Composite retanning agent based on bio-based polymer-plant extract as well as preparation method and application of composite retanning agent

Abstract

The invention relates to the technical field of leather chemical engineering and environment-friendly materials, in particular to a composite retanning agent based on bio-based polymer-plant extract and a preparation method and application thereof.The composite retanning agent is prepared from, by mass, 10%-30% of bio-based polymer, 5%-15% of natural plant extract, 5%-15% of organic solvent, 5%-15% of organic solvent and the balance water. 2%-10% of an inorganic auxiliary agent, 15%-25% of a water-soluble polymer material and the balance of deionized water; the sum of the mass percentages of the raw materials is 100%. The environment-friendly retanning agent has the advantages that the environment-friendly retanning agent remarkably improves the softness, tear strength and durability of leather, and meanwhile, the leather has excellent antibacterial and antioxidant properties; the chemical oxygen demand (COD) in the wastewater is reduced by more than 30%, no heavy metal is left, the environmental pollution is obviously reduced, and the wastewater treatment cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical fields of leather chemicals and environmental protection materials, and particularly to a composite retanning agent based on bio-based polymers - plant extracts, and a preparation method and application thereof. Background Art

[0002] In the leather retanning process, chromium salt retanning agents are traditionally widely used to enhance the strength, softness and durability of leather. However, the application of chromium salt retanning agents has obvious limitations. Especially in the context of continuously improving environmental protection requirements, the following main problems are faced:

[0003] During the use of chromium salt retanning agents, heavy metal-containing wastewater will be generated, especially toxic heavy metal ions mainly in the form of hexavalent chromium (Cr 6+ ). If such wastewater is not disposed of up to standard and discharged, it will cause serious pollution to water bodies and soil. These heavy metal pollutions not only affect the ecological environment, but also pose a serious threat to human health. Although the modern leather industry can reduce the content of chromium ions (especially hexavalent chromium (Cr 6+ )) in wastewater through wastewater treatment systems (such as precipitation, flocculation, reduction and other technologies). However, the current existing technologies have the following problems: such as the high treatment cost of metallic chromium, the complex disposal process, etc. These problems lead to a large burden and high cost in wastewater treatment, and it is difficult to achieve true green production.

[0004] In order to address the chromium pollution problem, a variety of chromium-free retanning agents have gradually emerged on the market, such as vegetable tanning agents, synthetic resin tanning agents, etc. Although these alternative solutions reduce heavy metal emissions to a certain extent, after treating leather with a single plant extract tanning agent, it is easy to cause the leather texture to become hard and uneven dyeing, and the light and heat resistance of the treated leather is poor, making it difficult to meet the application requirements with high performance and durability. Although such retanning agents can improve the softness of leather, they often contain a large amount of chemical additives, such as formaldehyde or volatile organic compounds. This not only leads to an increase in the production cost of leather, but also volatile organic compounds pose potential health risks. Especially when heated (or in summer) or used for a long time, toxic substances will be continuously released. Summary of the Invention

[0005] The present invention aims to overcome the deficiencies of the prior art, and provides a composite retanning agent based on bio-based polymers and plant extracts, and a preparation method and application thereof. Through the synergistic effect of bio-based polymers and plant extracts, the mechanical properties of leather are improved and pollutant emissions are reduced, and the chemical oxygen demand and heavy metals (especially Cr 6+) Residues are also significantly reduced, and the antibacterial and antioxidant properties of the leather are greatly improved, meeting the application requirements of the high-end leather market. At the same time, the present invention forms an environmentally friendly and efficient composite retanning agent, successfully overcoming the limitations of traditional technologies in terms of environmental friendliness and functionality.

[0006] The present invention is achieved through the following technical solutions: A composite retanning agent based on a biopolymer - plant extract is provided. The composite retanning agent is composed of the following raw materials by mass percentage, including 10% - 30% biopolymer, 5% - 15% natural plant extract, 2% - 10% inorganic auxiliary, 15% - 25% water-soluble polymer material, and the balance is deionized water; and the sum of the mass percentages of each raw material is 100%.

[0007] Through the above technical solutions, the environmentally friendly retanning agent of the present invention significantly improves the softness, tear resistance and durability of the leather, and at the same time has excellent antibacterial and antioxidant properties. Compared with traditional retanning agents, the composite retanning agent of the present invention reduces the chemical oxygen demand in wastewater by more than 30%, has no heavy metal residues, greatly reduces environmental pollution, significantly reduces the wastewater treatment cost, and has high application value and environmental protection advantages.

[0008] Furthermore, the biopolymer is selected from one or more of polylactic acid (PLA), polyhydroxyalkanoate (PHA), and chitosan.

