Functional sericin-based chrome-free tanning agent as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a functional sericin-based chrome-free tanning agent, which specifically comprises the following steps: mixing sericin powder, curcumin powder and deionized water, stirring, and filtering to obtain a mixed solution; under the protection of nitrogen, adding triglycidyl isocyanurate into the mixed solution, then adding a triethylamine catalyst, adjusting the pH value to 8.5-9.0 by using a NaOH solution, and carrying out condensation reflux stirring reaction to obtain a cross-linked product solution; and the cross-linked product solution is subjected to precipitation, standing, suction filtration, washing, drying and sieving, and the functional sericin-based chrome-free tanning agent is obtained. The sericin protein which is rich in amino acid, high in biological activity, good in oxidation resistance, high in biocompatibility and good in antibacterial effect is used as a main raw material; epoxy groups in TGIC molecules respectively react with amino groups on sericin molecules and hydroxyl groups on curcumin phenol molecules, and the chrome-free tanning agent with good antibacterial property, degradability and damp-heat-resistant stability is developed.

Description

Technical Field

[0001] The present invention belongs to the technical field of leather tanning, and in particular relates to a method for preparing a functional sericin-based chrome-free tanning agent, and also relates to the functional sericin-based chrome-free tanning agent and its application. Background Art

[0002] Leather tanning agents chemically react with leather collagen fibers, altering their molecular structure, thereby enhancing the leather's durability, water resistance, and abrasion resistance, while effectively delaying decay. Tanning agents also enhance the leather's softness and gloss. Common tanning agents include chrome tanning agents, vegetable tanning agents, and synthetic tanning agents. However, traditional chrome tanning agents contain the harmful heavy metal chromium, which causes environmental pollution and impacts human health. While chrome-free tanning agents offer environmental advantages, they often suffer from weak binding properties, limited functionality (such as a lack of antibacterial properties), and poor water resistance.

[0003] Vegetable tanning agents are environmentally friendly, biodegradable, and low in cost, but they react slowly and affect the appearance of leather; synthetic chrome-free tanning agents (such as organic acid tanning agents) are usually obtained through chemical synthesis, have a faster reaction speed and adjustability, and are suitable for large-scale production, but their production costs are high, and some synthetic tanning agents may affect the color and feel of the leather; sulfur tanning agents can react with collagen in leather through sulfides (such as sodium sulfide), and are more environmentally friendly, but will have an adverse effect on the texture and color of the leather; polymer tanning agents react with leather through polymers (such as polyammonium chloride), are suitable for large-scale production, but will affect the feel and tactile properties of the leather.

[0004] Sericin, a byproduct of silk processing, possesses excellent reproducibility, moisture retention, antioxidant properties, biocompatibility, and antibacterial properties. However, when used alone, it is susceptible to degradation and lacks sufficient mechanical properties. While curcumin exhibits antibacterial properties, its binding stability to leather collagen is poor. Therefore, there is an urgent need for a multifunctional, efficient, and environmentally friendly chrome-free tanning agent. Summary of the Invention

[0005] The first object of the present invention is to provide a method for preparing a functional sericin-based chrome-free tanning agent, which solves the problems of poor antibacterial properties and low moisture and heat stability of existing chrome-free tanning agents.

[0006] A second object of the present invention is to provide a functional sericin-based chrome-free tanning agent.

[0007] The third object of the present invention is to use the functional sericin-based chrome-free tanning agent in leather tanning.

[0008] The first technical solution adopted by the present invention is a method for preparing a functional sericin-based chrome-free tanning agent, which is specifically implemented according to the following steps: Step 1, mixing sericin powder, curcumin powder and deionized water, performing magnetic stirring to form a composite solution, and filtering to remove undissolved particles to obtain a mixed solution; Step 2: Under nitrogen protection, slowly add triglycidyl isocyanurate to the mixed solution obtained in step 1, then dropwise add triethylamine catalyst, and adjust the pH to 8.5-9.0 with NaOH solution, and perform condensation reflux stirring reaction to obtain a cross-linked product solution; Step 3: precipitate the cross-linked product solution, let it stand, filter it, wash it, dry it, and sieve it to obtain a functional sericin-based chrome-free tanning agent.

