Salt-free and chromium-free tanning method and tanned leather obtained

Abstract

The present invention belongs to the technical field of leather tanning, and discloses a salt-free and chromium-free tanning method. The method uses softened bare skin as raw material, and realizes an environmentally friendly and efficient tanning process by sequentially carrying out bio-based dialdehyde carboxylic acid pre-tanning, salt-free pickling and iron salt tanning. Among them, the amount of bio-based dialdehyde carboxylic acid added is 1wt%-5wt% of the weight of the bare skin, and the amount of iron salt added is 5wt%-30wt%. The dialdehyde group in the bio-based dialdehyde carboxylic acid can pre-tan and soften the bare skin, block the amino group and cross-link collagen, effectively prevent acid swelling, and realize salt-free pickling; its carboxyl group provides an additional binding site for the iron tanning agent, forming a strong cross-linking network and enhancing the tanning performance. In addition, the bio-based dialdehyde carboxylic acid can also scavenge free radicals and fix Fe 3+ , to avoid deterioration and deterioration of leather during storage. The present invention is not only environmentally friendly and has excellent tanning properties, but also has good storage stability for tanned leather, providing strong technical support for the clean transformation of the leather industry.

Description

Technical Field

[0001] The present invention relates to the technical field of leather tanning, in particular to a salt-free and chromium-free tanning method and the tanned leather obtained. Background Art

[0002] The traditional chrome tanning process, involving two steps—pickling and chrome tanning—inevitably results in the discharge of large amounts of chlorine- and chromium-containing wastewater, posing increasingly severe environmental challenges. The development of salt- and chrome-free tanning technologies has become a critical and pressing issue for the leather industry. Non-chrome metal tanning technologies, due to their high compatibility with subsequent dyeing and finishing processes, have become a research hotspot. Iron salt tanning agents, in particular, are considered an ideal alternative to chrome tanning agents due to their abundant reserves and low cost. However, the traditional iron salt tanning method still follows a "pickling followed by iron salt tanning" process, resulting in three major challenges: weak tanning properties; the generation of chlorine-containing wastewater; and the difficulty in preserving iron-tanned leather, which can easily harden and become brittle. These issues severely limit the widespread application of iron tanning technology. Therefore, the development of a salt- and chrome-free tanning technology that effectively addresses these issues while achieving low cost, high efficiency, and environmental friendliness is crucial for promoting the innovation and development of clean leathermaking technologies. Summary of the Invention

[0003] In view of the problems existing in the above-mentioned background technology, the present invention aims to provide a salt-free and chromium-free tanning method and tanned leather obtained which are environmentally friendly, have excellent tanning properties and good storage resistance.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] Using bated leather as raw material, the process is followed by bio-based dialdehyde carboxylic acid pre-tanning, salt-free pickling and iron salt tanning.

[0006] Wherein, based on the weight of the limed bare hide, the added amount of the bio-based dialdehyde carboxylic acid is 1wt%-5wt%; the added amount of the iron salt is 5wt%-30wt%.

[0007] Preferably, the softened bare hide comprises any one of softened sheep hide, softened goat hide and softened cow hide.

[0008] Preferably, the bio-based dialdehyde carboxylic acid comprises any one of dialdehyde sodium alginate, dialdehyde sodium carboxymethyl cellulose and dialdehyde carboxymethyl starch.

[0009] Preferably, the bio-based dialdehyde carboxylic acid pre-tanning is performed by permeating the raw material with the bio-based dialdehyde carboxylic acid for 30-360 minutes and then combining the raw material at 35-42° C. for 30-240 minutes.

[0010] Preferably, the salt-free pickling is performed by adjusting the pH of the reaction solution to 2.5-4.0 without using sodium chloride.

[0011] Preferably, the iron salt comprises iron sulfate or iron nitrate.

[0012] Preferably, the iron salt tanning is to penetrate the pre-tanned raw material with iron salt for 60-300 minutes, add alkali to pH 3.5-4.5, and combine at 35-42° C. for 60-180 minutes.

[0013] Preferably, the iron salt tanning process further contains a ligand, and the ligand comprises any one or more of sodium formate, sodium lactate, sodium tartrate and sodium citrate.

[0014] Preferably, the alkali extracting agent used in the alkali extraction comprises any one or more of sodium bicarbonate, sodium carbonate, magnesium oxide and automatic alkali extracting agent.

