Super-hydrophobic modified polyurethane leather and preparation method thereof

Abstract

The present application relates to polyurethane leather surface treatment technical field, especially to a kind of super-hydrophobic modified polyurethane leather and its preparation method;The super-hydrophobic modified polyurethane leather includes soft polyurethane inner layer and hard functional outer layer, and the hard functional outer layer contains poly ionic liquid brush grafting SiO2, forms gradient structure that SiO2 content decreases from outside to inside.The present application uses poly ionic liquid brush grafting SiO2 to change the defect that SiO2 is easily settled in polyurethane gel layer, competes with polyurethane gelation kinetics by steric hindrance-chemical anchoring synergic slow sinking mechanism, and cooperates with the chain extender BDO of moderate reactivity, provides a reasonable process window, the viscosity and NCO value of gel point are accurately controlled, to realize a new type of leather surface modification process, and realize the new leather structure that inner layer is soft, outer layer gradient hardness distribution and surface hydrophobic.

Description

Technical Field

[0001] This invention relates to the field of polyurethane leather surface treatment technology, and in particular to a superhydrophobic modified polyurethane leather and its preparation method. Background Technology

[0002] Polyurethane leather is widely used in furniture, automotive interiors, footwear, and electronic product packaging due to its excellent abrasion resistance, flexibility, and designability. However, traditional polyurethane leather faces several challenges in long-term use: First, its surface is easily soaked and adhered to by water, oil stains, and dirt, making cleaning and maintenance difficult; second, its surface hardness is insufficient, making it prone to scratches, and it lacks the "hard on the outside, soft on the inside" gradient feel similar to natural leather; third, humid environments easily become breeding grounds for microorganisms (such as bacteria and mold), posing hygiene and safety hazards.

[0003] To improve surface properties, some techniques often employ the addition of nanoparticles (such as SiO2) to construct rough surfaces for superhydrophobicity, or the blending of antibacterial agents to impart antibacterial functionality. However, these methods have inherent drawbacks:

[0004] (1) The contradiction between function and bulk performance: Simple blending of nano-SiO2 is prone to uneven distribution due to agglomeration and rapid sedimentation. Not only is it difficult to effectively enrich it on the surface to build a stable superhydrophobic layer, but it will also destroy the internal elastic network of the polyurethane matrix, resulting in material embrittlement or hard spots in the inner layer and loss of flexibility.

[0005] (2) Difficulty in achieving gradient structure: Achieving a continuous gradient transition from high surface hardness to high internal elasticity is the key to simulating the feel of natural leather and balancing durability and comfort. Conventional coating or blending techniques cannot accurately control the spatial distribution of fillers during the curing process, and cannot form a stable gradient structure.

[0006] (3) Difficulty in multifunctional synergy: Superhydrophobicity, high hardness and antibacterial properties originate from different mechanisms, often requiring the addition of multiple functional additives, which can easily lead to poor compatibility between components and complex interfaces, affecting the overall performance and long-term stability of the material.

[0007] Therefore, developing a novel material that can synergistically achieve superhydrophobicity, significant hardness gradient, and efficient antibacterial properties without sacrificing the excellent mechanical properties of polyurethane has become a pressing technical challenge in this field. The core lies in designing a novel functional filler that is both well-compatible with the polyurethane matrix and can spontaneously form a gradient structure through controllable migration / anchoring behavior. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a superhydrophobic modified polyurethane leather and its preparation method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A superhydrophobic modified polyurethane leather includes a soft polyurethane inner layer and a hard functional outer layer. The hard functional outer layer contains polyionic liquid brush-grafted SiO2 (PIL-g-SiO2), forming a gradient structure in which the SiO2 content decreases from the outside to the inside.

[0011] The surface water contact angle of the rigid functional outer layer is >150°, the hardness gradient difference is ΔShoreA≥30, and the antibacterial rate is >99%.

[0012] The flexible polyurethane inner layer comprises the following components in parts by weight:

[0013] 100 parts high NCO polyurethane, 5-8 parts chain extender;

[0014] The rigid functional outer layer comprises the following components in parts by weight:

[0015] 100 parts of polyionic liquid-grafted SiO2, 20-30 parts of low-NCO polyurethane, and 1.5-2 parts of chain extender.

