Low-chromium combined tanning process based on epoxy chitosan and chrome tanning agent

Abstract

The invention relates to a low-chromium combined tanning process based on epoxy chitosan and a chrome tanning agent. The low-chromium combined tanning process comprises the following steps of pickling, pretreatment, epoxy chitosan tanning, chrome tanning, alkali extraction and fixation, and wet blue leather is obtained. According to the method, the epoxy-based chitosan and the chrome tanning agent are combined for tanning, the shrinkage temperature and mechanical stability of the leather are improved through the strong cross-linking capacity of chromium ions, the hand feeling and fullness of the leather are improved by means of the epoxy-based chitosan, and the use amount of chrome is reduced.

Description

Technical Field

[0001] This invention relates to the field of leather manufacturing technology, and in particular to a low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agents. Background Technology

[0002] Leather tanning is a core process that determines the quality and performance of leather. It transforms raw hides into leather resistant to microbial degradation through the interaction of hide collagen and tanning agents. In traditional tanning processes, chrome tanning agents are widely used, holding a 90% market share globally. Chrome tanning agents, through the reaction of trivalent chromium salts with hide collagen, impart excellent elasticity, abrasion resistance, and luster to leather, and the production cycle is short and easy to control. However, chrome tanning agents suffer from low utilization rates, and their wastewater discharge causes chromium pollution, resulting in a waste of chromium resources. Furthermore, the high concentration of organic pollutants in the wastewater leads to excessive COD levels, resulting in high treatment costs, which is inconsistent with current "dual carbon" goals and green manufacturing concepts. Therefore, researching optimal low-chromium tanning processes is of universal significance. Summary of the Invention

[0003] This invention provides a low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agents to solve the pollution problems of the traditional chromium tanning process and the shortcomings of chitosan tanning alone and epoxy-based chitosan tanning. This invention designs a combined tanning process of epoxy-based chitosan and chromium tanning agents, which utilizes the strong cross-linking ability of chromium ions to improve the shrinkage temperature and mechanical stability of leather.

[0004] The present invention adopts the following technical solution: A low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agents includes the following steps: Pickling: Add the raw hide to a rotating drum, add 8% NaCl and rotate for 10 min; add 0.5% formic acid and rotate for 20 min; add 1-2% sulfuric acid and rotate for 60 min to obtain pickled hide; Pretreatment: Add 100-150% room temperature water to the pickled skin that has been soaked in acid; adjust the pH to 3.3-3.6 with formic acid, add 8-12% sodium sulfate, and stir for 120 minutes; add baking soda in 3-5 portions to adjust the pH to 7.8-8.2 to obtain the pretreated pickled skin; Epoxy chitosan tanning: Add the pretreated tanning agent to the drum, add 6-12% epoxy chitosan EC, and rotate for 240 min; add 1-3% catalyst ECA in portions to adjust the pH to ≥9.0, and rotate for 240 min; after tanning is completed, add 1-3% formic acid in portions to adjust the pH to 2.8-3.0, and drain the water. Further, the preparation of the above-mentioned epoxy-based chitosan EC is as follows: Shrimp and crab shells are washed, dried, and pulverized. They are first soaked in a 4% hydrochloric acid aqueous solution for 24-48 hours, and washed 2-3 times. Then, they are added to a subcritical apparatus with 10-30 times the volume of a 20-50% sodium hydroxide solution, and the temperature is controlled at 110℃-130℃ for 3-5 hours. The mixture is then cooled to 65-75℃, and 3%-8% hydrogen peroxide is slowly added, with stirring for 4-6 hours. After filtration, a triethanolamine:epoxyisopropane 1.2:1 isopropanol solution is added to the filtrate, and the temperature is raised to 70-90℃, with stirring for 8-10 hours. The filtrate obtained after filtration is ECL, which is freeze-dried to obtain epoxy-based chitosan EC. The catalyst ECA is triethylenetetramine, which promotes the reaction between epoxy-based chitosan and collagen.

[0005] Chrome tanning: First add 50% water to the drum, then add 1-2% chrome tanning agent and 0.1-0.3% protein filler, rotate for 60 min, add 1-2% chrome tanning agent, rotate for 90 min, and take the waste liquid for testing; Alkali removal: Add 0.5% sodium formate, rotate for 30 min, add 0.2-0.5% sodium bicarbonate, rotate for 20-60 min, and finally add 0.2% sodium bicarbonate, rotate for 240 min, with a pH of 4.0-4.2; Fixation: After alkali extraction, add 50% water, 0.2% antifungal agent, and 1.5% white tannin, rotate for 120 min, wash with water, drain, remove from drum and tumble dry to obtain wet blue leather.