[0009] Through the above technical solutions, polylactic acid (PLA) is prepared by fermenting renewable plant resources (such as corn or sugarcane). The molecular weight range is 20,000 - 150,000 Da, and its film-forming property is used to improve the mechanical strength and surface smoothness of the leather.

[0010] Polyhydroxyalkanoate (PHA) is a biodegradable polyester synthesized by bacteria, with the structure: -[O-CH(R)-CH 2 -CO] n -, where the R group is a hydrocarbon chain of C 1 -C 15 The carbon-hydrogen chain can adjust the flexibility of the material / leather. The molecular weight range is 30,000 - 100,000 Da.

[0011] Chitosan is derived from chitin and has good antibacterial and hydrophilic properties after deacetylation treatment. The molecular weight is 50,000 - 300,000 Da, and the degree of deacetylation of chitosan used in this scheme is 75 - 95%.

[0012] The specific combinations are as follows:

[0013]

[0014]

[0015] Based on the above combinations, the film-forming performance provided by PLA and the flexibility of PHA are complementary, significantly improving the tear strength, abrasion resistance and smoothness of leather. The combination of chitosan and tea polyphenols achieves effective inhibition of Escherichia coli and Staphylococcus aureus, making it suitable for leather applications with high hygiene requirements. The hydrophilicity of chitosan and the film-forming characteristics of PLA enhance the uniform distribution of dyes in leather fibers and improve color fastness. All three are of natural origin or biodegradable materials, reducing chemical pollutant emissions, with the COD in wastewater reduced by more than 30% and completely avoiding heavy metal residues. Different combinations meet the requirements of different application scenarios, such as outdoor leather products, automotive interiors, etc., providing multiple functions such as softness, UV resistance and durability.

[0016] Furthermore, the natural plant extract can be selected from one or more of tannin, tea polyphenols and flavonoids.

[0017] Through the above technical solution, tannin: extracted from natural wood or bark, mainly polyphenolic compounds. This material contains rich phenolic hydroxyl groups, which can react with the amino groups in leather collagen fibers to form a stable cross-linked structure, thereby enhancing the durability and antioxidant performance of leather. By binding to collagen fibers, it significantly improves the mechanical strength and anti-aging performance of leather, making it suitable for application fields with high durability requirements.

[0018] Tea polyphenols: derived from tea extracts, rich in polyphenolic compounds such as catechins. This material has excellent antibacterial, antioxidant and UV resistance properties. Its polyphenolic structure can effectively inhibit the growth of microorganisms and simultaneously slow down the oxidation and aging process of leather. By endowing leather with antibacterial function, tea polyphenols significantly extend the service life of leather, especially suitable for medical leather and outdoor leather products with high hygiene performance requirements.

[0019] Flavonoids: extracted from plants such as citrus peel and ginkgo leaves. The C 6 -C 3 -C 6 framework endows it with excellent antioxidant and UV resistance capabilities, which can effectively protect leather from the effects of light and oxidation, reducing discoloration and aging. It can significantly improve the light resistance and durability of leather, making it suitable for leather products used in high-light environments, such as outdoor furniture or automotive interiors.

[0020] Among them, tannin is a polyphenolic compound extracted from chestnut wood, locust tree or acacia tree, with a molecular weight range of 500 - 3000 Da. Its phenolic hydroxyl groups can react with amino acids in leather fibers, thereby stabilizing the leather structure and providing excellent antioxidant properties; tea polyphenols are mainly composed of catechins, with a molecular weight of 200 - 500 Da. They not only have antioxidant and antibacterial effects, but also can bind to proteins in leather by forming hydrogen bonds, enhancing the functionality of leather; flavonoid compounds are derived from ginkgo leaves or citrus plants, and the chemical structure is a typical C 6 -C 3 -C 6 framework, which can significantly improve the UV resistance of leather and provide additional antioxidant protection. Through the combination and application of these natural extracts, the composite retanning agent of the present invention has achieved significant improvements in environmental performance and functionality. Through the above different combinations and ratios, tannin, tea polyphenols and flavonoid compounds show significant synergistic effects in the composite retanning agent of the present invention, with improved mechanical properties, enhanced antibacterial properties, UV resistance and anti-aging properties, improved light resistance of leather, delayed aging and yellowing, effectively solving the limitations of the single function of traditional retanning agents.

[0021] Furthermore, the water-soluble polymer material is polyvinyl alcohol, and the molecular weight of the polyvinyl alcohol is 30000 - 150000 Da. The film-forming property and adhesion of polyvinyl alcohol significantly enhance the performance of the retanning agent, ensure uniform leather dyeing, and improve the mechanical properties and appearance quality of leather. The polyvinyl alcohol (PVA) solution is obtained by adding PVA to deionized water and heating and stirring at 75 - 90 °C for 40 - 60 minutes until completely dissolved.

