High-elasticity foaming material capable of realizing closed-loop regeneration foaming and preparation method of high-elasticity foaming material

Abstract

The invention discloses a high-elasticity foaming material capable of realizing closed-loop regeneration foaming and a preparation method thereof, and relates to the technical field of processing of high polymer materials, and the scheme is that the high-elasticity foaming material is prepared from thermoplastic elastomer particles, EVA or EVA / POE / SEBS blend, dicarboxylic acid and a cross-linking system in parts by mass; the cross-linking system is a peroxide cross-linking system or an ionic bond cross-linking system; the regenerated foamed product is obtained through premixing, melt blending granulation, secondary mixing, introduction of a cross-linking system, forming, high-pressure gas physical foaming, recycling, re-granulation and re-foaming. The device has the beneficial effects that the same-level closed-loop circulation of foaming products is realized, and recycled materials can be directly reused; the remoldability of a thermoplastic matrix is cooperated with a controllable cross-linked network, so that the stability of a processing window is improved, and the density and the elasticity are more easily kept consistent after re-foaming; high-pressure gas physical foaming is adopted, dependence of chemical foaming agents is reduced, the process is cleaner, and common extrusion / injection molding equipment is compatible.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, and in particular to a highly elastic foamed material that can be regenerated and foamed in a closed loop and its preparation method. Background Technology

[0002] In recent years, the midsoles, cushioning pads, and protective shock-absorbing components of athletic shoes have placed continuous demands on materials for "lightweighting, high resilience, and durability." This has prompted elastomer foaming technology to evolve from early reliance on chemical foaming and empirical formulations to an engineering-driven approach characterized by network structure control, rheological window matching, and high-pressure gas physical foaming. On the industry side, cross-linked elastomer foams such as EVA, POE, and SBS / SIS / SEBS have long dominated due to their cost and processing maturity. Meanwhile, thermoplastic elastomers such as TPU, TPEE, and PEBAX are rapidly expanding in supercritical gas foaming and high-end footwear materials, forming a parallel technological landscape of "traditional cross-linked foaming materials – thermoplastic physical foaming." Simultaneously, the requirements for carbon reduction and the circular economy have significantly increased. The footwear material industry is shifting from "recyclable promotion" to "verifiable closed-loop regeneration," focusing not only on whether products can be recycled but also on whether they can be reprocessed at the same application level and reliably achieve high-quality foamed structures and mechanical properties, thereby realizing the same-level recycling and large-scale implementation of material value.

[0003] However, judging from the current state of technology, the industry still lacks a universal solution that can simultaneously meet the two contradictions of "crosslinked foam materials cannot be remelted" and "the performance of thermoplastic foam materials degrades after recycling and re-foaming".

[0004] Firstly, in order to obtain stable cell structure and mechanical strength, traditional cross-linked elastomer foaming often uses irreversible cross-linked networks, which leads to the loss of thermoplasticity after the product is molded. Recycling usually only allows for downgrading and reuse or as a filler, making it difficult to return to the same grade of high-resilience foamed products. Even if there is a "recycling and remanufacturing" scheme, it is often still a "re-foaming with recycled materials added", which is highly dependent on the amount of recycled materials, compatibility modification and foaming system, making it difficult to form a true closed loop. Taking patent CN201380046489.X as an example, its core idea is to re-foam and cross-link in a blend system containing virgin EVA and waste EVA foam, and introduce compatibilizers (such as hydrogenated petroleum resin) in conjunction with conventional cross-linking agents and foaming agents to improve molding properties. This type of route has practical significance in "increasing the proportion of recycled foam material", but it still faces challenges at the engineering closed-loop level: recycled materials are more of a blended phase "absorbed" by the system, often accompanied by dependence on compatibility thickening and foaming systems, and it is difficult to answer the key question of "whether the same grade of high resilience foam material can still be stably obtained after recycling-reprocessing-refoaming".

