An epoxy-modified vegetable tannin chromium-free tanning agent and its preparation method

Abstract

The present invention belongs to the technical field of leather tanning, and particularly relates to an epoxy-modified vegetable tannin chromium-free tanning agent and a preparation method thereof. The epoxy-modified vegetable tannin chromium-free tanning agent is mainly prepared from vegetable tannin, epoxide and biological enzyme. The method first modifies the vegetable tannin with biological enzyme, and then moderately grafts and modifies the vegetable tannin catalyzed and oxidized by biological enzyme with epoxide through etherification reaction. The obtained epoxy-modified vegetable tannin chromium-free tanning agent is used for chromium-free tanning of leather, and generates multi-point cross-linking with raw hide collagen fiber network through quinone structure, phenolic hydroxyl group and epoxy group, etc., further improving the cross-linking degree of the chromium-free tanning agent and collagen fiber, increasing the shrinkage temperature, wet heat resistance stability and mechanical properties of the tanned leather, and simplifying the use process at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of leather tanning, and particularly relates to an epoxy-modified vegetable tannin chromium-free tanning agent and a preparation method thereof. Background Art

[0002] Tanning is a very important process in leather making. Due to traditional habits, production costs, leather performance, and leather diversity, chrome tanning is currently the most important tanning method. During chrome tanning, due to the incomplete utilization of chromium, the chromium content in the waste liquid after chrome tanning greatly exceeds the national standard, and a large amount of chromium-containing solid waste is generated, bringing great pressure to the environment. In recent years, with the increasing environmental protection requirements and the change of consumption concepts of people, it is very necessary to develop a new type of environmentally friendly tanning method to replace chrome tanning. Among them, tannins and epoxides, as one of the research directions of environmentally friendly chromium-free tanning agents, have been continuously concerned and studied.

[0003] CN 108285937 A discloses a method for applying bio-enzyme-catalyzed vegetable tannins and its application in leather tanning, particularly involving that bio-enzymes greatly improve the multi-point covalent cross-linking between vegetable tannins and raw hide collagen fiber networks, and a rapid tanning system is applied to the leather tanning process. In this tanning step, laccase, polyphenol oxidase, and horseradish peroxidase are used to catalyze the multi-point covalent cross-linking between vegetable tannins and raw hide collagen fiber networks, improving the covalent cross-linking degree between vegetable tannins and collagen fibers, thereby improving the heat and humidity resistance stability and other physical and mechanical properties of the leather. However, the shrinkage temperature of the tanned leather is only about 80°C.

[0004] The tannin components of vegetable tannins are mostly phenolic substances. Under the catalytic oxidation of bio-enzymes, these phenolic substances are oxidized to quinone structures and then undergo Schiff base reaction / Michael addition reaction with the active amino groups (-NH 2 ) of the raw hide collagen fiber network, so that the polyphenol tannin components of vegetable tannins form strong covalent cross-links between the raw hide collagen fiber networks. At the same time, the unoxidized phenolic hydroxyl structures can continue to bind to the active groups of collagen fibers in the form of hydrogen bonds, greatly improving the heat and humidity resistance stability of vegetable tanned leather and enhancing the physical and chemical properties such as physical and mechanical properties.

[0005] Gao Jing et al. studied the combined tanning method of epoxides and vegetable tanning agents. Under the conditions of pH 4.5 and 50 °C, the combined tanning process of condensed tannins and epoxides was used. After preliminary tanning with condensed tannins, epoxides were used, and the shrinkage temperature of the leather reached above 90 °C (Gao Jing, Li Jing, Liao Xuepin, Shi Bi. Research on the combined tanning method of vegetable tanning agent - epoxy resin. China Leather, 2012, 03: 8 - 12). The epoxy groups mainly react with the carboxyl, hydroxyl, amino groups on the collagen side chain and the phenolic hydroxyl groups of tannins. This scheme improves the shrinkage temperature of tanning, but the vegetable tannins and epoxides need to be added step by step for tanning, and the process is slightly complicated and time-consuming.

