Rapidly degradable foaming material for soles and preparation method thereof

Abstract

The invention relates to the technical field of polymer composite materials, and discloses a quickly degradable foaming material for soles and a preparation method thereof, the foaming material is prepared from the following components by mass: 70-85% of a main body degradable polymer matrix; the modified plant fiber is subjected to enzyme activation treatment and is anchored with chitosan microcapsules containing nitrogen, phosphorus and potassium nutritive salts; 1%-3% of a synergistic degradation accelerator; the surface of the modified plant fiber is provided with micron-sized pores and a nano-sized coarse structure which are formed by enzyme activation treatment, chitosan microcapsules are anchored on the modified plant fiber, and the main body degradable polymer matrix is selected from a blend of polylactic acid and poly (butylene succinate). The plant fibers which are activated by special enzymes and anchored with the slow-release nutritive salt microcapsules are ingeniously compounded with the biodegradable polymer matrix, so that the biodegradation starting efficiency and the overall degradation rate of the material are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer composite materials, in particular to a fast-degradable foaming material for shoe soles and a preparation method thereof. BACKGROUND

[0002] Currently, the main choices of foaming materials for shoe soles mainly include ethylene-vinyl acetate copolymer (EVA), polyurethane (PU) foam and various synthetic rubbers. These materials have been widely used in the shoe-making industry due to their excellent lightweight, shock-absorbing and wear-resistant properties. However, these petroleum-based synthetic polymer materials have high durability in the natural environment and are difficult to biodegrade after being discarded, which constitutes an increasingly severe environmental burden and poses a long-term potential threat to the soil and ecological system. In response to the environmental problems caused by traditional shoe sole materials, biodegradable polymers such as polylactic acid (PLA), polybutylene succinate (PBS) and some bio-based thermoplastic polyurethane (Bio-TPU) have become a hot research and development topic.

[0003] The introduction of natural plant fibers, such as bamboo fibers, wood powder or sugarcane residue fibers, into these biodegradable polymers is considered an effective way to improve their biodegradability and reduce material costs. Although the introduction of natural plant fibers can theoretically promote the decomposition process of the composite material in the natural environment, it still faces many challenges in practical applications. First, there is often a problem of poor interfacial compatibility between the plant fibers and the polymer matrix, which not only may weaken the macroscopic mechanical properties of the composite material, but more importantly, it limits the possibility of effective invasion and degradation of the material internal interface by microorganisms. Second, although the degradation rate of plant fibers themselves may be relatively fast, if they cannot effectively initiate or promote the coordinated degradation of the surrounding polymer matrix, the overall "fast degradation" goal of the material will be difficult to achieve. In addition, in the complex natural environment, the types, numbers and nutritional conditions of microorganisms vary significantly, and if the material itself cannot provide a suitable microenvironment and necessary nutrients for the early attachment, colonization and reproduction of microorganisms, the start-up stage of the biodegradation process will be significantly delayed, thus failing to meet the urgent need for rapid environmental disposal of waste.

[0004] The use of some chemical foaming agents may result in the residual of harmful substances in the final product, which is contrary to the original intention of developing environmentally friendly materials. Even if physical foaming technology is used, if the process control does not fully consider the protection and optimal distribution of functional components, it may lead to the loss of expected effects.

[0005] Specifically, if the structure and functional integrity of the plant fibers that have been specially modified to promote degradation cannot be effectively maintained, or the optimal distribution and efficient use of the synergistic degradation aid in the microstructure of the material cannot be achieved in key process steps such as melt blending or foaming molding. SUMMARY

[0006] The purpose of the present application is to provide a rapidly degradable foamed material for shoe soles and a preparation method thereof, to solve the problem of insufficient degradation rate and slow environmental absorption of existing biodegradable shoe sole materials.

[0007] To solve the above technical problems, the present application provides the following technical solutions.

[0008] In a first aspect, the present application provides a rapidly degradable foamed material for shoe soles, which adopts the following technical solutions:

[0009] A rapidly degradable foamed material for shoe soles, comprising the following components made in the following mass percentages:

[0010] 70-85% of a main degradable polymer matrix;

[0011] 10-25% of modified plant fibers with chitosan microcapsules containing nitrogen, phosphorus and potassium nutrient salts after enzyme activation treatment and anchoring;

[0012] 1-3% of a synergistic degradation promoter;

[0013] 0.3-1.5% of a nucleating agent.

[0014] By adopting the above technical solutions, the present application effectively solves the problem of slow degradation start and low rate of traditional degradable foamed materials by constructing a multi-component synergistic degradation system composed of modified plant fibers, a synergistic degradation promoter and a main degradable polymer matrix. The mechanism of action is as follows:

[0015] Constructing internal degradation initiation points: the core component in the present application is plant fibers modified by special functionalization. First, through specific enzyme activation treatment, micron-sized pores and nanoscale rough structures with high specific surface area are formed in situ on the surface of the plant fibers. This structure provides a physical basis for the attachment, colonization and erosion of subsequent microorganisms. Second, chitosan microcapsules coated with nitrogen, phosphorus and potassium (N, P, K) nutrient salts are anchored on the surface of these activated fibers. In the degradation environment, when microorganisms come into contact with these modified fibers, the chitosan wall material will gradually degrade, releasing N, P, K and other essential nutrients for microbial growth. The combination of these two modification methods makes each modified plant fiber become an efficient "degradation initiation point", which can be uniformly distributed inside the material and trigger and accelerate the biodegradation process of the entire material from the inside.

[0016] Multi-component synergistic accelerated degradation: the synergistic degradation promoter, as a low molecular weight component easily decomposed by microorganisms, provides an easily utilized carbon source for microorganisms in the early stage of degradation, promoting the rapid establishment of microbial communities. The acidic small molecule intermediates produced by its degradation can catalyze the hydrolysis of the ester bond of the main polymer matrix (such as polylactic acid). Therefore, the modified plant fiber provides a "base for settlement and reproduction" for microorganisms, while the synergistic degradation promoter provides an "initial energy and environmental catalyst". The two interact with the main polymer matrix to form an efficient synergistic degradation network from points (modified fibers) to surfaces (the entire matrix), thereby obtaining a foamed material with significantly improved biodegradation rate.

[0017] Preferably, the surface of the modified plant fiber has micron-sized pores and nanoscale rough structures formed by enzyme activation treatment, and the modified plant fiber is anchored with chitosan microcapsules.

