Method for preparing composite tanning agent by catalytically oxidizing starch through metal-based eutectic solvent

Abstract

The invention belongs to the field of tanning agents for leather making, and particularly discloses a method for preparing a composite tanning agent by catalytically oxidizing starch through a metal-based eutectic solvent. The preparation method comprises the following steps: blending metal inorganic salt and an organic solvent, heating and stirring to obtain a metal-based eutectic solvent, adding starch into the metal-based eutectic solvent, stirring, and finally adding hydrogen peroxide to oxidize the starch, thereby obtaining the metal-based modified starch composite tanning agent. The prepared composite tanning agent has excellent tanning performance, and tanned crust leather is high in shrinkage temperature and high in physical and mechanical performance. The preparation method is simple, fast, green, free of pollution, easy to industrially popularize and good in application prospect.

Description

Technical Field

[0001] The invention belongs to the field of leather tanning agents, and particularly relates to a method for preparing a composite tanning agent by catalyzing the oxidation of starch by a metal-based deep eutectic solvent. Background Art

[0002] Tanning is a crucial step in transforming raw hides into leather. Chrome tanning agents are a common tanning agent in the leather industry due to their excellent permeability and binding properties, resulting in chrome-tanned leather that is plump and soft. However, the large amount of solid waste and chrome tanning wastewater generated by chrome tanning exacerbates environmental pollution and threatens human health. Furthermore, the cost of treating chrome tanning wastewater is high. Therefore, to meet the needs of a sustainable and eco-friendly leather industry, the development of green and environmentally friendly chrome-free tanning agents is imperative.

[0003] Starch, a natural polymer material, is a polysaccharide formed by the polymerization of glucose molecules through glycosidic bonds. It possesses numerous hydroxyl groups and is widely available, renewable, natural, biodegradable, and pollution-free. It is widely used in the food, medical, and paper industries. However, starch has a relatively high molecular weight, typically between 10⁷ and 10⁸, making it impermeable to leather. Furthermore, the reactive groups that cross-link with leather are limited, resulting in poor tanning results. Therefore, starch cannot be used directly in leather tanning and requires modification.

[0004] Currently, the leather industry produces oxidized starch (OS) using sodium periodate, sodium hypochlorite, and hydrogen peroxide. However, sodium periodate and sodium hypochlorite are relatively expensive oxidants, and the reaction byproducts and oxidant residues are difficult to remove after oxidizing the starch. Hydrogen peroxide, as a green oxidant, produces water and oxygen as oxidation products, which meets the needs of an eco-friendly leather industry. However, the tanning properties of the oxidized starch are poor, requiring its use in combination with other tanning agents.

[0005] Deep eutectic solvents (DES) are eutectic mixtures composed of hydrogen bond acceptors and donors formed through hydrogen bonding. They are considered a novel green solvent due to their low cost, biodegradability, low toxicity, ease of preparation, and recyclability. Metal-based deep eutectic solvents are the most attractive and promising subclass of DES, but their research and application in the leather industry are limited. Research on the application of metal-based deep eutectic solvents in the leather industry is of great significance. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method for preparing a composite tanning agent by catalyzing the oxidation of starch using a metal-based deep eutectic solvent.

[0007] In one aspect, the present invention provides a method for preparing a composite tanning agent by catalyzing the oxidation of starch using a metal-based deep eutectic solvent, comprising the following steps:

[0008] Step 1: mixing a hydrogen bond donor and a metal salt in a certain molar ratio, heating and stirring to form a transparent solution, and cooling to obtain a metal-based deep eutectic solvent;

[0009] Step 2: Mixing starch with the metal-based deep eutectic solvent prepared in step 1, heating and stirring, to obtain a mixture of starch and the metal-based deep eutectic solvent;

[0010] Step 3: Add hydrogen peroxide to the mixture of starch and metal-based low eutectic solvent in step 2, heat and stir to react, and prepare a metal-based modified starch tanning agent.

[0011] Furthermore, in the method, the metal salt is aluminum chloride, ferric chloride, zinc chloride, zirconium oxychloride, or zirconium chloride and zirconium oxychloride.

[0012] Furthermore, in the method, the hydrogen bond donor is glycerol or ethylene glycol.

[0013] Furthermore, in the method, the molar ratio of the hydrogen bond donor to the metal salt in step 1 is 1:0.05-0.2.

[0014] Furthermore, in the method, the heating temperature in step 1 is 70 to 90° C., and the stirring time is 1 to 3 hours.

[0015] Furthermore, in the method, the starch in step 2 is corn starch, tapioca starch, wheat starch or potato starch.

