A method for preparing a leather-based eutectic gel based on chrome tanned leather base

Abstract

This invention relates to a method for preparing a leather-based eutectic gel based on chrome-tanned leather blanks. The method uses chrome-tanned leather blanks as raw materials, prepares a deep eutectic solvent using choline chloride and glycerol in a molar ratio of 1:2, and prepares an impregnation solution composed of monomers, an initiator, and the deep eutectic solvent. The chrome-tanned leather blanks are placed in the impregnation solution and stirred at 5–30°C for 4–48 hours. Subsequently, the chrome-tanned leather blanks are heated at 45–95°C for 1–12 hours to obtain the leather-based eutectic gel. The leather-based eutectic gel prepared by this method inherits the excellent mechanical strength of chrome-tanned leather blanks and further enhances the mechanical properties of the eutectic gel by forming an interpenetrating network structure with the original collagen fiber three-dimensional network in the chrome-tanned leather blank through a polymer three-dimensional network, thus effectively solving the defect of insufficient mechanical strength in traditional eutectic gels. The raw materials of this invention are readily available and inexpensive from the leather and chemical industries, and the preparation process is simple and 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 chrome-tanned leather blanks as raw materials, impregnating them with a solution containing monomers and deep eutectic solvents, and then polymerizing them in situ. Background Technology

[0002] Deep eutectic solvents (DESs), a novel type of green solvent formed by hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) in a specific ratio, have overcome the performance limitations of traditional organic solvents and ionic liquids due to their core advantages such as low vapor pressure (<1 Pa, 25℃, no volatile organic compound (VOC) emissions), wide liquid range (typically -40~200℃, adaptable to extreme conditions), high conductivity, strong solubility (can dissolve various substances such as organics, inorganics, and polymers), no purification required in the synthesis process (only simple mixing and heating, with 100% atom utilization), good environmental compatibility, and strong designability. They combine the solubility of organic solvents with the stability of ionic liquids, and have unique advantages such as green raw materials, simple synthesis, and biodegradability. They are regarded as "next-generation green solvents" and have great application potential in electrochemistry, resource recycling, biomass conversion, biomedicine and other fields.

[0003] Eutectic gels, as novel soft materials constructed by deep eutectic solvents (DESs) and gelling agents (polymers / small molecules) through hydrogen bonding and electrostatic interactions, combine the green properties and wide-temperature stability of DESs with the advantages of the three-dimensional network structure of gels. They achieve breakthroughs in mechanical properties, ion transport, and biocompatibility that are difficult to achieve with traditional gel materials, realizing the synergistic compatibility of "green properties, high performance, and multifunctionality". The essence of eutectic gels is a thermodynamically stable three-dimensional network system formed by multiple interactions between DESs and gelling factors. Its core characteristics include: 1) DESs-mediated network construction: DESs not only act as a solvent providing a dispersion medium, but their hydrogen-bonded network also synergistically interacts with gelling factors to regulate the structure and properties of the eutectic gel network; 2) Multifunctional integration: It combines the ion transport and environmentally friendly properties of DESs with the mechanical support and controlled-release functions of gels; 3) Wide performance tuning: By controlling the composition of DESs, the type and ratio of gelling factors, precise adjustment of properties such as mechanical strength and conductivity can be achieved; 4) Strong environmental adaptability: It is resistant to extreme temperatures (-40~150℃) and has low volatility, significantly improving stability compared to traditional hydrogels and organic gels. Eutectic gels have broad application value in flexible sensing, magnetoelectric sensing, flexible electronic patches, metal batteries, flexible energy storage devices, drug delivery, tissue engineering, antibacterial materials, intelligent drives, environmental remediation, and food preservation.

