A chrome-free tanning agent and its preparation method and application

Abstract

The present invention discloses a chrome-free tanning agent and a preparation method and application thereof. The chrome-free tanning agent comprises, by weight, 100 parts of starch, 40 to 100 parts of a saccharide modifier, 10 to 50 parts of an oxidant, 200 to 400 parts of a nano-silicon compound, and 50 to 100 parts of water. In the present invention, starch is degraded and oxidized to form a low-molecular polysaccharide containing carboxyl and aldehyde groups, and the polysaccharide molecules are bonded with the nano-silicon compound to form a stable organic-inorganic hybrid. The nano-hybrid of soft and hard molecules can easily penetrate into the leather during the tanning process, and the aldehyde and carboxyl groups carried can react with the amino groups of collagen in the skin. At the same time, the nano-silicon compound is bonded to the polysaccharide molecules, so that the leather can be given excellent fullness, firmness, softness and tear resistance.

Description

Technical Field

[0001] The invention relates to the technical field of leather tanning, and in particular to a chrome-free tanning agent and a preparation method and application thereof. Background Art

[0002] For many years, leather has been the material of choice for footwear, clothing, accessories, interiors, and for decorating houses and furniture. The quality of leather depends on its strength, flexibility, durability, availability, and ability to be decorated using various techniques. Tanning is a key processing step that determines the flexibility of leather and gives it a good feel and aesthetics. At present, the leather industry mainly uses chrome tanning, which produces a large amount of chromium-containing wastewater and chromium-containing solid waste, making it difficult to treat and increasing the cost of waste treatment for enterprises. With environmental protection requirements, chrome tanning has been subject to extremely stringent restrictions. Therefore, the development of chrome-free tanning and the elimination of chromium pollution from the source are urgent requirements for the leather industry to achieve sustainable development. Non-chrome metal tanning agents also have a certain history of application in the leather industry, but because of their strong hydrolysis and coordination effects, metal ions are easily deposited on the leather surface, which can easily cause over-tanning of leather or uneven absorption of leather, resulting in poor thermal stability, stiff feel, and poor sensory properties of leather. Therefore, non-chrome metal tanning agents have not yet been successfully promoted and applied.

[0003] Vegetable tanning is an early method used in mineral tanning, mainly using plant polyphenol extracts, commonly known as vegetable tannins. Vegetable tanning has some inherent disadvantages: high neutral salt content in vegetable tannins, increased hydrophilicity, slow tannin penetration, poor color fastness, and poor tear strength of vegetable tanned leather.

[0004] The most widely used synthetic tanning agents are mainly protein alkylating compounds such as glutaraldehyde and its derivatives, polycyclic aldehydes, glyoxal and more recently oxazolidines, used alone or in combination with resins or vegetable tannins. Leather tanned with synthetic tanning agents has certain drawbacks: the color of semi-processed leathers using such synthetic tanning agents can be wrongly called "wet white" because the leather will have a distinctive yellow process defect; the mechanical strength of the finished leather is poor; when using synthetic tanning agents, a real concern is the presence of monomeric free formaldehyde in their preparations as a synthesis by-product, exceeding the existing free formaldehyde content limit.