[0005] Secondly, to alleviate the reprocessing obstacles caused by irreversible crosslinking, micro-crosslinking or low gel content control routes have emerged, attempting to maintain melt processability while retaining a certain network support. Patent CN201911337222.1 proposes to form a micro-crosslinked structure with a gel content not exceeding a certain threshold for low-melting-point thermoplastic elastomers, and obtain foam material through physical foaming, while emphasizing melt recyclability; however, the reprocessing disclosed by this type of solution is more focused on proving processability by "melt pressing into films or remolding", and the evidence chain for "whether the recycled material can be re-entered into high-pressure gas foaming and maintain high resilience, low compression set and structural stability" is often insufficient for scenarios such as shoe midsoles.

[0006] In summary, existing technologies either remain at the level of downgrading and limited blending of cross-linked foamed materials, or emphasize "reprocessability" but fail to fully demonstrate "same-level refoaming," or achieve excellent cell structure in a single physical foaming but struggle to overcome the rheological degradation and performance decay caused by multiple cycles. The root cause of these defects lies in the fact that high-performance foaming is extremely sensitive to melt strength, network support, and processing window. The thermal history and oxidation chain breakage introduced by recycling and reprocessing amplify the risk of structural instability of the material during the foaming stage, creating a significant engineering gap between "recyclability" and "closed-loop regeneration (same-level refoaming)."

[0007] Therefore, the industry urgently needs a closed-loop recycling solution for highly elastic foamed products to address the challenges of traditional cross-linked elastomer foams, which are difficult to remelt and process due to irreversible networks, resulting in recycling remaining at a downgraded level; and the degradation of melt strength and rheological properties in thermoplastic elastomer foams after recycling and reprocessing, making it difficult to maintain stable cell structure and mechanical properties in regenerated foams. The required solution should, within reasonable process complexity and environmental friendliness constraints, improve the foaming stability and mechanical property consistency after recycling and reprocessing, and expand its applicability to different elastomer systems and processing equipment conditions as much as possible. This would meet the long-term requirements of high-rebound, durable, and dimensionally stable applications such as shoe midsoles, driving foamed materials from "recyclable" to "verifiable and scalable closed-loop recycling at the same level." Summary of the Invention

[0008] To achieve the above-mentioned objectives and address the aforementioned technical problems, this invention provides a highly elastic foamed material capable of closed-loop recyclable foaming, which is prepared from the following raw materials in parts by weight: A) 50-80 parts of thermoplastic elastomer particles; B) 30-50 parts of EVA or EVA / POE / SEBS blend; C) 2-6 parts of dicarboxylic acid; D) Crosslinking system, wherein the crosslinking system is a peroxide crosslinking system or an ionic crosslinking system.

[0009] Preferably, the thermoplastic elastomer particles are one or a combination of two or three of TPU, TPEE, and PEBAX.

[0010] Preferably, when B) is an EVA / POE / SEBS blend, the mass fractions of EVA, POE and SEBS in the blend are 50-70 wt%, 20-30 wt% of EVA, and 10-20 wt% of SEBS, and the sum of the mass fractions of the three is 100 wt%.

[0011] Preferably, the dicarboxylic acid is adipic acid or maleic acid.

[0012] Preferably, when the crosslinking system is a peroxide crosslinking system, the crosslinking agent is DCP or BIPB, with an amount of 0.1 to 0.2 parts, and the accelerator is TAIC or HVA-2, with an amount of 0.3 to 0.5 parts.

[0013] Preferably, when the crosslinking system is an ionic crosslinking system, the accelerator is one of zinc stearate, zinc chloride, and stannous chloride, with an amount of 0.1 to 0.4 parts, and the initiator is peroxide, with an amount of 0.02 to 0.05 parts.

[0014] The present invention also provides a method for preparing the closed-loop regenerable foamed high-elasticity foam material as described above, comprising the following steps: (1) Premix component B with dicarboxylic acid; (2) The thermoplastic elastomer particles are melt-blended with the premix obtained in step (1) and granulated to obtain blended particles; (3) The blended particles are subjected to secondary kneading, and the crosslinking system is added after the kneading torque is stabilized; (4) The material after adding the crosslinking system is extruded and granulated to obtain blended granules; (5) The blended granules are molded to obtain a preform; (6) The mold is foamed under high pressure gas conditions to obtain foamed material; Preferably, before performing step (1), a drying step is also included: drying the thermoplastic elastomer particles at 70-80°C for 4-6 hours, and drying EVA, POE, and SEBS at 50-60°C for 2-4 hours.

