A method for high absorption chrome tanning using cross-linking enzyme preparation

Abstract

The present application belongs to the field of leather industry production, and particularly relates to a method for high absorption chrome tanning by using cross-linking enzyme preparation. The method comprises the following steps: water immersion, unhairing and liming, deliming, softening, enzyme-assisted tanning, and acid immersion tanning. The enzyme-assisted tanning is assisted by using cross-linking enzyme preparation. The cross-linking enzyme preparation is not used in combination with the hydrolytic enzyme in the softening step. The cross-linking enzyme comprises glutamine transaminase (TG enzyme). The comprehensive activity of the cross-linking enzyme is controlled to be 1-30 U / ml in the application process, and the activity of the TG enzyme is controlled to be 1-20 U / ml. The process in the present application meets the environmental protection requirements. Firstly, the tanning agent absorption rate in the tanning process is successfully improved, and the waste discharge amount in the tanning process is reduced. Secondly, the cleaner cross-linking enzyme preparation is successfully used to replace the chemical auxiliary agent to improve the tanning agent absorption rate. Thirdly, the process operation is simplified.

Description

Technical Field

[0001] This invention belongs to the field of leather manufacturing, specifically relating to a method for high-absorption chrome tanning using cross-linking enzyme preparations. Background Technology

[0002] Tanning is a crucial process in leather tanning, transforming raw hides lacking durability into stable leather. Currently, chrome tanning is the dominant method in the market, accounting for over 80% of the market share. However, traditional tanning agents have insufficient absorption rates during tanning; for example, chrome tanning typically has an absorption rate of only 60%-70%, thus increasing environmental pollution and causing significant resource waste. To address these issues, tanning auxiliaries are often added during the combined pickling process to improve the absorption rate of tanning agents. This is achieved by treating the collagen fiber layer of the hide before tanning, thereby enhancing the penetration and binding of tanning agents. High-absorption chrome tanning auxiliaries include chemical auxiliaries such as aldehydes, acrylics, hyperbranched polymers, and nanocomposites. These auxiliaries need to be easy to operate and require minimal changes to existing processes to be suitable for practical application in production. Traditional high-absorption tanning auxiliaries are mainly chemical auxiliaries. While biological auxiliaries offer better cleaning properties compared to chemical auxiliaries, they have not yet been widely used in tanning. Because the activity of enzyme preparations is easily affected by tanning agents during the tanning process, leading to loss of activity and difficulty in exerting their effects, it is necessary to consider at what step the enzyme preparation should be added to fully exert its function. This invention proposes using cross-linking enzyme preparations for tanning assistance, adding them in conjunction with the pickling process before tanning, thereby improving the problems of insufficient absorption and low utilization efficiency of chromium tanning agents in traditional tanning methods. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method for high-absorption chrome tanning using cross-linking enzyme preparations. This invention first proposes using cross-linking enzymes to assist tanning. By pre-acting on the functional groups in the skin proteins, the cross-linking enzymes promote the binding of the chrome tanning agent to the coordination sites of skin collagen during the tanning process, thereby improving the absorption rate of the chrome tanning agent. This method is applicable to both chrome-only tanning and chrome-combined tanning methods.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] A method for high-absorption chrome tanning using cross-linking enzyme preparations includes the following steps:

[0006] The process includes soaking in water, hair removal, liming, deliming, softening, enzyme-assisted tanning, and acid tanning; the enzyme-assisted tanning uses a cross-linking enzyme preparation; the cross-linking enzyme preparation is not mixed with the hydrolytic enzyme in the softening step; the cross-linking enzyme includes transglutaminase (TG enzyme); the overall activity of the cross-linking enzyme is controlled at 1-30 U / ml during application, of which the activity of TG enzyme is controlled at 1-20 U / ml.

[0007] Preferably, the biological enzyme includes transglutaminase (TG enzyme) and tyrosinase.

[0008] Preferably, during the softening to enzymatic tanning process, the solution is changed, the pH of the solution is controlled at 7-8, and multiple water washes are avoided to prevent the temperature drop caused by water washing from affecting the enzyme's activity.

[0009] Preferably, during the process from enzyme-assisted tanning to acid soaking and softening, the solution can be changed or water can be added directly.

[0010] Preferably, during the enzyme-assisted tanning process, the raw hide is pretreated for 2-12 hours at a low liquor ratio (0.5-1), depending on the type of raw hide and the requirements of the finished leather. The temperature is 30-38℃, and the mechanical action is weak or moderate, not too strong, allowing the enzyme to slowly and gently penetrate the raw hide before reacting. The type of raw hide and the requirements of the finished leather have a significant impact on the control conditions of the enzyme-assisted tanning.