[0018] By adopting the above technical solution, the precisely defined surface microstructure is the physical basis for realizing its function. The micron-sized pores and nanoscale rough structures significantly increase the specific surface area of the fiber, providing a large number of attachment sites for microorganisms and facilitating effective contact between the degradation enzymes secreted by the microorganisms and the cellulose molecules. At the same time, this structure also provides a stable physical anchoring point for the chitosan microcapsules, ensuring that nutrients can be precisely distributed at the key interface where degradation occurs.

[0019] Preferably, the main degradable polymer matrix is selected from a blend of polylactic acid and polybutylene succinate or a bio-based thermoplastic polyester urethane.

[0020] By adopting the above technical solution, the use of these specific biodegradable polymers not only ensures that the material itself has good biodegradation potential, but also has mechanical properties and processing properties suitable for the preparation of shoe soles, achieving a balance between material functionality and environmental friendliness.

[0021] Preferably, the synergistic degradation promoter is an aliphatic polyester oligomer with a number average molecular weight of 1000-3000 grams per mole.

[0022] By adopting the above technical solution, the aliphatic polyester oligomer with a molecular weight in this range has low crystallinity and short molecular chains, making it easily recognized and rapidly decomposed by microorganisms in the composting environment, effectively playing the role of a degradation "booster". Its molecular weight also ensures its compatibility and stability during melt blending processing.

[0023] In a second aspect, the present application provides a method for preparing a rapidly degradable foamed material for shoe soles, for preparing the rapidly degradable foamed material for shoe soles as described in any one of the preceding embodiments, adopting the following technical solution:

[0024] A preparation method of a fast-degradable foamed material for shoe soles, comprising the following steps:

[0025] Step one, modification of plant fibers: enzyme activation treatment is performed on the plant fibers, and then chitosan microcapsules containing nitrogen, phosphorus and potassium nutrient salts are anchored on the surface of the plant fibers to obtain modified plant fibers;

[0026] Step two, melt blending: the modified plant fibers, a main body degradable polymer matrix, a synergistic degradation promoter and a nucleating agent are melt blended to obtain composite particles;

[0027] Step three, supercritical carbon dioxide foaming: the composite particles are saturated treated with supercritical carbon dioxide in an autoclave, and then foamed and formed by rapid pressure reduction.

[0028] By adopting the technical scheme, the preparation method of the present application ensures the successful construction of a high-efficiency synergistic degradation system in the final product by pretreating key components and coupling specific process steps.

[0029] Preparation of a functional unit: step one first prepares modified plant fibers that bear dual functions of degradation initiation and nutrient slow release. This step is the basis for realizing the core technical concept of the present application, and it integrates complex degradation promotion functions in an independent and easily dispersed component.

[0030] Homogenization and compounding of the system: the melt blending in step two is not only a simple physical mixing, but also a key process of uniformly dispersing the pre-prepared functional unit (modified plant fibers), the synergistic degradation promoter and the like into the main body polymer matrix, thereby laying a structural foundation for subsequent foaming and molding and uniform degradation performance of the final material.

[0031] Structure forming and function optimization: the supercritical carbon dioxide foaming in step three uses a clean physical foaming agent to endow the material with a porous lightweight structure. More importantly, in the saturation process at high temperature and high pressure, the low viscosity and high permeability of the supercritical carbon dioxide fluid help the small molecule synergistic degradation promoter migrate and enrich to the interface region between the modified plant fibers and the main body polymer, further strengthening the spatial synergistic effect between the degradation initiation point and the booster, and optimizing the degradation performance of the final product.

[0032] Preferably, the enzyme activation treatment of the plant fibers in step one is performed by using a mixture of cellulase and hemicellulase at a pH value of 4.5-5.5 and a temperature of 35-45℃ for 1-3 hours, so as to selectively form micron-sized pores and nanoscale rough structure networks on the surface of the plant fibers.

[0033] By adopting the technical scheme, the specific enzyme system and mild reaction condition can selectively hydrolyze part of the non-crystalline region cellulose and hemicellulose on the surface of the plant fiber, and avoid the serious damage to the overall structure of the fiber caused by traditional chemical treatment (such as strong acid and strong base). The precise and controllable "surface sculpture" process is the key to obtaining the ideal surface micro-morphology, thereby maximizing the function as the microbial attachment substrate and microcapsule carrier.

[0034] Preferably, the chitosan microcapsule anchoring nitrogen, phosphorus and potassium nutrient salt in step one is prepared by emulsification cross-linking method or ionic gel method, and the particle size of the chitosan microcapsule is 0.5-5.0 microns, the molar ratio of the coated nitrogen, phosphorus and potassium elements is 10:1:1-5:1:1, and the microcapsule is preferentially anchored on the micropores or high active sites formed on the surface of the enzyme-activated plant fiber.

[0035] By adopting the technical scheme, the specific preparation method and particle size range ensure that the microcapsule can effectively enter and fix in the micropores on the surface of the enzyme-activated fiber. The precise control of the molar ratio of N:P:K is optimized according to the stoichiometric requirement of microbial (especially cellulose-degrading bacteria) growth and metabolism, which ensures the balanced and efficient supply of nutrient elements.

[0036] Preferably, the melt blending in step two is carried out in a twin-screw extruder, the temperature of the homogenization zone is controlled at 160-190℃, and the temperature of the die zone is controlled at 155-185℃.

[0037] By adopting the technical scheme, the setting of the temperature range can ensure that the main polymer is fully melted and the components are uniformly mixed, while avoiding significant degradation of heat-sensitive components such as plant fiber, chitosan microcapsule and synergistic degradation promoter due to high temperature, thereby maintaining the structural and functional integrity of each functional component.

[0038] Preferably, the supercritical carbon dioxide saturation treatment in step three is carried out at a temperature of 90-130℃, a pressure of 12-18 MPa, and a saturation time of 1.5-3.0 hours; the rapid pressure reduction is to reduce the pressure to atmospheric pressure at an average rate of 8-12 MPa per second.

[0039] By adopting the technical scheme, these process parameters realize the optimal balance between the ideal foaming structure (such as bubble density and bubble size uniformity) and the interface enrichment effect of the degradation-promoting components. The appropriate temperature and pressure and saturation time ensure the sufficient dissolution and diffusion of carbon dioxide in the polymer matrix, and the high pressure reduction rate is the key to obtaining a high-density, fine-cell structure, which not only gives the material excellent physical properties, but also helps to increase the contact area between the material and the degradation environment.

