Recovery method for recoverable foaming material

Abstract

The invention discloses a method for recycling a recyclable foaming material, and aims to solve the problems of foaming shrinkage, performance degradation after recycling, non-uniform foam holes and the like of the existing polyurethane elastomer and realize multi-cycle high-value utilization of the material. The recyclable foaming material is characterized by being formed by polymerizing components such as a polyurethane acrylate prepolymer containing dynamic reversible covalent bonds. The foam material can be recycled after being treated by the recycling method, the tensile strength of the foam material is 4MPa to the maximum, the elongation at break is 400% to the maximum, the foam material has excellent flexibility and deformability, the performance of the foam material is equivalent to that of an original material, the foaming ratio is 20 times to the maximum, the foam material has excellent foaming stability, and the recycled material can maintain mechanics, foaming and excellent circulating resilience close to the original material. And multi-time high-value closed-loop cyclic utilization is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foaming materials, and particularly relates to a recycling method of recyclable foaming materials. BACKGROUND

[0002] With the global economy accelerating the transformation to a sustainable development model, the life cycle management of traditional materials is facing unprecedented challenges. Among them, the recyclability and recycling of high polymer materials have become the core issues to promote green transformation of manufacturing industry and realize efficient use of resources. Among many high polymer materials, polyurethane elastomers have been widely used in important fields of national economy such as automobiles, aerospace, medical devices, personal protective equipment and sports equipment due to their excellent mechanical properties, excellent wear resistance, adjustable hardness range and good processing adaptability. With the increasing demand for lightweight and high-performance materials, supercritical fluid foaming technology has become a key technology for preparing high-performance polyurethane foam materials due to its solvent-free, environmentally friendly, controllable cell structure and uniform foaming, which has greatly expanded the application boundaries and value of polyurethane materials.

[0003] Traditional polyurethane materials, especially thermosetting polyurethane, have permanent crosslinking networks inside which are difficult to dissociate after use. This irreversible crosslinking structure makes the recycling process extremely complex, usually relying on high-temperature melting or strong chemical reagents for degradation. Although these methods can to some extent realize the reshaping of material morphology, they are essentially achieved by destroying the molecular backbone or crosslinking bond, inevitably causing a series of structural damages such as molecular weight drop, crosslinking density reduction or key functional group inactivation. These damages cause the tensile strength, elongation at break and re-foaming performance (such as foaming ratio and cell uniformity) of the recycled products to be greatly deteriorated, making it difficult for the recycled materials to meet the strict requirements of material performance consistency and reliability in high-end application scenarios, thereby seriously hindering the closed-loop recycling of materials.

[0004] However, with the continuous development of related technologies and the increasingly stringent performance requirements of application scenarios, some inherent characteristics of the aforementioned technical solutions at the principle level have gradually revealed deep-seated limitations in addressing new challenges, leading to a non-obvious internal technical contradiction. The core of this contradiction lies in how to ensure that polyurethane elastomers can form stable, uniform, and high-performance foam structures during supercritical foaming, while simultaneously endowing them with dynamic reconfigurability that maintains near-original performance after multiple recycling cycles. Existing technologies present a dilemma of "you can't have your cake and eat it too." For example, while conventional thermoplastic polyurethane (TPU) possesses a certain degree of reprocessability, under supercritical foaming conditions, its melt strength is often insufficient to support the rapid expansion and stability of the foaming gas, easily leading to cell collapse, fusion, or uncontrolled shrinkage. This results in uneven foam structures and unstable performance, failing to meet the application requirements of high-performance foams. The reason for this is that the molecular chains of thermoplastic materials are mainly connected by physical entanglement or weak non-covalent bonds. During high-temperature foaming or reprocessing, these forces are easily disrupted, leading to a decrease in structural stability.

