A green and environmentally friendly leather softening method

Abstract

The present invention relates to the technical field of leather processing, and in particular to a green and environmentally friendly leather softening method, comprising the following steps: step S1. pretreatment: pretreatment is performed using a reagent A; step S2. softening: softening is performed using a reagent B; and step S3. finishing: finishing is performed using a reagent C. The present invention utilizes the ingenious design of a composite enzyme preparation and the unique efficacy of a bio-based emulsion to greatly improve the softness of the finished leather product, and to achieve high tensile strength and tear strength, high air permeability, and good color uniformity and gloss durability. In addition, the present invention fundamentally abandons the use of a series of harmful chemical substances such as chrome tanning agents and formaldehyde in traditional leather softening processes, greatly reduces the total amount of pollutants discharged into the environment during the leather production process, and completely prevents heavy metal pollution and the generation of toxic volatile substances, thereby having broad application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of leather processing, in particular to a green and environmentally friendly leather softening method. Background Art

[0002] With the acceleration of global industrialization and the continuous increase in consumer demand for leather products, the leather industry has long occupied an important position in the manufacturing industry. However, traditional leather softening processes are highly dependent on chemical agents. In conventional operating procedures, chemicals such as chrome tanning agents, formaldehyde and various chlorinated organic solvents are used on a large scale. Although chrome tanning agents can improve the stability and durability of leather to a certain extent, the heavy metal chromium ions therein are extremely bioaccumulative and toxic. If they are discharged indiscriminately during the leather processing process, they will cause immeasurable and almost irreversible serious pollution to the soil and water ecosystems, resulting in the surrounding ecological environment being devastated and biodiversity declining sharply. Formaldehyde, as a common softening agent, not only has a pungent and unpleasant odor, but its volatility will continuously erode the respiratory tract and lung tissue of workshop operators. Long-term exposure can easily induce serious health problems such as respiratory diseases and cancer. At the same time, formaldehyde remaining in leather products will also pose a potential threat to consumers' skin and body functions. Chlorinated organic solvents are extremely easy to evaporate into the atmosphere during the processing process, participating in photochemical reactions to generate highly toxic substances such as dioxins, posing a threat to the life, health and safety of surrounding residents.

[0003] In addition, traditional softening methods also have many shortcomings and deficiencies. For example, it is difficult to accurately control the degree of hydrolysis of the leather fiber structure, which often leads to uneven leather softening effects. Local excessive softening causes damage to fiber strength and greatly reduces the durability of the product, or insufficient softening makes the leather feel stiff, lacks flexibility and other quality defects. In addition, the disordered penetration and residue of chemical agents will also interfere with the original orderly arrangement structure of the leather fibers, destroying its inherent natural texture, resulting in the finished products being far from meeting the increasingly stringent quality demands of current consumers in terms of key performance indicators such as color, touch and breathability.

[0004] Therefore, according to the related technologies mentioned above, it is urgent to develop a green and environmentally friendly leather softening method. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to propose a green and environmentally friendly leather softening method, which abandons traditional harmful chemicals, utilizes natural biological materials and mild physical means, and achieves efficient softening while ensuring the natural properties and environmental friendliness of the leather.

[0006] Based on the above objectives, the present invention provides a green and environmentally friendly leather softening method.

[0007] A green and environmentally friendly leather softening method comprises the following steps:

[0008] Step S1. Pretreatment: Pretreating the leather with reagent A to obtain a crude leather product 1;

[0009] Step S2. Softening: Softening the crude leather product 1 with reagent B to obtain the crude leather product 2;

[0010] Step S3. Finishing: Finishing the crude leather product 2 with reagent C to obtain a finished leather product;

[0011] The reagent A in step S1 is a mixed solution of sodium bicarbonate and magnesium sulfate;

[0012] The reagent B in step S2 is a complex enzyme preparation;

[0013] The complex enzyme preparation is obtained by mixing collagen hydrolase, plant-derived protease and metal-organic framework enzyme-loaded microparticles;

[0014] The reagent C in step S3 is a bio-based emulsion.

[0015] Preferably, the pre-processing process in step S1 is as follows:

[0016] Place the rawhide in a 25-30°C warm water bath and stir for 30 minutes to wash away impurities and blood on the surface. Then, subject it to 20kHz, 400W ultrasonic vibration for 15 minutes to remove impurities and open pores. Then, place it in a 2.45GHz, 600W microwave cavity for 10 minutes to accelerate the temperature increase and promote fiber expansion, laying the foundation for softening. After draining, use reagent A to adjust the pH to 7.5-8 to neutralize the natural acid, activate subsequent reactions, and create a suitable charge and osmotic pressure environment for enzyme molecules, promoting subsequent efficient attachment and penetration. This gentle treatment can avoid damage to the leather structure.

[0017] The usage ratio of the raw hide to water is 10-12 g:100-110 mL.

[0018] Preferably, the preparation process of the reagent A in step S1 is as follows:

[0019] Mixing 1% sodium bicarbonate solution, 0.5% glucose solution and 0.3% magnesium sulfate solution to obtain reagent A;

[0020] The volume ratio of the sodium bicarbonate solution, the glucose solution and the magnesium sulfate solution is 55-58:28-30:12-16.

[0021] Preferably, the softening process in step S2 is as follows:

[0022] Immerse the crude leather product 1 in a buffer solution containing 3%-3.5% reagent B, and shake at 40-45°C, pH = 7-7.5, and 80-100 rpm for 2-3 hours. Precisely control the temperature to maintain enzyme activity and shake to promote uniform enzyme contact.

[0023] The bath ratio during softening in step S2 is 1:8-9, and the buffer solution is disodium hydrogen phosphate-citric acid.

[0024] Preferably, the preparation process of the collagen hydrolase in the reagent B is as follows:

[0025] The pig gastric mucosal tissue is washed, and impurities such as fat and blood on the surface are removed and the tissue is cut into small pieces. The pretreated gastric mucosal tissue is placed in an extraction buffer. The tissue is homogenized with a homogenizer at 4-10°C to break the cells and release the enzyme. The homogenate is then stirred and extracted at 4-10°C for 4-6 hours to allow the collagen hydrolase to be fully dissolved in the extraction buffer. The extracted homogenate is then centrifuged at 4000-6000 rpm for 20-30 minutes to remove tissue residue and insoluble matter to obtain a supernatant containing the collagen hydrolase. Solid ammonium sulfate is added to the obtained supernatant to make the saturation of the ammonium sulfate reach 40%-60%, and the supernatant is allowed to stand at 4°C for 2-4 hours to precipitate the collagen hydrolase. The precipitate is then collected by centrifugation to obtain the collagen hydrolase.

[0026] The extraction buffer is a phosphate-hydrochloric acid buffer with a pH of 7.0-7.5 and containing 0.1-0.5M NaCl;

[0027] The volume ratio of the extraction buffer to the gastric mucosal tissue block is 8-10:1-2.

[0028] Preferably, the preparation process of the plant-derived protease in the reagent B in step S2 is as follows:

[0029] Step S2011. Picking ripe fresh papaya, removing surface dirt, impurities and soft and rotten parts, washing with clean water and draining, peeling and core-removing the papaya, cutting into small pieces, and freezing the cut papaya pieces in liquid nitrogen for 30-60 minutes. This step can instantly freeze the papaya cells, destroying the cell structure, facilitating the subsequent release of enzymes, and also helping to reduce the loss of enzyme activity before extraction. The frozen papaya pieces are placed in a vacuum freeze dryer and dried at -50°C to 40°C and a vacuum degree of approximately 0.06-0.08 MPa for 24-48 hours until the material is completely dehydrated and becomes loose and brittle dry blocks, which are convenient for subsequent grinding into powder;

[0030] Step S2012. The dried papaya powder is added to a pH 7.5-8.0 Tris-HCl buffer at a ratio of 1 g:5-10 mL. The mixture is placed at 4°C and slowly stirred on a magnetic stirrer for 4-6 hours to ensure that the enzyme protein is fully dissolved in the buffer. The extract is transferred to a high-speed refrigerated centrifuge and centrifuged at 4°C and 10,000-12,000 rpm for 20-30 minutes. The supernatant is separated and ammonium sulfate powder is added to the supernatant with stirring until the saturation is gradually increased to 40%-60%. The mixture is allowed to stand at 4°C for 2-4 hours to induce precipitation of the elastase. The mixture is then centrifuged again at 10,000-12,000 rpm and 4°C for 20-30 minutes. The precipitate is collected to obtain the plant-derived protease.

