Non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties and method for its preparation

Abstract

The present application relates to a kind of non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic performance and its preparation method.First, the prepolymer is prepared using polyisocyanate and cationic hydrophilic monomer, then the prepolymer is quaternized by adding alkylating agent, finally, the emulsified quaternary ammonium salt type prepolymer is capped by adding mixed aqueous solution of bisulfite and sulfite, and then the solid content and pH are adjusted to obtain a non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic performance.Compared with general organic synthetic tanning agent, the non-aldehyde synthetic tanning agent developed in the present application has excellent water solubility, high moisture and heat stability of tanned wet skin, does not contain free formaldehyde, and is resistant to yellowing, overcoming the defects of insufficient positive charge of leather blank prepared by general chrome-free organic tanning system and difficulty in combining subsequent sizing material, especially the problems of poor fullness, poor elasticity and poor dyeability of finished leather caused by insufficient absorption of fatliquoring agent and dye, etc.Due to the presence of a large number of quaternary ammonium salt groups in the tanning agent molecule, the finished leather has excellent antibacterial and bacteriostatic performance, high use value, and good storage resistance and durability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of leather chemical industry, in particular to a non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties and a preparation method thereof. BACKGROUND

[0002] Leather products have become necessities in people's daily life due to their practicality, beauty and fashion. Leather is a commercial product obtained by continuous physical and chemical treatment of animal skin, and tanning is a key process for changing the skin into leather. The principle is that the tanning agent added in the tanning process can cross-link the collagen fibers in the dermis, so that the physical and chemical properties of the leather, such as moisture and heat stability, are significantly improved, and finally meet the use requirements. At present, chrome tanning is the most important and widely used tanning method in leather manufacturing, which can give leather high thermal stability, comfortable hand feeling and excellent leather performance. However, the discharge of chromium-containing wastewater and chromium-containing solid waste from the chrome tanning system is very difficult to handle, and if it is directly discharged, it will cause serious pollution to the environment. It is disturbing that some studies have shown that trivalent chromium with tanning property (coordination) can be converted into hexavalent chromium with high toxicity under certain conditions, which will obviously endanger human health. As a clean technology, chrome-free tanning technology can effectively realize the reduction of chromium, and has always been a hot research direction in tanning chemistry.

[0003] For decades, researchers have been working on chrome-free tanning agents and chrome-free ecological tanning technology. At present, chrome-free tanning agents are mainly divided into three categories: inorganic tanning agents, organic tanning agents, and inorganic-organic combined tanning agents. Inorganic tanning agents mainly refer to non-chromium metal tanning agents, such as zirconium tanning agents, aluminum tanning agents, iron tanning agents, titanium tanning agents, and rare earth tanning agents. Organic tanning agents include plant tanning agents, aldehyde tanning agents, and non-aldehyde synthetic tanning agents. Among non-chromium metal tanning agents, aluminum tanning, iron tanning, titanium tanning, and rare earth tanning have limited shrinkage temperature improvement for leather (~63-80°C), and the combination of tanning agents and skin collagen is not firm. The biggest disadvantage is that the finished leather is not resistant to washing, and the skin will be retanned after washing. Although zirconium tanned leather has the highest shrinkage temperature (~95°C) and is resistant to washing, zirconium tanning can only be carried out at very low pH, which will cause great damage to the skin collagen, resulting in low tear strength of zirconium tanned leather. Therefore, in recent years, researchers have gradually shifted their focus to the development of organic tanning systems. Among them, plant tanning agents have a history of thousands of years of use, especially considering that they come from natural plants such as roots, stems, leaves, fruits, and skins, which have outstanding environmental value. However, plant tanned leather is hard, high in cost, poor in durability, easily affected by external factors such as water and sweat, and the tanning agent itself has a certain color, which can only be used for the preparation of dark-colored leather. Aldehyde tanning agents achieve tanning by chemical combination of aldehyde groups in the molecule with basic groups such as amino groups on collagen fibers, mainly including formaldehyde, glutaraldehyde, and modified glutaraldehyde. However, these aldehyde tanned leather will produce free formaldehyde during use, which is harmful to health. Other non-aldehyde tanning agents, such as melamine resin tanning agents, urea-formaldehyde resin tanning agents, urea ring resin tanning agents, various oxazolidine tanning agents, and organic phosphorus salt tanning agents, also have high shrinkage temperature, but free formaldehyde is difficult to control. Because these tanning agents are basically in the form of formaldehyde derivatives, they produce tanning properties by releasing free formaldehyde. Moreover, these organic synthetic tanning agents mainly react with amino groups on collagen, resulting in a significant decrease in the positive charge of the tanned leather, and poor combination with anionic dyes, fatliquoring agents, and other chemicals added in subsequent processes, resulting in poor fullness and dyeability of the finished leather.

