Sheep leather chrome-free tanning process

Abstract

The invention relates to the technical field of leather processing, and provides a sheep leather chrome-free tanning process which comprises the following steps: S1, carrying out deliming softening and degreasing on sheep bare leather to obtain pretreated sheep bare leather; s2, after the pretreated sheep pelt is pickled with acid liquor, a chrome-free tanning agent is added for primary tanning, retanning, dyeing, finishing and finishing, and sheep leather is obtained; the chrome-free tanning agent comprises the following components in parts by weight: 1-2 parts of sulfuric acid, 8-12 parts of zirconium sulfate, 4-9.6 parts of dialdehyde sodium alginate, 14.4-20 parts of tannin extract, 3-6 parts of a masking agent and 100 parts of water. The tannin extract comprises a chestnut tannin extract and a valonia tannin extract. By means of the technical scheme, the problem that in the related technology, after sheep leather is tanned, the tearing strength is low is solved.

Description

Technical Field

[0001] This invention relates to the field of leather processing technology, specifically to a chromium-free tanning process for sheep leather. Background Technology

[0002] Leather tanning is the core process of transforming raw hides into durable, stable leather with excellent performance through chemical or physical methods. The choice of tanning agent directly determines the quality, safety, and environmental impact of leather products. In traditional leather tanning processes, chromium salts (especially trivalent chromium) have long held a dominant position due to their stable tanning effect and ability to impart excellent fullness, softness, and resistance to humid heat to leather. They are widely used in the production of various types of leather, including sheepskin.

[0003] However, traditional chrome tanning processes have many insurmountable drawbacks. On the one hand, chromium salts are highly toxic, and if the chromium-containing wastewater and waste residue generated during the production process are not properly treated, they will pollute the soil, water bodies and the atmosphere. On the other hand, after chromium-containing leather products are used and discarded, chromium ions may be slowly released, posing a potential threat to human health.

[0004] To address the environmental and safety concerns associated with chrome tanning, chrome-free tanning technology has become a research hotspot and development direction in the leather industry. Currently developed chrome-free tanning agents include single or compound systems such as zirconium salts, aluminum salts, and vegetable tanning agents. However, existing chrome-free tanning processes still have significant shortcomings. While leather tanned with a single zirconium salt exhibits improved environmental friendliness, insufficient collagen fiber cross-linking density results in poor mechanical properties such as tear strength, making it difficult to meet the requirements of high-end leather products. Therefore, there is an urgent need for a chrome-free tanning process that can significantly improve the tear strength of sheepskin. Summary of the Invention

[0005] This invention proposes a chromium-free tanning process for sheep leather, which solves the problem of low tear strength of sheep leather after tanning in related technologies.

[0006] The technical solution of the present invention is as follows: This invention proposes a chromium-free tanning process for sheepskin, comprising the following steps: S1. The naked sheepskin is deashed, softened, and degreased to obtain pretreated naked sheepskin; S2. The pretreated sheep hide is soaked in acid solution and then chromium-free tanning agent is added for initial tanning, retanning, dyeing, finishing and coating to obtain the sheep leather. The chromium-free tanning agent comprises the following components in parts by weight: 1-2 parts sulfuric acid, 8-12 parts zirconium sulfate, 4-9.6 parts sodium alginate dialdehyde, 14.4-20 parts tannin, 3-6 parts masking agent, and 100 parts water; The tannins include chestnut tannins and rubber tannins.

[0007] As a further technical solution, the mass ratio of sodium dialdehyde aldehyde, chestnut tannin, and rubber tannin is 1:1:1~2.

[0008] As a further technical solution, the preparation method of the chromium-free tanning agent includes the following steps: A1. Dissolve sulfuric acid in water and stir to obtain a sulfuric acid solution; A2. Add zirconium sulfate and masking agent to the sulfuric acid solution, stir, add sodium dialdehyde alkaloid and tannin, continue stirring to obtain a mixture, and spray dry the mixture to obtain the chromium-free tanning agent.

[0009] As a further technical solution, in step A1, the stirring temperature is 60~80℃, and the stirring time is 0.5~1h.

[0010] As a further technical solution, in step A2, the temperatures for stirring and continued stirring are each independently 70~80℃.

[0011] As a further technical solution, the preparation method of the dialdehyde sodium alginate includes the following steps: dissolving sodium alginate in a mixed solvent, adding sodium periodate, stirring in the dark, precipitating, filtering, washing, and drying to obtain the dialdehyde sodium alginate.