[0006] The patent application with the patent application number CN201911425500.9 mainly uses tannin-based polyether polyol, ECH, and solid caustic soda to react to obtain tannin-based epoxy resin under the action of a phase transfer catalyst and solid caustic soda. With epoxy as the main body, tannin-based polyether polyol is modified to obtain tannin-based epoxy resin, which has high reaction activity. When added to E-51 epoxy resin, it can significantly improve the flexibility of the cured product of E-51 epoxy resin. The excessive ECH reacts with the tannin-based polyether polyol, and the natural phenolic hydroxyl groups of tannins are reacted off, which is not suitable for leather tanning. Summary of the Invention

[0007] Based on the above technical background, the present invention provides an epoxy-modified vegetable tannin chromium-free tanning agent and its preparation method. The epoxy-modified vegetable tannin chromium-free tanning agent is mainly prepared from 50 - 60 parts by weight of vegetable tannin, 5 - 30 parts by weight of epoxide, and 50 - 150 U / g of vegetable tannin of biological enzyme. The epoxy-modified vegetable tannin chromium-free tanning agent does not contain chromium elements, will not produce chromium-containing solid waste, is environmentally friendly, and at the same time, the shrinkage temperature, wet heat resistance stability, and mechanical properties of the leather tanned with this chromium-free tanning agent are effectively improved, and the preparation process of this chromium-free tanning agent is simple and the preparation time is shortened.

[0008] The first aspect of the present invention lies in providing an epoxy-modified vegetable tannin chromium-free tanning agent, and the epoxy-modified vegetable tannin chromium-free tanning agent is mainly prepared from the following components:

[0009] Vegetable tannin 40 - 60 parts by weight;

[0010] Epoxide 5 - 30 parts by weight;

[0011] Biological enzyme 0.8 - 1.2 parts by weight.

[0012] Preferably, the epoxy-modified vegetable tannin chromium-free tanning agent is mainly prepared from the following components:

[0013] Vegetable tannin 50 parts by weight;

[0014] Epoxide 10 - 25 parts by weight;

[0015] 1 part by weight of bio-enzyme.

[0016] Preferably, the epoxide is selected from one or more of epichlorohydrin, ethylene oxide, and propylene oxide;

[0017] The bio-enzyme is selected from one or more of laccase, xylanase, and polyphenol oxidase.

[0018] More preferably, the epoxide is epichlorohydrin, and the bio-enzyme is laccase.

[0019] The second aspect of the present invention lies in providing a method for preparing the chromium-free tanning agent of epoxy-modified vegetable tannin extract described in the first aspect of the present invention. The method includes the following steps:

[0020] Step 1: Place the vegetable tannin extract in water and stir evenly, then add the bio-enzyme for reaction to obtain catalytically oxidized tannin extract.

[0021] Step 2: Add an alkaline solution to the catalytically oxidized tannin extract and stir evenly, then add the epoxide, raise the temperature and carry out an etherification reaction. After the reaction is completed, cool, adjust the pH to neutral, and freeze-dry to obtain the chromium-free tanning agent of epoxy-modified vegetable tannin extract.

[0022] Preferably, in Step 1, the vegetable tannin extract is stirred in water for 20 - 45 min.

[0023] After adding the bio-enzyme, adjust the pH of the reaction system to 4 - 5, and introduce air throughout the reaction process;

[0024] The reaction temperature is 20 - 30 °C, and the reaction time is 5 - 10 h.

[0025] Preferably, in Step 2, the alkaline solution is a sodium hydroxide solution with a mass fraction of 10%, add the alkaline solution to adjust the pH to 9 - 11, and stir for 20 - 40 min.

[0026] The etherification reaction temperature is 55 - 70 °C, and the etherification reaction time is 2 - 7 h;

[0027] Add an alkaline solution during the etherification reaction to control the pH of the etherification reaction system to 10.

[0028] After the reaction is completed, cool to 25 °C, adjust the pH to neutral with hydrochloric acid, and finally carry out freeze-drying.

[0029] The beneficial effects of the present invention:

[0030] (1) For the epoxy-modified vegetable tannin of the present invention, the vegetable tannin is first modified by bio-enzyme, and then the epoxide is used to moderately graft-modify the vegetable tannin catalyzed and oxidized by bio-enzyme through etherification reaction, so that the hydroxyl groups undergo moderate etherification reaction, and the epoxy groups are grafted onto the vegetable tannin catalyzed and oxidized by laccase. Through multiple-point crosslinking with the raw hide collagen fiber network by quinone structure, phenolic hydroxyl group and epoxy group, etc., the crosslinking degree between the chromium-free tanning agent and the collagen fiber is further improved, thereby improving the shrinkage temperature, wet heat stability and other physical and mechanical properties of the leather. For example, the tensile strength, elongation at break and tearing force of the tanned leather are also significantly improved.

