EVA recycled shoe material and foamed shoe material

Abstract

The application provides EVA regenerated shoe material and foamed shoe material, and relates to the technical field of shoe material.The EVA regenerated shoe material comprises the following raw material components in parts by weight: 60 parts of pure EVA, 30-60 parts of recycled EVA, 1-2 parts of a crosslinking agent, 0.6-5 parts of oxidized multi-walled carbon nanotubes, 10-30 parts of SEBS, 3-5 parts of polyolefin elastomer POE and 5-12 parts of maleic anhydride grafted EVA.The application adopts recycled EVA, constructs a ternary synergistic improvement system of oxidized MWNT, SEBS and maleic anhydride grafted EVA, and optimizes the performance of the EVA regenerated shoe material.

Description

Technical Field

[0001] This invention belongs to the field of footwear material technology, and relates to a recycled EVA footwear material and a foamed footwear material. Background Technology

[0002] Ethylene vinyl acetate (EVA) is a widely used polymer material, used in footwear such as in the midsoles of athletic shoes and slippers. When used as a shoe material, EVA requires cross-linking during processing. The large amount of waste generated during processing and the number of discarded shoes each year, if not effectively recycled and reused, will place significant pressure on the environment.

[0003] There are two main methods for recycling and reusing EVA: the first is to wash and crush waste EVA products (such as slippers and sneaker midsoles) into small particles, and then mix them into finished EVA products; the second is to crush waste EVA into small particles, de-crosslink them, and then mix them into finished EVA products. The second method is better for utilizing waste EVA, but it requires that the de-crosslinked EVA not be excessively depolymerized to avoid a significant decrease in the molecular weight of the EVA, which would be detrimental to the performance of the finished EVA product. For example, existing technology US20250122351A1 discloses a method for producing recyclable EVA from waste EVA through a multi-step thermal depolymerization process.

[0004] In addition, adding depolymerized and recycled waste EVA (recycled EVA) to pure EVA to prepare finished EVA products requires solving technical problems such as poor compatibility between recycled EVA and pure EVA and deterioration of mechanical properties. These technical problems need to be solved even more when the proportion of recycled EVA is high. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a recycled EVA shoe material and a foamed shoe material.

[0006] The technical solution of the present invention is as follows:

[0007] An EVA recycled shoe material, by weight, comprises: 60 parts pure EVA, 30-60 parts recycled EVA, 1-2 parts crosslinking agent, 0.6-5 parts oxidized multi-walled carbon nanotubes, 10-30 parts SEBS, 3-5 parts polyolefin elastomer POE and 5-12 parts maleic anhydride grafted EVA.

[0008] Preferably, the recycled EVA is obtained by thermal depolymerization of waste EVA.

[0009] More preferably, the thermal depolymerization process is as follows: temperature 170-190℃, time 10-30min, and external shearing force.

[0010] More preferably, the thermal depolymerization is performed using a HAAKE rheometer.

[0011] More preferably, the recycled EVA has a gel content of 5-15%.

[0012] Preferably, the VA content in both the pure EVA and the recycled EVA is 15-22%.

[0013] More preferably, the VA content in both the pure EVA and the recycled EVA is 16%.

[0014] Preferably, the crosslinking agent is selected from peroxide vulcanizing agents.

[0015] Preferably, the oxidized multi-walled carbon nanotubes are obtained by oxidizing multi-walled carbon nanotubes with mixed acid; The mixed acid is composed of concentrated sulfuric acid and concentrated nitric acid.

[0016] A foamed shoe material is obtained by supercritical foaming of EVA recycled shoe material as described in any of the above embodiments.

[0017] The beneficial effects of this invention are: (1) This invention uses oxidized multi-arm carbon nanotubes (oxidized MWNT) as a reinforcing filler, which has good compatibility with pure EVA and recycled EVA, and can also improve the compatibility between recycled EVA and pure EVA. At the same time, this invention also constructs a SEBS / EVA-g-MAH / oxidized MWNT ternary synergistic modification system, which improves the mechanical properties of EVA materials after adding recycled EVA.

[0018] (2) In this invention, the amount of oxidized MWNT added is small and the reinforcing effect is good, which can obtain lightweight and high-strength EVA material and improve the value of EVA material after adding recycled EVA.

[0019] (3) The present invention uses thermal depolymerization to recycle waste EVA, which can effectively depolymerize waste EVA and avoid over-depolymerization by controlling the depolymerization process. Attached Figure Description

[0020] Figure 1 This is a TEM image of multi-walled carbon nanotubes before oxidation.