[0005] Conversely, traditional permanently cross-linked thermosetting polyurethanes, while forming relatively stable cell structures during supercritical foaming, exhibit irreversible cross-linked networks once cured, rendering them virtually unrecyclable and completely blocking their recycling pathway. Even though some studies have attempted to introduce reversible non-covalent interactions, such as hydrogen bonds, ionic bonds, or simple dynamic covalent bonds, to construct material systems that balance performance and recyclability, these dynamic interactions often struggle to maintain structural integrity and reversibility during high-temperature reprocessing or multiple recycling cycles. Specifically, during prolonged high-temperature shearing and thermal processing, the dynamic equilibrium of these reversible bonds is disrupted, leading to reduced bonding efficiency or irreversible degradation of molecular chains. This causes the material's mechanical properties (such as tensile strength and elongation at break) to rapidly decline after several cycles, ultimately rendering it unusable. Furthermore, there is a lack of deep synergy between the material design of existing recycling processes and supercritical foaming processes. Recycled materials often exhibit a series of performance degradation problems during refoaming, including uneven cell distribution, significantly reduced expansion ratio, and poor compression resilience. This means that even if the material can be physically recycled and reprocessed, its performance after refoaming is far lower than that of the original material, making it impossible to truly achieve a high-value closed-loop cycle of "use-recycling-refoaming-reuse". This core contradiction largely restricts the long-term sustainable application and value realization of polyurethane foam materials in high-end fields. Summary of the Invention

[0006] This invention provides a recycling method for recyclable foamed materials, aiming to achieve a dynamic reconfigurability of polyurethane elastomer materials that can maintain near-original performance after multiple recycling cycles, thereby promoting the high-value closed-loop recycling of high-performance polyurethane foam materials.

[0007] To achieve the above-mentioned objective, the present invention provides a method for recycling recyclable foamed materials, the steps of which include the following:

[0008] S1, Shredding: The used recyclable foam material is shredded into fragments with a particle size of 0.5~10mm using mechanical shearing or crushing equipment;

[0009] S2, Internal mixing: Transfer the shredded fragments to an internal mixer and shear and mix the fragments at a speed of 10-150 rpm for 10-30 minutes at a temperature of 70-150℃.

[0010] S3, Hot pressing: Transfer the mixed material to a hot press, apply a pressure of 2-15 MPa at a temperature of 70-180°C, and continue hot pressing for 5-20 minutes.

[0011] S4, Re-supercritical foaming: The recycled elastomer after hot pressing is placed back into the autoclave, and supercritical fluid is injected into the autoclave. The total pressure inside the autoclave is controlled within the range of 3~30MPa. The elastomer is immersed at a temperature of 70~120℃ for 0.1~48h. Subsequently, by depressurizing to atmospheric pressure, the expansion of saturated gas is induced, resulting in recyclable foamed material E after re-supercritical foaming with a uniform and stable internal cell structure.

[0012] The recyclable foam material is prepared by the following method:

[0013] S5: Mixing: Under light-protected conditions, 35-90 parts of polyurethane acrylate prepolymer, 0.2-6 parts of reactive diluent, 0.2-6 parts of photoinitiator, 1-8 parts of inorganic nanofiller, and 1-20 parts of additives are added to a reaction vessel. The mixture is stirred continuously at 30-70℃ for 0.1-2 hours and dispersed uniformly by mechanical stirring. After uniform dispersion, 0.01-1wt% of polymerization inhibitor is added to obtain prepolymer mixture A. The prepolymer mixture A is cooled to 20-40℃, and 1-25 parts of thermosetting agent are added. The mixture is stirred uniformly again to obtain initial material B that can be used for photopolymer 3D printing and supercritical foaming.

[0014] S6, Photopolymerization: The initial material B is formed by photopolymerization 3D printing technology or photopolymerization molding technology, and a three-dimensional product C with a specific shape and preliminary cross-linking structure is formed under ultraviolet light irradiation conditions of 365~405nm;

[0015] S7, Supercritical foaming: The three-dimensional product C is placed in a high-pressure autoclave, and supercritical fluid is introduced. The product is impregnated for 0.1 to 48 hours at a temperature of 70 to 120°C and a pressure of 3 to 50 MPa to obtain an initial recyclable foam material D with a uniformly distributed closed-cell or open-cell structure.

[0016] The polyurethane acrylate prepolymer is prepared through the following steps:

[0017] A1. Take a quantitative amount of polyol with a molecular weight range of 500~5000 g / mol, and vacuum treat the polyol in a vacuum oven at 100~110℃ for 2~4 h to obtain a pretreated polyol with a water content of less than 300 ppm.