[0040] Preferably, the supercritical carbon dioxide saturation treatment in step three is also used to promote the penetration of the synergistic degradation promoter to the interface microzone of the modified plant fiber and the main body degradable polymer matrix, for the distribution optimization of the modified plant fiber as a degradation hotspot in the final foamed material cell structure.

[0041] By adopting the above technical solution, another important function of the supercritical treatment step is clarified in addition to physical foaming. By using the plasticizing and carrying effect of supercritical carbon dioxide on small molecule substances, the distribution of functional components on the microscale is actively optimized, the "boosters" (synergistic degradation promoters) are accurately guided to the surrounding of the "engines" (modified plant fibers), and the deep regulation and optimization of the material degradation performance are realized.

[0042] In summary, the present application includes at least one of the following beneficial technical effects:

[0043] 1. The present application significantly improves the biodegradation initiation efficiency and overall degradation rate of the material by skillfully compounding plant fibers activated by special enzymes and anchored with slow-release nutrient salt microcapsules with a biodegradable polymer matrix. Compared with the biodegradable composite materials of the prior art which simply physically mix plant fibers, the problems of limited degradation rate improvement of traditional modified fibers and difficulty of early microbial colonization and reproduction are solved.

[0044] 2. In the preparation method of the present application, the plant fibers are subjected to precise enzyme activation treatment, which constructs a unique surface microtopography, and combined with the targeted anchoring of nutrient salt microcapsules, the precise construction of degradation functional units is realized. Compared with the traditional method of only alkali treatment or graft modification of fibers, the problems of insignificant modification effect and single function are solved, and the plant fibers are endowed with the new function of actively inducing and continuously supporting microbial degradation.

[0045] 3. The present application uses supercritical carbon dioxide foaming process, and uses its special physical and chemical properties in the saturation stage to promote the penetration and enrichment of the synergistic degradation promoter to the interface of the modified fiber and the matrix. Unlike the conventional foaming process which only focuses on the formation of cell structure, the distribution of the degradation-promoting component in the micro area is optimized, the technical bottleneck of uneven distribution of functional additives in the traditional composite material and insufficient synergistic effect is solved, and the "degradation hotspot" in the material is more effective.

[0046] 4. The preparation method of the present application ensures the effective integration of each functional component and the realization of the expected function through the synergistic design of multiple steps from the microstructure regulation of plant fibers to the macro-foaming forming of the composite material. Compared with the preparation methods in the prior art, which are relatively independent and lack systematic correlation in each modification means or preparation link, the problem that the comprehensive performance of the final material is difficult to achieve the ideal state due to process mismatch is solved, and a systematic solution is provided for the preparation of high-performance rapidly degradable foamed materials. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The method flowchart of the present application is shown. DETAILED DESCRIPTION

[0048] The following will be described in detail in combination with the accompanying Figure 1 The present application will be further described in detail.

[0049] Example 1:

[0050] Preparation of modified plant fibers:

[0051] Enzyme activation treatment of plant fibers: take 100 grams of dried bamboo fibers (average length 1.0 mm), disperse in 2.0 liters of phosphate buffer with pH value of 5.0, add 1.0 gram of cellulase (enzyme activity 50,000 U / g) and 0.5 gram of hemicellulase (enzyme activity 30,000 U / g), stir at 120 rpm at 40℃ for 2 hours, after the reaction is completed, wash the fibers with deionized water repeatedly until neutral, then dry in an oven at 60℃ to constant weight.

[0052] Preparation and anchoring of chitosan microcapsules containing nitrogen, phosphorus and potassium nutrients: prepare a composite nutrient salt aqueous solution containing potassium dihydrogen phosphate, ammonium nitrate and potassium chloride, so that the molar ratio of N:P:K elements is 7.5:1:1, use this solution as the core material, use 2% chitosan acetic acid solution as the wall material, and prepare chitosan microcapsules with an average particle size of 2.5 microns by emulsion crosslinking method, add the enzyme-activated dried bamboo fibers to a water dispersion liquid containing 5% (mass fraction) of the above-mentioned microcapsules (the mass ratio of fibers to microcapsule dispersion liquid is 1:8), and gently stir at 30℃ for 2 hours to anchor the microcapsules on the surface of the fibers, then take out the fibers, rinse quickly, and dry in a vacuum oven at 55℃.

[0053] Melt blending preparation of composite particles:

[0054] The components are prepared in the following mass percentages: main degradable polymer matrix (blend of polylactic acid PLA and polybutylene succinate PBS, mass ratio 70:30) 79.6%, modified plant fiber prepared in Step 1 17.5%, synergistic degradation promoter (polycaprolactone PCL oligomer, number average molecular weight 2000 g / mol) 2.0%, nucleating agent (nanometer talc powder) 0.9%. The above components are pre-mixed in a high-speed mixer for 5 minutes, and then melt blended in a co-rotating twin-screw extruder. The temperature of each zone of the extruder is set as follows: feeding zone 140°C, compression zone 160°C, homogenization zone 175°C, die zone 170°C, and the screw rotation speed is 150 rpm. The extruded strip is cooled in a water tank and then pelletized, and dried in a 75°C vacuum oven for 6 hours.

[0055] Supercritical carbon dioxide foaming molding:

[0056] The dried composite particles prepared in Step 2, 150 grams, are loaded into a 1-liter autoclave, which is sealed and then purged with high-purity carbon dioxide. The temperature in the autoclave is raised to 110°C, and the pressure is raised to 15 megapascals. The material is saturated and infiltrated under these conditions for 2.25 hours. Then, while maintaining the saturation temperature, the pressure in the autoclave is rapidly reduced to atmospheric pressure at an average rate of 10 megapascals per second, obtaining a foamed material.

[0057] Example 2:

[0058] Preparation of modified plant fiber:

[0059] Enzymatic activation treatment of plant fiber: 100 grams of dried bagasse fiber (average length 0.5 mm) is dispersed in 1.5 liters of phosphate buffer with a pH of 4.5. Cellulase (enzyme activity 50,000 U / g) 0.5 grams and hemicellulase (enzyme activity 30,000 U / g) 0.25 grams are added. The reaction is stirred at 35°C at a speed of 100 rpm for 1 hour. After the reaction is completed, the fiber is repeatedly washed with deionized water until it is neutral, and then dried in an oven at 60°C to a constant weight.

