A self-healing, reprocessable, and recyclable rubber foam material

Abstract

This invention discloses a self-healing, reprocessable, and recyclable rubber foam material, belonging to the field of rubber foam material technology. The technical solution involves mixing an epoxidized natural rubber matrix, a reversible crosslinking agent, fillers, and other components, followed by a vulcanization process to obtain the rubber foam material matrix. Supercritical foaming technology is used for foaming, and the material is recycled and reprocessed through hot pressing and re-foaming processes. This invention achieves efficient self-healing by introducing dynamic ester bonds, significantly extending its service life. The optimized formulation balances self-healing performance and mechanical strength, enhancing the material's durability. Supercritical nitrogen foaming technology successfully prepares a low-density material, improving its lightweight properties. The material possesses excellent recyclability and can be reprocessed multiple times through hot pressing and supercritical foaming processes. Combined with biomass crosslinking agents and green processes, the material conforms to the concepts of green chemistry and sustainable development, exhibiting a low environmental impact.

Description

Technical Field

[0001] This invention relates to the field of rubber foam materials technology, and in particular to a self-healing, reprocessable and recyclable rubber foam material. Background Technology

[0002] Rubber materials, due to their excellent elasticity, processability, and physical and mechanical properties, are widely used in transportation, aerospace, construction, and many other fields, and have become one of the most widely used categories of polymer materials. The superior properties of rubber materials have led to widespread demand in modern industry. However, to improve the mechanical strength, durability, and service life of rubber materials, traditional cross-linking systems, such as sulfur vulcanization and peroxide vulcanization systems, are widely used. These cross-linking systems can effectively promote the formation of high-bond-energy covalent cross-linked networks between rubber molecular chains, thereby improving the mechanical properties and heat resistance of rubber. However, the stability of this covalent cross-linked network also makes it difficult to break or reassemble during use, thus preventing traditional rubber materials from self-healing or being recycled and reprocessed after damage, greatly limiting their development potential in certain specific applications. With the increasing demands for environmental protection and sustainable development in modern society, especially in the recycling and reprocessing of waste rubber, how to develop new rubber materials that possess both good mechanical properties and self-healing and recyclability has become a research hotspot in the field of materials science.

[0003] In recent years, significant progress has been made in the research of dynamically crosslinked rubber materials. In 2011, Professor Leibler's team introduced ester bonds as crosslinking bonds into an epoxy resin system, successfully preparing a "glass-like" material with self-healing and reprocessing capabilities, ushering in a new era of self-healing and recyclable thermosetting materials. Since then, more and more researchers have begun to focus on how to introduce dynamic covalent bonds into rubber materials to endow them with self-healing and recyclable properties. For example, researchers have used dynamic covalent bond structures such as disulfide bonds, β-hydroxy ester bonds, and imine bonds, and used external stimuli (such as heat, light, pH value, etc.) to achieve the breaking and recombination of these bonds, thereby enabling the rubber materials to possess self-healing and recyclable properties.

[0004] Despite some progress in the research of self-healing and recyclable rubber materials, existing technologies still have significant shortcomings. First, most existing reversible crosslinking systems rely on specific chemical reactions or external conditions (such as high temperatures, acidic or alkaline environments), which can lead to reduced material stability or complex preparation processes, limiting their large-scale application. For example, while crosslinking systems based on disulfide or ester bonds can provide good self-healing effects, their crosslinking processes and reaction conditions are quite demanding, and their self-healing ability may gradually decrease with repeated damage repair during long-term use. Furthermore, although supercritical fluid foaming technology has been proven to effectively reduce environmental pollution and has been applied in some high-end fields, its application in reversibly crosslinked rubber materials remains relatively rare, failing to fully realize its potential in preparing lightweight, environmentally friendly rubber foam materials.