[0015] Preferably, in step (1), EVA or EVA / POE / SEBS blend and dicarboxylic acid are first stirred evenly in a high-speed mixer to form a premix, and then the premix and thermoplastic elastomer particles are entered into step (2) for melt blending.

[0016] Preferably, the melt blending and granulation in step (2) are completed by a twin-screw extruder, the temperature range of each zone of the twin-screw extruder is 150℃~190℃, the screw speed is 200~350 rpm, and the blended particles are obtained; the secondary mixing in step (3) is completed in a mixer, the temperature of the mixer is 130℃~150℃, and the crosslinking system is added after the torque is stabilized.

[0017] Preferably, in step (4), the material after adding the crosslinking system is extruded and granulated by a single screw extruder to obtain blended granules. The temperatures of each zone of the single screw extruder are 130℃, 135℃, 145℃ and 135℃ respectively, so as to obtain a granule form that is easy to form in subsequent molding.

[0018] Preferably, in step (5), the molding is performed by injection molding, the injection molding machine mold temperature is 140-150℃, the mold temperature is 160-180℃, and the holding time is 6-10min.

[0019] Preferably, the high-pressure gas in step (6) is nitrogen, the pressure of the high-pressure gas is 20-40 MPa, the foaming temperature is 150-165°C, and the saturation time is 2-6 h; the high-pressure gas may also be a mixture of carbon dioxide and nitrogen.

[0020] Preferably, the recycled granules in step (7) are obtained by: crushing the foamed product obtained in step (6) to obtain foamed granules; melting and blending the foamed granules in a twin-screw extruder and extruding and granulating them to obtain recycled granules, or melting them in a mixer and then extruding and granulating them in a single-screw extruder to obtain recycled granules; and repeating steps (5) and (6) on the recycled granules to obtain recycled foamed products.

[0021] The beneficial effects of the technical solution provided by this invention are as follows: Breakthrough in recycling model: This innovative approach achieves a closed-loop, multi-cycle path of "midsole → recycling → direct refoaming → new midsole." This model eliminates the need for compatibilizers or large-scale blending of virgin materials, allowing recycled materials to be directly used for refoaming. This significantly simplifies the recycling process and reduces process complexity and reliance on raw materials.

[0022] Synergistic advantages of material selection and design: TPU, TPEE, and PEBAX, as highly elastic matrix materials, endow the products with excellent resilience and mechanical properties, while their thermoplastic nature provides good remodeling properties for subsequent recycling. Subsequently, combined with traditional foaming materials such as EVA, POE, and SEBS, and through the controllable design of the crosslinking system, a partially crosslinked network structure is formed. This network can be effectively remodeled during recycling, thus achieving a balance between high cost-effectiveness, easy foaming and processing, and recyclability.

[0023] Dual benefits in terms of environmental protection and cost: This technology significantly reduces the environmental burden of waste footwear materials, promoting the transformation of the footwear material industry towards a circular economy model. Simultaneously, by achieving closed-loop, efficient utilization of materials, it reduces the demand for virgin materials, lowers production energy consumption and waste disposal costs, thus offering significant advantages in both environmental protection and economic benefits. Attached Figure Description

[0024] Figure 1 The image shows a molten photograph of the foamed product and its recycling process according to Embodiment 1 of the present invention. Figure 2 The recycled pressing plate and foaming condition of Embodiment 1 of the present invention; Figure 3 This is a SEM image of the foaming material in Embodiment 1 of the present invention; Figure 4 This is a SEM image of the foam cells after recycling and re-foaming in Example 1 of the present invention; Figure 5 Here is a SEM image of the foaming material in Example 4 of this invention; Figure 6 This is a SEM image of the foam cells after recycling and re-foaming in Example 4 of the present invention; Figure 7 This is a SEM image of the foam cells after recycling and re-foaming in Example 5 of the present invention; Figure 8 This is a SEM image of the foam cells after recycling and re-foaming in Example 6 of the present invention; Figure 9 This is a SEM image of the foam cells after recycling and re-foaming in Comparative Example 2 of this invention; Figure 10 This is a SEM image of the foam cells of Comparative Example 3 of the present invention after recycling and re-foaming. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] Example 1 1) Formula (parts by weight) Thermoplastic elastomer: TPEE (4056) 60 parts Component B: 40 parts EVA Dicarboxylic acid: 4 parts maleic acid Initiator: 0.03 parts DCP Accelerator: 2 parts zinc stearate 2) Preparation method (1) Drying Dry the TPEE particles in an oven at 75°C for 5 hours. Place the EVA in an oven at 55°C and dry for 3 hours; seal and store for later use after drying.

