) is Example 4; c) is Example 5; and d) is Comparative Example 1. Figure 6 The melt crystallization curves of the recycled EVA composite materials prepared in Examples 1, 4, and 5 can be used to calculate the changes in the crystallinity of the materials. The crystallinity of Example 1 is 26%, that of Example 4 is 30%, and that of Example 5 is 37%, indicating that the crystallinity of the materials increases with the number of recycling cycles. Compared with the crystallinity of up to 68% in Comparative Example 1, the addition of zinc oxide / proanthocyanidin antioxidants significantly reduced the crystallinity of the recycled EVA foam material and improved the flexibility of the material.

[0048] The properties of the EVA composites prepared in all examples and comparative examples were tested, and the test results are shown in Table 1, which shows the physical and mechanical properties of the recycled EVA composites. The standards referenced for the tests are as follows: Hardness testing shall be performed in accordance with GB / T 39693.4-2025 "Determination of hardness of vulcanized rubber or thermoplastic rubber - Part 4: Determination of indentation hardness by Shore hardness tester (Shore hardness)".

[0049] Density testing was performed in accordance with GB / T 6343-2009, "Determination of Apparent Density of Foamed Plastics and Rubber".

[0050] The tensile strength and elongation at break tests were performed in accordance with GB / T 6344-2008 "Determination of tensile strength and elongation at break of flexible foam polymer materials".

[0051] The rebound rate test was conducted in accordance with GB / T 6670-2008 "Determination of rebound performance of flexible foam polymer materials by falling ball method".

[0052] DIN abrasion test refers to GB / T 9867-2008 "Determination of abrasion resistance of vulcanized rubber or thermoplastic rubber (rotary roller abrasion test method)".

[0053] Table 1 Physical and mechanical properties of recycled EVA composite materials

[0054] Comparing Examples 1, 2, and 3 with Comparative Example 1, it was found that with the increase of the amount of zinc oxide / proanthocyanidin composite antioxidant, the tensile strength and density of the EVA composite material showed a gradual decreasing trend, the DIN wear showed a trend of first decreasing and then leveling off, and the elongation at break showed a trend of first increasing and then decreasing. This indicates that the zinc oxide / proanthocyanidin composite antioxidant has a significant improving effect on the physical and mechanical properties of the EVA composite foam material. As the amount of zinc oxide / proanthocyanidin composite antioxidant increased to 5 parts, the improvement effect on the physical and mechanical properties of the EVA foam material slowed down, and the elongation at break decreased. This is because the zinc oxide / proanthocyanidin composite antioxidant partially agglomerated in the EVA matrix material, resulting in a decrease in the performance of the EVA composite foam material. However, too low a amount of zinc oxide / proanthocyanidin composite antioxidant cannot achieve a good aging resistance effect, resulting in poor physical and mechanical properties and wear resistance of the prepared EVA composite material.

[0055] Comparing Examples 1, 4, and 5, it was found that with the increase of the number of recycling cycles of EVA composite materials, the tensile strength, density, and DIN abrasion of the EVA composite materials showed a gradual increasing trend, while the elongation at break showed a gradual decreasing trend. This indicates that the increase in the number of recycling cycles of EVA composite materials will lead to a decrease in the physical and mechanical properties of EVA composite foam materials. Combined with DSC data analysis, this is because the crystallinity of the EVA matrix gradually increases during the multiple recycling and reuse process, resulting in a decrease in the elongation at break of the prepared EVA composite materials, while the strength, density, and DIN abrasion increase.

[0056] Among them, Example 4, which added 3 parts of zinc oxide / proanthocyanidin composite antioxidant for secondary recycling, was compared with Example 2, which did not add antioxidant for secondary recycling, and Example 5, which added 3 parts of antioxidant for tertiary recycling, was compared with Example 3, which did not add antioxidant for tertiary recycling. In comparison, Examples 4 and 5, which added the zinc oxide / proanthocyanidin composite antioxidant prepared by the present invention, had better mechanical properties. This shows that the zinc oxide / proanthocyanidin composite antioxidant prepared by the present invention can effectively inhibit the degradation of material performance in multiple recycling cycles of EVA composite foam material.

