Veneering material based on crushing and recycling of genuine leather and preparation method thereof

Abstract

The invention relates to the technical field of veneering materials, in particular to a veneering material based on genuine leather crushing and recycling and a preparation method of the veneering material. The method comprises the following steps: crushing genuine leather leftover materials, activating the crushed genuine leather leftover materials with a NaOH solution, and synchronously preparing double-bond-containing modified polyurethane and amino-modified nano-zinc oxide; and blending the three materials with 2, 3-dimercaptosuccinic acid and the like to form composite slurry, and carrying out hot-pressing cross-linking and surface anti-fouling treatment to obtain the veneering material. Amino groups of dermal fibers react with isocyanate groups of polyurethane to form covalent bonds, and double-bond self-crosslinking of modified polyurethane and bridging of nano-zinc oxide are performed to construct a high-strength structure; the self-repairing function is realized by utilizing reversible breakage and recombination of disulfide bonds and thiol-thioester exchange reaction; the amino-modified nano-zinc oxide is utilized to realize efficient bacteriostasis through coordination of zinc ion release and electrostatic adsorption. The veneering material prepared by the method is excellent in mechanical property, self-repairing and lasting in antibacterial property, and a green solution is provided for high-value utilization of leather leftover materials.

Description

Technical Field

[0001] The present invention relates to the technical field of veneering materials, and particularly to veneering materials based on the pulverization and recycling of genuine leather scraps and a preparation method thereof. Background Art

[0002] With the development of the leather industry, the recycling of genuine leather scraps from leather making has become an important topic in the field of resource recycling. These scraps are rich in genuine leather fibers. If directly discarded, it will not only cause waste of protein resources, but also lead to environmental pollution due to improper treatment. At present, in the industry, most often, after physical pulverization, they are blended with polymers such as polyurethane (PU) to prepare recycled leather or veneering materials. However, this type of technology faces multiple technical challenges in practical applications.

[0003] In the prior art, the combination of genuine leather fibers and the polymer matrix mainly relies on physical entanglement. Residual impurities and insufficient active groups on the fiber surface result in weak interfacial bonding force, and the mechanical properties of the materials are generally low. When subjected to deformation, fiber slippage or matrix cracking is likely to occur, which cannot meet the current higher requirements for veneering materials. In addition, the traditional process uses a static cross-linking system. After the material is damaged by external forces, there is no reversible repair mechanism, and fine cracks will quickly expand, leading to performance decline, and it is difficult to achieve self-repair function during long-term use. In terms of functionality, the antibacterial treatment of existing recycled leather mostly relies on spraying antibacterial agents later. Inorganic antibacterial agents (such as nano-zinc oxide) are prone to agglomeration in the matrix due to surface polarity differences, reducing the effective contact area, and the antibacterial rate is generally lower than 80%. Moreover, the antibacterial components are likely to be lost during the use process, and long-lasting antibacterial effects cannot be achieved. At the same time, complex surface treatment and multi-step blending processes lead to high production energy consumption and long processes, which are contrary to the industry trends of green manufacturing and low-cost. Summary of the Invention

[0004] The purpose of the present invention is to solve the drawbacks existing in the prior art, and to provide a veneering material based on the pulverization and recycling of genuine leather scraps and a preparation method thereof.