[0027] (2) Premixed Add 40 parts of EVA and 4 parts of maleic acid to a high-speed mixer and stir at room temperature until homogeneous to obtain a premix.

[0028] (3) One-time mixing and granulation (twin-screw extrusion) Add 60 parts of TPEE together with the above premix to a twin-screw extruder; Temperature range setting: 150℃–160℃–165℃–160℃; Screw speed: 240 rpm; The blended particles are obtained by melt blending, extrusion, water cooling, stretching, and pelletizing.

[0029] (4) Introduction of secondary mixing and cross-linking system (internal mixing) Add the blended particles to the internal mixer and set the temperature to 130°C; After the torque stabilizes, add 2 parts zinc stearate and 0.03 parts DCP, and continue to mix until evenly dispersed.

[0030] (5) Regranulation (single screw extrusion) The internally mixed material is extruded and granulated using a single-screw extruder; temperature range setting: 130℃–130℃–135℃–130℃; Cool and pelletize to obtain blended pellets for later use.

[0031] (6) Injection molding (preform preparation) Injection molding machine mold temperature: 130℃; Mold temperature: 170℃; Holding time: 8 min; open the mold and remove the blank.

[0032] (7) High-pressure nitrogen physical foaming The mold was placed in a foaming kettle, nitrogen gas was introduced and the pressure was increased to 22 MPa; Foaming temperature 155℃, saturation time 4 hours; The pressure was then quickly released, the foamed sample was removed, cooled and shaped to obtain the foamed product.

[0033] (8) Recycling and reprocessing The above-mentioned foamed products are crushed into small particles; Recycled granules are obtained by melting in an internal mixer followed by granulation using a single screw extruder. Repeat steps (6) and (7) with the recycled granules to obtain recycled foamed products.

[0034] Example 2 Prepared using the same method as in Example 1, except that: 1) The formula is changed to: 50 parts of TPEE (4056); Component B consists of 25 parts EVA, 15 parts POE, and 10 parts SEBS; The dicarboxylic acid is 6 parts maleic acid; Initiator DCP 0.02 parts; The accelerator is 2 parts ZnCl2.

[0035] 2) Temperature range of twin-screw extruder for single-stage mixing: 150℃–160℃–165℃–160℃; Secondary mixing temperature: 135℃; Single screw temperature range: 135℃–135℃–140℃–135℃; Injection mold opening temperature: 135℃.

[0036] Example 3 Prepared using the same method as in Example 1, except that: 1) The formula is changed to: 50 parts of TPEE (3078); Component B consists of 25 parts EVA, 10 parts POE, and 15 parts SEBS; Replace 6 parts of dicarboxylic acid with adipic acid; Initiator DCP 0.02 parts; Accelerator: 2 parts zinc stearate.

[0037] 2) The temperature zone of the twin-screw extruder for primary mixing has been adjusted to the high-end temperature zone: 170℃–180℃–185℃–190℃; Secondary mixing temperature: 145℃; Single screw temperature range: 145℃–145℃–150℃–145℃; Injection mold opening 145℃, mold 180℃, holding pressure for 6 minutes; The foaming conditions are: 165℃, 4MPa CO2 + 20MPa nitrogen.

[0038] 3) Recycling and reprocessing: The above-mentioned foamed products are crushed into small particles; Recycled granules are obtained by twin-screw granulation; Recycled foamed products are obtained by repeating the above injection molding and foaming process on recycled granules.

[0039] Example 4 Prepared using the same method as in Example 1, except that: 1) The formula was changed to: 50 parts of PEBAX as the thermoplastic elastomer; Component B consists of 35 parts EVA, 10 parts POE, and 5 parts SEBS; The dicarboxylic acid is 6 parts maleic acid; The initiator was 0.05 parts of BIPB; Accelerator: 2 parts zinc stearate.