[0031] (2) The chromium-free tanning agent of the epoxy-modified vegetable tannin of the present invention does not contain chromium element and will not produce chromium-containing solid waste, which is environmentally friendly. In addition, the preparation method of the chromium-free tanning agent of the epoxy-modified vegetable tannin is simple, the preparation time is short, and the preparation efficiency is high. Brief Description of the Drawings

[0032] Figure 1 Showing a photo of the leather tanned with the chromium-free tanning agent of the epoxy-modified vegetable tannin described in Example 2 of the present invention. Detailed Description of the Invention

[0033] The present invention will be described in detail below, and the features and advantages of the present invention will become clearer and more definite with these descriptions.

[0034] The first aspect of the present invention is to provide a chromium-free tanning agent of epoxy-modified vegetable tannin, and the chromium-free tanning agent of epoxy-modified vegetable tannin is mainly prepared from the following components:

[0035] Vegetable tannin 40-60 parts by weight;

[0036] Epoxide 5-30 parts by weight;

[0037] Bio-enzyme 0.8-1.2 parts by weight.

[0038] Preferably, the chromium-free tanning agent of the epoxy-modified vegetable tannin is mainly prepared from the following components:

[0039] Vegetable tannin 50 parts by weight;

[0040] Epoxide 10-25 parts by weight;

[0041] Bio-enzyme 1 part by weight.

[0042] The epoxide is selected from one or more of epichlorohydrin, ethylene oxide and propylene oxide, and preferably epichlorohydrin.

[0043] The bio-enzyme is selected from one or more of laccase, xylanase and polyphenol oxidase, and preferably laccase.

[0044] The second aspect of the present invention lies in providing a method for preparing the chromium-free tanning agent of epoxy-modified vegetable tannin described in the first aspect of the present invention. The method comprises the following steps:

[0045] Step 1: Place the vegetable tannin in water, stir evenly, and then add a biological enzyme for reaction to obtain catalytically oxidized tannin.

[0046] Step 2: Add an alkaline solution to the catalytically oxidized tannin, stir evenly, then add an epoxide, raise the temperature and carry out an etherification reaction. After the reaction is completed, cool, adjust the pH to neutral, and freeze-dry to obtain the chromium-free tanning agent of epoxy-modified vegetable tannin.

[0047] The above steps are specifically described below.

[0048] In Step 1, the vegetable tannin is placed in water and stirred for 20 - 45 min, preferably 30 min.

[0049] After adding the biological enzyme, adjust the pH of the reaction system to 4 - 5, preferably 4.5. Air is introduced throughout the reaction process.

[0050] The reaction temperature is 20 - 30 °C, preferably 25 °C.

[0051] The reaction time is 5 - 10 h, preferably 6 h.

[0052] In Step 2, the alkaline solution is sodium hydroxide or potassium hydroxide solution, preferably 10% sodium hydroxide solution by mass fraction.

[0053] Add the alkaline solution to adjust the pH to 9 - 11, and stir for 20 - 40 min, preferably adjust the pH to 10 and stir for 30 min.

[0054] The etherification reaction temperature is 55 - 70 °C, preferably 60 °C.

[0055] The etherification reaction time is 2 - 7 h, preferably 3 - 6 h.

[0056] Add an alkaline solution during the etherification reaction to control the pH of the etherification reaction system to 10.

[0057] After the reaction is completed, cool to 25 °C, adjust the pH to neutral with hydrochloric acid, and finally carry out freeze-drying to obtain the chromium-free tanning agent of epoxy-modified vegetable tannin.

[0058] Examples

[0059] The present invention is further illustrated by the following specific examples. These examples are only for illustrating the present invention and are not used to limit the scope of the present invention.

[0060] The raw materials used in the embodiments of the present invention are all commercially available.

[0061] Example 1

[0062] Put 50 parts of vegetable tannin extract into 100 parts of water, stir for 60 min, then add laccase with a dosage of 1 part (100 U / g of vegetable tannin extract), adjust the temperature to 25 °C, adjust the pH to 4.5 with hydrochloric acid, and react for 6 h. Slowly introduce air throughout the process to obtain catalytically oxidized tannin extract.