[0012] As a further technical solution, the mixed solvent is composed of water and anhydrous ethanol in a volume ratio of 4:1; The molar ratio of sodium alginate to sodium periodate is 1:1 to 1.2.

[0013] As a further technical solution, the masking agent is α-hydroxyphenylacetic acid and / or malic acid.

[0014] In this invention, by using α-hydroxyphenylacetic acid and malic acid as masking agents, the tear strength of sheepskin can be further improved.

[0015] As a further technical solution, when the masking agent is α-hydroxyphenylacetic acid and malic acid, the mass ratio of α-hydroxyphenylacetic acid and malic acid is 1:1~2.

[0016] As a further technical solution, during the initial tanning, the amount of the chromium-free tanning agent used is 6wt%~8wt% based on the weight of the pretreated sheep hide.

[0017] As a further technical solution, during the retanning process, the amount of the chromium-free tanning agent used is 3wt%~5wt% based on the weight of the pretreated sheep hide.

[0018] As a further technical solution, the initial tanning includes the following steps: adding chromium-free tanning agent and rotating for 2-3 hours, adding sodium bicarbonate to adjust the pH to 4-5, continuing to rotate for 50-60 minutes, washing with water, and exiting the drum.

[0019] The working principle and beneficial effects of this invention are as follows: In this invention, the tear strength of sheepskin is improved by combining sodium alginate dialdehyde, chestnut tannin, and rubber tannin in a chromium-free tanning agent. Sodium alginate dialdehyde targets and binds to the amino groups of collagen, while tannin targets and binds to the hydroxyl / amino groups of collagen. These three components act on different functional groups of collagen molecules, forming a multi-layered cross-linked network with a cross-linking density far higher than that of a single component, resulting in an exponential increase in the inter-fiber bonding strength. Simultaneously, chestnut tannin penetrates rapidly into the fine gaps between collagen fibers and exhibits high cross-linking activity with sodium alginate dialdehyde, optimizing the uniformity of the collagen cross-linked network. Rubber tannin forms a complex filling layer between fiber bundles, preventing Zr... 4+ Furthermore, the high density of phenolic hydroxyl groups in tannin can form multiple hydrogen bonds with collagen fibers, sodium dialdehyde aldehyde, and chestnut tannin, further enhancing the stability of the cross-linked network and preventing the fiber bundles from being pulled apart and broken during the tearing process. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 The chromium-free tanning agent comprises the following components in parts by weight: 1 part sulfuric acid, 8 parts zirconium sulfate, 9.6 parts sodium alginate dialdehyde, 9.6 parts chestnut tannin, 4.8 parts rubber tannin, 3 parts citric acid, and 100 parts water; The preparation method of dialdehyde sodium alginate includes the following steps: dissolving sodium alginate in a mixed solvent (the volume ratio of water to anhydrous ethanol is 4:1), the mass-volume ratio of sodium alginate to the mixed solvent is 1g:5mL, adding sodium periodate, the molar ratio of sodium alginate to sodium periodate is 1:1, stirring in the dark for 6h, adding anhydrous ethanol for precipitation, the mass-volume ratio of sodium alginate to anhydrous ethanol is 1g:6mL, filtering, washing, and drying to obtain dialdehyde sodium alginate; The preparation method of chromium-free tanning agent includes the following steps: A1. Dissolve sulfuric acid in water and stir at 60°C for 1 hour to obtain a sulfuric acid solution; A2. Zirconium sulfate and citric acid are added to a sulfuric acid solution and stirred at 70°C for 2 hours. Then, sodium dialdehyde alkaloid, chestnut tannin, and oak tannin are added and stirred at 70°C for another 2 hours to obtain a mixed solution. The mixed solution is then spray-dried to obtain a chromium-free tanning agent. The chrome-free tanning process for sheepskin includes the following steps: S1. The naked sheepskin is deashed, softened, and degreased to obtain pretreated naked sheepskin; S2. After the pretreated sheep hides are soaked in acid, chromium-free tanning agent is added (6 wt% of the weight of the pretreated sheep hides) and the mixture is turned for 2 hours. Sodium bicarbonate is added to adjust the pH to 4, and the mixture is turned for another 50 minutes. After washing with water, the sheep hides are removed from the drum and the initial tanning, retanning, dyeing, finishing and coating are completed to obtain sheep leather. During retanning, the amount of chromium-free tanning agent is 3 wt% of the weight of the pretreated sheep hides.