[0060] Preparation and anchoring of chitosan microcapsules containing nitrogen, phosphorus, and potassium nutrients: An aqueous solution of a composite nutrient salt containing potassium dihydrogen phosphate, ammonium nitrate, and potassium chloride is prepared, with a molar ratio of N:P:K elements of 5:1:1. This solution is used as the core material. Chitosan acetate solution with a concentration of 1% is used as the wall material, and sodium tripolyphosphate is used as the crosslinking agent. Chitosan microcapsules with an average particle size of 0.5 microns are prepared using the ionic gel method. The dried bagasse fiber after enzymatic activation treatment is added to a water dispersion containing 5% (mass fraction) of the above-mentioned microcapsules (mass ratio of fiber to microcapsule dispersion is 1:5). The mixture is gently stirred at 30°C for 1 hour, allowing the microcapsules to anchor to the surface of the fiber. Then the fiber is removed, quickly rinsed, and dried in a vacuum oven at 55°C.

[0061] Melt blending preparation of composite particles:

[0062] The components are prepared in the following mass percentages: main degradable polymer matrix (bio-based thermoplastic polyester urethane Bio-TPU) 85.0%, modified plant fiber prepared in Step 1 13.7%, synergistic degradation promoter (lactic acid-ethylene glycol copolymer PLGA oligomer, number average molecular weight 1000 g / mol) 1.0%, nucleating agent (nanosilica surface modified with silane coupling agent) 0.3%. The above components are pre-mixed in a high-speed mixer for 5 minutes, and then fed into a co-rotating twin-screw extruder for melt blending. The temperature settings of each zone of the extruder are as follows: feeding zone 130°C, compression zone 150°C, homogenization zone 160°C, die zone 155°C, and screw rotation speed 100 rpm. The extruded strip is cooled in a water tank and then cut into particles, which are dried in a 75°C vacuum oven for 6 hours.

[0063] Supercritical carbon dioxide foaming molding:

[0064] 100 grams of the dried composite particles prepared in Step 2 are loaded into a 0.5-liter autoclave, which is sealed and then purged with high-purity carbon dioxide. The temperature in the autoclave is raised to 90°C, and the pressure is raised to 12 megapascals. The saturated infiltration is maintained for 1.5 hours under these conditions, after which the pressure in the autoclave is rapidly reduced to atmospheric pressure at an average rate of 8 megapascals / second while maintaining the saturated temperature, to obtain the foamed material.

[0065] Example 3:

[0066] Preparation of modified plant fiber:

[0067] Enzymatic activation treatment of plant fiber: 100 grams of dried bamboo fiber (average length 2.0 mm) is dispersed in 2.5 liters of phosphate buffer with a pH of 5.5, and 2.0 grams of cellulase (enzyme activity 50,000 U / g) and 1.0 gram of hemicellulase (enzyme activity 30,000 U / g) are added. The reaction is stirred at 45°C at a speed of 150 rpm for 3 hours. After the reaction is completed, the fiber is repeatedly washed with deionized water until it is neutral, and then dried in an oven at 60°C to a constant weight.

[0068] Preparation and anchoring of chitosan microcapsules containing nitrogenous phosphorus and potassium nutrient salts: A water solution of complex nutrient salts containing potassium dihydrogen phosphate, ammonium nitrate and potassium chloride was prepared so that the molar ratio of N:P:K elements was 10:1:1. This solution was used as the core material, and chitosan acetic acid solution at 3% was used as the wall material to prepare chitosan microcapsules with an average particle size of 5.0 microns by emulsification cross-linking method. Dry bamboo fibers after enzyme activation treatment were added into a water dispersion liquid containing 10% (mass fraction) of the above microcapsules (the mass ratio of fibers to microcapsule dispersion liquid was 1:10), and the microcapsules were anchored on the surface of the fibers by gentle stirring at 35°C for 3 hours. Subsequently, the fibers were fished out, quickly rinsed, and then dried by freeze-drying method.

[0069] Melt blending preparation of composite particles:

[0070] The components were prepared according to the following mass percentages: main degradable polymer matrix (a blend of polylactic acid PLA and polybutylene succinate PBS, mass ratio 60:40) 70.5%, modified plant fibers prepared in step 1 25%, synergistic degradation promoter (polycaprolactone PCL oligomer, number average molecular weight 3000 g / mol) 3.0%, nucleating agent (nano-talc powder) 1.5%. The above components were pre-mixed in a high-speed mixer for 10 minutes, and then melt blended in a co-rotating twin-screw extruder. The temperature settings of the extruder were as follows: feeding zone 150°C, compression zone 170°C, homogenization zone 190°C, die zone 185°C, screw rotation speed 200 rpm. The extruded strip was cooled in a water tank and then pelletized, and dried in a 75°C vacuum oven for 8 hours.

[0071] Supercritical carbon dioxide foaming molding:

[0072] 200 grams of dry composite particles prepared in step 2 were loaded into a 1-liter autoclave, which was sealed and then high-purity carbon dioxide was introduced into the autoclave. The temperature in the autoclave was raised to 130°C, and the pressure was raised to 18 megapascals. The saturated infiltration was carried out at this condition for 3.0 hours. Subsequently, the pressure in the autoclave was rapidly reduced to atmospheric pressure at an average rate of 12 megapascals / second while maintaining the saturated temperature, and a foamed material was obtained.

[0073] Comparative Example 1:

[0074] Compared with Example 1, the difference is that in the melt blending preparation of the composite particles in step 2, the plant fibers used are ordinary bamboo fibers that have not been subjected to any enzyme activation treatment or anchored with chitosan microcapsules. The addition amount is still 17.5%, and the amount of the main degradable polymer matrix is adjusted to 79.6% accordingly. The use amounts of all other components, preparation steps and process parameters are the same as those of Example 1.

[0075] Comparative Example 2:

[0076] The difference compared with Example 1 is that in the melt blending preparation of step 2 composite particles, the amount of modified plant fiber prepared by the method of Example 1 step 1 is adjusted to 5%, the amount of main body degradable polymer matrix is adjusted to 92.1% accordingly, the amount of synergistic degradation promoter and nucleating agent remains unchanged, and all other preparation steps and process parameters are the same as Example 1.

