Epoxy-terminated polylysine-based chrome-free tanning agent as well as preparation method and application thereof

Abstract

The invention discloses an epoxy-terminated polylysine-based chrome-free tanning agent as well as a preparation method and application thereof, and belongs to the technical field of green biomass materials and ecological leather. The preparation method comprises the following steps: adding a polylysine solution into a glycerol triglycidyl ether solution, then adding a catalyst, and carrying out stirring reaction, dialysis, freeze drying and grinding to obtain the epoxy-terminated polylysine-based chrome-free tanning agent. An active epoxy group in a glycerol triglycidyl ether structure is grafted to a polylysine polymer through a covalent cross-linking reaction of amino and an epoxy group, terminal epoxidation modification of polylysine is realized by utilizing the characteristics of rich amino groups, high compatibility, high isotactic points, reproducibility and the like on polylysine, and in the leather tanning process, the terminal epoxidation modification of polylysine is realized. The tanning agent can generate strong crosslinking with leather collagen fibers, endows tanning with an isoelectric point, has strong binding capacity to anionic materials, and realizes high absorption of leather post-treatment materials and ecological leather manufacturing. Pollution in the wet dyeing and finishing process is avoided through the high electric point, and a thought is provided for design of a novel environment-friendly chrome-free tanning agent.

Description

Technical Field

[0001] This invention belongs to the field of green biomass materials and eco-leather technology, specifically relating to a terminal epoxy type polylysine-based chromium-free tanning agent, its preparation method, and its application. Background Technology

[0002] Chrome tanning has always been one of the most commonly used methods for leather tanning. It is favored for its durability and high heat resistance, but it faces significant challenges due to the scarcity of chromium resources, low absorption rates (60%-70%), and the environmental harm caused by toxic hexavalent chromium produced by the oxidation of chromium ions. Chrome tanning agents can impart excellent heat and water resistance to leather by coordinating with the carboxyl groups of collagen fibers. In this way, the unreacted amino groups in chrome-tanned leather act as cationic active sites, forming electrostatic interactions with anionic materials in subsequent processing. Therefore, anionic oils and dyes are commonly used in leather manufacturing. Other chromium-free metal-based tanning agents, such as aluminum or zirconium complexes, have similar tanning cross-linking mechanisms to chrome tanning agents, and therefore they are also highly compatible with anionic materials used in the post-tanning treatment of leather.

[0003] However, leather tanned with these chromium-free metal-based tanning agents is typically softer, has poor washability, and is prone to "surface over-tanning." Existing biomass tanning agents can enhance the hydrothermal stability of the resulting leather by cross-linking with the amino groups in collagen fibers (through aldehyde, epoxy, and phenolic hydroxyl groups). Unlike chrome-tanned leather, the amino groups in these tanned leathers are consumed during the tanning process, thus reducing their positive charge and lowering the isoelectric point (pI < 5). Therefore, their ability to bind with anionic materials in subsequent treatment stages (especially dyeing and fatliquoring) is significantly affected. This further impacts leather quality and increases the difficulty of wastewater treatment.

[0004] To address the issues of limited cross-linking methods between existing chromium-free tanning agents and collagen fibers, weak cross-linking bond strength, and low absorption rate during wet dyeing and finishing processes, there is an urgent need to find a new chromium-free tanning agent that can form multiple binding modes with collagen fibers, thereby improving the strength of cross-linking bonds and the absorption rate of anionic materials. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a terminal epoxy type polylysine-based chromium-free tanning agent, its preparation method and application, so as to solve the technical problems of weak cross-linking strength between existing chromium-free tanning agents and collagen fibers and low absorption rate of anionic materials.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent, comprising: Polylysine is dissolved in water, and the pH is adjusted to 7-9.5 to obtain a polylysine solution. Glycerol triglycidyl ether was dissolved in water and the pH was adjusted to 6-10 to obtain a glycerol triglycidyl ether solution. A polylysine solution was added to a glycerol triglycidyl ether solution, followed by a catalyst. After stirring, dialysis, freeze-drying, and grinding, a terminal epoxy-type polylysine-based chromium-free tanning agent was obtained.

[0007] Preferably, the molar ratio of polylysine to glycerol triglycidyl ether is 1:(1-20).

[0008] Preferably, polylysine is produced by actinomycete metabolism; The mass concentration of the polylysine solution is 0.10~0.20 g / mL; the mass concentration of the glycerol triglycidyl ether solution is 1~20 g / L.

[0009] Preferably, the relative molecular mass of polylysine is 2000-5000 Da.