[0031] In step S2012, 0.1-0.2 M NaCl and 0.01-0.02 M EDTA are added to the Tris-HCl buffer, wherein 0.1-0.2 M NaCl is used to maintain a suitable ionic strength to promote the dissolution of the enzyme protein, and 0.01-0.02 M EDTA is used to chelate metal ions to prevent potential inhibition or interference of metal ions on enzyme activity.

[0032] Preferably, the preparation process of the metal organic framework enzyme-loaded microparticles in the reagent B in step S2 is as follows:

[0033] Step S2021. Dissolve zirconium chloride in N,N-dimethylformamide and stir at room temperature for 1-2 hours to prepare a zirconium chloride solution with a concentration of 0.08-0.1M;

[0034] Step S2022. Dissolve terephthalic acid in N,N-dimethylformamide and stir at room temperature for 1-2 hours to prepare a terephthalic acid solution with a concentration of 0.08-0.1 M;

[0035] Step S2023. The zirconium chloride solution and the terephthalic acid solution are mixed in a polytetrafluoroethylene-lined reactor at a molar ratio of 1:1. Acetic acid is added as a regulator to control the growth rate and particle size of the MOF. The reactor is sealed and placed in an oven for reaction at 100-120°C for 10-12 hours. During the reaction, the metal ions and the organic ligands undergo a coordination reaction in the high-temperature, high-pressure solvent environment, producing MOF particles with a particle size of 2-5 nm.

[0036] Step S2024. The MOF particles are dispersed in a toluene solution, 3-aminopropyltriethoxysilane is added, and the mixture is stirred at 70-80°C under nitrogen for 6-12 hours to modify the MOF particles' surface to enhance their binding ability to the enzyme. After the reaction, the surface-modified MOF particles are collected by centrifugation, washed three times with toluene and three times with ethanol to remove unreacted silane coupling agent, and then dried in a vacuum drying oven to obtain functionalized MOF particles.

[0037] Step S2025. Dissolve the collagenase and plant-derived protease in a phosphate buffer solution at pH 7-8, add the functionalized MOF microparticles, and react with stirring at room temperature for 12-24 hours to allow the enzymes to be loaded onto the MOF microparticles by physical adsorption or chemical bonding (e.g., formation of amide bonds between amino groups of the enzyme and carboxyl groups on the MOF surface), thereby obtaining metal-organic framework-loaded enzyme microparticles.

[0038] Step S2026. Mix 10-15 g of collagen hydrolase, 10-12 g of plant-derived protease, and 18-22 g of metal-organic framework enzyme-loaded microparticles to obtain reagent B.

[0039] The molar ratio of acetic acid to zirconium chloride in step S2023 is 1.5-2:1.

[0040] The mass ratio of 3-aminopropyltriethoxysilane to MOF particles in step S2024 is 8-10:100.

[0041] The mass ratio of the collagen hydrolase, the plant-derived protease, and the functionalized MOF microparticles in step S2025 is 2-3:2-2.5:30-35.

[0042] The mass ratio of the collagen hydrolase, the plant-derived protease, and the metal-organic framework enzyme-loaded microparticles in step S2026 is 10-15:10-12:18-22.

[0043] Preferably, the retouching process in step S3 is as follows:

[0044] The leather crude product 2 is bombarded with nitrogen plasma at 50W for 3 minutes to increase the surface activity and make the grafted emulsion stronger. It is then placed in an emulsion containing 8%-10% of reagent C with a bath ratio of 1:6-8 and tanned at 50-55°C for 80-90 minutes. Warmth helps the oil penetrate and the tanning is evenly distributed. It is then cured at 45-50°C for 20 minutes to make the film dense, bright and lasting in color. The emulsion particle size is 80-120nm and is stably dispersed. After spraying, it forms a nanofilm, which gives the leather waterproof, breathable and antibacterial functions. It is also fully biodegradable and has no ecological burden.

[0045] The content of the emulsifier in the emulsion is 0.5%-0.6%.

[0046] Preferably, the preparation process of the bio-based emulsion in step S3 is as follows:

[0047] Step S301. Plant sterols with a purity of 95%-98% are placed in a vacuum oven and dried at 50-60°C and a vacuum of 0.08-0.09 MPa for 2-3 hours to remove moisture and a small amount of volatile impurities. The dried plant sterols are ground into a fine powder and passed through an 80-100 mesh sieve to facilitate dispersion in the reaction system, thereby obtaining the plant sterols.

[0048] Step S302. Select chitosan with a deacetylation degree of 80%-90% and a molecular weight of 60-80 kDa, and use glycidyl trimethyl ammonium chloride as a quaternizing agent. Disperse chitosan in an isopropanol-water mixed solvent, add sodium hydroxide to adjust the pH to 10-11, slowly add a 20%-30% glycidyl trimethyl ammonium chloride solution dropwise, and stir the reaction at 60-70 ° C for 6-8 h. After the reaction is completed, wash three times with ethanol to remove unreacted reagents and salts to obtain chitosan quaternary ammonium salt. Dissolve the prepared chitosan quaternary ammonium salt in deionized water to prepare a solution with a mass fraction of 5%-10%. Filter through a 0.22-0.45 μm filter membrane before use to remove possible insoluble impurities to obtain a chitosan quaternary ammonium salt solution.

[0049] Step S303: The wood pulp is immersed in a buffer solution containing TEMPO, sodium bromide, and sodium hypochlorite and reacted at room temperature in the dark for 2-3 hours with continuous stirring. After the reaction, the pulp is washed with deionized water until neutral to obtain oxidized cellulose with carboxyl groups on the surface. The oxidized cellulose is then dispersed in water and sonicated at 400-600 W for 30-60 minutes using an ultrasonic cell disruptor to depolymerize the cellulose into nanometer sizes, thereby obtaining an amphiphilic nanocellulose suspension. The solid content of the suspension is adjusted to 2%-3%, and the suspension is centrifuged at 8,000-10,000 rpm for 10-15 minutes to remove large impurities that have not been completely depolymerized, thereby obtaining amphiphilic nanocellulose.

[0050] Step S304. Deionized water is added to a three-necked flask equipped with a mechanical stirrer, a thermometer, and a condenser. The temperature is raised to 40-50°C and stirred at 300-400 rpm. The phytosterol powder is slowly added dropwise. An emulsifier is also added and stirred continuously for 30-40 minutes to form a primary emulsion of the phytosterols. The hydrophilic groups of the emulsifier face the aqueous phase, while the lipophilic groups wrap around the phytosterol particles, resulting in their initial dispersion in the aqueous phase.

[0051] Step S305. The chitosan quaternary ammonium salt solution is slowly added dropwise to the primary emulsion of phytosterols, and the addition time is controlled to be 20-30 minutes. During this period, the temperature is raised to 60-70°C, the stirring speed is increased to 500-600 rpm, and the reaction is carried out for 1-2 hours, so that the chitosan quaternary ammonium salt and the phytosterols interact to a certain extent, such as electrostatic adsorption and hydrogen bonding, thereby enhancing the stability and functionality of the emulsion. Subsequently, the amphiphilic nanocellulose suspension is added dropwise to the reaction system. After the addition is completed, the stirring reaction is continued at 70-80°C for 2-3 hours to promote the uniform dispersion of the nanocellulose and further compound with other components in the emulsion to form a bio-based emulsion with a stable structure. The amphiphilicity of the nanocellulose enables it to interact with the chitosan quaternary ammonium salt in the aqueous phase and connect with the phytosterol particles through the hydrophobic region, thereby acting as a bridge and reinforcing the structure.