[0016] Furthermore, in the method, the heating temperature in step 2 is 60-80°C.

[0017] Furthermore, in the method, the amount of hydrogen peroxide added in step three is 40% to 100% of the mass of the starch.

[0018] Furthermore, in the method, the reaction temperature in step 3 is 60-80° C., and the reaction time is 2-5 h.

[0019] Finally, a composite tanning agent prepared by the method described in the present invention is also provided.

[0020] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0021] (1) The present invention uses a metal-based deep eutectic solvent as a reaction medium and catalyst for hydrogen peroxide oxidation of starch. The metal-based deep eutectic solvent inhibits the hydrogen bonds between starch molecules and destroys the glycosidic bonds between glucose molecules, thereby opening the starch molecules and reducing the molecular weight, which is more conducive to hydrogen peroxide oxidation of starch.

[0022] (2) The modified oxidized starch composite tanning agent prepared by the present invention has an appropriate molecular weight of the oxidized starch and an increase in the types of groups on the molecule. The leather after tanning has a good shrinkage temperature, thickening rate and softness, and excellent mechanical properties and sensory properties.

[0023] (3) The preparation method provided by the present invention is simple, quick, green and pollution-free, easy to industrialize and popularize, and has good application prospects. DETAILED DESCRIPTION

[0024] The technical solutions of the present invention are described below with reference to the following embodiments; however, the present invention is not limited to the following embodiments.

[0025] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments, but the embodiments are not intended to limit the present invention.

[0026] The experimental methods and detection methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0027] Example 1

[0028] This embodiment is to prepare an aluminum-based modified starch tanning agent.

[0029] Step 1: Weigh 1 mol of glycerol and 0.1 mol of aluminum chloride into a beaker at a molar ratio of 1:0.1, stir at 70°C for 1 hour to form a transparent solution. After cooling to room temperature, the solvent remains transparent, thus obtaining an aluminum chloride-glycerol deep eutectic solvent.

[0030] Step 2: Weigh 10 g of corn starch and 50 g of aluminum chloride-glycerol deep eutectic solvent, heat at 60° C. with stirring for 30 min to obtain a mixture of corn starch and aluminum chloride-glycerol deep eutectic solvent.

[0031] Step 3: Weigh 6 g of hydrogen peroxide and slowly add it to the mixture of corn starch and aluminum chloride-glycerol deep eutectic solvent prepared in step 2, and heat at 60° C. with stirring for 4 hours to prepare an aluminum-modified starch tanning agent.

[0032] Example 2

[0033] This embodiment is to prepare an iron-based modified starch tanning agent.

[0034] Step 1: Weigh 1 mol of ethylene glycol and 0.05 mol of ferric chloride into a beaker at a molar ratio of 1:0.05, stir at 70°C for 2 hours to form a transparent solution, and cool to room temperature until the solvent remains transparent to obtain a ferric chloride-ethylene glycol deep eutectic solvent.

[0035] Step 2: Weigh 10 g of cassava starch and 50 g of ferric chloride-ethylene glycol deep eutectic solvent, stir and heat at 70° C. for 30 min to obtain a mixture of cassava starch and ferric chloride-ethylene glycol deep eutectic solvent.

[0036] Step 3: Weigh 4 g of hydrogen peroxide and slowly add it to the mixture of cassava starch and ferric chloride-ethylene glycol low eutectic solvent in step 2, stir and heat at 70° C. for 2 h to prepare an iron-based modified starch tanning agent.

[0037] Example 3

[0038] This example is about preparing zinc-based modified starch tanning agent.

[0039] Step 1: Weigh 1 mol of ethylene glycol and 0.2 mol of zinc chloride in a beaker at a molar ratio of 1:0.2, stir at 80°C for 2 hours to form a transparent solution. After cooling to room temperature, the solvent remains transparent, thereby obtaining a zinc chloride-ethylene glycol deep eutectic solvent.

[0040] Step 2: Weigh 10 g of wheat starch and 50 g of zinc chloride-ethylene glycol deep eutectic solvent, stir and heat at 80° C. for 30 min to obtain a mixture of wheat starch and zinc chloride-ethylene glycol deep eutectic solvent.

[0041] Step 3: Weigh 8 g of hydrogen peroxide and slowly add it to the mixture of wheat starch and zinc chloride-ethylene glycol low eutectic solvent in step 2, stir and heat at 80° C. for 5 h to prepare a zinc-based modified starch tanning agent.

[0042] Example 4

[0043] This example is about preparing a zirconium-based modified starch tanning agent.

