A method for preparing a sustainable green amphoteric organic chrome-free tanning agent

Abstract

This invention relates to the technical field of organic chromium-free tanning agents, and discloses a method for preparing a sustainable green amphoteric organic chromium-free tanning agent, comprising the following steps: (1) adding corn starch to water, then adding sodium periodate, stirring and reacting in the dark to obtain DCST product; (2) mixing ethylene glycol diglycidyl ether, acetone and tetramethylenediamine, then adding hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine dropwise, maintaining the reaction for a period of time after the addition is complete; after the reaction is complete, distilling under reduced pressure to obtain HHTT-EGDE product; (3) dispersing the HHTT-EGDE product in water to obtain HHTT-EGDE solution; mixing the HHTT-EGDE solution with the DCST product, heating and reacting to obtain organic chromium-free tanning agent. Leather tanned with the organic chromium-free tanning agent of this invention has higher Ts, better mechanical strength, whiteness and antibacterial properties.

Description

Technical Field

[0001] This invention belongs to the technical field of organic chromium-free tanning agents, and more specifically relates to a method for preparing a sustainable green amphoteric organic chromium-free tanning agent. Background Technology

[0002] Traditional leather tanning agents mainly include chrome tanning agents, aluminum tanning agents, zirconium tanning agents, and formaldehyde tanning agents. Metal salt tanning agents bind firmly to protein fibers, giving tanned leather softness, high strength, washability, and resistance to detanning. Finished leather has a light color, beautiful appearance, good dyeing and finishing properties, good extensibility, good resistance to damp heat, and good stability, with a shrinkage temperature around 100℃. Aldehydes and their derivatives are generally not used as primary tanning agents in leather making. They are mainly used in pre-tanning, retanning, and other compound tanning processes, and can be used in combination with inorganic tanning agents such as aluminum, chrome, and zirconium, or as synthetic tanning agents. Formaldehyde has a strong adsorption capacity for proteins and can significantly increase the shrinkage temperature of finished leather. However, because these tanning agents contain a large amount of metal ions, the subsequent treatment of tanning wastewater often causes irreversible environmental damage. Organic chromium-free tanning agents are an important component of the sustainable development of the leather manufacturing industry. However, leather tanned with organic chromium-free tanning agents has a low isoelectric point (pI<5), which leads to low absorption rates of traditional anionic wet finishing materials, resulting in poor leather quality and difficult-to-treat tanning wastewater. Furthermore, leather is susceptible to bacterial and mold damage during production, storage, and use, causing significant economic losses to businesses and users. Therefore, developing a green, environmentally friendly, and antibacterial chromium-free organic tanning agent offers a new perspective for the design and development of multifunctional green materials for sustainable industrial manufacturing.

[0003] Cellulose and starch are inexhaustible resources, important natural biopolymers synthesized from plants and animals, possessing excellent biocompatibility, biodegradability, renewability, cost-effectiveness, and non-toxicity. Dialdehyde starch is widely used in papermaking, textiles, leather tanning, construction, and medical fields. Tanning is most effective when the aldehyde content is greater than 90%, and degraded dialdehyde starch can further enhance its fixation effect on collagen fibers. However, leather tanned using only dialdehyde starch still exhibits a low shrinkage temperature (77.9℃), poor mechanical properties, and a yellowish color, failing to meet industrial production standards. It is well known that dialdehyde starch forms Schiff bases through cross-linking with collagen fibers, but low cross-linking degree is likely the main reason for the low T-value and poor mechanical properties of the leather. Introducing new active functional groups is key to solving this problem; multiple functional groups work synergistically to form multi-point cross-links with collagen fibers.