[0016] Preferably, the high-NCO polyurethane is a polyurethane prepolymer with NCO end-NCO content of 15-20% [colorless, transparent, viscous liquid, Wuhan Kemike Biomedical Technology Co., Ltd., with both ends being NCO; it is produced by reacting polytetrahydrofuran ether diol (PTMEG, Mn=1000±100) and 4,4'-diphenylmethane diisocyanate (MDI) in a molar ratio of 1:1.3, catalyzed by dibutyltin dilaurate (DBTDL), at 80±2℃ for 2-2.5h, with a viscosity of 3000-4000mPa·s (80℃), and needs to be stored under sealed, light-proof, and low-temperature (<40℃) conditions].

[0017] Preferably, the low-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 3-5% [colorless, transparent, viscous liquid, manufactured by Wuhan Kemike Biomedical Technology Co., Ltd., with NCO at both ends; it is prepared by reacting polytetrahydrofuran ether diol (PTMEG, Mn=1000±100) and 4,4'-diphenylmethane diisocyanate (MDI) in a molar ratio of 1:1.05 with dibutyltin dilaurate (DBTDL) catalyzed at 80±2℃ for 1.8-2.2h, with a viscosity of 2700-3800 mPa·s (80℃), and needs to be stored under sealed, light-proof, and low-temperature (<40℃) conditions];

[0018] Preferably, the chain extender is 1,4-butanediol (BDO).

[0019] Other chain extenders are not suitable for the reactivity of this invention:

[0020] Amine chain extenders (such as diethyltoluenediamine DETDA, Moca MOCA) form urea bonds with polyurethane prepolymers, resulting in high strength, high modulus, and good heat resistance, but may cause the gel layer to be too rigid; their reactivity is extremely high, the reaction rate is too fast (seconds), the viscosity increases instantaneously, and the process window is very narrow, making them unsuitable for this solution that requires precise control of coating time.

[0021] Low molecular weight polyether glycols (such as PPG with a molecular weight of 200-400) have lower reactivity. Although they are more flexible, they are slower to build up initial strength and result in a softer gel layer.

[0022] Small molecule diols (such as 1,4-butanediol BDO and ethylene glycol EG) exhibit moderate reactivity, forming urethane bonds with polyurethane prepolymers. They possess moderate strength and good flexibility. BDO is the most commonly used chain extender, capable of forming regular hard segment microdomains and providing excellent overall performance. The reaction rate is controllable (from several minutes to tens of minutes), providing a suitable process window for monitoring NCO% and viscosity.

[0023] Preferably, the polyionic liquid brush-grafted SiO2 comprises the following raw materials in parts by weight:

[0024] The mixture consists of 5-20 parts of nano-SiO2 particles with a particle size of 20-50 nm, 1-5 parts of γ-methacryloyloxypropyltrimethoxysilane, 10-50 parts of 1-vinylimidazolium, 10-70 parts of 2-bromoethanol, and 0.05-0.1 parts of azobisisobutyronitrile.

[0025] Furthermore, the synthesis steps of polyionic liquid brush grafted SiO2 are as follows:

[0026] (1) Preparation of silane-modified SiO2

[0027] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water. The pH of the mixed solution was adjusted to 3-5 using hydrochloric acid. Then, the solution was heated to 50-70℃ and stirred for 6-12 hours. After centrifugation, the solution was washed several times with ethanol and dried to obtain silane-modified SiO2 for later use.

[0028] Mechanism Reference Figure 1 Through acidic catalytic hydrolysis-condensation (pH 3-5), the acidic environment accelerates the hydrolysis of silane coupling agent (MPS) to generate highly active silanol (Si-OH), while simultaneously promoting its condensation reaction with hydroxyl groups on the SiO2 surface to form strong Si-O-Si covalent bonds. This allows γ-methacryloyloxypropyltrimethoxysilane to be grafted onto the SiO2 surface, resulting in the following structural characteristics:

[0029] ① The generated methoxysilane hydrolyzes to produce Si-OH, which can react with the hydroxyl groups on the surface of SiO2 to form a strong Si-O-Si covalent bond;

[0030] ② It has double bonds and can copolymerize with subsequent 1-vinylimidazolium ionic liquid monomers to generate polymer grafted SiO2;

[0031] ③ γ-Methacryloxypropyltrimethoxysilane has a propyl chain: -(CH2)3-. According to previous studies, the propyl chain achieves a dynamic "elastic" nature through C–C bond rotation, which can increase the impact resistance of rigid functional outer layers.

