Combined tanning process based on epoxy chitosan and organic chrome-free tanning agent

Abstract

The invention relates to a combined tanning process based on epoxy chitosan and an organic chrome-free tanning agent. The combined tanning process comprises the following steps of pickling, pretreatment, tanning, alkali extraction and fixation. A composite formula of epoxy chitosan and an organic chrome-free tanning agent is adopted, a multi-layer cross-linked network is established through active groups in molecular structures of the epoxy chitosan and the organic chrome-free tanning agent and collagenous fibers, the epoxy chitosan provides powerful covalent cross-linking points, the organic chrome-free tanning agent enhances transverse connection between the fibers, and a stable three-dimensional network structure is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of leather manufacturing, in particular to a combination tanning process based on epoxy chitosan and organic chrome-free tanning agent. BACKGROUND

[0002] With the continuous improvement of the limit standard of hexavalent chromium in the leather industry, the development of a chrome-free tanning system that can completely replace chrome tanning has become a key issue that the industry needs to solve. Currently, chrome-free tanning agents mainly include vegetable tanning agents, aldehyde tanning agents, zirconium tanning agents, and various types of organic synthetic tanning agents. Although these materials can achieve basic tanning effects, they still have obvious limitations in practical applications. Although vegetable tanning agents are derived from nature, the leather produced after tanning is dark in color, which is not conducive to the production of light-colored leather, and the finished leather is hard and has limited shrinkage temperature; aldehyde tanning agents can impart good softness to leather, but there is a risk of formaldehyde release, which affects product safety; zirconium tanned leather is white and heat-resistant, but the leather body is hard and has a poor hand feel; most organic tanning agents alone are difficult to establish a sufficient cross-linking network, resulting in a low shrinkage temperature of the finished leather and a significant gap in mechanical properties compared to chrome tanned leather.

[0003] In recent years, tanning agent materials based on biomass resources have received widespread attention. Chitosan, as a source of abundant and biodegradable amino polysaccharides, has active groups on its molecular chain that can cross-link with collagen fibers. However, pure chitosan has poor water solubility, large molecular size, and weak permeability, which limits its application effect in the tanning process. By modifying chitosan with epoxy groups, its water solubility and reactivity can be significantly enhanced, and its cross-linking ability with collagen fibers can be improved. However, single use of epoxy chitosan is still difficult to achieve ideal results in terms of softness and fullness of the finished leather. SUMMARY

[0004] The present application provides a combination tanning process based on epoxy chitosan and organic chrome-free tanning agent to overcome the problems existing in the above tanning process.

[0005] The present application adopts the following technical solutions: A combination tanning process based on epoxy chitosan and organic chrome-free tanning agent, comprising the following steps: Acid soaking: add rawhide to a rotating drum, add 100%-150% of normal temperature water, add 7%-10% of NaCl, rotate for 10 minutes, check the Baume degree at 7-10°Bé; add 0.5% of formic acid, rotate for 20 minutes; add 1% of sulfuric acid, rotate for 120 minutes; stop rotating for 5 minutes and stand for 55 minutes, to ensure thorough acid soaking; the pH value at the end of acid soaking is 2.8-3.0; Pre-treatment: add 20%-50% normal temperature water to the acid skin after pickling, add 5%-7% sodium sulphate, rotate for 30 min; add baking soda for 3-5 times, adjust pH=4.0-4.5, to obtain the pre-treated acid skin; Tanning: add the acid skin after pre-treatment to the rotating drum, add 1%-4% baking soda, adjust pH value to 6.0-8.0, rotate for 60-120 min; add 3%-5% organic chrome-free tanning agent (DWT, Sichuan Desai New Material Technology Co., Ltd.) and 10%-20% epoxy chitosan EC, add 2% white tannin, rotate for 90-180 min; add 1%-3% triethylene diamine, adjust pH≥9, rotate for 120 min; after tanning is completed, add 1%-3% multifunctional tanning agent (MAC, Sichuan Desai New Material Technology Co., Ltd.) for several times, adjust pH to 2.5-3.0; Preparation of the above-mentioned epoxy chitosan EC: wash shrimp shells and crab shells, dry and crush, first soak in 4% hydrochloric acid aqueous solution for 24-48 h, wash for 2-3 times; then add to a subcritical device, add 10-30 times of 20-50% sodium hydroxide solution, control temperature to 110℃-130℃, react for 3-5 h; cool to 65-75℃, slowly add 3%-8% hydrogen peroxide, stir for 4-6 h; filter, add triethanolamine: 1.2:1 isopropyl alcohol solution of epoxy isopropyl alcohol to the filtrate, heat to 70-90℃, stir for 8-10 h; filter the obtained filtrate to obtain ECL, freeze-dry to obtain epoxy chitosan EC.