[0010] Preferably, the molar ratio of catalyst to polylysine is (0.1-2):1; the catalyst is hexamethylenetetramine.

[0011] Preferably, the temperature of the stirring reaction is 30-50℃; the stirring reaction time is 2-10 h.

[0012] Preferably, the dialysis conditions include: dialysis at 25-35°C for 12-72 hours.

[0013] Preferably, the freeze-drying conditions include: freeze-drying at -40 to -80°C for 24-72 hours.

[0014] This invention also discloses a terminal epoxy-type polylysine-based chromium-free tanning agent, prepared by the above-described method for preparing terminal epoxy-type polylysine-based chromium-free tanning agents. The structural formula of the terminal epoxy-type polylysine-based chromium-free tanning agent is as follows: .

[0015] This invention also discloses the application of the terminal epoxy polylysine-based chromium-free tanning agent prepared by the above-mentioned method in leather cleaning production.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent. In the preparation process, polylysine is dissolved in water, and the pH of the solution is precisely controlled within the range of 7-9.5 using an alkaline adjuster. This alkaline environment effectively maintains the free state of the amino groups on the polylysine molecular chain, avoiding the reduction in reactivity caused by protonation, thus providing sufficient active sites for subsequent epoxy grafting. Simultaneously, glycerol triglycidyl ether is dissolved in water, and the pH of the solution is stabilized within the range of 6-10. This condition ensures the chemical stability of the epoxy groups and inhibits the epoxy ring-opening side reaction initiated by strong alkalinity, ensuring a sufficient number of active epoxy groups. Subsequently, the polylysine solution is slowly added to the glycerol triglycidyl ether solution. This order of addition promotes the preferential directional reaction of the epoxy groups with the free amino groups at the end of the polylysine chain, effectively avoiding intramolecular cross-linking side reactions and ensuring the formation of the terminal epoxy structure. After the catalyst is introduced into the reaction system, it promotes the ring-opening addition reaction of epoxy groups and amino groups under mild conditions, achieving precise epoxidation modification of polylysine chain ends. The numerous active epoxy and amino groups of the terminal epoxy polylysine-based chromium-free tanning agent can form covalent bonds and hydrogen bonds with various materials. Simultaneously, it can also be used as a crosslinking agent in organic synthesis, composite materials, and biomedicine. Then, through the principle that epoxy groups can form strong coordination with collagen, the numerous epoxy groups at the chain ends of the terminal epoxy polylysine-based chromium-free tanning agent react with collagen fibers to produce a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials. Through a crosslinking reaction, the tanning agent with numerous active epoxy and amino groups is introduced onto collagen fibers under the action of a catalyst. Utilizing the high isoelectric point and high adsorption properties of the terminal epoxy polylysine-based chromium-free tanning agent, the functional modification of polylysine in biomass materials is achieved. After the reaction, the mixture was dialyzed to remove unreacted small molecule impurities, ensuring product purity. The freeze-drying process was carried out at low temperature to maintain molecular configuration stability and prevent thermal deactivation of the epoxy groups. Finally, a uniform powder product was obtained through grinding for easy subsequent application. When the prepared chromium-free tanning agent with a certain molecular weight and terminal epoxy polylysine groups was used as a crosslinking agent in leather tanning and wet dyeing processes, it could form various binding mechanisms with leather collagen fibers, including coordination bonding, hydrogen bonding, and electrostatic attraction. Furthermore, the crosslinking between macromolecules and between the macromolecules and the leather fibers further enhanced the strength of the crosslinking bonds. The entire preparation route is simple, and the increase in isoelectric point avoids the pollution steps that require frequent addition of raw materials in the original tanning process, which is expected to provide potential insights for the innovative design of novel environmentally friendly chromium-free tanning agents.

[0017] Furthermore, the molar ratio of polylysine to glycerol triglycidyl ether is 1:(1-20); this allows the amino groups on the polylysine molecular chain to fully covalently cross-link with the epoxy groups of glycerol triglycidyl ether, while maintaining the product's water solubility and subsequent interaction with collagen fibers. This ratio control optimizes the controllability of the reaction process and ensures the stable formation of the terminal epoxy structure.