[0005] Current research on the self-healing and recyclability of rubber materials still faces many challenges, especially in improving their recyclability and reprocessing performance, reducing production costs, and achieving environmentally friendly treatment while meeting material performance requirements. This remains a pressing issue. Furthermore, developing lightweight and recyclable rubber materials using reversible cross-linking structures and environmentally friendly foaming techniques, without relying on high temperatures or other special conditions, remains an important research direction.

[0006] Therefore, solving these technical challenges, especially in developing green rubber materials that maintain high mechanical properties while possessing excellent self-healing and recyclability, is crucial for research in this field. Current research urgently needs to overcome the limitations of existing technologies, particularly in proposing more innovative and efficient solutions to synergistically improve self-healing and recyclability. Summary of the Invention

[0007] To achieve the aforementioned objectives and address the aforementioned technical problems, this invention provides a self-healing, reprocessable, and recyclable rubber foam material matrix, wherein the rubber foam material matrix is ​​prepared from the following raw materials in the indicated mass fractions:

[0008] The composition includes 80-100 parts of epoxidized natural rubber matrix, 2-6 parts of reversible crosslinking agent, 5-30 parts of filler, 2-6 parts of 1,2-dimethylimidazole, 2-4 parts of zinc stearate, 5-10 parts of n-octyl terephthalate, and 2 parts of antioxidant.

[0009] Preferably, the epoxidized natural rubber matrix is ​​epoxidized natural rubber or a blend of epoxidized natural rubber and other polymers, wherein the mass ratio of epoxidized natural rubber is 70%-100%, and the other polymers are one of polybutylene succinate and ethylene-vinyl acetate copolymer.

[0010] Preferably, the epoxy degree of the epoxidized natural rubber is 25%-50%.

[0011] Preferably, the reversible crosslinking agent is either malic acid or citric acid.

[0012] Preferably, the filler is one of carbon black, silica, lignin, and carboxymethyl cellulose.

[0013] Preferably, the antioxidant is one or two of antioxidant 2246 and antioxidant 1010.

[0014] The present invention also provides a method for preparing the self-healing, reprocessable, and recyclable rubber foam material matrix as described above. The preparation method comprises: mixing 80-100 parts of epoxidized natural rubber matrix, 2-6 parts of reversible crosslinking agent, 5-30 parts of filler, 2-6 parts of 1,2-dimethylimidazole, 2-4 parts of zinc stearate, 5-10 parts of n-octyl terephthalate, and 2 parts of antioxidant at a mixing temperature of 50-120°C to obtain a compound; and then vulcanizing the compound at a vulcanization temperature of 160°C for 20-60 minutes to obtain the rubber foam material matrix.

[0015] This invention also provides a method for preparing a self-healing, reprocessable, and recyclable rubber foam material, comprising the following steps:

[0016] A1. Place the rubber foam material matrix into a supercritical foaming device and remove the air inside the device;

[0017] A2 is saturated with nitrogen gas;

[0018] A3 is heated to the foaming temperature, and after the reaction is complete, the pressure is released to room temperature to obtain the rubber foam material.

[0019] The rubber foam material matrix is ​​prepared by the above-described preparation method.

[0020] Preferably, in step A2, the nitrogen gas pressure is 15-30 MPa and the saturation time is 2-6 h.

[0021] Preferably, in step A3, the foaming temperature is 80-110℃.

[0022] This invention also provides a method for recycling a self-healing, reprocessable, and recyclable rubber foam material, comprising the following steps:

[0023] B1 involves crushing the rubber foam material and hot-pressing it at 180°C for 60-120 minutes to obtain recyclable material;

[0024] B2 The recycled material is placed in a supercritical foaming device, and foamed at a foaming temperature of 80-140℃ under nitrogen conditions of 15-30MPa for 2-6 hours to obtain recycled foamed material.

[0025] The rubber foam material is prepared by the above-described preparation method.