[0009] The present invention is also characterized in that: In step 1, the stirring temperature is 25° C. to 30° C., the stirring speed is 500 to 800 rpm, and the stirring time is 30 to 60 minutes. The mass ratio of sericin to curcumin is 1:0.5 to 2.

[0010] In step 2, the reaction temperature is 55°C to 85°C, the reaction time is 3 to 6 hours, and the stirring speed is 800 to 1000 rpm.

[0011] In step 2, the molar ratio of sericin to TGIC is 1:0.5-1.2; The molar ratio of curcumin to TGIC is 1:0.3~1.2; the amount of triethylamine used is 2%~8% of the mass of sericin protein.

[0012] In step 3, specifically: The cross-linked product solution obtained in step 2 is cooled to 25°C-30°C, and anhydrous ethanol in an amount 2-3 times the volume of the reaction solution is slowly added to precipitate the product. The product is allowed to stand for complete precipitation and then filtered. The filter cake is washed three times with a mixture of ethanol and water, dried in a vacuum drying oven at 50°C-60°C for 12-24 hours, and crushed through a 200-mesh sieve to obtain a functional sericin-based chrome-free tanning agent.

[0013] The second technical solution adopted by the present invention is a chrome-free tanning agent prepared by the preparation method of a functional sericin-based chrome-free tanning agent.

[0014] The third solution adopted by the present invention is the use of a functional sericin-based chrome-free tanning agent in leather tanning.

[0015] The beneficial effects of the present invention are as follows: the present invention uses sericin, which is rich in amino acids, has strong biological activity, good antioxidant properties, strong biocompatibility, and good antibacterial effects, as the main raw material; the epoxy groups in the TGIC molecules react with the amino groups on the sericin molecules and the hydroxyl groups on the curcumin phenol molecules, respectively, to develop a chrome-free tanning agent with good antibacterial properties, degradability, and moisture-heat stability. DETAILED DESCRIPTION

[0016] The present invention is described in detail below with reference to specific embodiments.

[0017] The preparation method of the functional sericin-based chrome-free tanning agent of the present invention is specifically carried out according to the following steps: Step 1: sericin powder, curcumin powder, and deionized water are mixed and magnetically stirred to form a uniform, transparent orange-yellow composite solution, which is then filtered through a 0.45 μm filter membrane to remove undissolved particles, thereby obtaining a mixed solution. The stirring temperature is 25°C~30°C, the stirring speed is 500~800rpm, and the stirring time is 30~60min; The mass ratio of sericin to curcumin is 1:0.5~2; The amount of deionized water added was 70% of the total mass of sericin and curcumin; Step 2: Under nitrogen protection, slowly add triglycidyl isocyanurate (TGIC) to the mixed solution obtained in step 1, then add triethylamine catalyst dropwise, and adjust the pH to 8.5-9.0 using a 5 wt% NaOH solution, and perform a condensation reflux stirring reaction to obtain a cross-linked product solution; The reaction temperature is 55°C~85°C, the reaction time is 3~6 hours, and the stirring speed is 800~1000 rpm; The molar ratio of sericin to TGIC is 1:0.5-1.2; The molar ratio of curcumin to TGIC is 1:0.3~1.2; The dosage of triethylamine is 2%~8% of the mass of sericin protein; The epoxy groups (910 cm -1 ) characteristic peak disappears, confirming that the cross-linking reaction is complete.

[0018] Step 3: Cool the reaction mixture obtained in Step 2 to 25°C-30°C, slowly add 2-3 times the volume of anhydrous ethanol (purity ≥99.5%) to precipitate the product, let it stand for 1 hour to allow the product to completely precipitate, then filter it with suction. Wash the filter cake three times with a mixture of ethanol and water (ethanol:water volume ratio 3:1) to remove unreacted TGIC and catalyst. Dry in a vacuum drying oven at 50°C-60°C for 12-24 hours (vacuum pressure ≤0.1 MPa), and pulverize through a 200-mesh sieve to obtain a light yellow to brown solid powder of chrome-free tanning agent. The molecular structure of the obtained chrome-free tanning agent contains cross-linking bonds formed by the amino group of sericin and the epoxy group of TGIC, and ether bonds formed by the phenolic hydroxyl group of curcumin and the epoxy group of TGIC. The tanning agent particle size is 50-100 μm, and the water solubility is ≥95% (25°C).