[0018] A2, Under a nitrogen protective atmosphere, polyol and isocyanate are mixed, and the molar ratio of polyol to isocyanate is controlled at 1:1.3~3. The prepolymerization reaction is carried out by adding a catalyst at a temperature of 50~60℃ with an amount of 0.03 wt%~0.06 wt% of the total amount of polyol and isocyanate. After the addition is completed, the reaction temperature is controlled at 60~90℃ and the reaction continues for a period of time. The reaction process is monitored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). When the characteristic absorption peak of -NCO no longer changes, the reaction temperature is reduced to below 50℃ to obtain a prepolymer with isocyanate groups at the end.

[0019] A3, an acrylate compound containing amino groups is added dropwise to the prepolymer with isocyanate end groups, and the reaction is carried out at 40~50℃ for 0.5~2h. The reaction process is monitored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). When the infrared characteristic absorption peak of -NCO disappears, stirring is stopped to obtain a polyurethane acrylate prepolymer with urea bond or substituted urea bond urethane structure.

[0020] Furthermore, the supercritical fluid is carbon dioxide or nitrogen or a mixture of both.

[0021] Furthermore, in S4, the supercritical fluid is a gas mixture with a volume ratio of N2:CO2=12:8.

[0022] Furthermore, in S4, the pressure drop rate is 20~50MPa / s.

[0023] Furthermore, in A1, the polyol is one of polyester polyol or polyether polyol.

[0024] Further, in A2, the isocyanate is one or more of diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, or hydrogenated diphenylmethane diisocyanate.

[0025] Furthermore, in A2, the catalyst is dibutyltin dilaurate.

[0026] Furthermore, in A3, the amino-containing acrylate compound is preferably ethyl 2-(tert-butylamino)methacrylate.

[0027] Furthermore, in S5, the reactive diluent is selected from monofunctional (meth)acrylates or acrylamide compounds.

[0028] Furthermore, the monofunctional group is one or more of the following: (meth)acrylate isobornyl acrylate, acrylmorpholine, (meth)acrylate isobutyl ester, (meth)acrylate methyl ester, (meth)acrylate isooctyl ester, (meth)acrylate lauryl ester, (meth)acrylate dodecyl ester, and (meth)acrylate octadecyl ester.

[0029] Further, the photoinitiator in S5 is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, benzoylbenzene, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, or bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0030] Furthermore, the thermosetting agent component described in S5 is a diol and / or a diamine with bifunctional groups.

[0031] Further, the diol is one or more of 1,4-butanediol, ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1,4-cyclohexanediol, and hydrogenated bisphenol A.

[0032] Further, the diamine is one or more selected from 3,5-dimethylthiotoluene diamine, ethylenediamine, 3,3-dichloro-4,4-diaminodiphenylmethane, 2,4-diamino-3,5-dimethylthiochlorobenzene, 3-amino-5-tert-butylpyrazole, N,N-bis(tert-butyl)ethylenediamine, isophorone diamine, 4,4'-diaminodicyclohexylmethane, 3,3'-dimethyl-4,4'-diamino-dicyclohexylmethane, and 2-methyl-1,5-pentanediamine.

[0033] Furthermore, in S5, the inorganic nanofiller is one or more of nano-silica, nano-titanium oxide, carbon nanotubes, or graphene oxide, and the inorganic nanofiller has a particle size of 5 to 200 nm.

[0034] Compared to existing technologies, this invention introduces a specific polyurethane acrylate prepolymer system. This prepolymer cleverly incorporates dynamic covalent bonds that can reversibly dissociate and reconstruct under specific thermal conditions through a polyol end-capping reaction. This material design ensures that during supercritical foaming, re-thermosetting allows for partial dissociation of the dynamic covalent bonds to generate isocyanates, which react with the thermosetting agent to form high-molecular-weight polyurethane molecular chains. This reduces the crosslinking density of the printed parts and improves the tensile and foaming properties of the stretched elastomer. In the recycling and reprocessing stage, through precisely controlled mixing and hot-pressing processes, the system's dynamic reversible covalent bonds are efficiently dissociated and rebonded, enabling complete reconstruction of the polymer network and effectively avoiding molecular chain degradation and significant performance loss. Furthermore, the reconstructed material can successfully undergo re-supercritical foaming, exhibiting a foaming ratio, cell structure uniformity, and excellent mechanical properties and cycle resilience close to the original material.