[0005] Sugar substances are widely present in nature and have the advantages of being safe, non-toxic and renewable. Most of their structural units contain a vicinal diol structure, which can be selectively oxidized into two aldehyde groups with high reactivity under the action of periodic acid / periodate. According to the aldehyde tanning principle, such glycosylated derivatives can be used for the tanning of leather and fur. The related art discloses a technical scheme for dialdehyde modification and degradation of rice starch using sodium periodate. The product prepared by this scheme has a large molecular weight and a narrow distribution and can only be used for leather retanning and filling. The entire preparation operation process is cumbersome, time-consuming and inefficient. There is also a related art that discloses a method for preparing a high-concentration glycosylated aldehyde tanning agent. The scheme is time-consuming, and the light-proof reaction and separation of periodate steps are cumbersome and easily cause product quality problems caused by operational errors. Some related technologies also disclose a method for preparing an amino-modified glycosylated aldehyde tanning agent. The leather tanned by the tanning agent prepared by this scheme has good flexibility, but the bonding problem between the cationic group and aldehyde group of the tanning agent and the protein collagen causes the leather to have poor thermal stability. Summary of the invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art, and overcome the problems that the existing organic tanning agents have low aldehyde content, the operation of directly separating iodate is cumbersome, and the large molecular weight of the tanning agent causes low binding rate of tanned leather with collagen on leather. To this end, the purpose of the present invention is to provide a chrome-free tanning agent and its preparation method and application.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The first aspect of the present invention provides a chrome-free tanning agent, which comprises, by weight, 100 parts of starch, 40 to 100 parts of a sugar-based modifier, 10 to 50 parts of an oxidant, 200 to 400 parts of a nano-silicon compound, and 50 to 100 parts of water.

[0009] In the present invention, starch is degraded and oxidized to form a low-molecular polysaccharide containing carboxyl and aldehyde groups. The polysaccharide molecules are bonded to the nano-silicon compound to form a stable organic-inorganic hybrid. This nano-hybrid combining soft and hard molecules can easily penetrate into the leather during the tanning process. The aldehyde and carboxyl groups carried by the hybrid can react with the amino groups of the collagen in the skin. At the same time, the nano-silicon compound is bonded to the polysaccharide molecules, thereby giving the leather excellent fullness, firmness, softness and tear resistance.

[0010] In some embodiments of the present invention, the chrome-free tanning agent includes, by weight, 100 parts of starch, 50 to 80 parts of sugar-based modifier, 10 to 50 parts of oxidant, 250 to 350 parts of nano-silicon compound, and 80 to 100 parts of water.

[0011] In some embodiments of the present invention, the active matter content in the starch is ≥50%, and the degree of polymerization is 1.4-1.6.

[0012] In some embodiments of the present invention, the sugar base improving agent includes at least one of lactic acid, acetic acid, and hydrochloric acid.

[0013] In some embodiments of the present invention, the oxidant includes at least one of hydrogen peroxide, sodium persulfate, and ferric persulfate.

[0014] In some embodiments of the present invention, the nano silicon compound includes at least one of sodium silicate, sodium metasilicate, potassium silicate and potassium metasilicate.

[0015] The second aspect of the present invention provides a method for preparing the chrome-free tanning agent, comprising the following steps: heating and stirring starch, water, a sugar-based modifier, and an oxidant according to the composition in parts by weight, adding a nano-silicon compound with stirring after cooling, and adjusting the pH of the system to 2-4 to obtain the chrome-free tanning agent.

[0016] In some embodiments of the present invention, the heating and stirring is performed at a temperature of 60° C. to 120° C. for a time of 1 h to 5 h; preferably 80° C. to 100° C. for a time of 2 h to 4 h.

[0017] In some embodiments of the present invention, the method for preparing the chrome-free tanning agent further comprises stirring and adding the nano-silicon compound, and continuing stirring for 1 hour to 2 hours.

[0018] The third aspect of the present invention provides a leather tanning method, comprising tanning using the chrome-free tanning agent.

[0019] The fourth aspect of the present invention provides a use of the chrome-free tanning agent in leather tanning.

[0020] In some embodiments of the present invention, the tanning includes primary tanning and / or retanning.

[0021] In some embodiments of the present invention, in the primary tanning, the amount of the chrome-free tanning agent is 5 wt% to 10 wt% based on the weight of the grey leather.

[0022] In some embodiments of the present invention, in the retanning, the amount of the chrome-free tanning agent is 2 wt% to 8 wt% based on the weight of the grey leather.

