Veneer material based on leather crushing and recycling and preparation method thereof

Abstract

The present invention relates to the technical field of veneer materials, and in particular to veneer materials based on the crushing and recycling of genuine leather and a preparation method thereof. By crushing genuine leather tanning scraps and activating them with a NaOH solution, a modified polyurethane containing double bonds and amino-modified nano-zinc oxide are simultaneously prepared; the three are then blended with 2,3-dimercaptosuccinic acid and the like to form a composite slurry, and the veneer material is obtained by hot-pressing cross-linking and surface anti-fouling treatment. The present invention forms a high-strength structure by reacting the amino groups of genuine leather fibers with the isocyanate groups of polyurethane to form covalent bonds, as well as the double bonds of the modified polyurethane self-crosslinking and nano-zinc oxide bridging; the self-repairing function is achieved by utilizing the reversible rupture and recombination of disulfide bonds and the thiol-thioester exchange reaction; and the amino-modified nano-zinc oxide is utilized to achieve efficient antibacterial properties through the synergistic release of zinc ions and electrostatic adsorption. The veneer material prepared by the present invention has excellent mechanical properties, is self-repairable, and has long-lasting antibacterial properties, providing a green solution for the high-value utilization of genuine leather scraps.

Description

Technical Field

[0001] The present invention relates to the technical field of veneer materials, in particular to a veneer material based on dermis crushing and recycling and a preparation method thereof. Background Art

[0002] With the development of the leather industry, the recycling of genuine leather scraps has become a key issue in resource recycling. These scraps are rich in genuine leather fibers. Directly discarding them not only wastes protein resources but also causes environmental pollution due to improper handling. Currently, the industry typically produces regenerated leather or veneer materials by physically crushing them and then blending them with polymers such as polyurethane (PU). However, this technology faces multiple technical challenges in practical application.

[0003] Existing technologies primarily rely on physical entanglement to bond dermal fibers to the polymer matrix. This leads to residual impurities on the fiber surface and a lack of active groups, resulting in weak interfacial bonding and generally low mechanical properties. This makes the material susceptible to fiber slippage or matrix cracking when subjected to deformation, making it unable to meet the current higher demands for veneer materials. Furthermore, traditional processes utilize a static crosslinking system, which lacks a reversible repair mechanism after external damage. Microcracks rapidly propagate, leading to performance degradation and difficulty achieving self-repair during long-term use. Regarding functionality, existing antimicrobial treatments for regenerated leather often rely on post-application spraying of antimicrobial agents. However, inorganic antimicrobial agents (such as nano-zinc oxide) tend to aggregate in the matrix due to differences in surface polarity, reducing the effective contact area and resulting in an inhibition rate generally below 80%. Furthermore, the antimicrobial components are easily lost during use, preventing long-term antimicrobial efficacy. Furthermore, the complex surface treatment and multi-step blending process lead to high energy consumption and lengthy production processes, which are contrary to the industry trend towards green manufacturing and cost-effectiveness. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a veneer material based on the recycling of dermis and a preparation method thereof.

[0005] Based on the above purpose, the present invention provides a method for preparing a veneer material by recycling pulverized leather, which is characterized by comprising the following steps:

[0006] (1) After removing impurities from leather scraps, crush them using 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;

[0007] (2) Under nitrogen protection, polytetrahydrofuran diol is added to N,N-dimethylformamide, the temperature is raised to 70-80°C, and then hexamethylene diisocyanate is added. The reaction is carried out for 2-4 hours, and the mixture is cooled to room temperature. Deionized water is added, and the precipitate is collected by centrifugation. After washing and drying, an isocyanate-terminated prepolymer is obtained. The chemical reaction process is schematically shown as follows: Formula (1),

[0008] The product was characterized by FTIR infrared spectroscopy;

[0009] (3) Under nitrogen protection, add isocyanate-terminated prepolymer and dibutyltin dilaurate to anhydrous toluene, heat to 45-55°C with stirring, then add 2-mercaptoethyl acrylate, react for 3-5 hours, cool to room temperature, spin-dry toluene, add petroleum ether, stir for 20-40 minutes, collect the precipitate by centrifugation, wash and dry to obtain modified polyurethane. The chemical reaction process is shown in the following diagram: Formula (2), the product was characterized by FTIR infrared spectroscopy;