[0063] Add 10% sodium hydroxide solution to the catalytically oxidized tannin extract, adjust the pH to 10.0, stir for 30 min, then add 10 parts of epichlorohydrin, raise the temperature to 60 °C, dropwise add 10% sodium hydroxide solution during the etherification reaction to control the pH at 10.0, carry out the etherification reaction for 3 h, then cool to 25 °C, adjust the pH to 7.0 with hydrochloric acid, and then freeze-dry to obtain a chromium-free tanning agent of epoxy-modified vegetable tannin extract.

[0064] Example 2

[0065] Put 50 parts of vegetable tannin extract into 100 parts of water, stir for 60 min, then add laccase with a dosage of 1 part (100 U / g of vegetable tannin extract), adjust the temperature to 25 °C, adjust the pH to 4.5 with hydrochloric acid, and react for 6 h. Slowly introduce air throughout the process to obtain catalytically oxidized tannin extract.

[0066] Add 10% sodium hydroxide solution to the catalytically oxidized tannin extract, adjust the pH to 10.0, stir for 30 min, then add 15 parts of epichlorohydrin, raise the temperature to 60 °C, dropwise add 10% sodium hydroxide solution during the etherification reaction to control the pH at 10.0, carry out the etherification reaction for 4 h, then cool to 25 °C, adjust the pH to 7.0 with hydrochloric acid, and then freeze-dry to obtain a chromium-free tanning agent of epoxy-modified vegetable tannin extract.

[0067] Example 3

[0068] Put 50 parts of vegetable tannin extract into 100 parts of water, stir for 60 min, then add laccase with a dosage of 1 part (100 U / g of vegetable tannin extract), adjust the temperature to 25 °C, adjust the pH to 4.5 with hydrochloric acid, and react for 6 h. Slowly introduce air throughout the process to obtain catalytically oxidized tannin extract.

[0069] Add 10% sodium hydroxide solution to the catalytically oxidized tannin extract, adjust the pH to 10.0, stir for 30 min, then add 20 parts of epichlorohydrin, raise the temperature to 60 °C, dropwise add 10% sodium hydroxide solution during the etherification reaction to control the pH at 10.0, carry out the etherification reaction for 5 h, then cool to 25 °C, adjust the pH to 7.0 with hydrochloric acid, and then freeze-dry to obtain a chromium-free tanning agent of epoxy-modified vegetable tannin extract.

[0070] Example 4

[0071] Put 50 parts of vegetable tannin extract into 100 parts of water, stir for 60 min, then add laccase with a dosage of 1 part (100 U / g of vegetable tannin extract), adjust the temperature to 25 °C, adjust the pH to 4.5 with hydrochloric acid, and react for 6 h. Slowly introduce air throughout the process to obtain catalytically oxidized tannin extract.

[0072] Add 10% sodium hydroxide solution to the catalytically oxidized tannin extract, adjust the pH to 10.0, stir for 30 min, then add 25 parts of epichlorohydrin, raise the temperature to 60 °C, and dropwise add 10% sodium hydroxide solution during the etherification reaction to control the pH at 10.0. Carry out the etherification reaction for 6 h, then cool to 25 °C, adjust the pH to 7.0 with hydrochloric acid, and then carry out freeze-drying to obtain an epoxy-modified vegetable tannin chromium-free tanning agent.

[0073] Comparative example

[0074] Comparative example 1

[0075] Put 50 parts of vegetable tannin extract into 100 parts of water, stir for 60 min, then add laccase with a dosage of 1 part (100 U / g of vegetable tannin extract), adjust the temperature to 25 °C, adjust the pH to 4.5 with hydrochloric acid, and react for 6 h. Slowly introduce air throughout the process to obtain catalytically oxidized tannin extract.

[0076] Comparative example 2

[0077] Prepare the epoxy-modified vegetable tannin chromium-free tanning agent in a manner similar to that of Example 1, with the only difference being that the addition amount of laccase is 0.7 part.

[0078] Comparative example 3

[0079] Prepare the epoxy-modified vegetable tannin chromium-free tanning agent in a manner similar to that of Example 1, with the only difference being that the addition amount of laccase is 1.4 parts.