[0077] Comparative Example 3:

[0078] The difference compared with Example 1 is that in the melt blending preparation of step 2 composite particles, no synergistic degradation promoter (polycaprolactone PCL oligomer) is added, the amount of main body degradable polymer matrix is adjusted to 82.1% accordingly, the amount of modified plant fiber and nucleating agent remains unchanged, and all other preparation steps and process parameters are the same as Example 1.

[0079] Comparative Example 4:

[0080] The difference compared with Example 1 is that in the preparation method of step 1 modified plant fiber, specifically, the bamboo fiber is not subjected to the enzyme activation treatment described in Example 1, but a traditional alkali treatment method (for example, 100 grams of dried bamboo fiber is soaked in a 5% w / v NaOH aqueous solution, treated at 60°C for 2 hours, then washed with water to neutral and dried), then the alkali treated bamboo fiber is subjected to the subsequent preparation and anchoring of chitosan microcapsules containing nitrogen, phosphorus and potassium nutrients in step 1 of Example 1, and the amount of the modified plant fiber in the composite is still 17.5%, the amount of synergistic degradation promoter and nucleating agent remains unchanged, and the amount of main body degradable polymer matrix is adjusted to 79.6%. All other preparation steps and process parameters are the same as Example 1.

[0081] Comparative Experiment 1: Effect of modified plant fiber on biodegradation performance:

[0082] Experimental materials and equipment:

[0083] Test samples:

[0084] Sample A: foamed material prepared in Example 1.

[0085] Sample B: foamed material prepared in Comparative Example 1 (using ordinary bamboo fiber without any treatment).

[0086] Positive control: microcrystalline cellulose powder (known to have good biodegradability).

[0087] Negative control (blank control): compost containing only inoculum, without adding test sample.

[0088] Inoculum: Mature, screened, municipal solid waste compost, meeting the requirements of ISO 14855-1 for inoculum (e.g., pH, moisture content, volatile solids content, etc.).

[0089] Experimental setup: Several 2-liter wide-mouthed bioreactor flasks, incubator (controlled temperature 58 ± 2°C), gas flow meter, carbon dioxide absorption device (e.g., a gas washing bottle containing a known concentration of barium hydroxide solution or an online infrared carbon dioxide analyzer), air supply system (humidified air without carbon dioxide).

[0090] Other: Electronic balance, pH meter, oven, crusher, etc.

[0091] Experimental procedure:

[0092] Sample preparation: Sample A and Sample B were separately crushed and passed through a 2 mm sieve, then dried to constant weight in a 60°C oven. About 10 grams (dry weight) of each test sample and positive control sample were accurately weighed.

[0093] Reaction system construction: In each bioreactor flask, about 500 grams (dry weight) of inoculum was added, and an appropriate amount of deionized water was added to adjust the moisture content to 50-60%. The weighed test sample or positive control sample was thoroughly mixed with the inoculum. For the negative control, only the inoculum was added. Three parallel replicates were set up for each sample group.

[0094] Incubation and gas monitoring: All bioreactor flasks were placed in a constant temperature incubator at 58 ± 2°C. Humidified air without carbon dioxide was introduced into each reaction flask at a rate of 0.05-0.1 liters per minute. The gas discharged from the reaction flask passed through the carbon dioxide absorption device in turn.

[0095] If using barium hydroxide absorption method: The barium hydroxide solution was replaced regularly (e.g., daily at the beginning, and every 2-3 days later), and the remaining barium hydroxide was titrated with standard hydrochloric acid solution to calculate the amount of carbon dioxide produced during this period.

[0096] If using online infrared carbon dioxide analyzer: The carbon dioxide concentration and gas flow in the exhaust gas were recorded continuously or regularly, and the cumulative release of carbon dioxide was calculated.

[0097] Experimental period: The duration of the experiment is generally 45 to 90 days, or until the daily carbon dioxide release rate drops to less than 10% of the peak rate and lasts for several days.

[0098] Data recording and analysis: The cumulative carbon dioxide produced by each reaction flask was recorded regularly. According to the carbon content of the sample.

[0099] Experimental data:

[0100] Table 1: Comparison of biodegradation performance of foamed materials (carbon dioxide release method)

[0101] Time (days) Biodegradation rate (%) of Example 1 Biodegradation rate (%) of Comparative Example 1 0 0.0 0.0 7 8.3 2.1 14 19.5 6.8 21 35.2 13.5 28 51.8 22.1 35 66.3 30.7 45 78.9 41.2 60 85.1 48.6 75 87.5 53.3 90 88.2 55.8

[0102] Summary:

[0103] The experimental results clearly show that the foamed material of Example 1 using the specially modified plant fiber of the present application exhibits significantly better biodegradation performance than the foamed material of Comparative Example 1 under controlled composting conditions. Specifically, the Example 1 material exhibits higher cumulative carbon dioxide release and faster biodegradation rate throughout the entire test period, with a biodegradation rate of 88.2% at 90 days, which is much higher than the 55.8% of Comparative Example 1. This result fully demonstrates the significant advantages of the present application in promoting rapid biodegradation of foamed materials for shoe soles.

[0104] The difference in performance is due to the innovative design of the present application for the specific modification of plant fibers. First, the enzyme activation treatment of the plant fibers forms micron-sized pores and nanoscale rough structures on their surfaces, which greatly increases the specific surface area and accessible active sites of the fibers, providing more convenient physical conditions for the attachment, colonization and secretion of degrading enzymes by microorganisms. Second, the specific ratio of nitrogen, phosphorus and potassium nutrient salts is anchored on the surfaces of these enzyme-activated fibers by chitosan microcapsules, which can provide essential nutrients for microorganisms in the early stages of degradation, promote their rapid proliferation and form dominant bacterial populations, thereby effectively initiating and accelerating the decomposition process of cellulose and the surrounding polymer matrix. These specially modified plant fibers play the role of "degradation hotspots" within the material, triggering and continuously driving the biodegradation of the entire material from the inside.

[0105] In contrast, the ordinary bamboo fibers used in Comparative Example 1 without any treatment have smooth surfaces, few active sites, and may have poor interfacial bonding with the polymer matrix, making it difficult for microorganisms to effectively attach and erode. At the same time, due to the lack of pre-provisioned nutrient support, the early colonization and growth of microorganisms on the material surface will be relatively slow, making it difficult to quickly form an effective degradation bacterial population. Therefore, although the main polymer itself is degradable, due to the lack of effective degradation initiation mechanism and continuous microbial activity support, its overall biodegradation rate is much lower than that of Example 1. The strategy of the present application, which is to construct an efficient internal degradation initiation system through multi-component synergistic design, especially the fine functional modification of plant fibers, is the key to achieving rapid biodegradation of foamed materials.