[0011] The enzyme-assisted tanning method includes the following steps:

[0012] The softened raw hides are added to water at a concentration of 50-100% of their weight, and the temperature is controlled at 30-38°C with a pH of 8. An aqueous solution of cross-linking enzyme is also added. The drum is rotated at low speed for 2-12 hours, and then left to stand overnight. The resulting raw hides can be used for the next step of pickling.

[0013] More preferably, the method for high-absorption tanning using cross-linking enzyme preparations includes the following steps:

[0014] (1) After soaking the raw hide in water, removing hair, soaking in ash, and removing ash, add water of 120% of the raw hide mass to the drum and add 0.15% softening enzyme. Control the temperature at 36℃ and the pH at 8.5, and react for 1 hour.

[0015] (2) Add water accounting for 50-100% of the softened raw hide mass to the drum described in step (1), control the temperature at 30-38℃ and the pH at 8; and add an aqueous solution of cross-linking enzyme. Rotate the drum at low speed for 2-12 hours, and then stop the drum overnight.

[0016] (3) Add water of 30-50% of the weight of softened raw hide to the drum described in step (2), add sodium chloride of 7% of the weight of raw hide at 20°C, rotate for 30 min, add industrial formic acid of 0.5% of the weight of raw hide, rotate for 30 min, add industrial sulfuric acid of 0.3-0.5% of the weight of raw hide, react for 4 h, and check that the pH is 2.8;

[0017] (4) Add 3-6% chrome tanning agent and react for 1.5-6 hours. Add 1-1.5% sodium bicarbonate of softened raw hide by weight in three portions, with an interval of 20 minutes. Then continue to rotate for 1-3 hours and check that the pH is 3.8-4.2.

[0018] (5) Add water accounting for 50% of the weight of softened raw hide, control the temperature at 40℃, stop the drum overnight, and rotate it for 15-60 minutes the next day; or continue the combined tanning, add tannin accounting for 0-40% of the weight of raw hide, and add it into the drum in three batches.

[0019] More preferably, the tannin in step (5) is added to the drum in three parts. The first part is 10% tannin added at 25°C and rotated for 1 hour, with a pH of 4.1. The second part is 10% tannin added at 29°C and rotated for 3 hours, with a pH of 4.1. The third part is the remaining 20% ​​tannin added at 35°C and rotated for 4 hours, with a pH of 4.1. Then, the drum is processed according to conventional procedures.

[0020] The cross-linking enzymes in this invention are characterized by: ① having the ability to cross-link functional groups in proteins, such as amino, carboxyl, acyl, and thiol groups, including transglutaminase (TG enzyme) and oxidases including tyrosinase; ② being able to use TG enzyme alone or in combination with other cross-linking enzymes, but must contain TG enzyme; ③ having a total cross-linking enzyme activity controlled at 1-30 U / ml during application, with the TG enzyme activity controlled at 1-20 U / ml.

[0021] The TG enzyme activity in this invention was determined by the following method:

[0022] (1) Prepare reagent A: Weigh 1.000g N-benzyloxycarbonyl-L-glutamylglycine, 0.695g hydroxylamine hydrochloride, and 0.307g reduced glutathione (GSH), dissolve them in Tris-HCl buffer (pH 6.0, 0.2mol / L), adjust the pH to 6.00±0.05 with 1mol / L sodium hydroxide, and bring the volume to 100mL with Tris-HCl buffer.

[0023] (2) Weigh 0.1g of the enzyme to be tested, dissolve it in Tris-HCl buffer, transfer it to a volumetric flask and make up to volume. Control the enzyme activity of the solution after volume adjustment to be between 0.17U / mL and 0.23U / mL, which is the test solution.

[0024] (3) Preparation of Termination Reagent B: ① Dilute 36%–38% hydrochloric acid with water at a volume ratio of 1:3. ② Weigh 12.00g of trichloroacetic acid and dissolve it in 80mL of water, then bring the volume to 100mL. ③ Weigh 12.00g of trichloroacetic acid and dissolve it in 80mL of water, then bring the volume to 100mL. Mix ①, ②, and ③ at a volume ratio of 1:1:1 to obtain the termination reagent. The termination reagent must be prepared and used immediately.

[0025] (4) Mix 1 mL of reagent A with 0.4 mL of the test solution, incubate in a water bath at 37.0℃±0.5℃ for 10 min, and add 0.4 mL of reagent B to terminate the reaction. In another test tube, add the test solution, heat in a water bath at 95℃~100℃ for 10 min, and then centrifuge at 5000 r / min for 10 min. Take 0.4 mL of the supernatant, incubate in a water bath at 37℃ for 10 min, and add 0.4 mL of reagent B to terminate the reaction, serving as a blank control. Measure the absorbance of the sample test solution and the blank solution at 525 nm using a 1 cm quartz cuvette.