[0018] Furthermore, polylysine is produced by actinomycete metabolism; the mass concentration of the polylysine solution is 0.10–0.20 g / mL; the mass concentration of the glycerol triglycidyl ether solution is 1–20 g / L. The polylysine produced by actinomycete metabolism has a uniform and sufficient distribution of side-chain amino groups, providing a structural basis for the directional grafting of epoxy groups. Controlling the mass concentration of the polylysine solution within the range of 0.10–0.20 g / mL ensures sufficient exposure of amino groups to promote cross-linking reactions while avoiding mass transfer barriers caused by high viscosity. Simultaneously, limiting the mass concentration of the glycerol triglycidyl ether solution to the range of 1–20 g / L effectively balances the reactivity and selectivity of the epoxy groups, inhibiting the occurrence of side reactions. This multi-parameter synergistic regulation mechanism enables the reaction system to achieve molecular-level uniform contact under mild conditions, ensuring the complete retention of the epoxy groups at the end of the polylysine chain, thereby forming a structurally stable terminal epoxy-type polylysine-based chromium-free tanning agent.

[0019] Furthermore, the relative molecular mass of polylysine is 2000-5000 Da; the selection of this molecular weight range needs to balance the appropriate chain length and reactivity, avoiding insufficient amino groups due to excessively low molecular weight or steric hindrance caused by excessively high molecular weight. This ensures efficient grafting of epoxy groups to the ends of the molecular chain, enabling sufficient multi-crosslinking between the tanning agent and the leather collagen fibers, thereby maintaining the high isoelectric point stability of the tanned leather and improving the absorption performance of anionic materials during wet dyeing and finishing.

[0020] Furthermore, the molar ratio of catalyst to polylysine is (0.1-2):1; the catalyst is hexamethylenetetramine. Using hexamethylenetetramine as a catalyst, the nitrogen atoms in its molecule can specifically activate the epoxy groups in glycerol triglycidyl ether, promoting a directional ring-opening reaction with the amino groups on the polylysine molecular chain, thereby forming a stable covalent cross-linked structure. In this process, the molar ratio of catalyst to polylysine is strictly controlled within the range of (0.1-2):1, ensuring that the catalyst fully acts on the amino sites of polylysine under appropriate conditions. This avoids both insufficient reaction kinetics and incomplete cross-linking due to insufficient catalyst dosage, and excessive cross-linking or catalyst residue caused by excessive catalyst dosage. It can efficiently retain the epoxy groups at the ends of the polylysine chain, laying the foundation for subsequent strong cross-linking with collagen fibers.

[0021] Furthermore, the stirring temperature was 30-50℃, and the stirring time was 2-10 h. This ensured that the cross-linking reaction was fully completed to achieve complete cross-linking, while avoiding excessive time that could lead to unreacted monomer residues, thus maintaining the high activity of the terminal epoxy groups. This synergistic control mechanism of temperature and time ensured that the reaction system operated at the kinetic and thermodynamic equilibrium point, improving the controllability of the cross-linking reaction and the uniformity of the products.

[0022] Furthermore, the dialysis conditions include: dialysis at 25-35℃ for 12-72 hours; this ensures the high purity and structural stability of the terminal epoxy polylysine-based chromium-free tanning agent, providing a reliable guarantee for its efficient cross-linking with leather collagen fibers during leather tanning and the smooth implementation of subsequent wet dyeing and finishing processes.

[0023] Furthermore, the freeze-drying conditions include: freeze-drying at -40~-80℃ for 24-72 h; this allows the terminal epoxy polylysine-based chromium-free tanning agent to maintain the integrity of its active groups and the stability of the product structure while removing moisture.

[0024] This invention discloses a terminal epoxy-type polylysine-based chromium-free tanning agent. By directionally covalently crosslinking a large number of amino groups on the polylysine molecular chain with the epoxy groups of glycerol triglycidyl ether, the terminal epoxy-type polylysine-based chromium-free tanning agent retains the highly active terminal epoxy groups while partially consuming the amino groups, thus significantly increasing the isoelectric point of the product. The high isoelectric point effectively increases the positive charge density on the surface of the tanned leather, strengthening the electrostatic attraction with anionic materials and solving the problem of low absorption rate of anionic materials. Simultaneously, the strong coordination between the epoxy groups and the collagen fibers, and the formation of a multivalent crosslinking network, greatly enhance the strength and stability of the crosslinking bonds, overcoming the weakness of traditional chromium-free tanning agents in terms of crosslinking strength. Specifically, this technical solution is based on the chemical reaction pathway of polylysine and glycerol triglycidyl ether under the action of a catalyst. By precisely controlling the acid-base environment, mixing sequence, and post-treatment conditions of the reactants, the amino groups on the polylysine molecular chain and the epoxy groups of glycerol triglycidyl ether selectively react to form a product with a terminal epoxy structure. Therefore, during the leather tanning process, this product can form multiple cross-linking interactions with leather collagen fibers, including coordination bonding, hydrogen bonding, and electrostatic attraction, significantly enhancing the strength of the cross-linking bonds. At the same time, the high isoelectric point of the product effectively increases the positive charge density inside the leather collagen, thereby improving the electrostatic adsorption capacity for anionic materials and solving the technical problem of low material absorption efficiency in the wet dyeing and finishing stage.