[0032] (2) Preparation of ionic liquid monomers:

[0033] 1-Vinylimidazole and 2-bromoethanol were stirred at 80 °C for 12-36 h to obtain an ionic liquid monomer solution;

[0034] Mechanism Reference Figure 2 The reaction involves a nucleophilic substitution quaternization of 1-vinylimidazole (containing a tertiary amine nitrogen atom and a vinyl group) with 2-bromoethanol (containing a haloalkyl group and a hydroxyl group) upon heating (80°C). The more nucleophilic tertiary amine nitrogen atom (usually at the N-3 position) in the 1-vinylimidazole molecule attacks the carbon atom of 2-bromoethanol (attached to Br), and Br... - As a leaving group, it departs to generate 1-(2-hydroxyethyl)-3-vinylimidazolium bromide ion (abbreviated as [VHEIm]Br), which is an ionic liquid monomer (monomer synthesis). This reaction produces a vinyl group (CH2=CH-) and a quaternary ammonium cation (-N). + The novel monomer [VHEIm]Br, containing hydroxyl (-) and hydroxyl (-OH), has the following characteristics:

[0035] ① Vinyl groups retain their polymerization ability: The generated ionic liquid monomer contains vinyl groups, which copolymerize with SiO2 grafted with γ-methacryloyloxypropyltrimethoxysilane to obtain an olefin copolymer, thus realizing in-situ surface polymerization on SiO2.

[0036] ② Quaternary ammonium cations (-N) + - It possesses the general characteristics of ionic liquids, which can promote the solubility of SiO2 in polyurethane systems, while also providing excellent antibacterial properties on the surface.

[0037] ③ The hydroxyl group (-OH) can provide a certain degree of hydrophilicity and can also react with excess -NCO in the polyurethane system to achieve the anchoring effect of SiO2 in the polyurethane system during the reaction process.

[0038] (3) Synthesis of polyionic liquid brush grafted SiO2:

[0039] In an ionic liquid monomer solution, silane-modified SiO2, azobisisobutyronitrile (AIBN), and acetone were added, with acetone accounting for 30% of the total weight of the system. The mixture was heated to 70-80℃ and refluxed for 8-12 hours. Finally, it was vacuum dried at 80℃ to obtain a white powder, yielding polyionic liquid brush-grafted SiO2. (Mechanism referenced...) Figure 3 .

[0040] The ultimate goal of this invention is to utilize the contradiction between the gravitational sedimentation, dissolution and dispersion, and chemical anchoring reaction of SiO2 in a polyurethane system to reduce the sedimentation rate of SiO2, thereby forming a process in which the content of SiO2 gradually decreases from the surface to the interior of the polyurethane, i.e., a hard functional outer layer with gradually decreasing hardness from the surface to the interior. Therefore, the introduction of ionic liquids and hydroxyl groups is crucial to this invention. Ionic liquids can promote the uniformity of SiO2 dispersion, and hydroxyl groups can increase the reaction rate. That is, the anchoring reaction suspends SiO2, and under the action of opposite gravity, the sedimentation of SiO2 is slowed down. Otherwise, according to existing unmodified SiO2, it is impossible to form high hardness on the surface. Instead, a large amount of it penetrates into the gel matrix and destroys the elasticity of the matrix. This is the fundamental reason for the design of this invention.

[0041] Furthermore, according to previous research, introducing polymer brush structures (polyionic liquid brushes) with specific functions (ionicity, hydrophilicity / hydrophobicity, reactive hydroxyl groups, etc.) onto the surface of modified SiO2 may result in a slower sedimentation rate of SiO2, but this will not be studied in detail here.

