Environment-friendly EVA material for shoemaking and preparation method thereof

Abstract

The invention discloses an environment-friendly EVA (Ethylene Vinyl Acetate) material and belongs to the technical field of polymer composite materials. The environment-friendly EVA material is prepared from the following components: EVA resin, a bio-based dynamic cross-linking agent DBX-200, a natural fiber reinforced network, a hybrid flame-retardant filler, a bio-based plasticizer, zinc oxide, zinc stearate and an antioxidant. The bio-based dynamic cross-linking agent DBX-200 is introduced to replace a traditional toxic peroxide cross-linking system, pollution-free cross-linking is achieved, and the material is endowed with a self-repairing function. The natural fiber reinforced network is composed of silane coupling agent modified bamboo fibers and carboxylated nanocellulose, a multi-stage reinforced structure is formed, and the mechanical property is remarkably improved. The hybrid flame-retardant filler coats Mg (OH) 2 / HNTs through dopamine, so that synergistic flame retardance of a gas phase and a condensed phase is realized; the bio-based plasticizer is compounded by acetylated tributyl citrate and epoxidized cashew nut oil, and the plasticizing efficiency and the migration resistance are both considered. The material has the characteristics of high mechanical property, excellent flame retardance and environmental friendliness, and is suitable for the fields of shoemaking and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, and in particular to an environmentally friendly EVA material for shoemaking and a preparation method thereof. Background Art

[0002] As global environmental regulations become increasingly stringent, traditional ethylene-vinyl acetate copolymer (EVA) shoe materials, due to their reliance on peroxide cross-linking systems (such as DCP / TAIC) and petroleum-based additives, face technical bottlenecks such as insufficient environmental protection and difficulty in synergistically improving mechanical properties and flame retardancy.

[0003] 1. Environmental defects of traditional EVA materials: In existing technologies, EVA foam materials generally use peroxide and triallyl isocyanurate as the cross-linking system. However, during the high-temperature cross-linking process, toxic byproducts such as acetophenone and benzaldehyde will remain, making it difficult to meet environmental protection standards such as those of the European Union. In addition, the migration rate of petroleum-based plasticizers is as high as 5%-8%, and long-term use poses health risks. Although some studies have attempted to use bio-based plasticizers (such as epoxidized soybean oil), their compatibility with EVA is poor, resulting in a decrease in the hardness of the material by more than 30%.

[0004] 2. Conflict between mechanical properties and flame retardancy: Traditional EVA footwear materials are often enhanced with halogen-free flame retardants such as magnesium hydroxide or aluminum hydroxide. However, these additives must be at least 30wt% to meet UL94 V-0 flame retardancy requirements. However, high filler loadings increase material density and decrease tensile strength. Furthermore, the interfacial bonding between the flame retardant and the EVA matrix is weak, which can easily induce stress concentration and result in low elongation at break.

[0005] 3. Energy consumption and structural defects of the foaming process: Traditional EVA foaming relies on high-temperature molding or continuous extrusion, which consumes a lot of energy and produces poor cell uniformity. In addition, the filler is unevenly dispersed during the foaming process, further degrading the material's performance.

[0006] In summary, existing EVA shoe materials have multiple problems in terms of environmental protection, mechanical strength, flame retardancy and foaming process, and an innovative solution is urgently needed: developing a bio-based dynamic cross-linking system without peroxide residue to achieve efficient cross-linking and self-repair functions; through multi-level reinforcement of natural fibers / nanofillers and surface modification of hybrid flame-retardant fillers, synergistically improving mechanical and flame retardant properties; designing a gradient pressure relief supercritical foaming process to optimize the foam structure and reduce energy consumption. Summary of the Invention

[0007] The purpose of the present invention is to provide an environmentally friendly EVA material for shoemaking and a preparation method thereof, which solves the problems existing in the existing EVA shoe materials in terms of environmental protection, mechanical strength, flame retardancy and foaming process.

