Recyclable foaming sole material and preparation method thereof

Abstract

The invention discloses a recyclable foaming sole material and a preparation method thereof, and belongs to the technical field of footwear products. The preparation method comprises the following steps: providing the thermally reversible functional master batch; and blending the thermally reversible functional master batch with a polymer, a cross-linking agent and an auxiliary agent to obtain a blended material, and foaming to obtain the recoverable foamed sole material, the blended material is prepared from the following components in parts by weight: 15 to 40 parts of thermally reversible functional master batch, 30 to 55 parts of ethylene-vinyl acetate copolymer, 5 to 20 parts of polyolefin elastomer, 5 to 20 parts of olefin block copolymer, 0 to 20 parts of thermoplastic polyurethane, 2 to 6 parts of maleic anhydride grafted EVA (Ethylene Vinyl Acetate), 0.3 to 0.5 part of cross-linking agent and 0.5 to 1.5 parts of stearic acid. According to the method, defective products / material heads / material tails / leftover materials of the foamed shoe soles can be recycled, the adding proportion of the treated waste materials in the foamed shoe soles is high, the performance of the shoe soles is kept good, and high recycling value is achieved.

Description

Technical Field

[0001] This invention relates to the field of footwear technology, and in particular to a recyclable foamed sole material and its preparation method. Background Technology

[0002] Of the shoes newly produced globally each year, approximately 90% end up in landfills or incineration, making recycling difficult. Simultaneously, the production process of foamed soles generates significant material losses, such as defective soles and scrap material, accounting for about 20% of the total number of foamed soles produced. Currently, foamed soles for athletic shoes are primarily made from a combination of petrochemical products, such as ethylene vinyl acetate copolymer (EVA), POE, EPDM, OBC, SEBS, PE, TPU, TPEE, PEBAX, BIIR, and NR. These chemical polymers are refined and then polymerized from petrochemical raw materials. The large amounts of carbon dioxide released into the atmosphere after the combustion or incineration of footwear contribute to global warming. Furthermore, these plastic products are all high polymers; due to their high degree of polymerization and strong intermolecular forces, the polymer chains are difficult to break down and decompose, making them non-degradable. The large quantities of these discarded products create "white pollution." Petroleum is a non-renewable resource on Earth; the more these petrochemical products are used, the faster petroleum resources will be depleted. To reduce carbon dioxide emissions, mitigate the deteriorating impact of petrochemical products on the ecological environment, and alleviate oil shortages and depletion, the development of recyclable foamed shoe soles is an inevitable trend.

[0003] To better recycle defective EVA foam soles, scraps, and offcuts, current technologies typically involve crushing or pulverizing them before adding them directly to the sole formulation in a specific ratio. However, this approach has a drawback: because the EVA waste or foam sole has already undergone chemical cross-linking, it cannot be re-plasticized and melted. The larger the amount added, the more it negatively impacts the final performance of the foam sole. Ultimately, foam soles with added recycled materials can only be used in low-end / low-performance products, significantly limiting their application. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a recyclable foamed shoe sole material and its preparation method. This invention enables the recycling of defective foamed shoe soles, including scraps, offcuts, and waste materials. Furthermore, the proportion of processed waste materials added to the foamed shoe sole is relatively high, maintaining good shoe sole performance and possessing high recycling value, which helps reduce resource waste.

[0005] This invention provides a method for preparing recyclable foamed shoe sole material, comprising the following steps:

[0006] Provide thermally reversible masterbatch;

[0007] The thermally reversible functional masterbatch is blended with polymers, crosslinking agents and additives to obtain a blended material, which is then foamed to obtain a recyclable foamed shoe sole material.

[0008] By weight, the blended materials comprise: 15-40 parts of thermally reversible functional masterbatch, 30-55 parts of ethylene-vinyl acetate copolymer, 5-20 parts of polyolefin elastomer, 5-20 parts of olefin block copolymer, 0-20 parts of thermoplastic polyurethane, 2-6 parts of maleic anhydride-grafted EVA, 0.3-0.5 parts of crosslinking agent, 0.5-1.5 parts of stearic acid, 0-4 parts of foaming agent, and 0-1.5 parts of zinc oxide.

[0009] This invention prepares a recyclable foamed shoe sole material with thermally reversible crosslinking function, which has a high recycling rate. The thermally reversible crosslinking functionalization enables the recycling of defective foamed shoe soles, scraps, and offcuts. Furthermore, the proportion of treated waste material added to the foamed shoe sole can be increased to 50%, while maintaining ≥80% of the various performance characteristics of the shoe sole.