[0042] This invention also proposes a method for preparing the aforementioned superhydrophobic modified polyurethane leather, comprising the following steps:

[0043] S1. Preparation of gel layer

[0044] Heat the high-NCO polyurethane to 80°C, and add the chain extender slowly and evenly over 30-60 seconds while stirring at a high speed of 500-800 rpm. During this process, good stirring must be maintained to prevent excessive local cross-linking.

[0045] Maintain the temperature and stir, and take samples for titration every 1-2 minutes until NCO% drops to 7±1%. NCO% is determined by chemical titration of di-n-butylamine.

[0046] When NCO% drops to 7±1%, use a rotational viscometer to monitor the viscosity. When the viscosity reaches 20,000 - 40,000 mPa·s (80℃), it is the optimal coating point. At this point, the material should be in a "stringy" state. Stop the reaction immediately and quickly inject the material into a mold preheated to 100-105℃. The injection process should be completed within 1-2 minutes. This step requires speed to prevent the material from gelling in the reactor.

[0047] S2. Preparation of coating slurry

[0048] The coating slurry was prepared by brush-grafting SiO2 with polyionic liquid, low-NCO polyurethane and chain extender at room temperature under high-speed stirring at 500-800 rpm.

[0049] S3, Apply gradient layer

[0050] After the gel layer is injected into the mold, it is kept in the mold at 100-105℃ for 1-2 minutes. At this time, the surface of the material should lose its fluidity, but it still feels viscous when touched with a fine needle and can leave a mark. At this time, it will continue to react at high temperature, and the viscosity will increase further. There are a large number of highly active -NCO groups on the surface, but the whole can support the second layer of material.

[0051] Continue to inject the coating slurry onto the surface of the gel layer and keep it at 100-105℃ for 4-5 minutes to allow the coating slurry system to have a brief pre-reaction and initial SiO2 sedimentation / anchoring process, preventing the material from being excessively squeezed and destroying the gradient distribution when the mold is pressed.

[0052] S4, Pressure Vulcanization

[0053] Cover with a film, pressurize to 1-5 MPa, and maintain the temperature and pressure at 110℃ for 0.5-1 h;

[0054] The purpose of applying pressure is to suppress foaming (because the reaction may produce CO2), increase the density of the product, and promote the fusion between the two layers. The pressure needs to be balanced: if the pressure is too low, the product will have bubbles and will not be dense; if the pressure is too high, it may destroy the already formed SiO2 gradient distribution.

[0055] S5, two-stage vulcanization

[0056] Depressurize, adjust the temperature to 100-105℃, and keep warm for 5-10 hours to obtain the superhydrophobic modified polyurethane leather product.

[0057] Two-stage vulcanization is a crucial post-curing step in polyurethane processing. Its purpose is to allow unreacted -NCO groups to continue reacting, thereby perfecting the cross-linking network, stabilizing the final dimensions of the product, eliminating internal stress, and maximizing mechanical properties. The time and temperature need to be adjusted according to the thickness of the product.

[0058] During this process, the gel layer solidifies into a soft polyurethane inner layer with a Shore A hardness of 65-75. Meanwhile, during the curing process, SiO2 grafted onto the polyionic liquid in the gradient layer slowly settles into the gel layer. The gradient layer gradually diffuses and extends into the gel layer, with a diffusion thickness of 0.5-2 mm (related to the SiO2 particle size and the viscosity of the gel layer). After curing, a hard functional outer layer with a thickness of about 1-3 mm is formed, and its surface hardness is Shore D50-65.

[0059] Polyionic liquid brushes improve the dispersibility of SiO2 in polyurethane systems through their quaternary ammonium cations, and undergo an anchoring chemical reaction with excess isocyanate groups (-NCO) in the gel layer via their terminal hydroxyl groups. The mechanism is described in [reference needed]. Figure 4 The synergistic effect of the two significantly slowed down the settling rate of SiO2 particles.

[0060] By utilizing the competitive relationship between the slow sedimentation rate of SiO2 and the gelation process of polyurethane, SiO2 particles are distributed in a gradient distribution with gradually decreasing content from the surface to the interior of the outer polyurethane system. This achieves a gradient transition in leather hardness from the surface to the interior, as shown in the structure... Figure 5 As shown.

[0061] Preferably, the injection amount of coating slurry in S3 is 400-450 g / m³. 2 The resulting gradient layer (i.e., coating thickness) has a thickness of 0.5-1 mm.