[0008] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0009] An environmentally friendly EVA material is composed of the following components: EVA resin, a bio-based dynamic crosslinker DBX-200, a natural fiber reinforced network, a hybrid flame retardant filler, a bio-based plasticizer, zinc oxide, zinc stearate, and an antioxidant. In the material, relative to 100 parts by weight of the EVA resin, the content of the bio-based dynamic crosslinker DBX-200 is 4-5 parts by weight, the content of the natural fiber reinforced network is 20-30 parts by weight, the content of the hybrid flame retardant filler is 16-20 parts by weight, the content of the bio-based plasticizer is 20-24 parts by weight, the content of the zinc oxide is 1-3 parts by weight, the content of the zinc stearate is 1-2 parts by weight, and the content of the antioxidant is 0.5-0.7 parts by weight. The bio-based dynamic crosslinker DBX-200 is obtained by reacting cardanol glycidyl ether, furfurylamine, and CuI catalyst.

[0010] The environmentally friendly EVA material described in this invention overcomes the problems of traditional EVA materials, such as reliance on toxic crosslinkers and an imbalance between mechanical and flame retardant properties, by utilizing a reversible network of bio-based dynamic crosslinkers, multi-stage reinforcement of natural fibers, interfacial modification of flame-retardant fillers, and a plasticizer blend. Furthermore, a supercritical CO2 gradient pressure release foaming process combined with plasma surface treatment optimizes the cell structure (closed cell ratio ≥ 90%), achieving low-energy, highly environmentally friendly footwear material production.

[0011] According to a preferred embodiment of the present invention, the EVA resin is purchased from Dongguan Dongshuo Plastic Raw Materials Co., Ltd. and is model EV45LX.

[0012] According to a preferred embodiment of the present invention, the bio-based dynamic crosslinker DBX-200 is prepared by a reaction comprising: dissolving 100 parts by weight of cardanol glycidyl ether and 35 parts by weight of furfurylamine in tetrahydrofuran, adding 0.5 parts by weight of CuI catalyst for reaction, and removing the solvent by rotary evaporation.

[0013] In the present invention, the epoxy group of cardanol glycidyl ether and the amino group of furfurylamine react under CuI catalysis to form a dynamic imine bond (Schiff base), which gives the material reversible cross-linking ability; the epoxy group of the bio-based dynamic cross-linker DBX-200 undergoes a ring-opening reaction with the hydroxyl group of the EVA molecular chain to form a stable covalent cross-linked network, replacing the traditional peroxide cross-linking system (such as DCP).

[0014] According to a preferred embodiment of the present invention, the cardanol glycidyl ether is purchased from Hubei Xingyan New Material Technology Co., Ltd., and its packaging specifications include 50KG.

[0015] According to a preferred embodiment of the present invention, the furfurylamine is purchased from Hubei Zhonglong Kangsheng Fine Chemical Co., Ltd., and its CAS number is 617-89-0.

[0016] According to a preferred embodiment of the present invention, the CuI catalyst is purchased from Shanghai Xunkai Chemical Technology Co., Ltd.

[0017] According to a preferred embodiment of the present invention, the EVA resin is purchased from Dongguan Dongshuo Plastic Raw Materials Co., Ltd. and is model EV45LX.

[0018] According to a preferred embodiment of the present invention, the natural fiber reinforced network consists of bamboo fiber and nanocellulose; the bamboo fiber is soaked in a coupling agent KH550 and an ethanol solution and dried; and the nanocellulose is prepared by a TEMPO / NaClO oxidation method.

[0019] In the present invention, bamboo fiber is treated with KH550 silane coupling agent. After hydrolysis, the silane condenses with the hydroxyl groups on the fiber surface to form -Si-O- bonds, and forms hydrogen bonds with the polar groups of EVA through the amino groups. TEMPO oxidation introduces carboxyl groups (-COOH), which produce dipole interactions with the ester groups of EVA. The high aspect ratio of the nanofibers forms a three-dimensional physical cross-linked network in the matrix.

[0020] According to a preferred embodiment of the present invention, the bamboo fiber is purchased from Shanghai Tianzhu Textile Fiber Co., Ltd.

[0021] According to a preferred embodiment of the present invention, the coupling agent KH550 was purchased from Jinan Changyingda Chemical Co., Ltd.

[0022] According to a preferred embodiment of the present invention, the ethanol is purchased from Nantong Runfeng Petrochemical Co., Ltd., and its CAS number is 64-17-5.