[0005] Based on the above purpose, the present invention provides a preparation method of a veneering material for the pulverization and recycling of genuine leather scraps, which is characterized by including the following steps: (1) After removing impurities from genuine leather scraps from leather making, pulverize them using a double-roll grinder, control the particle size to be 50 - 80 μm, add them to a NaOH solution with a concentration of 5%, heat to 40 - 60 °C, stir for 30 - 60 min, centrifuge, wash with deionized water until the pH is neutral, and dry to obtain activated genuine leather fibers; (2)Under nitrogen protection, polytetrahydrofuran diol was added to N,N-dimethylformamide, and the temperature was raised to 70-80 °C. Then, hexamethylene diisocyanate was added, and the reaction was carried out for 2-4 h. After cooling to room temperature, deionized water was added, and the precipitate was collected by centrifugation, washed and dried to obtain an isocyanate-terminated prepolymer. The schematic diagram of the chemical reaction process is as follows: Formula (1), and the product was characterized by FTIR infrared spectroscopy; (3)Under nitrogen protection, the isocyanate-terminated prepolymer and dibutyltin dilaurate were added to anhydrous toluene, and the temperature was raised to 45-55 °C with stirring. Then, 2-mercaptoethyl acrylate was added, and the reaction was carried out for 3-5 h. After cooling to room temperature, toluene was removed by rotary evaporation, petroleum ether was added, and the mixture was stirred for 20-40 min. The precipitate was collected by centrifugation, washed and dried to obtain a modified polyurethane. The schematic diagram of the chemical reaction process is as follows: Formula (2), and the product was characterized by FTIR infrared spectroscopy; (4)After pre-drying nano-zinc oxide in a vacuum drying oven at 80-90 °C for 3-5 h, it was added to a mixed solution of anhydrous ethanol / deionized water, ultrasonically dispersed for 20-30 min, and then placed in a constant temperature water bath at 80-90 °C and stirred evenly. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and then silane coupling agent KH-550 was added, and the reaction was carried out for 2-4 h. After cooling to room temperature, it was filtered and washed. The obtained solid was Soxhlet extracted with anhydrous ethanol for 18-24 h, and then dried to obtain amino-modified nano-zinc oxide; (5)The modified polyurethane and amino-modified nano-zinc oxide were added to anhydrous N,N-dimethylformamide to prepare a pre-slurry. The pre-slurry, activated dermal fibers, 2,3-dimercaptosuccinic acid, dibutyltin dilaurate, ammonium persulfate, and polyethylene glycol dithioacetate were added to a high-speed mixer. First, it was stirred at 1000-2000 rpm for 5-10 min, and then the rotation speed was increased to 6000-8000 rpm, and high-speed shearing was carried out for 30-60 min to form a uniform and stable slurry; (6) Apply the uniform and stable slurry in the release mold, place it in a hot press, reduce the pressure to 30 - 40 MPa, and raise the temperature in stages: 0 - 20 min: raise the temperature from room temperature to 75 - 85 °C, with the heating rate controlled at 3 - 5 °C / min; 20 - 30 min: raise the temperature to 120 - 130 °C, with the heating rate of 3 - 5 °C / min; 30 - 45 min: keep the temperature at 120 - 130 °C for 15 - 25 min, cool to room temperature, after washing and drying, use a polishing machine to mechanically polish the material surface, with the polishing speed of 1000 - 2000 rpm and the polishing time of 10 - 20 min. Finally, immerse the material in the diluted fluoroacrylate emulsion for 10 - 15 min, take it out and dry for 1 - 3 h to form an anti - stain coating on the material surface, and obtain the veneer material based on the recycling of shredded genuine leather.

[0006] Preferably, in the step (1), the genuine leather tanning scraps and the 5% NaOH solution are in a weight ratio of 1:10 - 20.

[0007] Preferably, in the step (2), the polytetrahydrofuran diol, hexamethylene diisocyanate, N,N - dimethylformamide and deionized water are in a weight ratio of 1:2 - 2.5:8 - 12:10 - 20.

[0008] Preferably, in the step (3), the isocyanate - terminated prepolymer, dibutyltin dilaurate, 2 - mercaptoethyl acrylate, anhydrous toluene and petroleum ether are in a weight ratio of 1:0.03 - 0.05:0.3 - 0.5:8 - 12:8 - 12.

[0009] Preferably, in the step (4), the nano - zinc oxide, the mixed solution of anhydrous ethanol / deionized water and the silane coupling agent KH - 550 are in a weight ratio of 1:80 - 100:0.05 - 0.1.

[0010] Preferably, the mixed solution of anhydrous ethanol / deionized water in the step (4) refers to the mixture of anhydrous ethanol and water made according to a weight ratio of 3:1.

[0011] Preferably, in the step (5), the modified polyurethane, amino - modified nano - zinc oxide, activated genuine leather fibers, 2,3 - dimercaptosuccinic acid, dibutyltin dilaurate, ammonium persulfate, polyethylene glycol dithioacetate and anhydrous N,N - dimethylformamide are in a weight ratio of 60 - 70:5 - 10:30 - 40:1 - 3:0.05 - 0.1:0.05 - 0.1:0.5 - 2:120 - 140.

[0012] Preferably, in the step (5), multiple cross - linking reactions occur, specifically as follows: The amino group in the genuine leather fibers reacts with the isocyanate group in the modified polyurethane, and the schematic diagram of the reaction process is: In Equation (3), during the reaction, the amino group attacks the carbon atom of the isocyanate group as a nucleophile, initiating the reaction to form strong covalent bonds, replacing the traditional physical entanglement effect, achieving the chemical bonding between the fiber and the polymer, and significantly improving the mechanical strength of the material. The double bonds in the modified polyurethane will undergo self-crosslinking and also react with the sulfhydryl groups in 2,3-dimercaptosuccinic acid. The schematic diagram of the reaction process is as follows: In Equation (4), it further enhances the mechanical strength of the material. At the same time, a part of 2,3-dimercaptosuccinic acid will also undergo intermolecular coupling at high temperatures. The schematic diagram of the reaction process is as follows: In Equation (5), the generated disulfide bonds have the characteristics of reversible fracture-recombination. When subjected to external forces, they break to absorb energy and re-bond when standing still, endowing the material with certain self-healing ability. Combined with polyethylene glycol dithioacetate, the dynamic covalent bond recombination is achieved through the thiol-thioester exchange reaction, enhancing the self-healing ability of the material. The amino groups in the amino-modified nano-zinc oxide can react with the carboxyl groups in the dermal fibers and the isocyanate groups in the modified polyurethane. The schematic diagram of the reaction process is as follows: In Equation (6), through the bridging crosslinking of nano-zinc oxide, a "dermal fiber-zinc oxide-polymer" triple crosslinking is formed. The chemical covalent bonds provide the basic strength, the dynamic disulfide bonds dissipate the fracture energy, and the nano-bridging hinders the crack propagation. The combined action of the three makes the material have high strength, high toughness and self-healing functions, showing a huge improvement compared with the performance of traditional regenerated leather.