[0010] (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, 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;

[0011] (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;

[0012] (6) Apply the uniform and stable slurry to the release mold, put it into the hot press, reduce the pressure to 30-40 MPa, and heat it up in stages: 0-20 min: from room temperature to 75-85 ° C, the heating rate is controlled at 3-5 ° C / min, 20-30 min: heat it up to 120-130 ° C, the heating rate is about 3-5 ° C / min, 30-45 min: keep it at 120-130 ° C for 15-25 min, cool it to room temperature, wash and dry it, and then use a polishing machine to mechanically polish the surface of the material at a polishing speed of 1000-2000 rpm and a polishing time of 10-20 min. Finally, immerse the material in the diluted fluorinated acrylate emulsion for 10-15 min, take it out and dry it for 1-3 h, and form an anti-fouling coating on the surface of the material to obtain a veneer material based on leather crushing and recycling.

[0013] Preferably, the weight ratio of the genuine leather tanning scraps and the 5% NaOH solution in (1) is 1:10-20.

[0014] Preferably, the weight ratio of polytetramethylene diol, hexamethylene diisocyanate, N,N-dimethylformamide and deionized water in (2) is 1:2-2.5:8-12:10-20.

[0015] Preferably, 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.

[0016] Preferably, 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.

[0017] Preferably, the mixed solution of anhydrous ethanol / deionized water in (4) refers to a mixture of anhydrous ethanol and water in a weight ratio of 3:1.

[0018] Preferably, 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.

[0019] Preferably, multiple cross-linking reactions will occur in step (5), as follows:

[0020] The amino groups in the dermal fibers react with the isocyanate groups in the modified polyurethane. The reaction process is shown in the following diagram:

[0021] Formula (3), in the reaction, the amino group acts as a nucleophilic reagent to attack the carbon atom of the isocyanate group, initiating the reaction and forming a strong covalent bond, replacing the traditional physical entanglement effect, achieving the chemical combination of fiber and polymer, and significantly improving the mechanical strength of the material;

[0022] The double bonds in the modified polyurethane will undergo self-crosslinking and react with the thiol groups in 2,3-dimercaptosuccinic acid. The reaction process is shown in the following diagram: Formula (4) further enhances the mechanical strength of the material. At the same time, a portion of 2,3-dimercaptosuccinic acid will also undergo intermolecular coupling at high temperature. The reaction process diagram is as follows: Formula (5) shows that the generated disulfide bond has a reversible break-recombination characteristic. When subjected to external force, it breaks and absorbs energy, and recombines when left at rest, giving the material a certain self-repairing ability. When used with polyethylene glycol dithioacetate, the dynamic covalent bond is reorganized through the thiol-thioester exchange reaction, thereby improving the self-repairing ability of the material.

[0023] The amino groups in amino-modified nano zinc oxide can react with the carboxyl groups in dermal fibers and the isocyanate groups in modified polyurethane. The reaction process is shown in the following diagram: Formula (6) forms a triple cross-link of "dermal fiber-zinc oxide-polymer" through the bridging cross-linking of nano-zinc oxide. The chemical covalent bond provides basic strength, the dynamic disulfide bond dissipates fracture energy, and the nano-bridging hinders crack propagation. The three work together to make the material have high strength, high toughness and self-repairing function, which is a huge improvement compared to the performance of traditional recycled leather.

[0024] Preferably, the solid content of the diluted fluorinated acrylate emulsion in (6) is 5%.

[0025] Furthermore, the present invention also provides a veneer material based on the recycling of dermis by crushing and utilizing the above-mentioned preparation method.

[0026] Beneficial effects of the present invention:

[0027] 1. The present invention realizes the high-value utilization of waste dermal fibers through the in-depth development of leather tanning scraps. The dermal fibers are activated with NaOH solution to effectively remove impurities and expose active amino groups, so that the dermal fibers are transformed from traditional physical fillings into functional components that can participate in chemical cross-linking. This process not only avoids the environmental pollution caused by the incineration or landfill of scraps, but also converts protein-based fibers into high-strength composite substrates, significantly improving resource utilization. There is no need to add a large amount of synthetic fibers or toughening agents during the preparation process, reducing the consumption of chemical raw materials from the source, complying with the concepts of circular economy and green chemistry, and providing a sustainable solution for solid waste treatment in the leather industry.