[0023] According to a preferred embodiment of the present invention, the nanocellulose is prepared by oxidizing cellulose using 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and sodium hypochlorite (NaClO). This method selectively oxidizes the hydroxyl groups on the cellulose molecular chain to generate carboxyl groups, thereby achieving nanoscale dissociation and preparation of cellulose; the core of the TEMPO / NaClO oxidation method is that TEMPO generates oxidized TEMPO in the presence of sodium hypochlorite (NaClO). + This oxidation state can selectively oxidize the primary hydroxyl groups on the cellulose molecular chain to aldehydes, which are then oxidized to carboxylic acids. The entire process does not damage the cellulose backbone structure and can maximize the preservation of cellulose's mechanical properties.

[0024] According to a preferred embodiment of the present invention, the hybrid flame retardant filler is prepared by the following steps: dissolving Mg(OH)2 and HNTs in a Tris-HCl buffer solution with a pH of 8.5, adding dopamine hydrochloride, stirring, centrifuging, and drying.

[0025] In this method, Mg(OH)2 and HNTs are coated with polydopamine (PDA) through dopamine self-polymerization. The phenolic hydroxyl groups of PDA form hydrogen bonds with EVA, improving dispersibility. Mg(OH)2 decomposes endothermally to release water vapor, diluting the oxygen concentration. The tubular structure of the HNTs slows the diffusion of pyrolysis gases, and the PDA carbonizes to form a dense carbon layer.

[0026] According to a preferred embodiment of the present invention, the Mg(OH)2 is purchased from Gongyi Qianghong Magnesium Technology Co., Ltd.

[0027] According to a preferred embodiment of the present invention, the HNTs are nano-halloysite tubes, which are a natural aluminosilicate mineral with a chemical formula of Al2Si2O5(OH)4·nH2O. Their microstructure is a unique nanoscale hollow tube with a diameter of typically 30-100 nm and a length of about 0.5-2 μm.

[0028] According to a preferred embodiment of the present invention, the HNTs are purchased from Guangdong Jinaxin Materials Technology Co., Ltd.

[0029] According to a preferred embodiment of the present invention, the Tris-HCl buffer was purchased from Beijing Solebow Technology Co., Ltd.

[0030] According to a preferred embodiment of the present invention, the dopamine hydrochloride is purchased from Huhui (Shanghai) Biotechnology Co., Ltd.

[0031] According to a preferred embodiment of the present invention, the bio-based plasticizer consists of acetylated tributyl citrate and epoxidized cashew nut oil, and the mass ratio of the acetylated tributyl citrate to the epoxidized cashew nut oil is 5:5.

[0032] In the present invention, the acetyl group reduces polarity, is compatible with the amorphous region of EVA, and reduces friction between molecular chains; the epoxy group forms a dipole effect with the EVA ester group, and the long alkyl chain provides flexibility; acetylated tributyl citrate and epoxidized cashew nut oil are compounded in a ratio of 5:5 to balance plasticizing efficiency and thermal stability.

[0033] According to a preferred embodiment of the present invention, the acetylated tributyl citrate is purchased from Hubei Nona Technology Co., Ltd.

[0034] According to a preferred embodiment of the present invention, the epoxidized cashew nut oil is purchased from Shandong Runqi Biotechnology Co., Ltd.

[0035] According to a preferred embodiment of the present invention, the zinc oxide is purchased from Zhaoqing Xinrunfeng High-tech Materials Co., Ltd.

[0036] In the present invention, zinc oxide is used as a cross-linking activator to react with the epoxy group of DBX-200 to form a zinc complex, thereby reducing the activation of the cross-linking reaction.

[0037] According to a preferred embodiment of the present invention, the zinc stearate is purchased from Shandong Xuchen Chemical Technology Co., Ltd.

[0038] The long-chain alkyl group of zinc stearate in the present invention reduces the friction between EVA molecular chains and synergistically improves the dispersibility of the filler with zinc oxide.

[0039] According to a preferred embodiment of the present invention, the antioxidant consists of Irganox 1010 and PS802, and the mass ratio of Irganox 1010 to PS802 is 2:1.

[0040] In the present invention, the phenolic hydroxyl groups of Irganox 1010 capture free radicals (such as R· generated by EVA chain breakage), interrupting the oxidation chain reaction; the thioether groups of PS802 decompose peroxides (ROOH) into stable alcohols, thereby inhibiting yellowing of the material.