[0022] The present invention provides a method for preparing a composite retanning agent based on bio-based polymers - plant extracts, which specifically includes the following steps:

[0023] Step S1: Preparation of bio-based polymer solution and plant extract solution

[0024] Bio-based polymers (such as polylactic acid PLA and polyhydroxyalkanoates PHA) are dissolved under appropriate temperature and stirring conditions to prepare a solution; plant extracts (such as tannin, tea polyphenols, flavonoid compounds) are prepared into a uniform solution.

[0025] Step S2: Preparation of the composite retanning agent

[0026] The obtained bio-based polymer solution and plant extract solution are mixed in a certain proportion, and inorganic additives and water-soluble polymer materials are slowly added under stirring, and the pH value is adjusted to 5.0 - 5.2, and continuous stirring is carried out until fully mixed to obtain a uniform composite retanning agent.

[0027] In step S1, the preparation process of the bio-based polymer solution is as follows:

[0028] First step: Weigh polylactic acid (PLA) and polyhydroxyalkanoate (PHA) in proportion, add them to deionized water, and stir at a constant temperature of 50 - 60 °C for 30 - 60 minutes until completely dissolved to form a uniform solution.

[0029] Second step: Dissolve chitosan in deionized water, add an appropriate amount of acetic acid with a concentration of 1 - 2%, dissolve it, and stir until it is transparent and uniform, with the temperature controlled at 40 - 50 °C.

[0030] In step S1, the preparation process of the plant extract solution is as follows:

[0031] First step: Dissolve tannin extract, tea polyphenols, and flavonoid compounds separately in deionized water in a certain proportion, control the temperature at 45 - 55 °C, and stir for 30 minutes until completely dissolved.

[0032] Second step: Combine the three plant extract solutions and continue to stir evenly.

[0033] Finally, the application of the above composite retanning agent in the leather retanning process is provided. The leather retanning process includes the following steps:

[0034] Step 1) Leather pretreatment: After wetting and deliming the leather, adjust the pH to 5.0 - 5.5.

[0035] Step 2) Retanning process: In a leather retanning machine, add the composite retanning agent. The retanning temperature is 50 - 60 °C, and the retanning time is 4 - 6 h. Regularly adjust the pH until the composite retanning agent penetrates evenly. Among them, the addition amount of the composite retanning agent accounts for 5% - 10% of the wet weight of the leather.

[0036] Step 3) Post - retanning treatment: Neutralize the leather, adjust the pH to 6.5 - 7.0, and then carry out the dyeing process.

[0037] Furthermore, in step 3), the tear strength of the obtained leather is 8.5 N / mm, the water absorption rate is 12%, and the abrasion loss is 15 mg.

[0038] Furthermore, in step 3), under UV irradiation detection, the obtained leather has a low yellowing index and a color fastness ≥ 3 grades.

[0039] Beneficial effects

[0040] The retanning agent developed in the present invention, which does not contain heavy metals and chemical pollutants, effectively reduces the negative impact on the environment and meets the requirements of increasingly strict environmental protection regulations. At the same time, by optimizing the process, the COD and heavy metal residues in the wastewater are reduced, further improving the environmental protection performance.

[0041] Different from existing plant extracts or synthetic resin-based formaldehyde-free retanning agents, the present invention adopts a composite system of bio-based polymers and plant extracts, without relying on collagen sources, thereby reducing raw material limitations and increasing the functional diversity of retanning agents. Through synergistic effects, simultaneous improvements in multiple functions such as mechanical properties, dyeing uniformity, antibacterial and antioxidant properties are achieved, completely resolving the contradiction between performance improvement and environmental friendliness. Brief Description of the Drawings

[0042] Figure 1 is a real scene photo of the composite retanning agent obtained in Example 1;

[0043] Figure 2 is a real scene photo of the composite retanning agent obtained in Example 2. Detailed Embodiments

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be particularly noted that the embodiments described herein are only used to explain the technical content of the present invention and do not constitute a limitation on the protection scope of the present invention.

[0045] Based on the technical solution of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention. The experimental methods involved in the following embodiments, unless otherwise specified, generally adopt conventional experimental conditions or are operated according to the recommended conditions of relevant reagent and equipment manufacturers. Unless otherwise specified, all percentages, ratios and proportions are calculated by weight.

[0046] The reagents and raw materials used in the embodiments and comparative examples of the present invention, unless otherwise specified, can be obtained through commercial channels. The above content is intended to provide technical reference, and can be appropriately adjusted according to actual needs during specific application without affecting the core technical content and its protection scope of the present invention.