[0035] The recycling method of this invention uses a relatively low thermal processing temperature, which effectively reduces the possibility of thermal degradation of polymer molecular chains in multiple cycles, thereby supporting multiple high-value closed-loop recycling of materials, which meets the requirements of sustainable manufacturing and green development.

[0036] The recyclable foamed material of this invention, after being processed by a recycling method, exhibits a maximum tensile strength of 4 MPa, approaching or reaching the tensile strength level of the virgin material, significantly superior to most existing recyclable elastomer systems. Its elongation at break can reach up to 400%, indicating excellent flexibility and deformation capacity, comparable to the virgin material. The foaming ratio can reach up to 20 times; even at this high foaming ratio, the cell structure remains uniform and intact, without cell collapse or severe fusion, demonstrating excellent foaming stability. After undergoing 50 cycles of 50% compressive strain, the energy loss rate of the recyclable foamed material is at most 9.8%, stabilizing below 15% after multiple cycles. The small hysteresis loop area of ​​the cyclic compressive stress-strain curve indicates good deformation resistance and energy dissipation efficiency, making it suitable for applications requiring long-term dynamic load bearing. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the reprocessing and supercritical foaming of recyclable foam materials.

[0038] Figure 2 SEM image and cell diameter distribution of PES-PUA foam, a recyclable foaming material.

[0039] Figure 3 SEM image and cell diameter distribution of PES-PUA foam-1-R, a recyclable foam material.

[0040] Figure 4 SEM image and cell diameter distribution of PES-PUA foam-2-R, a recyclable foaming material. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to embodiments. It should also be understood that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. The specific mass, reaction time, temperature, process parameters, etc., in the examples are merely examples within a suitable range. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0042] The polyurethane acrylate prepolymer (PES-PUA) is prepared through the following steps:

[0043] Polybutylene adipate (PEG) with a number-average molecular weight of 2000 g / mol was selected as the polyester polyol. The polyol was vacuum-treated in a vacuum oven at 110°C for 2 hours, resulting in a pretreated polyol with a water content of 255 ppm. Under a nitrogen atmosphere, 1000 g of PEG and 250 g of diphenylmethane diisocyanate (molecular weight of diphenylmethane diisocyanate was 250, and the molar ratio of PEG to diphenylmethane diisocyanate was 1:2) were mixed and added dropwise at 50°C with a catalyst of 0.05 g dibutyltin dilaurate to initiate a prepolymerization reaction. After the addition was complete, the reaction temperature was maintained at 80°C for a further period. The reaction system underwent attenuated total reflection. The reaction process was monitored using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR). When the characteristic absorption peak of -NCO no longer changed, the reaction temperature was lowered to 50℃ to obtain a prepolymer with isocyanate end groups. 185g of ethyl 2-(tert-butylamino)methacrylate was added dropwise to the prepolymer with isocyanate end groups. The reaction was carried out at 40~50℃ for 2h under the catalysis of dibutyltin dilaurate. The reaction process was monitored using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR). When the infrared characteristic absorption peak of -NCO disappeared, stirring was stopped to complete the end capping, resulting in a polyurethane acrylate prepolymer PES-PUA with dynamic reversible covalent bonds.

[0044] The polyether-type polyurethane acrylate prepolymer (PE-PUA) is prepared through the following steps:

[0045] Polytetrahydrofuran glycol with a number-average molecular weight of 1500 g / mol was selected as the polyether polyol. The polyol was vacuum-treated in a vacuum oven at 110℃ for 2 hours, resulting in a pretreated polyether polyol with a water content of 214 ppm. Under a nitrogen atmosphere, 750 g of polytetrahydrofuran glycol and 375 g of diphenylmethane diisocyanate (molecular weight of diphenylmethane diisocyanate was 250, and the molar ratio of polybutylene adipate to diphenylmethane diisocyanate was 1:3) were mixed and added dropwise at 50℃ with a catalyst of 0.04 g dibutyltin dilaurate for prepolymerization. After the addition was complete, the reaction temperature was maintained at 80℃ for a further period. The reaction progress was monitored using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Once the characteristic absorption peak of -NCO no longer changed, the reaction temperature was adjusted. The temperature was lowered to 50°C to obtain a prepolymer with isocyanate end groups. 185g of ethyl 2-(tert-butylamino)methacrylate was added dropwise to the prepolymer with isocyanate end groups. The reaction was carried out at 40-50°C for 0.5h under the catalysis of dibutyltin dilaurate. The reaction process was monitored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). When the infrared characteristic absorption peak of -NCO disappeared, stirring was stopped to complete the end-capping and obtain the polyether-type polyurethane acrylate prepolymer PE-PUA.