[0023] The beneficial effects of the present invention are:

[0024] In the present invention, starch is degraded and oxidized to form low-molecular polysaccharides containing carboxyl groups and aldehyde groups. The polysaccharide molecules are bonded with nano-silicon compounds to form a stable organic-inorganic hybrid. The nano-hybrid combining soft and hard molecules can easily penetrate into the leather during the tanning process. The aldehyde groups and carboxyl groups carried by the hybrid can react with the amino groups of collagen in the skin. At the same time, the nano-silicon compounds are bonded to the polysaccharide molecules, thereby giving the leather excellent fullness, firmness, softness and tear resistance.

[0025] The raw materials used in the chrome-free tanning agent of the present invention are renewable resources, safe and environmentally friendly, and are conducive to the green development of the leather industry. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below by specific examples. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial sources or can be obtained by prior art methods. Unless otherwise specified, the experiments or test methods are conventional methods in the art.

[0027] Example 1

[0028] This embodiment prepares a chrome-free tanning agent, and the specific process is as follows:

[0029] Take 100 parts of starch, add 80 parts of water, 50 parts of lactic acid and 20 parts of hydrogen peroxide, heat to 80℃~100℃ under closed stirring, stir and react for 4 hours to allow the sugar group to form small molecule carboxyl and aldehyde groups, cool to room temperature, add 250 parts of sodium silicate solution dropwise under high-speed stirring, continue stirring at low speed for 2 hours after the addition, and finally adjust the pH of the reaction solution to 2-4.

[0030] After testing, the mass volume concentration of the tanning agent is 80%, the molecular weight is 198g / mol, and the viscosity is 16.3mPa·s. When the tanning agent is used for the primary tanning of leather, the dosage of the saccharide aldehyde tanning agent is 8% based on the weight of the gray leather.

[0031] Example 2

[0032] This embodiment prepares a chrome-free tanning agent, and the specific process is as follows:

[0033] Take 100 parts of starch, add 100 parts of water, 80 parts of lactic acid and 20 parts of ferric persulfate, heat to 80℃~100℃ under closed stirring, stir and react for 2 hours to allow the sugar group to form small molecule carboxyl and aldehyde groups, cool to room temperature, add 350 parts of sodium silicate solution dropwise under high-speed stirring, continue stirring at low speed for 1 hour after the addition, and finally adjust the pH of the reaction solution to 2-4.

[0034] After testing, the mass volume concentration of the tanning agent is 82%, the molecular weight is 225g / mol, and the viscosity is 18.2mPa·s. When the tanning agent is used for the primary tanning of leather, the weight of the gray leather is used as the dosage basis, and the dosage of the sugar-based aldehyde tanning agent is 9%.

[0035] Example 3

[0036] This embodiment prepares a chrome-free tanning agent, and the specific process is as follows:

[0037] Take 100 parts of starch, add 80 parts of water, 50 parts of lactic acid and 20 parts of hydrogen peroxide, heat to 80℃~100℃ under closed stirring, stir and react for 4 hours to allow the sugar group to form small molecule carboxyl and aldehyde groups, add 350 parts of sodium silicate solution dropwise under high-speed stirring, continue stirring at low speed for 1 hour after the addition, and finally adjust the pH of the reaction solution to 2-4.

[0038] Comparative Example 1

[0039] This comparative example prepares a tanning agent, and the specific process is as follows:

[0040] Take 100 parts of starch, add 80 parts of water, 50 parts of lactic acid and 20 parts of hydrogen peroxide, heat to 80℃~100℃ under closed stirring, stir and react for 4 hours to allow the sugar group to form small molecule carboxyl and aldehyde groups, cool to room temperature, and finally adjust the pH of the reaction solution to 2-4.

[0041] The mass volume concentration of the tanning agent is 36%, the molecular weight is 98g / mol, and the viscosity is 10.3mPa·s. When the tanning agent is used for the primary tanning of leather, the dosage of the saccharide aldehyde tanning agent is 45% based on the weight of the gray leather.