[0041] According to a preferred embodiment of the present invention, the Irganox 1010 is purchased from Dongguan Kangjin New Material Technology Co., Ltd.

[0042] According to a preferred embodiment of the present invention, the PS802 is purchased from BASF.

[0043] According to a preferred embodiment of the present invention, the DCP (dicumyl peroxide) is purchased from Suzhou Senfida Chemical Co., Ltd.

[0044] According to a preferred embodiment of the present invention, the plasticizer DOP is purchased from Guangzhou Haocheng Chemical Technology Co., Ltd.

[0045] The present invention also provides a method for preparing an environmentally friendly EVA material, comprising the following steps:

[0046] S1. Add bamboo fiber and nanocellulose into a high-speed shearing machine and premix them;

[0047] S2. Add EVA, plasticizer, and hybrid filler to an internal mixer, turn on DBD plasma, and mix at 115°C for 10 minutes; then add bio-based dynamic crosslinker DBX-200, zinc oxide, and zinc stearate in sequence, and continue mixing for 5 minutes.

[0048] S3. Twin-screw extrusion granulation: Use a co-rotating twin-screw extruder, zone temperature: zone 1 105℃, zone 2 125℃, zone 3 135℃, zone 4 125℃, die head pressure 12MPa;

[0049] S4, the pellets are placed in an autoclave and supercritical CO2 is injected for 40 minutes;

[0050] S5, three-stage pressure release: first stage: 15MPa→8MPa, keep warm for 3 minutes; second stage: 8MPa→3MPa, keep warm for 2 minutes; third stage: 3MPa→normal pressure to obtain foamed embryo;

[0051] S6. The foamed body is cured in a hot air oven at 80°C for 2 hours; and the surface is treated with an atmospheric pressure plasma jet.

[0052] According to a preferred embodiment of the present invention, in step S1, the speed of the high-speed shearing machine is 8000 rpm, the temperature is 60° C., and the premixing time is 10 min; in step S2, the speed of the internal mixer is 50 rpm.

[0053] According to a preferred embodiment of the present invention, in step S4, the temperature of the supercritical CO2 is 130°C and the pressure is 15 MPa; in step S6, the atmospheric pressure plasma jet has a helium flow rate of 20 L / min and a power of 400 W.

[0054] According to a preferred embodiment of the present invention, the high-speed shearing machine is purchased from Cangzhou Yixuan Testing Instrument Co., Ltd., model GS-1.

[0055] According to a preferred embodiment of the present invention, the internal mixer is purchased from Xihua Machinery Technology (Dongguan) Co., Ltd. Model XH-401A.

[0056] According to a preferred embodiment of the present invention, the DBD plasma is purchased from Sichuan Zhiyan Technology Co., Ltd.

[0057] According to a preferred embodiment of the present invention, the twin-screw extruder is purchased from Xiamen Gangyuan Plastic Industry Co., Ltd.

[0058] According to a preferred embodiment of the present invention, the autoclave is purchased from Fang Ding Technology Co., Ltd.

[0059] According to a preferred embodiment of the present invention, the oven is purchased from Changzhou Qibao Drying Equipment Co., Ltd. and is model QB-01.

[0060] According to a preferred embodiment of the present invention, the atmospheric pressure plasma jet is generated by a SPA-2600 atmospheric plasma cleaning machine, which is purchased from Sindin.

[0061] In this method, bamboo fiber is pretreated with an ethanol solution of KH550 silane coupling agent to form -Si-O- bonds on its surface, allowing it to bind to polar groups in EVA via amino groups. Nanocellulose is then oxidized with TEMPO to introduce carboxyl groups (-COOH), which interact with the ester groups in the EVA. The two are premixed in a high-speed shearing machine to achieve the synergistic construction of a macroscopic (bamboo fiber) and microscopic (nanocellulose) reinforcement network, enhancing interfacial bonding strength.

[0062] In this method, a dielectric barrier discharge (DBD) plasma is activated during the banburying stage. High-energy electrons bombard the EVA surface, forming active free radical sites that promote a ring-opening reaction between the epoxy groups of the bio-based crosslinker DBX-200 and the EVA hydroxyl groups. Simultaneously, the plasma activates the surface of the hybrid flame-retardant filler (Mg(OH)2 / HNTs@PDA), strengthening hydrogen bonding with the matrix and reducing the risk of filler agglomeration. Zinc oxide reacts with the bio-based crosslinker DBX-200 to form a zinc complex. Combined with a banburying temperature of 115°C (lower than the 130-150°C of traditional processes), this reduces the crosslinking activation energy and energy consumption.