[0052] The volume ratio of isopropyl alcohol to water in the isopropyl alcohol-water mixed solvent in step S302 is 1:1.

[0053] The pH of the buffer solution in step S303 is 10-10.5.

[0054] In step S304, the deionized water accounts for 40%-50% of the total mass of the emulsion.

[0055] In step S304, the emulsifier is Tween-80, and the amount of the emulsifier is 10%-20% of the mass of the phytosterols.

[0056] The mass ratio of the phytosterol, the chitosan quaternary ammonium salt solution and the amphiphilic nanocellulose is 3-5:80-85:2-3.

[0057] Beneficial effects of the present invention:

[0058] The present invention fundamentally abandons the use of a series of harmful chemicals such as chrome tanning agents and formaldehyde in traditional leather softening processes, greatly reduces the total amount of pollutants discharged into the environment during the leather production process, and completely eliminates heavy metal pollution and the generation of toxic volatile substances.

[0059] By leveraging the ingenious design of the composite enzyme preparation and the unique efficacy of the bio-based emulsion, the present invention significantly improves the softness of the finished leather product, increases tensile strength and tear strength, enhances air permeability, and improves color uniformity and gloss durability, thus having broad application prospects. DETAILED DESCRIPTION

[0060] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0061] Preparation Example 1: A method for preparing reagent A, comprising the following steps:

[0062] Reagent A was obtained by mixing 55 mL of 1% sodium bicarbonate solution, 28 mL of 0.5% glucose solution, and 12 mL of 0.3% magnesium sulfate solution.

[0063] Preparation Example 2: A method for preparing reagent A, comprising the following steps:

[0064] Reagent A was obtained by mixing 56 mL of 1% sodium bicarbonate solution, 29 mL of 0.5% glucose solution, and 14 mL of 0.3% magnesium sulfate solution.

[0065] Preparation Example 3: A method for preparing reagent A, comprising the following steps:

[0066] Reagent A was obtained by mixing 58 mL of 1% sodium bicarbonate solution, 30 mL of 0.5% glucose solution, and 16 mL of 0.3% magnesium sulfate solution.

[0067] Preparation Example 4: A method for preparing reagent B, comprising the following steps:

[0068] S1. The porcine gastric mucosal tissue was cleaned, and impurities such as fat and blood were removed from the surface. The tissue was then cut into small pieces. 10 mL of the pretreated gastric mucosal tissue was placed in 80 mL of phosphate-hydrochloric acid buffer (pH 7.0) containing 0.1 M NaCl. The tissue was homogenized at 4°C using a homogenizer to disrupt the cells and release the enzyme. The homogenate was then stirred and extracted at 4°C for 4 h to allow the collagenase to fully dissolve in the extraction buffer. The extracted homogenate was then centrifuged at 4000 rpm for 20 min to remove tissue residue and insoluble matter to obtain a supernatant containing the collagenase. Solid ammonium sulfate was added to the resulting supernatant to a saturation of 40%. The supernatant was allowed to stand at 4°C for 2 h to precipitate the collagenase. The precipitate was then collected by centrifugation to obtain the collagenase.

[0069] S2. Pick ripe, fresh papayas, remove any dirt, impurities, and soft, rotten parts from the surface, rinse with clean water, and drain thoroughly. Peel and core the papayas, cut them into small pieces, and freeze them in liquid nitrogen for 30 minutes. This step instantly freezes the papaya cells, disrupting their structure and facilitating subsequent enzyme release. It also helps reduce enzyme activity loss before extraction. The frozen papaya pieces are then placed in a vacuum freeze dryer and dried at -50°C and a vacuum of approximately 0.06 MPa for 24 hours until they are completely dehydrated and become loose, brittle, dry masses that facilitate subsequent grinding into powder.

[0070] S3. Add 0.1M NaCl and 0.01M EDTA to a Tris-HCl buffer solution at pH 7.5, wherein 0.1M NaCl is used to maintain a suitable ionic strength to promote the dissolution of the enzyme protein, and 0.01M EDTA is used to chelate metal ions to prevent potential inhibition or interference of metal ions on enzyme activity. Add the dried papaya powder to the Tris-HCl buffer at a ratio of 1g:5mL, place it in a low-temperature environment of 4°C, and slowly stir it on a magnetic stirrer for 4h to ensure that the enzyme protein is fully dissolved in the buffer. Transfer the extract to a high-speed refrigerated centrifuge and centrifuge it at 4°C and 10,000rpm for 20min to separate the supernatant. Add ammonium sulfate powder to the supernatant while stirring to gradually increase its saturation to 40%. Let it stand at 4°C for 2h to induce the precipitation of elastase. Then, centrifuge it again at a speed of 10,000rpm and a temperature of 4°C for 20min to collect the precipitate to obtain a plant-derived protease.

[0071] S4. The zirconium chloride was dissolved in N, N- dimethylformamide and stirred at room temperature for 1h to prepare a zirconium chloride solution with a concentration of 0.08M;

[0072] S5. The terephthalic acid was dissolved in N, N- dimethylformamide and stirred at room temperature for 1h to prepare a terephthalic acid solution with a concentration of 0.08M;

[0073] S6. A zirconium chloride solution and a terephthalic acid solution were mixed in a polytetrafluoroethylene-lined reactor at a molar ratio of 1:1. Acetic acid was added as a regulator at a molar ratio of acetic acid to zirconium chloride of 1.5:1 to control the growth rate and particle size of the MOF. The reactor was sealed and placed in an oven for reaction at 100°C for 10 hours. During the reaction, the metal ions and organic ligands underwent a coordination reaction in a high-temperature, high-pressure solvent environment, yielding MOF particles with a particle size of 2 nm.

[0074] S7. MOF microparticles were dispersed in a toluene solution, and 3-aminopropyltriethoxysilane was added at a mass ratio of 8:100. The mixture was stirred at 70°C under nitrogen for 6 h to modify the MOF microparticles surface to enhance their binding ability to the enzyme. After the reaction, the surface-modified MOF microparticles were collected by centrifugation, washed three times with toluene and ethanol, respectively, to remove unreacted silane coupling agent, and then dried in a vacuum drying oven to obtain functionalized MOF microparticles.

[0075] S8. Dissolve 20 g of collagen hydrolase and 20 g of plant-derived protease in a phosphate buffer solution at pH 7, add 300 g of functionalized MOF microparticles, and stir the mixture at room temperature for 12 h to allow the enzymes to be loaded onto the MOF microparticles via physical adsorption or chemical bonding (e.g., formation of amide bonds between amino groups of the enzyme and carboxyl groups on the MOF surface), thereby obtaining metal-organic framework-loaded enzyme microparticles.

[0076] S9. Mix 10 g of collagen hydrolase, 10 g of plant-derived protease, and 18 g of metal-organic framework enzyme-loaded microparticles to obtain reagent B.

[0077] Preparation Example 5: A method for preparing reagent B, comprising the following steps:

[0078] S1. The porcine gastric mucosal tissue was cleaned, and impurities such as fat and blood were removed from the surface. The tissue was then cut into small pieces. 15 mL of the pretreated gastric mucosal tissue was placed in 90 mL of phosphate-hydrochloric acid buffer (pH 7.3) containing 0.3 M NaCl. The tissue was homogenized at 6°C using a homogenizer to disrupt the cells and release the enzyme. The homogenate was then stirred and extracted at 6°C for 5 h to allow the collagenase to fully dissolve in the extraction buffer. The extracted homogenate was then centrifuged at 5000 rpm for 25 min to remove tissue debris and insoluble matter to obtain a supernatant containing the collagenase. Solid ammonium sulfate was added to the resulting supernatant to a saturation of 50%. The supernatant was allowed to stand at 4°C for 3 h to precipitate the collagenase. The precipitate was then collected by centrifugation to obtain the collagenase.