[0047] Example 1: Preparation and Application of Poly(lactic acid) / Tea Polyphenols / Polyvinyl Alcohol Composite Retanning Agent

[0048] A method for preparing a composite retanning agent based on bio-based polymers-plant extracts, comprising the following steps:

[0049] Step S1. The preparation processes of the bio-based polymer solution and the natural plant extract solution are as follows:

[0050] The preparation process of the bio-based polymer solution is as follows: First step: At a temperature of 55±2°C, weigh 15 g of poly(lactic acid) PLA and add it to 500 mL of deionized water, and stir at a constant temperature of 50-60°C for 30-60 minutes until completely dissolved to form a uniform solution;

[0051] Step 2: Dissolve chitosan in deionized water, add an appropriate amount of acetic acid with a concentration of 1-2%, dissolve it, stir until it is transparent and uniform, and control the temperature at 40-50°C.

[0052] The preparation process of the natural plant extract solution is as follows: Dissolve 5 g of tea polyphenols in 200 mL of deionized water, control the temperature at 45°C, and stir for 30 minutes until completely dissolved;

[0053] Step S2: First, add 10 g of polyvinyl alcohol (PVA) to 150 mL of deionized water, heat and stir at 85°C for 50 minutes until completely dissolved to obtain a PVA solution; then slowly add the tea polyphenol solution to the PLA solution, stir for 15 minutes to fully mix the two; subsequently, slowly pour the PVA solution into the above mixture, then add 5 wt% kaolin, and continuously stir for 30 minutes to ensure uniform dispersion; finally, adjust the pH of the solution to 5.0-5.2, and let it stand for 30 minutes to obtain a stable composite retanning agent.

[0054] In addition, an application of the composite retanning agent in the leather retanning process is provided. The leather retanning process includes the following steps:

[0055] Step 1) Leather pretreatment: Adjust the pH of 1000 g of wet leather after soaking and deliming to 5.2;

[0056] Step 2) Retanning process: In a leather retanning machine, add the composite retanning agent, the retanning temperature is 55±2°C, the retanning time is 5 h, and the pH is adjusted regularly until the composite retanning agent uniformly penetrates; wherein, the addition amount of the composite retanning agent accounts for 8% of the wet weight of the leather;

[0057] Step 3) Post-retanning treatment: Neutralize the leather, adjust the pH to 6.8-7.0, and then carry out the dyeing process.

[0058]

[0059] The experimental results show that the leather treated with the composite retanning agent of the present invention exhibits excellent performance in terms of anti-tear strength, antibacterial rate, water absorption rate, and wastewater COD. Specifically as follows: The anti-tear strength reaches 8.5 N / mm, which is 21% higher than that of the traditional chromium salt retanning agent (7.0 N / mm) and significantly higher than that of the single vegetable tanning agent (5.8 N / mm); The antibacterial rate is as high as 95.5%, which is 91% and 59% higher than those of the traditional chromium salt retanning agent (50.0%) and the single vegetable tanning agent (60%) respectively, meeting the requirements of medical and high hygienic performance; The water absorption rate is reduced to 13%, which is significantly better than that of the traditional chromium salt retanning agent (18.5%) and the single vegetable tanning agent (15%); The wastewater COD value is reduced to 429 mg / L, which is 33% less than that of the traditional chromium salt retanning agent (650 mg / L), showing excellent environmental protection performance.

[0060] In step 3), the anti-tear strength of the obtained leather is 8.5 N / mm, and the water absorption rate of the leather is 12%, which is significantly lower than that of the traditional chromium salt retanning agent (18.5%) and the single vegetable tanning agent (15.0%), indicating its good moisture resistance and dense structure; Under the standard abrasion test conditions, the abrasion loss is 15 mg, and the wear resistance is improved, which is beneficial to extending the service life of leather products; At the same time, through ultraviolet irradiation detection, the obtained leather has a low yellowing index (ΔE = 1.4), stable color, and good anti-ultraviolet aging ability; In the post-dyeing test, the color fastness reaches level 3 or above, meeting the requirements of high-end leather products for color retention under conditions such as light and washing. These performance verification results all show that the composite retanning agent in this example has significant advantages in improving the appearance stability and durability of leather.

[0061] Example 2: Preparation and application of polyhydroxyalkanoate (PHA) / chitosan / tannin composite retanning agent A method for preparing a composite retanning agent based on biopolymer-plant extract, comprising the following steps:

[0062] Step S1: The preparation processes of the biopolymer solution and the natural plant extract solution are as follows:

[0063] The preparation process of the biopolymer solution is as follows: First step: At 60 ± 2 °C, weigh 12 g of polyhydroxyalkanoate PHA and add it to 300 mL of deionized water, and stir at a constant temperature of 58 °C for 45 minutes until completely dissolved to form a uniform solution;

[0064] Second step: Dissolve 8 g of chitosan in deionized water, add 200 mL of acetic acid with a concentration of 1%, dissolve, and stir until transparent and uniform, with the temperature controlled at 50 °C.