[0063] The present invention precisely controls the temperature by zoning: 105°C in zone one prevents premature recombination of dynamic imine bonds, 125°C in zone two promotes compatibility of plasticizer (ATBC / ECO) with EVA, 135°C in zone three optimizes melt fluidity, and 125°C in zone four stabilizes the cross-linked network; the lubricating effect of zinc stearate combined with twin-screw shear dispersion reduces the die pressure to 12MPa (traditional process>15MPa), reducing equipment wear; the present invention adopts supercritical CO2 gradient pressure relief foaming technology; through three-stage gradient pressure relief: the first stage (15→8MPa): uniform bubble nucleation is formed under high pressure; the second stage (8→3MPa): the medium pressure section stabilizes bubble growth; the third stage (3→normal pressure): the low pressure section suppresses bubble collapse; the closed cell rate is achieved ≥90% (traditional process ≤80%), thereby improving the material's cushioning performance and resilience.

[0064] This process achieves efficient and low-consumption preparation of environmentally friendly EVA materials through multi-level fiber dispersion, plasma-assisted cross-linking, gradient foaming and surface modification, and its overall performance is better than traditional processes.

[0065] The present invention also provides an application of the environmentally friendly EVA material in shoemaking.

[0066] The beneficial effects of the present invention are:

[0067] The environmentally friendly EVA material and preparation method provided by this invention achieves the synergistic optimization of environmental performance and material properties through multi-dimensional technological innovation. In terms of crosslinking system design, the bio-based dynamic crosslinker DBX-200 uses renewable raw materials to construct a dynamic imine bond network. This not only completely replaces traditional toxic peroxide crosslinkers and eliminates the formation of harmful byproducts, but its dynamically reversible properties also endow the material with excellent self-healing capabilities. Combined with the catalytic effect of the zinc-based activation system on the crosslinking reaction, the processing temperature threshold is significantly lowered, breaking through the high-temperature limitations of traditional processes and achieving energy conservation and consumption reduction.

[0068] In terms of reinforcing system construction, a multidimensional reinforcement network is formed through hierarchical modification of natural fibers. Silane coupling of bamboo fibers forms stable interfacial chemical bonds, while surface polarity modification of nanocellulose enhances the micromechanical interlocking effect. The synergistic effect of the two results in a breakthrough improvement in the material's mechanical properties. The flame retardant system innovatively utilizes a hybrid design of mineral fillers and bio-based coatings. Through the complementary mechanisms of gas-phase flame retardancy and condensed-phase flame retardancy, it improves flame retardancy efficiency while overcoming the negative effects of traditional flame retardants on mechanical properties. The plasticizing system, through structural regulation of bio-based molecules, establishes intermolecular stabilizing forces while maintaining flexibility, completely resolving the performance degradation caused by plasticizer migration.

[0069] At the manufacturing level, plasma-assisted activation technology enhances filler dispersion, combined with a precisely temperature-controlled twin-screw extrusion process to achieve coordinated regulation of melt fluidity and cross-linking networks. Innovative supercritical fluid gradient pressure relief foaming technology precisely controls cell morphology evolution, resulting in a highly uniform closed-cell structure. The post-processing phase utilizes a dual process of low-temperature curing and plasma surface modification, optimizing the integrity of the material's internal network while constructing a highly active surface interface layer, significantly enhancing the bond between the finished product and the shoe coating.

[0070] This technology system uses core innovations such as bio-based material substitution, interface functional modification, and multi-mechanism synergistic efficiency enhancement to fully realize the green and low-carbon preparation process while ensuring the material's high rebound, high cushioning, and high durability performance, providing the footwear industry with an innovative solution that is both eco-friendly and high-performance. DETAILED DESCRIPTION

[0071] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0072] 1. Implementation

[0073] Example 1

[0074] (1) Synthesis of bio-based dynamic crosslinker DBX-200: Dissolve 100 g of cardanol glycidyl ether and 35 g of furfurylamine in 200 mL of tetrahydrofuran, add 0.5 g of CuI catalyst, and react at 80°C under nitrogen for 8 hours. Remove the solvent by rotary evaporation to obtain a yellow viscous liquid.