[0004] On the other hand, although tanning can effectively improve the anti-enzyme and bacterial performance of leather products, due to the presence of a large amount of protein in leather, which lacks antibacterial ability, and the fact that leather products are easily contaminated with sweat and dirt in daily life, and are prone to bacterial growth in humid environments, which can harm human health and even cause mold, greatly shortening the service life of leather. Therefore, in order to make leather have certain antibacterial properties, some antibacterial materials are usually added during the production of leather, such as nano-silver, nano-zinc oxide, nano-titanium dioxide, tetracycline, isothiazolinone antibacterial and antiviral preparations, and negative cation release agents. However, these exogenous antibacterial materials generally have the problems of poor combination with collagen, easy migration, and short-lasting antibacterial performance. SUMMARY

[0005] In order to solve the above problems, the present application provides a non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties and a preparation method thereof. The non-aldehyde synthetic tanning agent is used to overcome the defects of general synthetic tanning agents, such as easy release of formaldehyde after tanning, low positive charge of the leather blank, affecting the subsequent absorption and fixation of the retanning and dyeing and finishing materials, poor fastness of leather dyeing, and flat and thin leather body. The present application also solves the problems of existing antibacterial materials for leather, easy migration, easy mold of leather, and not durable antibacterial performance. The quaternary ammonium salt organic cation and the carbamoyl sulfonate anion reactive group are introduced into the molecular structure of the tanning agent, which not only gives it excellent water solubility, but also gives the leather appropriate positive charge and excellent antibacterial performance. Due to the high reactivity of carbamoyl sulfonate with collagen amino groups, the non-aldehyde synthetic tanning agent developed by the present application is anchored between collagen fibers in the form of a covalent urea bond, forming effective cross-linking and significantly improving the shrinkage temperature of the leather blank. In particular, because the quaternary ammonium salt structure is fixed on the molecular chain of the tanning agent, the leather has durable antibacterial properties.

[0006] The technical solutions of the present application are as follows:

[0007] A non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties, the structure general formula is shown in (1), (2), (3) or (4):

[0008] (1)

[0009] (2)

[0010] (3)

[0011] (4)

[0012] Wherein, R- is CH3-, CH3CH2-, CH3(CH2)3- or CH3(CH2) 15 -;

[0013] X - is I - , Br - , Cl - or CH3OSO2 - ;

[0014] R' is Na or K.

[0015] The preparation method of the above-mentioned non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties comprises the following steps:

[0016] (1) Preparation of quaternary ammonium pre-polymer: after vacuum dehydration, the cationic hydrophilic monomer, polyisocyanate is added to the reactor, and reacted at 50-80℃ for 2h-5h. After the NCO reaction reaches the theoretical value, the temperature is lowered to 30℃, and a small amount of diluent is added to adjust the viscosity. Add an appropriate amount of alkylating agent, and continue to react at a certain temperature for 0.5h-8h, then lower the system temperature to 3℃-30℃.