[0065] The preparation process of the natural plant extract solution is as follows: Dissolve 6 g of tannin in 150 mL of deionized water, control the temperature at 50 °C, stir for 20 minutes until completely dissolved;

[0066] Step S2: First, add 10 g of polyvinyl alcohol (PVA) to 150 mL of deionized water, heat and stir at 85 °C for 50 minutes until completely dissolved to obtain a PVA solution;

[0067] Add the tannin solution to the PHA solution and stir. After mixing evenly, add the chitosan solution. After stirring for 30 minutes, add 4 wt% talcum powder. After mixing evenly (for 15 - 20 minutes), adjust the pH to 5.0 and continue stirring for 1 hour to obtain the composite retanning agent.

[0068] In addition, an application of the composite retanning agent in the leather retanning process is provided. The leather retanning process includes the following steps:

[0069] Step 1) Leather pretreatment: Immerse 1000 g of sheepskin in lime and remove hair, then adjust the pH to 5.3;

[0070] Step 2) Retanning process: In a leather retanning machine, add the composite retanning agent, the retanning temperature is 50 °C, the retanning time is 4 h, and regularly adjust the pH until the composite retanning agent uniformly penetrates; among them, the addition amount of the composite retanning agent accounts for 10% of the weight of the wet leather;

[0071] Step 3) Post - retanning treatment: Neutralize, dye and fatliquor the sheepskin, and finally dry it into leather.

[0072]

[0073] The experimental results show that the composite retanning agent of the present invention is superior to the traditional chrome - salt retanning agent and the single - plant retanning agent in terms of softness, folding resistance, antibacterial property and environmental protection. The specific data are as follows: The leather softness reaches 9.0 (scoring 1 - 10), which is 28% higher than that of the traditional chrome - salt retanning agent and the single - plant retanning agent (both are 7.0); The number of folding resistance reaches 160,000 times, which is 78% higher than that of the traditional chrome - salt retanning agent (100,000 times), significantly enhancing the durability of the leather; The antibacterial rate is increased to 92.0%, which is much higher than that of the traditional chrome - salt retanning agent (50.0%) and the single - plant retanning agent (55.0%), and is suitable for medical leathers with high requirements for hygienic performance; The COD value of the wastewater is reduced to 190 mg / L, which is 62% lower than that of the traditional chrome - salt retanning agent (650 mg / L), showing significant environmental protection advantages.

[0074] Example 3: Preparation and application of poly(lactic acid) (PLA) / flavonoid compound composite retanning agent A method for preparing a composite retanning agent based on a bio - based polymer - plant extract includes the following steps:

[0075] Step S1. The preparation processes of the biobased polymer solution and the natural plant extract solution are as follows:

[0076] The preparation process of the biobased polymer solution is as follows: First step: At 55 ± 2 °C, weigh 14 g of polylactic acid (PLA) and polyhydroxyalkanoate (PHA), add them to 300 mL of deionized water, and stir at a constant temperature of 58 °C for 45 minutes until completely dissolved to form a homogeneous solution.

[0077] Second step: Dissolve 6 g of flavonoids in 150 mL of deionized water, stir for 30 min while controlling the temperature at 50 °C to obtain a flavonoid solution. Specifically, due to the poor solubility of flavonoids in water, most flavonoid substances have a neutral or weakly acidic phenolic structure and limited hydrophilicity, so it is difficult to dissolve them fully in deionized water alone. Appropriately increasing the temperature can improve the dissolution rate and solubility (thermodynamic support), and at the same time, avoid the destruction of the flavonoid structure at too high a temperature.

[0078] The preparation process of the natural plant extract solution is as follows: Dissolve 6 g of tannin extract in 150 mL of deionized water, control the temperature at 50 °C, and stir for 20 minutes until completely dissolved.

[0079] Step S2. First, add 10 g of polyvinyl alcohol (PVA) to 150 mL of deionized water, heat and stir at 85 °C for 50 minutes until completely dissolved to obtain a PVA solution.

[0080] Add the flavonoid solution and the tannin extract solution to the polylactic acid solution in sequence, and continuously stir for 20 minutes. Then add 5 wt% kaolin and stir for 10 minutes. Finally, adjust the pH to 5.13 and stir for 20 minutes to obtain a composite retanning agent.

[0081] In addition, an application of the composite retanning agent in the leather retanning process is provided. The leather retanning process includes the following steps:

[0082] Step 1) Leather pretreatment: Select 1000 g of limed and unhaired cowhide, and adjust its pH to 5.2.