[0004] Traditional eutectic gels suffer from low mechanical properties (fracture strength generally below 0.5 MPa) due to the plasticizing effect of DESs. Recent strategies to enhance the mechanical properties of eutectic gels mainly include: 1) Dual-network design: a rigid first network provides strength support, while a flexible second network dissipates energy. For example, PVA-chemically cross-linked polymer eutectic gels can achieve a fracture strength of around 10 MPa and a toughness of around 50 MJ / m³; 2) Electrostatic anchoring mechanism: through the electrostatic interaction between gelling agents and functional components (such as liquid metals), network stability and mechanical durability are improved. For example, metal gels maintain structural integrity even under 1100% tensile strain; 3) Interfacial eutectic control: utilizing the synergistic crystallization of two-dimensional materials and polymers to form a highly layered superlattice structure, reducing interfacial energy dissipation and increasing the loss angle tan θ. The lowest δ value is only 0.02; 4) DESs component optimization: Select high-viscosity, strong hydrogen-bonded DESs, or introduce metal ions to form coordination crosslinks to improve network density. For example, the fracture strength of ZnCl2 / choline chloride / ethylene glycol eutectic gel can be increased to about 2.3 MPa. Nevertheless, due to the limitations of the mechanical strength of the polymer three-dimensional network in the eutectic gel itself, the mechanical properties of the eutectic gel are still insufficient and difficult to meet the requirements of high-load application scenarios. Therefore, it is very important and urgent to develop new eutectic gel materials with both high mechanical strength and good flexibility, which is of great significance for promoting the high-value utilization of eutectic gel materials in complex high-load environments. Summary of the Invention

[0005] Animal hides, as a natural biomass material, have played a crucial role in the development of human civilization due to their unique collagen fiber network structure, excellent mechanical properties, and biocompatibility. Their use dates back to ancient times—early humans processed animal hides into clothing and shelter to protect themselves from the cold and wild animals. With the progress of civilization, animal hide processing technology has continuously evolved, gradually forming distinctive industries such as leather manufacturing and traditional leather crafts, becoming an important material for cultural heritage preservation and economic development.

[0006] Tanning is the core process in the modern leather industry for transforming animal hides into leather. Essentially, it involves the interaction between tanning agents and collagen to build a stable cross-linked network, thereby regulating the structure and properties of the leather. Tanning introduces tanning agents to form stable cross-links with the hide's collagen, disrupting the original aggregation state of collagen in the raw hide and reconstructing the fiber network structure. This endows the leather with excellent mechanical properties (such as tensile strength, tear strength, elongation at break, folding strength, and abrasion resistance), chemical stability, and durability, directly determining its application scenarios and service life. In particular, since its industrial application in the early 20th century, chrome tanning has become the dominant tanning process in the leather industry due to its unique cross-linking advantages; over 70% of leather products worldwide are prepared using chrome tanning technology. Compared with tanning methods such as vegetable tanning and aldehyde tanning, chrome tanning forms a stable six-coordinate cross-linked network with the collagen in the hide through trivalent chromium, which increases the shrinkage temperature of the raw hide from about 60℃ to 110~120℃, increases the tensile strength by 3~5 times, and at the same time gives the leather excellent comprehensive properties (such as a soft and full hand feel, excellent dyeing performance and water washing stability).

[0007] Based on the above analysis, and considering the excellent mechanical properties and environmental stability of chrome-tanned leather, this invention uses the three-dimensional collagen fiber network skeleton of chrome-tanned leather as the basic framework of the eutectic gel. Polymerizable monomers and a deep eutectic solvent are introduced through an impregnation process. The monomers then undergo in-situ polymerization in the interfiber spaces of the chrome-tanned leather. The resulting polymer crosslinked network forms an interpenetrating network structure with the original three-dimensional collagen fiber network in the chrome-tanned leather, thus forming a novel high-strength leather-based eutectic gel material. This leather-based eutectic gel inherits the high mechanical strength and flexibility of the three-dimensional collagen fiber network skeleton of chrome-tanned leather while retaining the excellent properties of traditional eutectic gels, and is expected to meet the application requirements in high-mechanical-load environments.