[0075] (2) Natural fiber reinforced network treatment: Bamboo fiber: soaked in 5% KH550 ethanol solution at 60°C for 2 hours and dried to constant weight; Nanocellulose preparation: using TEMPO / NaClO oxidation method, bamboo pulp was dispersed in pH = 6.8 phosphate buffer, TEMPO and NaClO were added for oxidation for 3 hours, centrifuged, washed with water, ultrasonically dispersed and then freeze-dried.

[0076] (3) Preparation of hybrid flame retardant filler: Mg(OH)2 and HNTs were dispersed in a Tris-HCl buffer solution with a mass ratio of 3:1 at pH = 8.5, 5 wt% dopamine hydrochloride was added, magnetic stirring was performed for 24 h, centrifuged, dried and then ground.

[0077] (4) Mixing and extrusion:

[0078] S1: 20 g of bamboo fiber and 5 g of nanocellulose were added to a high-speed shearing machine (8000 rpm, 60 °C) and premixed for 10 min;

[0079] S2: 100 g EVA resin (EV45LX), 22 g bio-based plasticizer (acetylated tributyl citrate: epoxidized cashew oil 5:5), and 18 g hybrid flame retardant filler were added to an internal mixer and mixed for 10 min with DBD plasma (50 rpm, 115°C). 4.5 g bio-based dynamic crosslinker DBX-200, 2 g zinc oxide, 1.5 g zinc stearate, and 0.6 g antioxidant (Irganox 1010: PS802 = 2:1) were added and mixed for another 5 min.

[0080] S3: Twin-screw extrusion granulation (zone 1 105°C, zone 2 125°C, zone 3 135°C, zone 4 125°C), die head pressure 12 MPa;

[0081] Supercritical foaming: the pellets were placed in an autoclave, injected with supercritical CO2 (130°C, 15 MPa) for saturation for 40 min, and then depressurized in three stages (15 → 8 → 3 → 0 MPa, keeping warm for 3 / 2 min);

[0082] Post-treatment: The foamed body was cured at 80°C for 2 h, and the surface was treated with helium plasma jet (20 L / min, 400 W).

[0083] Example 2

[0084] The specific implementation method is the same as that of Example 1, except that the natural fiber reinforcement network content is adjusted to 30g (25g bamboo fiber, 5g nanocellulose); the hybrid flame retardant filler content is 20g (Mg(OH)2:HNTs=4:1); and the bio-based plasticizer content is 24g (acetylated tributyl citrate: epoxidized cashew oil=5:5).

[0085] Example 3

[0086] The specific implementation method is the same as Example 1, except that the content of the bio-based dynamic crosslinker DBX-200 is 5 g; the content of the hybrid flame retardant filler is 16 g (Mg(OH)2:HNTs=2:1); and the antioxidant is adjusted to 0.7 g (Irganox1010:PS802=2:1).

[0087] Comparative Example 1

[0088] The specific implementation method is the same as that of Example 1, except that the bio-based dynamic cross-linking agent DBX-200 is replaced by an equal amount of DCP (dicumyl peroxide); and the DBD plasma-assisted internal mixing is eliminated.

[0089] Comparative Example 2

[0090] The specific implementation method is the same as that of Example 1, except that the natural fiber reinforcement network is eliminated and replaced with an equal amount of calcium carbonate filler; and ordinary plasticizer DOP is used instead of bio-based plasticizer.

[0091] Comparative Example 3

[0092] The specific implementation method is the same as that of Example 1, except that the hybrid flame-retardant filler is replaced with an equal amount of ordinary Mg(OH)2; the supercritical CO2 gradient pressure relief is cancelled, and normal pressure foaming is adopted.

[0093] 2. Performance Testing

[0094] The environmentally friendly EVA materials for shoemaking prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following method:

[0095] 1. Environmental testing

[0096] (1) Biobased content test

[0097] Method: ASTM D6866 was used to analyze the biobased carbon content of the materials using radioactive carbon isotopes (14C). Procedure: The samples were crushed and burned to generate CO2. The 14C / 12C ratio was measured using an accelerator mass spectrometer to calculate the biobased carbon percentage.