[0017] (2) Preparation of capped tanning agent emulsion: add a measured amount of bisulfite, sulfite aqueous solution to the solution of quaternary ammonium salt type pre-polymer obtained in step (1) at one time, stir quickly, and disperse strongly to obtain a non-aldehyde synthetic tanning agent tanning agent emulsion with a blue-white color. Add deionized water to adjust the solid content to 35%, add an acidic compound, and further adjust the emulsion pH to about 4-6.

[0018] Further, the cationic hydrophilic monomer in step (1) is any one or more of N-methyl diethanolamine, N-(2-cyanoethyl) diethanolamine, N-ethyldiethanolamine, N-propyldiethanolamine, N,N-dimethylamino-N',N'-di(2-hydroxyethyl)-1,3-propanediamine, N,N-dimethylamino-N',N'-di(2-hydroxypropyl)-1,3-propanediamine, 3-(dimethylamine)-1,2-propanediol, N,N-dimethyl-(2-dihydroxymethyl)butylamine, N,N-diethyl-(2-dihydroxymethyl)butylamine, 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether, 1,2-ethanediol di(3-diethylamino-2-hydroxypropanol) ether.

[0019] Further, the polyisocyanate in step (1) is any one or more of dimethylene phenylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated toluene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated phenylmethane diisocyanate, 1,5-pentane diisocyanate, L-lysine diisocyanate, dimer acid diisocyanate.

[0020] Further, the diluent in step (1) is any one of dipropylene glycol dimethyl ether, diethylene glycol dimethyl ether, propylene glycol methyl ether acetate, propylene carbonate.

[0021] Further, the amount of diluent in step (1) is not more than 3% of the total mass of polyisocyanate and cationic hydrophilic monomer.

[0022] Further, the alkylating agent in step (1) is any one of methyl iodide, ethyl iodide, ethyl bromide, butyl bromide, n-hexadecyl bromide, methyl chloride, ethyl chloride, benzyl chloride, dimethyl sulfate.

[0023] Further, the amount of the alkylating agent in step (1) is 1-2 times the molar amount of the cationic hydrophilic monomer. The alkylating reaction temperature is 30-80℃.

[0024] Further, the bisulfite in step (2) is any one of sodium bisulfite or potassium bisulfite; the sulfite is any one of sodium sulfite or potassium sulfite.

[0025] Further, the mass fraction of the mixed aqueous solution of the bisulfite and the sulfite in step (2) is 20-35%.

[0026] Further, the acid compound in step (2) is any one of hydrochloric acid, sulfuric acid, phosphoric acid, citric acid, formic acid, acetic acid.

[0027] Further, the dispersion rotation speed in step (2) is 1000-2000r / min, and the dispersion time is 20-60min.

[0028] Further, the molar ratio of the polyisocyanate, the cationic hydrophilic monomer, the bisulfite, and the sulfite in steps (1) and (2) is 1-3:0.5-2:1-6:0.1-2.

[0029] The present application has the following advantages:

[0030] (1) The synthetic tanning agent developed in the present application is a chrome-free and formaldehyde-free tanning agent, which is safe and non-toxic in use, and the tanned leather product does not contain heavy metal chromium and free formaldehyde. At the same time, the tanning agent molecule contains a large number of cationic quaternary ammonium salt groups, which can impart significant antibacterial and bacteriostatic properties to the tanned leather.

[0031] (2) The tanning agent developed in the present application contains an amidoformyl sulfonic acid group, which has excellent water solubility and is suitable for water field tanning operation of leather. Moreover, it has high activity to react with the amino group of leather collagen under weak alkaline conditions (pH≥8) to form urea bond and covalently bind to collagen molecules, resulting in crosslinking between collagen fibers and bringing tanning effect. Moreover, as the tanning process proceeds, the molecular weight of the tanning agent gradually increases, further crosslinking the three-dimensional fiber network of collagen with different spacings, and the tanning effect is enhanced, so that the shrinkage temperature of the tanned wet white leather is high (Ts≥80℃), and the leather body appears full due to the filling of tanning agents with different molecular weights. Since it does not contain aldehyde, it is resistant to yellowing, and the tanned wet white leather is white. The tanning agent of the present application is especially suitable for the preparation of high-grade light-colored leather.