[0021] Figure 2 This is a TEM image of oxidized MWNT. Detailed Implementation

[0022] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0023] On the one hand, the present invention proposes a recycled EVA shoe material, which, by weight, comprises: 60 parts pure EVA, 30-60 parts recycled EVA, 1-2 parts crosslinking agent, 0.6-5 parts oxidized multi-walled carbon nanotubes (oxidized MWNT), 10-30 parts SEBS, 3-5 parts polyolefin elastomer POE and 5-12 parts maleic anhydride grafted EVA (EVA-g-MAH).

[0024] The raw material components of the EVA recycled shoe material of the present invention include a high amount of recycled EVA, with the amount of recycled EVA reaching 50% or higher of the amount of pure EVA. A synergistic modification system is constructed by using a combination of oxidized MWNT, SEBS and EVA-g-MAH (grafting rate can be 1-1.4%), which significantly improves the compatibility of various raw material components in the EVA recycled shoe material and the mechanical properties of the EVA recycled shoe material.

[0025] The vinyl and vinyl acetate structures in EVA have different polarities. The vinyl structure has low polarity, while the vinyl acetate structure has high polarity. Therefore, EVA has an "amphoteric" characteristic. The polarity of recycled EVA is lower than that of pure EVA due to thermal chain scission and other reasons, resulting in insufficient compatibility between recycled EVA and pure EVA. In response to the structural characteristics of EVA used in shoe materials (relatively low VA content and relatively low polarity), this invention uses oxidized MWNT as a filler. The surface of oxidized MWNT contains hydroxyl, carbonyl, and carboxyl groups, and has moderate polarity (the polarity of oxidized MWNT is lower than that of carboxylated MWNT and aminated MWNT; the main surface groups of carboxylated MWNT are carboxyl groups, and the main surface groups of aminated MWNT are amino groups; both carboxylated and aminated MWNT can be obtained directly from the market). It can form hydrogen bond interactions with ester groups and carboxyl groups on pure EVA and recycled EVA, and can even partially form esterification structures. In particular, the interaction with recycled EVA is strong, which can improve the compatibility between recycled EVA and pure EVA. Combined with the compatibility effect of the compatibilizer EVA-g-MAH, the various raw material components of recycled EVA shoe materials can have good compatibility.

[0026] SEBS is a hydrogenated saturated thermoplastic elastomer of SBS. When added to EVA footwear materials, it improves the material's resilience, compression set resistance, toughness, and abrasion resistance. It forms a synergistic modification system with MWNT oxide and EVA-g-MAH, enhancing the mechanical properties of EVA footwear materials. Polyolefin elastomer POE can optimize the melt flow during EVA footwear material processing, reducing flow marks on the green surface during molding and improving molding performance.

[0027] Based on cost and the efficacy of oxidized MWNT, the amount of oxidized MWNT can be further reduced to 1-3 parts.

[0028] In some embodiments, recycled EVA is obtained from waste EVA through thermal depolymerization. Obtaining recycled EVA from waste EVA through thermal depolymerization is a common method in the art. Waste EVA (such as scraps from EVA injection molding, waste EVA midsoles, etc.) needs to be washed, crushed into small particles, and then subjected to thermal depolymerization.

[0029] In some embodiments, the thermal depolymerization process involves a temperature of 170-190°C, a time of 10-30 minutes, and an external shearing force. The external shearing force can improve the efficiency of thermal depolymerization. For example, the thermal depolymerization process can be 170°C × 10 minutes, 180°C × 20 minutes, 190°C × 10 minutes, 180°C × 15 minutes, 170°C × 30 minutes, 180°C × 20 minutes, etc., which can improve the depolymerization effect while avoiding over-depolymerization. During thermal depolymerization, an appropriate amount of antioxidant, such as antioxidant 1010, can be added to the waste EVA to reduce the depolymerization rate and avoid excessive depolymerization of the EVA main chain, thus obtaining recycled EVA with suitable properties.

[0030] In some embodiments, thermal depolymerization is performed using a HAAKE rheometer. During the thermal depolymerization of waste EVA, the rotor of the HAAKE rheometer has a good shearing effect on the waste EVA, which can improve the efficiency of thermal depolymerization.