[0004] Furthermore, during the preparation, storage, and use of leather, it is highly susceptible to the growth of bacteria and mold. Warm and humid environments provide ideal conditions for microbial growth. Bacteria and mold erode the collagen fibers of leather, causing damage to the texture, reducing its mechanical properties, affecting its appearance, and shortening its lifespan. In addition, bacteria and mold can cause skin infections in users, and leather rot can result in significant economic losses. Therefore, from the perspective of green and sustainable development, antibacterial treatment of leather is imperative. Summary of the Invention

[0005] The main objective of this invention is to address the aforementioned problems by providing a sustainable, green, amphoteric, organic, chromium-free tanning agent. Using hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine (HHTT), ethylene glycol diglycidyl ether (EGDE), and dialdehyde starch (DCST) as raw materials, an organic, chromium-free tanning agent (HHTT-EGDE-DCST) with high pI, antibacterial properties, amphoteric activity, and epoxy-terminated structure was prepared. This provides new insights into developing new green materials for the sustainable development of the leather manufacturing industry and offers new perspectives on developing a low-carbon and environmentally friendly industrialization path.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a method for preparing a sustainable, green, amphoteric organic chromium-free tanning agent, comprising the following steps:

[0007] (1) Add corn starch (CST) to water, then add sodium periodate to adjust the pH to 3-4, and stir the reaction in the dark; after the reaction is complete, separate the solid to obtain DCST product;

[0008] (2) After mixing ethylene glycol diglycidyl ether, acetone and tetramethylenediamine, hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine was added dropwise. After the addition was completed, the reaction was maintained for a period of time. After the reaction was completed, the product was distilled under reduced pressure to obtain HHTT-EGDE.

[0009] (3) Disperse the HHTT-EGDE product in water and adjust the pH to 10-11 until it is completely dissolved to obtain an HHTT-EGDE solution; mix the HHTT-EGDE solution with the DCST product and heat to react to obtain an organic chromium-free tanning agent.

[0010] Ethylene glycol diglycidyl ether (EGDE) is an economical and environmentally friendly crosslinking agent. Because each end of the EGDE molecule is linked to a highly reactive epoxy group, it can react with amino and hydroxyl groups under alkaline conditions. To achieve multi-point crosslinking between the tanning agent and collagen fibers, the COH and COC groups of hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine (HHTT) are first bonded to the epoxy groups of EGDE. The abundant COH and COC groups in HHTT bind more firmly to the epoxy groups, forming a more stable bond structure. Hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine, as a highly efficient, broad-spectrum, and environmentally friendly preservative and bactericide, is used in the preparation of organic chromium-free tanning agents, effectively inhibiting the growth of bacteria and mold on leather. The HHTT-EGDE solution is then mixed with the DCST product, and ethylene glycol diglycidyl ether is grafted onto dialdehyde corn starch (DCST) with an aldehyde content greater than 90%, forming a structure in which starch macromolecules are encapsulated on the outside. This allows the antibacterial agent to bind effectively, enhancing the long-lasting antibacterial effect. As a result, the tanned leather has higher Ts, better mechanical strength, whiteness, and antibacterial properties.

[0011] More preferably, in step (1), the ratio of corn starch to water is 30g: 400-500mL.

[0012] More preferably, in step (1), the molar ratio of sodium periodate monomer to pyranose glycosyl unit in corn starch is 1:1.

[0013] More preferably, in step (1), the time for the light-protected stirring reaction is 40 to 50 hours.

[0014] Further preferred, in step (1), the specific steps for separating the solid after the reaction are completed are as follows: cool the solution to room temperature, add anhydrous ethanol, stir until all solids are separated, and then filter under vacuum; resuspend the solid in water, filter under vacuum again, and repeat several times; then resuspend the solid in an ethanol-water solution, filter under vacuum, and repeat several times; finally wash with anhydrous ethanol, and the final product is dried under vacuum.

[0015] More preferably, in step (2), the ratio of the amount of ethylene glycol diglycidyl ether, acetone, tetramethylenediamine and hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine added is 15g:15-20mL:10mL:10-13.5g.

[0016] More preferably, in step (2), the dropping rate is one drop every 5 seconds; the reaction time is maintained for 3 to 6 hours; and the temperature of vacuum distillation is 60 to 70°C.