[0010] In this embodiment of the invention, a thermally reversible functional masterbatch is first prepared by grafting and crosslinking high-vinyl-content hydrogenated styrene elastomer, high-ENB-content EPDM, trans-polyisoprene with norbornene, polyethylene glycol dinorbornene, and 2,4-di-tert-butylperoxide in a twin-screw high-temperature melting reactor. The thermally reversible functional groups of norbornene and polyethylene glycol dinorbornene then undergo a Diels-Alder reaction.

[0011] Preferably, the thermally reversible functional masterbatch is synthesized according to the following operation: 10-30 parts by weight of hydrogenated styrene elastomer, 10-30 parts by weight of EPDM, 40-60 parts by weight of trans-polyisoprene, 1-10 parts by weight of norbornene, 0.5-5 parts by weight of polyethylene glycol dinorbornene, and 0.5-1 parts by weight of 2,4-di-tert-butylperoxide isopropylbenzene are mixed in a twin-screw high-temperature melting equipment and subjected to a graft crosslinking reaction. The processing temperature is set to 120-150°C, and then extruded to obtain the masterbatch; the EPDM is copolymerized from ethylene, propylene, and ethylene-bis(norbornene).

[0012] Preferably, in the synthesis of the thermally reversible functional masterbatch, the hydrogenated styrene elastomer is copolymerized from styrene and butadiene, and has a glass transition temperature of 18~22℃; the EPDM has an ethylene-bis(norbornene) content greater than 5%, which can be 6~8%; and the trans-polyisoprene has a melting point of 50~70℃.

[0013] Regarding the composition of the thermally reversible functional masterbatch, the embodiments of the present invention select polymers containing double bonds, such as SOE with high vinyl content, EPDM with high ENB content, and trans-polyisoprene. The SOE with high vinyl content can be present in parts by weight of 10, 20, or 30; it is a novel hydrogenated styrene elastomer copolymerized from styrene, 1,2-butadiene, and 1,4-butadiene. In its molecular structure, the side groups of the 1,2-butadiene structure are vinyl groups, and these vinyl groups contain unsaturated C=C double bonds. Higher vinyl content facilitates cross-linking reactions. Simultaneously, the glass transition temperature of SOE is around 20°C, which is beneficial for improving the shock absorption performance of the foamed material. In some embodiments, the preferred hydrogenated styrene elastomer is SOE L609 (Asahi Kasei Corporation, hardness 61A).

[0014] In the aforementioned formulation, EPDM is copolymerized from ethylene, propylene, and a third monomer, wherein the third monomer is ethylene-neobornene (ENB), and its weight parts can be 10 parts, 20 parts, or 30 parts. Its structure also contains moderately unsaturated C=C double bonds; the higher the ENB content, the easier it is to produce a cross-linking reaction. A higher ENB content results in a higher degree of cross-linking, which is more beneficial for improving the strength of the network structure, thereby enhancing the compressive properties of the foamed material. In some embodiments, the preferred variety is EPDM 5565 (Dow Chemical Company, ENB content 7.5%).

[0015] The trans-polyisoprene can be present in parts by weight of 40, 50, or 60. Its main chain structure contains unsaturated C=C double bonds, and the trans-1,4 structure content can be above 98%. It has high crystallinity, high chain regularity, a glass transition temperature of -70 to -50°C, and a melting point of 50 to 70°C. The trans-chain segments of trans-polyisoprene readily fold and crystallize at room temperature. When uncured, it is a thermoplastic. Trans-1,4-polyisoprene contains a large number of double bonds. During moderate curing and crosslinking, the chain segments between the crosslinking points can still undergo thermal motion and crystallization, exhibiting a crystalline network structure polymer, i.e., possessing thermo-elastic elastomer properties. When curing reaches a critical crosslinking density, it becomes an amorphous crosslinked network. In some embodiments, the preferred trans-polyisoprene variety is TP301 (Kuraray Corporation, hardness 95A).

[0016] The norbornene enediic anhydride can be present in parts of 1, 5, 6, or 10 by weight. It is an important acid anhydride reagent that can react with nucleophiles such as alcohols and amines to form corresponding esters, amides, and other compounds. Norbornene enediic anhydride is a weak acid, but appropriate acid / base catalysts and reaction conditions can promote the reaction.

[0017] The aforementioned polyethylene glycol dinorbornene is a block copolymer composed of two norbornene units and one polyethylene glycol (PEG) structural unit alternately linked together. The ultra-high reactivity of the norbornene moiety enhances the reaction between the PEG segment and other functional groups. In some embodiments, the PEG dinorbornene can be present in parts by weight of 0.5 parts, 0.7 parts, or 1 part, and its molecular weight can be 20,000; it is also a commercially available product.

