A method for preparing a leather-based eutectic gel using chrome-free tanned hides

Abstract

This invention relates to a method for preparing leather-based eutectic gels using chromium-free tanned leather blanks. The method uses chromium-free tanned leather blanks from the leather industry as raw materials. A deep eutectic solvent is prepared using choline chloride and glycerol in a molar ratio of 1:2. An impregnation solution consisting of monomers, an initiator, and the deep eutectic solvent is prepared. The chromium-free tanned leather blank is placed in the impregnation solution and stirred at 5–30°C for 4–48 hours. Subsequently, the chromium-free tanned leather blank is heated at 40–80°C for 2–12 hours to obtain the leather-based eutectic gel. The leather-based eutectic gel prepared by this method inherits the original high mechanical strength of the chromium-free tanned leather blank, solving the problem of insufficient mechanical strength in traditional eutectic gels. Furthermore, the mechanical properties of the leather-based eutectic gel can be effectively controlled by adjusting the type of chromium-free tanned leather blank and monomers, thereby meeting the requirements of different application environments. The raw materials of this invention are readily available and inexpensive, the preparation process is simple, and it is easy to industrialize.

Description

Technical Field

[0001] This invention relates to the field of eutectic gel and leather-based functional materials, specifically to a method for preparing a high-strength leather-based eutectic gel by using chromium-free tanned leather blanks as raw materials, through solution impregnation treatment containing monomers and deep eutectic solvents, and then in-situ polymerization. Background Technology

[0002] Deep eutectic solvents (DESs) are low-melting-point eutectic systems formed by the self-assembly of hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) through intermolecular hydrogen bonds. They offer advantages such as being green, low-cost, designable, and easy to prepare, making them an ideal alternative to ionic liquids. The formation of DESs is driven by a hydrogen bond network; strong hydrogen bonds and van der Waals forces form between HBAs and HBDs, disrupting the regular lattice of individual components and resulting in a eutectic system with a melting point significantly lower than that of the individual components. DESs systems exhibit non-ideal mixing behavior, a broadened liquid phase range, and significantly improved thermal stability and solubility. Compared to traditional organic solvents and ionic liquids, DESs have readily available raw materials, no side reactions, and good biocompatibility, leading to rapid development in catalysis, separation, electrochemistry, biomass utilization, and pharmaceuticals.

[0003] Eutectic gels are a class of gel-like composite materials formed through polymer crosslinking, molecular self-assembly, or inorganic framework compositing using deep eutectic solvents (DESs) as the dispersion medium. Their core characteristic is combining the green properties of DESs with the advantages of the three-dimensional network structure of gel materials. As a functional extension of deep eutectic solvents, eutectic gels perfectly inherit the low volatility (VOC≈0 g / m³) and high environmental compatibility (BOD) of DESs. 28 The composite material boasts high conductivity (>80%), structural designability, and wide-temperature stability. Furthermore, the construction of a three-dimensional network overcomes the shortcomings of pure DESs, such as high fluidity and insufficient mechanical strength, achieving synergistic optimization of mechanical properties, electrical conductivity, and environmental tolerance. Since the first eutectic gel based on the choline chloride-urea system was reported in 2015, this type of novel composite material has rapidly emerged in fields such as flexible electronics, energy storage, biomedicine, and intelligent sensing. Especially between 2023 and 2025, breakthroughs in technologies such as supramolecular design, natural framework composites, and multimodal sensing have enabled eutectic gels to achieve significant performance leaps in applications such as high-voltage battery electrolytes (lithium-ion transference number up to 0.88), extreme environment sensors (stable operation from -60 to 100°C), and underwater adhesives (underwater adhesion strength 1.3 times higher than in air), demonstrating enormous potential to replace traditional hydrogels and ionomers and becoming a research hotspot in the field of green functional materials.