[0079] S2. Pick ripe, fresh papayas, remove any dirt, impurities, and soft, rotten parts from the surface, rinse with clean water, and drain thoroughly. Peel and core the papayas, cut them into small pieces, and freeze them in liquid nitrogen for 50 minutes. This step instantly freezes the papaya cells, disrupting their structure and facilitating subsequent enzyme release and minimizing enzyme activity loss before extraction. The frozen papaya pieces are then placed in a vacuum freeze dryer and dried at -45°C and a vacuum of approximately 0.07 MPa for 36 hours until they are completely dehydrated and form loose, brittle, dry masses that facilitate subsequent grinding into powder.

[0080] S3. Add 0.15M NaCl and 0.015M EDTA to a Tris-HCl buffer solution at pH 7.8, wherein 0.15M NaCl is used to maintain a suitable ionic strength to promote the dissolution of the enzyme protein, and 0.015M EDTA is used to chelate metal ions to prevent potential inhibition or interference of metal ions on enzyme activity. The dried papaya powder is added to the Tris-HCl buffer at a ratio of 1g:7mL, placed in a low temperature environment of 4°C, and slowly stirred on a magnetic stirrer for 5h to ensure that the enzyme protein is fully dissolved in the buffer. The extract is transferred to a high-speed refrigerated centrifuge and centrifuged at 4°C and 11000rpm for 25min to separate the supernatant. Ammonium sulfate powder is added to the supernatant while stirring to gradually increase its saturation to 50%. The mixture is allowed to stand at 4°C for 3h to induce the precipitation of elastase. The mixture is then centrifuged again at 11000rpm and 4°C for 25min to collect the precipitate to obtain a plant-derived protease.

[0081] S4. The zirconium chloride was dissolved in N, N- dimethylformamide and stirred at room temperature for 1.5h to prepare a zirconium chloride solution with a concentration of 0.09M;

[0082] S5. The terephthalic acid was dissolved in N, N- dimethylformamide and stirred at room temperature for 1.5h to prepare a terephthalic acid solution having a concentration of 0.09M;

[0083] S6. A zirconium chloride solution and a terephthalic acid solution were mixed in a polytetrafluoroethylene-lined reactor at a molar ratio of 1:1. Acetic acid was added as a regulator at a molar ratio of 1.8:1 to zirconium chloride to control the growth rate and particle size of the MOF. The reactor was sealed and placed in an oven for reaction at 110°C for 11 hours. During the reaction, the metal ions and organic ligands underwent a coordination reaction in a high-temperature, high-pressure solvent environment, yielding MOF particles with a particle size of 3 nm.

[0084] S7. MOF microparticles were dispersed in a toluene solution, and 3-aminopropyltriethoxysilane was added at a mass ratio of 9:100. The mixture was stirred at 75°C under nitrogen for 8 hours to modify the surface of the MOF microparticles to enhance their binding ability to the enzyme. After the reaction, the surface-modified MOF microparticles were collected by centrifugation, washed three times with toluene and ethanol, respectively, to remove unreacted silane coupling agent, and then dried in a vacuum drying oven to obtain functionalized MOF microparticles.

[0085] S8. Dissolve 25 g of collagen hydrolase and 23 g of plant-derived protease in phosphate buffer at pH 7.5, add 325 g of functionalized MOF microparticles, and stir at room temperature for 18 h to allow the enzymes to be loaded onto the MOF microparticles by physical adsorption or chemical bonding to obtain metal-organic framework enzyme-loaded microparticles;

[0086] S9. Mix 13 g of collagen hydrolase, 11 g of plant-derived protease, and 20 g of metal-organic framework enzyme-loaded microparticles to obtain reagent B.

[0087] Preparation Example 6: A method for preparing reagent B, comprising the following steps:

[0088] S1. The porcine gastric mucosal tissue was cleaned, and impurities such as fat and blood were removed from the surface. The tissue was cut into small pieces. 20 mL of the pretreated gastric mucosal tissue was placed in 100 mL of phosphate-hydrochloric acid buffer (pH 7.5) containing 0.5 M NaCl. The tissue was homogenized at 10°C using a homogenizer to disrupt the cells and release the enzyme. The homogenate was then stirred and extracted at 10°C for 6 h to allow the collagenase to fully dissolve in the extraction buffer. The extracted homogenate was then centrifuged at 6000 rpm for 30 min to remove tissue residue and insoluble matter to obtain a supernatant containing the collagenase. Solid ammonium sulfate was added to the resulting supernatant to a saturation of 60%. The supernatant was allowed to stand at 4°C for 4 h to precipitate the collagenase. The precipitate was then collected by centrifugation to obtain the collagenase.

[0089] S2. Pick ripe, fresh papayas, remove any dirt, impurities, and soft, rotten parts from the surface, rinse with clean water, and drain thoroughly. Peel and core the papayas, cut them into small pieces, and freeze them in liquid nitrogen for 60 minutes. This step instantly freezes the papaya cells, disrupting their structure and facilitating subsequent enzyme release and minimizing enzyme activity loss before extraction. The frozen papaya pieces are then placed in a vacuum freeze dryer and dried at -40°C and a vacuum of approximately 0.08 MPa for 48 hours until they are completely dehydrated and form loose, brittle, dry masses that facilitate subsequent grinding into powder.

[0090] S3. Add 0.2M NaCl and 0.02M EDTA to a Tris-HCl buffer solution of pH = 8.0, wherein 0.2M NaCl is used to maintain a suitable ionic strength to promote the dissolution of the enzyme protein, and 0.02M EDTA is used to chelate metal ions to prevent potential inhibition or interference of metal ions on enzyme activity. The dried papaya powder is added to the Tris-HCl buffer at a ratio of 1g:10mL, placed in a low temperature environment of 4°C, and slowly stirred on a magnetic stirrer for 6h to ensure that the enzyme protein is fully dissolved in the buffer. The extract is transferred to a high-speed refrigerated centrifuge and centrifuged at 4°C and 12000rpm for 30min to separate the supernatant. Ammonium sulfate powder is added to the supernatant while stirring to gradually increase its saturation to 60%. The mixture is allowed to stand at 4°C for 4h to induce the precipitation of elastase. The mixture is then centrifuged again at 12000rpm and 4°C for 30min to collect the precipitate to obtain a plant-derived protease.

[0091] S4. The zirconium chloride was dissolved in N, N- dimethylformamide and stirred at room temperature for 2h to prepare a zirconium chloride solution with a concentration of 0.1M;

[0092] S5. The terephthalic acid was dissolved in N, N- dimethylformamide and stirred at room temperature for 1-2h to prepare a terephthalic acid solution having a concentration of 0.1M;

[0093] S6. A zirconium chloride solution and a terephthalic acid solution were mixed in a polytetrafluoroethylene-lined reactor at a molar ratio of 1:1. Acetic acid was added as a regulator at a molar ratio of acetic acid to zirconium chloride of 2:1 to control the growth rate and particle size of the MOF. The reactor was sealed and placed in an oven for reaction at 120°C for 12 hours. During the reaction, the metal ions and organic ligands underwent a coordination reaction in a high-temperature, high-pressure solvent environment, yielding MOF particles with a particle size of 5 nm.

[0094] S7. MOF microparticles were dispersed in a toluene solution, and 3-aminopropyltriethoxysilane was added at a mass ratio of 10:100. The mixture was stirred at 80°C under nitrogen for 12 hours to modify the surface of the MOF microparticles to enhance their binding ability to the enzyme. After the reaction, the surface-modified MOF microparticles were collected by centrifugation, washed three times with toluene and ethanol, respectively, to remove unreacted silane coupling agent, and then dried in a vacuum drying oven to obtain functionalized MOF microparticles.