[0031] In some embodiments, the gel content of recycled EVA is 5-15%. The gel content after EVA crosslinking is generally around 50%, or even higher, such as 70-80%. During the depolymerization process of recycled EVA, crosslinking points break, and the EVA main chain may also break simultaneously. If the depolymerization of the crosslinking points of the recycled EVA is complete or nearly complete, the EVA main chain will also experience significant breakage, resulting in an excessively low molecular weight of the recycled EVA and affecting the mechanical properties of the recycled EVA shoe material. A gel content of 5-15% for recycled EVA has a good effect on recycled EVA shoe materials, providing sufficient depolymerization while avoiding excessive depolymerization. For example, the gel content of recycled EVA can be 5%, 7%, 8%, 10%, 12%, 13%, 15%, etc.

[0032] The degree of depolymerization of recycled EVA can be characterized by gel content, which is well known to those skilled in the art. For example, soluble components in depolymerized EVA can be extracted using toluene or xylene, and the weight ratio of the remaining insoluble components to the original recycled EVA is the gel content.

[0033] In some embodiments, the VA content in pure EVA and recycled EVA is 15-22% on its own, which is considered low to medium VA content EVA. For example, the VA content in pure EVA and recycled EVA is 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, etc. In this invention, the VA content in recycled EVA refers to the VA content in the waste EVA before recycling. Due to the breakage of the main chain and side chains during thermal depolymerization, the VA content in recycled EVA will fluctuate slightly compared to the waste EVA before recycling.

[0034] In some embodiments, the VA content in pure EVA and recycled EVA is 16% on its own, and the melt flowability, crystallinity, and hardness are in a balanced range, making it the mainstream base material for shoe material foaming. Moreover, the polarity of EVA with a VA content of 16% is closer to that of MWNT oxide, which can more fully utilize the compatibility and reinforcing properties of MWNT oxide.

[0035] In some embodiments, the crosslinking agent is selected from peroxide vulcanizing agents. For example, the crosslinking agent may be bis-tert-butylperoxyisopropylbenzene, dicumyl peroxide, etc.

[0036] In some embodiments, oxidized multi-walled carbon nanotubes are obtained by oxidizing multi-walled carbon nanotubes with mixed acid. Mixed acids are composed of concentrated sulfuric acid and concentrated nitric acid. For example, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:3.

[0037] A method for preparing oxidized MWNTs is as follows: 100 mL of mixed acid solution and 5 g of multi-walled carbon nanotubes are placed in a beaker and ultrasonically dispersed for 30 min. Then, the mixture is refluxed in a 90℃ constant temperature oil bath for 3 h. The volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution is 1:3. After the reaction is complete, the mixture is filtered through a 0.22 μm microporous membrane and washed with deionized water until neutral. The filtered solid is collected and dried in an 80℃ drying oven for 24 hours. Finally, it is ground into a powder with a particle size of 100-200 mesh. TEM images of the multi-walled carbon nanotubes before oxidation and the oxidized MWNTs after oxidation are attached. Figure 1 and attached Figure 2 As shown, oxidized MWNTs still maintain a good tubular structure with intact and continuous tube walls, without obvious fractures, peeling, or collapse defects, indicating that the oxidation process did not destroy the bulk structure of carbon nanotubes. At the same time, the surface of oxidized MWNTs is slightly rough, with slight surface modification traces visible in some areas.

[0038] The preparation method of the EVA recycled shoe material of the present invention is not particularly limited. One method is as follows: after drying and removing water from each raw material component, add it to a mixer and stir and mix at 80-100℃ for 20-40 minutes to obtain a blended rubber compound; put the blended rubber compound into a flat vulcanizing machine for hot pressing and vulcanization molding at a temperature of 180℃ for 10 minutes and a pressure of 5-10MPa to obtain the EVA recycled shoe material.

[0039] Depending on performance requirements or application scenarios, the raw material components of the EVA recycled shoe material of the present invention may also include antioxidants, UV stabilizers, anti-yellowing agents, heat-resistant additives, and other raw material components.

[0040] On the other hand, the present invention also proposes a foamed shoe material, which is obtained by supercritical foaming of the EVA recycled shoe material described in any of the above embodiments.

[0041] Supercritical foaming can be performed using supercritical nitrogen fluid, with a foaming pressure of 18-25 MPa, a foaming temperature of 150-170℃, a holding time of 1-2 hours, and a depressurization rate of 0.2-0.5 MPa / min. The foamed shoe material of this invention has good mechanical properties, low compression set, and high tensile strength, tear strength, and resilience.