[0083] Step 2) Retanning process: In a leather retanning machine, add the composite retanning agent, the retanning temperature is 55 °C, the retanning time is 5 h, regularly adjust the pH, and turn the drum every 30 minutes until the composite retanning agent uniformly penetrates; among them, the addition amount of the composite retanning agent accounts for 8% of the weight of the wet leather.

[0084] Step 3) Post-retanning treatment: Neutralize the leather to pH 6.89, and then carry out the processes of dyeing, fatliquoring and drying to obtain the final leather.

[0085]

[0086] The experimental results show that the leather treated with the composite retanning agent of the present invention exhibits significant advantages in terms of tear strength, softness, light resistance, antioxidant performance and environmental friendliness. The specific properties are as follows: The tear strength reaches 8.3 N / mm, which is 19%-43% higher than that of the traditional chromium salt retanning agent (7.0 N / mm) and the single vegetable tanning agent (5.8 N / mm) respectively; the softness score is 8.5, which is 18%-42% higher than that of the traditional chromium salt retanning agent (7.2) and the single vegetable tanning agent (6.0); the light resistance is excellent, and the yellowing index ΔE is reduced to 1.4, which is 50%-60% lower than that of the traditional chromium salt retanning agent (2.8) and the single vegetable tanning agent (3.5); the antioxidant performance score reaches 4.8 (full score 5 points), which is 60%-92% higher than that of the traditional chromium salt retanning agent (3.0) and the single vegetable tanning agent (2.5). In addition, the COD value of the wastewater is significantly reduced to 190 mg / L, which is 70%-62% lower than that of the traditional chromium salt retanning agent (650 mg / L) and the single vegetable tanning agent (500 mg / L) respectively.

[0087] Comparative Example 1: Comparison between a commercially available environmentally friendly formaldehyde-free retanning agent and the chitosan-flavonoid compound composite retanning agent of the present invention

[0088] Test method

[0089] Use a commercially available environmentally friendly formaldehyde-free retanning agent for retanning at a dosage of 8% of the wet weight of the leather, a temperature of 60 °C, and a time of 5 hours.

[0090] Use a composite retanning agent of chitosan and flavonoids for retanning at a dosage of 6% of the wet weight of the leather, a retanning temperature of 58 °C, and a time of 4 hours.

[0091] Test results: The wear resistance of the leather treated with the commercially available environmentally friendly formaldehyde-free retanning agent is increased by 10%, and the water absorption rate is reduced by 20%; the wear resistance of the leather treated with the composite retanning agent of the present invention is increased by 25%, and the water absorption rate is reduced by 30%, showing a more excellent waterproof effect.

[0092] From these comparative tests, it can be seen that the composite retanning agent of the present invention is significantly superior to the traditional retanning agent in key indicators such as tear strength, water absorption rate, and wear resistance, and the COD is reduced by more than 70% compared with the traditional chromium salt retanning agent. It is superior to the traditional retanning agent and some existing environmentally friendly products in terms of environmental friendliness and functionality, fully verifying its potential and feasibility for industrial application.

[0093] Example 4: Preparation and application of polyhydroxyalkanoate (PHA) / tea polyphenol / flavonoid compound composite retanning agent

[0094] A method for preparing a composite retanning agent based on a biopolymer-plant extract, comprising the following steps:

[0095] Step S1. The preparation processes of the biobased polymer solution and the natural plant extract solution are as follows:

[0096] The preparation process of the biobased polymer solution is as follows: At 60 °C, weigh 10 g of polyhydroxyalkanoate (PHA) and add it to 400 mL of deionized water. Stir at a constant temperature of 60 °C for 45 minutes until completely dissolved to form a homogeneous solution;

[0097] The preparation process of the natural plant extract solution is as follows:

[0098] Dissolve 6 g of tea polyphenols in 150 mL of deionized water, control the temperature at 50 °C, and stir for 30 minutes until completely dissolved; slowly add 4 g of flavonoids to the tea polyphenol solution and continue to stir for 20 minutes until fully dissolved.

[0099] Step S2. First, add 10 g of polyvinyl alcohol (PVA) to 150 mL of deionized water, heat and stir at 85 °C for 50 minutes until completely dissolved to obtain a PVA solution; at 50 °C, combine and mix the above PHA solution, the tea polyphenol-flavonoid mixed solution with 5 g of tannin extract solution (previously dissolved in 100 mL of water), adjust the pH to 4.8 - 5.0, and stir for 1 hour to obtain a stable composite retanning agent.