[0018] In embodiments of the present invention, with the assistance of the peroxide initiator 2,4-di-tert-butylperoxide, the C=C double bonds in the above three unsaturated polymers are all conducive to grafting with the anhydride groups of norbornene at high temperatures. The grafted anhydride decomposes into carboxyl groups, which then undergo esterification addition with the hydroxyl groups in polyethylene glycol dinorbornene, thereby crosslinking the linear molecular chains of the grafted polymer into a three-dimensional network structure and forming DA thermally reversible crosslinking bonds. Under high-temperature conditions, the thermally reversible crosslinking bonds undergo a reverse DA reaction, thereby decrosslinking the thermally reversible crosslinking network and imparting a certain degree of thermoplasticity to the thermally reversible masterbatch. When the temperature decreases, the material undergoes a DA reaction again, realizing the recrosslinking of the polymer. Therefore, the aforementioned thermally reversible functional masterbatch maintains a crosslinked state at room temperature and decrosslinks at a heat treatment temperature of 170°C, exhibiting thermoplasticity and enabling repeated processing.

[0019] In this embodiment of the invention, the above-mentioned raw materials are mixed evenly using a high-speed mixer (e.g., 2000 rad / min for 5 min). The resulting mixture is poured into the feed trough of a twin-screw granulator. The temperatures of the first, second, third, and fourth zones are preferably set to 120, 130, 140, and 150°C, respectively. The screw speed is adjusted to 50-60 rpm, and the cutting speed is adjusted to 15-20 rpm. Graft crosslinking is carried out under high-temperature melting, and then granulation is performed to prepare a thermally reversible functional masterbatch.

[0020] In some embodiments, by adjusting the selection of 10-30 parts of SOE with high vinyl content, 10-30 parts of EPDM with high ENB content, 40-60 parts of trans-polyisoprene TPI, 1-10 parts of norbornene, 0.5-5 parts of polyethylene glycol dinorbornene, and 0.5-1 parts of 2,4-di-tert-butyl peroxide, thermally reversible functional masterbatches with different hardnesses can be obtained, such as those with a hardness of 60-81A.

[0021] After obtaining the thermally reversible functional masterbatch, this embodiment of the invention blends it with materials such as EVA / POE / OBC / TPU. The resulting blend is then foamed to obtain a recyclable foamed shoe sole material with thermally reversible crosslinking function. The thermally reversible functional masterbatch comprises 15-40 parts by weight, and the ethylene-vinyl acetate copolymer comprises 30-55 parts by weight. This invention mainly utilizes thermally reversible crosslinking technology to introduce thermally reversible groups capable of undergoing the Diels-Alder reaction into the formulation, thereby facilitating the thermally crosslinking of the foamed material at a certain temperature and achieving thermally de-crosslinking at another temperature.

[0022] Preferably, in the blended material, the VA content of the ethylene vinyl acetate copolymer (EVA) is 18-40% by mass; the hardness of the polyolefin elastomer (POE) is 60-84A; the hardness of the olefin block copolymer (OBC) is 60-80A; and the hardness of the thermoplastic polyurethane (TPU) is 80-95A.

[0023] In embodiments of the present invention, the EVA has good resilience properties, and preferably commercially available varieties include: EVA 7470M (Formosa Plastics Corporation, VA content 26%) and EVA 33121 (Taiwan Polymer Corporation, VA content 33%). For example, the EVA is provided in quantities of 30 parts, 40 parts, and 55 parts.

[0024] In the preferred formulation of this invention, 5-20 parts of POE, 5-20 parts of OBC, and 5-20 parts of TPU are used. POE is short for polyolefin elastomer, whose main component is ethylene-octene copolymer, exhibiting excellent toughness and processability. A preferred commercially available variety is POE 8003 (Dow Chemical, hardness 84A), which can be 10 or 15 parts by weight. Meanwhile, OBC material, namely ethylene-octene block copolymer, has good heat resistance and resilience. Specifically, OBC can be 10 or 15 parts by weight, with a preferred commercially available variety being OBC 9107 (Dow Chemical, hardness 60A).

[0025] The TPU preferably includes aliphatic polyester polyurethane with a hardness of 80-95A, and the preferred variety is FPX303B (Lubrizol, hardness 88A); its weight parts can be 5 parts or 10 parts.

[0026] Preferably, in the blend, the grafting rate of the maleic anhydride-grafted EVA is ≥2%; the crosslinking agent is a peroxide crosslinking agent. Further, the maleic anhydride-grafted EVA includes brands with a grafting rate ≥2%, with Fusabond C250 (Dow Chemical Company, grafting rate 0.5-1%) being a preferred variety. The peroxide crosslinking agent includes one of dicumyl peroxide and 1,4-di-tert-butylperoxyisopropylbenzene (BIBP), with BIBP being a preferred variety.