[0042] The technical solution of the present invention will be further described and explained below with reference to various preparation examples and embodiments. Unless otherwise specified, the parts mentioned in the following preparation examples and embodiments are parts by weight.

[0043] Preparation Examples 1-3: Preparation of Recycled EVA Preparation Example 1 The cleaned and crushed waste EVA (recycled from waste EVA slippers) was added to the HAAKE rheometer. The rotor speed was 30 r / min, the pyrolysis temperature was 170℃, and the time was 15 min to obtain recycled EVA.

[0044] The gel content of the recovered EVA was measured to be 12%.

[0045] Preparation Example 2 The cleaned and crushed waste EVA (recycled from waste EVA slippers) was added to the HAAKE rheometer. The rotor speed was 15 r / min, the pyrolysis temperature was 190℃, and the time was 10 min to obtain recycled EVA.

[0046] The gel content of the recovered EVA was measured to be 15%.

[0047] Preparation Example 3 The cleaned and crushed waste EVA (recycled from waste EVA slippers) was added to the HAAKE rheometer. The rotor speed was 30 r / min, the pyrolysis temperature was 180℃, and the time was 30 min to obtain recycled EVA.

[0048] The gel content of the recovered EVA was measured to be 5%.

[0049] Comparative Preparation Example 1 The cleaned and crushed waste EVA (recycled from waste EVA slippers) was added to the HAAKE rheometer. The rotor speed was 30 r / min, the pyrolysis temperature was 180℃, and the time was 45 min to obtain recycled EVA.

[0050] The gel content of the recovered EVA was measured to be 2%.

[0051] Comparative Preparation Example 2 The cleaned and crushed waste EVA (recycled from waste EVA slippers) was added to the HAAKE rheometer. The rotor speed was 30 r / min, the pyrolysis temperature was 160℃, and the time was 10 min to obtain recycled EVA.

[0052] The gel content of the recovered EVA was measured to be 19%.

[0053] Example 1 EVA recycled shoe material, the raw material composition is as follows: 60 parts pure EVA, 40 parts recycled EVA obtained from Preparation Example 1, 1.5 parts di-tert-butylperoxyisopropylbenzene, 1 part MWNT oxide, 20 parts SEBS, 4 parts POE and 10 parts EVA-g-MAH (grafting rate 1.2%).

[0054] After drying and removing water from each raw material component, it is added to a mixer and stirred and mixed at 80°C for 30 minutes to obtain a blended rubber compound. The blended rubber compound is then placed in a flat vulcanizing machine for hot pressing and vulcanization molding at a temperature of 180°C, a time of 10 minutes, and a pressure of 10 MPa to obtain EVA recycled shoe material.

[0055] Example 2 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the recycled EVA obtained in Preparation Example 1 is replaced with an equal weight of the recycled EVA obtained in Preparation Example 2. The remaining steps remain unchanged.

[0056] Example 3 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the recycled EVA obtained in Preparation Example 1 is replaced with an equal weight of the recycled EVA obtained in Preparation Example 3. The remaining steps remain unchanged.

[0057] Comparative Example 1 The difference between this comparative example and Example 1 is that in Example 1, the recycled EVA obtained in Preparation Example 1 was replaced with an equal weight of the recycled EVA obtained in Comparative Preparation Example 1. The remaining steps remained unchanged.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that in Example 1, the recycled EVA obtained in Preparation Example 1 was replaced with an equal weight of the recycled EVA obtained in Comparative Preparation Example 2. All other steps remained unchanged.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that in Example 1, oxidized MWNT was replaced with an equal weight of amination-modified MWNT. The remaining steps remained unchanged.

[0060] Comparative Example 4 The difference between this comparative example and Example 1 is that in Example 1, oxidized MWNT was replaced with an equal weight of carboxylated MWNT. The remaining steps remained unchanged.

[0061] Comparative Example 5 The difference between this comparative example and Example 1 is that in Example 1, 1 part of MWNT oxide was replaced with 15 parts of talc (average particle size 2 μm). The remaining steps remained unchanged.

[0062] Example 4 EVA recycled shoe material, the raw material composition is as follows: 60 parts pure EVA, 30 parts recycled EVA obtained from Preparation Example 1, 1.5 parts di-tert-butylperoxyisopropylbenzene, 1 part MWNT oxide, 20 parts SEBS, 3 parts POE and 5 parts EVA-g-MAH (grafting rate 1.2%).