[0015] The invention also discloses tanned leather obtained by adopting any of the above salt-free and chromium-free tanning technologies.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) Significantly improved environmental friendliness: The present invention simultaneously achieves salt-free pickling and chrome-free tanning, significantly reduces chloride ion emissions, and solves the problem of chromium pollution from the source, thereby greatly reducing the impact of the leather industry on the environment and demonstrating excellent ecological and environmental performance.

[0018] (2) Improved tanning performance: The present invention cleverly combines biomass dialdehyde carboxylic acid tanning agent with iron salt for combined tanning, which significantly enhances the tanning effect of iron salt and greatly improves the wet and hot stability of iron tanned leather, providing a tanning solution with superior performance for leather processing.

[0019] (3) Enhanced storage stability of iron-tanned leather: In order to address the defects of traditional iron-tanned leather that is prone to aging, hardening and brittleness, the present invention effectively improves the aging resistance of iron-tanned leather, greatly enhances the storage stability and service life of iron salt tanned leather, and further broadens the application scope and market potential of iron-tanned leather. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a diagram of the tanning principle of an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments.It should be understood that these descriptions are exemplary only, and are not intended to limit the scope of the present invention.In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.Unindicated specific conditions in the embodiment are carried out according to the conditions of normal conditions or manufacturer's advice.Reagents used or instruments are not indicated by manufacturers, and are conventional products that can be obtained by commercial purchase.

[0022] The embodiment provided by the present invention is a salt-free and chrome-free tanning technology:

[0023] Using bated leather as raw material, the process is followed by bio-based dialdehyde carboxylic acid pre-tanning, salt-free pickling and iron salt tanning.

[0024] Wherein, based on the weight of the limed bare hide, the added amount of the bio-based dialdehyde carboxylic acid is 1wt%-5wt%; the added amount of the iron salt is 5wt%-30wt%.

[0025] The traditional iron salt tanning method follows the process flow of "pickling first, then iron salt tanning". During the pickling process, the reason why the bare skin swells is that the acid combines with the collagen amino group, causing the amino group to be protonated and the skin collagen to carry a positive charge. Due to the repulsion between the charges, the bare skin swells significantly. In order to suppress this acidic swelling phenomenon, it is usually necessary to add neutral salts. The mechanism of action of neutral salts is to increase the concentration of diffusible ions in the external solution, balance the osmotic pressure inside and outside the skin collagen, and promote the penetration of water molecules from the inside of the skin to the outside of the skin, thereby effectively inhibiting the expansion of the bare skin in the pickling solution. However, the introduction of neutral salts inevitably brings about the problem of discharging chlorine-containing wastewater, which increases the difficulty of wastewater treatment. In order to solve this problem, the applicant conducted a large number of experiments and found that the use of bio-based dialdehyde carboxylic acid to pre-tan the softened bare skin can prevent the bare skin from swelling during the pickling process. The principle is that bio-based dialdehyde carboxylic acid is a biomass material with both dialdehyde and carboxyl functional groups. The dialdehyde groups can covalently bond with the amino groups in skin collagen to form a Schiff base structure. This blocks the amino groups to reduce the positive charge of the skin while also cross-linking the collagen in the skin, thereby preventing acid swelling. Ultimately, safe, salt-free pickling is achieved.

[0026] The tanning effect of traditional iron tanning is relatively limited, resulting in insufficient cross-linking and fixation of collagen fibers by iron tanning agents. The present invention innovatively introduces bio-based dialdehyde carboxylic acid to pre-tan softened bare skin. By covalently binding the dialdehyde group in the bio-based dialdehyde carboxylic acid molecule with the amino group in the skin collagen, additional carboxyl binding sites are successfully introduced. In the subsequent iron tanning process, the carboxyl group of the bio-based dialdehyde carboxylic acid can effectively promote the absorption and fixation of the iron tanning agent, thereby building a more stable and tough cross-linked network structure ( Figure 1 ), which significantly improved the tanning performance of iron tanning agents.