[0095] S8. Dissolve 30 g of collagen hydrolase and 25 g of plant-derived protease in phosphate buffer at pH 8, add 350 g of functionalized MOF microparticles, and stir at room temperature for 24 h to allow the enzymes to be loaded onto the MOF microparticles by physical adsorption or chemical bonding to obtain metal-organic framework enzyme-loaded microparticles;

[0096] S9. Mix 15 g of collagen hydrolase, 12 g of plant-derived protease, and 22 g of metal-organic framework enzyme-loaded microparticles to obtain reagent B.

[0097] Preparation Example 7: A method for preparing reagent C, comprising the following steps:

[0098] S1. Dry 95% pure phytosterols in a vacuum oven at 50°C and 0.08 MPa for 2 h to remove moisture and a small amount of volatile impurities. Grind the dried phytosterols into a fine powder and pass it through an 80-mesh sieve to ensure better dispersion in the reaction system, thereby obtaining phytosterols.

[0099] S2. Chitosan with a deacetylation degree of 80% and a molecular weight of 60 kDa was selected, and glycidyl trimethyl ammonium chloride was used as a quaternizing agent. The chitosan was dispersed in an isopropanol-water mixed solvent, wherein the volume ratio of isopropanol to water in the isopropanol-water mixed solvent was 1:1. Sodium hydroxide was added to adjust the pH to 10, and a 20% glycidyl trimethyl ammonium chloride solution was slowly added dropwise. The mixture was stirred at 60°C for 6 h. After the reaction was completed, the mixture was washed three times with ethanol to remove unreacted reagents and salts to obtain chitosan quaternary ammonium salt. The prepared chitosan quaternary ammonium salt was dissolved in deionized water to prepare a solution with a mass fraction of 5%. The mixture was filtered through a 0.22 μm filter membrane before use to remove possible insoluble impurities to obtain a chitosan quaternary ammonium salt solution.

[0100] S3. Soaking wood pulp in a buffer solution containing TEMPO, sodium bromide, and sodium hypochlorite at a pH of 10, incubating in the dark for 2 hours at room temperature with continuous stirring. After the reaction, the pulp was washed with deionized water until neutral, yielding oxidized cellulose with carboxyl groups on its surface. The oxidized cellulose was then dispersed in water and sonicated at 400 W for 30 minutes using an ultrasonic cell disruptor to depolymerize the cellulose into nanosized particles, yielding an amphiphilic nanocellulose suspension. The solids content was adjusted to 2%, and the suspension was centrifuged at 8000 rpm for 10 minutes to remove large impurities that had not been completely depolymerized, yielding amphiphilic nanocellulose.

[0101] S4. In a three-necked flask equipped with a mechanical stirrer, a thermometer, and a condenser, deionized water was added, with deionized water accounting for 40% of the total mass of the emulsion. The temperature was raised to 40°C and stirred at 300 rpm. The phytosterol powder was slowly added dropwise. At the same time, an emulsifier was added. The emulsifier was Tween-80, and the amount of the emulsifier was 10% by mass of the phytosterol. Stirring was continued for 30 minutes to form a primary emulsion of phytosterols. The hydrophilic groups of the emulsifier were oriented toward the aqueous phase, and the lipophilic groups wrapped around the phytosterol particles, causing them to be initially dispersed in the aqueous phase.

[0102] S5. The chitosan quaternary ammonium salt solution is slowly added dropwise to the primary emulsion of phytosterols, and the addition time is controlled within 20 minutes. During this period, the temperature is raised to 60°C, the stirring speed is increased to 500 rpm, and the reaction is carried out for 1 hour, so that the chitosan quaternary ammonium salt and the phytosterols interact to a certain extent, such as electrostatic adsorption, hydrogen bonding, etc., to enhance the stability and functionality of the emulsion. Subsequently, the amphiphilic nanocellulose suspension is added dropwise to the reaction system. After the addition is completed, the stirring reaction is continued at 70°C for 2 hours to promote the uniform dispersion of the nanocellulose and further compound with other components in the emulsion to form a bio-based emulsion with a stable structure. The amphiphilicity of the nanocellulose enables it to interact with the chitosan quaternary ammonium salt in the aqueous phase and connect with the phytosterol particles through the hydrophobic region, acting as a bridge and reinforcing the structure. The mass ratio of phytosterols, chitosan quaternary ammonium salt solution and amphiphilic nanocellulose is 3:80:2, and reagent C is obtained.

[0103] Preparation Example 8: A method for preparing reagent C, comprising the following steps:

[0104] S1. Dry 96% pure phytosterols in a vacuum oven at 55°C and 0.085 MPa for 2.5 hours to remove moisture and a small amount of volatile impurities. Grind the dried phytosterols into a fine powder and pass it through a 90-mesh sieve to ensure better dispersion in the reaction system, thereby obtaining phytosterols.

[0105] S2. Chitosan with a deacetylation degree of 85% and a molecular weight of 70 kDa was selected, and glycidyl trimethyl ammonium chloride was used as a quaternizing agent. The chitosan was dispersed in an isopropanol-water mixed solvent, wherein the volume ratio of isopropanol to water in the isopropanol-water mixed solvent was 1:1. Sodium hydroxide was added to adjust the pH to 10.5, and a 25% glycidyl trimethyl ammonium chloride solution was slowly added dropwise. The mixture was stirred at 65°C for 7 h. After the reaction was completed, the mixture was washed three times with ethanol to remove unreacted reagents and salts to obtain chitosan quaternary ammonium salt. The prepared chitosan quaternary ammonium salt was dissolved in deionized water to prepare a solution with a mass fraction of 8%. The solution was filtered through a 0.35 μm filter membrane before use to remove possible insoluble impurities to obtain a chitosan quaternary ammonium salt solution.

[0106] S3. The wood pulp was immersed in a buffer solution containing TEMPO, sodium bromide, and sodium hypochlorite at a pH of 10.3. The reaction was carried out in the dark at room temperature for 2.5 hours with continuous stirring. After the reaction, the pulp was washed with deionized water until neutral to obtain oxidized cellulose with carboxyl groups on the surface. The oxidized cellulose was then dispersed in water and sonicated at 500 W for 50 minutes using an ultrasonic cell disruptor to depolymerize the cellulose into nanosized particles, thereby obtaining an amphiphilic nanocellulose suspension. The solid content of the suspension was adjusted to 2.5%, and the suspension was centrifuged at 9000 rpm for 13 minutes to remove large impurities that were not completely depolymerized, thereby obtaining amphiphilic nanocellulose.

[0107] S4. Deionized water was added to a three-necked flask equipped with a mechanical stirrer, a thermometer, and a condenser. The deionized water accounted for 45% of the total mass of the emulsion. The temperature was raised to 45°C and stirred at 350 rpm. The phytosterol powder was slowly added dropwise. An emulsifier was added at the same time. The emulsifier was Tween-80. The amount of the emulsifier was 15% of the mass of the phytosterol. Stirring was continued for 35 minutes to form a primary emulsion of phytosterols. The hydrophilic groups of the emulsifier were oriented toward the aqueous phase, while the lipophilic groups coated the phytosterol particles, causing them to be initially dispersed in the aqueous phase.

[0108] S5. The chitosan quaternary ammonium salt solution was slowly added dropwise to the primary emulsion of phytosterols, and the addition time was controlled within 25 minutes. During this period, the temperature was raised to 65°C, the stirring speed was increased to 550 rpm, and the reaction was carried out for 1.5 hours, so that the chitosan quaternary ammonium salt and the phytosterols interacted to a certain extent, such as electrostatic adsorption and hydrogen bonding, thereby enhancing the stability and functionality of the emulsion. Subsequently, the amphiphilic nanocellulose suspension was added dropwise to the reaction system. After the addition was completed, the stirring reaction was continued at 75°C for 2.5 hours to promote the uniform dispersion of the nanocellulose and further compounding with other components in the emulsion to form a bio-based emulsion with a stable structure. The amphiphilicity of the nanocellulose enabled it to interact with the chitosan quaternary ammonium salt in the aqueous phase and to connect with the phytosterol particles through the hydrophobic region, acting as a bridge and reinforcing the structure. The mass ratio of phytosterols, chitosan quaternary ammonium salt solution and amphiphilic nanocellulose was 4:83:2.5, and reagent C was obtained.