[0080] Experimental example

[0081] Experimental example 1 Leather tanning test

[0082] The chrome-free tanning agent of epoxy-modified vegetable tannin prepared in Examples 1-4, the catalytic oxidation tannin and the vegetable tannin prepared in Comparative Example 1 were respectively used to tan leather. When the chrome-free tanning agent of epoxy-modified vegetable tannin, the catalytic oxidation tannin and the vegetable tannin were used to tan leather, the dosage of the tanning agent was calculated according to 10% of the dosage of the vegetable tannin, and then the tanned leather was tested. The shrinkage temperature of the leather sample was determined according to QB / T 2713-2005. The tensile strength, elongation at break and tearing strength of the leather sample were determined according to the ISO 3376-2011 standard; the thickness of the leather was measured by the multi-point measurement method, that is, 9 points were selected at equal intervals on each sample block to measure its thickness, and the average value was taken to calculate the thickening rate; the softness of the leather sample was determined according to QB / T 4870-2015. The test results are shown in Table 1. The control group in Table 1 tanned leather according to the following steps: first, the leather was pre-tanned with vegetable tannin (dosage: 10% of the leather mass), and then the leather was retanned with polyethylene glycol diglycidyl ether (dosage: 2% of the leather mass).

[0083] Table 1

[0084]

[0085] Note: The plumpness was manually evaluated by leather engineers and scored on a scale of 1-5: the higher the number, the better the plumpness performance.

[0086] As can be seen from Table 1, after the leather was tanned with the chrome-free tanning agent of epoxy-modified vegetable tannin of the present invention, the shrinkage temperature of the tanned leather was increased to above 89.6 °C, the softness was increased to above 4.0, and it also had good plumpness and good heat and humidity resistance stability. At the same time, the tensile strength, elongation at break and tearing strength of the tanned leather were also significantly improved. The elongation at break could reach above 79.2%, and the tearing strength reached above 42.9 N, which was better than the comprehensive performance of the leather tanned only with vegetable tannin, the tannin prepared in Comparative Example 1 and the control group.

[0087] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for preparing an epoxy-modified vegetable tannin chromium-free tanning agent, characterized in that, the epoxy-modified vegetable tannin chromium-free tanning agent is mainly prepared from the following components: 40 - 60 parts by weight of vegetable tannin; 5 - 30 parts by weight of epoxide; 0.8 - 1.2 parts by weight of bio-enzyme; the method comprises the following steps: Step 1: Place the vegetable tannin in water and stir evenly, then add the bio-enzyme for reaction to obtain catalytically oxidized tannin; Step 2: Add an alkaline solution to the catalytically oxidized tannin and stir evenly, then add the epoxide thereto, raise the temperature and carry out an etherification reaction. After the reaction is completed, cool, adjust the pH to neutral, and freeze-dry to obtain the epoxy-modified vegetable tannin chromium-free tanning agent.

2. The method according to claim 1, characterized in that, the epoxy-modified vegetable tannin chromium-free tanning agent is mainly prepared from the following components: 50 parts by weight of vegetable tannin; 10 - 25 parts by weight of epoxide; 1 part by weight of bio-enzyme.

3. The method according to claim 1, characterized in that, the epoxide is selected from one or more of epichlorohydrin, ethylene oxide and propylene oxide; the bio-enzyme is selected from one or more of laccase, xylanase and polyphenol oxidase.

4. The method according to claim 3, characterized in that, the epoxide is epichlorohydrin and the bio-enzyme is laccase.

5. The method according to claim 1, characterized in that, in Step 1, the vegetable tannin is placed in water and stirred for 20 - 45 min.

6. The method according to claim 1, characterized in that, in Step 1, after adding the bio-enzyme, adjust the pH of the reaction system to 4 - 5, and introduce air throughout the reaction process; the temperature of the reaction is 20 - 30 °C and the time of the reaction is 5 - 10 h.

7. The method according to claim 1, characterized in that, in Step 2, the alkaline solution is a 10% by mass sodium hydroxide solution, add the alkaline solution to adjust the pH to 9 - 11, and stir for 20 - 40 min.

8. The method according to claim 1, characterized in that, in Step 2, the temperature of the etherification reaction is 55 - 70 °C and the time of the etherification reaction is 2 - 7 h; add an alkaline solution during the etherification reaction to control the pH of the etherification reaction system to 10.

9. The method according to claim 1, characterized in that, in Step 2, after the reaction is completed, cool to 25 °C, adjust the pH to neutral with hydrochloric acid, and finally carry out freeze-drying.

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