[0098] (2) VOC emission test

[0099] Methods: According to GB / T 29899-2013, a closed environment was simulated using a climate chamber method (temperature 23°C, humidity 50%, air exchange rate 0.5 times / h). Gas was collected using an adsorption tube and volatile organic compounds (VOCs) such as benzene, aldehydes, and ketones were quantitatively analyzed by GC-MS.

[0100] 2. Mechanical strength test

[0101] (1) Tensile strength and elongation at break

[0102] Methods: According to GB / T 1040.3-2006, dumbbell-shaped specimens were stretched at a rate of 500 mm / min using a universal material testing machine until fracture, and the maximum load and gauge length change were recorded.

[0103] Calculation: Tensile strength = maximum force / (specimen width × thickness), elongation at break = (gauge length at break - initial gauge length) / initial gauge length × 100%.

[0104] 3. Flame retardancy test

[0105] (1) Limiting oxygen index (LOI)

[0106] Method: According to GB / T 2406.2-2009, the sample was fixed vertically in a combustion tube, nitrogen and oxygen mixed gas was introduced, and the minimum volume fraction of oxygen required for the material to self-extinguish was determined.

[0107] (2) UL94 vertical burning rating

[0108] Procedure: The specimen (125 mm × 13 mm × 3 mm) was fixed vertically and the flame was kept in contact with the bottom for 10 seconds before removal.

[0109] Record the afterflame time and whether the molten droplets ignite the absorbent cotton to determine the V-0 / V-1 / V-2 grade.

[0110] (3) Smoke density test

[0111] Method: Use a smoke density chamber (ASTM E662) to burn the sample and measure the specific optical density (Ds) by the light attenuation method.

[0112] 4. Foaming process performance test

[0113] (1) Closed-cell ratio

[0114] Method: According to GB / T 20876-2007, the apparent density (ρ_a) and true density (ρ_t) of the foam were measured using a true density meter, and the closed cell ratio was calculated as (1-ρ_a / ρ_t)×100%.

[0115] (2) Rebound rate

[0116] Procedure: According to ASTM D3574, the foam is compressed to 50% deformation and maintained for 22 hours. After release, the residual deformation is measured. Resilience = (initial thickness - residual deformation) / initial thickness × 100%

[0117] 5. Test results of various properties of EVA materials:

[0118] Table 1: Performance test results of various embodiments and comparative examples

[0119]

[0120] As can be seen from Table 1, Examples 1-3 reduce VOC emissions to 0.8-1.1 mg / m² by using bio-based dynamic cross-linking agents (bio-based carbon content 78-82%) and dopamine-coated flame retardant technology. 3 (Comparative Example 3 is 3.8 mg / m 3 ), meeting the A+ environmental protection standard of GB / T29899-2013, and the biobased content increased by 73%-82% compared to Comparative Example 3 (45%), meeting the EU EN16785-1 certification requirements. In terms of mechanical properties, the tensile strength (17.8-19.2 MPa) and elongation at break (460-485%) of the examples were increased by 42%-54% and 64%-73% respectively compared to Comparative Example 3 (12.5 MPa, 280%). This is due to the enhanced interfacial bonding strength of the bamboo fiber-nanocellulose interlocking network. Comparative Example 3, due to the lack of fiber reinforcement, has a decreased dynamic fatigue life and significant interface delamination. In terms of flame retardancy, the Example uses a Mg(OH)2 / HNTs hybrid system to achieve an LOI value of ≥33% and a UL94 V-0 rating. During combustion, a 200μm continuous char layer is formed to suppress molten droplets. In contrast, Comparative Example 3 only achieves an LOI of 26% and a UL94 V-2 rating due to the uneven dispersion of ordinary flame retardants, and the molten droplets ignite the absorbent cotton. During the foaming process, the Example uses supercritical CO2 gradient pressure relief technology to increase the closed cell ratio to 88%-92% (Comparative Example 3 is 65%) and the rebound rate to 87%-91% (Comparative Example 3 is only 60%). The cell size is uniformly distributed between 50-150μm. Comparative Example 3, however, suffers from cell rupture and high density due to normal pressure foaming. In summary, the Example's innovations in bio-based substitution, fiber reinforcement, flame retardant synergy, and gradient foaming process systematically address the technical bottlenecks of traditional EVA shoe materials in terms of environmental protection, mechanical strength, flame retardant efficiency, and foaming uniformity.