[0027] Preferably, the foaming is a chemical foaming method, and the blended material includes: 1-3.5 parts of foaming agent and 0.5-1 parts of zinc oxide; the foaming agent is an azo foaming agent and / or bicarbonate. Further, embodiments of the present invention employ a chemical foaming IP injection molding process or MD molding process, selecting either azodicarbonamide or sodium bicarbonate as the foaming agent; a preferred variety is AC 808 (azodicarbonamide).

[0028] See Figure 1 The implementation steps of the IP (Injection Molding) process in this embodiment of the invention are described below:

[0029] ① Weighing: Based on the dosage of the formula, BIBP and foaming agent can be weighed as the first group; stearic acid and zinc oxide can be weighed as the second group; EVA / POE / OBC / TPU / Fusabond C250 / thermally reversible functional masterbatch can be weighed as the third group.

[0030] ② Mixing: First, pour the third batch of material into the internal mixer and turn on the machine. When the temperature rises to 90-100℃, pour in the second batch of material. When the temperature rises to 100-110℃, pour in the third batch of material. When the temperature rises to 120-130℃, pour out the mixed material.

[0031] ③ Material preparation: Pour the mixed material into the material preparation machine. The temperatures of the first, second, third, and fourth zones can be adjusted to 90, 95, 100, and 105℃ respectively. Adjust the screw speed to 40-50 rpm and the cutting speed to 15-20 rpm.

[0032] ④ Foaming: Pour the prepared material into the injection foaming molding machine. The temperatures of the first, second, third, and fourth feeding zones can be adjusted to 95, 100, 105, and 110℃ respectively. The temperatures of the upper and lower mold plates should be adjusted to 175±3℃ and 175±3℃ respectively. Set the material quantity according to the mold requirements (mold size 18cm*10cm*1cm, material quantity can be set to 90±10g based on foaming ratio 1.9±0.05), injection time to 20±5 seconds, and vulcanization foaming time to 600±30 seconds.

[0033] ⑤ Baking: The temperatures of the first, second, third, and fourth zones of the warm oven can be adjusted to 80, 90, 95, and 100℃ respectively, with a rotation speed of 60 rad / min; the foamed material is fed into the oven opening, and the oven length should be 30 meters; the baking time from start to finish should be 40 minutes, and finally a shoe sole with various properties that meet the requirements of foamed midsoles for sports shoes is produced.

[0034] See Figure 2 The implementation steps of the MD (secondary molding) process in this embodiment of the invention are described as follows:

[0035] The processes of ① weighing, ② mixing, and ③ granulation are consistent with those of the IP process ①, ②, and ③.

[0036] ④ Small foaming: Pour the prepared granules into a flat mold for small foaming to complete the first foaming. The foaming temperature is 173±2℃ and the foaming time is 450±30 seconds.

[0037] ⑤ Molding: After the small foamed semi-finished product has cooled for 24 hours, it is pressed into a flat molding die to complete the molding of the finished product. The hot pressing temperature is 173±2℃ and the hot pressing time is 420±20 seconds; the cooling water temperature is 25±2℃ and the cooling time is 420±20 seconds.

[0038] Preferably, the foaming is a supercritical physical foaming method using nitrogen or carbon dioxide, and the blended material does not contain a foaming agent. More preferably, the supercritical physical foaming process uses nitrogen (N2) or CO2, more preferably N2.

[0039] See Figure 3 The implementation steps of the supercritical physical foaming process in this embodiment of the invention are described below:

[0040] ① Weighing materials: Based on the dosage of the formula, weigh BIBP as the first group; weigh stearic acid and zinc oxide as the second group; weigh the remaining materials EVA / POE / OBC / TPU / SEBS / Fusabond C250 / thermal reversible functional masterbatch as the third group.

[0041] The processes of ② mixing and ③ granulation are consistent with those of IP process ② and ③.

[0042] ④IP Injection Preform: Pour the prepared granules into the injection foaming molding machine. The temperatures of the first, second, third, and fourth feeding zones can be adjusted to 95, 100, 105, and 110℃ respectively. The temperatures of the upper and lower mold plates can be adjusted to 175±3℃ and 175±3℃ respectively. Set the material quantity according to the mold requirements (mold size 18cm*10cm*1cm, based on a foaming ratio of 1.9±0.05, the material quantity can be set to 90±10g). The injection time is 20±5 seconds, and the vulcanization time is 330±30 seconds. Then, remove the shoe sole preform.