[0032] (3) The synthetic tanning agent developed in this invention overcomes the problem that after the general synthetic tanning agent combines with collagen amino groups, the positive charge of the leather blank decreases, resulting in an excessive negative charge on the leather body, which is not conducive to the combination of retanning agents, fatliquoring agents, dyes and other substances (mainly some anionic materials) in the subsequent retanning and dyeing processes. It avoids some problems of organic tanning such as poor dyeing and thin and flat leather. Attached Figure Description

[0033] Figure 1 SEM and elemental energy dispersive spectroscopy (EDS) images of the cross-section of wet white cowhide tanned in Example 1;

[0034] Figure 2 The images show the 2D and 3D super-depth-of-field images of the grain surface of the wet white cowhide tanned in Example 1. Detailed Implementation

[0035] The following description is merely a preferred embodiment of the present invention and is only used to describe the present invention. It should not be construed as a limitation on the scope of the present invention.

[0036] Example 1

[0037] (1) 1 mol of N,N-dimethyl-(2-dihydroxymethyl)butylamine and 2.5 mol of 1,5-pentanediisocyanate, which were dehydrated under vacuum at 105℃, were added to a reactor and reacted at 50℃ for 2 h. After the NCO reaction reached the theoretical value, the temperature was lowered to 30℃, a small amount of dipropylene glycol dimethyl ether was added for dilution, and then 1 mol of dimethyl sulfate was added. The reaction was continued at 30℃ for 0.5 h, and then the system was cooled to 5℃ to obtain a prepolymer solution.

[0038] (2) A 30% (w / w) aqueous solution containing 3 mol sodium bisulfite and 0.3 mol sodium sulfite was added to the prepolymer solution obtained in step (1) and strongly dispersed at 1000 r / min for 30 min to obtain a slightly blue non-aldehyde synthetic tanning agent emulsion. Deionized water was added to adjust the solid content to 35%, and dilute sulfuric acid solution was added to adjust the pH of the emulsion to 4 to obtain the non-aldehyde synthetic tanning agent, the structural formula of which is as follows:

[0039]

[0040] Example 2

[0041] (1) 1.5 mol of N,N-diethyl-(2-dihydroxymethyl)butylamine and 3 mol of hexamethylene diisocyanate, which were dehydrated under vacuum at 105℃, were added to the reactor and reacted at 60℃ for 3 h. After the NCO reaction reached the theoretical value, the temperature was lowered by 30℃, a small amount of diethylene glycol dimethyl ether was added for dilution, and then 1.6 mol of iodomethane was added. The temperature was raised to 60℃ and the reaction was continued for 2 h. The system was then cooled to 10℃ to obtain the prepolymer solution.

[0042] (2) To the prepolymer solution obtained in step (1), a mixed aqueous solution containing 3.3 mol of sodium bisulfite and 0.4 mol of sodium sulfite with a mass fraction of 30% was added at one time, and was dispersed at a speed of 1500 r / min for 50 min to obtain a milky white non-aldehyde synthetic tanning agent emulsion. Deionized water was added to adjust the solid content to 35%, dilute hydrochloric acid solution was added, and the pH of the emulsion was adjusted to 5 to obtain a non-aldehyde synthetic tanning agent, the structural formula of which is as follows:

[0043]

[0044] Example 3

[0045] (1) 1 mol of 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether and 3 mol of isofuroline diisocyanate after vacuum dehydration at 105°C were added to a reactor, and reacted at 80°C for 3 h. After the NCO reaction reached the theoretical value, the temperature was lowered to 30°C, propylene glycol methyl ether acetate was added for dilution, 1.1 mol of n-hexadecyl bromide was added, the temperature was raised to 80°C, and the reaction was continued for 6 h. Then the system was cooled to 20°C to obtain a prepolymer solution.