[0046] The preparation of PES-PUE foam from recyclable initial materials comprises, by weight, 75 parts of polyurethane acrylate prepolymer (PES-PUA) prepared by the above method, 16.95 parts of isoborneol acrylate reactive diluent, 1 part of 2,4,6-trimethylbenzoyl diphenylphosphine oxide photoinitiator, 15 parts of thermosetting agent component 4,4'-diaminodicyclohexylmethane, 1 part of 20nm nano-silica inorganic nanofiller, and 1 part of antioxidant Irganox 1010 additive. The recycled foam material D is obtained through the following steps:

[0047] S5, Mixing: Under light-protected conditions, polyurethane acrylate prepolymer (PES-PUA), isoborneol acrylate reactive diluent, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, nano silica, and antioxidant Irganox 1010 were added to a reaction vessel and stirred continuously at 50°C for 2 hours. The mixture was then uniformly dispersed by mechanical stirring. After uniform dispersion, 0.05 wt% of hydroquinone monomethyl ether, a polymerization inhibitor, was added to obtain prepolymer mixture A. Prepolymer mixture A was cooled to 20°C, and the thermosetting agent component was added. The mixture was stirred again to obtain initial material B, which can be used for photopolymer 3D printing and supercritical foaming.

[0048] S6, Photocuring: The initial material B is poured into a self-made rectangular mold and irradiated with an LED ultraviolet light array with a wavelength of 395nm. The light intensity is set to 30 mW / cm and irradiated for 30 seconds to allow the material to complete curing and molding, and obtain a three-dimensional product C of a preliminary cross-linked elastomer sheet with a size of 100mm×50mm×5mm.

[0049] S7, Supercritical foaming: The three-dimensional product C is placed in a high-pressure autoclave, and a supercritical fluid is introduced. The supercritical fluid is a mixture of carbon dioxide and nitrogen in a volume ratio of 12:8. The foaming temperature is controlled at 100°C and the pressure is 15MPa for 3 hours. Subsequently, the pressure is reduced to atmospheric pressure at a decreasing rate of 50MPa / s, which causes the saturated gas to expand, resulting in an initial recyclable foam material D with a uniform and stable internal cell structure and a uniformly distributed closed-cell or open-cell structure. This recyclable foam material D is denoted as PES-PUE foam.

[0050] PES-PUE internally was examined using a desktop scanning electron microscope (COXEM, model EM-30, South Korea). + Structural scanning, refer to Figure 2 The obtained PES-PUE has a uniform cell structure with an average cell diameter of about 20 micrometers and a foaming ratio of 11.5 times.

[0051] The properties of the initially foamed PES-PUE foam were tested. The tensile strength was measured using a universal testing machine (Shimadzu Corporation, Japan, model AGX-100 plus), and the result was 5 MPa. The elongation at break was 360%.

[0052] The preparation of PE-PUE foam, the initial material for recyclable foaming material, includes, by weight, 75 parts of polyether-type polyurethane acrylate prepolymer (PE-PUA) prepared by the above method, 16.95 parts of isoborneol acrylate reactive diluent, 1 part of 2,4,6-trimethylbenzoyl diphenylphosphine oxide photoinitiator, 15 parts of thermosetting agent component 4,4'-diaminodicyclohexylmethane, 1 part of 20nm nano-silica inorganic nanofiller, and 1 part of antioxidant Irganox 1010 additive. The preparation steps are the same as those for PES-PUE foam preparation. This recyclable foaming material D is denoted as PE-PUE foam.

[0053] The properties of the PE-PUE foam after initial foaming were tested. The tensile strength was measured to be 3.5 MPa using a universal testing machine (Shimadzu Corporation, Japan, model AGX-100 plus), and the elongation at break was 420%.