[0043] ⑤ Supercritical foaming under pressure: Place the small rough blank into a supercritical physical foaming tank under pressure, N2 pressure 15~30MPa, foaming temperature 110~155℃, heat preservation and pressure holding time 60~120min, then depressurize, take out the foamed shoe sole, and cool to room temperature.

[0044] ⑥ Molding: Let the supercritical foamed semi-finished product stand and cool for 24 hours, then put it into a flat molding die to complete the molding of the finished product; the hot pressing temperature is 173±2℃, the hot pressing time is 420±20 seconds; the cooling water temperature is 25±2℃, the cooling time is 420±20 seconds, and the product is obtained.

[0045] This invention provides a recyclable foamed shoe sole material, prepared by the preparation method described above; the recyclable foamed shoe sole material has a resilience rate of 58-66% and exhibits good performance.

[0046] Preferably, the foamed sole material is prepared from recycled powder to make EVA foamed soles. It can be processed by a high-speed pulverizer to form sole powder with a particle size of 800-1000 mesh, which is used in EVA-based foaming formulations.

[0047] Preferably, the amount of recycled shoe sole material powder added to the EVA foamed shoe sole is 20-50 parts by weight. The preparation of the recycled EVA shoe sole foam can be carried out using one of the following processes: IP (injection molding), MD (medium-time molding), or supercritical physical foaming (without adding AC foaming agent to the formula). In some embodiments, the main matrix is ​​EVA / POE, but OBC / TPU, etc., can also be added. The recycling process of this invention is simple, the cost is low, and it is conducive to mass production. This invention can add 50 parts of the shoe sole powder from the embodiments, and the final foamed shoe sole maintains more than 80% of the various properties compared to the formula without added shoe sole recycled powder, with minimal impact on performance.

[0048] Through technological innovations such as formulation, this invention enables the recycling of defective foamed shoe soles, including scraps, offcuts, and waste materials. Furthermore, the proportion of processed waste materials added to the foamed shoe sole is relatively high, maintaining good sole performance, resulting in high recycling value and environmental friendliness, and significantly reducing resource waste. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the IP process steps for the preparation and realization of foamed shoe sole materials in some embodiments;

[0050] Figure 2 This is a schematic diagram of the MD process steps for the preparation and realization of foamed shoe sole materials in some embodiments;

[0051] Figure 3 This is a schematic diagram of the supercritical physical foaming process for preparing and realizing foamed shoe sole materials in some embodiments. Detailed Implementation

[0052] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0053] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention. The substances used in the embodiments of this invention are commercially available, except that the thermally reversible functional masterbatch is self-made.

[0054] Preparation of thermally reversible functional masterbatches: SOE L609, EPDM 5565, TP 301, norbornene, polyethylene glycol dinorbornene, and 2,4-di-tert-butyl peroxide were mixed evenly using a high-speed mixer (2000 rad / min, 5 min), as shown in the following formulation (preparing functional masterbatches A / B / C / D / E / F respectively). The mixture was poured into the feed trough of a twin-screw granulator. The temperatures of the first, second, third, and fourth zones were set to 120, 130, 140, and 150℃ respectively, and the screw speed was adjusted to 50-60 rpm and the cutting speed to 15-20 rpm. Graft crosslinking was performed under high-temperature melting, followed by granulation to prepare thermally reversible functional masterbatches.

[0055] Table 1. Formulation and performance of thermally reversible functional masterbatch

[0056]

[0057] The sources of each raw material are as follows:

[0058] SOE L609: Hardness 61A, tensile strength 26MPa, elongation 640%, Asahi Kasei Corporation.

[0059] EPDM 5565: ENB content 7.5%, Mooney viscosity 65 (ML 1+4 / 125℃), molecular weight 200,000, Dow Chemical Company.

[0060] TP 301: Hardness 95A, tensile strength 29MPa, elongation 450%, melting point 67℃, glass transition temperature -68℃, Kuraray Corporation.

[0061] Norborneol olefinic anhydride: molecular weight 164.158, white crystalline powder, Hubei Shineng Chemical Technology Co., Ltd.

[0062] Polyethylene glycol dinorbornene: molecular weight 20,000, Xi'an Kaixin Biotechnology Co., Ltd.

[0063] The performance test data above shows that by adjusting the selection of SOE with high vinyl content (10-30 parts), EPDM with high ENB content (10-30 parts), trans-polyisoprene (TPI) (40-60 parts), norbornene (1-10 parts), polyethylene glycol dinorbornene (0.5-5 parts), and 2,4-di-tert-butyl peroxide (0.5-1 parts), thermally reversible functional masterbatches with different hardness can be obtained.