[0100] In addition, an application of the composite retanning agent in the leather retanning process is provided. The leather retanning process includes the following steps:

[0101] Step 1) Leather pretreatment: Adjust the pH of 1000 g of wet cowhide after soaking and deliming to 5.05;

[0102] Step 2) Retanning process: In a leather retanning machine, add the composite retanning agent, the retanning temperature is 55 °C, the retanning time is 5 h, regularly adjust the pH, and turn the drum every 30 minutes until the composite retanning agent uniformly penetrates; wherein, the addition amount of the composite retanning agent accounts for 8% of the wet weight of the leather;

[0103] Step 3) Post-retanning treatment: Neutralize the leather, adjust the pH to 6.89, and then carry out the dyeing process.

[0104]

[0105] Example 5: Preparation and Application of Poly(lactic acid) (PLA) / Chitosan / Tea Polyphenol Composite Retanning Agent

[0106] A method for preparing a composite retanning agent based on biobased polymers - plant extracts includes the following steps:

[0107] Step S1. The preparation processes of the biobased polymer solution and the natural plant extract solution are as follows:

[0108] The preparation process of the bio-based polymer solution is as follows: The first step: Weigh 15 g of polylactic acid (PLA) and add it to 400 mL of deionized water at 55 ± 2 °C. Stir for 40 minutes under the constant temperature condition of 60 °C until it is completely dissolved to form a uniform solution.

[0109] The second step: Dissolve 10 g of chitosan in deionized water, add 200 mL of acetic acid with a concentration of 1%, dissolve it, and stir for 30 min until it is transparent and uniform. Control the temperature at 50 °C.

[0110] The preparation process of the natural plant extract solution is as follows: Dissolve 5 g of tea polyphenols in 100 mL of deionized water, control the temperature at 50 °C, and stir for 20 minutes until it is completely dissolved.

[0111] Step S2: First, add 10 g of polyvinyl alcohol (PVA) to 150 mL of deionized water, heat and stir at 85 °C for 50 minutes until it is completely dissolved to obtain a PVA solution.

[0112] Add the chitosan solution and the tea polyphenol solution to the PLA solution in sequence. After stirring evenly, add 5 wt% kaolin, adjust the pH to 5.0 - 5.2, and stir for 30 minutes to obtain a composite retanning agent.

[0113] In addition, an application of the composite retanning agent in the leather retanning process is provided. The leather retanning process includes the following steps:

[0114] Step 1) Leather pretreatment: Adjust the pH of 1000 g of wet leather after soaking and deliming to 5.2.

[0115] Step 2) Retanning process: In a leather retanning machine, add the composite retanning agent. The retanning temperature is 50 ± 2 °C, and the retanning time is 5 h. Regularly adjust the pH, and turn the drum every 30 minutes until the composite retanning agent uniformly penetrates. Among them, the addition amount of the composite retanning agent accounts for 8% of the wet weight of the leather.

[0116] Step 3) Post-retanning treatment: Neutralize the leather, adjust the pH to 6.86, and then carry out the dyeing process.

[0117]

[0118] In step 3), the tear strength of the obtained leather is 8.5 N / mm. The composite retanning agent used in this example has a significant effect on improving leather properties. The softness is provided synergistically by chitosan and polylactic acid (PLA). The film-forming property of PLA enhances the bonding between fibers, and chitosan imparts good flexibility to the leather, resulting in a softness score of 9.2. Under the combined action of tea polyphenols and chitosan, the antibacterial rate is as high as 96.5%. By acting on the cell wall through its phenolic hydroxyl groups, it effectively inhibits the growth of common bacteria. The number of flexing cycles reaches 158,000 times, reflecting the improvement of the toughness and fatigue strength of the leather. The yellowing index is low, and the color fastness is ≥3 levels. It is suitable for scenarios with high durability requirements. In addition, the composite system contains no heavy metals and is derived from natural materials, significantly reducing the wastewater COD to 190 mg / L, and having good environmental protection advantages.

[0119] Example 6: Preparation and application of polylactic acid (PLA) / flavonoid / tannin composite retanning agent

[0120] A method for preparing a composite retanning agent based on a bio-based polymer-plant extract, comprising the following steps:

[0121] Step S1: The preparation processes of the bio-based polymer solution and the natural plant extract solution are as follows:

[0122] The preparation process of the bio-based polymer solution is as follows: Weigh 14 g of polylactic acid (PLA) and add it to 300 mL of deionized water at 55 ± 2 °C. Stir at a constant temperature of 60 °C for 45 minutes until completely dissolved to form a uniform solution;

[0123] The preparation process of the natural plant extract solution is as follows: Dissolve 6 g of flavonoids in 150 mL of deionized water, control the temperature at 50 °C, and stir for 30 minutes until completely dissolved; Dissolve 8 g of tannin in 150 mL of deionized water and stir at 50 °C for 20 minutes.

[0124] Step S2: First, add 10 g of polyvinyl alcohol (PVA) to 150 mL of deionized water, heat and stir at 85 °C for 50 minutes until completely dissolved to obtain a PVA solution;

[0125] Add the chitosan solution and the tea polyphenol solution to the PLA solution in sequence. After stirring evenly, add 5 wt% kaolin, adjust the pH to 5.14, and stir for 30 minutes to obtain the composite retanning agent.