[0054] The preparation of PE / PES-PUE foam, the initial material for recyclable foaming materials, differs in that the polyurethane acrylate prepolymer used is a polyurethane-type polyurethane acrylate prepolymer and a polyether-type polyurethane acrylate prepolymer, which are formulated in a 1:1 ratio. The preparation steps are the same as those for PES-PUE foam. This recyclable foaming material D is denoted as PE / PES-PUE foam.

[0055] The properties of the PE / PES-PUE foam after initial foaming were tested. The tensile strength was measured to be 4.0 MPa using a universal testing machine (Shimadzu Corporation, Japan, model AGX-100 plus), and the elongation at break was 384%.

[0056] The recyclable foamed materials obtained above—PES-PUA foam, PE-PUE foam, and PE / PES-PUE foam—were divided into two groups and processed according to the following method:

[0057] Group 1: After placing PES-PUA foam, PE-PUE foam, and PE / PES-PUE foam indoors for 60 days, the resulting products were recorded as PES-PUA foam-1, PE-PUE foam-1, and PE / PES-PUE foam-1, respectively.

[0058] Group 2: PES-PUA foam, PE-PUE foam, and PE / PES-PUE foam were placed in an air-conditioned aging test chamber for aging at 80℃ for 72 hours. The resulting products were recorded as PES-PUA foam-2, PE-PUE foam-2, and PE / PES-PUE foam-2, respectively.

[0059] Example 1:

[0060] The PES-PUA foam-1 recycling method is referred to... Figure 1 The steps include the following:

[0061] S1, Shredding: PES-PUA foam-1 is shredded into fragments with a particle size of 5mm using mechanical shearing or pulverizing equipment;

[0062] S2, Internal mixing: Transfer the shredded fragments to an internal mixer and shear and mix the fragments at 100 rpm for 20 minutes at 130°C.

[0063] S3, Hot pressing: The mixed material is transferred to a hot press and hot-pressed at 130°C for 10 minutes under a pressure of 10 MPa.

[0064] S4, Re-supercritical foaming: The recycled elastomer after hot pressing is placed back into a high-pressure reactor. A supercritical gas mixture with a volume ratio of N2:CO2=12:8 is injected into the high-pressure reactor. The total pressure inside the reactor is controlled at 20MPa. The mixture is impregnated at 95℃ for 16h. Then, the pressure is reduced to atmospheric pressure at a decreasing rate of 50MPa / s, which causes the saturated gas to expand. This results in a recyclable foamed material E after re-supercritical foaming, which forms a uniform and stable cell structure inside. This material is denoted as PES-PUA foam-1-R.

[0065] Internal imaging of PES-PUE foam-1-R using a desktop scanning electron microscope (COXEM, model EM-30, South Korea). + Structural scanning, refer to Figure 3 The obtained PES-PUE foam-1-R has a uniform cell structure, with an average cell diameter of about 28 micrometers and a foaming ratio of 12 times.

[0066] The performance of PES-PUA foam-1-R was tested, and the results are as follows: tensile strength is 3.9 MPa, elongation at break is 350%, and energy loss rate is 9.8% after 50 cycles of 50% compressive strain. The data shows that after one recycling, reprocessing, and re-foaming, the various performance indicators of the material can still be maintained at a level close to that of the original material.

[0067] Example 2:

[0068] Similar to Example 1, the material used is PE-PUE foam-1, and the resulting product is denoted as PE-PUE foam-1-R.

[0069] The performance of PE-PUE foam-1-R was tested, and the results are shown in Table 1.

[0070] Example 3:

[0071] Similar to Example 1, the material used is PE / PES-PUE foam-1, and the resulting product is denoted as PE / PES-PUE foam-1-R.

[0072] The performance of PE / PES-PUE foam-1-R was tested, and the results are shown in Table 1.

[0073] Example 4:

[0074] Similar to Example 1, the material used is PES-PUA foam-2, and the resulting product is denoted as PES-PUA foam-2-R.

[0075] Internal imaging of PES-PUE foam-2-R using a desktop scanning electron microscope (COXEM, model EM-30, South Korea). + Structural scanning, refer to Figure 4The obtained PES-PUE foam-2-R has a uniform cell structure, with an average cell diameter of about 28 micrometers and a foaming ratio of 8 times.