[0006] Further, the ratio of the above-mentioned epoxy-based chitosan EC to the chrome tanning agent is 6:3; or, the ratio of the above-mentioned epoxy-based chitosan EC to the chrome tanning agent is 9:2.

[0007] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following advantages: 1. Optimize the combination and ratio of tanning agents to achieve synergistic performance improvement: Combine epoxy-based chitosan EC with chromium tanning agent for tanning. Utilize the strong cross-linking ability of chromium ions to improve the shrinkage temperature and mechanical stability of leather. Epoxy-based chitosan EC is used to improve the feel and fullness of leather and reduce the amount of chromium used.

[0008] 2. Designed distributed tanning process to enhance the interaction between tanning agents and collagen: A step-by-step process of "epoxy-based chitosan tanning followed by chrome tanning" is adopted. First, epoxy-based chitosan (EC) forms a preliminary cross-linking network with collagen fibers, and then chrome tanning agent is added for deep cross-linking. During the tanning process, the pH is precisely controlled to 4.0 for fixation, ensuring that both tanning agents can fully combine with different functional groups on the collagen fibers, maximizing the cross-linking density.

[0009] 3. Controlling process parameters to ensure sample stability and environmental friendliness: Sodium sulfate is added during the pre-tanning stage to optimize collagen fiber state; a special catalyst is added during the tanning of epoxy-based chitosan to enhance reaction activity; and chromium tanning agent is added twice during chromium tanning, along with protein filler, to improve tanning uniformity. By controlling parameters such as drum speed, reaction time, and temperature, process repeatability is ensured, while significantly reducing chromium content and COD value in wastewater, alleviating environmental pressure.

[0010] 4. Significantly improved environmental performance and greatly reduced pollution load: It solves the problems of low utilization rate and serious wastewater pollution in traditional chrome tanning processes; it also solves the problem of insufficient performance of single epoxy chitosan tanning. The pollution load of wastewater is significantly reduced, with chromium content of 762 mg / L, which is about 62% less than that of conventional pure chrome tanning process. The COD value of wastewater is 3683 mg / L, which is 35.2% less than that of pure epoxy chitosan tanning. This greatly reduces the risk of water and soil pollution and lowers wastewater treatment costs.

[0011] 5. Excellent overall performance of the leather, meeting practical needs: the shrinkage temperature of wet blue leather reaches 98.10℃, and the thermal stability is good; the physical and mechanical properties meet the requirements of QB / T 1873—2023 "Chrome Tanned Leather for Footwear Uppers" standard, with a tensile strength of 16.92 N / mm2 and a tear strength of 91.38 N. Detailed Implementation

[0012] To better understand the above technical solution, a detailed explanation is provided below with reference to specific implementation methods (in this invention, the weight of the raw hide is used as the basis for the amount of subsequent chemical materials used. For example, if the raw hide weighs 100 kg, then 150% water is 150 kg of water).

[0013] Example 1: In this embodiment, the ratio of epoxy-based chitosan EC to chromium tanning agent is 6:3. A low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agents includes the following steps: Pickling: Add the raw hide to a rotating drum, add 8% NaCl and rotate for 10 min; add 0.5% formic acid and rotate for 20 min; add 1% sulfuric acid and rotate for 60 min to obtain pickled hide; Pretreatment: Add 100% room temperature water to the acid-treated soda skin; adjust the pH to 3.3-3.6 with formic acid, add 8% sodium sulfate (Chengdu Kelong Chemical Reagent Factory), and rotate for 120 minutes; add baking soda in 3 portions to adjust the pH to 7.8-8.2; the pretreated soda skin is obtained. Epoxy chitosan tanning: Add the pretreated tannin to a drum, add 6% epoxy chitosan EC, and rotate for 240 min; add 1% catalyst (triethylene tetraamine) in portions, adjust pH to ≥ 9.0, and rotate for 240 min; after tanning is complete, add 1-3% formic acid in portions, adjust pH to 2.8-3.0, and drain.