[0064] In this study, by fixing the amounts of norbornenic anhydride and polyethylene glycol dinorbornene and adjusting the ratio of SOE / EPDM / TPI, the final performance of the functional masterbatch depends on the original performance data of the three materials. With a fixed SOE / EPDM / TPI ratio and adjusted amounts of norbornenic anhydride and polyethylene glycol dinorbornene, a higher addition amount results in a stronger grafting reaction, higher crosslinking strength, and is more conducive to crosslinking into a three-dimensional network structure. This leads to higher hardness and tensile strength in the functional masterbatch, but a slight decrease in elongation. Considering all factors, the preferred amounts are 1-10 parts of norbornenic anhydride and 0.5-5 parts of polyethylene glycol dinorbornene.

[0065] Example 1

[0066] ① Weighing: Based on the dosage of the formula in Table 2, weigh BIBP and foaming agent as the first group; weigh stearic acid and zinc oxide as the second group; weigh EVA / POE / OBC / TPU / Fusabond C250 / thermally reversible functional masterbatch as the third group.

[0067] ② Mixing: First, pour the third batch of material into the internal mixer and turn on the machine. When the temperature rises to 90-100℃, pour in the second batch of material. When the temperature rises to 100-110℃, pour in the third batch of material. When the temperature rises to 120-130℃, pour out the mixed material.

[0068] ③ Material preparation: Pour the mixed material into the material preparation machine. Adjust the temperatures of the first, second, third, and fourth zones to 90, 95, 100, and 105℃ respectively. Adjust the screw speed to 40-50 rpm and the cutting speed to 15-20 rpm.

[0069] ④ Foaming: Pour the prepared material into the injection foaming molding machine. Adjust the temperatures of the first, second, third, and fourth feeding zones to 95, 100, 105, and 110℃ respectively. Adjust the temperatures of the upper and lower mold plates to 175±3℃ and 175±3℃ respectively. Set the material quantity according to the mold requirements (mold size 18cm*10cm*1cm, based on a foaming ratio of 1.9±0.05, the material quantity can be set to 90±10g), the injection time to 20±5 seconds, and the vulcanization foaming time to 600±30 seconds.

[0070] ⑤ Baking: Set the temperatures of the first, second, third, and fourth zones of the warm oven to 80, 90, 95, and 100℃ respectively, and the rotation speed to 60 rad / min; send the foamed material into the oven opening, and select an oven length of 30 meters; the baking time from start to finish is 40 minutes to obtain the foamed shoe sole material, the properties of which are shown in Table 3.

[0071] Examples 2-8

[0072] Following the steps of Example 1, thermally reversible functional masterbatches of different hardness or proportions were added to obtain foamed shoe sole materials. The formulation composition is shown in Table 2, and the material properties are shown in Table 3.

[0073] Comparative Example 1

[0074] Following the implementation steps of Example 1, without adding thermally reversible functional masterbatch, foamed shoe sole material is obtained.

[0075] Table 2. Formulation composition of Examples 1-8 and Comparative Example 1

[0076]

[0077] Table 3 Material properties of Examples 1-8 and Comparative Example 1

[0078]

[0079] The sources of each raw material are as follows:

[0080] EVA 7470M: Hardness 82A, VA content 26%, tensile strength 16.2MPa, elongation 756%, Formosa Plastics Corporation.

[0081] POE 8003: Hardness 84A, tensile strength 18.2MPa, elongation 640%, Dow Chemical Company.

[0082] OBC 9107: Hardness 60A, tensile strength 5.1MPa, elongation 600%, Dow Chemical Company.

[0083] TPU FPX303B: Hardness 88A, tensile strength 18MPa, elongation 730%, Lubrizol Corporation.

[0084] Fusabond C250 is a modified copolymer of ethylene-vinyl acetate-maleic anhydride with a grafting rate of 0.5-1%, a hardness of 84A, a tensile strength of 11.4 MPa, and an elongation of 660%. It is manufactured by Dow Chemical Company.

[0085] BIBP: AkzoNobel.

[0086] Foaming agent AC 808: Hangzhou Haihong Fine Chemical Co., Ltd.

[0087] Stearic acid: Dukuda, Indonesia.

[0088] ZnO 997: Baishi brand zinc oxide, Hongbai Chemical Technology Co., Ltd.

[0089] Self-made thermally reversible functional masterbatches A / B / C / D / E / F were blended and foamed with polymers such as EVA / POE / OBC / TPU to prepare shoe soles with properties meeting the requirements for foamed midsoles in athletic shoes. When the amount of EVA / POE / OBC / TPU added was fixed, the various properties differed depending on the thermally reversible functional masterbatches A / B / C / D / E / F. Masterbatch A was beneficial for improving the rebound and compression performance of the foamed shoe sole, while masterbatch C was beneficial for improving the shock absorption, delamination tear, and tensile properties. Adjusting the amount of masterbatch C added between 15-40 parts, with increasing addition, the shock absorption performance further improved, but the rebound performance decreased somewhat. Considering all performance aspects, the optimal addition amount for each masterbatch was 15-40 parts.