[0025] This invention discloses the application of a terminal epoxy-type polylysine-based chromium-free tanning agent in clean leather production. By strongly coordinating the terminal epoxy group structure of the chromium-free tanning agent with the amino groups on the collagen fibers of the leather, and utilizing the high-density amino groups provided by the polylysine group to maintain the high isoelectric point of the leather, the cross-linking strength with the collagen fibers is significantly improved, and the electrostatic adsorption capacity for anionic materials is enhanced. Furthermore, this technical solution avoids the weak bond problem caused by the single cross-linking form of traditional chromium-free tanning agents. The stable covalent cross-linking bond formed between the terminal epoxy group and the collagen fibers effectively enhances the binding strength. Simultaneously, the free amino groups retained by the polylysine group increase the isoelectric point of the tanned leather, significantly improving the electrostatic adsorption efficiency of anionic materials during subsequent dyeing and fatliquoring processes. Therefore, this application not only solves the technical bottleneck of low anionic material absorption rate in the wet dyeing and finishing stage, but also reduces the difficulty of wastewater treatment through its chromium-free characteristics, achieving the dual goals of improving leather quality and reducing production pollution. Attached Figure Description

[0026] Figure 1 This is a synthetic route diagram of the terminal epoxy type polylysine-based chromium-free tanning agent disclosed in this invention; Figure 2 The infrared absorption spectrum of the terminal epoxy polylysine-based chromium-free tanning agent in Example 4 of this invention; Figure 3 This is a comparison chart of the shrinkage temperature and thickening rate of leather with untanned raw hide (PS) and commercially available leather TWS (Sichuan Tingjiang New Material Co., Ltd.) and F-90 (Starr Leather Chemical Co., Ltd.) in actual tanning applications of the end-epoxy polylysine-based chromium-free tanning agent in Example 4 of the present invention. Figure 4 The images shown are electron microscope images of leather cross sections before and after tanning in actual tanning applications of the terminal epoxy polylysine-based chromium-free tanning agent in Example 4 of this invention; where (a) is raw hide; (b) is PG tanned leather; (c) is commercially available tanned leather F-90; and (d) is commercially available tanned leather TWS. Figure 5 This is a comparison chart of the dyeing absorption rate and fatliquoring absorption rate of the end-epoxy polylysine-based chromium-free tanning agent in Example 4 of the present invention to anionic materials in actual tanning applications during wet dyeing and finishing processes, and its comparison with commercially available leather TWS (Sichuan Tingjiang New Material Co., Ltd.) and F-90 (Star Leather Chemical Co., Ltd.). Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0029] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0030] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0031] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0032] In this invention, unless otherwise specified, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply a shortened representation of these numerical combinations.

[0033] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0034] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0035] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0036] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0037] This invention discloses a terminal epoxy-type polylysine-based chromium-free tanning agent with the following structural formula:

[0038] This terminal epoxy polylysine-based chromium-free tanning agent is a PG-terminated epoxy polylysine-based chromium-free tanning agent.

[0039] This invention provides a method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent, comprising: 1) Preparation of polylysine solution Using polylysine, a biomass material produced by actinomycete metabolism, as a matrix, a polylysine solution was prepared, and its pH was adjusted to neutral to weakly alkaline (7.0-9.5) to prepare a polylysine solution with a mass concentration of 0.10~0.20 g / mL.

[0040] 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of a 1-20 g / L glycerol triglycidyl ether solution was adjusted to 6.0-10.0. The polylysine solution obtained in step 1) was poured into a dropping funnel and added dropwise to the glycerol triglycidyl ether solution at a rate of 1 drop / second. A catalyst was then added to the solution. After stirring at 30-50℃ for 2-10 h, the mixture was dialyzed at 25-35℃ for 12-72 h, freeze-dried under vacuum at -40~-80℃ for 24-72 h, and ground to obtain a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0041] In step 2), the molar ratio of glycerol triglycidyl ether in the chromium-free tanning agent with terminal epoxy polylysine is 1:1-1:20. Step 2) describes the preparation method of the chromium-free tanning agent with terminal epoxy polylysine groups, which includes the following steps: 1) Add polylysine dropwise to the glycerol triglycidyl ether solution through a separatory funnel and mix. 2) Add hexamethylenetetramine as a catalyst and stir to react; 3) Unreacted glycerol triglycidyl ether was removed by dialysis to obtain a PG-terminated epoxy polylysine chromium-free tanning agent solution; 4) A PG-terminated epoxy polylysine-based chromium-free tanning agent was obtained by vacuum freeze-drying for 24-72 h; In step 1), the relative molecular mass of the polylysine polymer is 2000-5000 Da; In step 2), the molar ratio of catalyst to polylysine is (0.1-2):1; the catalyst is hexamethylenetetramine.