[0013] Preferably, the solid content of the diluted fluorinated acrylate emulsion in (6) is 5%.

[0014] Furthermore, the present invention also provides a veneering material based on the crushing and recycling of dermal leather, which is prepared by the above preparation method.

[0015] The beneficial effects of the present invention: 1. Through the in-depth development of dermal leather scraps, the present invention realizes the high-value utilization of waste dermal fibers. The dermal fibers are activated and treated with a NaOH solution to effectively remove impurities and expose active amino groups, converting the dermal fibers from traditional physical filling to functional components that can participate in chemical crosslinking. This process not only avoids environmental pollution caused by incineration or landfill of scraps, but also converts protein-based fibers into high-strength composite substrates, significantly improving the resource utilization rate. During the preparation process, there is no need to add a large amount of synthetic fibers or toughening agents additionally, reducing the consumption of chemical raw materials from the source, conforming to the concept of circular economy and green chemistry, and providing a sustainable solution for the solid waste treatment in the leather industry.

[0016] 2. The present invention forms a "chemical covalent bond - dynamic disulfide bond - nano-zinc oxide bridging" triple cross-linked structure through the covalent bonding between the amino groups on the surface of dermal fibers and the isocyanate groups of modified polyurethane, the self-crosslinking of polyurethane double bonds, and the thiol-ene reaction initiated by 2,3-dimercaptosuccinic acid. The dermal fibers and the polymer matrix are upgraded from physical entanglement to chemical bonding, the interfacial bonding force is increased several times, the tensile strength and elongation at break are optimized synchronously. The amino-modified nano-zinc oxide, as a nano-level cross-linking node, is uniformly dispersed in the matrix to hinder crack propagation, endowing the material with the synergistic properties of high strength and high toughness.

[0017] 3. The present invention constructs a dynamic covalent bond network by utilizing the reversible cleavage-recombination characteristics of the disulfide bonds formed by the intermolecular coupling of 2,3-dimercaptosuccinic acid and combining with the thiol-thioester exchange reaction of polyethylene glycol dithioacetate. When the material is damaged by external force, the disulfide bonds break to absorb energy and prevent crack propagation. When standing, self-repair is achieved through bond recombination without external intervention or additional repair agents. This self-repair function significantly extends the service life of the material, reduces the overall replacement caused by minor damage, and is especially suitable for materials that are prone to wear during long-term use, reducing maintenance costs and improving use reliability.

[0018] 4. The present invention conducts amino modification on nano-zinc oxide through the silane coupling agent KH-550, significantly improving its dispersibility in the polymer matrix, avoiding agglomeration and increasing the specific surface area, thus greatly increasing the zinc ion release efficiency and the contact area of antibacterial sites. The electrostatic attraction between the amino groups and the negative charges on the bacterial cell wall further enhances the contact efficiency between nano-zinc oxide and microorganisms, forming a "contact sterilization - zinc ion release sterilization" dual mechanism. This antibacterial system does not require post-spraying treatment, and the antibacterial components are evenly distributed inside and on the surface of the material, with a long-lasting and stable antibacterial effect, showing broad-spectrum antibacterial performance, meeting the application requirements of scenarios with high hygiene and safety requirements such as medical and household. Description of the Drawings

[0019] Figure 1 is the FTIR infrared spectrum of the isocyanate-terminated prepolymer prepared in Example 2 of the present invention; Figure 2 is the FTIR infrared spectrum of the modified polyurethane prepared in Example 2 of the present invention. Detailed Embodiments

[0020] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0021] The sources of the reagent raw materials used in the embodiments of the present invention are as follows: Dermal leather scraps (self-produced); polytetrahydrofuran diol was purchased from Shanghai Macklin Biochemical Co., Ltd., average Mn: 2,000; hexamethylene diisocyanate was purchased from Shanghai Macklin Biochemical Co., Ltd., purity 99%; dibutyltin dilaurate was purchased from Shanghai Macklin Biochemical Co., Ltd., purity 95%; 2-mercaptoethyl acrylate was purchased from Hefei Shenghang Medical Technology Co., Ltd., purity 95%; nano zinc oxide was purchased from Shanghai Darui Fine Chemicals Co., Ltd., purity 98%; silane coupling agent KH-550 was from Shanghai Macklin Biochemical Co., Ltd., purity 99%; ammonium persulfate was purchased from Shanghai Macklin Biochemical Co., Ltd., purity 98.5%; polyethylene glycol dithioacetate was from Jilin Shengchuang Biotechnology Co., Ltd., purity 95%; fluorinated acrylate emulsion was purchased from Jining Baiyi Chemical Co., Ltd., solid content 47%.