[0019] The obtained functional sericin-based chrome-free tanning agent is used for tanning, and the specific tanning process is as follows: Dissolve the tanning agent powder in water at a concentration of 3% to 12% of the leather weight to prepare a tanning solution with a mass concentration of 10% to 15%; adjust the pH of the tanning solution to 8.0 to 9.0 using a 10 wt% Na2CO3 solution, and allow the solution to react with the pickled leather at 35°C to 45°C for 4 to 8 hours; After tanning, the leather's shrinkage temperature is ≥80°C, its thickness increase is ≥10%, and its antibacterial rate is ≥90% (tested according to ISO 20743). After tanning, the leather's tensile strength increases by 30%-50%, and its tear strength increases by 25%-40%.

[0020] In the present method, sericin, which is rich in amino acids, exhibits strong bioactivity, excellent antioxidant properties, strong biocompatibility, and excellent antibacterial properties, is used as the primary raw material. The epoxy groups in the TGIC molecule react with the amino groups on the sericin molecule and the hydroxyl groups on the curcumin molecule, respectively, to develop a chrome-free tanning agent with excellent antibacterial properties, biodegradability, and wet-heat stability. This tanning agent has the following advantages: 1) It is free of chromium, chlorine, phosphorus and other pollution during use, and does not release free formaldehyde. It is in line with the sustainable development trend of green revolution materials and provides a key material basis for ecological leather manufacturing.

[0021] 2) The present invention uses natural protein as the raw material for the chrome-free tanning agent, avoiding the environmental pollution issues associated with traditional chrome tanning. It not only provides multiple benefits such as environmental protection, antibacterial and antioxidant properties, but also enhances the mechanical properties and durability of leather.

[0022] 3) A large number of amino groups and hydroxyl groups are introduced into the molecular structure of chrome-free tanning agents, which have higher reactivity and can undergo Schiff base reaction with the amino groups on collagen, etc., which is beneficial to improving the mechanical strength of tanned leather and the absorption rate of tanning agents.

[0023] 4) The chrome-free tanning agent has excellent antibacterial effect on leather after tanning, which improves the durability and hygiene of the leather and can improve the odor of the leather.

[0024] Example 1 The method for preparing the functional sericin-based chrome-free tanning agent of the present invention comprises the following steps: 10g of sericin powder and 5g of curcumin powder were weighed and added to 10.5g of deionized water. The mixture was magnetically stirred at 25°C and 500 rpm for 40 minutes to form a homogeneous, transparent orange-yellow composite solution. The solution was then filtered through a 0.45 μm filter to remove undissolved particles and set aside. The composite solution was transferred to a three-necked flask equipped with a condenser reflux system. Under nitrogen, 7.2g of triglycidyl isocyanurate (TGIC) was slowly added to the flask, along with 0.5g of triethylamine catalyst, and the pH was adjusted to 8.5 using a 5 wt% NaOH solution. The reaction was continued at 65°C for 4 hours to obtain a cross-linked product solution. After the solution was cooled to 25°C, 30mL of anhydrous ethanol (≥99.5% purity) was slowly added to precipitate the product. The product was allowed to stand for 1 hour to completely precipitate, then filtered using a Buchner funnel and washed three times with an ethanol-water mixture to remove unreacted TGIC and catalyst. The mixture was dried in a vacuum drying oven at 60°C for 12 hours (vacuum pressure ≤ 0.1 MPa), crushed and passed through a 200-mesh sieve to obtain a light yellow to brown solid powder of a chrome-free tanning agent; the tanning agent powder was dissolved in water at an amount of 12% of the leather mass, the pH of the tanning solution was adjusted to 8.0 using a 10 wt% Na2CO3 solution, and the mixture was reacted with acid leather at 35°C for 4 hours to obtain the finished leather.