[0042] In step 2), the stirring temperature is 30-50℃ and the stirring time is 2-10 h.

[0043] In step 2), the dialysis time is 12-72 h; the vacuum freeze-drying temperature is -40~-80℃, and the time is 24-72 h.

[0044] This invention discloses a method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent. First, a terminal epoxy-type polylysine-based chromium-free tanning agent is prepared by chemically cross-linking a large number of amino groups on the polylysine molecular chain, a microbial metabolite, with glycerol triglycidyl ether. The synthesis conditions are mild and the method is simple. The numerous active epoxy and amino groups in this terminal epoxy-type polylysine-based chromium-free tanning agent can form covalent bonds and hydrogen bonds with various materials. Simultaneously, it can also be used as a cross-linking agent in organic synthesis, composite materials, and biomedicine. Then, based on the principle that epoxy groups can form strong coordination with skin collagen, the numerous epoxy groups at the end of the terminal epoxy-type polylysine-based chromium-free tanning agent chain undergo tanning with skin collagen fibers, resulting in a highly compatible terminal epoxy-type polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials. A tanning agent with numerous active epoxy and amino groups is introduced onto leather collagen fibers via a cross-linking reaction under the action of a catalyst. Utilizing the high isoelectric point and high adsorption properties of the terminal epoxy polylysine-based chromium-free tanning agent, the functional modification of polylysine in biomass materials is achieved. When the prepared terminal epoxy polylysine-based chromium-free tanning agent with a certain molecular weight is applied as a cross-linking agent in leather tanning and wet dyeing processes, it can form various binding mechanisms with leather collagen fibers, including coordination bonding, hydrogen bonding, and electrostatic attraction. Furthermore, the cross-linking between macromolecules and between the macromolecules and the leather fibers further enhances the strength of the cross-linking bonds. The entire preparation route is simple, and the increased isoelectric point avoids the polluting steps required by frequent addition of raw materials in the original tanning and wet dyeing processes. This approach holds promise for providing potential insights into the innovative design of novel environmentally friendly chromium-free tanning agents.

[0045] This invention discloses a terminal epoxy-type polylysine-based chromium-free tanning agent prepared by the above-mentioned preparation method, along with its preparation method and applications. Leather tanned with this terminal epoxy-type polylysine-based chromium-free tanning agent has the following advantages: 1. Higher shrinkage temperature: The active functional groups at the end of the terminal epoxy-type polylysine-based chromium-free tanning agent can cross-link with amino groups and other groups on the leather collagen, thereby exhibiting a tanning effect. Experimental data shows that the shrinkage temperature of leather tanned with this terminal epoxy-type polylysine-based chromium-free tanning agent is about 15% to 20% higher than that of untanned leather, and its mechanical properties and wash resistance are significantly improved. 2. Significant anion absorption effect: The highly compatible terminal epoxy-type polylysine-based chromium-free tanning agent, which also has excellent adsorption of anion materials, can provide amino groups during the cross-linking process with leather collagen fibers, increasing the positive charge in the leather collagen and showing a significant increase in absorption rate compared to raw hides. This advantage will help chromium-free tanned leather be applied in a wider range of manufacturing applications and further increase the profits of manufacturing enterprises. 3. The product is environmentally friendly; this invention uses glycerol triglycidyl ether and polylysine as reaction raw materials to prepare a terminal epoxy type polylysine-based chromium-free tanning agent, its preparation method and application; both the raw materials and the product are non-toxic and have no side effects.

[0046] This invention also discloses the application of the above-mentioned terminal epoxy polylysine-based chromium-free tanning agent in the clean production of leather, which effectively avoids the health risks associated with chromium tanning, reduces the difficulty of treating leather waste liquid, and still maintains the performance of traditional chromium-containing tanning agents, which is in line with the concept of sustainable development in the leather industry.

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0048] Example 1 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 10 g of polylysine with a molecular weight of 2000-5000 Da in 100 mL of water, mix well, and adjust the pH of the polylysine solution to 7 with sodium hydroxide solution.