[0090] Recycling Example 1-17

[0091] The process is the same as in the examples, using IP process; the formulation and product performance are as follows (material performance testing is as described above).

[0092] Table 4 Formulation of Recovery Examples 1-9 of the Present Invention

[0093]

[0094] Table 5 Material properties of recycled examples 1-9 of the present invention

[0095]

[0096] Table 6. Formulation composition of recovery examples 10-17 and comparative example 2 of the present invention.

[0097]

[0098] Table 7 Material properties of Recycled Examples 10-17 and Comparative Example 2 of the present invention

[0099]

[0100] Note: Examples 1'-8' and Comparative Example 1' above are examples in which the powder (particle size of 800-1000 mesh) obtained by crushing the foamed shoe soles of Examples 1-8 and Comparative Example 1 is added to the recycling example.

[0101] A comparison of the test data from recycled examples 1-6 and 9 shows that: when foaming was performed with a fixed ratio of EVA / POE / sample example sole powder or comparative example 1 sole powder of 35:15:50, the addition of 50 parts of sample example sole powder resulted in a foamed sole whose performance remained above 80% of the original formula, with minimal impact on overall performance. However, the addition of 50 parts of comparative example 1 sole powder significantly worsened the performance of the foamed sole compared to the formula without recycled sole powder, in terms of rebound, compression, shock absorption, delamination, and tensile strength.

[0102] A comparison of the test data from recycling examples 3, 7, and 8 shows that the higher the amount of thermally reversible functional masterbatch added to the foamed shoe sole formulation of the examples, the better it is for the recycled shoe sole powder to retain its performance. This indicates that the C=C double bonds of the unsaturated polymer introduced into the formulation can react with the thermally reversible groups in norbornene and polyethylene glycol dinorbornene to undergo a Diels-Alder reaction. This facilitates the reverse DA reaction of the foamed shoe sole material under high-temperature conditions, thereby decrosslinking the thermally reversible crosslinking network and imparting thermoplasticity to the thermally reversible masterbatch.

[0103] A comparison of the test data from recycling examples 2, 10, 11, 12, and 13 shows that as the amount of sole powder added in the examples increases from 20 parts to 50 parts, the performance change is larger, but not significant. When the amount added reaches 60 parts, the rebound and compression performance decrease significantly. Therefore, the preferred amount of sole powder added in the examples is 20-50 parts.

[0104] A comparison of the test data from recycled examples 9, 14, 15, 16, and 17 shows that as the amount of shoe sole powder added in Comparative Example 1 increases, the performance changes gradually become more pronounced. When the added amount reaches 30 parts, the various properties can no longer meet the performance requirements of the foamed shoe sole. This is because the EVA waste material or the foamed shoe sole has already undergone a chemical cross-linking reaction and cannot be plasticized and melted again. The larger the amount added, the more it acts as a filler in the formula and cannot form a cross-linking network again, thus affecting the various properties of the final foamed shoe sole.

[0105] Existing recycling technologies for discarded EVA foam soles involve crushing or pulverizing the soles / outlets and then adding them directly to the sole formulation in a certain proportion. However, because the EVA waste or foam soles have already undergone chemical cross-linking, they cannot be replasticized and melted. The larger the amount added, the more it affects the performance of the final foam sole. This invention, for the first time, introduces a masterbatch that can produce a reversible Diels-Alder cross-linking reaction into the formulation. This thermally reversible functional masterbatch maintains its cross-linking state at room temperature and de-cross-links at heat processing temperatures, exhibiting thermoplasticity and allowing for repeated processing. The treated foam sole material can be added to the new foam sole formulation in a proportion of up to 50%, while maintaining ≥80% of the sole's performance. Compared to the existing method of adding less than 30% of defective / outlets / residue / scrap materials, this increases both the amount of recycled sole material added and the recycling rate.

[0106] This invention first involves grafting and crosslinking high-vinyl content SOE, high-ENB content EPDM, trans-polyisoprene with norbornene, polyethylene glycol dinorbornene, and 2,4-di-tert-butyl peroxide in a twin-screw high-temperature melting apparatus. With the assistance of the peroxide initiator 2,4-di-tert-butyl peroxide, the carbon-carbon double bonds in these three unsaturated polymers readily react with the anhydride groups of norbornene at high temperatures. The grafted anhydride decomposes into carboxyl groups, which then undergo esterification with the hydroxyl groups in polyethylene glycol dinorbornene, thereby crosslinking the linear molecular chains of the grafted polymers into a three-dimensional network structure and forming DA thermally reversible crosslinking bonds. Furthermore, the optimal dosage of the three polymers / grafting agent / crosslinking agent was explored, representing a pioneering achievement in EVA-based foamed shoe sole technology.