[0040] 2) Temperature range of twin-screw extruder for single-stage mixing: 150℃–160℃–165℃–160℃; Secondary mixing temperature: 130℃; Single screw temperature range: 130℃–130℃–135℃–130℃; Injection mold opening 130℃, mold 160℃, holding pressure for 10 minutes; Foaming conditions: 150℃, 25MPa nitrogen.

[0041] Example 5 Prepared using the same method as in Example 1, except that: 1) The formula was changed to: 70 parts of thermoplastic elastomer, TPU; Component B consists of 15 parts EVA, 6 parts POE, and 9 parts SEBS; The dicarboxylic acid is 4 parts adipic acid; Initiator DCP 0.02 parts; The accelerator is 1 part stannous chloride.

[0042] 2) Temperature range of twin-screw extruder for single-stage mixing: 160℃–170℃–175℃–180℃; Secondary mixing temperature: 135℃; Single screw temperature range: 135℃–135℃–140℃–135℃; Injection mold opening 135℃, mold 160℃, holding pressure for 10 minutes; Foaming conditions: 150℃, 4MPa CO2 + 20MPa nitrogen.

[0043] Example 6 Prepared using the same method as in Example 1, except that: 1) The formula was changed to: 70 parts TPU; Component B consists of 15 parts EVA, 6 parts POE, and 9 parts SEBS; The dicarboxylic acid is 2 parts of adipic acid; The crosslinking system is a peroxide crosslinking system: 0.2 parts of crosslinking agent BIPB and 0.3 parts of accelerator TAIC.

[0044] 2) Temperature range of twin-screw extruder for single-stage mixing: 160℃–170℃–175℃–180℃; Secondary mixing temperature: 135℃; Single screw temperature range: 135℃–135℃–140℃–135℃; Injection mold opening 135℃, mold 160℃, holding pressure for 10 minutes; Foaming conditions: 150℃, 4MPa CO2 + 20MPa nitrogen.

[0045] Example 7 Prepared using the same method as in Example 1, except that: 1) The source of raw materials was changed to recycled materials: The foamed products obtained in Examples 3, 4 and 5 were crushed and then mixed in any proportion to obtain recycled mixtures; 2) The recycled mixture is granulated by twin-screw extrusion to obtain recycled granules; 3) The recycled granules were directly subjected to the same injection molding and high-pressure gas physical foaming steps as in Example 1 to obtain recycled foamed products. The foaming conditions were: 150°C, 2MPa CO2 + 20MPa nitrogen.

[0046] Comparative Example 1 Prepared using the same method as in Example 1, except that: 1) The formula is: 60 parts of thermoplastic elastomer (TPU); Component B consists of 40 parts of EVA; The crosslinking system uses a peroxide system, with 0.4 parts of BIPB as the crosslinking agent and 1.0 part of TAIC as the accelerator; POE and SEBS are not included.

[0047] 2) The temperature range for single-stage compounding twin-screw extrusion is 160℃–170℃–175℃–180℃; The secondary mixing temperature is 135℃; The single-screw extrusion temperature range is 135℃–135℃–140℃–135℃; Injection mold temperature 135℃, mold temperature 160℃, holding pressure time 10min; The foaming conditions are 150℃ and 22MPa nitrogen.

[0048] Comparative Example 2 Prepared using the same method as in Example 1, except that: 1) The formula consists of 100 parts TPU, without EVA, POE, SEBS, dicarboxylic acid, or crosslinking systems; 2) The remaining process steps are the same as in Example 1.

[0049] Comparative Example 3 Prepared using the same method as in Example 6, except that: The formulation is the same as in Example 6, but without the addition of dicarboxylic acid; that is, it still uses 70 parts TPU, 15 parts EVA, 6 parts POE, 9 parts SEBS, 0.2 parts crosslinking agent BIPB, and 0.3 parts accelerator TAIC.