[0026] The beneficial effects of the technical solution provided by this invention are as follows:

[0027] Excellent self-healing properties: By introducing dynamic ester bonds (formed by ring-opening reactions between epoxy groups and carboxylic acid groups in malic or citric acid), the rubber foam material provided by this invention can achieve highly efficient self-healing after damage. The sample of this invention can achieve a repair efficiency of up to 89.2% within 2 hours, greatly extending the material's service life. This self-healing effect stems from the reversibility of the dynamic ester bonds, which can break at the damage site and recombine under external conditions (such as temperature and pressure) to restore the material's mechanical properties. This mechanism ensures effective repair of the material after multiple damages, thereby extending its service life and solving the problem of traditional covalently cross-linked materials' inability to self-heal.

[0028] Excellent mechanical properties: The prepared materials exhibit high tensile strength, with the highest tensile strength reaching 15.162 MPa. By adjusting the proportion of the reversible crosslinking agent and the formulation of other additives, this invention achieves an optimal balance between the material's mechanical properties and self-healing ability. This technical effect, through the introduction of dynamic ester bonds, not only enhances the material's strength but also improves its durability in practical applications.

[0029] Low density and good foaming properties: Using supercritical nitrogen as a foaming agent, this invention successfully prepared low-density rubber foam materials with a foam density as low as 0.118 g / cm³. 3 This significantly improves the material's lightweight properties. The low density not only reduces the material's weight but also enables its application in various lightweight structural applications, aligning with the principles of green chemistry and sustainable development. Supercritical fluid foaming technology utilizes the excellent solubility and diffusivity of nitrogen in the supercritical state to ensure the uniformity and stability of the foam structure, while avoiding the environmental pollution problems that may arise from traditional chemical foaming methods.

[0030] Excellent recyclability and reprocessing performance: The rubber foam material of this invention possesses excellent recyclability and reprocessing capabilities. Through a simple hot-pressing and supercritical foaming process, the material retains its good physical properties even after multiple heat treatments and foaming processes. Specifically, after hot-pressing at 180°C for 60-120 minutes, the material can be recycled and further processed through supercritical foaming to maintain its good foaming characteristics. This recycling method not only improves the resource utilization efficiency of the material but also reduces waste generation, conforming to the principles of green chemistry and a circular economy.

[0031] Green and Sustainable: By using biomass materials such as malic acid or citric acid as crosslinking agents and combining them with supercritical fluid foaming technology, this invention provides a rubber foam material with a low environmental impact production process. Malic acid and citric acid, as naturally sourced chemicals, not only reduce dependence on petroleum-based resources but also make the final product more environmentally friendly. Compared to traditional rubber foam materials, the material of this invention can be reused through simple recycling methods, greatly improving the material's sustainability. Attached Figure Description

[0032] Figure 1 This is a SEM image of Embodiment 3 of the present invention;

[0033] Figure 2 This is a SEM image of Embodiment 4 of the present invention;

[0034] Figure 3 This is a SEM image of Embodiment 5 of the present invention;

[0035] Figure 4 The image shows a physical sample of Embodiment 3 of the present invention; a is a rubber foam material, b is a pulverized rubber foam material, and c is a recycled and stretched strip of rubber material. Detailed Implementation

[0036] 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.

[0037] Example 1

[0038] Preparation of a self-healing, reprocessable, and recyclable rubber foam matrix: 100 parts of epoxidized natural rubber with an epoxy degree of 50%, 2 parts of malic acid, 10 parts of silica, 2 parts of 1,2-dimethylimidazole, 4 parts of zinc stearate, 10 parts of n-octyl terephthalate, and 2 parts of antioxidant 2246 are mixed at a mixing temperature of 50°C to obtain a compound. The compound is then vulcanized at a vulcanization temperature of 160°C for 30 minutes to obtain the rubber foam matrix.

[0039] Preparation of self-healing, reprocessable, and recyclable rubber foam materials:

[0040] A1. Place the rubber foam material matrix into a supercritical foaming device and remove the air inside the device;

[0041] A2 is saturated with nitrogen gas at a pressure of 20 MPa for 2 hours.