[0022] Example 1: The specific preparation method of the veneering material based on the crushing and recycling of dermal leather scraps includes the following steps: (1) After removing impurities from 400 g of dermal leather scraps, they were crushed using a two-roll grinder, with the particle size controlled at 50 - 80 μm. Then they were added to a 5% NaOH solution, heated to 40 °C, stirred for 30 min, centrifuged, washed with deionized water until the pH was neutral, and dried to obtain activated dermal fibers; (2) Under nitrogen protection, 300 g of polytetrahydrofuran diol was added to 2.4 kg of N,N-dimethylformamide, heated to 70 °C, and then 600 g of hexamethylene diisocyanate was added. The reaction was carried out for 2 h, cooled to room temperature, 3 kg of deionized water was added, and the precipitate was collected by centrifugation, washed and dried to obtain an isocyanate-terminated prepolymer; (3) Under nitrogen protection, 700 g of the isocyanate-terminated prepolymer and 21 g of dibutyltin dilaurate were added to 5.6 kg of anhydrous toluene. The mixture was stirred and heated to 45 °C, and then 210 g of 2-mercaptoethyl acrylate was added. The reaction was carried out for 3 h, cooled to room temperature, the toluene was rotary evaporated, 5.6 kg of petroleum ether was added, stirred for 20 min, and the precipitate was collected by centrifugation, washed and dried to obtain a modified polyurethane; (4) After pre-drying 70 g of nano zinc oxide in a vacuum drying oven at 80 °C for 3 h, it was added to a mixed solution of 5.6 kg of anhydrous ethanol / deionized water (prepared by mixing ethanol and water in a weight ratio of 3:1), ultrasonically dispersed for 20 min, then placed in a constant temperature water bath at 80 °C and stirred evenly. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and then 3.5 g of silane coupling agent KH-550 was added. The reaction was carried out for 2 h, cooled to room temperature, filtered and washed. The obtained solid was Soxhlet extracted with anhydrous ethanol for 18 h, and then dried to obtain amino-modified nano zinc oxide; (5) 600 g of modified polyurethane and 50 g of amino-modified nano zinc oxide were added to 1.2 kg of anhydrous N,N-dimethylformamide to prepare a pre-slurry. The pre-slurry, 300 g of activated dermis fibers, 10 g of 2,3-dimercaptosuccinic acid, 0.5 g of dibutyltin dilaurate, 0.5 g of ammonium persulfate, and 5 g of polyethylene glycol dithioacetate were added to a high-speed blender. First, it was stirred at 1000 rpm for 5 min, then the rotation speed was increased to 6000 rpm, and high-speed shearing was carried out for 30 min to form a uniform and stable slurry. (6) The uniform and stable slurry was coated in a release mold and placed in a hot press. The pressure was reduced to 30 MPa, and the temperature was raised in stages: 0 - 20 min: from room temperature to 75 °C, with the heating rate controlled at 3 °C / min; 20 - 30 min: raised to 120 °C, with the heating rate of about 3 °C / min; 30 - 45 min: kept at 120 °C for 15 min, cooled to room temperature, washed and dried. Then, a polishing machine was used to mechanically polish the surface of the material at a polishing rotation speed of 1000 rpm for 10 min. Finally, the material was immersed in a diluted fluoroacrylate emulsion (solid content of 5%) for 10 min, taken out and dried for 1 h to form an anti-fouling coating on the surface of the material, and a veneer material based on the pulverized and recycled dermis leather was obtained.