[0026] Enzyme activity definition: The amount of enzyme required to catalyze the formation of 1.0 μmol of hydroxamic acid salt from N-benzyloxycarbonyl-L-glutamylglycine (CBZ-Gln-Gly, CAS: 6610-42-0) and hydroxylamine per minute at 37℃ and pH 6.0 is 1 unit, and the unit is U.

[0027] This invention utilizes a bio-enzyme preparation with cross-linking protein capabilities for pretreatment before tanning, which can improve the absorption rate of tanning agents during the tanning process. This method can effectively reduce waste emissions in leather tanning, achieving cleaner production. This method does not significantly alter existing leather tanning processes, making it easy to apply in actual production, and can increase the tanning agent absorption rate by 5%-15%.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The process in this invention meets environmental protection requirements, and its beneficial effects include the following three aspects: ① It successfully improves the absorption rate of tanning agents during the tanning process and reduces the amount of waste discharged during the tanning process; ② It successfully uses cleaner cross-linking enzyme preparations to replace chemical auxiliaries to improve the absorption rate of tanning agents; ③ The process operation is simplified. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer with the description. However, the embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0031] Table 1 Partial flow chart of high-absorption tanning process using bio-enzyme preparations.

[0032]

[0033] Note: ① After softening, wash with warm water for 10 minutes, then change the solution and apply enzyme-assisted tanning.

[0034] After the enzyme-assisted tanning step, the solution is added directly for pickling and tanning.

[0035] ②The raw hides are weighed, and the amount of additives added during the softening process is based on the weight of the raw hides;

[0036] ③ The raw hides are weighed during the softening and liquid-changing process. The amount of enzyme-assisted tanning and acid-tanning additives added is based on the weight of the softened hides.

[0037] Example 1

[0038] A method for high-absorption chrome tanning using cross-linking enzyme preparations involves soaking raw hides in water, dehairing, liming, deliming, softening, enzyme-assisted tanning, pickling, and tanning. The process flow for softening, enzyme-assisted tanning, pickling, and tanning is shown in Table 1. In this embodiment, the enzyme-assisted tanning, pickling, and tanning processes are as follows:

[0039] (1) Enzymatic tanning: The drum is run at low speed. Water accounting for 60% of the softened hide weight is added. The temperature is 35℃ and the pH is 8. TG enzyme dissolved in 45℃ water is added from the feed port. The activity is 8U / ml. The drum is run for 2 hours and then stopped overnight.

[0040] (2) Acid soaking: Add water accounting for 40% of the weight of the skin, and the temperature is 20℃; add sodium chloride accounting for 7% of the weight of the skin, rotate for 30 minutes, add formic acid accounting for 0.5% of the weight of the skin, rotate for 30 minutes, add sulfuric acid accounting for 0.5% of the weight of the skin, react for 4 hours, and check that the pH is 2.8.

[0041] (3) Add 5% chromium tanning agent by weight of the hide, react for 3 hours, add 1.2% sodium bicarbonate by weight of the hide in three portions with an interval of 20 minutes, and then continue to rotate for 2 hours. Check that the pH is 3.8.

[0042] (4) Add water accounting for 50% of the skin weight, temperature 40℃, stop drumming overnight for 12 hours, and turn it for 30 minutes the next morning.

[0043] The results of the tanned leather properties are shown in Table 2.

[0044] Comparative Example 1

[0045] A tanning method involves sequentially subjecting raw hides to soaking in water, hair removal, liming, deliming, softening, pickling, and tanning processes. The pickling and tanning steps are as follows:

[0046] (1) Acid soaking: Based on the weight of the softened raw hide, add water accounting for 100% of the hide weight: the temperature is 20℃; add sodium chloride accounting for 7% of the hide weight, rotate for 30 min, add formic acid accounting for 0.5% of the hide weight, rotate for 30 min, add sulfuric acid accounting for 0.5% of the hide weight, react for 4 h, and check that the pH is 2.8.

[0047] (2) Tanning: First, add 5% of the weight of the hide with chrome tanning agent and react for 3 hours. Then add 1.2% of the weight of the hide with baking soda in three portions, with an interval of 20 minutes. Then continue to rotate for 2 hours and check that the pH is 3.8.

[0048] (3) Then, add water accounting for 50% of the leather weight, keep the temperature at 40℃, stop the drum overnight, and turn it for 30 minutes the next morning. The obtained sample is the blank control sample for chrome tanning.