[0017] More preferably, in step (3), the ratio of the amount of HHTT-EGDE product dispersed in water is 4g: 40-50mL.

[0018] More preferably, in step (3), the HHTT-EGDE solution and the DCST product are mixed at a molar ratio of HHTT-EGDE to DCST of 1.1 to 1.5:1, and more preferably at a molar ratio of 1.3 to 1.5:1.

[0019] Since DCST is a polymer, the molar ratio was derived by calculating using Hill's formula.

[0020] More preferably, in step (3), the heating reaction is carried out at 50-60°C for 2-3 hours.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) Starch is an inexhaustible resource and an important natural biopolymer synthesized from plants and animals. It has excellent biocompatibility, biodegradability, renewability, cost-effectiveness, and non-toxicity. As a highly selective oxidant, sodium periodate can oxidize C2-OH and C3-OH to aldehyde groups to obtain dialdehyde starch (DCST). The tanning effect is best when the aldehyde content is greater than 90%. The degraded DST can further improve the fixation effect on collagen fibers.

[0023] (2) Ethylene glycol diglycidyl ether (EGDE) is an economical and environmentally friendly crosslinking agent. First, ethylene glycol diglycidyl ether is grafted onto HHTT, which promotes the combination of ethylene glycol diglycidyl ether and the COH and COC groups on HHTT. In this way, the other end of ethylene glycol diglycidyl ether retains a terminal epoxy group, which can combine with the C6-OH group of dialdehyde corn starch (DCST) with an aldehyde content of more than 90%. The two epoxy groups combine with two different reagents with different functions, each performing its own function, so that the tanned leather has a higher Ts, better mechanical strength and whiteness.

[0024] (3) Hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine (HHTT) is a highly efficient, broad-spectrum, and environmentally friendly preservative and bactericide used in the preparation of organic chromium-free tanning agents, which can effectively prevent the growth of bacteria and mold on leather. Attached Figure Description

[0025] Figure 1 Comparison of chemical and mechanical properties of HHTT-EGDE and DCST monomers at different molar ratios;

[0026] Figure 2Comparison of shrinkage temperature (Ts) of leather tanned with three tanning agents: HHTT-EGDE-DCST, TWS, and F-90;

[0027] Figure 3 Comparison of elongation at break of leather tanned with three tanning agents: HHTT-EGDE-DCST, TWS, and F-90;

[0028] Figure 4 Comparison of tensile strength of leather tanned with three tanning agents: HHTT-EGDE-DCST, TWS, and F-90;

[0029] Figure 5 Comparison of tear strength of leather tanned with three tanning agents: HHTT-EGDE-DCST, TWS, and F-90;

[0030] Figure 6 Comparison of the softness of leather tanned with three tanning agents: HHTT-EGDE-DCST, TWS, and F-90;

[0031] Figure 7 Comparison of the thickness increase rate of leather tanned with three tanning agents: HHTT-EGDE-DCST, TWS, and F-90;

[0032] Figure 8 Comparison of the inhibition rates of two bacteria (Escherichia coli and Staphylococcus aureus) on leather tanned with HHTT-EGDE-DCST. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments, and the technical content and effects thereof are not limited thereto.

[0034] Example 1

[0035] (1) Preparation of DCST: First, 30g of CST and 408mL of distilled water were added to a 1000mL three-necked flask, and the flask was placed in an oil bath at 35℃ and mechanically stirred for 5min. Then, 43.6g of sodium periodate (the molar ratio of sodium periodate monomer to pyranose units in starch was 1:1) was added, and the pH of the solution was adjusted to 3.5 using 1M sulfuric acid. The solution was stirred in the dark for 48h. The solution was cooled to room temperature, and three volumes of anhydrous ethanol were added. The mixture was stirred with a glass rod until all solids were separated, and then the solution was vacuum filtered. Next, the product was resuspended in 100mL of water, and the solution was vacuum filtered. This operation was repeated 3 times. Then, the product was resuspended in 100mL of an ethanol-water solution with a volume ratio of 9:1, and the solution was vacuum filtered. This operation was repeated 3 times. Finally, the product was washed with 100mL of anhydrous ethanol, and the solution was ultrafiltered. The final product was dried in a vacuum drying oven at 40℃ for 24h to obtain the DCST product.