[0022] Example 2 The chromium-free tanning agent comprises the following components in parts by weight: 1.5 parts sulfuric acid, 10 parts zirconium sulfate, 9.6 parts sodium alginate dialdehyde, 9.6 parts chestnut tannin, 4.8 parts rubber tannin, 5 parts citric acid, and 100 parts water; The preparation method of dialdehyde sodium alginate includes the following steps: dissolving sodium alginate in a mixed solvent (the volume ratio of water to anhydrous ethanol is 4:1), the mass-volume ratio of sodium alginate to the mixed solvent is 1g:5mL, adding sodium periodate, the molar ratio of sodium alginate to sodium periodate is 1:1.2, stirring in the dark for 6h, adding anhydrous ethanol to precipitate, the mass-volume ratio of sodium alginate to anhydrous ethanol is 1g:6mL, filtering, washing, and drying to obtain dialdehyde sodium alginate; The preparation method of chromium-free tanning agent includes the following steps: A1. Dissolve sulfuric acid in water and stir at 80°C for 0.5 hours to obtain a sulfuric acid solution; A2. Zirconium sulfate and citric acid are added to a sulfuric acid solution and stirred at 80°C for 2 hours. Then, sodium dialdehyde alkaloid, chestnut tannin, and oak tannin are added and stirred at 80°C for another 2 hours to obtain a mixed solution. The mixed solution is then spray-dried to obtain a chromium-free tanning agent. The chrome-free tanning process for sheepskin includes the following steps: S1. The naked sheepskin is deashed, softened, and degreased to obtain pretreated naked sheepskin; S2. After the pretreated sheep hides are soaked in acid, chromium-free tanning agent is added (7wt% of the weight of the pretreated sheep hides) and the mixture is rotated for 2.5 hours. Sodium bicarbonate is added to adjust the pH to 4.5, and the mixture is rotated for another 55 minutes. The hides are then washed with water and removed from the drum to complete the initial tanning, retanning, dyeing, finishing, and coating processes to obtain sheep leather. During retanning, the amount of chromium-free tanning agent used is 5wt% of the weight of the pretreated sheep hides.

[0023] Example 3 The chromium-free tanning agent comprises the following components in parts by weight: 2 parts sulfuric acid, 12 parts zirconium sulfate, 9.6 parts sodium alginate dialdehyde, 9.6 parts chestnut tannin, 4.8 parts rubber tannin, 6 parts citric acid, and 100 parts water; The preparation method of dialdehyde sodium alginate includes the following steps: dissolving sodium alginate in a mixed solvent (the volume ratio of water to anhydrous ethanol is 4:1), the mass-volume ratio of sodium alginate to the mixed solvent is 1g:5mL, adding sodium periodate, the molar ratio of sodium alginate to sodium periodate is 1:1, stirring in the dark for 6h, adding anhydrous ethanol for precipitation, the mass-volume ratio of sodium alginate to anhydrous ethanol is 1g:6mL, filtering, washing, and drying to obtain dialdehyde sodium alginate; The preparation method of chromium-free tanning agent includes the following steps: A1. Dissolve sulfuric acid in water and stir at 80°C for 0.5 hours to obtain a sulfuric acid solution; A2. Add zirconium sulfate and malic acid to sulfuric acid solution and stir at 80°C for 2 hours. Add dialdehyde sodium alginate, chestnut tannin and rubber tannin and continue stirring at 80°C for 2 hours to obtain a mixture. After spray drying the mixture, obtain chromium-free tanning agent. The chrome-free tanning process for sheepskin includes the following steps: S1. The naked sheepskin is deashed, softened, and degreased to obtain pretreated naked sheepskin; S2. After the pretreated sheep hide is soaked in acid, a chromium-free tanning agent is added (8 wt% of the weight of the pretreated sheep hide) and rotated for 3 hours. Sodium bicarbonate is added to adjust the pH to 5, and the mixture is rotated for another 60 minutes. The hide is then washed with water and removed from the drum to complete the initial tanning, retanning, dyeing, finishing, and coating processes to obtain sheep leather. During retanning, the amount of chromium-free tanning agent used is 5 wt% of the weight of the pretreated sheep hide.