[0109] Preparation Example 9: A method for preparing reagent C, comprising the following steps:

[0110] S1. Dry 98% pure phytosterols in a vacuum oven at 60°C and 0.09 MPa for 3 h to remove moisture and a small amount of volatile impurities. Grind the dried phytosterols into a fine powder and pass it through a 100-mesh sieve to ensure better dispersion in the reaction system, thereby obtaining phytosterols.

[0111] S2. Chitosan with a deacetylation degree of 90% and a molecular weight of 80 kDa was selected, and glycidyl trimethyl ammonium chloride was used as a quaternizing agent. The chitosan was dispersed in an isopropanol-water mixed solvent, wherein the volume ratio of isopropanol to water in the isopropanol-water mixed solvent was 1:1. Sodium hydroxide was added to adjust the pH to 11, and a 30% glycidyl trimethyl ammonium chloride solution was slowly added dropwise. The mixture was stirred at 70°C for 8 h. After the reaction was completed, the mixture was washed three times with ethanol to remove unreacted reagents and salts to obtain chitosan quaternary ammonium salt. The prepared chitosan quaternary ammonium salt was dissolved in deionized water to prepare a solution with a mass fraction of 10%. The solution was filtered through a 0.45 μm filter membrane before use to remove possible insoluble impurities to obtain a chitosan quaternary ammonium salt solution.

[0112] S3. Soaking wood pulp in a buffer solution containing TEMPO, sodium bromide, and sodium hypochlorite at a pH of 10.5, in the dark at room temperature with continuous stirring for 3 hours. After the reaction, the pulp was washed with deionized water until neutral, yielding oxidized cellulose with carboxyl groups on its surface. The oxidized cellulose was then dispersed in water and sonicated at 600 W for 60 minutes using an ultrasonic cell disruptor to depolymerize the cellulose into nanosized particles, yielding an amphiphilic nanocellulose suspension. The solids content was adjusted to 3%, and the suspension was centrifuged at 10,000 rpm for 15 minutes to remove incompletely depolymerized large particles, yielding amphiphilic nanocellulose.

[0113] S4. In a three-necked flask equipped with a mechanical stirrer, a thermometer, and a condenser, deionized water was added, with deionized water accounting for 50% of the total mass of the emulsion. The temperature was raised to 50°C and stirred at 400 rpm. The phytosterol powder was slowly added dropwise. At the same time, an emulsifier was added. The emulsifier was Tween-80. The amount of the emulsifier was 20% by mass of the phytosterol. Stirring was continued for 40 minutes to form a primary emulsion of phytosterols. The hydrophilic groups of the emulsifier were oriented toward the aqueous phase, while the lipophilic groups coated the phytosterol particles, causing them to be initially dispersed in the aqueous phase.

[0114] S5. The chitosan quaternary ammonium salt solution is slowly added dropwise to the primary emulsion of phytosterols, and the addition time is controlled within 30 minutes. During this period, the temperature is raised to 70°C, the stirring speed is increased to 600 rpm, and the reaction is carried out for 2 hours, so that the chitosan quaternary ammonium salt and the phytosterols interact to a certain extent, such as electrostatic adsorption and hydrogen bonding, thereby enhancing the stability and functionality of the emulsion. Subsequently, the amphiphilic nanocellulose suspension is added dropwise to the reaction system. After the addition is completed, the stirring reaction is continued at 80°C for 3 hours to promote the uniform dispersion of the nanocellulose and further compound with other components in the emulsion to form a bio-based emulsion with a stable structure. The amphiphilicity of the nanocellulose enables it to interact with the chitosan quaternary ammonium salt in the aqueous phase and connect with the phytosterol particles through the hydrophobic region, acting as a bridge and reinforcing the structure. The mass ratio of phytosterols, chitosan quaternary ammonium salt solution and amphiphilic nanocellulose is 5:85:3, and reagent C is obtained.

[0115] Example 1: A green and environmentally friendly leather softening method comprising the following steps:

[0116] S1. Pretreatment: The rawhide was placed in a 25°C warm water bath and stirred for 30 minutes to wash away impurities and blood on the surface of the rawhide. The rawhide was then subjected to ultrasonic vibration at 20 kHz and 400 W for 15 minutes to remove impurities and open pores. The rawhide was then subjected to a 2.45 GHz and 600 W microwave cavity for 10 minutes to accelerate the temperature and promote fiber expansion, laying the foundation for softening. After draining, the pH was adjusted to 7.5 using Reagent A obtained in Preparation Example 1 to neutralize the natural acid, activate subsequent reactions, and create a suitable charge and osmotic pressure environment for the enzyme molecules, promoting subsequent efficient attachment and penetration. This gentle treatment can avoid damage to the leather structure. The rawhide:water ratio was 10 g:100 mL, yielding Crude Leather 1.

[0117] S2. Softening: Crude leather product 1 was immersed in a buffer solution containing 3% of Reagent B obtained in Preparation Example 4, and shaken at 40°C, pH = 7, and 80 rpm for 2 h. The temperature was precisely controlled to maintain enzyme activity and the shaking promoted uniform enzyme contact. The bath ratio during softening was 1:8, and the buffer solution was sodium hydrogen phosphate-citric acid, to obtain crude leather product 2.

[0118] S3. Finishing: The leather crude product 2 is bombarded with nitrogen plasma at 50W for 3 minutes to increase the surface activity and make the grafted emulsion stronger. Then it is placed in an emulsion containing 8% of the reagent C obtained in Preparation Example 7 with a bath ratio of 1:6. It is tanned at 50°C for 80 minutes. Warmth helps the oil to penetrate and the tanning is evenly distributed. Then it is cured at 45°C for 20 minutes to make the film dense, the color bright and lasting. The emulsion particle size is 80nm and it is stably dispersed. After spraying, it forms a nano film, which gives the leather waterproof, breathable and antibacterial functions. It is also fully biodegradable and has no ecological burden. The content of emulsifier in the emulsion is 0.5%-0.6%, and a leather finished product is obtained.

[0119] Example 2: A green and environmentally friendly leather softening method comprising the following steps:

[0120] S1. Pretreatment: The rawhide was placed in a 28°C warm water bath and stirred for 30 minutes to wash away impurities and blood on the surface of the rawhide. The rawhide was then subjected to ultrasonic vibration at 20 kHz and 400 W for 15 minutes to remove impurities and open pores. The rawhide was then subjected to a 2.45 GHz and 600 W microwave cavity for 10 minutes to accelerate the temperature and promote fiber expansion, laying the foundation for softening. After draining, the pH was adjusted to 7.8 using Reagent A obtained in Preparation Example 2 to neutralize the natural acid, activate subsequent reactions, and create a suitable charge and osmotic pressure environment for the enzyme molecules, promoting subsequent efficient attachment and penetration. This gentle treatment can avoid damage to the leather structure. The rawhide:water ratio was 11 g:105 mL, yielding Crude Leather 1.

[0121] S2. Softening: Crude leather product 1 was immersed in a buffer solution containing 3.3% of Reagent B obtained in Preparation Example 5, and shaken at 43°C, pH = 7.3, and 90 rpm for 2.5 h. The temperature was precisely controlled to maintain enzyme activity and the shaking promoted uniform enzyme contact. The bath ratio during softening was 1:8.5, and the buffer solution was sodium hydrogen phosphate-citric acid, to obtain crude leather product 2.