[0042] Comparative Example 2

[0043] This comparative example prepares a tanning agent, and the specific process is as follows:

[0044] Take 100 parts of starch, add 100 parts of water, 80 parts of lactic acid and 20 parts of ferric persulfate, heat to 80℃~100℃ under closed stirring, stir and react for 2 hours to allow the sugar group to form small molecule carboxyl and aldehyde groups, cool to room temperature, and finally adjust the pH of the reaction solution to 2-4.

[0045] After testing, the mass volume concentration of the tanning agent is 28%, the molecular weight is 106g / mol, and the viscosity is 11.8mPa·s. When the tanning agent is used for the primary tanning of leather, the dosage is 52% based on the weight of the gray leather.

[0046] Comparative Example 3

[0047] This comparative example prepares a tanning agent, and the specific process is as follows:

[0048] Take 100 parts of sucrose by weight, dissolve it in 500 parts of water, then add 150 parts of sodium periodate to react in the dark for 12 hours. After the reaction is completed, adjust the pH to 6.0 with sodium hydroxide, stir, filter and separate the iodate precipitate, and collect the filtrate to obtain the saccharide aldehyde tanning agent.

[0049] Comparative Example 4

[0050] This comparative example prepares a tanning agent, and the specific process is as follows:

[0051] Take 100 parts of vegetable tannin extract, add 80 parts of water, 50 parts of lactic acid and 20 parts of ferric persulfate, heat to 80-100°C under closed stirring, stir and react for 4 hours, add 350 parts of sodium silicate solution dropwise under high-speed stirring, continue stirring at low speed for 1 hour after the addition, and finally adjust the pH of the reaction solution to 2-4.

[0052] Comparative Example 5

[0053] This comparative example prepares a tanning agent, and the specific process is as follows:

[0054] Take 85 parts of starch, 5 parts of cerium sulfate, and 4 parts of sodium silicate:

[0055] (1) dissolving starch in 90 parts of deionized water and stirring thoroughly to obtain solution 1;

[0056] (2) dissolving a cerium salt in 5 parts of deionized water to obtain a solution 2;

[0057] (3) dissolving sodium silicate in 5 parts of deionized water to obtain solution 3;

[0058] (4) First, slowly add solution 3 to solution 1, stir thoroughly, then add solution 2, stir and mix thoroughly again, allow to react fully for 13 to 15 hours, then concentrate under reduced pressure at 65°C, precipitate solid matter, filter, and dry to obtain a finished product. The stirring speed in step (4) is 150 r / min.

[0059] Comparative Example 6

[0060] This comparative example prepares a tanning agent, and the specific process is as follows:

[0061] Take 85 parts of vegetable tannin extract, 5 parts of cerium sulfate, and 4 parts of sodium silicate:

[0062] (1) dissolving starch in 90 parts of deionized water and stirring thoroughly to obtain solution 1;

[0063] (2) dissolving a cerium salt in 5 parts of deionized water to obtain a solution 2;

[0064] (3) dissolving sodium silicate in 5 parts of deionized water to obtain solution 3;

[0065] (4) First, slowly add solution 3 to solution 1, stir thoroughly, then add solution 2, stir and mix thoroughly again, allow to react fully for 13 to 15 hours, then concentrate under reduced pressure at 65°C, precipitate solid matter, filter, and dry to obtain a finished product. The stirring speed in step (4) is 150 r / min.

[0066] Comparative Example 7

[0067] This comparative example adopts commercially available TWS chromium-free organic tanning agent, and the preparation raw materials mainly include polysaccharide, periodate, water, and inorganic reducing agent.