[0014] Chrome tanning: First, add 50% water to the drum, then add 1.5% chrome tanning agent (Brother Technology Co., Ltd.) and 0.1% protein filler (FB, Sichuan Desel New Material Technology Co., Ltd.), and rotate for 60 min; then add 1.5% chrome tanning agent, rotate for 90 min, and take the waste liquid for testing.

[0015] Alkali extraction: Add 0.5% sodium formate and rotate for 30 min; add 0.2% sodium bicarbonate and rotate for 20 min; finally add 0.2% sodium bicarbonate and rotate for 240 min, pH=4.0-4.2.

[0016] Fixation: After alkali extraction, add 50% water, 0.2% antifungal agent, and 1.5% white tannin, rotate for 120 min, wash with water, drain, remove from drum and tumble dry to obtain wet blue leather.

[0017] Example 2: In this embodiment, the ratio of epoxy-based chitosan EC to chromium tanning agent is 9:2. A low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agents includes the following steps: Pickling: Add the raw hide to a rotating drum, add 8% NaCl and rotate for 10 min; add 0.5% formic acid and rotate for 20 min; add 2% sulfuric acid and rotate for 60 min to obtain pickled hide; Pretreatment: Add 150% room temperature water to the acid-treated skin; adjust the pH to 3.3-3.6 with formic acid, add 12% sodium sulfate (Chengdu Kelong Chemical Reagent Factory), and rotate for 120 minutes; add baking soda in 5 portions to adjust the pH to 7.8-8.2; the pretreated skin is obtained. Epoxy chitosan tanning: Add the pretreated tannin to a drum, add 9% epoxy chitosan EC, and rotate for 240 min; add 3% catalyst (triethylene tetraamine) in portions, adjust pH to ≥ 9.0, and rotate for 240 min; after tanning is complete, add 1-3% formic acid in portions, adjust pH to 2.8-3.0, and drain.

[0018] Chrome tanning: First, add 50% water to the drum, then add 1% chrome tanning agent (Brother Technology Co., Ltd.) and 0.3% protein filler (FB, Sichuan Desel New Material Technology Co., Ltd.), and rotate for 60 min; then add 1% chrome tanning agent and rotate for 90 min. Take the waste liquid for testing.

[0019] Alkali removal: Add 0.5% sodium formate and rotate for 30 min; add 0.5% sodium bicarbonate and rotate for 60 min; finally add 0.2% sodium bicarbonate and rotate for 240 min, pH=4.0-4.2.

[0020] Fixation: After alkali extraction, add 50% water, 0.2% antifungal agent, and 1.5% white tannin, and rotate for 120 minutes. Wash with water, drain, and remove from drum to obtain wet blue leather.

[0021] Comparative Example 1: Conventional pure chrome tanning process (without epoxy-based chitosan EC) Pickling: Add the raw hide to a rotating drum, add 8% NaCl and rotate for 10 min; add 0.5% formic acid and rotate for 20 min; add 1-2% sulfuric acid and rotate for 60 min to obtain pickled hide; Pretreatment: Add 100% room temperature water to the acid-treated skin; adjust the pH to 3.3-3.6 with formic acid, add 8% sodium sulfate (Chengdu Kelong Chemical Reagent Factory), and rotate for 120 minutes to obtain the pretreated skin; Chrome tanning: First, add 50% water to the drum, then add 2.5% chrome tanning agent (Brother Technology Co., Ltd.) and 0.1% protein filler (FB, Sichuan Desel New Material Technology Co., Ltd.), and rotate for 60 min; then add 2.5% chrome tanning agent and rotate for 90 min. Take the waste liquid for testing.

[0022] Alkali removal: Add 0.5% sodium formate and rotate for 30 min; add 0.2% sodium bicarbonate and rotate for 60 min; finally add 0.2% sodium bicarbonate and rotate for 240 min, pH=4.0-4.2.

[0023] Fixation: After alkali extraction, add 50% water, 0.2% antifungal agent, and 1.5% white tannin, and rotate for 120 minutes. Wash with water, drain, and remove from drum to obtain wet blue leather.

