Method for preparing self-repairing waterborne polyurethane based on chrome tanned leather shavings

Abstract

The invention discloses a method for preparing self-repairing waterborne polyurethane based on chrome tanned leather shavings, which specifically comprises the following steps: hydrolyzing the chrome tanned leather shavings to obtain chromium-containing collagen; the preparation method comprises the following steps: carrying out a reaction on poly (trimethylene ether glycol) and isophorone isocyanate to obtain a polyurethane prepolymer; the preparation method comprises the following steps: dissolving 2, 2-dimethylolpropionic acid in N, N-dimethylformamide, and carrying out a reaction with a polyurethane prepolymer to obtain a polyurethane prepolymer mixture; dissolving chromium-containing collagen in formic acid and dimethyl sulfoxide, and adding the polyurethane prepolymer mixture to carry out cross-linking reaction; adding triethylamine to carry out neutralization reaction, adding deionized water to carry out shearing emulsification, and standing. The chrome tanned leather shavings are hydrolyzed into the chromium-containing collagen through three times of acidolysis, coordinate bonds of Cr < 3 + > and the collagen are reserved, metal coordinate bonds are formed through Cr < 3 + > in the collagen and urethane bonds in a polyurethane chain and serve as dynamic reversible cross-linking points, the material is endowed with excellent self-repairing capacity, and meanwhile the mechanical property of the material is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of polymer material preparation technology, specifically relating to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps. Background Technology

[0002] Waterborne polyurethane (WPU) is an environmentally friendly polymer material characterized by its non-toxicity, non-flammability, and low VOC content, and is widely used in coatings, adhesives, leather finishing agents, and other fields. However, traditional waterborne polyurethane is prone to performance degradation and shortened lifespan due to damage (such as scratches and cracks) during long-term use. Therefore, endowing it with self-healing capabilities is key to improving its durability and extending its service life.

[0003] Currently, the main strategies for constructing self-healing polymer materials include microencapsulation of repair agents, reversible covalent bonds (such as the Diels-Alder reaction), and non-covalent dynamic bonds (such as hydrogen bonds, ionic bonds, and metal coordination bonds). Among these, designs based on dynamic metal coordination bonds have attracted much attention due to their mild repair conditions and high efficiency. Metal ions (such as Fe) 3+ Zn 2+ Co 2+ (e.g., chromium ions) can form a dynamically reversible cross-linked network with carboxyl, amino, pyridyl, and other groups on the polymer chain. When the material is damaged, the breaking and recombination of coordination bonds can achieve self-repair at the damaged site. 3+ Chromium has abundant coordination ability and high coordination bond strength, making it an ideal metal center for constructing dynamic networks. However, existing technologies typically require additional purification or the addition of chromium salts as functional components, which is costly and complex.

[0004] The leather industry generates a large amount of chrome-tanned leather scraps annually, whose main components are collagen and trivalent chromium. Currently, these solid wastes are mostly disposed of through landfill or incineration, which not only wastes resources but also poses environmental risks. Therefore, chrome-tanned leather scraps can be hydrolyzed to obtain chromium-containing collagen, which can then be used as a self-healing monomer to prepare self-healing waterborne polyurethane. The resulting waterborne polyurethane has broad application prospects in leather finishing agents, adhesives, and other fields, possessing both environmental and economic value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, wherein the waterborne polyurethane has good self-healing properties and mechanical properties.

[0006] The technical solution adopted in this invention is a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps:

[0007] Step 1: Prepare chromium-containing collagen; Step 2: Prepare a polyurethane prepolymer mixture using polytrimethylene ether glycol, isophorone isocyanate, 2,2-dimethylolpropionic acid and N,N-dimethylformamide; prepare a self-healing waterborne polyurethane using chromium-containing collagen, formic acid, dimethyl sulfoxide, the polyurethane prepolymer mixture and triethylamine.

[0008] The invention is further characterized in that, Step 1 specifically involves: Step 1.1: Mix 25-27 parts of chrome-tanned leather scraps, 16-20 parts of concentrated sulfuric acid, and 350-370 parts of deionized water, and hydrolyze to obtain a primary hydrolysate. Step 1.2: Mix 23-25 ​​parts of the primary hydrolysate, 25-30 parts of concentrated sulfuric acid, and 250-270 parts of deionized water, and hydrolyze to obtain the secondary hydrolysate; Step 1.3: Mix 20-22 parts of the secondary hydrolysate, 15-20 parts of acetic acid, and 250-270 parts of deionized water, and hydrolyze to obtain a tertiary hydrolysate; filter and dry the tertiary hydrolysate to obtain chromium-containing collagen.