[0023] Example 2: The specific preparation method of the veneer material based on the pulverized and recycled dermis leather includes the following steps: (1) After removing impurities from 500 g of leather-making offcuts, they were pulverized using a two-roll grinder, with the particle size controlled at 50 - 80 μm. They were added to a NaOH solution with a concentration of 5%, heated to 50 °C, stirred for 45 min, centrifuged, washed with deionized water until the pH was neutral, and dried to obtain activated dermis fibers. (2) Under nitrogen protection, 300 g of polytetrahydrofuran diol was added to 3 kg of N,N-dimethylformamide, heated to 75 °C, and then 660 g of hexamethylene diisocyanate was added. The reaction was carried out for 3 h, cooled to room temperature, 4.5 kg of deionized water was added, and the precipitate was collected by centrifugation, washed and dried to obtain an isocyanate-terminated prepolymer. (3) Under nitrogen protection, 700 g of the isocyanate-terminated prepolymer and 28 g of dibutyltin dilaurate were added to 7 kg of anhydrous toluene. The temperature was raised to 50 °C with stirring, and then 280 g of 2-mercaptoethyl acrylate was added. The reaction was carried out for 4 h, cooled to room temperature. After spinning off toluene, 7 kg of petroleum ether was added, stirred for 30 min, and the precipitate was collected by centrifugation, washed and dried to obtain modified polyurethane. (4) After pre-drying 100 g of nano-zinc oxide in a vacuum drying oven at 85 °C for 4 h, it was added to a mixed solution of 9 kg of anhydrous ethanol / deionized water (prepared by mixing ethanol and water in a weight ratio of 3:1), ultrasonically dispersed for 25 min, then placed in a constant temperature water bath at 85 °C and stirred evenly. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and then 8 g of silane coupling agent KH-550 was added. After reacting for 3 h, it was cooled to room temperature, filtered and washed. The obtained solid was extracted with anhydrous ethanol in a Soxhlet extractor for 21 h, and then dried to obtain amino-modified nano-zinc oxide; (5) 650 g of modified polyurethane and 75 g of amino-modified nano-zinc oxide were added to 1.3 kg of anhydrous N,N-dimethylformamide to prepare a pre-slurry. The pre-slurry, 350 g of activated dermal fibers, 20 g of 2,3-dimercaptosuccinic acid, 0.75 g of dibutyltin dilaurate, 0.75 g of ammonium persulfate, and 15 g of polyethylene glycol dithioacetate were added to a high-speed mixer. First, it was stirred at 1500 rpm for 8 min, and then the rotation speed was increased to 7000 rpm, and high-speed shearing was carried out for 45 min to form a uniform and stable slurry; (6) The uniform and stable slurry was coated in a release mold and placed in a hot press. The pressure was reduced to 35 MPa, and the temperature was raised in stages: 0 - 20 min: from room temperature to 80 °C, and the heating rate was controlled at 4 °C / min; 20 - 30 min: raised to 125 °C, and the heating rate was about 4 °C / min; 30 - 45 min: kept at 125 °C for 20 min, cooled to room temperature, washed and dried. Then, a polishing machine was used to mechanically polish the surface of the material. The polishing rotation speed was 1500 rpm, and the polishing time was 15 min. Finally, the material was immersed in a diluted fluorinated acrylate emulsion (solid content of 5%) for 12 min, taken out and dried for 2 h to form an anti-fouling coating on the surface of the material, and a veneer material based on the recycling of crushed leather was obtained.

[0024] Example 3: The specific preparation method of the veneer material based on the recycling of crushed leather includes the following steps: (1) After removing impurities from 500 g of leather-making scraps, they were crushed by a double-roll grinder, and the particle size was controlled at 50 - 80 μm. Then they were added to a 5% NaOH solution, heated to 60 °C, stirred for 60 min, centrifuged, and washed with deionized water until the pH was neutral. After drying, activated dermal fibers were obtained; (2) Under nitrogen protection, 500 g of polytetrahydrofuran diol was added to 6 kg of N,N-dimethylformamide, heated to 80 °C, and then 1.25 kg of hexamethylene diisocyanate was added. After reacting for 4 h, it was cooled to room temperature, 10 kg of deionized water was added, and the precipitate was collected by centrifugation, washed and dried to obtain an isocyanate-terminated prepolymer; (3) Under nitrogen protection, 800 g of isocyanate-terminated prepolymer and 40 g of dibutyltin dilaurate were added to 9.6 kg of anhydrous toluene. The mixture was heated to 55 °C with stirring, and then 400 g of 2-mercaptoethyl acrylate was added. The reaction was carried out for 5 h, cooled to room temperature, and after the toluene was evaporated to dryness, 9.6 kg of petroleum ether was added. The mixture was stirred for 40 min, and the precipitate was collected by centrifugation, washed and dried to obtain modified polyurethane; (4) After pre-drying 120 g of nano-zinc oxide in a vacuum drying oven at 90 °C for 5 h, it was added to a mixed solution of 12 kg of anhydrous ethanol / deionized water (prepared by mixing ethanol and water in a weight ratio of 3:1), ultrasonically dispersed for 30 min, and then placed in a constant temperature water bath at 90 °C and stirred evenly. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and then silane coupling agent KH-550 was added. The reaction was carried out for 4 h, cooled to room temperature, filtered and washed. The obtained solid was extracted with anhydrous ethanol in a Soxhlet extractor for 24 h, and then dried to obtain amino-modified nano-zinc oxide; (5) (5) 700 g of modified polyurethane and 100 g of amino-modified nano-zinc oxide were added to 1.4 kg of anhydrous N,N-dimethylformamide to prepare a pre-slurry. The pre-slurry, 400 g of activated dermal fibers, 30 g of 2,3-dimercaptosuccinic acid, 1 g of dibutyltin dilaurate, 1 g of ammonium persulfate, and 20 g of polyethylene glycol dithioacetate were added to a high-speed mixer. First, it was stirred at 2000 rpm for 10 min, and then the rotation speed was increased to 8000 rpm, and high-speed shearing was carried out for 60 min to form a uniform and stable slurry; (6) (6) The uniform and stable slurry was coated in a release mold and placed in a hot press. The pressure was reduced to 40 MPa, and the temperature was increased in stages: 0 - 20 min: from room temperature to 85 °C, and the heating rate was controlled at 5 °C / min; 20 - 30 min: increased to 130 °C, and the heating rate was about 5 °C / min; 30 - 45 min: kept at 130 °C for 25 min, cooled to room temperature, washed and dried. Then, the surface of the material was mechanically polished with a polishing machine at a polishing speed of 2000 rpm for 20 min. Finally, the material was immersed in a diluted fluorinated acrylate emulsion (solid content 5%) for 15 min, taken out and dried for 3 h to form an anti-fouling coating on the surface of the material, and a veneer material based on the recycling of crushed leather was obtained. (7) (8)