[0025] The shrinkage temperature (Ts) of the tanned finished leather reaches 84°C, the thickening rate is 12%, the antibacterial rate (Staphylococcus aureus) is 93%, and the tensile strength is increased by 35%.

[0026] Example 2 The method for preparing the functional sericin-based chrome-free tanning agent of the present invention comprises the following steps: 10g of sericin powder and 10g of curcumin powder were weighed and mixed, then added to 14g of deionized water. The mixture was magnetically stirred at 28°C and 650 rpm for 60 minutes to form a homogeneous, transparent orange-yellow composite solution. Undissolved particles were removed by filtration through a 0.45 μm filter and set aside. The composite solution was transferred to a three-necked flask equipped with a reflux condenser. Under nitrogen, 9g of triglycidyl isocyanurate (TGIC) was slowly added to the flask, along with 0.8g of triethylamine catalyst, and the pH was adjusted to 8.7 using a 5 wt% NaOH solution. The reaction was continued at 75°C for 5 hours to obtain a cross-linked product solution. After the product solution was cooled to 28°C, 35ml of anhydrous ethanol (≥99.5% purity) was slowly added to precipitate the product. The product was allowed to stand for 1 hour to completely precipitate, then filtered using a Buchner funnel and washed three times with an ethanol-water mixture to remove unreacted TGIC and catalyst. The mixture was dried in a vacuum drying oven at 55°C for 18 hours (vacuum pressure ≤ 0.1 MPa), crushed and passed through a 200-mesh sieve to obtain a light yellow to brown solid powder of a chrome-free tanning agent; the tanning agent powder was dissolved in water at an amount of 10% of the leather mass, the pH of the tanning solution was adjusted to 8.5 using a 10 wt% Na2CO3 solution, and the mixture was reacted with sheep acid hide at 40°C for 6 hours to obtain the finished leather.

[0027] The shrinkage temperature (Ts) of the tanned finished leather reaches 83.5°C, the thickening rate is 15%, and the antibacterial rate (Staphylococcus aureus) is 96%.

[0028] Example 3 The method for preparing the functional sericin-based chrome-free tanning agent of the present invention comprises the following steps: 10g of sericin powder and 20g of curcumin powder were weighed and mixed, then added to 21g of deionized water. The mixture was magnetically stirred at 800 rpm at 30°C for 50 minutes to form a homogeneous, transparent orange-yellow composite solution. Undissolved particles were removed by filtration through a 0.45 μm filter and set aside. The composite solution was transferred to a three-necked flask equipped with a reflux condenser. Under nitrogen, 10.8g of triglycidyl isocyanurate (TGIC) was slowly added to the flask, along with 0.2g of triethylamine catalyst, and the pH was adjusted to 9.0 using 5 wt% NaOH solution. The reaction was continued at 85°C for 6 hours to obtain a cross-linked product solution. After the product solution was cooled to 30°C, 32ml of anhydrous ethanol (≥99.5% purity) was slowly added to precipitate the product. The product was allowed to stand for 1 hour to completely precipitate, then filtered using a Buchner funnel and washed three times with an ethanol-water mixture to remove unreacted TGIC and catalyst. The mixture was dried in a vacuum drying oven at 50°C for 24 hours (vacuum pressure ≤ 0.1 MPa), crushed and passed through a 200-mesh sieve to obtain a light yellow to brown solid powder of a chrome-free tanning agent; the tanning agent powder was dissolved in water at an amount of 10% of the leather mass, the pH of the tanning solution was adjusted to 9.0 using a 10 wt% Na2CO3 solution, and the mixture was reacted with sheep acid hide at 45°C for 8 hours to obtain the finished leather.

[0029] The shrinkage temperature (Ts) of the tanned finished leather reaches 83°C, the thickening rate is 18%, the antibacterial rate (Staphylococcus aureus) is 98%, and the tear strength is increased by 50%.