[0063] After drying and removing water from each raw material component, it is added to a mixer and stirred and mixed at 80°C for 30 minutes to obtain a blended rubber compound. The blended rubber compound is then placed in a flat vulcanizing machine for hot pressing and vulcanization molding at a temperature of 180°C, a time of 10 minutes, and a pressure of 10 MPa to obtain EVA recycled shoe material.

[0064] Example 5 The difference between this embodiment and Embodiment 4 is that in Embodiment 4, the recovered EVA was adjusted from 30 parts to 60 parts, the oxidized MWNT was adjusted from 1 part to 3 parts, the POE was adjusted from 3 parts to 5 parts, and the EVA-g-MAH was adjusted from 5 parts to 12 parts. The remaining steps remain unchanged.

[0065] Example 6 The difference between this embodiment and Embodiment 5 is that in Embodiment 5, the amount of MWNT oxide was changed from 3 parts to 5 parts. The remaining steps remain unchanged.

[0066] Comparative Example 6 The difference between this comparative example and Example 4 is that MWNT oxide was not added in Example 4. The remaining steps remain unchanged.

[0067] Comparative Example 7 The difference between this comparative example and Example 4 is that SEBS was not added in Example 4. The remaining steps remain unchanged.

[0068] Comparative Example 8 The difference between this comparative example and Example 4 is that EVA-g-MAH was not added in Example 4. The remaining steps remain unchanged.

[0069] The recycled EVA shoe materials obtained in Examples 1-6 and Comparative Examples 1-8 were subjected to supercritical foaming to obtain foamed shoe materials. Supercritical foaming process: supercritical N2 fluid, foaming pressure 20MPa, foaming temperature 150℃, heat preservation and pressure holding time 1.5h, and pressure relief rate 0.3MPa / min.

[0070] The performance of the foamed shoe material is shown in Table 1 below. Among them, the compression set was tested according to ISO 7743-2017 standard, with the strain set at 50%, the strain loading / releasing rate at 20 mm / min, and the cyclic compression at 8h; the resilience was tested according to ASTM D3574 standard using the falling ball method, with a ball drop height of 400mm; the tensile strength and tear strength were tested using an electronic tensile testing machine; and the density was tested using the drainage method.

[0071] Table 1

[0072] As can be seen from the results in Table 1 above, the EVA recycled shoe material of the present invention, in addition to pure EVA and recycled EVA, adds raw material components such as oxidized MWNT, POE, SEBS and EVA-g-MAH, and after supercritical foaming, has good mechanical properties, low compression set, high resilience, high tensile strength, high tear strength and low density.

[0073] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A type of recycled EVA shoe material, characterized in that, By weight, the raw material components include: 60 parts pure EVA, 30-60 parts recycled EVA, 1-2 parts crosslinking agent, 0.6-5 parts oxidized multi-walled carbon nanotubes, 10-30 parts SEBS, 3-5 parts polyolefin elastomer POE and 5-12 parts maleic anhydride grafted EVA.

2. The EVA recycled shoe material according to claim 1, characterized in that, The recycled EVA is obtained by thermal depolymerization of waste EVA.

3. The EVA recycled shoe material according to claim 2, characterized in that, The process of thermal depolymerization is as follows: temperature 170-190℃, time 10-30min, and external shearing force.

4. The EVA recycled shoe material according to claim 3, characterized in that, The pyrolysis polymerization was carried out using a HAAKE rheometer.

5. The EVA recycled shoe material according to claim 4, characterized in that, The recycled EVA has a gel content of 5-15%.

6. The EVA recycled shoe material according to claim 1, characterized in that, The VA content in both the pure EVA and the recycled EVA is 15-22%.

7. The EVA recycled shoe material according to claim 6, characterized in that, The VA content in both the pure EVA and the recycled EVA is 16%.

8. The EVA recycled shoe material according to claim 1, characterized in that, The crosslinking agent is selected from peroxide vulcanizing agents.

9. The EVA recycled shoe material according to claim 1, characterized in that, The oxidized multi-walled carbon nanotubes are obtained by oxidizing multi-walled carbon nanotubes with mixed acid; The mixed acid is composed of concentrated sulfuric acid and concentrated nitric acid.

10. A foamed shoe material, characterized in that, It is obtained by supercritical foaming of the EVA recycled shoe material as described in any one of claims 1-9.

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