[0106] Comparative Experiment 2: Effect of plant fiber modification method on biodegradation performance:

[0107] Experimental materials and equipment:

[0108] Test samples:

[0109] Sample A: Foamed material prepared in Example 1 (its plant fibers were treated by enzyme activation and anchored microcapsules).

[0110] Sample C: Foamed material prepared in Comparative Example 4 (its plant fibers were treated by alkali and anchored microcapsules).

[0111] Positive control: Microcrystalline cellulose powder.

[0112] Negative control (blank control): Compost containing only inoculum.

[0113] Inoculum: Mature, screened municipal solid waste compost, meeting the requirements of ISO 14855-1 standard for inoculum.

[0114] Experimental apparatus: Same as described in Comparative Experiment 1 (2-liter wide-mouth bioreactor flask, constant-temperature incubator, gas flow meter, carbon dioxide absorption device, etc.).

[0115] Others: Electronic balance, pH meter, oven, pulverizer, etc.

[0116] Experimental steps:

[0117] Sample preparation: Sample A and Sample C were respectively pulverized and passed through a 2-millimeter screen, and then dried to constant weight in a 60°C oven. About 10 grams (dry weight) of each test sample and positive control sample were accurately weighed.

[0118] Reaction system construction: In each bioreactor flask, about 500 grams (dry weight) of inoculum was added, and an appropriate amount of deionized water was added to adjust the moisture content to 50%-60%. The weighed test sample or positive control sample was thoroughly mixed with the inoculum. For the negative control, only the inoculum was added. Three parallel replicates were set up for each sample group.

[0119] Culture and gas monitoring: All bioreactor flasks were placed in a constant-temperature incubator at 58±2°C. Carbon dioxide-free humidified air was introduced into each reactor at a rate of 0.05-0.1 liters per minute. The gas discharged from the reactor passed through a carbon dioxide absorption device in turn. The method of measuring carbon dioxide (barium hydroxide absorption method or online infrared analyzer method) was the same as in Comparative Experiment 1.

[0120] Experimental period: The duration of the experiment was generally 45 to 90 days, or until the daily carbon dioxide release rate fell to less than 10% of the peak rate and lasted for several days.

[0121] Data recording and analysis: The cumulative carbon dioxide produced by each reactor was recorded regularly. The theoretical maximum carbon dioxide production was calculated based on the carbon content of the sample.

[0122] Experimental data:

[0123] Table 2: Effect of different fiber modification methods on the biodegradability of foamed materials (carbon dioxide release method)

[0124] Time (days) Biodegradation rate (%) of Example 1 (enzyme activation treatment) Biodegradation rate (%) of Comparative Example 4 (alkali treatment) 0 0.0 0.0 7 8.3 3.5 14 19.5 9.1 21 35.2 17.3 28 51.8 28.6 35 66.3 39.2 45 78.9 51.8 60 85.1 60.3 75 87.5 65.1 90 88.2 67.7

[0125] Summary:

[0126] As can be seen from the comparison of experimental data, the biodegradability of the foamed material of Example 1 using enzyme activation treatment of plant fibers is significantly better than that of Comparative Example 4 using traditional alkali treatment of plant fibers. In a 90-day test period, the biodegradation rate of Example 1 reached 88.2%, while that of Comparative Example 4 was 67.7%, and the former showed significant advantages in degradation rate and final degradation degree.

[0127] The enzyme activation treatment technology of the present application can selectively form micron-sized pore structures and nanometer-sized rough networks on the surface of plant fibers by precisely controlling the synergistic effect of cellulase and hemicellulase and the reaction conditions. This unique surface micro-morphology not only greatly increases the specific surface area of the fibers, but more importantly, creates a large number of active sites that are easy for microorganisms to attach, colonize and erode. These sites act as "landing platforms" and "attack channels" for microorganisms, allowing microorganisms to contact cellulose molecules more quickly and deeply, thereby efficiently initiating the degradation process. At the same time, this precisely regulated surface structure also provides an ideal substrate for the effective anchoring of subsequent nutrient salt microcapsules, ensuring that nutrients can precisely act on the key interface where degradation occurs.

[0128] Although traditional alkali treatment can also remove part of the lignin and hemicellulose on the surface of plant fibers to some extent and make the fiber surface relatively rough, its mode of action is more drastic and lacks selectivity, making it difficult to form a fine and ordered micro-porous structure as in enzyme activation treatment. Alkali treatment can more likely cause swelling or partial damage to the fiber as a whole, and the resulting surface topography has limited effect on the specific attachment of microorganisms and the promotion of efficient enzymatic action. Therefore, although the fibers in Comparative Example 4 also anchor nutrient salt microcapsules, due to the less effective "pretreatment" of the fiber surface than enzyme activation treatment, the early colonization efficiency of microorganisms and the subsequent degradation catalytic activity are relatively low, ultimately reflected in the overall biodegradation rate and degree being inferior to Example 1. The present application finely carves and polishes the surface of plant fibers through mild and efficient enzymatic reactions, endowing them with excellent properties of actively inducing and efficiently supporting microbial degradation.

[0129] Comparative Test 3: Effect of synergistic degradation promoters on biodegradability:

[0130] Experimental materials and equipment:

[0131] Test samples:

[0132] Sample A: Foamed material prepared in Example 1 (containing synergistic degradation promoter).

[0133] Sample D: Foamed material prepared in Comparative Example 3 (not containing synergistic degradation promoter, the amount of host polymer matrix is correspondingly increased).

[0134] Positive control: Microcrystalline cellulose powder.

[0135] Negative control (blank control): Inoculum only.

[0136] Inoculum: Matured, screened municipal solid waste compost, meeting the requirements of ISO 14855-1 standard for inoculum.

[0137] Experimental setup: Same as described in Comparative Experiment 1 and Comparative Experiment 2 (2-liter wide-mouth bioreactor flask, constant-temperature incubator, gas flow meter, carbon dioxide absorption device, etc.).

[0138] Others: Electronic balance, pH meter, oven, pulverizer, etc.