[0024] Example 4 The only difference between this embodiment and Embodiment 3 is that the amount of sodium dialdehyde esterase is 8 parts, the amount of chestnut wood tannin is 8 parts, and the amount of oak tannin is 8 parts.

[0025] Example 5 The only difference between this embodiment and Embodiment 3 is that the amount of sodium dialdehyde esterase is 6 parts, the amount of chestnut wood tannin is 6 parts, and the amount of oak tannin is 12 parts.

[0026] Example 6 The only difference between this embodiment and Embodiment 3 is that the amount of sodium dialdehyde esterase is 4 parts, the amount of chestnut wood tannin is 4 parts, and the amount of oak tannin is 16 parts.

[0027] Example 7 The only difference between this embodiment and Embodiment 5 is that citric acid is replaced with malic acid.

[0028] Example 8 The only difference between this embodiment and Example 5 is that citric acid is replaced with α-hydroxyphenylacetic acid.

[0029] Example 9 The only difference between this embodiment and Embodiment 5 is that 6 parts of citric acid are replaced with 3 parts of α-hydroxyphenylacetic acid and 3 parts of malic acid.

[0030] Example 10 The only difference between this embodiment and Embodiment 5 is that 6 parts of citric acid are replaced with 2 parts of α-hydroxyphenylacetic acid and 4 parts of malic acid.

[0031] Comparative Example 1 The only difference between this comparative example and Example 3 is that the chromium-free tanning agent includes the following components in parts by weight: 2 parts sulfuric acid, 12 parts zirconium sulfate, 16 parts chestnut tannin, 8 parts rubber tannin, 6 parts malic acid, and 100 parts water. The preparation method of chromium-free tanning agent includes the following steps: A1. Dissolve sulfuric acid in water and stir at 80°C for 0.5 hours to obtain a sulfuric acid solution; A2. Zirconium sulfate and malic acid are added to a sulfuric acid solution and stirred at 80°C for 2 hours. Chestnut tannin and oak tannin are then added and stirred at 80°C for another 2 hours to obtain a mixed solution. The mixed solution is then spray-dried to obtain a chromium-free tanning agent.

[0032] Comparative Example 2 The only difference between this comparative example and Example 3 is that the chromium-free tanning agent includes the following components in parts by weight: 2 parts sulfuric acid, 12 parts zirconium sulfate, 16 parts sodium dialdehyde alkaloid, 8 parts tannin, 6 parts malic acid, and 100 parts water. The preparation method of chromium-free tanning agent includes the following steps: A1. Dissolve sulfuric acid in water and stir at 80°C for 0.5 hours to obtain a sulfuric acid solution; A2. Add zirconium sulfate and malic acid to sulfuric acid solution and stir at 80°C for 2 hours. Add sodium dialdehyde ester and tannin and continue stirring at 80°C for 2 hours to obtain a mixture. After spray drying, the mixture is used to obtain chromium-free tanning agent.

[0033] Comparative Example 3 The only difference between this comparative example and Example 3 is that the chromium-free tanning agent includes the following components in parts by weight: 2 parts sulfuric acid, 12 parts zirconium sulfate, 12 parts sodium dialdehyde alkaloid, 12 parts chestnut tannin, 6 parts malic acid, and 100 parts water. The preparation method of chromium-free tanning agent includes the following steps: A1. Dissolve sulfuric acid in water and stir at 80°C for 0.5 hours to obtain a sulfuric acid solution; A2. Zirconium sulfate and malic acid are added to a sulfuric acid solution and stirred at 80°C for 2 hours. Then, sodium alginate and chestnut tannin are added and stirred at 80°C for another 2 hours to obtain a mixed solution. The mixed solution is then spray-dried to obtain a chromium-free tanning agent.

[0034] Comparative Example 4 The only difference between this comparative example and Example 3 is that rubber tannin is replaced with larch tannin.

[0035] Comparative Example 5 The only difference between this comparative example and Example 3 is that rubber tannin is replaced with hardwood tannin.

[0036] The tear strength of the sheep leather obtained in Examples 1-10 and Comparative Examples 1-5 was tested respectively: Tear strength: The tear strength was tested according to the method specified in GB / T 17928-2023 "Physical and Mechanical Tests of Leather - Determination of Pinhole Tear Strength". During the test, the tensile testing machine moved at a constant speed of 100 mm / min. The results are shown in Table 1 below.