[0027] In addition, traditional iron-tanned leather is usually difficult to withstand the test of long-term storage and is prone to hardening and brittleness during storage. The reason is that, on the one hand, iron ions act as photocatalysts and generate active free radicals that are destructive to collagen during storage, resulting in a decline in leather performance; on the other hand, although Fe 3 + However, under the action of reducing components in leather, Fe 3+ Will be reduced to non-tanning Fe 2+ , thus inducing the de-tanning phenomenon, further aggravating the aging of the leather. It is for the above reasons that the quality of tanned leather using iron salts as tanning agents in the prior art is poor and is not common. The present invention solves this problem for the first time and can significantly enhance the storage stability of iron-tanned leather. The key means is to combine the bio-based dialdehyde carboxylic acid pre-tanning with iron salt tanning for the first time. Specifically: Bio-based dialdehyde carboxylic acid uses polysaccharide as raw material, which not only has a certain free radical scavenging ability, but can also effectively remove the active free radicals generated by iron-tanned leather during storage to avoid damage to the leather; and the carboxyl group in the bio-based dialdehyde carboxylic acid reacts with Fe 3+ A more solid closed structure is formed, making Fe 3+ Difficult to be reduced to Fe 2+ , thus effectively preventing the occurrence of de-tanning.

[0028] Based on the above theory, as long as the bio-based aldehyde acid tanning agent contains both dialdehyde and carboxylic acid, it can achieve the effect of the present invention. For example, dialdehyde sodium alginate, dialdehyde sodium carboxymethyl cellulose and dialdehyde carboxymethyl starch. In the embodiment of the present invention, during the pre-tanning of bio-based dialdehyde carboxylic acid, the addition amount of bio-based dialdehyde carboxylic acid is 1wt%-5wt% based on the weight of the limed bare hide. Within this addition amount range, the effect of the bio-based dialdehyde carboxylic acid is more fully exerted. If the addition amount is less than 1wt%, too little addition amount will lead to insufficient pre-tanning of the bare hide, making it difficult to avoid the acid swelling phenomenon during salt-free pickling, and at the same time making the subsequent iron tanning effect poor, and the storage performance cannot be significantly improved; if the addition amount is higher than 5wt%, first of all, the leather making cost will become higher, and secondly, a large amount of bio-based dialdehyde carboxylic acid will be present on the surface of the tanned leather, making it difficult for the iron tanning agent to penetrate, resulting in surface binding, thereby causing the tanned leather to not be "thoroughly tanned" and the subsequent iron tanning effect to decrease.

[0029] During bio-based dialdehyde carboxylic acid pre-tanning, the tanning agent penetration time, binding time, and binding temperature involved are all conventional tanning parameters in the prior art and can be adaptively selected by those skilled in the art based on the type of hide, tanning agent, and desired tanning effect. Therefore, these parameters are not limited in this disclosure and are provided for illustrative purposes only. For example, the dialdehyde carboxylic acid tanning agent may have a penetration time of 30-360 minutes in the raw material, a binding temperature of 35-42°C, and a binding time of 30-240 minutes.

[0030] In some preferred embodiments, the softened bare hide is any one of softened goat hide, softened sheep hide and softened cow hide.

[0031] Salt-free pickling refers to pickling the pre-tanned material without the addition of sodium chloride. The pH of the acid solution and reaction solution (i.e., bath) used are controlled using methods commonly used in the art. For example, formic acid and / or sulfuric acid can be used to adjust the pH of the reaction solution to 2.5-4.0.

[0032] In some preferred embodiments, the commonly used iron salt tanning agents include iron sulfate and iron nitrate.

[0033] It is well known in the prior art that during iron salt tanning, in order to further improve the tanning effect, ligands such as sodium formate, sodium lactate, sodium tartrate and sodium citrate may be added simultaneously with the tanning.

[0034] In some optional embodiments, during iron salt tanning, the alkali extracting agent used for alkali extraction is an alkaline substance commonly used in the art, including any one or more of sodium bicarbonate, sodium carbonate, magnesium oxide and automatic alkali extracting agent.

[0035] In order to make the technical solution of the present invention clearer, a salt-free and chromium-free tanning method provided by the present invention is described in detail below through multiple specific embodiments and comparative examples.