[0044] Step 1: Weigh 1 mol of ethylene glycol and 0.05 mol of zirconium chloride into a beaker at a molar ratio of 1:0.05, stir and dissolve at 90°C for 1 hour to form a transparent solution. After cooling to room temperature, the solvent remains transparent, thereby obtaining a zirconium chloride-ethylene glycol deep eutectic solvent.

[0045] Step 2: Weigh 10 g of potato starch and 50 g of zirconium chloride-ethylene glycol deep eutectic solvent, stir and heat at 70° C. for 30 min to obtain a mixture of potato starch and zirconium chloride-ethylene glycol deep eutectic solvent.

[0046] Step 3: Weigh 6 g of hydrogen peroxide and slowly add it to the mixture of potato starch and zirconium chloride-ethylene glycol low eutectic solvent in step 2, stir and heat at 70°C for 2 hours to prepare a zirconium-based modified starch tanning agent.

[0047] Example 5

[0048] This example is about preparing a zirconium-based modified starch tanning agent.

[0049] Step 1: Weigh 1 mol of ethylene glycol and 0.2 mol of zirconium oxychloride into a beaker at a molar ratio of 1:0.2, stir and dissolve at 70°C for 1 hour to form a transparent solution. After cooling to room temperature, the solvent remains transparent, thereby obtaining a zirconium oxychloride-ethylene glycol deep eutectic solvent.

[0050] Step 2: Weigh 10 g of corn starch and 50 g of zirconium oxychloride-ethylene glycol deep eutectic solvent, heat at 70° C. with stirring for 30 min to obtain a mixture of corn starch and zirconium oxychloride-ethylene glycol deep eutectic solvent.

[0051] Step 3: Weigh 8 g of hydrogen peroxide and slowly add it to the mixture of corn starch and zirconium oxychloride-ethylene glycol low eutectic solvent in step 2, stir and heat at 70°C for 2 hours to prepare a zirconium-based modified starch tanning agent.

[0052] Example 6

[0053] This example is about preparing zirconium-aluminum based modified starch tanning agent.

[0054] Step 1: Weigh 1 mol of ethylene glycol, 0.1 mol of aluminum chloride, and 0.05 mol of zirconium chloride into a beaker. The molar ratio of ethylene glycol to aluminum salt and zirconium salt is 1:0.2. Stir and dissolve at 80°C for 3 hours to form a transparent solution. After cooling to room temperature, the solvent remains transparent, thus obtaining a zirconium chloride aluminum-ethylene glycol eutectic solvent.

[0055] Step 2: Weigh 10 g of cassava starch and 50 g of aluminum zirconium chloride-ethylene glycol deep eutectic solvent, and heat with stirring at 80° C. for 30 min to obtain a mixture of cassava starch and aluminum zirconium chloride-ethylene glycol deep eutectic solvent.

[0056] Step 3: Weigh 10 g of hydrogen peroxide and slowly add it to the mixture of cassava starch and aluminum zirconium chloride-ethylene glycol low eutectic solvent in step 2, stir and heat at 80° C. for 2 h to obtain a zirconium aluminum-based modified starch tanning agent.

[0057] Comparative Example

[0058] In this comparative example, water was used as the solvent and Fe-Cu catalyzed the oxidation of starch peroxide (H-OS).

[0059] Step 1: Weigh 10g corn starch, 0.008g ferrous sulfate and 0.002g copper sulfate, add 50ml water, and heat with stirring at 70°C for 30min.

[0060] Step 2: Weigh 10 g of hydrogen peroxide and slowly add it to the mixture of corn starch and water in step 1, heat at 70° C. with stirring for 4 h to prepare a water-oxidized starch tanning agent (H-OS).

[0061] Test Case

[0062] In order to evaluate the tanning performance of the metal-based oxidized starch composite tanning agent prepared by the present invention, this test example carried out tanning application experiments on different metal salt low eutectic solvents, H-OS, commercially available chrome-free tanning agent TWS, and the metal-based oxidized starch composite tanning agents prepared in Examples 1-6. At the same time, a control group was set up, and the control group was not treated with any tanning agent. The tanning performance of different tanning agents was evaluated by testing the shrinkage temperature and physical and mechanical properties of the leather. The results are shown in Tables 1 and 2.