[0076] The performance of PES-PUA foam-2-R was tested, and the results are shown in Table 1.

[0077] Example 5:

[0078] Similar to Example 1, the material used is PE / PES-PUE foam-2, and the resulting product is denoted as PE-PUE foam-2-R.

[0079] The performance of PE-PUE foam-2-R was tested, and the results are shown in Table 1.

[0080] Example 6:

[0081] Similar to Example 1, the material used is PE / PES-PUE foam-2, and the resulting product is denoted as PE / PES-PUE foam-2-R.

[0082] The performance of PE / PES-PUE foam-2-R was tested, and the results are shown in Table 1.

[0083] Table 1

[0084] Cell diameter (microns) Cell morphology Foam expansion Tensile strength (MPa) Elongation at break % Energy loss rate PES-PUE foam 20 Uniform 11.5 5 360 -- PE-PUE foam -- Uniform -- 3.5 420 -- PE / PES-PUE foam -- Uniform -- 4 384 -- Example 1 28 Uniform 12 3.9 350 9.8 Example 2 -- Uniform 18.2 3.2 430 8.1 Example 3 -- Uniform 15.1 3.5 375 9.1 Example 4 12 Uniform 8 3.3 300 11.5 Example 5 -- Uniform 15.2 2.7 370 9.6 Example 6 -- Uniform 12.5 2.8 310 10.9

[0085] As shown in Table 1, the data indicates that after one recycling, reprocessing, and re-foaming process, the material's various performance indicators can still be maintained at levels close to those of the original material.

[0086] Compared with the initial foaming of PES-PUE foam and the foaming ratio of PES-PUE foam after being placed indoors for 60 days in Example 1, the foam cell diameter and foaming ratio did not change much, while the tensile strength and elongation at break decreased slightly. The recycled material can meet the functional requirements of indoor application scenarios.

[0087] Compared with the initial foaming of PES-PUE foam and the use under specific conditions of high temperature scenario (aging temperature of 80℃ and aging time of 72h) in Example 4, the cell diameter and foaming ratio both decreased significantly, indicating that the recycled material will have a relatively obvious degradation under high temperature scenario. However, the data on its tensile strength, elongation at break and energy loss rate show that the recyclable material of the present invention can be recycled and used within an acceptable range.

[0088] The recyclable material prepared in this invention undergoes further complete reconstruction of the dynamically reversible covalent bonds that can be dissociated during the recycling process, forming a new, dense, and intact polymer network. The hot-pressing process not only effectively eliminates any porosity and defects that may exist within the material, but also allows for precise reshaping of the macroscopic shape of the recycled material, while ensuring the integrity and uniformity of the dynamically cross-linked network, thereby restoring the structural integrity and mechanical properties of the material.