[0036] In the following examples and comparative examples, the chloride ion concentration in tanning wastewater was determined according to HJ / T 84-2016, "Water Quality—Determination of Inorganic Anions—Ion Chromatography." Iron-tanned leather was dyed and finished according to conventional processes to produce iron-tanned crust leather. Its shrinkage temperature was measured using a Sunshine Electronics Research Institute MSW-YD4 shrinkage temperature meter. Furthermore, the softness of the crust leather was measured using a Gaotie GT-303 softness meter, and the tensile strength and tear strength were measured using a Gaotie AI-7000S servo-controlled computer system tensile testing machine. To simulate the aging process, the crust leather was heat-aged in a 50°C forced air drying oven for 24 hours, turning over every 12 hours. After 24 hours, the heat-aged crust leather was removed.

[0037] Example 1

[0038] To softened cowhide, 120 wt% water and 3 wt% sodium dialdehyde alginate, based on the weight of the limed hide, were added. The mixture was allowed to infiltrate for 180 minutes, followed by binding at 42°C for 240 minutes. The pH of the bath was then adjusted to 3.2 in the absence of salt. The bath was then replaced with 40 wt% water, 16 wt% ferric sulfate, and 4 wt% sodium formate. After infiltration for 180 minutes, the bath was alkali-enriched to a pH of 4.0. The bath was then allowed to infiltrate at 42°C for 120 minutes and allowed to stand overnight to produce iron-tanned leather.

[0039] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 95.2°C, the softness was 8.1 mm, and the tensile strength was 14.5 N / mm. 2 , tear strength is 45.4N / mm; after heat aging, the shrinkage temperature of the crust leather is 94.8℃, the softness is 8.0mm, and the tensile strength is 14.2N / mm 2 , the tear strength is 44.8N / mm, and the specific results are shown in Table 1.

[0040] Comparative Example 1

[0041] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not use bio-based dialdehyde carboxylic acid to pre-tan the softened cowhide, but instead uses the traditional "salt pickling + iron tanning" method for leather tanning. The detailed process steps are as follows:

[0042] To softened cowhide, 120 wt% water and 8 wt% sodium chloride, based on the weight of the limed hide, were added to adjust the bath pH to 3.2. Subsequently, 80 wt% of the acid solution was removed, and 16 wt% ferric sulfate and 4 wt% sodium formate were added. After infiltration for 180 minutes, the alkali solution was raised to a bath pH of 4.0. The leather was then combined at 42°C for 120 minutes and allowed to stand overnight to obtain iron-tanned leather.

[0043] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 13.4 g / L, the shrinkage temperature of the crust leather was 83.5°C, the softness was 6.8 mm, and the tensile strength was 13.8 N / mm 2 , tear strength is 42.1N / mm; after heat aging, the shrinkage temperature of the crust leather is 78.6℃, the softness is 5.6mm, and the tensile strength is 7.4N / mm 2 , the tear strength is 12.6N / mm, and the specific results are shown in Table 1.

[0044] According to the test results of Example 1 and Comparative Example 1, the following results can be obtained:

[0045] Example 1 uses bio-based dialdehyde carboxylic acid for pre-tanning treatment, followed by salt-free pickling, and finally iron salt tanning. Due to the pre-tanning effect of bio-based dialdehyde carboxylic acid, the bare skin will not experience acid swelling during the pickling process without adding neutral salt, so the concentration of chloride ions in the tanning wastewater is extremely low, only 0.2g / L. These trace amounts of chloride ions mainly come from the salt used for pickling of raw hides and the residual salt in the chemical materials used in the leather preparation section. In the subsequent iron salt tanning process, the additional carboxyl groups introduced by the bio-based dialdehyde carboxylic acid can form a coordination bond with the iron tanning agent, thereby forming a strong macromolecular cross-linked network between the collagen fiber network. This makes the shrinkage temperature of the iron-tanned crust leather as high as 95.2°C, the softness of the crust leather reaches 8.1mm, and the tensile strength reaches 14.5N / mm 2 , the tear strength reaches 45.4N / mm. In addition, due to the scavenging effect of bio-based dialdehyde carboxylic acid on active free radicals and Fe 3+ The iron tanned leather has no obvious detanning and deterioration after heat aging, and the shrinkage temperature is still as high as 94.8℃. The softness of the leather is 8.0mm and the tensile strength reaches 14.2N / mm. 2 The tear strength reaches 44.8N / mm, indicating that the iron-tanned leather has not hardened and become brittle, and has excellent storage stability.