[0009] During hydrolysis, the hydrolysis temperature was 35-40℃ and the hydrolysis time was 10-12h.

[0010] In step 2, the preparation process of the polyurethane prepolymer mixture is as follows: 4-6 parts of polytrimethylene ether glycol and 9-11 parts of isophorone isocyanate were reacted at 80°C for 3 h to obtain a polyurethane prepolymer; then 0.7-0.9 parts of 2,2-dimethylolpropionic acid were dissolved in 2.1-2.8 parts of N,N-dimethylformamide and mixed with the polyurethane prepolymer, and reacted at 80°C for 1.5 h to obtain a polyurethane prepolymer mixture.

[0011] In step 2, the preparation process of self-healing waterborne polyurethane is as follows: Dissolve 0.3-0.5 parts of chromium-containing collagen in 1-3 parts of formic acid and 3-5 parts of dimethyl sulfoxide, then add the above-mentioned polyurethane prepolymer mixture, and carry out a crosslinking reaction at 75°C for 0.5 h; then lower the temperature to 40°C, add 5-7 parts of triethylamine for a neutralization reaction for 0.5 h, and finally add 20-30 parts of deionized water for shear emulsification. Pour the emulsion into a polytetrafluoroethylene plate and let it stand at room temperature to obtain collagen-modified self-healing waterborne polyurethane.

[0012] The shear emulsification time was 1.0 h, and the rotation speed was 1000 r / min. The settling time was 8-10 days.

[0013] The beneficial effects of this invention are: The method of this invention involves hydrolyzing chrome-tanned leather scraps to obtain chromium-containing collagen, which is then used as a self-healing monomer to prepare self-healing waterborne polyurethane. The chromium content in the collagen is utilized... 3+ The metal coordination bonds formed with the urethane bonds in the polyurethane chain serve as dynamic and reversible crosslinking points, endowing the material with excellent self-healing capabilities while retaining its mechanical properties. At room temperature, the tensile strength and elongation at break of the film reach 25.2 MPa and 299.1%, respectively, with a self-healing efficiency as high as 85%. The resulting waterborne polyurethane shows broad application prospects in leather finishing agents, adhesives, and other fields, possessing both environmental and economic value. Attached Figure Description

[0014] Figure 1 This is a comparison chart of the tensile strength of the chromium-containing collagen-modified waterborne polyurethane of this invention and commercially available waterborne polyurethane. Figure 2 This is a comparison chart of the elongation at break of the chromium-containing collagen-modified waterborne polyurethane of this invention and commercially available waterborne polyurethane. Figure 3 This is a comparison chart of the self-healing efficiency of the chromium-containing collagen-modified waterborne polyurethane of this invention and commercially available waterborne polyurethane. Figure 4 This is a graph showing the relationship between the self-healing time and tensile strength of the chromium-containing collagen-modified waterborne polyurethane of this invention. Figure 5 This is a graph showing the relationship between the self-healing time and elongation at break of the chromium-containing collagen-modified waterborne polyurethane of this invention. Figure 6 This is a graph showing the relationship between the self-healing time and self-healing efficiency of the chromium-containing collagen-modified waterborne polyurethane of this invention. Detailed Implementation

[0015] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0016] This invention relates to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps: Step 1: Prepare chromium-containing collagen; specifically: Step 1.1: Mix 25-27 parts of chrome-tanned leather scraps, 16-20 parts of concentrated sulfuric acid, and 350-370 parts of deionized water, and hydrolyze the mixture at a temperature of 35-40℃ for 10-12 hours to obtain a primary hydrolysate. Step 1.2: Mix 23-25 ​​parts of the primary hydrolysate, 25-30 parts of concentrated sulfuric acid, and 250-270 parts of deionized water, and perform hydrolysis at a temperature of 35-40℃ for 10-12 hours to obtain the secondary hydrolysate. Step 1.3: Mix 20-22 parts of the secondary hydrolysate, 15-20 parts of acetic acid, and 250-270 parts of deionized water, and perform hydrolysis at a temperature of 35-40℃ for 10-12 hours to obtain a tertiary hydrolysate; filter the tertiary hydrolysate and dry it at 40℃ to obtain chromium-containing collagen. Step 2: Prepare collagen-modified self-healing waterborne polyurethane, specifically as follows: 4-6 parts of polytrimethylene ether glycol (PO3G) and 9-11 parts of isophorone isocyanate (IPDI) were reacted at 80°C for 3 h to obtain a polyurethane prepolymer; then 0.7-0.9 parts of 2,2-dimethylolpropionic acid (DMPA) were dissolved in 2.1-2.8 parts of N,N-dimethylformamide (DMF) and mixed with the polyurethane prepolymer, and reacted at 80°C for 1.5 h to obtain a polyurethane prepolymer mixture; Dissolve 0.3-0.5 parts of chromium-containing collagen in 1-3 parts of formic acid and 3-5 parts of dimethyl sulfoxide (DMSO), then add the above-mentioned polyurethane prepolymer mixture, and carry out a crosslinking reaction at 75°C for 0.5 h; then lower the temperature to 40°C, add 5-7 parts of triethylamine (TEA) for a neutralization reaction for 0.5 h, and finally add 20-30 parts of deionized water for high-speed (1000 r / min) shear emulsification for 1.0 h. Pour the emulsion into a polytetrafluoroethylene plate and let it stand at room temperature for 8-10 days to obtain collagen-modified self-healing waterborne polyurethane.