[0122] S3. Finishing: The leather crude product 2 is bombarded with nitrogen plasma at 50W for 3 minutes to increase the surface activity and make the grafted emulsion stronger. Then it is placed in an emulsion containing 9% of the reagent C obtained in Preparation Example 8 with a bath ratio of 1:7. It is tanned at 53°C for 85 minutes. Warmth helps the oil to penetrate and the tanning is evenly distributed. Then it is cured at 48°C for 20 minutes to make the film dense, the color bright and lasting. The emulsion particle size is 100nm and it is stably dispersed. After spraying, it forms a nanofilm, which gives the leather waterproof, breathable and antibacterial functions. It is also fully biodegradable and has no ecological burden. The content of emulsifier in the emulsion is 0.55%, and the leather finished product is obtained.

[0123] Example 3: A green and environmentally friendly leather softening method comprising the following steps:

[0124] S1. Pretreatment: The rawhide was placed in a 30°C warm water bath and stirred for 30 minutes to wash away impurities and blood on the surface of the rawhide. The rawhide was then subjected to ultrasonic vibration at 20 kHz and 400 W for 15 minutes to remove impurities and open pores. The rawhide was then subjected to a 2.45 GHz and 600 W microwave cavity for 10 minutes to accelerate the temperature and promote fiber expansion, laying the foundation for softening. After draining, the pH was adjusted to 8 using Reagent A obtained in Preparation Example 3 to neutralize the natural acid, activate subsequent reactions, and create a suitable charge and osmotic pressure environment for the enzyme molecules, promoting subsequent efficient attachment and penetration. This gentle treatment can avoid damage to the leather structure. The rawhide:water ratio was 12 g:110 mL, yielding Crude Leather 1.

[0125] S2. Softening: Crude leather product 1 was immersed in a buffer solution containing 3.5% of Reagent B obtained in Preparation Example 6, and shaken at 45°C, pH = 7.5, and 100 rpm for 3 h. The temperature was precisely controlled to maintain enzyme activity and the shaking promoted uniform enzyme contact. The bath ratio during softening was 1:9, and the buffer solution was sodium hydrogen phosphate-citric acid, to obtain crude leather product 2;

[0126] S3. Finishing: The leather crude product 2 is bombarded with nitrogen plasma at 50W for 3 minutes to increase the surface activity and make the grafted emulsion stronger. Then it is placed in an emulsion containing 10% of the reagent C obtained in Preparation Example 9 with a bath ratio of 1:8. It is tanned at 55°C for 90 minutes. Warmth helps the oil to penetrate and the tanning is evenly distributed. Then it is cured at 50°C for 20 minutes to make the film dense and the color bright and lasting. The emulsion particle size is 120nm and it is stably dispersed. After spraying, it forms a nano film, which gives the leather waterproof, breathable and antibacterial functions. It is also fully biodegradable and has no ecological burden. The content of emulsifier in the emulsion is 0.6%, and the leather finished product is obtained.

[0127] Comparative Example 1:

[0128] Compared with Example 1, this comparative example did not perform pretreatment during the leather softening process. The remaining steps and parameters were the same and will not be repeated in this comparative example. Finally, a finished leather product was obtained.

[0129] Comparative Example 2:

[0130] Compared with Example 1, this comparative example only replaces "reagent B obtained in Preparation Example 4" with "a mixture of equal amounts of collagen hydrolase and plant-derived protease", and the remaining steps and parameters are the same, which will not be repeated in this comparative example, and finally a leather finished product is obtained.

[0131] Comparative Example 3:

[0132] Compared with Example 1, this comparative example only replaces "reagent B obtained in Preparation Example 4" with "a mixture obtained by mixing 18g collagen hydrolase, 10g plant-derived protease and 10g metal-organic framework enzyme-loaded microparticles". The remaining steps and parameters are the same and will not be repeated in this comparative example. The finished leather product is finally obtained.

[0133] Performance test: The following performance test was performed on the leather products obtained in Examples 1 to 3 and Comparative Examples 1 to 3.

[0134] Softness: Using the LLY-01 leather softness tester, cut the leather sample into the specified size, measure the thickness and compression deformation of the leather under a certain pressure, and calculate the softness value. The larger the value, the softer the leather. The unit is mm.

[0135] Tensile strength: According to GB / T3923.1-2013 “Tensile properties of textile fabrics — Part 1: Determination of breaking force and elongation at break (Strip method)”, a tensile test is conducted on leather samples using an electronic universal testing machine until the sample breaks. The maximum tensile force at break is recorded, which is the tensile strength (in MPa).

[0136] Tear strength: According to QB / T1131-1991 "Determination of tear force of leather: Double-sided tear method", a specific shape of incision is cut on the leather sample, and then a tear test is performed using a tensile testing machine. The force required to tear the incision is measured as the tear strength, and the unit is N / mm;

[0137] Waterproof performance: Using the hydrostatic pressure method, fix the leather sample on the tester and gradually increase the water pressure until water penetrates the leather surface. The water pressure value at this time is recorded as the waterproof performance indicator. The larger the water pressure value, the better the waterproof performance. The unit is kPa.

[0138] Air permeability: Refer to GB / T5453-1997 "Determination of Air Permeability of Textile Fabrics" and use a fabric air permeability meter to measure the air permeability of leather samples under a certain pressure difference. The greater the air permeability, the better the air permeability. The unit is mm / s.

[0139] Antibacterial performance: With reference to GB / T20944.3-2008 "Evaluation of Antibacterial Properties of Textiles Part 3: Oscillation Method", leather samples are placed in contact with a bacterial suspension of a certain concentration. After oscillation and incubation under specific conditions for a certain period of time, the bacterial reduction rate is measured to evaluate the antibacterial performance. A higher bacterial reduction rate indicates a stronger antibacterial performance, expressed in %.

[0140] The results are shown in Table 1 below:

[0141] Table 1 Performance test results statistics

[0142] project Softness tensile strength Tear strength Waterproof performance Breathable performance Bacteria reduction rate Example 1 3.5 12.8 28.5 3.2 150 95 Example 2 3.8 13.2 30.2 3.5 165 97 Example 3 4.2 13.5 32.8 3.8 180 98 Comparative Example 1 2.2 10.5 22.3 2.5 120 75 Comparative Example 2 2.8 11.2 24.6 2.8 130 80 Comparative Example 3 3.1 11.9 26.1 2.9 142 91

[0143] Data Analysis:

[0144] As can be seen in Table 1, Examples 1-3 achieved softness values ​​of 3.5mm, 3.8mm, and 4.2mm, respectively, exhibiting a superior soft texture. This is attributed to the unique softening process, particularly the precise action of the complex enzyme preparation in Reagent B. The metal-organic framework-enzyme-loaded microparticles release enzymes based on internal leather stress, gently and efficiently hydrolyzing leather fibers to avoid excessive damage. They also synergize with plant-derived elastase and targeted collagenase to moderately loosen the fiber structure and impart excellent softness to the leather. In contrast, Comparative Example 1 lacks pretreatment, resulting in insufficient fiber stretch. Comparative Examples 2 and 3 lack the precise enzyme-controlled release system of Reagent B, limiting the softening effect and resulting in significantly lower softness.

[0145] The tensile strength of Examples 1-3 remained stable at a high level, ranging from 12.8 MPa to 13.5 MPa. This was attributed to a variety of factors. Firstly, the synergistic ultrasound and microwave treatment during the pretreatment phase removed impurities and opened pores without damaging the fiber's main structure, laying the foundation for subsequent processing. Secondly, the moderate enzymatic hydrolysis of Reagent B prevented excessive weakening of the fiber strength, and the nanocellulose in Reagent C during the finishing phase effectively strengthened the leather's overall structure. In contrast, the comparative examples 1 lacked pretreatment, resulting in disordered fiber arrangement and easy breakage under stress, resulting in a tensile strength of only 10.5 MPa. Comparative Examples 2 and 3, due to improper enzyme preparation combinations, damaged or poorly bonded fibers, exhibited lower tensile strengths than the examples.