[0046] Comparative Example 1 used the traditional iron tanning method, which first carried out salt pickling treatment and then iron salt tanning. Since neutral salt was added during the pickling process to suppress the acid swelling of the bare leather, the chloride ion concentration in the tanning wastewater was as high as 13.4 g / L. In the subsequent iron salt tanning process, the iron tanning agent had difficulty forming a stable cross-linked structure between the collagen fiber network. As a result, the shrinkage temperature of the obtained iron tanned leather was only 83.5°C, the softness was 6.8mm, and the tensile strength was 13.8N / mm 2 , the tear strength is 42.1N / mm. In addition, due to the generation of active free radicals and Fe 3+ Due to the reducing effect, the iron-tanned crust leather showed obvious detanning and deterioration after heat aging, which was manifested in the shrinkage temperature dropping to 78.6℃, the softness dropping to 5.6mm, and the tensile strength dropping to 7.4N / mm. 2 , the tear strength dropped to 12.6 N / mm. These results indicate that traditional iron-tanned leather hardened and became brittle after heat aging, and had poor storage stability.

[0047] Through the analysis of the above embodiments and comparative examples, it can be clearly seen that the "bio-based dialdehyde carboxylic acid pre-tanning + salt-free pickling + iron salt tanning" method adopted in the present invention, compared with the traditional "salt pickling + iron salt tanning", not only shows significant advantages in ecology and tanning properties, but also the tanned leather has better storage resistance, providing strong technical support for the clean transformation of the leather industry.

[0048] Table 1 Test results

[0049] .

[0050] Example 2

[0051] To softened sheepskin, 40 wt% water and 1 wt% sodium dialdehyde carboxymethylcellulose (DDCMC) were added, based on the weight of the limed hide. The mixture was infiltrated for 30 minutes and then bonded at 38°C for 120 minutes. The pH of the bath was then adjusted to 2.5 in the absence of salt. The bath was then replaced with 120 wt% water, 5 wt% ferric nitrate, and 1 wt% sodium lactate. After infiltration for 300 minutes, the bath was alkali-enriched to a pH of 4.5. The mixture was then bonded at 35°C for 60 minutes and allowed to stand overnight to produce iron-tanned leather.

[0052] The chloride ion concentration in the tanning wastewater in this embodiment was determined to be 0.1 g / L, the shrinkage temperature of the crust leather was 88.7°C, the softness was 7.8 mm, and the tensile strength was 13.8 N / mm. 2 , tear strength is 42.6N / mm; after heat aging, the shrinkage temperature of the crust leather is 87.9℃, the softness is 7.7mm, and the tensile strength is 13.2N / mm 2 , the tear strength is 41.9N / mm.

[0053] Example 3

[0054] To bated goat hides, 200 wt% water and 5 wt% dialdehyde carboxymethyl starch, based on the weight of the limed hide, were added. After 360 minutes of infiltration, the bath was combined at 35°C for 30 minutes. The pH of the bath was then adjusted to 4.0 in the absence of salt. The bath was then replaced with 200 wt% water, 30 wt% ferric sulfate, and 8 wt% sodium tartrate. After 60 minutes of infiltration, the bath was alkaline-treated with magnesium oxide to a pH of 3.5. The bath was combined at 42°C for 180 minutes and allowed to stand overnight to produce iron-tanned leather.

[0055] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 98.2°C, the softness was 8.4 mm, and the tensile strength was 17.2 N / mm. 2 , tear strength is 53.8N / mm; after heat aging, the shrinkage temperature of the crust leather is 98.0℃, the softness is 8.3mm, and the tensile strength is 17.1N / mm 2 , the tear strength is 52.8N / mm.

[0056] Example 4

[0057] To softened cowhide, 40% by weight of water and 1% by weight of sodium dialdehyde carboxymethylcellulose (DDCMC) were added, based on the weight of the limed hide. The mixture was allowed to penetrate for 360 minutes, followed by binding at 35°C for 30 minutes. The pH of the bath was then adjusted to 2.5 in the absence of salt. The bath was then replaced with 200% by weight of water, 5% by weight of ferric nitrate, and 8% by weight of sodium citrate. After 60 minutes of penetration, the bath was alkali-enriched to a pH of 4.0, and binding was continued at 42°C for 180 minutes. The mixture was then allowed to stand overnight to produce iron-tanned leather.