[0049] 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of a 1 g glycerol triglycidyl ether solution was adjusted to 6. The polylysine solution obtained in step 1) was poured into a dropping funnel and added dropwise to the glycerol triglycidyl ether solution at a rate of 1 drop / second. Then, 0.5 g of hexamethylenetetramine catalyst was added to the solution. After stirring at 30 °C for 10 h, the mixture was dialyzed at 25 °C for 72 h, freeze-dried under vacuum at -40 °C for 72 h, and ground to obtain a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0050] Example 2 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 12 g of polylysine with a molecular weight of 2000-5000 Da in 100 mL of water, mix well, and adjust the pH of the polylysine solution to 7.5 with sodium hydroxide solution.

[0051] 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of 5 g glycerol triglycidyl ether solution was adjusted to 7. The polylysine solution obtained in step 1) was poured into a dropping funnel and added dropwise to the glycerol triglycidyl ether solution at a rate of 1 drop / second. Then, 1.5 g of hexamethylenetetramine catalyst was added to the solution. After stirring at 35 °C for 9 h, the mixture was dialyzed at 27 °C for 60 h, freeze-dried under vacuum at -50 °C for 60 h, and ground to obtain a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0052] Example 3 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 14 g of polylysine with a molecular weight of 2000-5000 Da in 100 mL of water, mix well, and adjust the pH of the polylysine solution to 8 with sodium hydroxide solution.

[0053] 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of 8g of glycerol triglycidyl ether solution was adjusted to 8. The polylysine solution obtained in step 1) was poured into a dropping funnel and added dropwise to the glycerol triglycidyl ether solution at a rate of 1 drop / second. Then, 3g of hexamethylenetetramine catalyst was added to the solution. After stirring at 40 ℃ for 8 h, the mixture was dialyzed at 30 ℃ for 48 h, freeze-dried under vacuum at -60 ℃ for 48 h, and ground to obtain a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0054] Example 4 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 16 g of polylysine with a molecular weight of 2000-5000 Da in 100 mL of water, mix well, and adjust the pH of the polylysine solution to 8.5 with sodium hydroxide solution.

[0055] 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of 6.7 g of glycerol triglycidyl ether solution was adjusted to 8.5. The polylysine solution obtained in step 1) was poured into a dropping funnel and added dropwise to the glycerol triglycidyl ether solution at a rate of 1 drop / second. Then, 4 g of hexamethylenetetramine catalyst was added to the solution. After stirring at 45 °C for 6 h, the mixture was dialyzed at 32 °C for 48 h, freeze-dried under vacuum at -65 °C for 48 h, and ground to obtain a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0056] See Figure 1This is a synthetic route diagram of the chromium-free tanning agent with terminal epoxy polylysine group disclosed in this invention. As can be seen from the diagram, the entire equipment process is simple and can produce a highly compatible chromium-free tanning agent with terminal epoxy polylysine group that has excellent adsorption of anionic materials.

[0057] See Figure 2 This is the infrared absorption spectrum of the chromium-free tanning agent with terminal epoxy polylysine groups in Example 4 of the present invention; as can be seen from the spectrum, PG has an infrared absorption of 1564 cm⁻¹. -1 1675 cm -1 and 1108cm -1 Characteristic peaks of amino and amide II (-CONH) groups belonging to polylysine and broad characteristic peaks of COC belonging to GTE were observed. Compared with the infrared spectra of glycerol triglycidyl ether and polylysine, the infrared spectrum of PG showed a significant difference at 1108 cm⁻¹. -1 The characteristic peak of COC and 1564 cm⁻¹ -1 The characteristic peak of -NH2 at this point shows a significant decrease, which is due to the covalent bonding between the epoxy group on glycerol triglycidyl ether and the amino group on polylysine, resulting in the consumption of some amino groups. Furthermore, compared to polylysine, the infrared spectrum of PG shows a significantly lower peak at 1342 cm⁻¹. -1 850 cm -1 756 cm -1 A distinct characteristic peak appears at the [location], which is a characteristic absorption peak attributed to the terminal epoxy group. This indicates that the terminal epoxy group is retained after grafting. The results ultimately demonstrate the successful preparation of a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0058] See Figure 3 This is a comparison chart of the shrinkage temperature and thickening rate of leather with untanned raw hide (PS) and commercially available leather TWS (Sichuan Tingjiang New Material Co., Ltd.) and F-90 (Star Leather Chemical Co., Ltd.) in actual tanning applications of the PG-terminated epoxy polylysine-based chromium-free tanning agent in Example 4 of the present invention. As can be seen from the chart, the PG-terminated epoxy polylysine-based chromium-free tanning agent prepared in this invention has better shrinkage temperature and thickening rate than untanned raw hide (PS) and commercially available leather (TWS, F-90).