[0050] Comparative Example 4 Prepared using the same method as in Example 1, except that: Formulation: Thermoplastic elastomer-free, containing only 60 parts EVA, 20 parts POE, and 20 parts SEBS. The crosslinking system is the peroxide system BIPB, used in a quantity of 0.6 parts. Foaming conditions are 100℃ and 20MPa nitrogen. The foamed product is then pulverized into small particles; its recyclability is assessed using an internal mixer.

[0051] Experimental test: 1. Apparent density was tested according to GB / T6343-2009; 2. Shore C hardness was tested according to ASTM D2240; 3. Ball rebound shall be tested according to ISO 8307; 4. Tensile strength shall be tested in accordance with GB / T 10654-2001; 5. Delamination tear test shall be performed in accordance with GB / T 3903.29; 6. Compression set shall be tested in accordance with GB / T 6669, under the conditions of (50℃, 6h).

[0052] Table 1 Test Data

[0053] The data in Table 1 show that, under different thermoplastic elastomer types, different B component morphologies (EVA or EVA / POE / SEBS), and different crosslinking systems (ionic bonds or peroxides), all Examples 1-6 can obtain foamed materials that balance lightweight, elastic recovery, and mechanical strength. Furthermore, all of them exhibit "reprocessability," indicating that this type of system can maintain a formable rheological window and sufficient melt support after recycling and remelting shearing, thus allowing it to re-enter the high-pressure gas foaming process. Simultaneously, the examples maintain a density and resilience level similar to the initial foaming after re-foaming, indicating that the cyclic thermal history did not cause irreversible performance collapse, and the material structure possesses reshapeability and cyclic stability.

[0054] Comparative Example 1, despite acceptable initial performance, exhibited "unreworkable" behavior. This reflects that excessively strong peroxide crosslinking forms a permanent network that is difficult to reshape, hindering melt regranulation and remolding, thus preventing closed-loop regeneration. Comparative Example 2, while showing processability and initial foaming capability, exhibited significantly higher compression set and a marked increase in density after refoaming, with no rebound data. This suggests that pure thermoplastic elastomer systems are more prone to thermomechanical degradation during recycling and reprocessing, leading to a decrease in molecular weight, deterioration of melt strength and gas pore-forming stability, resulting in refoaming densification and difficulty in maintaining elasticity. Although refoaming is possible, it is difficult to achieve the desired results. For product application; Comparative Example 3, after removing dicarboxylic acid while retaining the crosslinking system, showed increased compression set, decreased rebound, and further weakened performance after re-foaming, indicating that dicarboxylic acid plays a key role in the interfacial stability / compatibility and network synergy of the system. Its absence weakens stress transmission and pore formation stability, and amplifies the performance degradation during the regeneration cycle; Comparative Example 4, as a traditional crosslinked foam material route, can obtain the material in one foaming, but it is also not reprocessable or refoamable. Its one-time performance also fails to simultaneously take into account elasticity and deformation resistance, which reflects the limitations of the traditional crosslinked foam system in closed-loop regeneration and performance consistency.

[0055] Overall, the data in Table 1 demonstrates that the present invention, through the combination of "the remodelability of the thermoplastic matrix + the synergistic effect of dicarboxylic acid + controllable crosslinking strength", enables the material to achieve stable re-foaming and maintain key mechanical and elastic indicators after recycling and reprocessing, thereby effectively responding to the technical requirement of "closed-loop regeneration without degradation" for high-elasticity foamed materials.

[0056] Figure 3 and Figure 4 and Figure 5 and Figure 6 These are two sets of foaming material formulations and cell structure diagrams of the recycled and re-foamed materials. It can be seen that the density increases slightly after recycling and re-foaming, but the cells are uniform and the structure is intact.

[0057] Figure 7 and Figure 8 It can be seen that the two basic formulations are the same, but one is a peroxide system and the other is an ion-crosslinked system. Both crosslinking systems can foam under this ratio. Under the same process conditions, the foamed material from the peroxide system has a slightly higher density, higher hardness, and lower compressive strength. This is because EVA, POE, etc., form CC bonds in this system, resulting in a high degree of crosslinking. However, since TPU thermoplastic elastomer accounts for 70 parts, both can be recycled. Comparing the cell size of the recycled and re-foamed products, it can be seen that the peroxide-based cells exhibit a bimodal pattern of large and small pores. This is because although EVA and other components crosslinked with peroxide can be broken down by melt shearing during the mixing process, their CC bonds are difficult to break. Therefore, the crosslinked phase has small pores, while the TPU phase has larger pores. In contrast, the ion-crosslinked system, after recycling and re-foaming, still results in more uniform cell size.