[0068] Test example

[0069] The mass volume concentration of the tanning agent in Examples 1-2 and Comparative Examples 1-2 and the amount of the tanning agent used during tanning are shown in Table 1:

[0070] Table 1

[0071] Compare Projects Tanning mass volume concentration Tanning agent dosage Example 1 80％ 8％ Comparative Example 1 36％ 45％ Example 2 82％ 9％ Comparative Example 2 28％ 52％

[0072] As can be seen from Table 1, the effective content of the tanning agent of the present invention is much higher than that of the tanning agent prepared by the method provided in the comparative example. The amount of the tanning agent of the present invention used in the primary tanning of leather is significantly less than that of the tanning agent prepared by the method provided in the comparative example.

[0073] The tanning agents of Example 3 and Comparative Examples 3 to 7 were subjected to a parallel comparative test on leather tanning. The leathers used in the leather tanning tests were all Australian bull hides. Except for the tanning agents, other chemical materials and tanning agent process conditions were the same.

[0074] The leather was tanned with the tanning agents of Example 3 and Comparative Examples 3 to 7 at a tanning agent dosage of 9%. The shrinkage temperature, elongation at break and tensile strength of the tanned leather were tested according to the reference standards (QB / T 2710-2018, QB / T 2713-2005). The test results are shown in Table 2.

[0075] Table 2 Test parameters of leather tanned by various tanning agents

[0076] Test items Example 3 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Shrinkage temperature(℃) 108 103 93 95 96 105 Elongation at break (%) 20.6 18.6 11.2 11.8 11.5 19.2 <![CDATA[Expansion strength (N·mm -2 )]]> 6.3 5.6 3.3 3.1 3.3 5.0

[0077] As can be seen from Table 2, the leather tanned with the chrome-free tanning agent prepared by the present invention improves the stability of the collagen in the leather, makes the finished leather feel fuller, has a denser tissue structure, has a greater tensile strength, and both the bonding force and stability are improved.

[0078] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A chrome-free tanning agent, characterized in that: In parts by weight, it comprises 100 parts of starch, 40 parts to 100 parts of sugar-based modifier, 10 parts to 50 parts of oxidant, 200 parts to 400 parts of nano-silicon compound, and 50 parts to 100 parts of water; The sugar base improver includes at least one of lactic acid, acetic acid and hydrochloric acid; The oxidant comprises at least one of hydrogen peroxide, sodium persulfate, and ferric persulfate; The nano silicon compound includes at least one of sodium silicate, sodium metasilicate, potassium silicate and potassium metasilicate.

2. The chrome-free tanning agent according to claim 1, characterized in that: The active matter content in the starch is ≥50%.

3. The chrome-free tanning agent according to claim 1, characterized in that: The chrome-free tanning agent comprises, by weight, 100 parts of starch, 50 to 80 parts of a sugar-based modifier, 10 to 50 parts of an oxidant, 250 to 350 parts of a nano-silicon compound, and 80 to 100 parts of water.

4. A method for preparing a chrome-free tanning agent according to any one of claims 1 to 3, characterized in that: The following steps are involved: Starch, water, a sugar-based modifier and an oxidant are heated and stirred according to the composition in parts by weight, and after cooling, a nano-silicon compound is added with stirring, and the pH of the system is adjusted to 2-4 to obtain the chrome-free tanning agent.

5. The method for preparing a chrome-free tanning agent according to claim 4, characterized in that: The method for preparing the chrome-free tanning agent further comprises stirring and adding the nano silicon compound, and then continuing to stir for 1 hour to 2 hours.

6. A leather tanning method, characterized in that: The method comprises using the chrome-free tanning agent as described in any one of claims 1 to 3 for tanning.

7. Use of the chrome-free tanning agent as described in any one of claims 1 to 3 in leather tanning.

8. The use according to claim 7, characterized in that: The tanning includes primary tanning and / or retanning; in the primary tanning, the amount of the chrome-free tanning agent is 5wt% to 10wt% based on the weight of the grey leather.

9. The use according to claim 8, characterized in that: In the retanning, the amount of the chrome-free tanning agent is 2wt% to 8wt% based on the weight of the grey leather.