[0062] Compared with the prior art, the beneficial effects of the present invention are:

[0063] 1. This invention uses polyionic liquid to graft SiO2 to overcome the defect of SiO2's easy sedimentation in polyurethane gel layers. By competing with the polyurethane gelation kinetics through the steric hindrance-chemical anchoring synergistic slow sedimentation mechanism, and with the selection of BDO chain extender with moderate reactivity, a reasonable process window is provided, which facilitates precise control of the viscosity and NCO value at the gel point. This results in a novel leather surface modification process and a novel leather structure with a soft inner layer, a gradient hardness distribution on the outer layer, and a hydrophobic surface.

[0064] 2. This invention utilizes the ingenious synergy between polyionic liquid brush grafting of SiO2 (PIL-g-SiO2) and a stepwise reaction molding process to achieve the following product performance:

[0065] (1) Excellent superhydrophobic properties (water contact angle > 150°)

[0066] This invention successfully constructs a stable micro-nano composite roughening structure by preferentially enriching PIL-g-SiO2 on the outermost layer of leather. The nano-SiO2 particles provide primary nanoscale roughness, while the grafted polyionic liquid brush contributes secondary microscale roughness due to the stacking and oscillation of its molecular chains. Simultaneously, the polyionic liquid itself possesses low surface energy. The organic combination of the "micro-nano roughening structure" and the "low surface energy chemical components" achieves a static water contact angle exceeding 150°, endowing the leather with excellent stain resistance and self-cleaning properties.

[0067] (2) Significant hardness gradient (ΔShoreA≥30)

[0068] A gradient hardness outer layer is achieved through a synergistic slow-sinking mechanism of "steric hindrance-chemical anchoring" of PIL-g-SiO2:

[0069] Steric hindrance effect: The polyionic liquid brush grafted onto the SiO2 surface extends fully in the polyurethane system, generating huge steric hindrance, which effectively prevents the aggregation and rapid sedimentation of SiO2 particles.

[0070] Chemical anchoring effect: The hydroxyl groups (-OH) at the end of the PIL brush can undergo covalent bonding with the excess isocyanate groups (-NCO) during the gelation process of the soft polyurethane inner layer, just like casting a "chemical anchor" to anchor the SiO2 particles in the forming polymer network.

[0071] Gradient Formation: The aforementioned dual effect significantly slows down the settling rate of SiO2 particles under gravity. During the post-coating insulation stage, the slow-settling PIL-g-SiO2 particles "race" with the rapidly gelling polyurethane system, ultimately resulting in a continuous gradient distribution of SiO2 particles with decreasing concentration from the outside to the inside. As rigid particles, the concentration gradient of SiO2 directly translates into a hardness gradient transition, thus achieving a perfect combination of high surface hardness (Shore D50-65) and high inner elasticity (Shore A65-75), resulting in a feel similar to natural leather.

[0072] (3) Highly effective and long-lasting antibacterial properties (antibacterial rate >99%)

[0073] The antibacterial properties originate from the quaternary ammonium cations in the polyionic liquid brush. These positively charged cations can adsorb negatively charged bacterial cell membranes through electrostatic interactions, thereby disrupting the membrane structure and causing leakage of cell contents, thus achieving highly efficient physical sterilization. This mechanism is less likely to induce microbial resistance, and because the polyionic liquid is covalently grafted onto SiO2 and solidified into a film, it is not easily migrated or lost, ensuring the durability of the antibacterial effect.

[0074] (4) Excellent comprehensive mechanical properties and structural stability

[0075] Because the gradient distribution of PIL-g-SiO2 is controllable and natural, it avoids the chaotic distribution of rigid fillers in the matrix, maximizing the preservation of the softness, elasticity, and toughness of the underlying polyurethane layer. Simultaneously, the stepwise vulcanization process of pressure vulcanization + two-stage vulcanization ensures a sufficient and complete cross-linked network, eliminates internal stress, and results in a dense, dimensionally stable product with optimal mechanical properties.