[0058] Figure 9 It can be seen that pure TPU has a low density after foaming. However, because it is a thermoplastic elastomer and does not cross-link, its compression set is relatively large. During reprocessing, molecular chain breakage occurs, the molecular weight decreases, and the melt strength decreases. Although it can still be foamed, the foamed samples show uneven cell structure, large cross-cells, and delamination, making them unsuitable for use as finished products.

[0059] Figure 10 It can be seen that there is no dicarboxylic acid in the system, and TPU and EVA lack compatibilizers. After the peroxide crosslinks EVA, POE and SEBS, the interface bonding with TPU is not good. At the weak points of the interface bonding, phenomena such as through holes and pores appear. Therefore, obvious pores of different sizes can be seen. Such pore structure will directly affect the material's resilience and compression set properties, causing these properties to decline and thus affecting its service life.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A highly elastic foamed material capable of closed-loop recyclable foaming, characterized in that, It is produced from the following raw materials in parts by weight: A) 50-80 parts of thermoplastic elastomer particles; B) 30-50 parts of EVA or EVA / POE / SEBS blend; C) 2-6 parts of dicarboxylic acid; D) Crosslinking system, wherein the crosslinking system is a peroxide crosslinking system or an ionic crosslinking system.

2. The foamed material according to claim 1, characterized in that, The thermoplastic elastomer particles are one or a combination of two or three of TPU, TPEE, and PEBAX.

3. The foamed material according to claim 1, characterized in that, When B) is an EVA / POE / SEBS blend, the mass fractions of EVA, POE and SEBS in the blend are 50-70 wt%, 20-30 wt% of EVA, and 10-20 wt% of SEBS, and the sum of the mass fractions of the three is 100 wt%.

4. The foamed material according to claim 1, characterized in that, The dicarboxylic acid is adipic acid or maleic acid.

5. The foamed material according to claim 1, characterized in that, When the crosslinking system is a peroxide crosslinking system, the crosslinking agent is DCP or BIPB, with an amount of 0.1 to 0.2 parts, and the accelerator is TAIC or HVA-2, with an amount of 0.3 to 0.5 parts.

6. The foamed material according to claim 1, characterized in that, When the crosslinking system is an ionic crosslinking system, the accelerator is one of zinc stearate, zinc chloride, and stannous chloride, with an amount of 0.1 to 0.4 parts, and the initiator is peroxide, with an amount of 0.02 to 0.05 parts.

7. A method for preparing a closed-loop regenerable foamed material as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Premix component B with dicarboxylic acid; (2) The thermoplastic elastomer particles are melt-blended with the premix obtained in step (1) and granulated to obtain blended particles; (3) The blended particles are subjected to secondary kneading, and the crosslinking system is added after the kneading torque is stabilized; (4) The material after adding the crosslinking system is extruded and granulated to obtain blended granules; (5) The blended granules are molded to obtain a preform; (6) The mold is foamed under high pressure gas conditions to obtain foamed material.

8. The preparation method according to claim 7, characterized in that, In step (5), injection molding is used. The injection molding machine mold temperature is 140-150℃, the mold temperature is 160-180℃, and the holding time is 6-10 min.

9. The preparation method according to claim 7, characterized in that, The high-pressure gas mentioned in step (6) is nitrogen, with a pressure of 20-40 MPa, a foaming temperature of 150-165°C, and a saturation time of 2-6 h; the high-pressure gas may also be a mixture of carbon dioxide and nitrogen.

10. The preparation method according to claim 7, characterized in that, It also includes the following closed-loop regeneration steps: The foamed product obtained in step (6) is crushed to obtain foamed granules; the foamed granules are melt-blended and extruded into granules by a twin-screw extruder to obtain recycled granules, or melted by a mixer and then extruded into granules by a single-screw extruder to obtain recycled granules; and the recycled granules are subjected to the same steps (5) and (6) of claim 7 to obtain recycled foamed products.

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