[0030] Table 1 Performance comparison of chrome-free tanning agents and traditional chrome tanning agents in Examples 1-3

[0031] The performance of the chrome-free tanning agents of Examples 1-3 was compared with that of traditional chrome tanning agents, as shown in Table 1. It can be seen that the sericin-based chrome-free tanning agents represented by Examples 1-3 are superior to traditional chrome tanning agents in terms of comprehensive performance, environmental protection and safety, especially in terms of antibacterial and thickening capabilities.

[0032] Example 4 The preparation method of the functional sericin-based chrome-free tanning agent of the present invention is specifically carried out according to the following steps: Step 1: sericin powder, curcumin powder, and deionized water are mixed and magnetically stirred to form a uniform, transparent orange-yellow composite solution, which is then filtered through a 0.45 μm filter membrane to remove undissolved particles, thereby obtaining a mixed solution. The stirring temperature was 25 °C, the stirring rate was 500 rpm, and the stirring time was 30 min; The mass ratio of sericin to curcumin was 1:0.5; Step 2: Under nitrogen protection, slowly add triglycidyl isocyanurate (TGIC) to the mixed solution obtained in step 1, then add triethylamine catalyst dropwise, and adjust the pH to ‌8.5 using a 5 wt% NaOH solution, and perform condensation reflux stirring reaction to obtain a cross-linked product solution; The reaction temperature was 55°C, the reaction time was 3 hours, the stirring speed was 800 rpm, the molar ratio of sericin to TGIC was 1:0.5, the molar ratio of curcumin to TGIC was 1:0.3, and the amount of triethylamine used was 2% of the mass of sericin. Step 3: The reaction mixture from Step 2 is cooled to 25°C. Anhydrous ethanol (twice the volume of the reaction mixture) is slowly added to precipitate the product. The mixture is allowed to stand for one hour to allow the product to completely precipitate. The product is then filtered using suction. The filter cake is washed three times with a mixture of ethanol and water to remove unreacted TGIC and catalyst. The mixture is dried in a vacuum oven at 50°C for 12 hours and pulverized through a 200-mesh sieve to obtain a light yellow to brown solid powder of the chrome-free tanning agent.

[0033] Example 5 The preparation method of the functional sericin-based chrome-free tanning agent of the present invention is specifically carried out according to the following steps: Step 1: sericin powder, curcumin powder, and deionized water are mixed and magnetically stirred to form a uniform, transparent orange-yellow composite solution, which is then filtered through a 0.45 μm filter membrane to remove undissolved particles, thereby obtaining a mixed solution. The stirring temperature was 28 °C, the stirring rate was 600 rpm, and the stirring time was 40 min; The mass ratio of sericin to curcumin was 1:1; Step 2: Under nitrogen protection, slowly add triglycidyl isocyanurate to the mixed solution obtained in step 1, then dropwise add triethylamine catalyst, and adjust the pH to 9.0 using a 5 wt% NaOH solution, and perform condensation reflux stirring reaction to obtain a cross-linked product solution; The reaction temperature was 65°C, the reaction time was 5 h, and the stirring speed was 900 rpm. The molar ratio of sericin to TGIC is 1:0.5-1.2; The molar ratio of curcumin to TGIC was 1:0.8; the amount of triethylamine used was 4% of the mass of sericin protein; Step 3: The reaction solution obtained in Step 2 is cooled to 30°C. Anhydrous ethanol (twice the volume of the reaction solution) is slowly added to precipitate the product. The product is allowed to stand for 1 hour to allow complete precipitation. After that, it is filtered using suction. The filter cake is washed three times with a mixture of ethanol and water to remove unreacted TGIC and catalyst. The product is dried in a vacuum oven at 55°C for 20 hours and pulverized through a 200-mesh sieve to obtain a light yellow to brown solid powder of the chrome-free tanning agent.