[0004] The preparation of eutectic gels is based on the DESs system, and gelation is achieved through network construction. Common preparation methods include: (1) Polymerization and cross-linking method: polymerizable monomers (such as acrylic acid, N-vinylpyrrolidone), cross-linking agents and initiators are dissolved in DESs, and free radical polymerization is initiated by ultraviolet light, heating and other methods to form a three-dimensional polymer cross-linking network, thereby achieving gelation and fixation of DESs. (2) Mixed gelation method: by adjusting the proportion of DESs components or adding gelling factors (such as cellulose, gelatin), gelation is induced by non-covalent interactions such as intermolecular hydrogen bonds and van der Waals forces. (3) Solvent exchange method: through molecular substitution and interface reconstruction between DESs and pre-formed gel networks (such as hydrogels, organic gels or polymer matrices), stable loading and gelation fixation of DESs are achieved.

[0005] In typical eutectic gel structures, DESs exert a strong plasticizing effect on the polymer network, resulting in a fracture strength generally <0.5 MPa and an extremely low modulus in pure eutectic gels, making them unsuitable for high loads. Furthermore, crosslinking is usually unevenly distributed, and network strength is insufficient, allowing micro-defects to easily propagate into macroscopic cracks under cyclic stress, leading to poor mechanical toughness. Therefore, developing novel eutectic gel materials that combine high mechanical strength with good flexibility is crucial and urgent, and is of great significance for promoting the high-value utilization of eutectic gel materials in complex environments. Summary of the Invention

[0006] Skin-based cocrystal gels utilize the natural three-dimensional network framework of collagen fibers from animal skin as the basic structure. By employing appropriate methods (e.g., impregnating DESs containing polymerizable monomers and then polymerizing in situ within the collagen fiber framework to form a cocrystal gel), a polymer cross-linking network dispersed within the DESs is introduced, allowing it to interpenetrate with the original three-dimensional collagen fiber network structure, resulting in a novel composite material. Skin-based cocrystal gels inherit the high mechanical strength and flexibility of the animal skin collagen fiber three-dimensional network framework while also possessing the characteristics of general cocrystal gels. Therefore, they exhibit great application potential in fields such as flexible electronics and sensing, energy storage, biomedicine, and materials for extreme environments.

[0007] The above analysis shows that the three-dimensional network framework of animal skin collagen fibers (referred to as the skin collagen framework), the polymer network, and DESs are interconnected and mutually influential, coupling to form a skin-based eutectic gel. The construction of the polymer network requires the preservation of the skin collagen framework; therefore, the structure and properties of the skin collagen framework profoundly influence and constrain the formation, structure, and properties of the polymer network, playing a dominant role. In particular, the mechanical properties of the skin collagen framework are the primary key factor controlling the construction, structure, and properties of the skin-based eutectic gel. In other words, the most effective way to improve the mechanical strength of the skin-based eutectic gel is to increase the mechanical strength of the skin collagen framework.

[0008] In the leather industry, tanning involves the interaction between tanning agents and collagen molecules (such as covalent cross-linking, metal coordination, and hydrogen bonding) to densify and stabilize the three-dimensional network structure of collagen fibers. This ultimately endows leather with the core characteristics of strength, flexibility, and durability, fundamentally determining its mechanical properties and usability. The essence of tanning is the formation of "cross-linking bridges" between collagen fibers by tanning agent molecules, inhibiting collagen fiber slippage and aggregation, while simultaneously optimizing the interfiber structure, thus achieving improved and controllable mechanical properties. Tanned animal hides are called leather, and compared to untanned animal hides, leather exhibits significantly improved mechanical properties such as tensile strength, tear strength, flexibility, folding resistance, and fatigue resistance. Therefore, inspired by the superior mechanical strength of tanned leather compared to untanned natural animal hides, this invention uses chrome-free tanned leather blanks as raw materials and employs a "top-down" strategy, using the three-dimensional network structure of its tanned collagen fibers as the matrix framework for a eutectic gel, to prepare a novel leather-based eutectic gel material with high mechanical strength. The preparation process of the leather-based eutectic gel is as follows: 1) Impregnation: Using appropriate physical and mechanical treatment (such as stirring), the monomer, initiator and deep eutectic solvent are allowed to penetrate and be evenly distributed in the interfiber gaps of the collagen fiber three-dimensional network structure of the chrome-free tanned leather blank; 2) Polymerization: Under immobilization conditions, the monomer is allowed to undergo in-situ polymerization in the chrome-free tanned leather blank to form a polymer cross-linking network, and form a network interpenetrating structure with the original collagen fiber three-dimensional network in the chrome-free tanned leather blank to obtain the leather-based eutectic gel.