[0059] See Figure 4The images show electron microscope (EMS) images of cross-sections of leather before and after tanning using the terminal epoxy polylysine-based chromium-free tanning agent in Example 4 of this invention. (a) is raw hide; (b) is PG tanned leather; (c) is commercially available F-90 tanned leather; and (d) is commercially available TWS tanned leather. The images show that the collagen fibers in PS are bonded together in clumps, without collagen fiber bundles. The collagen fibers in F-90 and TWS tanned leathers are scattered and disordered, with collagen bundles clumped together. Leather tanned using PG tanning agent exhibits a high degree of collagen fiber dispersion and larger gaps, which facilitates the penetration of subsequent dyes and fatliquoring agents.

[0060] See Figure 5 This invention, in Example 4, demonstrates the dye absorption rate and fatliquoring absorption rate of the PG-terminated epoxy polylysine-based chromium-free tanning agent during wet dyeing and finishing processes in practical tanning applications. The results are compared with those of commercially available tanned leathers, TWS (Sichuan Tingjiang New Materials Co., Ltd.) and F-90 (Starr Leather Chemical Co., Ltd.). The figure shows that the PG-terminated epoxy polylysine-based chromium-free tanning agent achieves a fatliquoring agent absorption rate of 92.7%, significantly higher than F-90 (52.8%) and TWS (61.6%) tanned leathers. Simultaneously, its dye absorption rate is 98.6%, far exceeding that of TWS (82.2%) and F-90 (65.5%) tanned leathers.

[0061] Example 5 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 10 g of polylysine with a molecular weight of 2000-5000 Da in 100 mL of water, mix well, and adjust the pH of the polylysine solution to 9 with sodium hydroxide solution.

[0062] 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of 13g of glycerol triglycidyl ether solution was adjusted to 9. The polylysine solution obtained in step 1) was poured into a dropping funnel and added dropwise to the glycerol triglycidyl ether solution at a rate of 1 drop / second. Then, 5g of hexamethylenetetramine catalyst was added to the solution. After stirring at 50 ℃ for 4 h, the mixture was dialyzed at 35 ℃ for 36 h, freeze-dried under vacuum at -70 ℃ for 36 h, and ground to obtain a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0063] Example 6 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 10 g of polylysine with a molecular weight of 2000-5000 Da in 100 mL of water, mix well, and adjust the pH of the polylysine solution to 9.5 with sodium hydroxide solution.

[0064] 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of 15g of glycerol triglycidyl ether solution was adjusted to 10. The polylysine solution obtained in step 1) was poured into a dropping funnel and added dropwise to the glycerol triglycidyl ether solution at a rate of 1 drop / second. Then, 10g of hexamethylenetetramine catalyst was added to the solution. After stirring at 50 ℃ for 2 h, the mixture was dialyzed at 35 ℃ for 24 h, freeze-dried under vacuum at -80 ℃ for 24 h, and ground to obtain a highly compatible terminal epoxy polylysine-based chromium-free tanning agent with excellent adsorption of anionic materials.

[0065] Example 7 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 15g of polylysine with a molecular weight of 2000 Da (concentration 0.15g / mL) in 100mL of water, mix well, and adjust the pH to 8 with sodium hydroxide solution; 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups Dissolve 1 g of glycerol triglycidyl ether in 1 L of water (concentration 1 g / L) and adjust the pH to 7 (intermediate value); the molar ratio of polylysine to GTE is 1:10; add the polylysine solution dropwise to the GTE solution at 1 drop / second, and add 0.375 g of hexamethylenetetramine catalyst (molar ratio of polylysine to polylysine 0.1:1); stir the reaction at 35 °C for 7 h, dialyze at 32 °C for 12 h, freeze dry at -55 °C for 48 h, and grind to obtain the product.

[0066] Example 8 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 20g of polylysine with a molecular weight of 3500 Da (concentration 0.20g / mL) in 100mL of water, mix well, and adjust the pH to 8.5 with sodium hydroxide solution; 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups Dissolve 20g of glycerol triglycidyl ether in 1L of water (concentration 20g / L) and adjust the pH to 9; the molar ratio of polylysine to GTE is 1:20; add the polylysine solution dropwise to the GTE solution at 1 drop / second, and add 5.7g of hexamethylenetetramine catalyst (molar ratio of polylysine to polylysine 2:1); stir the reaction at 45℃ for 5h, dialyze at 30℃ for 30h, freeze dry at -60℃ for 36h, and grind to obtain the product.