[0028] 2. This invention forms a triple crosslinked structure of "chemical covalent bonds, dynamic disulfide bonds, and nano-zinc oxide bridges" through covalent bonding between amino groups on the surface of dermal fibers and modified polyurethane isocyanate groups, self-crosslinking of polyurethane double bonds, and a thiol-ene reaction initiated by 2,3-dimercaptosuccinic acid. This upgrades the physical entanglement of dermal fibers and the polymer matrix to a chemical bond, increasing interfacial bonding strength several-fold and simultaneously optimizing tensile strength and elongation at break. Amino-modified nano-zinc oxide, acting as nanoscale crosslinking nodes, is evenly dispersed throughout the matrix, hindering crack propagation and endowing the material with synergistic properties of high strength and toughness.

[0029] 3. This invention utilizes the reversible breakage and recombination properties of disulfide bonds generated by intermolecular coupling of 2,3-dimercaptosuccinic acid, combined with the thiol-thioester exchange reaction of polyethylene glycol dithioacetate, to construct a dynamic covalent bond network. When the material is damaged by external forces, the disulfide bonds break, absorbing energy to prevent crack propagation. When left stationary, the bonds recombine to achieve self-repair, without the need for external intervention or additional repair agents. This self-repairing function significantly extends the service life of the material, reducing the need for overall replacement due to minor damage. It is particularly suitable for materials that are prone to wear during long-term use, reducing maintenance costs and improving reliability.

[0030] 4. The present invention uses the silane coupling agent KH-550 to modify the nano-zinc oxide with amino groups, significantly improving its dispersibility in the polymer matrix, avoiding agglomeration and increasing the specific surface area, thereby significantly increasing the zinc ion release efficiency and the contact area of the antibacterial site. The electrostatic attraction between the amino group and the negative charge of the bacterial cell wall further enhances the contact efficiency between the nano-zinc oxide and the microorganisms, forming a dual mechanism of "contact sterilization-zinc ion release sterilization". This antibacterial system does not require post-spraying treatment, and the antibacterial components are evenly distributed inside and on the surface of the material. The antibacterial effect is long-lasting and stable, showing broad-spectrum antibacterial properties, meeting the application needs of medical, household and other scenarios with high hygiene and safety requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the FTIR infrared spectrum of the isocyanate-terminated prepolymer prepared in Example 2 of the present invention;

[0032] Figure 2 This is the FTIR infrared spectrum of the modified polyurethane prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] 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.

[0034] The sources of the reagents and raw materials used in the examples of the present invention are as follows:

[0035] Genuine leather tanning scraps (self-produced); polytetrahydrofuran diol was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., average Mn: 2,000; hexamethylene diisocyanate was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., purity 99%; dibutyltin dilaurate was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., purity 95%; 2-mercaptoethyl acrylate was purchased from Hefei Shenghang Pharmaceutical 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 purchased from Shanghai Maclean Biochemical Technology Co., Ltd., purity 99%; ammonium persulfate was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., purity 98.5%; polyethylene glycol dithioacetate was purchased from Jilin Shengchuang Biotechnology Co., Ltd., purity 95%; fluorinated acrylate emulsion was purchased from Jining Baiyi Chemical Co., Ltd., solid content 47%.

[0036] Example 1: A specific preparation method of a veneer material based on dermal crushing and recycling, comprising the following steps:

[0037] (1) After removing impurities from 400 g of leather scraps, the scraps were crushed using a double-roll mill to control the particle size to 50-80 μm, 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 leather fibers;

[0038] (2) Under nitrogen protection, 300 g of polytetrahydrofuran diol was added to 2.4 kg of N,N-dimethylformamide, the temperature was raised to 70 ° C, and 600 g of hexamethylene diisocyanate was added. The reaction was continued for 2 h, and the mixture was cooled to room temperature. 3 kg of deionized water was added, and the precipitate was collected by centrifugation. After washing and drying, an isocyanate-terminated prepolymer was obtained.