[0042] A3 is heated to 80°C, and after the reaction is complete, the pressure is released to room temperature to obtain the rubber foam material.

[0043] Recycling of self-healing, reprocessable, and recyclable rubber foam materials:

[0044] B1 involves crushing the rubber foam material and hot-pressing it at 180°C for 120 minutes to obtain recyclable material.

[0045] B2 places the recycled material in a supercritical foaming device, foams at a temperature of 80°C, under nitrogen conditions of 20 MPa, and foams for 2 hours to obtain recycled foamed material.

[0046] Example 2-10

[0047] Prepared using the same method as in Embodiment 1, except as shown in Tables 1 and 2.

[0048] Comparative Examples 1-2

[0049] Prepared using the same method as in Embodiment 1, except as shown in Table 3.

[0050] Table 1 List of conditions for the embodiments

[0051]

[0052]

[0053] Table 2 List of conditions for the embodiments

[0054]

[0055] Table 3 List of Comparative Conditions

[0056]

[0057]

[0058] Experimental test:

[0059] 1. Mechanical Properties: The material and its foamed samples were cut into dumbbell-shaped tensile specimens and subjected to tensile tests using an electronic universal testing machine at room temperature and a testing speed of 500 mm / min. Five samples were tested under each set of process conditions, and the average value was calculated.

[0060] 2. Structure and Morphology: The fracture morphology of the material samples was observed using scanning electron microscopy (SEM, JSM-7610FPULS). These samples were fractured in liquid nitrogen and mounted on a platform with a conductive adhesive film. The fracture surface was then sputter-coated with gold three times at a current of 3 mA, each time for 60 s. The micropore diameters in the SEM images of the samples were calculated using ImageJ software.

[0061] 3. Self-healing rate: The self-healing efficiency is represented by the ratio of tensile strength before and after self-healing. Self-healing efficiency η = σ / σ0, where σ is the tensile strength after self-healing and σ0 is the tensile strength before self-healing.

[0062] Table 4 Summary of Experimental Data

[0063]

[0064]

[0065] Self-healing performance: Experimental data show that the self-healing rates of Examples 1 to 10 are all high, indicating that the material can efficiently recover its mechanical properties after damage occurs, achieving the technical effect of this invention – excellent self-healing performance. Comparative Experiments 1 and 2 both show a lack of self-healing ability and are unable to repair damage. This indicates that traditional rubber foam materials lack a dynamic ester bond self-healing mechanism and cannot achieve recovery after material damage, demonstrating the unique advantages of this invention in self-healing.

[0066] Mechanical Properties: In the examples, the tensile strength gradually increased with changes in filler and crosslinking agent, demonstrating that the present invention can balance the relationship between self-healing ability and mechanical strength by adjusting the crosslinking agent ratio and adding different additives. Comparative experiments show that traditional materials have higher mechanical properties, but due to their lack of self-healing function, they cannot provide the comprehensive advantages of the material of the present invention. In particular, although comparative experiment 1 showed high strength, it could not repair itself, indicating poor damage resistance.

[0067] Density and Foaming Performance: The density of the material varies depending on the formulation of the examples. Overall, the foaming density of the examples is low, indicating that the present invention can effectively reduce the weight of the material through supercritical foaming technology, meeting the requirements of low density and good foaming performance. Comparative Experiment 2 is a low-density material, but it lacks durability due to its inability to self-heal. While Comparative Experiment 1 has a better foaming effect, it also exhibits poor overall performance due to its inability to repair itself.

[0068] Reprocessing performance: The materials in all embodiments can be reprocessed and foamed while maintaining good physical properties. The change in foam density after reprocessing indicates that the material has good recyclability and reprocessing performance. This technical effect, achieved through hot pressing and supercritical foaming processes, ensures the recyclability of the material and maintains good foaming characteristics even after multiple heat treatments. Comparative experiments 1 and 2 failed to achieve reprocessing and foaming, failing to meet the requirements for recycling and reprocessing, indicating that traditional materials have poor recycling performance after use and cannot compare with the material of this invention in terms of environmental protection and sustainability.