[0036] (2) Preparation of HHTT-EGDE: 15g EGDE, 15mL acetone, and 10mL tetramethylenediamine were added to a 250mL three-necked flask and mechanically stirred until homogeneous. The flask was then immersed in an oil bath at 30℃. 13.3g HHTT was added to a 100mL constant pressure funnel. The funnel was inserted into the three-necked flask, and HHTT was added dropwise at a rate of 1 drop every 5 seconds. After the addition was complete, the reaction was maintained for 4 hours. Finally, the liquid was poured into a 250mL eggplant-shaped flask and evaporated under reduced pressure at 60℃ to remove unreacted EGDE, acetone, and tetramethylenediamine. The resulting brownish-red viscous liquid of HHTT-EGDE was dried in a vacuum drying oven at 40℃ for 24 hours to obtain the HHTT-EGDE product.

[0037] (3) Preparation of HHTT-EGDE-DCST: First, disperse 4g of HHTT-EGDE product in 40mL of distilled water and add it to a 250mL beaker. Adjust the pH of the solution to 10.0 using 1M NaOH. When it is completely dissolved, transfer the solution to a constant pressure dropping funnel to obtain the HHTT-EGDE solution. Add the HHTT-EGDE solution and DCST product to a 250mL three-necked flask at a molar ratio of HHTT-EGDE to DCST of 1.1:1. Then place the flask in an oil bath at 50℃ and, with continuous mechanical stirring, place a constant pressure dropping funnel on the three-necked flask at a flow rate of 5 drops per second until the mixture can drip completely. After terminating the reaction for 3 hours, cool the solution to room temperature. The washing steps are the same as those for the preparation of DCST (except for the water washing step) to obtain the organic chromium-free tanning agent.

[0038] Example 2

[0039] The amphoteric organic chromium-free tanning agent and the leather were prepared according to the method in Example 1, but in step (3), only the molar ratio of HHTT-EGDE and DCST monomers was changed to 1.2:1.

[0040] Example 3

[0041] The amphoteric organic chromium-free tanning agent and the leather were prepared according to the method in Example 1, but in step (3), only the molar ratio of HHTT-EGDE and DCST monomers was changed to 1.3:1.

[0042] Example 4

[0043] The amphoteric organic chromium-free tanning agent and the leather were prepared according to the method in Example 1, but in step (3), only the molar ratio of HHTT-EGDE and DCST monomers was changed to 1.4:1.

[0044] Example 5

[0045] The preparation of the amphoteric organic chromium-free tanning agent and the tanning of leather were carried out according to the method in Example 1, but in step (3), only the molar ratio of HHTT-EGDE and DCST monomers was changed to 1.5:1.

[0046] Example 6

[0047] The amphoteric organic chromium-free tanning agent and the leather were prepared according to the method in Example 3, but the parameter settings in step (2) were different.

[0048] (1) Preparation of DCST: First, 30g of CST and 408mL of distilled water were added to a 1000mL three-necked flask, and the flask was placed in an oil bath at 35℃ and mechanically stirred for 5min. Then, 43.6g of sodium periodate (the molar ratio of sodium periodate monomer to pyranose units in starch was 1:1) was added, and the pH of the solution was adjusted to 3.5 using 1M sulfuric acid. The solution was stirred in the dark for 48h. The solution was cooled to room temperature, and three volumes of anhydrous ethanol were added. The mixture was stirred with a glass rod until all solids were separated, and then the solution was vacuum filtered. Next, the product was resuspended in 100mL of water, and the solution was vacuum filtered. This operation was repeated 3 times. Then, the product was resuspended in 100mL of an ethanol-water solution with a volume ratio of 9:1, and the solution was vacuum filtered. This operation was repeated 3 times. Finally, the product was washed with 100mL of anhydrous ethanol, and the solution was ultrafiltered. The final product was dried in a vacuum drying oven at 40℃ for 24h to obtain the DCST product.