[0039] (3) Under nitrogen protection, 700 g of isocyanate-terminated prepolymer and 21 g of dibutyltin dilaurate were added to 5.6 kg of anhydrous toluene, and the temperature was raised to 45 °C while stirring. 210 g of 2-mercaptoethyl acrylate was then added and the mixture was reacted for 3 h. The mixture was cooled to room temperature, and the toluene was dried by spin drying. 5.6 kg of petroleum ether was added and the mixture was stirred for 20 min. The precipitate was collected by centrifugation, washed, and dried to obtain a modified polyurethane.

[0040] (4) After 70 g of nano zinc oxide was pre-dried in a vacuum drying oven at 80 ° C for 3 h, it was added to 5.6 kg of anhydrous ethanol / deionized water mixed solution (ethanol and water were mixed in a weight ratio of 3:1), ultrasonically dispersed for 20 min, and then placed in a constant temperature water bath at 80 ° C with uniform stirring. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and 3.5 g of silane coupling agent KH-550 was added. The reaction was continued for 2 h, and the mixture was 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.

[0041] (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 dermal fiber, 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. The mixture was stirred at 1000 rpm for 5 min, and then the speed was increased to 6000 rpm and high-speed shearing was performed for 30 min to form a uniform and stable slurry.

[0042] (6) The uniform and stable slurry is coated on the release mold, placed in a hot press, decompressed to 30 MPa, and heated in stages: 0-20 min: from room temperature to 75 ° C, the heating rate is controlled at 3 ° C / min, 20-30 min: heated to 120 ° C, the heating rate is about 3 ° C / min, 30-45 min: kept at 120 ° C for 15 min, cooled to room temperature, washed and dried, and the surface of the material is mechanically polished using a polishing machine with a polishing speed of 1000 rpm and a polishing time of 10 min. Finally, the material is immersed in a diluted fluorinated acrylate emulsion (solid content of 5%) for 10 min. After being taken out and dried for 1 hour, an anti-fouling coating is formed on the surface of the material to obtain a veneer material based on leather crushing and recycling.

[0043] Example 2: A specific preparation method of a veneer material based on dermal crushing and recycling, comprising the following steps:

[0044] (1) After removing impurities from 500 g of leather scraps, the material was crushed using a double-roll mill to control the particle size to 50-80 μm, 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;

[0045] (2) Under nitrogen protection, 300 g of polytetrahydrofuran diol was added to 3 kg of N,N-dimethylformamide, the temperature was raised to 75 ° C, and 660 g of hexamethylene diisocyanate was added. The mixture was reacted 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;

[0046] (3) Under nitrogen protection, 700 g of isocyanate-terminated prepolymer and 28 g of dibutyltin dilaurate were added to 7 kg of anhydrous toluene, and the temperature was raised to 50 °C while stirring. 280 g of 2-mercaptoethyl acrylate was then added and the mixture was reacted for 4 h. The mixture was cooled to room temperature, and the toluene was dried by spin drying. 7 kg of petroleum ether was added and the mixture was stirred for 30 min. The precipitate was collected by centrifugation, washed, and dried to obtain a modified polyurethane.

[0047] (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 9 kg of a mixed solution of anhydrous ethanol / deionized water (ethanol and water were mixed in a weight ratio of 3:1), ultrasonically dispersed for 25 min, and then placed in a constant temperature water bath at 85 ° C with uniform stirring. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and 8 g of silane coupling agent KH-550 was added. The reaction was continued for 3 h, and the mixture was cooled to room temperature, filtered, and washed. The obtained solid was Soxhlet extracted with anhydrous ethanol for 21 h, and then dried to obtain amino-modified nano zinc oxide.

[0048] (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 fiber, 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 blender. The mixture was stirred at 1500 rpm for 8 min, and then the speed was increased to 7000 rpm and high-speed shearing was performed for 45 min to form a uniform and stable slurry.

[0049] (6) The uniform and stable slurry is coated on the release mold, placed in a hot press, reduced to 35 MPa, and heated in stages: 0-20 min: from room temperature to 80 ° C, the heating rate is controlled at 4 ° C / min, 20-30 min: heated to 125 ° C, the heating rate is about 4 ° C / min, 30-45 min: kept at 125 ° C for 20 min, cooled to room temperature, washed and dried, and the surface of the material is mechanically polished using a polishing machine with a polishing speed of 1500 rpm and a polishing time of 15 min. Finally, the material is immersed in a diluted fluorinated acrylate emulsion (solid content of 5%) for 12 min. After being taken out and dried for 2 h, an anti-fouling coating is formed on the surface of the material to obtain a veneer material based on leather crushing and recycling.