[0139] Experimental procedure:

[0140] Sample preparation: Sample A and Sample D were pulverized and passed through a 2-mm sieve, and then dried to constant weight in a 60°C oven. About 10 grams (dry weight) of each test sample and positive control sample were accurately weighed.

[0141] Reaction system construction: In each bioreactor flask, about 500 grams (dry weight) of inoculum was added, and an appropriate amount of deionized water was added to adjust the moisture content to 50%-60%. The weighed test sample or positive control sample was thoroughly mixed with the inoculum. For the negative control, only the inoculum was added. Three parallel replicates were set up for each sample group.

[0142] Culture and gas monitoring: All bioreactor flasks were placed in a constant-temperature incubator at 58±2°C. Carbon dioxide-free humidified air was introduced into each reactor at a rate of 0.05-0.1 liters per minute. The gas discharged from the reactor passed through a carbon dioxide absorption device in turn. The method of measuring carbon dioxide (barium hydroxide absorption method or online infrared analyzer method) was the same as that described in the aforementioned comparative experiments.

[0143] Experimental period: The duration of the experiment was generally 45 to 90 days, or until the daily carbon dioxide release rate decreased to less than 10% of the peak rate and lasted for several days.

[0144] Data recording and analysis: The cumulative carbon dioxide production of each reaction bottle was recorded periodically. The theoretical maximum carbon dioxide production (ThCO2) was calculated according to the carbon content of the sample. The biodegradation rate was calculated by the same method as the comparative experiment.

[0145] Experimental data:

[0146] Table 3: Effect of synergistic degradation promoter on the biodegradation performance of foamed materials (carbon dioxide release method)

[0147] Time (days) Biodegradation rate (%) of Example 1 (containing synergistic degradation promoter) Biodegradation rate (%) of Comparative Example 3 (not containing synergistic degradation promoter) 0 0.0 0.0 7 8.3 4.3 14 19.5 10.5 21 35.2 19.2 28 51.8 29.8 35 66.3 40.1 45 78.9 52.7 60 85.1 61.9 75 87.5 67.3 90 88.2 70.4

[0148] Summary:

[0149] The experimental results show that the foamed material of Example 1 containing the synergistic degradation promoter has a significant improvement in biodegradation performance compared to the foamed material of Comparative Example 3 without the addition of the promoter. In the 90-day test, the biodegradation rate of Example 1 reached 88.2%, while the biodegradation rate of Comparative Example 3 was 70.4%. This difference proves that the synergistic degradation promoter plays a key positive role in accelerating the overall biodegradation process in the composite material system of the present application.

[0150] This performance improvement is closely related to the specific mechanism of action of the synergistic degradation promoter. The low molecular weight aliphatic polyester oligomer used in the present application, due to its relatively short molecular chain and low crystallinity, is more easily recognized and utilized by microorganisms in the material, serving as an "early carbon source" or "easy breakthrough point". After the microorganisms preferentially degrade these oligomers, on the one hand, they can more quickly establish a viable microbial community, laying the foundation for subsequent degradation of the main polymer; on the other hand, the degradation products of these oligomers, such as short-chain organic acids, can locally change the pH of the material microenvironment, or catalyze the hydrolysis of the ester bonds of the main degradable polymer (such as polylactic acid, polybutylene succinate), thereby indirectly accelerating the degradation process of the main polymer.

[0151] In addition, in the preparation process of the present application, especially in the supercritical carbon dioxide saturation foaming stage, the high temperature and high pressure supercritical fluid environment helps the synergistic degradation promoter, a small molecule substance, to penetrate and enrich in the interfacial microzone between the modified plant fiber and the main degradable polymer matrix. This preferential distribution in the key interfacial region allows the synergistic degradation promoter to more effectively interact with the modified plant fiber (degradation hot spot) and the main polymer, further strengthening the synergistic degradation effect between the multiple components within the material. Therefore, the introduction of the synergistic degradation promoter not only simply adds a degradable component, but also optimizes the entire degradation network through its unique chemical structure and specific behavior in the material, thereby achieving a significant enhancement of the biodegradation performance of the foamed material.

[0152] Comparative Test 4: Effect of key pro-degradant component content on biodegradation performance

[0153] Experimental materials and equipment:

[0154] Test samples:

[0155] Sample A: Foamed material prepared in Example 1 (special modified plant fiber content of 17.5%).

[0156] Sample E: Foamed material prepared in Comparative Example 2 (special modified plant fiber content of 5%).

[0157] Positive control: Microcrystalline cellulose powder.

[0158] Negative control (blank control): Compost containing only inoculum.

[0159] Inoculum: Mature, screened municipal solid waste compost, meeting the requirements of ISO 14855-1 standard for inoculum.

[0160] Experimental apparatus: Same as described in the aforementioned comparative tests (2-liter wide-mouth bioreactor flask, constant-temperature incubator, gas flow meter, carbon dioxide absorption device, etc.).

[0161] Others: Electronic balance, pH meter, oven, pulverizer, etc.

[0162] Experimental procedure:

[0163] Sample preparation: Sample A and Sample E were pulverized and passed through a 2-mm sieve, and then dried to constant weight in a 60°C oven. About 10 grams (dry weight) of each test sample and the positive control sample were accurately weighed.

[0164] Reaction system construction: In each bioreactor flask, about 500 grams (dry weight) of inoculum was added, and an appropriate amount of deionized water was added to adjust the moisture content to 50%-60%. The weighed test sample or positive control sample was thoroughly mixed with the inoculum. For the negative control, only the inoculum was added. Three parallel replicates were set up for each sample group.

[0165] Culture and gas monitoring: All bioreactor flasks were placed in a constant-temperature incubator at 58±2°C. Carbon dioxide-free humidified air was introduced into each reactor flask at a rate of 0.05-0.1 liters per minute. The gas discharged from the reactor flasks passed through a carbon dioxide absorption device in turn. The carbon dioxide determination method (barium hydroxide absorption method or online infrared analyzer method) was the same as in the aforementioned comparative tests.

[0166] Experimental period: The duration of the experiment was generally 45 to 90 days, or until the daily carbon dioxide release rate fell to less than 10% of the peak rate and lasted for several days.

[0167] Data recording and analysis: The cumulative carbon dioxide production of each reaction bottle was recorded periodically. The theoretical maximum carbon dioxide production was calculated based on the carbon content of the sample.