[0067] Example 9 A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent includes the following steps: 1) Preparation of polylysine solution Dissolve 10g of polylysine with a molecular weight of 5000 Da (concentration 0.10g / mL) in 100mL of water, mix well, and adjust the pH to 9.0 with sodium hydroxide solution; 2) Synthesis of Chromium-Free Tanning Agents with Terminal Epoxy Polylysine Groups The pH of 10g glycerol triglycidyl ether solution (concentration 10g / L) was adjusted to 8.0, and the molar ratio of polylysine to GTE was 1:5. The polylysine solution was added dropwise to the GTE solution at 1 drop / second, and 1.5g of hexamethylenetetramine catalyst (molar ratio 0.3:1) was added. The reaction was stirred at 40℃ for 6h, dialyzed at 35℃ for 24h, freeze-dried at -80℃ for 24h, and then ground to obtain the product.

[0068] In summary, this invention discloses a terminal epoxy-type polylysine-based chromium-free tanning agent, its preparation method, and its application. Through a covalent cross-linking reaction between amino and epoxy groups, the active epoxy groups in the glycerol triglycidyl ether structure are grafted onto the polylysine polymer. Utilizing the abundant amino groups, high compatibility, high isoelectric point, and renewability of polylysine, terminal epoxidation modification of polylysine is achieved, resulting in a chromium-free cross-linking agent. When applied to the leather tanning process, this agent not only exhibits strong cross-linking with leather collagen fibers but also imparts a high isoelectric point to the tanned leather and excellent binding capacity for anionic materials, achieving the dual advantages of high absorption in leather finishing materials and eco-friendly leather manufacturing. The preparation route of this invention is simple, and the high isoelectric point avoids pollution problems in wet dyeing and finishing processes, providing potential ideas for the innovative design of novel environmentally friendly chromium-free tanning agents. The highly compatible terminal epoxy-type polylysine-based chromium-free tanning agent prepared using the method of this invention possesses excellent tanning effects, and both the raw materials and products are environmentally friendly. The preparation method is simple and easy to implement, making it suitable for large-scale production.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a terminal epoxy-type polylysine-based chromium-free tanning agent, characterized in that, include: Polylysine is dissolved in water, and the pH is adjusted to 7-9.5 to obtain a polylysine solution. Glycerol triglycidyl ether was dissolved in water and the pH was adjusted to 6-10 to obtain a glycerol triglycidyl ether solution. A polylysine solution was added to a glycerol triglycidyl ether solution, followed by a catalyst. After stirring, dialysis, freeze-drying, and grinding, a terminal epoxy-type polylysine-based chromium-free tanning agent was obtained.

2. The method for preparing the terminal epoxy-type polylysine-based chromium-free tanning agent according to claim 1, characterized in that, The molar ratio of polylysine to glycerol triglycidyl ether is 1:(1-20).

3. The method for preparing the terminal epoxy-type polylysine-based chromium-free tanning agent according to claim 1, characterized in that, The polylysine is produced by actinomycete metabolism; The mass concentration of the polylysine solution is 0.10~0.20 g / mL; the mass concentration of the glycerol triglycidyl ether solution is 1~20 g / L.

4. The method for preparing the terminal epoxy-type polylysine-based chromium-free tanning agent according to claim 1, characterized in that, The relative molecular mass of the polylysine is 2000-5000 Da.

5. The method for preparing the terminal epoxy-type polylysine-based chromium-free tanning agent according to claim 1, characterized in that, The molar ratio of the catalyst to polylysine is (0.1-2):1; the catalyst is hexamethylenetetramine.

6. The method for preparing the terminal epoxy-type polylysine-based chromium-free tanning agent according to claim 1, characterized in that, The temperature of the stirring reaction is 30-50℃; the time of the stirring reaction is 2-10 h.

7. The method for preparing the terminal epoxy-type polylysine-based chromium-free tanning agent according to claim 1, characterized in that, The dialysis conditions include: dialysis at 25-35℃ for 12-72 hours.

8. The method for preparing the terminal epoxy-type polylysine-based chromium-free tanning agent according to claim 1, characterized in that, The freeze-drying conditions include: freeze-drying at -40~-80℃ for 24-72 h.

9. A terminal epoxy-type polylysine-based chromium-free tanning agent, characterized in that, The chromium-free tanning agent is prepared by the method described in any one of claims 1-8, wherein the structural formula of the chromium-free tanning agent is as follows: 。 10. The application of the terminal epoxy polylysine-based chromium-free tanning agent prepared by the method of any one of claims 1-8 in leather cleaning production.

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