[0046] (2) To the prepolymer solution obtained in step (1), a mixed aqueous solution containing 3.3 mol of sodium bisulfite and 0.4 mol of sodium sulfite with a mass fraction of 30% was added at one time, and was dispersed at a speed of 1500 r / min for 50 min to obtain a milky white non-aldehyde synthetic tanning agent emulsion. Deionized water was added to adjust the solid content to 35%, dilute hydrochloric acid solution was added, and the pH of the emulsion was adjusted to 5 to obtain a non-aldehyde synthetic tanning agent, the structural formula of which is as follows:

[0047]

[0048] Example product application

[0049] Commercially available pickled cowhide was used for tanning experiments (the amount of chemicals used was calculated based on the weight of the acid skin. The specific tanning process is shown in Table 1). The shrinkage temperature, tensile strength, tear strength and sensory state of the white wet leather obtained by tanning were measured, and the results are shown in Table 2. According to the process described in Table 3, the tanned cowhide white wet leather was dyed and fat-liquored, and the dye uptake and observation results of the dyeing effect are shown in Table 4. Further, according to the bacteria solution absorption method in Appendix B of the national standard QB / T 2881-2013, the number of living bacteria of the raw leather after being inoculated with Klebsiella pneumoniae and Staphylococcus aureus for 24 h and Candida albicans for 48 h was detected, and the antibacterial rate of the leather was calculated, and the results are shown in Table 5.

[0050] Table 1 Tanning process parameters of synthetic tanning agent

[0051]

[0052] Table 2 shrinkage temperature of white wet leather, mechanical properties, appearance results of cowhide

[0053]

[0054] Table 3 tanning, dyeing and fat-liquoring process of leather

[0055]

[0056] Table 4 sensory evaluation of leather blank and absorption effect of dyeing waste liquid

[0057]

[0058] Table 5 detection results of antibacterial properties of leather blank

[0059]

[0060] From Table 2, it can be seen that the non-aldehyde synthetic tanning agent developed in the application has high shrinkage temperature (≥80℃) of the tanned white wet leather, good mechanical properties, and clean and fine grain of the leather body. From Table 4, it can be seen that the leather blank tanned by the tanning agent has soft and full leather, good hand feeling, and correct color after conventional fat-liquoring and dyeing, and the waste liquid has clear color, indicating that the tanning agent has good absorption and fixation properties of subsequent fat-liquoring agent and dye. From Table 5, it can be seen that the antibacterial rate of the leather blank reaches more than 90%, indicating that the tanning agent developed in the application has excellent antibacterial and bacteriostatic properties.

[0061] In order to further illustrate the beneficial effects of the application, the cross section and grain morphology of the cowhide tanned by Example 1 in Table 2 were observed by scanning electron microscope and super depth of field electron microscope. From the 2D and 3D images of the cross section of the tanned cowhide, it can be seen that the collagen fibers of the tanned cowhide are fully dispersed and have obvious fibrous structure, indicating that the cross-linking effect of the tanning agent is remarkable. Figure 1 In addition, from the 2D and 3D images of the grain of the tanned cowhide, it can be seen that the grain of the tanned cowhide is very fine. Figure 2 From the 2D and 3D images of the grain of the tanned cowhide, it can be seen that the grain of the tanned cowhide is very fine.

Claims

1. A non-aldehyde synthetic tanning agent having antibacterial and bacteriostatic properties, characterized in that it comprises: The tanning agent structure general formula is shown as (1), (2), (3) or (4): （1） ； （2） ； （3） ； （4） ； wherein R- is CH3-, CH3CH2-, CH3(CH2)3- or CH3(CH2) 15 -; X - for I - , Br - , Cl - or CH3OSO2 - ; R' is Na or K.