[0049] The results of the tanned leather properties are shown in Table 2.

[0050] Compared with Comparative Example 1, Example 1 shows that the chromium content in the leather increased significantly, while the chromium content in the waste chromium solution decreased, thus effectively improving the chromium absorption rate without reducing the leather performance.

[0051] Example 2

[0052] A method for high-absorption chrome tanning using cross-linking enzyme preparations involves the following steps for raw hides: soaking, hair removal and liming, deliming, softening, enzyme-assisted tanning, pickling, and tanning. The softening, enzyme-assisted tanning, and pickling processes are shown in Table 1. The enzyme-assisted tanning, pickling, and tanning steps are as follows:

[0053] Enzymatic tanning: The drum is run at low speed. Water is added, which accounts for 80% of the weight of the softened hide. The temperature is 35℃ and the pH is 8. The compound enzyme (containing TG enzyme and tyrosinase) is dissolved in 45℃ water and added from the feed port. The total activity is 25U / ml, of which the TG enzyme activity is 20U / ml and the tyrosinase activity is 5U / ml. The drum is rotated for 6 hours.

[0054] Acid immersion: At 25°C, add sodium chloride at 7% of the softened pelt weight, rotate for 30 minutes, add formic acid at 0.5% of the softened pelt weight, rotate for 30 minutes, add sulfuric acid at 0.5% of the softened pelt weight, react for 4 hours, and check that the pH is 2.8.

[0055] Tanning: Add 6% chrome tanning agent by weight of the hide and react for 2 hours. Add 1.2% sodium bicarbonate by weight of the hide in three portions, 20 minutes apart. Then continue to rotate for 2 hours. Check that the pH is 3.8. Add hot water to make the internal temperature reach 40°C. Stop the drum and let it sit overnight. Rotate for 15 minutes the next morning.

[0056] The results of the tanned hides and furs are shown in Table 2.

[0057] Comparative Example 2

[0058] A chrome tanning method involves sequentially subjecting raw hides to soaking, hair removal, liming, deliming, softening, pickling, and tanning processes. The pickling and tanning steps are as follows:

[0059] Acid soaking: Run the drum at low speed, add water accounting for 80% of the softened tare weight; the temperature is 25℃, add sodium chloride accounting for 7% of the tare weight, rotate for 30 minutes, add formic acid accounting for 0.5% of the tare weight, rotate for 30 minutes, add sulfuric acid accounting for 0.5% of the tare weight, react for 4 hours, and check that the pH is 2.8.

[0060] Tanning: Add 6% chrome tanning agent by weight of softened hide, react for 2 hours, add 1.2% sodium bicarbonate by weight of hide in three portions, 20 minutes apart, then continue to rotate for 2 hours. Check that the pH is 3.8, add hot water to make the internal temperature reach 40℃, stop the drum and let it sit overnight, then rotate for 15 minutes the next morning.

[0061] The results of the tanned leather properties are shown in Table 2.

[0062] Compared with Comparative Example 2, Example 2 shows that the chromium content in the leather increased significantly, while the chromium content in the waste chromium solution decreased, thus effectively improving the chromium absorption rate without reducing the leather performance.

[0063] Example 3

[0064] A method for high-absorption chrome tanning using cross-linking enzyme preparations involves the following steps for raw hides: soaking in water, hair removal and liming, deliming, softening, enzyme-assisted tanning, pickling, and tanning. The softening step is shown in Table 1. The enzyme-assisted tanning, pickling, and tanning steps are as follows:

[0065] Enzyme-assisted tanning: Run the drum at low speed, add water accounting for 60% of the softened hide weight; temperature is 35℃; pH is 8; add TG enzyme dissolved in 45℃ water through the feed port, with an activity of 10U / ml, rotate for 2 hours, then stop the drum and let it sit overnight.

[0066] Acid soaking: After changing the solution, add water at 100% of the softened tare weight, and the temperature is 25℃; add sodium chloride at 7% of the tare weight, rotate for 30 minutes, add formic acid at 0.5% of the softened tare weight, rotate for 30 minutes, add sulfuric acid at 0.3% of the softened tare weight, react for 3 hours, and check that the pH is 2.8.

[0067] Tanning: First, add 3% of the softened hide weight of chrome tanning agent and react for 1.5 hours. Then, add 1% of the softened hide weight of baking soda in three portions, with an interval of 20 minutes between each addition. Then, continue to rotate for 1 hour and check that the pH is 4.1. Continue to rotate for another 4 hours.