[0025] (9) Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that after removing impurities from the leather scraps, they were crushed by a two-roll grinder and not added to a 5% NaOH solution. (10) (11)

[0026] (12) Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that step (3) was omitted. The specific preparation process is as follows: The specific preparation method of the veneer material based on the recycling of crushed leather includes the following steps: (13) (1) After removing impurities from 500 g of leather-making waste leather, it was crushed using a double-roll grinder, with the particle size controlled at 50 - 80 μm. It was added to a 5% NaOH solution, heated to 50 °C, stirred for 45 min, centrifuged, washed with deionized water until the pH was neutral, and dried to obtain activated leather fibers; (2) Under nitrogen protection, 300 g of polytetrahydrofuran diol was added to 3 kg of N,N-dimethylformamide, heated to 75 °C, and then 660 g of hexamethylene diisocyanate was added. The reaction was carried out for 3 h, cooled to room temperature, 4.5 kg of deionized water was added, and the precipitate was collected by centrifugation, washed, and dried to obtain an isocyanate-capped prepolymer; (3) After pre-drying 100 g of nano-zinc oxide in a vacuum drying oven at 85 °C for 4 h, it was added to a mixed solution of 9 kg of anhydrous ethanol / deionized water (prepared by mixing ethanol and water in a weight ratio of 3:1), ultrasonically dispersed for 25 min, then placed in a constant temperature water bath at 85 °C and stirred evenly. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and then 8 g of silane coupling agent KH-550 was added. The reaction was carried out for 3 h, cooled to room temperature, filtered, and washed. The obtained solid was extracted with anhydrous ethanol in a Soxhlet extractor for 21 h, and then dried to obtain amino-modified nano-zinc oxide; (4) 650 g of isocyanate-capped prepolymer and 75 g of amino-modified nano-zinc oxide were added to 1.3 kg of anhydrous N,N-dimethylformamide to prepare a pre-slurry. The pre-slurry, 350 g of activated leather fibers, 20 g of 2,3-dimercaptosuccinic acid, 0.75 g of dibutyltin dilaurate, 0.75 g of ammonium persulfate, and 15 g of polyethylene glycol dithioacetate were added to a high-speed mixer. First, it was stirred at 1500 rpm for 8 min, and then the rotation speed was increased to 7000 rpm, and high-speed shearing was carried out for 45 min to form a uniform and stable slurry; (5) The uniform and stable slurry was coated in a release mold, placed in a hot press, and the pressure was reduced to 35 MPa. The temperature was increased in stages: 0 - 20 min: from room temperature to 80 °C, with the heating rate controlled at 4 °C / min; 20 - 30 min: increased to 125 °C, with the heating rate about 4 °C / min; 30 - 45 min: kept at 125 °C for 20 min, cooled to room temperature, washed and dried. Then, the surface of the material was mechanically polished using a polishing machine at a polishing speed of 1500 rpm for 15 min. Finally, the material was immersed in a diluted fluorinated acrylate emulsion (solid content of 5%) for 12 min, taken out and dried for 2 h to form an anti-fouling coating on the surface of the material, and a veneer material based on the recycling of waste leather was obtained.

[0027] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the amino modification of nano-zinc oxide in step (4) was omitted, and nano-zinc oxide was directly used in the subsequent steps.

[0028] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that nano-zinc oxide is not added.

[0029] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that 2,3-dimercaptosuccinic acid is not added.

[0030] Performance Test: 1. Mechanical property test: The veneer materials prepared in Examples 1-3 and Comparative Examples 1-5 were made into standard dumbbell-shaped specimens with dimensions of 150 mm × 25 mm × 2 mm. Using a universal material testing machine, they were stretched at a rate of 50 mm / min, and the tensile strength and elongation at break of the materials were recorded. The experimental results are shown in Table 1.

[0031] 2. Self-healing rate test: The veneer materials prepared in Examples 1-3 and Comparative Examples 1-5 were made into specimens of uniform size with dimensions of 100 mm × 50 mm × 2 mm. A cut with a depth of 20 μm, a width of 50 μm, and a length of 10 mm was made on the surface of the specimen with a blade, and it was left standing in a constant temperature oven at 25°C for 24 h. A white light interferometer was used to quantify the scratch recovery rate: R = (initial scratch volume - post-repair volume) / initial scratch volume × 100%. The experimental results are shown in Table 1.