[0050] Example 3: A specific preparation method of a veneer material based on dermal crushing and recycling, comprising the following steps:

[0051] (1) After removing impurities from 500 g of leather scraps, the material was crushed using a double-roll mill to control the particle size to 50-80 μm, added to a 5% NaOH solution, heated to 60 °C, stirred for 60 min, centrifuged, washed with deionized water until the pH was neutral, and dried to obtain activated leather fibers;

[0052] (2) Under nitrogen protection, 500 g of polytetrahydrofuran diol was added to 6 kg of N,N-dimethylformamide, the temperature was raised to 80 ° C, and 1.25 kg of hexamethylene diisocyanate was added. The mixture was reacted for 4 h, cooled to room temperature, and 10 kg of deionized water was added. The precipitate was collected by centrifugation, washed, and dried to obtain an isocyanate-terminated prepolymer;

[0053] (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, and the temperature was raised to 55 °C while stirring. Then, 400 g of 2-mercaptoethyl acrylate was added and the mixture was reacted for 5 h. The mixture was cooled to room temperature, and the toluene was dried by spin drying. Then, 9.6 kg of petroleum ether was added and the mixture was stirred for 40 min. The precipitate was collected by centrifugation, washed, and dried to obtain a modified polyurethane.

[0054] (4) 120 g of nano zinc oxide was pre-dried in a vacuum drying oven at 90 ° C for 5 h, then added to 12 kg of anhydrous ethanol / deionized water mixed solution (ethanol and water were mixed in a weight ratio of 3:1), ultrasonically dispersed for 30 min, and then placed in a constant temperature water bath at 90 ° C with uniform stirring. 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 continued for 4 h, cooled to room temperature, filtered, washed, and the obtained solid was Soxhlet extracted with anhydrous ethanol for 24 h, and then dried to obtain amino-modified nano zinc oxide.

[0055] (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 fiber, 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 blender. The mixture was stirred at 2000 rpm for 10 min, and then the speed was increased to 8000 rpm and high-speed shearing was performed for 60 min to form a uniform and stable slurry.

[0056] (6) The uniform and stable slurry is coated on the release mold, placed in a hot press, reduced to 40 MPa, and heated in stages: 0-20 min: from room temperature to 85 ° C, the heating rate is controlled at 5 ° C / min, 20-30 min: heated to 130 ° C, the heating rate is about 5 ° C / min, 30-45 min: kept at 130 ° C for 25 min, cooled to room temperature, washed and dried, and the surface of the material is mechanically polished using a polishing machine with a polishing speed of 2000 rpm and a polishing time of 20 min. Finally, the material is immersed in a diluted fluorinated acrylate emulsion (solid content of 5%) for 15 min. After being taken out and dried for 3 h, an anti-fouling coating is formed on the surface of the material to obtain a veneer material based on leather crushing and recycling.

[0057] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the leather scraps are free of impurities and crushed using a double-roll grinder before being added to a 5% NaOH solution.

[0058] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that step (3) is omitted. The specific preparation process is as follows: The specific preparation method of the veneer material based on the recycling of dermis comprises the following steps:

[0059] (1) After removing impurities from 500 g of leather scraps, the material was crushed using a double-roll mill to control the particle size to 50-80 μm, 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;

[0060] (2) Under nitrogen protection, 300 g of polytetrahydrofuran diol was added to 3 kg of N,N-dimethylformamide, the temperature was raised to 75 ° C, and 660 g of hexamethylene diisocyanate was added. The mixture was reacted 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;

[0061] (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 9 kg of a mixed solution of anhydrous ethanol / deionized water (ethanol and water were mixed in a weight ratio of 3:1), ultrasonically dispersed for 25 min, and then placed in a constant temperature water bath at 85 ° C with uniform stirring. The pH value was adjusted to 6.5 with 10% dilute hydrochloric acid, and 8 g of silane coupling agent KH-550 was added. The reaction was continued for 3 h, and the mixture was cooled to room temperature, filtered, and washed. The obtained solid was Soxhlet extracted with anhydrous ethanol for 21 h, and then dried to obtain amino-modified nano zinc oxide.