[0006] Alkali extraction: add 0.5% sodium formate, rotate for 30 min; add 0.2%-0.5% baking soda, rotate for 20-60 min; finally add 0.2% baking soda, rotate for 240 min, pH=4.0-4.2; Fixing: after alkali extraction is completed, add 50% water and 0.2% mildew inhibitor, rotate for 120 min, wash with water, drain water, take out the drum and put on the horse, to obtain white wet leather.

[0007] From the above description of the present application, compared with the prior art, the present application has the following advantages: 1. The present application adopts a composite formula of epoxy chitosan and organic chrome-free tanning agent, and a multi-level cross-linking network is established between the active groups in the molecular structures of the two and collagen fibers, the epoxy chitosan provides strong covalent cross-linking points, and the organic chrome-free tanning agent enhances the lateral connection between fibers, forming a stable three-dimensional network structure.

[0008] 2. The present application selects an organic chrome-free tanning agent and self-made epoxy chitosan which do not contain metal salt, bisphenol, compound, organic phosphine salt, and have outstanding environmental protection performance, avoids using traditional chemical materials containing chromium and aldehyde, maximally reduces the discharge of three wastes, and meets the green tanning requirements.

[0009] 3. The process of the present application does not use chromium salt throughout, thereby eliminating the generation of chromium-containing wastewater and waste residue from the source, and the harmful substance content of the wastewater is far lower than that of the traditional chromium tanning process, thereby reducing the environmental protection treatment cost of enterprises.

[0010] 4. The white wet leather prepared by the synergistic effect of epoxy chitosan and organic chromium-free tanning agent and the precise process parameter control has a shrinkage temperature of ≥75℃, reaching the QB / T 5796-2023 leather standard for chromium-free tanning for shoe upper. DETAILED DESCRIPTION

[0011] In order to better understand the above technical solutions, the following will be described in detail in combination with specific embodiments (the weight of rawhide is taken as the basis for the amount of subsequent chemical materials. For example, if the weight of rawhide is 100 kg, then 300% of water is 300 kg of water).

[0012] Example 1 A combination tanning process based on epoxy chitosan and organic chromium-free tanning agent, comprising the following steps: acid dipping: the rawhide is added into a rotating drum, 100% normal temperature water is added, 7% NaCl is added, and the rotating is performed for 10 min; the brix is checked to be 7°Bé; 0.5% formic acid is added, and the rotating is performed for 20 min; 1% sulfuric acid is added, and the rotating is performed for 120 min; the rotating and stopping are combined in the mode of rotating for 5 min and standing for 55 min to ensure thorough acid dipping; and the pH value at the end of acid dipping is adjusted to be 2.8-3.0; pretreatment: the acid-dipped acid hide is added into a rotating drum, 20% normal temperature water is added, 5% sodium sulphate is added, and the rotating is performed for 30 min; baking soda is added in three times to adjust the pH value to 4.0-4.5, and the pretreated acid hide is obtained; tanning: the acid hide obtained by pretreatment is added into a rotating drum, 1% baking soda is added to adjust the pH value to 6.0-8.0, and the rotating is performed for 60 min; 3% organic chromium-free tanning agent (DWT, Sichuan Deser New Material Technology Co., Ltd.) and 10% epoxy chitosan are added, 2% white tannin is added, and the rotating is performed for 90 min; 1% triethylenediamine is added to adjust the pH value to ≥9, and the rotating is performed for 120 min; after the tanning is completed, 1% multifunctional tanning aid (MAC, Sichuan Deser New Material Technology Co., Ltd.) is added in several times, and the pH value is adjusted to 2.5-3.0; alkali extraction: 0.5% sodium formate is added, the rotating is performed for 30 min; 0.2% baking soda is added, the rotating is performed for 20 min; finally, 0.2% baking soda is added, the rotating is performed for 240 min, and the pH value is 4.0-4.2; fixing: after the alkali extraction is completed, 50% water and 0.2% mildewproof agent are added, the rotating is performed for 120 min, the water is washed, the water is drained, the drum is taken off, and the horse is mounted to obtain the white wet leather.