[0057] Comparing Example 5, which added 3 parts of zinc oxide / proanthocyanidin composite antioxidant and recycled three times, and Comparative Example 4, which added 1.5 parts of proanthocyanidin and 1.5 parts of zinc oxide and recycled three times, it can be seen that Example 5, which used zinc oxide / proanthocyanidin composite antioxidant, has superior physical and mechanical properties. This is because during the preparation of the composite antioxidant, zinc oxide and proanthocyanidin form sufficient hydrogen bonds and coordination bonds to bridge the structure, which synergistically enhances the structural stability of the EVA foam recycled material and solves the problem of weak bridging effect and poor dispersibility when proanthocyanidin and zinc oxide are compounded.

[0058] Multiple heat recovery processes promote EVA molecular chain rearrangement and crystallization, leading to a continuous increase in crystallinity. Macroscopically, this manifests as increased material brittleness, decreased elongation at break, and increased density and wear resistance. The zinc oxide / proanthocyanidin composite antioxidant, through interfacial interactions, inhibits the orderly crystallization of molecular chains, delaying crystallinity growth and mitigating mechanical property degradation during recycling from a crystalline perspective. Therefore, Example 4 (secondary recycling) and Example 5 (tertiary recycling) maintain higher elongation, lower wear resistance, and more balanced strength compared to Comparative Examples 2 and 3 (without antioxidants). Comparative Example 4, with its simple zinc oxide and proanthocyanidin physical compound system, suffers from weak interfacial chemical bridging, poor filler dispersion, and weak heterogeneous nucleation, resulting in limited crystallization inhibition and higher crystallinity. The zinc oxide / proanthocyanidin composite antioxidant-coated complex achieves uniform dispersion through sufficient hydrogen and coordination bonds, effectively hindering molecular chain crystallization. Lower crystallinity leads to superior elongation, strength, and wear resistance, demonstrating that interfacial regulation of crystallization is the core intrinsic factor for improved mechanical properties.

[0059] From the density results, the zinc oxide / proanthocyanidin composite antioxidant prepared in this invention exhibits nucleation activity. The complex of zinc oxide and proanthocyanidins acts as a heterogeneous nucleating agent, reducing crystallinity, refining pores, and improving the uniformity of the pore structure. Comparative Examples 1, 2, and 3, which did not add antioxidants, showed uneven nucleation due to material degradation. Comparative Example 4, which used proanthocyanidins and zinc oxide alone, could not effectively control the formation and stability of pores due to the poor dimensional stability of zinc oxide and the poor dispersibility of proanthocyanidins. The zinc oxide / proanthocyanidin composite antioxidant significantly improves the mechanical properties, wear resistance, and foaming stability of EVA foam recycled materials through the chemical synergistic effect of hydrogen bonds and coordination bonds and the physical regulation effect of heterogeneous nucleation. In particular, in Example 1, when the amount of zinc oxide / proanthocyanidin composite antioxidant added was 3 parts, a good balance was achieved between performance and cost, and the material could be recycled at least three times, providing an effective solution for the high-value recycling of EVA foam materials.

[0060] In summary, as the number of recycling cycles of EVA composite materials increases, their crystallinity increases, simultaneously leading to embrittlement and mechanical degradation. The zinc oxide / proanthocyanidin composite antioxidant inhibits the regular arrangement of EVA molecular chains and reduces the crystallinity of the system through interfacial interactions. Reduced crystallinity means an increase in the range of amorphous regions, resulting in greater space for molecular chain movement and improved material flexibility, elongation at break, and foam structure stability. Therefore, the composite additive of this invention not only maintains the basic mechanical properties of the original material in EVA foam composite materials but also significantly improves tensile strength and wear resistance. Furthermore, it exhibits excellent wear resistance, maintaining a relatively low DIN abrasion value even with recycled material accounting for 50% of the mass. This not only saves production costs but also reduces dust during processing and is environmentally friendly.