[0008] Specifically, the present invention aims to provide a method for preparing a leather-based eutectic gel, characterized by the following process flow: 1) Weighing the chrome-tanned leather blank and adding it to an impregnation solution of 200% to 800% of the weight of the chrome-tanned leather blank, and stirring at 5 to 30°C for 4 to 48 hours; 2) Taking out the impregnated chrome-tanned leather blank and placing it between two smooth flat plates, while keeping the chrome-tanned leather blank flat, heating it at 45 to 95°C for 1 to 12 hours to obtain a leather-based eutectic gel. The chrome-tanned leather blank used in this method is any one of cowhide chrome-tanned leather blank, pigskin chrome-tanned leather blank, and sheepskin chrome-tanned leather blank; the impregnation solution used to prepare the leather-based eutectic gel is composed of monomer, initiator, and deep eutectic solvent, and their mass ratio is monomer:initiator:deep eutectic solvent = 100:0.1~1.0:50~200; the monomer in the impregnation solution is any one of acrylic acid, methacrylic acid, acrylamide, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, 1-vinyl-2-pyrrolidone, or a mixture thereof; 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, and their molar ratio is choline chloride:glycerol = 1:2.

[0009] The method for preparing skin-based eutectic gel provided by this invention has the following advantages: First, this invention uses chrome-tanned leather blanks with excellent mechanical properties as the basic framework of the eutectic gel. The derived leather-based eutectic gel will inherit the original high mechanical strength of the chrome-tanned leather blanks. At the same time, the polymer three-dimensional network formed by in-situ polymerization of monomers and the original collagen fiber three-dimensional network in the chrome-tanned leather blanks form an interpenetrating network structure, which will further improve the mechanical properties of the eutectic gel, thus effectively solving the defect of poor mechanical strength of traditional eutectic gels.

[0010] Secondly, the mechanical properties of the eutectic gel prepared by this invention can be controlled by using chrome-tanned leather blanks of different types of leather, or by selecting different types of monomers to construct polymer three-dimensional networks with different structures and properties, thereby meeting the mechanical property requirements of different application environments.

[0011] Third, the raw materials for preparing the leather-based eutectic gel in this invention are derived from the leather industry and the chemical industry. The raw materials are readily available and inexpensive, and the preparation process is simple and easy to industrialize. Detailed Implementation

[0012] 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.

[0013] 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 hydroxypropyl 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 = 100:0.6:120. Goat chrome-tanned leather blanks were weighed and added to an impregnation solution equal to 500% of their weight. The mixture was stirred at 15°C for 16 hours. Subsequently, the impregnated goat chrome-tanned leather blanks were removed and placed between two smooth plates. While maintaining the flatness of the blanks, the mixture was heated at 60°C for 8 hours to obtain a leather-based eutectic gel.

[0014] 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 1-vinyl-2-pyrrolidone 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 = 100:0.2:60. A chrome-tanned sheepskin blank was weighed and added to an impregnation solution equal to 400% of its weight. The mixture was stirred at 10°C for 32 hours. Subsequently, the impregnated chrome-tanned sheepskin blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 90°C for 2 hours to obtain a leather-based eutectic gel.

[0015] 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 acrylic acid 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 = 100:0.9:180. A chrome-tanned cowhide blank was weighed and added to an impregnation solution equal to 200% of its weight. The mixture was stirred at 25°C for 48 hours. Subsequently, the impregnated chrome-tanned cowhide blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 70°C for 5 hours to obtain a leather-based eutectic gel.

[0016] 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 = 100:0.1:50. Pigskin chrome-tanned leather blanks were weighed and added to an impregnation solution equal to 800% of their weight. The mixture was stirred at 5°C for 8 hours. Subsequently, the impregnated pigskin chrome-tanned leather blanks were removed and placed between two smooth plates. While maintaining the flatness of the blanks, they were heated at 45°C for 12 hours to obtain a leather-based eutectic gel.

[0017] 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 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 = 100:0.5:140. Goat chrome-tanned leather blanks were weighed and added to an impregnation solution equal to 600% of their weight. The mixture was stirred at 30°C for 4 hours. Subsequently, the impregnated goat chrome-tanned leather blanks were removed and placed between two smooth flat plates. While maintaining the flatness of the blanks, the mixture was heated at 80°C for 3 hours to obtain a leather-based eutectic gel.