[0107] The waste material processed by the technology of this invention can be added to the new foamed shoe sole formula at a ratio of up to 50%, while maintaining the performance of the shoe sole at ≥80%. On the one hand, this can effectively reduce the pollution caused by defective foamed shoe soles / material heads / tails / scraps. On the other hand, the higher the amount added, the more beneficial it is to reduce dependence on petrochemical products, greatly reducing the waste of resources and having extremely high recycling value.

[0108] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only for the purpose of helping to understand the method and core ideas of the present invention. The above descriptions are only preferred embodiments of the present invention. It should be noted that due to the limitations of textual expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a recyclable foamed shoe sole material, characterized in that, Includes the following steps: Provide thermally reversible masterbatch; The thermally reversible functional masterbatch is blended with polymers, crosslinking agents and additives to obtain a blended material, which is then foamed to obtain a recyclable foamed shoe sole material. By weight, the blended materials include: 15-40 parts of thermally reversible functional masterbatch, 30-55 parts of ethylene-vinyl acetate copolymer, 5-20 parts of polyolefin elastomer, 5-20 parts of olefin block copolymer, 0-20 parts of thermoplastic polyurethane, 2-6 parts of maleic anhydride-grafted EVA, 0.3-0.5 parts of crosslinking agent, 0.5-1.5 parts of stearic acid, 0-4 parts of foaming agent, and 0-1.5 parts of zinc oxide.

2. The method for preparing recyclable foamed shoe sole material according to claim 1, characterized in that, The thermally reversible functional masterbatch is synthesized according to the following operation: 10-30 parts by weight of hydrogenated styrene elastomer, 10-30 parts by weight of EPDM, 40-60 parts by weight of trans-polyisoprene, 1-10 parts by weight of norbornene, 0.5-5 parts by weight of polyethylene glycol dinorbornene, and 0.5-1 parts by weight of 2,4-di-tert-butylperoxide isopropylbenzene are mixed in a twin-screw high-temperature melting equipment and subjected to a graft crosslinking reaction. The processing temperature is set to 120-150°C, and then extruded to obtain the masterbatch. The EPDM is copolymerized from ethylene, propylene, and ethylene-bis(norbornene).

3. The method for preparing recyclable foamed shoe sole material according to claim 2, characterized in that, In the synthesis of the thermally reversible functional masterbatch, the hydrogenated styrene elastomer is copolymerized from styrene and butadiene, and has a glass transition temperature of 18~22℃; the EPDM has an ethylene-bis(norbornene) content of greater than 5%; and the trans-polyisoprene has a melting point of 50~70℃.

4. The method for preparing recyclable foamed shoe sole material according to any one of claims 1-3, characterized in that, In the blended materials, the VA content of the ethylene vinyl acetate copolymer is 18-40% by mass; the hardness of the polyolefin elastomer is 60-84A; the hardness of the olefin block copolymer is 60-80A; and the hardness of the thermoplastic polyurethane is 80-95A.

5. The method for preparing recyclable foamed shoe sole material according to any one of claims 1-3, characterized in that, In the blended material, the grafting rate of maleic anhydride-grafted EVA is ≥2%; the crosslinking agent is a peroxide crosslinking agent.

6. The method for preparing recyclable foamed shoe sole material according to any one of claims 1-3, characterized in that, The foaming is a chemical foaming method, and the blended material includes: 1-3.5 parts of foaming agent and 0.5-1 parts of zinc oxide; the foaming agent is an azo foaming agent and / or bicarbonate.

7. The method for preparing recyclable foamed shoe sole material according to any one of claims 1-3, characterized in that, The foaming is a supercritical physical foaming method using nitrogen or carbon dioxide, and the blended material does not contain a foaming agent.

8. A recyclable foamed shoe sole material, characterized in that, It is prepared by the preparation method according to any one of claims 1-7; the recyclable foamed sole material has a resilience of 58-66%.

9. The recyclable foamed shoe sole material according to claim 8, characterized in that, The foamed sole material is prepared from recycled powder to make EVA foamed soles.

10. The recyclable foamed shoe sole material according to claim 9, characterized in that, The amount of recycled powder of foamed shoe sole material added to the EVA foamed shoe sole is 20-50 parts by weight.

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