[0009] Specifically, the purpose of this invention is to provide a method for preparing a leather-based eutectic gel, characterized by the following process flow: 1) Weighing the chrome-free tanned leather blank and adding it to an impregnation solution of 200% to 800% of the weight of the chrome-free tanned leather blank, and stirring at 5 to 30°C for 4 to 48 hours; 2) Taking out the impregnated chrome-free tanned leather blank and placing it between two smooth flat plates, while keeping the chrome-free tanned leather blank flat, heating it at 40 to 80°C for 2 to 12 hours to obtain the leather-based eutectic gel. The chromium-free tanned leather blanks used in this method can be any one of the following: cowhide chromium-free tanned leather blanks, pigskin chromium-free tanned leather blanks, and sheepskin chromium-free tanned leather blanks; the type of chromium-free tanned leather blanks can be any one of the following: metal chromium-free tanned leather blanks, organic chromium-free tanned leather blanks, and organo-metal combined chromium-free tanned leather blanks; metal chromium-free tanned leather blanks can be any one of the following: aluminum tanned leather blanks, zirconium tanned leather blanks, titanium tanned leather blanks, zeolite tanned leather blanks, and multi-metal tanned leather blanks; organic chromium-free tanned leather blanks can be any one of the following: aldehyde tanned leather blanks, organophosphorus tanned leather blanks, and organic synthetic tanned leather blanks; the impregnation solution used to prepare the leather-based eutectic gel consists of monomers, initiators, and deep eutectic solvents. The impregnation solution is composed of monomers, initiators, and deep eutectic solvents in a mass ratio of 100:0.1~1.0:50~200. The monomers in the impregnation solution are any one or a mixture of acrylic acid, methacrylic acid, acrylamide, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and 1-vinyl-2-pyrrolidone. The initiator in the impregnation solution is any one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride. The deep eutectic solvent in the impregnation solution is composed of choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2.

[0010] The method for preparing skin-based eutectic gel provided by this invention has the following advantages: First, this invention uses chromium-free tanned leather blanks as raw materials, which possess excellent physical and mechanical properties. Therefore, the leather-based eutectic gel prepared from these blanks will inherit the original high mechanical strength of the chromium-free tanned leather blanks, thus solving the problem of poor mechanical strength in traditional eutectic gels.

[0011] Secondly, in addition to using chrome-free tanned leather blanks of different tanning types and leather grades as raw materials to regulate the mechanical strength of the eutectic gel, the present invention can also adjust the structure and properties of the polymer network by selecting monomer types, thereby adjusting the mechanical strength of the eutectic gel to meet the mechanical performance requirements of different application environments.

[0012] Third, the skin-based eutectic gel prepared by this invention also has the advantages of general eutectic gels, such as good conductivity, environmental stability, and thermal stability, which can meet the needs of complex application environments.

[0013] Fourth, the chromium-free tanned leather blanks used in this invention are derived from the leather industry, and the raw materials are readily available and inexpensive; the impregnation solution used in this invention has simple components, readily available raw materials, and is inexpensive; the preparation process of this invention is simple and easy to industrialize. Detailed Implementation

[0014] The following embodiments are provided to illustrate the present invention in more detail. It should be noted that the following embodiments should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention are still within the scope of protection of the present invention.

[0015] Example 1 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using acrylic acid as the monomer, ammonium persulfate as the initiator, and the deep eutectic solvent as the solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.5:100. A goat aluminum-tanned leather blank was weighed and added to an impregnation solution equal to 600% of its weight. The mixture was stirred at 20°C for 12 hours. Subsequently, the impregnated goat aluminum-tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 60°C for 5 hours to obtain a leather-based eutectic gel.

[0016] Example 2 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using hydroxyethyl methacrylate as a monomer, potassium persulfate as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.2:80. The sheep titanium-tanned leather blank was weighed and added to an impregnation solution equal to 300% of its weight. The mixture was stirred at 25°C for 20 hours. Subsequently, the impregnated sheep titanium-tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 70°C for 3 hours to obtain a leather-based eutectic gel.