[0126] In addition, an application of the composite retanning agent in the leather retanning process is provided. The leather retanning process includes the following steps:

[0127] Step 1) Leather pretreatment: Adjust the pH of 1000 g of wet leather after soaking and deliming to 5.0;

[0128] Step 2) Retanning process: In a leather retanning machine, add a compound retanning agent. The retanning temperature is 55 ± 2 °C, and the retanning time is 5 h. Regularly adjust the pH and turn the drum every 30 minutes until the compound retanning agent uniformly penetrates. Among them, the addition amount of the compound retanning agent accounts for 8% of the wet weight of the leather.

[0129] Step 3) Post-treatment after retanning: Neutralize the leather, adjust the pH to 6.89, and then carry out the dyeing process.

[0130]

[0131] The experimental results show that this compound retanning agent is significantly superior to traditional chromium salt retanning agents and single vegetable tanning agents in key performance indicators such as tear strength, softness, and light fastness. At the same time, the COD value of the wastewater is reduced by 72%, showing obvious environmental protection advantages.

[0132] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A composite retanning agent based on bio-based polymer-plant extract, characterized in that: The composite retanning agent is composed of the following raw materials by mass percentage, including 10%-30% of bio-based polymer, 5%-15% of natural plant extract, 2%-10% of inorganic auxiliary agent, 15%-25% of water-soluble high molecular material, and the balance is deionized water; and the sum of the mass percentages of the raw materials is 100%.

2. The bio-based polymer-plant extract composite retanning agent according to claim 1, characterized in that: The bio-based polymer is selected from one or more of polylactic acid, polyhydroxyalkanoate and chitosan.

3. The bio-based polymer-plant extract-based composite retanning agent according to claim 1, characterized in that: The natural plant extract is selected from one or more of tannin, tea polyphenols and flavonoids.

4. The bio-based polymer-plant extract-based composite retanning agent according to claim 1, characterized in that: The water-soluble polymer material is polyvinyl alcohol, and the molecular weight of the polyvinyl alcohol is 30000-150000Da.

5. A method for preparing the bio-based polymer-plant extract composite retanning agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1, preparing a bio-based polymer solution and a natural plant extract solution; Step S2, mixing the obtained bio-based polymer solution and the natural plant extract solution in a certain proportion, and slowly adding the inorganic auxiliary agent and the water-soluble polymer material under stirring, adjusting the pH, and continuously stirring until fully mixed, to obtain the composite retanning agent.

6. The method for preparing a composite retanning agent based on bio-based polymer-plant extract according to claim 5, characterized in that: In step S1, the preparation process of the bio-based polymer solution is as follows: Step 1: weigh polylactic acid PLA and polyhydroxyalkanoate PHA in proportion, add them into deionized water, and stir them at a constant temperature of 50-60°C for 30-60 minutes until they are completely dissolved to form a uniform solution; Step 2: Dissolve chitosan in deionized water, add appropriate amount of acetic acid with a concentration of 1-2%, dissolve, stir until transparent and uniform, and control the temperature at 40-50°C.

7. The method for preparing a composite retanning agent based on bio-based polymers and plant extracts according to claim 5, characterized in that: In step S1, the preparation process of the natural plant extract solution is as follows: Step 1: Dissolve tannin extract, tea polyphenols and flavonoids in deionized water in a certain proportion, control the temperature at 45-55°C, stir for 30 minutes, and completely dissolve; Step 2: Combine the three plant extract solutions and continue stirring until evenly combined.

8. Use of the composite retanning agent according to any one of claims 1 to 4 in a leather retanning process, characterized in that: The leather retanning process comprises the following steps: Step 1) leather pretreatment: after soaking and deashing the leather, adjust the pH to 5.0-5.5; Step 2) Retanning process: Add the composite retanning agent into a leather retanning machine, the retanning temperature is 50-60° C., the retanning time is 4-6 hours, and the pH is adjusted regularly until the composite retanning agent is evenly penetrated; wherein the addition amount of the composite retanning agent accounts for 5%-10% of the wet weight of the leather; Step 3) Post-tanning treatment: The leather is neutralized, the pH is adjusted to 6.5-7.0, and then the dyeing process is carried out.

9. The use according to claim 8, characterized in that: In step 3), the leather obtained has a tearing strength of >7.2 N / mm, a water absorption rate of <14%, and an abrasion loss of <25 mg.

10. The use according to claim 8, characterized in that: In step 3), the obtained leather has a low yellowing index and a color fastness of ≥ grade 3 under UV irradiation detection.

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