[0168] II. Experimental data:

[0169] Table 4: Effect of special modified plant fiber content on the biodegradation performance of foamed materials (carbon dioxide release method)

[0170] Time (days) Biodegradation rate (%) of Example 1 (modified fiber content 17.5%) Biodegradation rate (%) of Comparative Example 2 (modified fiber content 5%) 0 0.0 0.0 7 8.3 1.8 14 19.5 5.3 21 35.2 10.7 28 51.8 17.5 35 66.3 25.9 45 78.9 36.1 60 85.1 45.3 75 87.5 50.8 90 88.2 54.2

[0171] Summary:

[0172] The experimental data shows that the content of special modified plant fiber has a significant impact on the biodegradation performance of foamed materials. The biodegradation rate and final degradation degree of Example 1 sample containing 17.5% special modified plant fiber are much higher than those of Comparative Example 2 sample containing only 5% of the modified fiber during the entire 90-day test period. The final biodegradation rate of Example 1 reaches 88.2%, while that of Comparative Example 2 is only 54.2%, which fully demonstrates that maintaining a certain amount of plant fiber with special functional treatment in the system of the present application is crucial for achieving rapid biodegradation of the material.

[0173] This performance difference is directly related to the multiple roles played by special modified plant fiber in the material and its distribution density. These fibers, which have been activated by enzymes and anchored slow-release nutrient salts, are the "catalytic core" and "nutrition supply station" of microbial degradation activities. When their content is high (such as Example 1), these "degradation hotspots" are more widely and densely distributed in the material matrix, providing more initial sites for microbial attachment and erosion, and providing essential nutrients for microbial early reproduction and activity maintenance in a wider range. This enables the microorganisms to form an effective degradation network inside the material more quickly, thereby synergistically accelerating the decomposition of the entire composite material.

[0174] When the content of special modified plant fiber is low (such as Comparative Example 2), although these fibers themselves still have excellent degradation-promoting function, due to their sparse distribution in the material, the number of "degradation hotspots" per unit volume of material is greatly reduced. This will result in limited initial attachment sites for microorganisms and insufficient local supply of nutrients, making it difficult to quickly build an efficient degradation channel and microbial community inside the material. Therefore, the start and expansion of the degradation process will be relatively slow, and even if the main polymer is degradable, the overall material degradation rate and degree will be significantly restricted.

Claims

1. A rapidly degradable foamed material for shoe soles, characterized by, The following components are prepared in mass percentage: Main body degradable polymer matrix 70%-85%; Modified plant fiber 10%-25% with chitosan microcapsules containing nitrogen, phosphorus and potassium nutrient salts after enzyme activation treatment and anchoring; Synergistic degradation promoter 1%-3%; Nucleating agent 0.3%-1.5%.

2. The rapidly degradable foamed material for shoe soles according to claim 1, wherein The surface of the modified plant fiber has micron-sized pores and nanoscale rough structures formed by enzyme activation treatment, and the modified plant fiber is anchored with chitosan microcapsules.

3. The rapidly degradable foamed material for shoe soles according to claim 1, wherein The main body degradable polymer matrix is selected from a blend of polylactic acid and polybutylene succinate or a bio-based thermoplastic polyester urethane.

4. The rapidly degradable foamed material for shoe soles according to claim 1, wherein The synergistic degradation promoter is an aliphatic polyester oligomer with a number average molecular weight of 1000-3000 grams per mole.

5. A process for the preparation of a rapidly degradable foamed material for shoe soles for the preparation of a rapidly degradable foamed material for shoe soles according to any one of claims 1 to 4, characterized in that, The following steps are included: Step one, modification of plant fiber: enzyme activation treatment of plant fiber, followed by anchoring chitosan microcapsules containing nitrogen, phosphorus and potassium nutrient salts on its surface to obtain modified plant fiber; Step two, melt blending: melt blending of the modified plant fiber, main body degradable polymer matrix, synergistic degradation promoter and nucleating agent to obtain composite particles; Step three, supercritical carbon dioxide foaming: saturating treatment of the composite particles with supercritical carbon dioxide in an autoclave, and then foaming by rapid pressure reduction.

6. The method of claim 5, wherein the rapidly degradable foamed material for shoe soles is prepared by adding 0.1 to 10 parts by weight of the foaming agent to 100 parts by weight of the base material. The enzyme activation treatment of the plant fiber in step one is using a mixture of cellulase and hemicellulase, under the conditions of pH 4.5-5.5, temperature 35-45℃, and reaction time 1-3 hours, to selectively form micron-sized pores and nanoscale rough structure networks on the surface of the plant fiber.

7. The method for preparing the rapidly degradable foamed material for shoe soles according to claim 5, characterized in that, The anchoring of chitosan microcapsules containing nitrogen, phosphorus and potassium nutrient salts in step one is using emulsion crosslinking or ionic gelation methods to prepare chitosan microcapsules with a particle size of 0.5-5.0 microns, and the molar ratio of the coated nitrogen, phosphorus and potassium elements is 10:1:1-5:1:1, and the microcapsules are preferentially anchored on the micropores or high activity sites formed on the surface of the enzyme-activated plant fiber.

8. The method of claim 5, wherein the rapidly degradable foamed material for shoe soles is prepared by adding 0.1 to 10 parts by weight of the foaming agent to 100 parts by weight of the base material. The melt blending in step two is carried out in a twin-screw extruder, with the temperature control of the homogenization zone at 160-190℃, and the temperature control of the die zone at 155-185℃.

9. The method for preparing the rapidly degradable foamed material for shoe soles according to claim 5, characterized in that, The supercritical carbon dioxide saturation treatment in step three is under the conditions of temperature 90-130℃, pressure 12-18 megapascals, and saturation time 1.5-3.0 hours; the rapid pressure reduction is to reduce the pressure to atmospheric pressure at an average rate of 8-12 megapascals per second.

10. The method of claim 5, wherein the rapidly degradable foamed material for shoe soles is prepared by adding 0.1 to 10 parts by weight of the foaming agent to 100 parts by weight of the base material. The supercritical carbon dioxide saturation treatment in step three also promotes the penetration of the synergistic degradation promoter into the interfacial microzone of the modified plant fiber and the main body degradable polymer matrix, and optimizes the distribution of the modified plant fiber as a degradation hotspot in the final foamed material cell structure.

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