[0013] Example 2 A tanning process based on the combination of epoxy chitosan and organic chrome-free tanning agent, comprising the following steps: Acid dipping: add rawhide to the drum, add 150% normal temperature water, add 10% NaCl, rotate for 10 min, check the Baume degree at 10°Bé; add 0.5% formic acid, rotate for 20 min; add 1% sulfuric acid, rotate for 120 min; stop combining with 5 min rotation and 55 min standing; ensure thorough acid dipping; adjust the pH value at the end of acid dipping to 2.8-3.0; Pretreatment: add 50% normal temperature water to the acid hide treated by acid dipping, add 7% sodium sulphate, rotate for 30 min; add baking soda in 5 times, adjust to pH=4.0-4.5, to obtain the pretreated acid hide; Tanning: add the acid hide obtained by pretreatment to the drum, add baking soda 4%, adjust the pH value to 6.0-8.0, rotate for 120 min; add 5% organic chrome-free tanning agent (DWT, Sichuan Desai New Material Technology Co., Ltd.) and 10%-20% epoxy chitosan, add 2% white tannin, rotate for 180 min; add 3% triethylene diamine, adjust the pH≥9, rotate for 120 min; after tanning is completed, add 3% multifunctional tanning aid (MAC, Sichuan Desai New Material Technology Co., Ltd.) in several times, adjust the pH to 2.5-3.0; Alkali extraction: add 0.5% sodium formate, rotate for 30 min; add 0.5% baking soda, rotate for 60 min; finally add 0.2% baking soda, rotate for 240 min, adjust the pH=4.0-4.2; Fixing: after alkali extraction is completed, add 50% water and 0.2% mildewproof agent, rotate for 120 min, wash with water, drain water, take out the drum and put on the horse, to obtain white wet leather.

[0014] The white wet leather of the present application is tested, specifically as follows: The above is only a specific embodiment of the present application, but the design concept of the present application is not limited thereto, and any non-essential modification of the present application using this concept shall be regarded as an act of infringing the protection scope of the present application.

Claims

1. A combined tanning process based on epoxy-based chitosan and organic chromium-free tanning agents, characterized in that: Includes the following steps: Pickling: Add the raw hides to the drum, add 100%-150% room temperature water, add 7%-10% NaCl, rotate for 10 minutes, and check the Baumé degree to be 7-10°Bé; add 0.5% formic acid, rotate for 20 minutes; add 1% sulfuric acid, rotate for 120 minutes; combine rotation for 5 minutes and standing for 55 minutes to ensure thorough pickling; the pH value at the end of pickling should be 2.8-3.

0. Pretreatment: Add 20%-50% room temperature water and 5%-7% sodium sulfate to the pickled skin that has been soaked in acid, and stir for 30 minutes; add baking soda in 3-5 portions to adjust the pH to 4.0-4.5 to obtain the pretreated pickled skin; Tanning: Add the pretreated sourdough to a drum, add 1%-4% baking soda to adjust the pH to 6.0-8.0, and tumble for 60-120 minutes; add 3%-5% organic chromium-free tanning agent and 10%-20% epoxy chitosan, add 2% white tannin, and tumble for 90-180 minutes; add 1%-3% triethylenediamine to adjust the pH to ≥9, and tumble for 120 minutes; after tanning is complete, add 1%-3% multifunctional tanning aid in batches to adjust the pH to 2.5-3.0; Alkali extraction: Add 0.5% sodium formate and rotate for 30 min; add 0.2%-0.5% sodium bicarbonate and rotate for 20-60 min; finally add 0.2% sodium bicarbonate and rotate for 240 min, pH=4.0-4.2; Fixation: After alkali extraction, add 50% water and 0.2% mildew inhibitor, rotate for 120 minutes, wash with water, drain, remove from drum and tumble dry to obtain white wet leather.

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