[0076] (5) Good process controllability and reproducibility

[0077] The selection of BDO, a chain extender with moderate reactivity, provides a reasonable process window, facilitating precise control of the viscosity and NCO value at the gel point. The post-coating heat treatment step provides crucial time for SiO2 gradient self-assembly, while subsequent pressurization and two-stage vulcanization ensure the macroscopic quality of the product and the final network stability, respectively. The entire process flow is scientifically designed, with each step interconnected, ensuring the stability and reproducibility of the final product's performance.

[0078] 3. In summary, this invention cleverly resolves the contradiction between multifunctional integration and material properties through molecular structure design and process innovation, successfully preparing a high-value-added polyurethane leather material that combines superhydrophobicity, significant hardness gradient, high-efficiency antibacterial properties, and good mechanical properties, with broad prospects for industrial application. Attached Figure Description

[0079] Figure 1 The reaction formula for preparing silane-modified SiO2 proposed in this invention is as follows;

[0080] Figure 2 The reaction formula for preparing the ionic liquid monomer proposed in this invention is as follows;

[0081] Figure 3 The synthesis reaction formula for SiO2 grafted onto polyionic liquid brushes proposed in this invention;

[0082] Figure 4 This is a schematic diagram illustrating the anchoring chemical reaction principle of polyionic liquid brush grafted SiO2 in the gel layer in this invention.

[0083] Figure 5 This is a schematic diagram of the gradient structure of SiO2 content in the hard functional outer layer of the present invention. Detailed Implementation

[0084] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0085] I. Synthesis of SiO2 grafted onto polyionic liquid brushes

[0086] Preparation Example 1

[0087] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water. The pH of the mixed solution was adjusted to 3-5 using hydrochloric acid. The solution was then heated to 50°C and stirred for 12 hours. After centrifugation, the mixture was washed several times with ethanol and dried to obtain silane-modified SiO2 for later use.

[0088] 1-Vinylimidazole and 2-bromoethanol were stirred at 80°C for 36 h, and then silane-modified SiO2, azobisisobutyronitrile and acetone were added. The amount of acetone accounted for 30% of the total weight of the system. The mixture was heated to 70°C and refluxed for 12 h. Finally, it was vacuum dried at 80°C to obtain a white powder, thus obtaining polyionic liquid brush-grafted SiO2.

[0089] The polyionic liquid brush-grafted SiO2 comprises 5 kg of SiO2 particles (500 nm in diameter), 1 kg of γ-methacryloyloxypropyltrimethoxysilane, 10 kg of 1-vinylimidazolium, 10 kg of 2-bromoethanol, and 0.05 kg of azobisisobutyronitrile.

[0090] Preparation Example 2

[0091] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water. The pH of the mixed solution was adjusted to 3-5 using hydrochloric acid. The solution was then heated to 60°C and stirred for 9 hours. After centrifugation, the mixture was washed several times with ethanol and dried to obtain silane-modified SiO2 for later use.

[0092] 1-Vinylimidazole and 2-bromoethanol were stirred at 80°C for 24 hours, and then silane-modified SiO2, azobisisobutyronitrile and acetone were added. The amount of acetone accounted for 30% of the total weight of the system. The mixture was heated to 75°C and refluxed for 10 hours. Finally, it was vacuum dried at 80°C to obtain a white powder, thus obtaining polyionic liquid brush-grafted SiO2.

[0093] The polyionic liquid brush-grafted SiO2 comprises 12 kg of SiO2 particles (500 nm in diameter), 3 kg of γ-methacryloyloxypropyltrimethoxysilane, 30 kg of 1-vinylimidazolium, 40 kg of 2-bromoethanol, and 0.08 kg of N-diisobutyronitrile.

[0094] Preparation Example 3

[0095] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water. The pH of the mixed solution was adjusted to 3-5 using hydrochloric acid. The solution was then heated to 70°C and stirred for 6 hours. After centrifugation, the mixture was washed several times with ethanol and dried to obtain silane-modified SiO2 for later use.

[0096] 1-Vinylimidazole and 2-bromoethanol were stirred at 80°C for 12 hours, and then silane-modified SiO2, azobisisobutyronitrile and acetone were added. The amount of acetone accounted for 30% of the total weight of the system. The mixture was heated to 80°C and refluxed for 8 hours. Finally, it was vacuum dried at 80°C to obtain a white powder, thus obtaining polyionic liquid brush-grafted SiO2.