[0037] Table 1. Tear strength test results

[0038] By comparing the data of Example 3 and Comparative Examples 1-5, Example 3, using a chromium-free tanning agent containing sodium alginate, chestnut tannin, and rubber tannin, produced sheep leather with greater tear strength than Comparative Examples 1-5. This indicates that adding sodium alginate, chestnut tannin, and rubber tannin to a chromium-free tanning agent can improve the tear strength of sheep leather. By comparing the data of Examples 3-6, Examples 4-5, by adjusting the mass ratio of sodium alginate, chestnut tannin, and rubber tannin to 1:1:1-2, further improved the tear strength of sheep leather.

[0039] By comparing the data from Examples 5 and 7-10, it was found that the sheep leather produced in Examples 9-10, by adding α-hydroxyphenylacetic acid and malic acid as masking agents, had a greater tear strength than that of Examples 5 and 7-8. This indicates that by adding α-hydroxyphenylacetic acid and malic acid as masking agents, the tear strength of sheep leather can be further improved.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A chrome-free tanning process for sheepskins, characterized in that, The method comprises the following steps: S1, the sheep skin is softened by removing lime and degreasing to obtain pretreated sheep skin; S2, the pretreated sheep skin is immersed in acid solution, then a chrome-free tanning agent is added for initial tanning, retanning, dyeing, finishing and coating to obtain the sheep leather; The chrome-free tanning agent comprises the following components in parts by weight: 1-2 parts of sulfuric acid, 8-12 parts of zirconium sulfate, 4-9.6 parts of dialdehyde sodium alginate, 14.4-20 parts of tannin, 3-6 parts of masking agent and 100 parts of water; The tannin comprises chestnut wood tannin and oak tannin.

2. A chrome-free tanning process of sheep leather as claimed in claim 1 wherein, The mass ratio of the dialdehyde sodium alginate, chestnut wood tannin and oak tannin is 1:1:1-2.

3. A chrome-free tanning process of sheep leather as claimed in claim 1 wherein, The preparation method of the chrome-free tanning agent comprises the following steps: A1, sulfuric acid is dissolved in water to obtain a sulfuric acid solution; A2, zirconium sulfate and a masking agent are added to the sulfuric acid solution, then dialdehyde sodium alginate and tannin are added, and the mixture is continuously stirred to obtain a mixed solution, which is spray-dried to obtain the chrome-free tanning agent.

4. A chrome-free tanning process for sheepskins according to claim 3, characterized in that, In step A1, the stirring temperature is 60-80℃, and the stirring time is 0.5-1h; In step A2, the stirring and continuous stirring temperatures are independently 70-80℃.

5. A chrome-free tanning process of sheep leather as claimed in claim 1 wherein, The preparation method of the dialdehyde sodium alginate comprises the following steps: sodium alginate is dissolved in a mixed solvent, sodium periodate is added, and the mixture is stirred in the dark, precipitated, filtered, washed and dried to obtain the dialdehyde sodium alginate.

6. A chrome-free tanning process for sheepskins according to claim 5, characterized in that, The mixed solvent is composed of water and anhydrous ethanol in a volume ratio of 4:1; The molar ratio of the sodium alginate and sodium periodate is 1:1-1.

2.

7. A chrome-free tanning process of sheep leather as claimed in claim 1 wherein, The masking agent is α-hydroxyphenylacetic acid and / or malic acid.

8. A chrome-free tanning process of sheep leather according to claim 7, characterized in that, When the masking agent is α-hydroxyphenylacetic acid and malic acid, the mass ratio of the α-hydroxyphenylacetic acid and malic acid is 1:1-2.

9. A chrome-free tanning process of sheep leather as claimed in claim 1 wherein, In the initial tanning, the amount of the chrome-free tanning agent is 6wt%-8wt% based on the weight of the pretreated sheep skin; In the retanning, the amount of the chrome-free tanning agent is 3wt%-5wt% based on the weight of the pretreated sheep skin.

10. A chrome-free tanning process of sheep leather as claimed in claim 1 wherein, The initial tanning comprises the following steps: after the chrome-free tanning agent is added, the mixture is rotated for 2-3h, sodium bicarbonate is added to adjust the pH to 4-5, the mixture is continuously rotated for 50-60min, and then the mixture is washed and taken out.

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