[0063] Table 1 Shrinkage temperature of leather after tanning with different tanning agents

[0064] Material Shrinkage temperature (℃) Material Shrinkage temperature (℃) <![CDATA[AlCl3-DES]]> 53.2 Example 1 67.5 <![CDATA[FeCl3-DES]]> 55.4 Example 2 71.6 <![CDATA[ZnCl2-DES]]> 51.6 Example 3 62.1 <![CDATA[ZrCl4-DES]]> 62.7 Example 4 72.2 <![CDATA[ZrOCl2-DES]]> 56.8 Example 5 81.5 H-OS 51.9 Example 6 85.8 control group 49.9 TWS 82.8

[0065] Table 2 Physical and mechanical properties of leather after tanning with different tanning agents

[0066]

[0067]

[0068] As can be seen from Table 1, the shrinkage temperature of leather after tanning with different metal salt low eutectic solvents (AlCl3-DES, FeCl3-DES, ZnCl2-DES, ZrCl4-DES, ZrOCl2-DES) is higher than that of the control group (49.9°C), indicating that metal salt low eutectic solvents have a certain tanning effect on leather, but the shrinkage temperature after tanning alone is slightly increased. The shrinkage temperature of H-OS after tanning (51.9°C) is slightly higher than that of the control group, and it has almost no tanning property. The shrinkage temperature of the metal-based oxidized starch composite tanning agent prepared in Examples 1-6 after tanning is significantly higher than that of the control group and other metal salt low eutectic solvents and H-OS, which indirectly proves that the catalytic oxidation of starch by metal-based low eutectic solvents improves the starch oxidation efficiency and tanning performance. Among them, the shrinkage temperature of Example 6 is the highest, reaching 85.8°C, which exceeds the commercially available chrome-free tanning agent TWS (82.8°C), indicating that the metal-based oxidized starch composite tanning agent prepared by the present invention has good tanning performance.

[0069] As can be seen from Table 2, in terms of physical and mechanical properties, compared with the control group, the leather tanned with different metal salt deep eutectic solvents has different degrees of improvement in tensile strength, elongation at break and tear strength, indicating that metal salt deep eutectic solvents are helpful in improving the physical and mechanical properties of leather.

[0070] The physical and mechanical properties of leather after H-OS tanning were not significantly improved, and some indicators were even lower than those of the control group, indicating that its tanning effect was relatively poor.

[0071] The overall physical and mechanical properties of the leather tanned with the metal-based oxidized starch composite tanning agent prepared in Examples 1-6 were superior to those of the control group, the metal salt deep eutectic solvent, and H-OS. Among them, the tensile strength of Example 6 reached 15.8 MPa, the elongation at break was 86.7%, and the tear strength was 82.3 N / mm. All indicators performed outstandingly, and some indicators were superior to the commercially available chrome-free tanning agent TWS. This further proves that the metal-based oxidized starch composite tanning agent prepared by the present invention can effectively enhance the physical and mechanical properties of leather.

[0072] As described above, the basic principles, main features and advantages of the present invention are well described. The above embodiments and descriptions are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the scope of protection determined by the present invention.

Claims

1. A method for preparing a composite tanning agent by catalyzing the oxidation of starch using a metal-based deep eutectic solvent, characterized in that: The following steps are involved: Step 1: mixing a hydrogen bond donor and a metal salt in a certain molar ratio, heating and stirring to form a transparent solution, and cooling to obtain a metal-based deep eutectic solvent; Step 2: Mixing starch with the metal-based deep eutectic solvent prepared in step 1, heating and stirring, to obtain a mixture of starch and the metal-based deep eutectic solvent; Step 3: Add hydrogen peroxide to the mixture of starch and metal-based low eutectic solvent in step 2, heat and stir to react, and prepare a metal-based modified starch tanning agent.

2. The method according to claim 1, characterized in that The metal salt is aluminum chloride, iron chloride, zinc chloride, zirconium oxychloride or zirconium chloride and zirconium oxychloride.

3. The method according to claim 1, characterized in that The hydrogen bond donor is glycerol or ethylene glycol.

4. The method according to claim 1, wherein The molar ratio of the hydrogen bond donor to the metal salt in step 1 is 1:0.05-0.

2.

5. The method according to claim 1, wherein The heating temperature in step 1 is 70-90° C., and the stirring time is 1-3 h.

6. The method according to claim 1, characterized in that The starch in step 2 is corn starch, tapioca starch, wheat starch or potato starch.

7. The method according to claim 1, characterized in that The heating temperature in step 2 is 60-80°C.

8. The method according to claim 1, characterized in that The amount of hydrogen peroxide added in step 3 is 40% to 100% of the mass of the starch.

9. The method according to claim 1, characterized in that The reaction temperature in step 3 is 60-80° C., and the reaction time is 2-5 h.

10. The composite tanning agent prepared by the method according to any one of claims 1 to 9.

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