[0068] Then add 40% of the softened tannin powder into the drum in three batches: the first batch of 10% tannin is added at 25°C and the drum is rotated for 1 hour, resulting in a pH of 4.1; the second batch of 10% tannin is added at 29°C and the drum is rotated for 3 hours, resulting in a pH of 4.1; the third batch of the remaining 20% ​​tannin is added at 35°C and the drum is rotated for 4 hours, resulting in a pH of 4.1. Then the drum is processed according to the conventional process.

[0069] Table 2 Evaluation of Leather Performance in Examples and Comparative Examples

[0070]

Claims

1. A method for high-absorption chrome tanning using a cross-linking enzyme preparation, characterized in that, Includes the following steps: The process includes soaking in water, hair removal, liming, deliming, softening, enzymatic tanning, pickling, and tanning; the enzymatic tanning is carried out using a cross-linking enzyme preparation; the cross-linking enzyme preparation is not mixed with the hydrolytic enzyme in the softening step; the cross-linking enzyme includes transglutaminase; the overall activity of the cross-linking enzyme is controlled at 1-30 U / ml during application, wherein the activity of transglutaminase is controlled at 1-20 U / ml.

2. The method for high-absorption chrome tanning using a cross-linking enzyme preparation according to claim 1, characterized in that, The cross-linking enzymes include transglutaminase and tyrosinase.

3. The method for high-absorption chrome tanning using a cross-linking enzyme preparation according to claim 1, characterized in that, During the softening to enzymatic tanning process, the solution should be changed frequently, and the pH of the solution should be controlled at 7-8 to avoid excessive washing, which would reduce enzyme activity.

4. The method for high-absorption chrome tanning using a cross-linking enzyme preparation according to claim 1, characterized in that, During the process from enzyme-assisted tanning to acid softening, the solution can be changed or water can be added directly.

5. A method for high-absorption chrome tanning using a cross-linking enzyme preparation according to claim 1, characterized in that, During the enzyme-assisted tanning process, the pretreatment is carried out at a liquor ratio of 0.5-1 and a temperature of 30-38℃ for 2-12 hours.

6. The method for high-absorption chrome tanning using a cross-linking enzyme preparation according to claim 5, characterized in that, The enzyme-assisted tanning method includes the following steps: The softened raw hides are added to water at a concentration of 50-100% of their weight, and the temperature is controlled at 30-38°C with a pH of 8. An aqueous solution of cross-linking enzyme is also added. The drum is rotated at low speed for 2-12 hours, and then left to stand overnight. The resulting raw hides are used for the next step of pickling.

7. The method for high-absorption chrome tanning using a cross-linking enzyme preparation according to claim 6, characterized in that, The method for high-absorption tanning using cross-linking enzyme preparations includes the following steps: (1) After soaking the raw hide in water, removing hair, soaking in ash, and removing ash, add water of 120% of the raw hide mass to the drum and add 0.15% softening enzyme, which is a hydrolytic enzyme. Control the temperature at 36°C and the pH at 8.5, and react for 1 hour. (2) Add water accounting for 50-100% of the softened raw hide mass to the drum described in step (1), control the temperature at 30-38℃ and the pH at 8; and add an aqueous solution of cross-linking enzyme. Rotate the drum at low speed for 2-12 hours and then stop the drum overnight. (3) Add water of 30-50% of the weight of softened raw hide to the drum described in step (2), add sodium chloride of 7% of the weight of raw hide at 20°C, rotate for 30 min, add industrial formic acid of 0.5% of the weight of raw hide, rotate for 30 min, add industrial sulfuric acid of 0.3-0.5% of the weight of raw hide, react for 4 h, and check that the pH is 2.8; (4) Add 3-6% chromium tanning agent, react for 1.5-6 h, add 1-1.5% sodium bicarbonate of softened raw hide by weight in three portions, 20 min apart, and then continue to rotate for 1-3 h. Check the pH to be 3.8-4.

2. (5) Add water accounting for 50% of the weight of softened raw hide, control the temperature at 40℃, stop the drum overnight, and rotate it for 15~60 minutes the next day; or continue the combined tanning, add tannin accounting for 0-40% of the weight of raw hide, and add it into the drum in three batches.

8. A method for high-absorption chrome tanning using a cross-linking enzyme preparation according to claim 7, characterized in that, The tannin in step (5) is added to the drum in three parts. The first tannin is added at 10% temperature at 25°C and rotated for 1 hour, with a pH of 4.

1. The second tannin is added at 10% temperature at 29°C and rotated for 3 hours, with a pH of 4.

1. The third tannin is added at the remaining 20% ​​temperature at 35°C and rotated for 4 hours, with a pH of 4.

1. Then it is processed according to the conventional process.

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