[0032] 3. Antibacterial effect test: The veneer materials prepared in Examples 1-3 and Comparative Examples 1-5 were made into square specimens of 2 cm × 2 cm. After ultraviolet sterilization, they were placed in a 24-well plate, and 1 ml of bacterial suspension (1×10 5 CFU / ml) was added to each well. After sealing, it was left standing at 37°C for 24 h. The materials were taken out, and the surface bacteria were eluted by shaking with 1 ml of sterile PBS buffer. 100 μl of the dilution was spread on an LB agar plate, and the number of colonies was counted after culturing at 37°C for 24 h. The antibacterial rate was calculated as = (1 - ) × 100%, where the control group was the bacterial suspension without the veneer material. The experiment was carried out three times using bacterial suspensions prepared from Escherichia coli, Staphylococcus aureus, and Candida albicans respectively. The experimental results are shown in Table 1.

[0033] Table 1 Performance Test Results

[0034] Performance Analysis: As can be seen from the experimental data in Table 1, the veneering materials prepared based on the pulverized and recycled dermal skin by Examples 1-3 of the present invention have excellent mechanical properties and self-healing ability not possessed by traditional materials, and have good bactericidal and antibacterial ability against some common strains in daily life. Among them, the comprehensive performance of Example 2 is the best. From the perspective of mechanical properties, this may be because the hydrolysis of proteins on the surface of dermal fibers by NaOH treatment exposes a large number of amino groups, which can undergo nucleophilic addition reactions with the isocyanate groups in the modified polyurethane to form covalent bonds, replacing traditional physical entanglement and contributing to the improvement of interfacial bonding force. In Comparative Example 1, fewer active groups of the unactivated fibers are exposed, and they are only bonded by van der Waals forces, which are prone to slippage during stretching, resulting in a decrease in strength. At the same time, the double bonds introduced by 2-mercaptoethyl acrylate react with the mercapto groups of 2,3-dimercaptosuccinic acid through the thiol-ene reaction to form thioether bonds, and the double bonds self-crosslink to form a three-dimensional network structure. The crosslinking density is increased compared with ordinary polyurethane materials, thereby improving the mechanical properties of the materials. Finally, the amino-modified nano-zinc oxide reacts with the carboxyl groups of dermal fibers and the isocyanate groups of polyurethane to form a "fiber-zinc oxide-polymer" triple crosslinking node. The uniform dispersion of the nanoparticles hinders crack propagation. Through these three preparation methods of the present invention, the mechanical properties of the materials are greatly improved.

[0035] From the perspective of the self-healing rate, this may be because the double bonds of the modified polyurethane are covalently grafted with the mercapto groups of 2,3-dimercaptosuccinic acid through the thiol-ene reaction, enabling the mercapto groups to be evenly distributed on the polyurethane chain, shortening the adjacent mercapto group spacing, improving the intermolecular coupling efficiency at high temperatures, and forming a high-density disulfide bond network. In Comparative Example 2, there are no double bonds, and the mercapto groups exist in a free state, with a low coupling probability and a decrease in the self-healing rate. At the same time, the thioester groups provided by polyethylene glycol dithioacetate will also undergo a thiol-thioester exchange reaction with 2,3-dimercaptosuccinic acid, reducing the activation energy of bond recombination. In Comparative Example 5, there is no 2,3-dimercaptosuccinic acid, and this reaction cannot proceed, resulting in a significant decrease in the self-healing rate. Finally, the amino-modified nano-zinc oxide enhances the network denseness through chemical bridging, blocking the crack propagation path with nanoparticles. During repair, the disulfide bonds can be accurately recombined along the original crosslinking points, further improving the repair rate of the materials.

[0036] In terms of antibacterial effect, this may be due to the bactericidal effect of zinc ion release. Nano-zinc oxide has a large specific surface area, and the released zinc ions can damage the phospholipid bilayer of the bacterial cell membrane and inhibit the activity of DNA polymerase, showing excellent antibacterial rates against Escherichia coli, Staphylococcus aureus, and Candida albicans. At the same time, the amino group plays a synergistic role in antibacterial. The amino group grafted by silane coupling agent KH-550 improves the dispersibility of nanoparticles. The electrostatic attraction between the amino group and the negative charge of the bacterial cell wall improves the contact efficiency, facilitating the better contact of zinc ions with bacteria and exerting the antibacterial effect. Finally, the surface fluorinated acrylate emulsion forms a low surface energy coating, which can reduce the adhesion of bacteria. Combined with the active bactericidal effect of nano-zinc oxide, a double barrier of "physical adhesion resistance + chemical sterilization" is formed.