[0089] This invention ensures efficient dissociation and rebonding of dynamically reversible covalent bonds through precisely controlled intensive mixing and hot pressing processes. This allows for complete reconstruction of the polymer network, minimizing molecular chain degradation and significant performance loss. Furthermore, the recycling method employs relatively low thermal processing temperatures (70°C to 150°C for intensive mixing and 70°C to 180°C for hot pressing), effectively reducing the likelihood of thermal degradation of the polymer molecular chains during multiple cycles. This further supports multiple high-value closed-loop recycling of the material, fully aligning with the principles of sustainable manufacturing and green development.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for recycling recyclable foamed materials, characterized in that, The steps include the following: S1, Shredding: The used recyclable foam material is shredded into fragments with a particle size of 0.5~10mm using mechanical shearing or crushing equipment; S2, Internal mixing: Transfer the shredded fragments to an internal mixer and shear and mix the fragments at a speed of 10-150 rpm for 10-30 minutes at a temperature of 70-150℃. S3, Hot pressing: Transfer the mixed material to a hot press, apply a pressure of 2-15 MPa at a temperature of 70-180°C, and continue hot pressing for 5-20 minutes. S4, Re-supercritical foaming: The recycled elastomer after hot pressing is placed back into the autoclave, and supercritical fluid is injected into the autoclave. The total pressure inside the autoclave is controlled within the range of 3~30MPa. The elastomer is immersed at a temperature of 70~120℃ for 0.1~48h. Subsequently, by depressurizing to atmospheric pressure, the expansion of saturated gas is induced, resulting in recyclable foamed material E after re-supercritical foaming with a uniform and stable internal cell structure. The recyclable foam material is prepared by the following method: S5: Mixing: Under light-protected conditions, 35-90 parts of polyurethane acrylate prepolymer, 0.2-6 parts of reactive diluent, 0.2-6 parts of photoinitiator, 1-8 parts of inorganic nanofiller, and 1-20 parts of additives are added to a reaction vessel. The mixture is stirred continuously at 30-70℃ for 0.1-2 hours and dispersed uniformly by mechanical stirring. After uniform dispersion, 0.01-1wt% of polymerization inhibitor is added to obtain prepolymer mixture A. The prepolymer mixture A is cooled to 20-40℃, and 1-25 parts of thermosetting agent are added. The mixture is stirred uniformly again to obtain initial material B that can be used for photopolymer 3D printing and supercritical foaming. S6, Photopolymerization: The initial material B is formed by photopolymerization 3D printing technology or photopolymerization molding technology, and a three-dimensional product C with a specific shape and preliminary cross-linking structure is formed under ultraviolet light irradiation conditions of 365~405nm; S7, Supercritical foaming: The three-dimensional product C is placed in a high-pressure autoclave, and supercritical fluid is introduced. The product is impregnated for 0.1 to 48 hours at a temperature of 70 to 120°C and a pressure of 3 to 50 MPa to obtain an initial recyclable foam material D with a uniformly distributed closed-cell or open-cell structure.

2. The method for recycling recyclable foamed materials according to claim 1, characterized in that, in, In S5, the polyurethane acrylate prepolymer is prepared by the following steps: A1. Take a quantitative amount of polyol with a molecular weight range of 500~5000 g / mol, and vacuum treat the polyol in a vacuum oven at 100~110℃ for 2~4 h to obtain a pretreated polyol with a water content of less than 300 ppm. A2, under a nitrogen protective atmosphere, polyol and isocyanate are mixed, and the molar ratio of polyol to isocyanate is controlled at 1:1.3~3. The mixture is added dropwise at 50~60℃ with a catalyst of 0.03 wt%~0.06 wt% of the total amount of polyol and isocyanate. After the addition is complete, the reaction temperature is controlled at 60~90℃ and the reaction continues for a period of time. The reaction process is monitored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). When the characteristic absorption peak of -NCO no longer changes, the reaction temperature is lowered to below 50℃ to obtain a prepolymer with isocyanate end groups. A3. An acrylate compound containing amino groups is added dropwise to the prepolymer with isocyanate end groups. The reaction is carried out at 40-50°C for 0.5-2 hours. The reaction process is monitored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). When the infrared characteristic absorption peak of -NCO disappears, stirring is stopped to obtain a polyurethane acrylate prepolymer with urea bonds or substituted urea bonds.

3. The method for recycling recyclable foamed materials according to claim 1, characterized in that, The supercritical fluid is carbon dioxide or nitrogen or a mixture of both.

4. The method for recycling recyclable foamed materials according to claim 1, characterized in that, In S4, the supercritical fluid is a mixture of gases with a volume ratio of N2:CO2=12:

8.

5. The method for recycling recyclable foamed materials according to claim 1, characterized in that, In S4, the pressure drop rate is 20~50MPa / s.

6. The recyclable foamed material according to claim 2, characterized in that, In A1, the polyol is one of polyester polyol or polyether polyol.

7. The recyclable foamed material according to claim 1, characterized in that, In A2, the isocyanate is one or more of diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, or hydrogenated diphenylmethane diisocyanate.

8. The recyclable foamed material according to claim 1, characterized in that, In A3, the amino-containing acrylate compound is preferably ethyl 2-(tert-butylamino)methacrylate.

9. The recyclable foamed material according to claim 1, characterized in that, In S5, the reactive diluent is selected from monofunctional (meth)acrylates or acrylamide compounds.

10. A recyclable foamed material according to claim 9, characterized in that, One or more of the monofunctional (meth)acrylate isobornyl acrylate, acrylmorpholine, isobutyl (meth)acrylate, methyl (meth)acrylate, isooctyl (meth)acrylate, lauryl methacrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate.

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