[0049] (2) Preparation of HHTT-EGDE: 15g EGDE, 20mL acetone, and 10mL tetramethylenediamine were added to a 250mL three-necked flask and mechanically stirred until homogeneous. The flask was then immersed in an oil bath at 30℃. 11.5g HHTT was added to a 100mL constant pressure funnel. The funnel was inserted into the three-necked flask, and HHTT was added dropwise at a rate of 1 drop every 5 seconds. After the addition was complete, the reaction was maintained for 4.5h. Finally, the liquid was poured into a 250mL eggplant-shaped flask and evaporated under reduced pressure at 60℃ to remove unreacted EGDE, acetone, and tetramethylenediamine. The resulting brownish-red viscous liquid of HHTT-EGDE was dried in a vacuum drying oven at 40℃ for 24h to obtain the HHTT-EGDE product.

[0050] (3) Preparation of HHTT-EGDE-DCST: First, disperse 4g of HHTT-EGDE product in 40mL of distilled water and add it to a 250mL beaker. Adjust the pH of the solution to 10.0 using 1M NaOH. When it is completely dissolved, transfer the solution to a constant pressure dropping funnel to obtain the HHTT-EGDE solution. Add the HHTT-EGDE solution and DCST product to a 250mL three-necked flask at a molar ratio of HHTT-EGDE to DCST of 1.3:1. Then place the flask in an oil bath at 50℃ and, with continuous mechanical stirring, place a constant pressure dropping funnel on the three-necked flask at a flow rate of 5 drops per second until the mixture can be completely dripped. After terminating the reaction for 3 hours, cool the solution to room temperature. The washing steps are the same as those for the preparation of DCST (except for the water washing step) to obtain the organic chromium-free tanning agent.

[0051] Example 7

[0052] The amphoteric organic chromium-free tanning agent was prepared and the leather was tanned according to the method in Example 3, but the parameter settings in step (3) were different.

[0053] (1) Preparation of DCST: First, 30g of CST and 408mL of distilled water were added to a 1000mL three-necked flask, and the flask was placed in an oil bath at 35℃ and mechanically stirred for 5min. Then, 43.6g of sodium periodate (the molar ratio of sodium periodate monomer to pyranose units in starch was 1:1) was added, and the pH of the solution was adjusted to 3.5 using 1M sulfuric acid. The solution was stirred in the dark for 48h. The solution was cooled to room temperature, and three volumes of anhydrous ethanol were added. The mixture was stirred with a glass rod until all solids were separated, and then the solution was vacuum filtered. Next, the product was resuspended in 100mL of water, and the solution was vacuum filtered. This operation was repeated 3 times. Then, the product was resuspended in 100mL of an ethanol-water solution with a volume ratio of 9:1, and the solution was vacuum filtered. This operation was repeated 3 times. Finally, the product was washed with 100mL of anhydrous ethanol, and the solution was ultrafiltered. The final product was dried in a vacuum drying oven at 40℃ for 24h to obtain the DCST product.

[0054] (2) Preparation of HHTT-EGDE: 15g EGDE, 15mL acetone, and 10mL tetramethylenediamine were added to a 250mL three-necked flask and mechanically stirred until homogeneous. The flask was then immersed in an oil bath at 30℃. 13.3g HHTT was added to a 100mL constant pressure funnel. The funnel was inserted into the three-necked flask, and HHTT was added dropwise at a rate of 1 drop every 5 seconds. After the addition was complete, the reaction was maintained for 4 hours. Finally, the liquid was poured into a 250mL eggplant-shaped flask and evaporated under reduced pressure at 60℃ to remove unreacted EGDE, acetone, and tetramethylenediamine. The resulting brownish-red viscous liquid of HHTT-EGDE was dried in a vacuum drying oven at 40℃ for 24 hours to obtain the HHTT-EGDE product.