[0034] Example 6 The preparation method of the functional sericin-based chrome-free tanning agent of the present invention is specifically carried out according to the following steps: Step 1: sericin powder, curcumin powder, and deionized water are mixed and magnetically stirred to form a uniform, transparent orange-yellow composite solution, which is then filtered through a 0.45 μm filter membrane to remove undissolved particles, thereby obtaining a mixed solution. The stirring temperature was 30 °C, the stirring rate was 800 rpm, and the stirring time was 60 min; The mass ratio of sericin to curcumin was 1:2; Step 2: Under nitrogen protection, slowly add triglycidyl isocyanurate to the mixed solution obtained in step 1, then dropwise add triethylamine catalyst, and adjust the pH to 9.0 using a 5 wt% NaOH solution, and perform condensation reflux stirring reaction to obtain a cross-linked product solution; The reaction temperature is 55°C~85°C, the reaction time is 3~6 hours, and the stirring speed is 800~1000 rpm; The molar ratio of sericin to TGIC was 1:1.2; The molar ratio of curcumin to TGIC was 1:1.2; The amount of triethylamine used is 8% of the mass of sericin protein; Step 3: The reaction mixture from Step 2 is cooled to 30°C. Anhydrous ethanol (3 times the volume of the reaction mixture) is slowly added to precipitate the product. The product is allowed to stand for 1 hour to allow complete precipitation. The product is then filtered and the filter cake is washed three times with a mixture of ethanol and water to remove unreacted TGIC and catalyst. The product is then dried in a vacuum drying oven at 60°C for 24 hours (vacuum pressure ≤ 0.1 MPa) and pulverized through a 200-mesh sieve to obtain a light yellow to brown solid powder of the chrome-free tanning agent.

Claims

1. A method for preparing a functional sericin-based chrome-free tanning agent, characterized in that: Please follow the steps below to implement it: Step 1, mixing sericin powder, curcumin powder and deionized water, performing magnetic stirring to form a composite solution, and filtering to remove undissolved particles to obtain a mixed solution; Step 2: Under nitrogen protection, slowly add triglycidyl isocyanurate to the mixed solution obtained in step 1, then dropwise add triethylamine catalyst, and adjust the pH to 8.5-9.0 with NaOH solution, and perform condensation reflux stirring reaction to obtain a cross-linked product solution; Step 3: precipitate the cross-linked product solution, let it stand, filter it, wash it, dry it, and sieve it to obtain a functional sericin-based chrome-free tanning agent.

2. The method for preparing a functional sericin-based chrome-free tanning agent according to claim 1, wherein: In step 1, the stirring temperature is 25° C. to 30° C., the stirring rate is 500 to 800 rpm, and the stirring time is 30 to 60 min.

3. The method for preparing a functional sericin-based chrome-free tanning agent according to claim 1, wherein: In step 1, the mass ratio of sericin to curcumin is 1:0.5-2.

4. The method for preparing a functional sericin-based chrome-free tanning agent according to claim 1, wherein: In step 2, the reaction temperature is 55° C. to 85° C., the reaction time is 3 to 6 hours, and the stirring speed is 800 to 1000 rpm.

5. The method for preparing a functional sericin-based chrome-free tanning agent according to claim 1, wherein: In step 2, the molar ratio of sericin to TGIC is 1:0.5-1.2; The molar ratio of curcumin to TGIC is 1:0.3~1.2; the amount of triethylamine used is 2%~8% of the mass of sericin protein.

6. The method for preparing a functional sericin-based chrome-free tanning agent according to claim 1, wherein: In the step 3, specifically: The cross-linked product solution obtained in step 2 is cooled to 25°C-30°C, and anhydrous ethanol in an amount 2-3 times the volume of the reaction solution is slowly added to precipitate the product. The product is allowed to stand for complete precipitation and then filtered. The filter cake is washed three times with a mixture of ethanol and water, dried in a vacuum drying oven at 50°C-60°C for 12-24 hours, and crushed through a 200-mesh sieve to obtain a functional sericin-based chrome-free tanning agent.

7. A chrome-free tanning agent prepared by the method for preparing a functional sericin-based chrome-free tanning agent according to any one of claims 1 to 6.

8. Use of the functional sericin-based chrome-free tanning agent according to any one of claims 1 to 6 in leather tanning.

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