[0058] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 85.4°C, the softness was 7.4 mm, and the tensile strength was 16.2 N / mm 2 , tear strength is 49.7N / mm; after heat aging, the shrinkage temperature of the crust leather is 84.9℃, the softness is 7.4mm, and the tensile strength is 16.1N / mm 2 , the tear strength is 49.2N / mm.

[0059] Example 5

[0060] To softened sheepskin, 120 wt% water and 3 wt% dialdehyde carboxymethyl starch, based on the weight of the limed hide, were added. The mixture was allowed to soak for 180 minutes, followed by binding at 42°C for 240 minutes. The pH of the bath was then adjusted to 3.2 in the absence of salt. The bath was then replaced with 40 wt% water, 16 wt% ferric sulfate, and 4 wt% sodium formate. After soaking for 180 minutes, the bath was alkali-enriched to a pH of 3.5. The mixture was then bound at 38°C for 120 minutes and allowed to stand overnight to produce iron-tanned leather.

[0061] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 96.7°C, the softness was 8.7 mm, and the tensile strength was 12.9 N / mm 2 , tear strength is 41.5N / mm; after heat aging, the shrinkage temperature of the crust leather is 95.9℃, the softness is 8.6mm, and the tensile strength is 12.8N / mm 2 , the tear strength is 40.4N / mm.

[0062] Example 6

[0063] To bated goat hides, 40 wt% water and 1 wt% sodium dialdehyde carboxymethylcellulose (DDCMC) were added, based on the weight of the limed hide. The mixture was infiltrated for 30 minutes and then combined at 38°C for 120 minutes. The pH of the bath was then adjusted to 2.5 in the absence of salt. The bath was then replaced with 120 wt% water, 16 wt% ferric nitrate, 4 wt% sodium formate, and 4 wt% sodium tartrate. After infiltration for 180 minutes, the alkali solution was added to a pH of 4.0. The mixture was combined at 35°C for 60 minutes and allowed to stand overnight to produce iron-tanned leather.

[0064] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 92.9°C, the softness was 8.2 mm, and the tensile strength was 18.3 N / mm. 2 , tear strength is 55.6N / mm; after heat aging, the shrinkage temperature of the crust leather is 92.5℃, the softness is 8.1mm, and the tensile strength is 18.2N / mm 2 , the tear strength is 54.8N / mm.

[0065] Example 7

[0066] To softened cowhide, 200 wt% water and 5 wt% dialdehyde carboxymethyl starch, based on the weight of the limed hide, were added. The mixture was infiltrated for 30 minutes and then bonded at 38°C for 120 minutes. The pH of the bath was then adjusted to 4.0 in the absence of salt. The bath was then replaced with 120 wt% water, 30 wt% ferric nitrate, 0.5 wt% sodium lactate, and 0.5 wt% sodium citrate. After infiltration for 300 minutes, the bath was alkali-enriched to a pH of 3.5. The mixture was then bonded at 35°C for 60 minutes and allowed to stand overnight to produce iron-tanned leather.

[0067] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 97.3°C, the softness was 8.3 mm, and the tensile strength was 13.9 N / mm 2 , tear strength is 44.7N / mm; after heat aging, the shrinkage temperature of the crust leather is 96.8℃, the softness is 8.2mm, and the tensile strength is 13.6N / mm 2 , the tear strength is 43.9N / mm.

[0068] Example 8

[0069] To softened sheepskin, 200 wt% water and 5 wt% sodium dialdehyde alginate, based on the weight of the limed hide, were added. The mixture was infiltrated for 360 minutes and then bonded at 35°C for 360 minutes. The pH of the bath was then adjusted to 4.0 in the absence of salt. The bath was then replaced with 200 wt% water, 30 wt% ferric sulfate, 4 wt% sodium tartrate, and 4 wt% sodium citrate. After infiltration for 60 minutes, the bath was alkali-enriched to a pH of 4.0. The bath was then bonded at 42°C for 180 minutes and allowed to stand overnight to produce iron-tanned leather.

[0070] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 98.4°C, the softness was 9.1 mm, and the tensile strength was 12.6 N / mm 2 , tear strength is 40.4N / mm; after heat aging, the shrinkage temperature of the crust leather is 98.3℃, the softness is 8.9mm, and the tensile strength is 12.4N / mm2 , the tear strength is 40.1N / mm.