Claims

1. A high-performance recyclable EVA composite material, comprising, by weight, ethylene-vinyl acetate copolymer, azodicarbonamide, dicumyl peroxide, stearic acid, zinc stearate, and zinc oxide, characterized in that: The components also include recycled EVA foam and composite antioxidants.

2. The high-performance recyclable EVA composite material according to claim 1, characterized in that: The composite antioxidant is a zinc oxide / proanthocyanidin composite antioxidant obtained by linking proanthocyanidins and zinc oxide through hydrogen bonds and coordination bonds, with zinc oxide as the carrier and proanthocyanidins as the loading material.

3. The high-performance recyclable EVA composite material according to claim 1, characterized in that: The mass ratio of the EVA foam recycled material and composite antioxidant to the ethylene-vinyl acetate copolymer is (0.97-1.07):(0.02-0.11):

1.

4. The high-performance recyclable EVA composite material according to claim 1, characterized in that: The EVA foam recycled material is waste generated during the EVA shoe material foaming process, with a density of 0.1-0.15 g / cm³. 3 The tensile strength is 0.6-0.8 MPa, and the elongation at break is 330-370%.

5. The high-performance recyclable EVA composite material according to claim 1, characterized in that: The preparation method of the composite antioxidant specifically includes the following steps: T1. Add proanthocyanidins and deionized water to a flask and sonicate to dissolve them completely. Then, slowly add zinc salt to the flask while stirring at 800-1000 rpm in an ice-water bath at 6-8℃. Stir until dissolved. Then, purge argon gas into the flask and stir for 20-40 minutes under argon protection to ensure that the dissolved zinc salt fully contacts and coordinates with the hydroxyl groups of proanthocyanidins. Under stirring conditions, add alkaline solution dropwise to the flask until the pH reaches 7.5-8.5 and no zinc hydroxide precipitate is formed. After the addition is complete, continue stirring for 1-3 hours to ensure the adsorption of zinc hydroxide and proanthocyanidins. After the reaction is complete, collect the precipitate to obtain a composite precipitate. T2. Filter and wash the composite precipitate obtained in step T1 until it is neutral, and then dry it to obtain the zinc oxide / proanthocyanidin composite antioxidant.

6. The high-performance recyclable EVA composite material according to claim 5, characterized in that: In step T1, the mass ratio of proanthocyanidins to zinc salt is 1:(2-4).

7. The high-performance recyclable EVA composite material according to claim 6, characterized in that: The drying process parameters in step T2 are: drying at 75-85℃ for 6-10 hours.

8. A method for preparing a high-performance recyclable EVA composite material according to any one of claims 1-7, characterized in that, Includes the following steps: S1. After uniformly mixing ethylene-vinyl acetate copolymer, treated EVA foam recycled material, stearic acid, crosslinking agent dicumyl peroxide, foaming agent azodicarbonamide, zinc stearate and zinc oxide, the mixture is then uniformly mixed using a two-roll mill and then passed through a thin mill 4-6 times to obtain a 2-4 mm rubber sheet. S2. Place the mixture obtained in step S1 into the preheated mold cavity of the flat vulcanizing machine for molding and foaming to obtain a high-performance recyclable EVA composite material.

9. The method for preparing a high-performance recyclable EVA composite material according to claim 8, characterized in that: In step S1, the processed EVA foam recycled material is obtained by mixing EVA foam recycled material with zinc oxide / proanthocyanidin composite antioxidant in a certain proportion, and then mixing it evenly for 10-20 minutes using a two-roll mill. After the rubber compound is completely mixed evenly, it is passed through a thin mill 4-6 times to obtain a rubber compound sheet with a thickness of 2-4 mm.

10. The method for preparing a high-performance recyclable EVA composite material according to claim 8, characterized in that: The process parameters for compression molding foaming in step S2 are: foaming temperature 160-170℃, foaming pressure 11.5-12.5MPa, and foaming time 270-330s.

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