[0024] Comparative Example 2: Single-epoxy chitosan tanning process (without chromium tanning agents) Pickling: Add the raw hide to a rotating drum, add 8% NaCl and rotate for 10 min; add 0.5% formic acid and rotate for 20 min; add 1-2% sulfuric acid and rotate for 60 min to obtain pickled hide; Pretreatment: Add 100% room temperature water to the acid-treated skin; adjust the pH to 3.3-3.6 with formic acid, add 12% sodium sulfate (Chengdu Kelong Chemical Reagent Factory), and rotate for 120 minutes; add baking soda in 5 portions to adjust the pH to 7.8-8.2; the pretreated skin is obtained. Epoxy chitosan tanning: Add the pretreated tannin to a drum, add 15% epoxy chitosan EC, and rotate for 240 min; add 1% catalyst (triethylene tetraamine) in portions, adjust pH to ≥ 9.0, and rotate for 240 min; after tanning is complete, add 1% formic acid in portions, adjust pH to 2.8-3.0, and drain.

[0025] Alkali removal: Add 0.5% sodium formate and rotate for 30 min; add 0.2% sodium bicarbonate and rotate for 20-60 min; finally add 0.2% sodium bicarbonate and rotate for 240 min, pH=4.0-4.2.

[0026] Fixation: After alkali extraction, add 50% water, 0.2% antifungal agent, and 1.5% white tannin, and rotate for 120 minutes. Wash with water, drain, and remove from drum to obtain wet blue leather.

[0027] The wet blue leathers obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were tested, and the specific data comparison is as follows: This invention designs a tanning process combining epoxy-modified chitosan (EC) and chrome tanning agent, utilizing the strong cross-linking ability of chromium ions to enhance the shrinkage temperature and mechanical stability of leather. Using acid leather as raw material, a combined tanning process is adopted, first tanning with epoxy-modified chitosan and then with chrome tanning. The optimal dosage is optimized by changing the ratio of epoxy-modified chitosan to chrome tanning agent. The shrinkage temperature, tear strength, tensile strength of wet blue leather, and the chromium content and COD value of tanning waste liquor are used as evaluation indicators to determine the optimal low-chromium combined tanning process, providing a reference for the tanning process of eco-friendly leather.

[0028] Chitosan, derived from the shells of crustaceans such as shrimp and crab, is a natural amino polysaccharide. Its abundance is second only to cellulose, and it possesses both biocompatibility and biodegradability, thus avoiding heavy metal pollution at the source. However, chitosan has high film-forming brittleness, low cross-linking degree, and its water solubility is greatly affected by pH. When used alone in leather tanning, it can easily lead to cracking, stiffness, and poor resistance to damp heat. Epoxy-based chitosan (EC) can improve fiber cross-linking uniformity and enhance the feel and fullness of leather, but its heat stability is slightly lower.

[0029] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agents, characterized in that, Includes the following steps: Pickling: Add the raw hide to a rotating drum, add 8% NaCl and rotate for 10 min; add 0.5% formic acid and rotate for 20 min; add 1-2% sulfuric acid and rotate for 60 min to obtain pickled hide; Pretreatment: Add 100-150% room temperature water to the pickled skin that has been soaked in acid; adjust the pH to 3.3-3.6 with formic acid, add 8-12% sodium sulfate, and stir for 120 minutes; add baking soda in 3-5 portions to adjust the pH to 7.8-8.2 to obtain the pretreated pickled skin; Epoxy chitosan tanning: Add the pretreated tanning bark to a drum, add 6-12% epoxy chitosan, and rotate for 240 min; add 1-3% catalyst in portions to adjust the pH to ≥9.0, and rotate for 240 min; after tanning is complete, add 1-3% formic acid in portions to adjust the pH to 2.8-3.0, and drain. Chrome tanning: First add 50% water to the drum, then add 1-2% chrome tanning agent and 0.1-0.3% protein filler, rotate for 60 min, add 1-2% chrome tanning agent, rotate for 90 min, and take the waste liquid for testing; Alkali removal: Add 0.5% sodium formate, rotate for 30 min, add 0.2-0.5% sodium bicarbonate, rotate for 20-60 min, and finally add 0.2% sodium bicarbonate, rotate for 240 min, with a pH of 4.0-4.2; Fixation: After alkali extraction, add 50% water, 0.2% antifungal agent, and 1.5% white tannin, rotate for 120 min, wash with water, drain, remove from drum and tumble dry to obtain wet blue leather.

2. The low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agent as described in claim 1, characterized in that: The ratio of the epoxy-based chitosan to the chromium tanning agent is 6:

3.

3. The low-chromium combined tanning process based on epoxy-based chitosan and chromium tanning agent as described in claim 1, characterized in that: The ratio of the epoxy-based chitosan to the chromium tanning agent is 9:2.

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