[0055] (3) Preparation of HHTT-EGDE-DCST: First, disperse 4g of HHTT-EGDE product in 40mL of distilled water and add it to a 250mL beaker. Adjust the pH of the solution to 10.0 using 1M NaOH. When it is completely dissolved, transfer the solution to a constant pressure dropping funnel to obtain the HHTT-EGDE solution. Add the HHTT-EGDE solution and DCST product to a 250mL three-necked flask at a molar ratio of HHTT-EGDE to DCST of 1.3:1. Then place the flask in an oil bath at 60℃ and, with continuous mechanical stirring, place a constant pressure dropping funnel on the three-necked flask at a flow rate of 5 drops per second until the mixture can drip completely. After terminating the reaction for 2 hours, cool the solution to room temperature. The washing steps are the same as those for the preparation of DCST (except for the water washing step) to obtain the organic chromium-free tanning agent.

[0056] Comparative Example 1

[0057] The preparation of the amphoteric organic chromium-free tanning agent and the tanning of leather were carried out according to the method in Example 3, but step (2) was different.

[0058] (1) Preparation of DCST: First, 30g of CST and 408mL of distilled water were added to a 1000mL three-necked flask, and the flask was placed in an oil bath at 35℃ and mechanically stirred for 5min. Then, 43.6g of sodium periodate (the molar ratio of sodium periodate monomer to pyranose units in starch was 1:1) was added, and the pH of the solution was adjusted to 3.5 using 1M sulfuric acid. The solution was stirred in the dark for 48h. The solution was cooled to room temperature, and three volumes of anhydrous ethanol were added. The mixture was stirred with a glass rod until all solids were separated, and then the solution was vacuum filtered. Next, the product was resuspended in 100mL of water, and the solution was vacuum filtered. This operation was repeated 3 times. Then, the product was resuspended in 100mL of an ethanol-water solution with a volume ratio of 9:1, and the solution was vacuum filtered. This operation was repeated 3 times. Finally, the product was washed with 100mL of anhydrous ethanol, and the solution was ultrafiltered. The final product was dried in a vacuum drying oven at 40℃ for 24h to obtain the DCST product.

[0059] (2) Preparation of HHTT-EGDE: Take 2.12g of EGDE and 40mL of distilled water and add them to a 250mL three-necked flask. After stirring mechanically until homogeneous, adjust the pH of the solution to 10.0 using 1M NaOH to obtain the EGDE solution.

[0060] (3) Preparation of HHTT-EGDE-DCST: HHTT, EGDE solution, and DCST product were added to a 250 mL three-necked flask at a molar ratio of 0.54:0.76:1. The flask was then placed in an oil bath at 50 °C. Under continuous mechanical stirring, a constant pressure dropping funnel was placed on the three-necked flask, and the flow rate was 5 drops per second until the mixture could be completely dripped. After terminating the reaction for 3 hours, the solution was cooled to room temperature. The washing steps were the same as those for the preparation of DCST (except for the water washing step), yielding an organic chromium-free tanning agent.

[0061] Comparative Example 2

[0062] The preparation of the amphoteric organic chromium-free tanning agent and the tanning of leather were carried out according to the method in Example 3, but the amount of HHTT added in step (2) was too much, 16g.

[0063] Comparative Example 3

[0064] The amphoteric organic chromium-free tanning agent and the leather were prepared according to the method in Example 3, but in step (3), only the molar ratio of HHTT-EGDE and DCST monomers was changed to 1.7:1.

[0065] Comparative Example 4

[0066] The amphoteric organic chromium-free tanning agent and the leather were prepared according to the method in Example 3, but the oil bath reaction time in step (3) was only 1 hour.