[0017] The method of this invention hydrolyzes chrome-tanned leather scraps into chrome-containing collagen through three acid hydrolysis processes, the purpose of which is to retain Cr. 3+ Coordination bonds with collagen, and utilizing the Cr in collagen 3+ It forms metal coordination bonds with the urethane bonds in the polyurethane chain, serving as a dynamically reversible crosslinking point, which not only endows the material with excellent self-healing ability but also enhances its mechanical properties.

[0018] Example 1 This invention relates to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps: Step 1: Preparation of chromium-containing collagen; Step 1.1: Mix 25 parts of chrome-tanned leather scraps, 16 parts of concentrated sulfuric acid and 350 parts of deionized water, and hydrolyze the mixture at 35°C for 10 hours to obtain a primary hydrolysate. Step 1.2: Mix 23 parts of the primary hydrolysate, 25 parts of concentrated sulfuric acid, and 250 parts of deionized water, and perform hydrolysis at 35°C for 10 hours to obtain the secondary hydrolysate. Step 1.3: Mix 20 parts of the secondary hydrolysate, 15 parts of acetic acid and 250 parts of deionized water, and hydrolyze at 35°C for 10 hours to obtain chromium-containing collagen. Step 2: Prepare collagen-modified self-healing waterborne polyurethane, specifically as follows: A clean three-necked flask was used to react 4 parts of polytrimethylene ether glycol (PO3G) and 9 parts of isophorone isocyanate (IPDI) at 80°C for 3 h to obtain a polyurethane prepolymer. Then, 0.7 parts of 2,2-dimethylolpropionic acid (DMPA) were dissolved in 2.1 parts of N,N-dimethylformamide (DMF) and reacted with the prepolymer at 80°C for 1.5 h. Next, 0.3 parts of chromium-containing collagen were dissolved in 1 part of formic acid and 3 parts of dimethyl sulfoxide (DMSO) and added to the three-necked flask, where a crosslinking reaction was carried out at 75°C for 0.5 h. Subsequently, the temperature was lowered to 40°C, and 5-7 parts of triethylamine (TEA) were added for neutralization for 0.5 h. Finally, 20 parts of deionized water were added for high-speed (1000 r / min) shear emulsification for 1.0 h. The emulsion was poured into a polytetrafluoroethylene plate and allowed to stand at room temperature for 8 days to obtain a collagen-modified waterborne polyurethane membrane.

[0019] Example 2 This invention relates to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps: Step 1: Preparation of chromium-containing collagen; Step 1.1: Mix 26 parts of chrome-tanned leather scraps, 18 parts of concentrated sulfuric acid and 360 parts of deionized water, and hydrolyze the mixture at 37°C for 11 hours to obtain a primary hydrolysate. Step 1.2: Mix 24 parts of the primary hydrolysate, 27.5 parts of concentrated sulfuric acid and 260 parts of deionized water, and perform hydrolysis at 37°C for 11 hours to obtain the secondary hydrolysate. Step 1.3: Mix 21 parts of the secondary hydrolysate, 17.5 parts of acetic acid and 260 parts of deionized water, and hydrolyze at 37°C for 11 hours to obtain chromium-containing collagen. Step 2: Prepare collagen-modified self-healing waterborne polyurethane, specifically as follows: A clean three-necked flask was used to react 5 parts of polytrimethylene ether glycol (PO3G) and 10 parts of isophorone isocyanate (IPDI) at 80°C for 3 h to obtain a polyurethane prepolymer. Then, 0.8 parts of 2,2-dimethylolpropionic acid (DMPA) were dissolved in 2.4 parts of N,N-dimethylformamide (DMF) and reacted with the prepolymer at 80°C for 1.5 h. Next, 0.4 parts of chromium-containing collagen were dissolved in 2 parts of formic acid and 4 parts of dimethyl sulfoxide (DMSO) and added to the three-necked flask, where a crosslinking reaction was carried out at 75°C for 0.5 h. Subsequently, the temperature was lowered to 40°C, and 6 parts of triethylamine (TEA) were added for neutralization for 0.5 h. Finally, 25 parts of deionized water were added for high-speed (1000 r / min) shear emulsification for 1.0 h. The emulsion was poured into a polytetrafluoroethylene plate and allowed to stand at room temperature for 9 days to obtain a collagen-modified waterborne polyurethane membrane.