[0069] Green and Sustainable Development: This invention, through the use of naturally derived crosslinking agents (malic acid or citric acid) and supercritical fluid foaming technology, effectively reduces dependence on traditional petroleum-based resources and lowers the environmental impact of the production process. The examples demonstrate the material's reprocessability and recyclability, which aligns with the principles of green chemistry and the circular economy. While the material in the comparative experiment possesses certain foaming capacity and mechanical properties, its inability to be repaired and recycled makes it unsuitable for sustainable development.

[0070] The SEM images from the examples show that as the amount of crosslinking agent increases, the degree of crosslinking of the material increases, the size and number of cells in the foamed material decrease, and the density of the foamed material increases accordingly, while the self-healing efficiency decreases.

[0071] This invention, through an innovative dynamic ester bond self-healing mechanism, combined with supercritical fluid foaming technology and green and environmentally friendly materials, successfully achieves high-efficiency self-healing, excellent mechanical properties, low-density foaming, and good recyclability and reprocessing performance, possessing broad application prospects and sustainable development advantages.

[0072] 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 self-repairing reworkable and recyclable rubber foamed material matrix, characterized in that, The rubber foaming material matrix is prepared from the following raw materials in mass fraction: The reversible cross-linking agent is any one of malic acid or citric acid; The self-repairing, reworkable and recyclable rubber foaming material matrix is prepared by the following preparation method: The rubber foaming material matrix is prepared by mixing the epoxidized natural rubber matrix, reversible cross-linking agent, filler, 1,2 dimethyl imidazole, zinc stearate, n-octyl terephthalate and antioxidant at a mixing temperature of 50-120 DEG C, and then vulcanizing the mixed rubber at a vulcanization temperature of 160 DEG C for 20-60 min. The epoxidized natural rubber matrix is epoxidized natural rubber or a blend of epoxidized natural rubber and other polymers, with the mass ratio of epoxidized natural rubber being 70%-100%, and the other polymer being one of polybutylene succinate and ethylene-vinyl acetate copolymer.

2. The self-repairing reworkable and recyclable rubber foamed material matrix according to claim 1, characterized in that, The epoxidized natural rubber has an epoxidation degree of 25%-50%.

3. Self-repairing reworkable and recyclable rubber foamed material matrix according to claim 2, characterized in that, The filler is one of carbon black, white carbon black, lignin and carboxymethyl cellulose, and the antioxidant is one or both of antioxidant 2246 and antioxidant 1010.

4. The self-repairing reworkable and recyclable rubber foamed material matrix according to claim 1, characterized in that, The preparation method comprises the following steps:

5. A process for the preparation of self-repairing reworkable and recyclable rubber foamed material matrix according to any one of claims 1-4, characterized by, The preparation method comprises the following steps:

6. A process for the preparation of a self-repairing reworkable and recyclable rubber foamed material, characterized by, A1putting the rubber foaming material matrix into a supercritical foaming device to remove air in the device; A2saturating by introducing nitrogen gas, with the nitrogen gas pressure being 15-30 MPa and the saturation time being 2-6 h; A3increasing the temperature to a foaming temperature, and releasing pressure to normal temperature after the reaction is completed, to obtain the rubber foaming material, with the foaming temperature being 80-110 DEG C, The rubber foaming material matrix is prepared by the preparation method of claim 5. The preparation method comprises the following steps:

7. A method for recycling a self-repairing, reworkable and recyclable rubber foamed material, characterized in that, B1pulverizing the rubber foaming material and hot-pressing at 180 DEG C for 60-120 min to obtain a recycled material; B2putting the recycled material into a supercritical foaming device, foaming at a foaming temperature of 80-140 DEG C under the condition of 15-30 MPa nitrogen gas, and saturating for 2-6 h to obtain a recycled foaming material; The rubber foaming material is prepared by the preparation method of claim 6. ​

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