[0017] Example 3 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using 1-vinyl-2-pyrrolidone as the monomer, azobisisobutyramidine hydrochloride as the initiator, and the deep eutectic solvent as the solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.1:50. A bovine zirconium-tanned leather blank was weighed and added to an impregnation solution equal to 400% of its weight. The mixture was stirred at 10°C for 36 hours. Subsequently, the impregnated bovine zirconium-tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 50°C for 10 hours to obtain a leather-based eutectic gel.

[0018] Example 4 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using acrylamide as the monomer, ammonium persulfate as the initiator, and the deep eutectic solvent as the solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:1.0:200. Pigskin zeolite-tanned leather blanks were weighed and added to an impregnation solution equal to 200% of their weight. The mixture was stirred at 5°C for 48 hours. Subsequently, the impregnated pigskin zeolite-tanned leather blanks were removed and placed between two smooth plates. While maintaining the flatness of the blanks, they were heated at 40°C for 12 hours to obtain a leather-based eutectic gel.

[0019] Example 5 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using methacrylic acid as the monomer, potassium persulfate as the initiator, and the deep eutectic solvent as the solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.7:140. The goat zirconium-aluminum-titanium bonded tanned leather blank was weighed and added to an impregnation solution equal to 800% of its weight. The mixture was stirred at 15°C for 4 hours. Subsequently, the impregnated goat zirconium-aluminum-titanium bonded tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 45°C for 11 hours to obtain a leather-based eutectic gel.

[0020] Example 6 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using hydroxypropyl acrylate as the monomer, azobisisobutyramidine hydrochloride as the initiator, and the deep eutectic solvent as the solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.3:60. The sheep aldehyde-tanned leather blank was weighed and added to an impregnation solution equal to 500% of its weight. The mixture was stirred at 30°C for 8 hours. Subsequently, the impregnated sheep aldehyde-tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 80°C for 2 hours to obtain a leather-based eutectic gel.

[0021] Example 7 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using 2-hydroxyethyl acrylate as a monomer, ammonium persulfate as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.4:70. The bovine organophosphorus tanned leather blank was weighed and added to an impregnation solution equal to 700% of its weight. The mixture was stirred at 18°C ​​for 40 hours. Subsequently, the impregnated bovine organophosphorus tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 65°C for 4 hours to obtain a leather-based eutectic gel.

[0022] Example 8 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using methacrylic acid and acrylamide (mass ratio 1:4) as monomers, potassium persulfate as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.9:180. The pigskin organic synthetic tanning blank was weighed and added to an impregnation solution equal to 250% of its weight. The mixture was stirred at 27°C for 30 hours. Subsequently, the impregnated pigskin organic synthetic tanning blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 55°C for 8 hours to obtain a leather-based eutectic gel.

[0023] Example 9 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using acrylic acid and 2-hydroxyethyl acrylate (mass ratio 1:1) as monomers, azobisisobutyramidine hydrochloride as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.6:90. Goat zeolite-aldehyde-bonded tanned leather blanks were weighed and added to an impregnation solution equal to 350% of their weight, and stirred at 18°C ​​for 44 hours. Subsequently, the impregnated goat zeolite-aldehyde-bonded tanned leather blanks were removed and placed between two smooth plates. While maintaining the flatness of the blanks, they were heated at 75°C for 3 hours to obtain a leather-based eutectic gel.

[0024] Example 10 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using hydroxypropyl acrylate and acrylamide (mass ratio 3:2) as monomers, ammonium persulfate as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.8:160. The sheep aluminum-aldehyde bonded tanned leather blank was weighed and added to an impregnation solution equal to 750% of its weight. The mixture was stirred at 22°C for 10 hours. Subsequently, the impregnated sheep aluminum-aldehyde bonded tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 60°C for 6 hours to obtain a leather-based eutectic gel.