[0020] Example 3 This invention relates to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps: Step 1: Preparation of chromium-containing collagen; Step 1.1: Mix 27 parts of chrome-tanned leather scraps, 20 parts of concentrated sulfuric acid and 370 parts of deionized water, and hydrolyze the mixture at 40°C for 12 hours to obtain a primary hydrolysate. Step 1.2: Mix 25 parts of the primary hydrolysate, 30 parts of concentrated sulfuric acid, and 270 parts of deionized water, and perform hydrolysis at 40°C for 12 hours to obtain the secondary hydrolysate. Step 1.3: Mix 22 parts of the secondary hydrolysate, 20 parts of acetic acid and 270 parts of deionized water, and hydrolyze at 40°C for 12 hours to obtain chromium-containing collagen. Step 2: Prepare collagen-modified self-healing waterborne polyurethane, specifically as follows: A clean three-necked flask was used to react 6 parts of polytrimethylene ether glycol (PO3G) and 11 parts of isophorone isocyanate (IPDI) at 80°C for 3 h to obtain a polyurethane prepolymer. Then, 0.9 parts of 2,2-dimethylolpropionic acid (DMPA) were dissolved in 2.7 parts of N,N-dimethylformamide (DMF) and reacted with the prepolymer at 80°C for 1.5 h. Next, 0.5 parts of chromium-containing collagen were dissolved in 3 parts of formic acid and 5 parts of dimethyl sulfoxide (DMSO) and added to the three-necked flask for crosslinking at 75°C for 0.5 h. Subsequently, the temperature was lowered to 40°C, and 7 parts of triethylamine (TEA) were added for neutralization for 0.5 h. Finally, 30 parts of deionized water were added for high-speed (1000 r / min) shear emulsification for 1.0 h. The emulsion was poured into a polytetrafluoroethylene plate and allowed to stand at room temperature for 10 days to obtain a collagen-modified waterborne polyurethane membrane.

[0021] Example 4 This invention relates to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps: Step 1: Prepare chromium-containing collagen; specifically: Step 1.1: Mix 25 parts of chrome-tanned leather scraps, 16 parts of concentrated sulfuric acid and 350 parts of deionized water, and hydrolyze the mixture at 40°C for 11 hours to obtain a primary hydrolysate. Step 1.2: Mix 23 parts of the primary hydrolysate, 25 parts of concentrated sulfuric acid, and 250 parts of deionized water, and perform hydrolysis at 35°C for 10 hours to obtain the secondary hydrolysate. Step 1.3: Mix 20 parts of the secondary hydrolysate, 15 parts of acetic acid, and 250 parts of deionized water, and hydrolyze the mixture at 35°C for 10 hours to obtain a tertiary hydrolysate. Filter the tertiary hydrolysate and dry it at 40°C to obtain chromium-containing collagen. Step 2: Prepare collagen-modified self-healing waterborne polyurethane, specifically as follows: Four parts of polytrimethylene ether glycol (PO3G) and nine parts of isophorone isocyanate (IPDI) were reacted at 80°C for 3 h to obtain a polyurethane prepolymer; then 0.7 parts of 2,2-dimethylolpropionic acid (DMPA) were dissolved in 2.1 parts of N,N-dimethylformamide (DMF) and mixed with the polyurethane prepolymer, and reacted at 80°C for 1.5 h to obtain a polyurethane prepolymer mixture; 0.3 parts of chromium-containing collagen were dissolved in 1 part of formic acid and 3 parts of dimethyl sulfoxide (DMSO), and then the above-mentioned polyurethane prepolymer mixture was added. The mixture was subjected to a crosslinking reaction at 75°C for 0.5 h. Subsequently, the temperature was lowered to 40°C, and 5 parts of triethylamine (TEA) were added for a neutralization reaction for 0.5 h. Finally, 20 parts of deionized water were added for high-speed (1000 r / min) shear emulsification for 1.0 h. The emulsion was poured into a polytetrafluoroethylene plate and allowed to stand at room temperature for 8 days to obtain collagen-modified self-healing waterborne polyurethane.