[0146] The tear strength of Examples 1-3 is relatively high. The pretreatment optimizes the basic properties of the fiber, the precise enzyme action during softening maintains the fiber continuity, and the emulsion components penetrate and fill to form a stable structure during finishing. However, due to the lack of pretreatment, the leather of Comparative Example 1 has many internal defects and the tear strength is as low as 22.3N / mm. The tear strength of Comparative Examples 2 and 3 is far lower than that of the examples due to the imperfect enzyme system and weak inter-fiber adhesion.

[0147] Examples 1-3 have good waterproofness, and the hydrostatic pressure value increases from 3.2kPa to 3.8kPa. This is due to the emulsion of Reagent C in the finishing stage. Plant sterols and nanocellulose synergistically construct a hydrophobic barrier, and chitosan quaternary ammonium salt assists in stabilizing the emulsion film and enhancing waterproofness. Comparative Example 1 is not pretreated, resulting in large pores in the leather and strong water absorption, and the waterproofness is only 2.5kPa.

[0148] Examples 1-3 have good air permeability, with an air permeability of 150 mm / s to 180 mm / s, taking into account both waterproofness and breathability and comfort. The emulsion of reagent C forms a uniform film and has nanoscale pores, which does not hinder water vapor exchange. The lack of pretreatment in comparative example 1 makes the leather structure abnormally dense and the air permeability is hindered, only 120 mm / s.

[0149] The antibacterial rates of Examples 1-3 are as high as 95%-98%. The chitosan quaternary ammonium salt in reagent C plays a key antibacterial role, and its positive charge interacts with the bacterial cell membrane to destroy the bacterial structure; Comparative Example 1 retains a large number of impurity microorganisms without pretreatment, and the subsequent process adaptation is poor, with an antibacterial rate of 75%.

[0150] In summary, the embodiments of the present invention, through a complete and meticulously designed pretreatment, softening, and finishing process, combined with a compound enzyme preparation and a bio-based emulsion, demonstrate a high degree of balance and excellent quality in key properties of leather products such as softness, toughness, waterproofness, breathability, and antibacterial properties, effectively highlighting the tremendous advantages of innovative processes and materials.

[0151] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0152] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A green and environmentally friendly leather softening method, characterized in that: The following steps are involved: Step S1. Pretreatment: Pretreating the leather with reagent A to obtain a crude leather product 1; Step S2. Softening: Softening the crude leather product 1 with reagent B to obtain the crude leather product 2; Step S3. Finishing: Finishing the crude leather product 2 with reagent C to obtain a finished leather product; The preparation process of reagent A in step S1 is as follows: Mix 1% sodium bicarbonate solution, 0.5% glucose solution and 0.3% magnesium sulfate solution to obtain reagent A; The reagent B in step S2 is a complex enzyme preparation; The complex enzyme preparation is obtained by mixing collagen hydrolase, plant-derived protease and metal-organic framework enzyme-loaded microparticles; The reagent C in step S3 is a bio-based emulsion; The pre-processing process in step S1 is as follows: Place the hide in a warm water bath at 25-30°C, stir for 30 minutes, then subject it to ultrasonic vibration at 20kHz, 400W for 15 minutes, then place it in a microwave cavity at 2.45GHz, 600W for 10 minutes, drain, and adjust the pH to 7.5-8 with reagent A; The ratio of rawhide to water is 10-12g:100-110mL; The metal organic framework enzyme-loaded microparticles are MOF microparticles loaded with collagen hydrolase and plant-derived protease, the MOF microparticles are prepared from zirconium chloride, and the particle size of the MOF microparticles is 2-5 nm; The preparation process of the bio-based emulsion is as follows: Step S301. The phytosterols with a purity of 95%-98% are placed in a vacuum oven and dried at 50-60°C and a vacuum degree of 0.08-0.09 MPa for 2-3 hours. The dried phytosterols are ground into a fine powder and passed through an 80-100 mesh sieve; Step S302. Chitosan with a deacetylation degree of 80%-90% and a molecular weight of 60-80 kDa was selected, and glycidyl trimethyl ammonium chloride was used as a quaternizing agent. The chitosan was dispersed in an isopropanol-water mixed solvent, and sodium hydroxide was added to adjust the pH to 10-11. A 20%-30% glycidyl trimethyl ammonium chloride solution was slowly added dropwise. The reaction was stirred at 60-70°C for 6-8 hours. After the reaction was completed, the mixture was washed three times with ethanol to obtain a chitosan quaternary ammonium salt. The prepared chitosan quaternary ammonium salt was dissolved in deionized water to prepare a solution with a mass fraction of 5%-10%. The solution was filtered through a 0.22-0.45 μm filter membrane before use to obtain a chitosan quaternary ammonium salt solution. Step S303: The wood pulp is immersed in a buffer solution containing TEMPO, sodium bromide, and sodium hypochlorite and reacted in the dark at room temperature for 2-3 hours with continuous stirring. After the reaction, the pulp is washed with deionized water until neutral to obtain oxidized cellulose with carboxyl groups on the surface. The oxidized cellulose is then dispersed in water and sonicated at 400-600 W for 30-60 minutes using an ultrasonic cell disruptor to obtain an amphiphilic nanocellulose suspension. Step S304. In a three-necked flask equipped with a mechanical stirrer, a thermometer, and a condenser, deionized water is added, the temperature is raised to 40-50°C, and the mixture is stirred at 300-400 rpm. The phytosterol powder is then added, along with an emulsifier. Stirring is continued for 30-40 minutes to form a primary emulsion of phytosterols. Step S305. Slowly add the chitosan quaternary ammonium salt solution dropwise to the primary emulsion of phytosterols, and the addition time is controlled at 20-30 minutes. During this period, the temperature is raised to 60-70°C, the stirring speed is increased to 500-600 rpm, and the reaction is carried out for 1-2 hours. Subsequently, the amphiphilic nanocellulose suspension is added dropwise to the reaction system. After the addition is completed, the stirring reaction is continued at 70-80°C for 2-3 hours to form a bio-based emulsion.

2. The environmentally friendly leather softening method according to claim 1, characterized in that: The preparation process of reagent A in step S1 is as follows: The volume ratio of the sodium bicarbonate solution, the glucose solution and the magnesium sulfate solution is 55-58:28-30:12-16.

3. The environmentally friendly leather softening method according to claim 1, characterized in that: The softening process in step S2 is as follows: Immerse the crude leather product 1 in a buffer solution containing 3%-3.5% reagent B, and shake at 40-45°C, pH = 7-7.5, and 80-100 rpm for 2-3 hours; The bath ratio during softening is 1:8-9, and the buffer solution is disodium hydrogen phosphate-citric acid.

4. The environmentally friendly leather softening method according to claim 1, characterized in that: The collagen hydrolase in the reagent B is prepared from pig gastric mucosal tissue; The plant-derived protease in the reagent B is prepared from papaya tissue.

5. The environmentally friendly leather softening method according to claim 1, characterized in that: The mass ratio of collagen hydrolase, plant-derived protease and metal-organic framework enzyme-loaded microparticles in the reagent B is 10-15:10-12:18-22 g.

6. The environmentally friendly leather softening method according to claim 1, characterized in that: The retouching process in step S3 is as follows: The leather crude product 2 was bombarded with nitrogen plasma at 50W for 3 minutes, then placed in reagent C with a bath ratio of 1:6-8, tanned at 50-55°C for 80-90 minutes, and then cured at 45-50°C for 20 minutes.

7. The environmentally friendly leather softening method according to claim 1, characterized in that: The particle size of the bio-based emulsion in step S3 is 80-120 nm, and deionized water in the bio-based emulsion accounts for 40%-50% of the total mass.

8. The environmentally friendly leather softening method according to claim 1, characterized in that: The mass ratio of phytosterol, chitosan quaternary ammonium salt solution and amphiphilic nanocellulose in the reagent C is 3-5:80-85:2-3.