[0037] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a veneer material based on the crushing and recycling of genuine leather, characterized in that: The following steps are involved: (1) After removing impurities from leather scraps, crush them with a double-roll mill to control the particle size to 50-80 μm, add them to a 5% NaOH solution, heat them to 40-60°C, stir them for 30-60 min, centrifuge them, wash them with deionized water until the pH is neutral, and dry them to obtain activated leather fibers; (2) Under nitrogen protection, polytetrahydrofuran diol is added to N,N-dimethylformamide, the temperature is raised to 70-80°C, hexamethylene diisocyanate is added, the reaction is carried out for 2-4 hours, the reaction is cooled to room temperature, deionized water is added, the precipitate is collected by centrifugation, and the isocyanate-terminated prepolymer is obtained after washing and drying; (3) Under nitrogen protection, add the isocyanate-terminated prepolymer and dibutyltin dilaurate into anhydrous toluene, heat to 45-55°C with stirring, then add 2-mercaptoethyl acrylate, react for 3-5h, cool to room temperature, spin-dry the toluene, add petroleum ether, stir for 20-40min, collect the precipitate by centrifugation, wash and dry to obtain the modified polyurethane; (4) After pre-drying the nano zinc oxide in a vacuum drying oven at 80-90°C for 3-5 hours, add it to a mixed solution of anhydrous ethanol / deionized water, ultrasonically disperse it for 20-30 minutes, and then place it in a constant temperature water bath at 80-90°C with uniform stirring. Adjust the pH value to 6.5 with 10% dilute hydrochloric acid, then add silane coupling agent KH-550, react for 2-4 hours, cool to room temperature, filter and wash, and extract the obtained solid with anhydrous ethanol Soxhlet for 18-24 hours, and then dry it to obtain amino-modified nano zinc oxide; (5) Add modified polyurethane and amino-modified nano zinc oxide to anhydrous N,N-dimethylformamide to prepare a pre-slurry, add the pre-slurry, activated dermal fiber, 2,3-dimercaptosuccinic acid, dibutyltin dilaurate, ammonium persulfate, and polyethylene glycol dithioacetate into a high-speed mixer, stir at 1000-2000 rpm for 5-10 minutes, then increase the speed to 6000-8000 rpm, and high-speed shear for 30-60 minutes to form a uniform and stable slurry; (6) Apply the uniform and stable slurry to the release mold, put it into a hot press, reduce the pressure to 30-40MPa, and increase the temperature in stages: 0-20min: from room temperature to 75-85℃, the heating rate is controlled at 3-5℃ / min, 20-30min: increase to 120-130℃, the heating rate is 3-5℃ / min, 30-45min: keep warm at 120-130℃ for 15-25min, cool to room temperature, wash and dry, use a polishing machine to mechanically polish the surface of the material, the polishing speed is 1000-2000rpm, the polishing time is 10-20min, finally immerse the material in a diluted fluorinated acrylate emulsion, the immersion time is 10-15min, take it out and dry it for 1-3h, form an anti-fouling coating on the surface of the material, and obtain a veneer material based on genuine leather crushing and recycling.

2. The method for preparing veneer material based on genuine leather crushing and recycling according to claim 1, characterized in that: The weight ratio of the genuine leather scraps and the 5% NaOH solution in (1) is 1:10-20.

3. The method for preparing veneer material based on genuine leather crushing and recycling according to claim 1, characterized in that: The weight ratio of polytetrahydrofuran diol, hexamethylene diisocyanate, N,N-dimethylformamide and deionized water in (2) is 1:2-2.5:8-12:10-20.

4. The method for preparing veneer material based on genuine leather crushing and recycling according to claim 1, characterized in that: The weight ratio of the isocyanate-terminated prepolymer, dibutyltin dilaurate, 2-mercaptoethyl acrylate, anhydrous toluene and petroleum ether in (3) is 1:0.03-0.05:0.3-0.5:8-12:8-12.

5. The method for preparing veneer material based on genuine leather crushing and recycling according to claim 1, characterized in that: The weight ratio of the nano zinc oxide, the mixed solution of anhydrous ethanol / deionized water and the silane coupling agent KH-550 in (4) is 1:80-100:0.05-0.

1.

6. The method for preparing veneer material based on genuine leather crushing and recycling according to claim 1, characterized in that: The anhydrous ethanol / deionized water mixed solution in (4) refers to anhydrous ethanol and water mixed in a weight ratio of 3:

1.

7. The method for preparing veneer material based on genuine leather crushing and recycling according to claim 1, characterized in that: The weight ratio of the modified polyurethane, amino-modified nano zinc oxide, activated dermal fiber, 2,3-dimercaptosuccinic acid, dibutyltin dilaurate, ammonium persulfate, polyethylene glycol dithioacetate and anhydrous N,N-dimethylformamide in (5) is 60-70:5-10:30-40:1-3:0.05-0.1:0.05-0.1:0.5-2:120-140.

8. The method for preparing veneer material based on genuine leather crushing and recycling according to claim 1, characterized in that: The solid content of the diluted fluorinated acrylic emulsion in (6) is 5%.

9. The veneer material based on the crushing and recycling of genuine leather is prepared by the preparation method described in any one of claims 1 to 8.

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