[0067] Tanning of the leather: A piece of raw cowhide (PS) after de-acidification was cut into three equal-weight slices along the spine, named A, B, and C respectively, and tanned according to international leather tanning methods. A and B were tanned using the aldehyde organic retanning agent TWS and the organic chromium-free tanning agent of this invention, respectively, while C was tanned using Cranofin F-90. After tanning, the shrinkage temperature (Ts), elongation at break, tensile strength, softness, tear strength, antibacterial rate, and thickening rate of the leather were measured.

[0068] Shrinkage temperature: Measured using a shrinkage temperature measuring instrument. The simple instrument consists of a 500mL beaker, an electric furnace, a thermometer, a graduated dial, a sample clamp, and a pointer connected to it. During the test, the leather sample is clamped and placed in a beaker filled with water. The thermometer is suspended beside the sample, and the sample is heated at a uniform rate until it reaches a certain temperature and suddenly shrinks. At this moment, the pointer deviates from the graduated dial, and the temperature at this instant is recorded.

[0069] Elongation at break, tensile strength, and tear strength were tested using a tensile testing machine.

[0070] Softness: Tested using a leather hardness tester, which uses one or more hardness needles or cylinders to apply pressure to the leather and then measures the depth of indentation to determine the softness of the leather.

[0071] Thickness gain: The thickness of the leather sample is measured using a leather thickness measuring instrument. The leather is cut to the required shape and size, placed on a platform and flattened. The thickness gauge will display a reading.

[0072] Antibacterial rate: The antibacterial rate against Staphylococcus aureus was tested after the leather was tanned.

[0073] Table 1

[0074]

[0075] Based on the results of the above embodiments, such as Figure 1 As shown, the tanning agent prepared by reacting HHTT-EGDE and DCST monomers in a molar ratio of 1.4:1 exhibits superior mechanical and chemical properties.

[0076] The performance of the organic chromium-free tanning agent in this invention and two conventional tanning agents (TWS and F-90) were compared, such as... Figure 2As shown, generally, the better the tanning performance of the tanning agent, the higher the Ts value imparted to the leather. The organic chromium-free tanning agent of this invention produces the highest Ts value for leather, followed by TWS, while the F-90 tanning agent produces the worst Ts value for leather.

[0077] like Figure 3 , Figure 4 , Figure 5 As shown, in terms of mechanical properties, the elongation at break of the leather tanned with the organic chromium-free tanning agent of this invention is slightly lower than that of F-90- and TWS-tanned leather. This result proves that the leather tanned with the organic chromium-free tanning agent of this invention has high rigidity and poor extensibility. The tensile strength of the leather tanned with the organic chromium-free tanning agent of this invention is almost twice that of F-90- and TWS-tanned leather, and its tear strength is more than twice that of F-90- and TWS-tanned leather. Because leather tanning is a process of changing the surface wettability of leather from hydrophilic to hydrophobic, and the essence of tanning may be attributed to the enhancement of the hydrophobicity of collagen fibers, it is particularly important to understand the impact of hydrophobicity on the overall properties of collagen fibers, which may provide a new strategy for leather manufacturing. Another COH group contained in HHTT of the organic chromium-free tanning agent of this invention has a hydrophobic effect, which makes the tanned leather exhibit higher collagen fiber dispersibility. When the leather is subjected to stress, the collagen fibers with higher dispersibility can better dissipate the force, thus exhibiting superior mechanical strength.

[0078] Depend on Figure 6 and Figure 7 It can be seen that softness and thickness are key indicators for evaluating the feel of leather. For example... Figure 6 As shown, the organic chromium-free tanning agent of this invention produces leather with superior softness compared to F-90- and TWS-tanned leather. Some HHTT-EGDE-DCST molecules contain groups saturated with epoxy groups, namely N-(CH2). n Long chains, thus exhibiting a free state, can act as a lubricant between collagen fibers. Therefore, the organic chromium-free tanning agent used in this invention produces leather with good softness. For example... Figure 7 As shown, the thickening rate of leather tanned with the organic chromium-free tanning agent of this invention is more than 4 times that of F-90 tanned leather and more than 5 times that of TWS tanned leather.