2. A method for preparing a non-aldehyde synthetic tanning agent having antibacterial and bacteriostatic properties according to claim 1, characterized in that, The method comprises the following steps: (1) Preparation of quaternary ammonium pre-polymer: after vacuum dehydration, the cationic hydrophilic monomer and polyisocyanate are added into a reactor and reacted at 50-80 DEG C for 2-5 h; after the NCO reaction reaches the theoretical value, the temperature is lowered to 30 DEG C, a diluent is added to adjust the viscosity; an appropriate amount of alkylating agent is added, and the system is cooled to 3-30 DEG C after continued reaction at a certain temperature for 0.5-8 h; (2) Preparation of capped tanning agent emulsion: the quaternary ammonium salt type pre-polymer solution obtained in step (1) is added with a metered amount of bisulfite and sulfite aqueous solution at one time, and a non-formaldehyde synthetic tanning agent emulsion of light blue to white color is obtained through rapid stirring and strong dispersion; deionized water is added to adjust the solid content to 35%, an acidic compound is added to further adjust the emulsion pH to 4-6, and the product is obtained.

3. The method for preparing a non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties according to claim 2, characterized in that, The cationic hydrophilic monomer in step (1) is any one or more of N-methyldiethanolamine, N-(2-cyanoethyl)diethanolamine, N-ethyldiethanolamine, N-propyldiethanolamine, N,N-dimethyl-N',N'-di(2-hydroxyethyl)-1,3-propanediamine, N,N-dimethyl-N',N'-di(2-hydroxypropyl)-1,3-propanediamine, 3-(dimethylamine)-1,2-propanediol, N,N-dimethyl-(2-dimethylol)butylamine, N,N-diethyl-(2-dimethylol)butylamine, 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether, and 1,2-ethanediol di(3-diethylamino-2-hydroxypropanol) ether; The polyisocyanate in step (1) is any one or more of dimethylene phenylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated toluene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated phenylmethane diisocyanate, 1,5-pentane diisocyanate, L-lysine diisocyanate, and dimer acid diisocyanate; The diluent in step (1) is any one of dipropylene glycol dimethyl ether, diethylene glycol dimethyl ether, propylene glycol methyl ether acetate, and propylene carbonate; The amount of the diluent in step (1) is not more than 3% of the total mass of the polyisocyanate and the cationic hydrophilic monomer; The alkylating agent in step (1) is any one of methyl iodide, ethyl iodide, ethyl bromide, butyl bromide, n-hexadecyl bromide, methyl chloride, ethyl chloride, benzyl chloride, and dimethyl sulfate; The amount of the alkylating agent in step (1) is 1-2 times the molar amount of the cationic hydrophilic monomer; the alkylating reaction temperature is 30-80 DEG C.

4. The method for preparing a non-aldehyde synthetic tanning agent having antibacterial and bacteriostatic properties according to claim 2, characterized in that, The bisulfite in step (2) is any one of sodium bisulfite and potassium bisulfite; the sulfite is any one of sodium sulfite and potassium sulfite; The mixed aqueous solution of the bisulfite and the sulfite in step (2) has a mass fraction of 20-35%; The acidic compound in step (2) is any one of hydrochloric acid, sulfuric acid, phosphoric acid, citric acid, formic acid, and acetic acid. The dispersing speed in step (2) is 1000-2000 r / min, and the dispersing time is 20-60 min.

5. The method for preparing a non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties according to claim 2, characterized in that, The cationic hydrophilic monomer is any one or more of 3-(dimethylamine)-1,2-propanediol, N,N-dimethyl-(2-dimethylol)butylamine, N,N-diethyl-(2-dimethylol)butylamine, 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether, and 1,2-ethanediol di(3-diethylamino-2-hydroxypropanol) ether.

6. The method for preparing a non-aldehyde synthetic tanning agent with antibacterial and bacteriostatic properties according to claim 2, characterized in that, The molar ratio of the polyisocyanate, the cationic hydrophilic monomer, the bisulfite, and the sulfite in steps (1) and (2) is 1-3:0.5-2:1-6:0.1-2.

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