[0097] The polyionic liquid brush-grafted SiO2 comprises 20 kg of SiO2 particles (500 nm in diameter), 5 kg of γ-methacryloyloxypropyltrimethoxysilane, 50 kg of 1-vinylimidazolium, 70 kg of 2-bromoethanol, and 0.1 kg of azobisisobutyronitrile.

[0098] Comparative Preparation Example 1

[0099] The formulation and steps were the same as those in Preparation Example 2, except that hydrochloric acid was not added to adjust the pH, and the pH of the mixed solution was tested to be 7.1.

[0100] Comparative Preparation Example 2

[0101] The formulation and steps are basically the same as those in Preparation Example 2, except that 2-bromoethanol is not added, and the steps are as follows:

[0102] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water. The pH of the mixed solution was adjusted to 3-5 using hydrochloric acid. The solution was then heated to 60°C and stirred for 9 hours. After centrifugation, the mixture was washed several times with ethanol and dried to obtain silane-modified SiO2 for later use.

[0103] 1-Vinylimidazole was added to silane-modified SiO2, azobisisobutyronitrile, and acetone, with acetone accounting for 30% of the total weight of the system. The mixture was heated to 75°C and refluxed for 10 hours. Finally, it was vacuum dried at 80°C to obtain a white powder, thus obtaining polyionic liquid brush-grafted SiO2.

[0104] Comparative preparation example 3

[0105] The formulation and steps are basically the same as those in Preparation Example 2, except that 1-vinylimidazole and 2-bromoethanol are not added. The steps are as follows:

[0106] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixture of ethanol and water. The pH of the mixture was adjusted to 3-5 using hydrochloric acid. The mixture was then heated to 60°C and stirred for 9 hours. After centrifugation, the mixture was washed several times with ethanol and dried to obtain silane-modified SiO2, which directly replaced the polyionic liquid-grafted SiO2 in the coating slurry in equal amounts.

[0107] Comparative preparation example 4

[0108] The polyionic liquid grafted with SiO2 in the coating slurry was directly replaced with an equal amount of SiO2 particles.

[0109] II. Preparation of Superhydrophobic Modified Polyurethane Leather

[0110] Example 1

[0111] formula:

[0112] The flexible polyurethane inner layer comprises the following components in parts by weight:

[0113] 100 parts of high-NCO polyurethane and 5 parts of chain extender; the high-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 15%, and the chain extender is BDO;

[0114] The rigid functional outer layer comprises the following components in parts by weight:

[0115] 100 parts of polyionic liquid brush-grafted SiO2 (Preparation Example 1), 30 parts of low-NCO polyurethane, and 2 parts of chain extender. The low-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 3%.

[0116] Preparation method:

[0117] S1. Preparation of gel layer

[0118] Heat the high-NCO polyurethane to 80°C, and add the chain extender slowly and evenly over 30-60 seconds while stirring at a high speed of 500-800 rpm. During this process, good stirring must be maintained to prevent excessive local cross-linking.

[0119] Maintain the temperature and stir, and take samples for titration every 1-2 minutes until NCO% drops to 7±1%. NCO% is determined by chemical titration of di-n-butylamine.

[0120] When the NCO% drops to 7±1%, use a rotational viscometer to monitor the viscosity. When the viscosity reaches 20,000 - 40,000 mPa·s (80℃), stop the reaction immediately and quickly inject the material into a mold preheated to 100-105℃. The injection process should be completed within 1-2 minutes.

[0121] S2. Preparation of coating slurry

[0122] The coating slurry was prepared by brush-grafting SiO2 with polyionic liquid, low-NCO polyurethane and chain extender at room temperature under high-speed stirring at 500-800 rpm.

[0123] S3, Apply gradient layer

[0124] After the gel layer is injected into the mold, it is kept at 100°C for 2 minutes. Then, the coating slurry is injected onto the surface of the gel layer at a rate of 400 g / m². 2 Keep warm at 100℃ for 5 minutes;

[0125] S4, Pressure Vulcanization

[0126] Cover with a film, pressurize to 1 MPa, and maintain the temperature and pressure at 110℃ for 1 hour;

[0127] S5, two-stage vulcanization

[0128] Depressurize, adjust the temperature to 100℃, and keep warm for 10 hours to obtain the superhydrophobic modified polyurethane leather product.