[0079] Depend on Figure 8 It can be seen that the organic chromium-free tanning agent tanned leather of the present invention (Example 4) has a good inhibitory effect on the growth of Escherichia coli and Staphylococcus aureus. Furthermore, the organic chromium-free tanning agent tanned leather of the present invention achieves inhibition rates of 99.94% and 99.98% against Escherichia coli and Staphylococcus aureus, respectively.

[0080] As shown in Table 1, in Comparative Example 1, the softness remained almost unchanged, while other mechanical and chemical properties all showed varying degrees of decline. In Comparative Example 2, except for the antibacterial rate, which remained almost unchanged, all other properties showed varying degrees of decline. In Comparative Example 3, changing the molar ratio of HHTT-EGDE and DCST monomers was the most critical factor affecting the properties of the tanning agent, thus all properties decreased. In Comparative Example 4, changing the oil bath time had a significant impact on the shrinkage temperature of the tanned leather, while the impact on other properties was relatively small.

[0081] The above embodiments of the present invention are merely illustrative examples and are not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A process for the preparation of a sustainable green amphoteric organic chrome-free tanning agent characterized in that, The method comprises the following steps: (1) corn starch is added into water, then sodium periodate is added, the molar ratio of sodium periodate to glucopyranosyl unit in corn starch is 1:1, the pH is adjusted to 3-4, and the reaction is stirred in the dark; after the reaction is completed, the solid is separated to obtain a DCST product with an aldehyde group content of more than 90%; (2) ethylene glycol diglycidyl ether, acetone and tetramethylene diamine are mixed, then hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine is added dropwise at a rate of one drop per 5 seconds, the addition amount ratio of ethylene glycol diglycidyl ether, acetone, tetramethylene diamine and hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine is 15 g: 15-20 mL: 10 mL: 10-13.5 g, after the dropwise addition is completed, the reaction is maintained for 3-6 hours; after the reaction is completed, vacuum distillation is performed to obtain a HHTT-EGDE product; (3) the HHTT-EGDE product is dispersed in water, the pH is adjusted to 10-11 until complete dissolution to obtain a HHTT-EGDE solution; the HHTT-EGDE solution is mixed with the DCST product at a molar ratio of HHTT-EGDE to DCST of 1.1-1.5:1, and the mixture is reacted at 50-60°C for 2-3 hours to obtain an organic chromium-free tanning agent.

2. The preparation method of the sustainable green amphoteric organic chromium-free tanning agent as described in claim 1, characterized in that, In step (1), the addition amount ratio of corn starch to water is 30 g: 400-500 mL.

3. The preparation method of the sustainable green amphoteric organic chromium-free tanning agent as described in claim 1, characterized in that, In step (1), the time for the reaction in the dark is 40-50 hours.

4. A process for the preparation of a sustainable green amphoteric organic chrome-free tanning agent according to any one of claims 1 to 3, characterized in that, In step (2), the temperature for the vacuum distillation is 60-70°C.

5. The preparation method of the sustainable green amphoteric organic chromium-free tanning agent as described in claim 1, characterized in that, In step (3), the addition amount ratio of the HHTT-EGDE product to water is 4 g: 40-50 mL.

6. The method for preparing the sustainable green amphoteric organic chromium-free tanning agent as described in claim 1, characterized in that, In step (1), after the reaction is completed, the solid is separated by the following specific steps: the solution is cooled to room temperature, anhydrous ethanol is added, and stirring is performed until all the solid is separated, then vacuum filtration is performed; the solid is resuspended in water, and vacuum filtration is repeated for several times; then the solid is resuspended in an ethanol-water solution, and vacuum filtration is repeated for several times; finally, the solid is washed with anhydrous ethanol, and the final product is vacuum dried.

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