[0022] Example 5 This invention relates to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps: Step 1: Prepare chromium-containing collagen; specifically: Step 1.1: Mix 26 parts of chrome-tanned leather scraps, 17 parts of concentrated sulfuric acid and 355 parts of deionized water, and hydrolyze the mixture at 38°C for 11 hours to obtain a primary hydrolysate. Step 1.2: Mix 24 parts of the primary hydrolysate, 28 parts of concentrated sulfuric acid, and 265 parts of deionized water, and perform hydrolysis at 38°C for 11 hours to obtain the secondary hydrolysate. Step 1.3: Mix 21 parts of the secondary hydrolysate, 18 parts of acetic acid, and 260 parts of deionized water, and hydrolyze the mixture at 38°C for 11 hours to obtain the tertiary hydrolysate. Filter the tertiary hydrolysate and dry it at 40°C to obtain chromium-containing collagen. Step 2: Prepare collagen-modified self-healing waterborne polyurethane, specifically as follows: Five parts of polytrimethylene ether glycol (PO3G) and ten parts of isophorone isocyanate (IPDI) were reacted at 80°C for 3 h to obtain a polyurethane prepolymer; then 0.8 parts of 2,2-dimethylolpropionic acid (DMPA) were dissolved in 2.5 parts of N,N-dimethylformamide (DMF) and mixed with the polyurethane prepolymer, and reacted at 80°C for 1.5 h to obtain a polyurethane prepolymer mixture; 0.4 parts of chromium-containing collagen were dissolved in 1.5 parts of formic acid and 3.5 parts of dimethyl sulfoxide (DMSO), and then the above-mentioned polyurethane prepolymer mixture was added. The mixture was subjected to a crosslinking reaction at 75°C for 0.5 h. Subsequently, the temperature was lowered to 40°C, and 5.5 parts of triethylamine (TEA) were added for a neutralization reaction for 0.5 h. Finally, 25 parts of deionized water were added for high-speed (1000 r / min) shear emulsification for 1.0 h. The emulsion was poured into a polytetrafluoroethylene plate and allowed to stand at room temperature for 9 days to obtain collagen-modified self-healing waterborne polyurethane.

[0023] Example 6 This invention relates to a method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, which is implemented according to the following steps: Step 1: Prepare chromium-containing collagen; specifically: Step 1.1: Mix 27 parts of chrome-tanned leather scraps, 20 parts of concentrated sulfuric acid and 370 parts of deionized water, and hydrolyze the mixture at 40°C for 12 hours to obtain a primary hydrolysate. Step 1.2: Mix 25 parts of the primary hydrolysate, 30 parts of concentrated sulfuric acid, and 270 parts of deionized water, and perform hydrolysis at 40°C for 12 hours to obtain the secondary hydrolysate. Step 1.3: Mix 22 parts of the secondary hydrolysate, 20 parts of acetic acid, and 270 parts of deionized water, and hydrolyze the mixture at 40°C for 12 hours to obtain the tertiary hydrolysate. Filter the tertiary hydrolysate and dry it at 40°C to obtain chromium-containing collagen. Step 2: Prepare collagen-modified self-healing waterborne polyurethane, specifically as follows: Six parts of polytrimethylene ether glycol (PO3G) and 11 parts of isophorone isocyanate (IPDI) were reacted at 80°C for 3 h to obtain a polyurethane prepolymer; then 0.9 parts of 2,2-dimethylolpropionic acid (DMPA) were dissolved in 2.8 parts of N,N-dimethylformamide (DMF) and mixed with the polyurethane prepolymer, and reacted at 80°C for 1.5 h to obtain a polyurethane prepolymer mixture; 0.5 parts of chromium-containing collagen were dissolved in 3 parts of formic acid and 5 parts of dimethyl sulfoxide (DMSO), and then the above-mentioned polyurethane prepolymer mixture was added. The mixture was subjected to a crosslinking reaction at 75°C for 0.5 h. Subsequently, the temperature was lowered to 40°C, and 7 parts of triethylamine (TEA) were added for a neutralization reaction for 0.5 h. Finally, 30 parts of deionized water were added for high-speed (1000 r / min) shear emulsification for 1.0 h. The emulsion was poured into a polytetrafluoroethylene plate and allowed to stand at room temperature for 10 days to obtain collagen-modified self-healing waterborne polyurethane.