[0018] 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 2-hydroxyethyl acrylate as a monomer, azobisisobutyramidine hydrochloride as an initiator, and the deep eutectic solvent as a solvent in a mass ratio of monomer:initiator:deep eutectic solvent = 100:1.0:200. A sheep chrome-tanned leather blank was weighed and added to an impregnation solution equal to 300% of its weight. The mixture was stirred at 20°C for 40 hours. Subsequently, the impregnated sheep chrome-tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 95°C for 1 hour to obtain a leather-based eutectic gel.

[0019] 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 hydroxyethyl methacrylate 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 = 100:0.4:100. A chrome-tanned cowhide blank was weighed and added to an impregnation solution equal to 450% of its weight. The mixture was stirred at 18°C ​​for 24 hours. Subsequently, the impregnated chrome-tanned cowhide 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.

[0020] 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 acrylic acid and 2-hydroxyethyl acrylate (mass ratio 1:3) 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 = 100:0.8:160. Pigskin chrome-tanned leather blanks were weighed and added to an impregnation solution equal to 700% of their weight, and stirred at 8°C for 44 hours. Subsequently, the impregnated pigskin chrome-tanned leather blanks were removed and placed between two smooth plates. While maintaining the flatness of the blanks, they were heated at 55°C for 11 hours to obtain a leather-based eutectic gel.

[0021] 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 hydroxypropyl acrylate and acrylamide (mass ratio 4:1) 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 = 100:0.3:80. Goat chrome-tanned leather blanks were weighed and added to an impregnation solution equal to 350% of their weight. The mixture was stirred at 28°C for 12 hours. Subsequently, the impregnated goat chrome-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 10 hours to obtain a leather-based eutectic gel.

[0022] 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 methacrylic acid and 2-hydroxyethyl acrylate (mass ratio 2:3) 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 = 100:0.7:150. A sheep chrome-tanned leather blank was weighed and added to an impregnation solution equal to 550% of its weight. The mixture was stirred at 22°C for 20 hours. Subsequently, the impregnated sheep chrome-tanned leather blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 75°C for 6 hours to obtain a leather-based eutectic gel.

[0023] 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 acrylamide and 1-vinyl-2-pyrrolidone (mass ratio 1:1) 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 = 100:0.4:110. A chrome-tanned cowhide blank was weighed and added to an impregnation solution comprising 650% of its weight. The mixture was stirred at 12°C for 36 hours. Subsequently, the impregnated chrome-tanned cowhide blank was removed and placed between two smooth plates. While maintaining the flatness of the blank, it was heated at 85°C for 2 hours to obtain a leather-based eutectic gel.

[0024] 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 acrylic acid and hydroxyethyl methacrylate (mass ratio 3:1) 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 = 100:0.5:130. Pigskin chrome-tanned leather blanks were weighed and added to an impregnation solution equal to 250% of their weight, and stirred at 10°C for 28 hours. Subsequently, the impregnated pigskin chrome-tanned leather blanks were removed and placed between two smooth plates. While maintaining the flatness of the blanks, they were heated at 55°C for 9 hours to obtain a leather-based eutectic gel.

[0025] 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.

[0026] 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-tanned leather blank and add it to an impregnation solution of 200%~800% of the weight of the chrome-tanned leather blank, and stir at 5~30℃ for 4~48 hours; 2) Take out the impregnated chrome-tanned leather blank, place it between two smooth plates, and heat it at 45~95℃ for 1~12 hours while keeping the chrome-tanned leather blank flat to obtain leather-based eutectic gel.

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

3. 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.

4. The method for preparing a skin-based eutectic gel according to claims 1 and 3, 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.

5. The method for preparing a skin-based eutectic gel according to claims 1 and 3, 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.

6. The method for preparing a skin-based eutectic gel according to claims 1 and 3, 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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