[0062] (4) 650 g of isocyanate-terminated 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 dermal fiber, 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 blender. The mixture was stirred at 1500 rpm for 8 min, and then the speed was increased to 7000 rpm and high-speed shearing was performed for 45 min to form a uniform and stable slurry.

[0063] (5) The uniform and stable slurry is coated on the release mold, placed in a hot press, reduced to 35 MPa, and heated in stages: 0-20 min: from room temperature to 80 ° C, the heating rate is controlled at 4 ° C / min, 20-30 min: heated to 125 ° C, the heating rate is about 4 ° C / min, 30-45 min: kept at 125 ° C for 20 min, cooled to room temperature, washed and dried, and the surface of the material is mechanically polished using a polishing machine with a polishing speed of 1500 rpm and a polishing time of 15 min. Finally, the material is immersed in a diluted fluorinated acrylate emulsion (solid content of 5%) for 12 min. After being taken out and dried for 2 h, an anti-fouling coating is formed on the surface of the material to obtain a veneer material based on leather crushing and recycling.

[0064] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that step (4) of amino-modifying the nano-zinc oxide is omitted, and the nano-zinc oxide is directly used in the subsequent steps.

[0065] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that no nano zinc oxide is added.

[0066] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that 2,3-dimercaptosuccinic acid is not added.

[0067] Performance test: 1. Mechanical property test: The veneer materials prepared in Examples 1-3 and Comparative Examples 1-5 were prepared into standard dumbbell-shaped specimens with dimensions of 150 mm × 25 mm × 2 mm. They were stretched at a rate of 50 mm / min using a universal material testing machine, and the tensile strength and elongation at break of the materials were recorded. The experimental results are shown in Table 1.

[0068] 2. Self-repair rate test: The veneer materials prepared in Examples 1-3 and Comparative Examples 1-5 were prepared into uniformly sized specimens with dimensions of 100 mm × 50 mm × 2 mm. A 20 μm deep, 50 μm wide, and 10 mm long incision was made on the surface of the specimen using a blade. The specimens were placed in a 25°C constant temperature oven for 24 hours. The scratch recovery rate was quantified using a white light interferometer: R = (initial scratch volume - repaired volume) / initial scratch volume × 100%. The experimental results are shown in Table 1.

[0069] 3. Antibacterial effect test: The veneer materials prepared in Examples 1-3 and Comparative Examples 1-5 were prepared into 2 cm × 2 cm square samples, and after UV sterilization, they were placed in a 24-well plate. 1 ml of bacterial suspension (1 × 10 5 CFU / ml), sealed and placed at 37℃ for 24h, the material was taken out, and the surface bacteria were washed off with 1ml sterile PBS buffer, 100μl of the dilution was spread on LB agar plate, and the number of colonies was counted after incubation at 37℃ for 24h, and the antibacterial rate was calculated as (1 ) × 100%, where the control group was a bacterial suspension without veneer material. The experiment was conducted three times using Escherichia coli, Staphylococcus aureus, and Candida albicans to prepare bacterial suspensions. The experimental results are shown in Table 1.

[0070] Table 1 Performance test results

[0071]

[0072] Performance Analysis:

[0073] From the experimental data in Table 1, it can be seen that the veneer materials based on dermal crushing and recycling prepared by Examples 1-3 of the present invention have excellent mechanical properties and self-repairing capabilities that traditional materials do not have, and have good bactericidal and antibacterial capabilities against some common bacteria in daily life. Among them, Example 2 has the best comprehensive performance. From the perspective of mechanical properties, this may be because the NaOH treatment hydrolyzes the protein on the surface of the dermal fiber, exposing a large number of amino groups, which can react with the isocyanate groups in the modified polyurethane to form covalent bonds, replacing traditional physical entanglement and helping to improve the interfacial bonding force. In Comparative Example 1, the active groups of the unactivated fibers are less exposed and only rely on van der Waals forces to bind. They are easy to slip when stretched, resulting in a decrease in strength. At the same time, the double bonds introduced by 2-mercaptoethyl acrylate react with 2,3- -The thiol groups of dimercaptosuccinic acid react to form thioether bonds, and at the same time, the double bonds self-crosslink to form a three-dimensional network structure. The crosslinking density is improved compared to ordinary polyurethane materials, thereby improving the mechanical properties of the material; finally, the amino-modified nano-zinc oxide reacts with the carboxyl groups of the dermal fibers and the isocyanate groups of the polyurethane through the amino groups to form a "fiber-zinc oxide-polymer" triple crosslinking node. The nanoparticles are evenly dispersed to hinder crack propagation. Through this three-step preparation method, the present invention greatly improves the mechanical properties of the material.