[0121] The above-described embodiments merely illustrate several implementations of the present invention. 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 a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. An environmentally friendly EVA material, characterized in that: The material consists of the following components: EVA resin, bio-based dynamic crosslinker DBX-200, natural fiber reinforcement network, hybrid flame retardant filler, bio-based plasticizer, zinc oxide, zinc stearate and antioxidant; In the material, relative to 100 parts by weight of the EVA resin, the content of the bio-based dynamic crosslinker DBX-200 is 4-5 parts by weight, the content of the natural fiber reinforced network is 20-30 parts by weight, the content of the hybrid flame retardant filler is 16-20 parts by weight, the content of the bio-based plasticizer is 20-24 parts by weight, the content of the zinc oxide is 1-3 parts by weight, the content of the zinc stearate is 1-2 parts by weight, and the content of the antioxidant is 0.5-0.7 parts by weight; The bio-based dynamic crosslinker DBX-200 is obtained by reacting cardanol glycidyl ether, furfurylamine, and CuI catalyst.

2. The environmentally friendly EVA material according to claim 1, wherein: The reaction steps include: dissolving 100 parts by weight of cardanol glycidyl ether and 35 parts by weight of furfurylamine in tetrahydrofuran, adding 0.5 parts by weight of CuI catalyst for reaction, and removing the solvent by rotary evaporation.

3. The environmentally friendly EVA material according to claim 1, wherein: The natural fiber reinforcement network consists of bamboo fiber and nanocellulose; the bamboo fiber is soaked in a coupling agent KH550 and an ethanol solution and then dried; and the nanocellulose is prepared by a TEMPO / NaClO oxidation method.

4. The environmentally friendly EVA material according to claim 1, wherein The hybrid flame retardant filler is prepared by the following steps: dissolving Mg(OH)2 and HNTs in a Tris-HCl buffer solution with a pH of 8.5, adding dopamine hydrochloride, stirring, centrifuging and drying.

5. The environmentally friendly EVA material according to claim 1, wherein The bio-based plasticizer consists of acetylated tributyl citrate and epoxidized cashew nut oil, and the mass ratio of the acetylated tributyl citrate to the epoxidized cashew nut oil is 5:

5.

6. The environmentally friendly EVA material according to claim 1, wherein: The antioxidant consists of Irganox 1010 and PS802, and the mass ratio of Irganox 1010 to PS802 is 2:

1.

7. The method for preparing the environmentally friendly EVA material according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Add bamboo fiber and nanocellulose into a high-speed shearing machine and premix them; S2. Add EVA, plasticizer, and hybrid filler to an internal mixer, turn on DBD plasma, and mix at 115°C for 10 minutes; then add bio-based dynamic crosslinker DBX-200, zinc oxide, and zinc stearate in sequence, and continue mixing for 5 minutes. S3. Twin-screw extrusion granulation: Use a co-rotating twin-screw extruder, zone temperature: zone 1 105℃, zone 2 125℃, zone 3 135℃, zone 4 125℃, die head pressure 12MPa; S4, the pellets are placed in an autoclave and supercritical CO2 is injected for 40 minutes; S5, three-stage pressure release: first stage: 15MPa→8MPa, keep warm for 3 minutes; second stage: 8MPa→3MPa, keep warm for 2 minutes; third stage: 3MPa→normal pressure to obtain foamed embryo; S6. The foamed body is cured in a hot air oven at 80°C for 2 hours; and the surface is treated with an atmospheric pressure plasma jet.

8. The method for preparing the environmentally friendly EVA material according to claim 7, characterized in that: In step S1, the speed of the high-speed shearing machine is 8000 rpm, the temperature is 60° C., and the premixing time is 10 min; in step S2, the speed of the internal mixer is 50 rpm.

9. The method for preparing the environmentally friendly EVA material according to claim 7, characterized in that: In step S4, the temperature of the supercritical CO2 is 130°C and the pressure is 15 MPa; in step S6, the atmospheric pressure plasma jet has a helium flow rate of 20 L / min and a power of 400 W.

10. An application of the environmentally friendly EVA material according to any one of claims 1 to 6, characterized in that: Application of the environmentally friendly EVA material in shoemaking.

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