[0071] Example 9

[0072] To softened goat leather, 120 wt% water and 3 wt% dialdehyde carboxymethyl starch, based on the weight of the limed hide, were added. The mixture was infiltrated for 180 minutes and then bonded at 42°C for 240 minutes. The pH of the bath was then adjusted to 3.2 in the absence of salt. The bath was then replaced with 40 wt% water, 5 wt% ferric nitrate, 2 wt% sodium lactate, and 2 wt% sodium tartrate. After infiltration for 300 minutes, the bath was alkali-enriched to a pH of 4.5. The mixture was then bonded at 38°C for 120 minutes and allowed to stand overnight to produce iron-tanned leather.

[0073] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 90.1°C, the softness was 7.9 mm, and the tensile strength was 20.1 N / mm. 2 , tear strength is 58.4N / mm; after heat aging, the shrinkage temperature of the crust leather is 89.9℃, the softness is 7.8mm, and the tensile strength is 19.9N / mm 2 , the tear strength is 57.8N / mm.

[0074] Example 10

[0075] To softened cowhide, 120 wt% water and 3 wt% sodium dialdehyde carboxymethylcellulose (DDCMC) were added, based on the weight of the limed hide. The mixture was allowed to penetrate for 180 minutes and then bonded at 42°C for 240 minutes. The pH of the bath was then adjusted to 3.5 in the absence of salt. The bath was then replaced with 120 wt% water, 16 wt% ferric sulfate, and 4 wt% sodium tartrate. After 180 minutes of penetration, the bath was alkali-enriched to a pH of 4.0. The bath was then bonded at 38°C for 120 minutes and allowed to stand overnight to produce iron-tanned leather.

[0076] The chloride ion concentration in the tanning wastewater in this embodiment was measured to be 0.2 g / L, the shrinkage temperature of the crust leather was 94.9°C, the softness was 8.2 mm, and the tensile strength was 14.8 N / mm. 2 , tear strength is 46.1N / mm; after heat aging, the shrinkage temperature of the crust leather is 94.7℃, the softness is 8.0mm, and the tensile strength is 14.5N / mm 2 , the tear strength is 45.9N / mm.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A salt-free and chrome-free tanning method, characterized in that: Using bated leather as raw material, the process is followed by bio-based dialdehyde carboxylic acid pre-tanning, salt-free pickling and iron salt tanning. Wherein, based on the weight of the limed bare hide, the added amount of the bio-based dialdehyde carboxylic acid is 1wt%-5wt%; the added amount of the iron salt is 5wt%-30wt%.

2. The salt-free and chrome-free tanning method according to claim 1, wherein: The softened bare hide comprises any one of softened sheep hide, softened goat hide and softened cow hide.

3. The salt-free and chrome-free tanning method according to claim 1, wherein: The bio-based dialdehyde carboxylic acid comprises any one of dialdehyde sodium alginate, dialdehyde sodium carboxymethyl cellulose and dialdehyde carboxymethyl starch.

4. The salt-free and chrome-free tanning method according to claim 1, wherein: The bio-based dialdehyde carboxylic acid pre-tanning is performed by permeating the raw material with the bio-based dialdehyde carboxylic acid for 30-360 minutes and then combining the raw material at 35-42° C. for 30-240 minutes.

5. The salt-free and chrome-free tanning method according to claim 1, wherein: The salt-free pickling is to adjust the pH of the reaction solution to 2.5-4.0 without using sodium chloride.

6. The salt-free and chrome-free tanning method according to claim 1, wherein: The iron salt comprises iron sulfate or iron nitrate.

7. The salt-free and chrome-free tanning method according to claim 1, wherein: The iron salt tanning comprises the following steps: using iron salt to penetrate the pre-tanned raw material for 60-300 minutes, raising the alkali to pH 3.5-4.5, and combining at 35-42° C. for 60-180 minutes.

8. The salt-free and chrome-free tanning method according to claim 7, wherein: The iron salt tanning process also contains a ligand, which includes any one or more of sodium formate, sodium lactate, sodium tartrate and sodium citrate.

9. The salt-free and chrome-free tanning method according to claim 7, wherein: The alkali extracting agent used in the alkali extraction comprises any one or more of sodium bicarbonate, sodium carbonate, and magnesium oxide.

10. Tanned leather obtained by the salt-free and chromium-free tanning method according to any one of claims 1 to 9.

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