[0074] From the perspective of self-repair rate, this may be because the double bonds of the modified polyurethane and the thiol groups of 2,3-dimercaptosuccinic acid are covalently grafted through a thiol-ene reaction, so that the thiol groups can be evenly distributed on the polyurethane chain, the distance between adjacent thiol groups is shortened, the intermolecular coupling efficiency is improved at high temperature, and a high-density disulfide bond network is formed. In comparative example 2, there is no double bond, the thiol group exists in a free state, the coupling probability is low, and the self-repair rate decreases; at the same time, the thiol group provided by polyethylene glycol dithioacetate will also undergo a thiol-thioester exchange reaction with 2,3-dimercaptosuccinic acid, reducing the bond recombination activation energy, while in comparative example 5, there is no 2,3-dimercaptosuccinic acid, the reaction cannot proceed, and the self-repair rate is greatly reduced; finally, amino-modified nano-zinc oxide enhances the network density through chemical bridging, and the crack propagation path is blocked by nanoparticles. During repair, the disulfide bonds can be accurately reorganized along the original cross-linking points, further improving the repair rate of the material.

[0075] From the perspective 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 destroy the phospholipid bilayer of bacterial cell membranes, inhibiting DNA polymerase activity. It has excellent antibacterial rates against Escherichia coli, Staphylococcus aureus, and Candida albicans. At the same time, the amino group also plays a synergistic role in antibacterial effect. The amino group grafted with the silane coupling agent KH-550 improves the dispersibility of nanoparticles. The amino group and the negative charge of the bacterial cell wall are electrostatically attracted, improving contact efficiency. This facilitates better contact between zinc ions and bacteria, exerting an antibacterial effect. Finally, the fluorinated acrylic emulsion on the surface forms a low surface energy coating, which can reduce bacterial adhesion. Combined with the active bactericidal effect of nano-zinc oxide, it forms a dual barrier of "physical adhesion resistance + chemical sterilization."

[0076] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing veneer materials based on the recycling of dermis, characterized in that: The following steps are involved: (1) After removing impurities from leather scraps, crush them using 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, and then 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, washed, and dried to obtain an isocyanate-terminated prepolymer; (3) Under nitrogen protection, add the isocyanate-terminated prepolymer and dibutyltin dilaurate to anhydrous toluene, heat to 45-55°C with stirring, then add 2-mercaptoethyl acrylate, react for 3-5 hours, cool to room temperature, spin-dry the toluene, add petroleum ether, stir for 20-40 minutes, 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, 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 the hot press, reduce the pressure to 30-40 MPa, and heat it up in stages: 0-20 min: from room temperature to 75-85 ° C, the heating rate is controlled at 3-5 ° C / min, 20-30 min: heat it up to 120-130 ° C, the heating rate is 3-5 ° C / min, 30-45 min: keep it at 120-130 ° C for 15-25 min, cool it to room temperature, wash and dry it, and then use a polishing machine to mechanically polish the surface of the material at a polishing speed of 1000-2000 rpm and a polishing time of 10-20 min. Finally, immerse the material in the diluted fluorinated acrylate emulsion for 10-15 min, take it out and dry it for 1-3 h, forming an anti-fouling coating on the surface of the material to obtain a veneer material based on leather crushing and recycling.

2. The method for preparing veneer materials based on dermis 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 materials based on dermis crushing and recycling according to claim 1, characterized in that: The weight ratio of polytetramethylene glycol, 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 materials based on dermis 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 materials based on dermis 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 materials based on dermis 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 materials based on dermis crushing and recycling according to claim 1, characterized in that: 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) 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.

8. The method for preparing veneer materials based on dermis 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 recycling of dermis is prepared by the preparation method according to any one of claims 1 to 8.

Images