[0025] Example 11 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using 1-vinyl-2-pyrrolidone and 2-hydroxyethyl acrylate (mass ratio 1:2) as monomers, potassium persulfate as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.4:120. The aldehyde-synthetic tanning agent bound leather blank was weighed and added to an impregnation solution containing 450% of the aldehyde-synthetic tanning agent bound leather blank weight. The mixture was stirred at 28°C for 16 hours. Subsequently, the impregnated aldehyde-synthetic tanning agent bound leather blank was removed and placed between two smooth plates. While maintaining the flatness of the aldehyde-synthetic tanning agent bound leather blank, it was heated at 50°C for 7 hours to obtain a leather-based eutectic gel.

[0026] Example 12 A deep eutectic solvent was prepared using choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2. An impregnation solution was prepared using hydroxyethyl methacrylate and acrylic acid (mass ratio 5:2) as monomers, azobisisobutyramidine hydrochloride as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.6:110. Pigskin titanium-organophosphorus bonded tanned leather blanks were weighed and added to an impregnation solution equal to 550% of their weight. The mixture was stirred at 20°C for 24 hours. Subsequently, the impregnated pigskin titanium-organophosphorus bonded tanned leather blanks were removed and placed between two smooth plates. While maintaining the flatness of the blanks, the mixture was heated at 50°C for 9 hours to obtain a leather-based eutectic gel.

[0027] The tensile strength of the leather-based eutectic gel prepared in the above embodiments was determined by the method described in QB / T2710-2018 (Determination of tensile strength and elongation of leather physical and mechanical tests), and its electrical conductivity was determined by an electrochemical workstation. The results are shown in Table 1.

[0028] Table 1

Claims

1. A method for preparing a skin-based eutectic gel, characterized in that... The process flow of this method is as follows: 1) Weigh the chrome-free tanned leather blank and add it to an impregnation solution of 200%~800% of the weight of the chrome-free tanned leather blank. Stir at 5~30℃ for 4~48 hours; 2) Take out the impregnated chrome-free tanned leather blank and place it between two smooth plates. While keeping the chrome-free tanned leather blank flat, heat it at 40~80℃ for 2~12 hours to obtain leather-based eutectic gel.

2. The method for preparing a skin-based eutectic gel according to claim 1, characterized in that... The chromium-free tanned leather blank used to prepare the leather-based eutectic gel can be any one of the following: chromium-free cowhide tanned leather blank, chromium-free pigskin tanned leather blank, and chromium-free sheepskin tanned leather blank.

3. The method for preparing a skin-based eutectic gel according to claims 1 and 2, characterized in that... The chromium-free tanned leather blank used to prepare the leather-based eutectic gel can be any one of the following: metal chromium-free tanned leather blank, organic chromium-free tanned leather blank, and organo-metal combined chromium-free tanned leather blank.

4. The method for preparing a skin-based eutectic gel according to claims 1 and 3, characterized in that... The chromium-free tanned leather blank used to prepare the leather-based eutectic gel is any one of aluminum tanned leather blank, zircon tanned leather blank, titanium tanned leather blank, zeolite tanned leather blank, and multi-metal tanned leather blank.

5. The method for preparing a skin-based eutectic gel according to claims 1 and 3, characterized in that... The organic chromium-free tanned leather preform used to prepare the leather-based eutectic gel is any one of aldehyde tanned leather preform, organophosphorus tanned leather preform, and organic synthetic tanned leather preform.

6. The method for preparing a skin-based eutectic gel according to claim 1, characterized in that... The impregnation solution used to prepare skin-based eutectic gels consists of monomers, initiators, and deep eutectic solvents, with a mass ratio of monomer:initiator:deep eutectic solvent = 100:0.1~1.0:50~200.

7. The method for preparing a skin-based eutectic gel according to claims 1 and 6, characterized in that... The monomers in the impregnation solution used to prepare the skin-based eutectic gel are any one of acrylic acid, methacrylic acid, acrylamide, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, 1-vinyl-2-pyrrolidone, or mixtures thereof.

8. The method for preparing a skin-based eutectic gel according to claims 1 and 6, characterized in that... The initiator in the impregnation solution used to prepare the skin-based eutectic gel is any one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride.

9. A method for preparing a skin-based eutectic gel according to claims 1 and 6, characterized in that... The deep eutectic solvent in the impregnation solution used to prepare the skin-based eutectic gel consists of choline chloride and glycerol in a molar ratio of choline chloride:glycerol = 1:2.

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