[0024] Figure 1 , 2 Figures 3 and 4 are comparisons of the tensile strength, elongation at break, and self-healing efficiency of the chromium-containing collagen-modified waterborne polyurethane film of this invention and commercially available waterborne polyurethane films. As can be seen from the figures, the waterborne polyurethane of this invention has a tensile strength of up to 25.2 MPa, an elongation at break of 299.1%, and a self-healing efficiency of 85%, all of which are higher than those of commercially available waterborne polyurethane. Figure 4 , 5 Figures 6 and 7 respectively show the relationship between the self-healing time of the chromium-containing collagen-modified waterborne polyurethane of this invention and its tensile strength, elongation at break, and self-healing efficiency. As can be seen from the figures, the film achieves a maximum self-healing efficiency of 85% after 8 hours at room temperature (below 40°C).

Claims

1. A method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps, characterized in that, The specific steps are as follows: Step 1: Prepare chromium-containing collagen; Step 2: Prepare a polyurethane prepolymer mixture using polytrimethylene ether glycol, isophorone isocyanate, 2,2-dimethylolpropionic acid and N,N-dimethylformamide; prepare a self-healing waterborne polyurethane using chromium-containing collagen, formic acid, dimethyl sulfoxide, the polyurethane prepolymer mixture and triethylamine.

2. The method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps as described in claim 1, characterized in that, In step 1, specifically: Step 1.1: Mix 25-27 parts of chrome-tanned leather scraps, 16-20 parts of concentrated sulfuric acid, and 350-370 parts of deionized water, and hydrolyze to obtain a primary hydrolysate. Step 1.2: Mix 23-25 ​​parts of the primary hydrolysate, 25-30 parts of concentrated sulfuric acid, and 250-270 parts of deionized water, and hydrolyze to obtain the secondary hydrolysate; Step 1.3: Mix 20-22 parts of the secondary hydrolysate, 15-20 parts of acetic acid, and 250-270 parts of deionized water, and hydrolyze to obtain a tertiary hydrolysate; filter and dry the tertiary hydrolysate to obtain chromium-containing collagen.

3. The method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps as described in claim 2, characterized in that, During hydrolysis, the hydrolysis temperature was 35-40℃ and the hydrolysis time was 10-12h.

4. The method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps as described in claim 1, characterized in that, In step 2, the preparation process of the polyurethane prepolymer mixture is as follows: 4-6 parts of polytrimethylene ether glycol and 9-11 parts of isophorone isocyanate were reacted at 80°C for 3 h to obtain a polyurethane prepolymer; then 0.7-0.9 parts of 2,2-dimethylolpropionic acid were dissolved in 2.1-2.8 parts of N,N-dimethylformamide and mixed with the polyurethane prepolymer, and reacted at 80°C for 1.5 h to obtain a polyurethane prepolymer mixture.

5. The method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps as described in claim 4, characterized in that, In step 2, the preparation process of the self-healing waterborne polyurethane is as follows: Dissolve 0.3-0.5 parts of chromium-containing collagen in 1-3 parts of formic acid and 3-5 parts of dimethyl sulfoxide, then add the above-mentioned polyurethane prepolymer mixture, and carry out a crosslinking reaction at 75°C for 0.5 h; then lower the temperature to 40°C, add 5-7 parts of triethylamine for a neutralization reaction for 0.5 h, and finally add 20-30 parts of deionized water for shear emulsification. Pour the emulsion into a polytetrafluoroethylene plate and let it stand at room temperature to obtain collagen-modified self-healing waterborne polyurethane.

6. The method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps as described in claim 5, characterized in that, The shear emulsification time was 1.0 h, and the rotation speed was 1000 r / min.

7. The method for preparing self-healing waterborne polyurethane based on chrome-tanned leather scraps as described in claim 5, characterized in that, The settling time is 8-10 days.

8. The self-healing waterborne polyurethane prepared by the method for preparing self-healing waterborne polyurethane based on chrome tanned leather scraps as described in any one of claims 1-7.

9. The application of the self-healing waterborne polyurethane as described in claim 8 in leather finishing agents.

Images