[0129] Example 2

[0130] formula:

[0131] The flexible polyurethane inner layer comprises the following components in parts by weight:

[0132] 100 parts of high-NCO polyurethane and 6 parts of chain extender; the high-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 18%, and the chain extender is BDO;

[0133] The rigid functional outer layer comprises the following components in parts by weight:

[0134] 100 parts of polyionic liquid brush-grafted SiO2 (Preparation Example 2), 25 parts of low-NCO polyurethane, and 1.8 parts of chain extender. The low-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 4%.

[0135] Preparation method:

[0136] S1. Preparation of gel layer

[0137] Heat the high-NCO polyurethane to 80°C, and add the chain extender slowly and evenly over 30-60 seconds while stirring at a high speed of 500-800 rpm. During this process, good stirring must be maintained to prevent excessive local cross-linking.

[0138] Maintain the temperature and stir, and take samples for titration every 1-2 minutes until NCO% drops to 7±1%. NCO% is determined by chemical titration of di-n-butylamine.

[0139] When the NCO% drops to 7±1%, use a rotational viscometer to monitor the viscosity. When the viscosity reaches 20,000 - 40,000 mPa·s (80℃), stop the reaction immediately and quickly inject the material into a mold preheated to 100-105℃. The injection process should be completed within 1-2 minutes.

[0140] S2. Preparation of coating slurry

[0141] The coating slurry was prepared by brush-grafting SiO2 with polyionic liquid, low-NCO polyurethane and chain extender at room temperature under high-speed stirring at 500-800 rpm.

[0142] S3, Apply gradient layer

[0143] After the gel layer is injected into the mold, it is kept at 102℃ for 1.5 minutes. Then, the coating slurry is injected onto the surface of the gel layer at a rate of 420 g / m². 2 Hold at 102℃ for 4.5 minutes;

[0144] S4, Pressure Vulcanization

[0145] Cover with a film, pressurize to 3 MPa, and maintain the temperature and pressure at 110℃ for 0.7 hours;

[0146] S5, two-stage vulcanization

[0147] Depressurize, adjust the temperature to 102℃, and keep warm for 7 hours to obtain the superhydrophobic modified polyurethane leather product.

[0148] Example 3

[0149] formula:

[0150] The flexible polyurethane inner layer comprises the following components in parts by weight:

[0151] 100 parts of high-NCO polyurethane and 8 parts of chain extender; the high-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 20%, and the chain extender is BDO;

[0152] The rigid functional outer layer comprises the following components in parts by weight:

[0153] 100 parts of polyionic liquid brush-grafted SiO2 (Preparation Example 3), 20 parts of low-NCO polyurethane, and 1.5 parts of chain extender were prepared. The low-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 5%.

[0154] Preparation method:

[0155] S1. Preparation of gel layer

[0156] Heat the high-NCO polyurethane to 80°C, and add the chain extender slowly and evenly over 30-60 seconds while stirring at a high speed of 500-800 rpm. During this process, good stirring must be maintained to prevent excessive local cross-linking.

[0157] Maintain the temperature and stir, and take samples for titration every 1-2 minutes until NCO% drops to 7±1%. NCO% is determined by chemical titration of di-n-butylamine.

[0158] When the NCO% drops to 7±1%, use a rotational viscometer to monitor the viscosity. When the viscosity reaches 20,000 - 40,000 mPa·s (80℃), stop the reaction immediately and quickly inject the material into a mold preheated to 100-105℃. The injection process should be completed within 1-2 minutes.

[0159] S2. Preparation of coating slurry

[0160] The coating slurry was prepared by brush-grafting SiO2 with polyionic liquid, low-NCO polyurethane and chain extender at room temperature under high-speed stirring at 500-800 rpm.

[0161] S3, Apply gradient layer

[0162] After the gel layer is injected into the mold, it is kept at 105℃ for 1 minute. Then, the coating slurry is injected onto the surface of the gel layer at a rate of 450 g / m². 2 Keep warm at 105℃ for 4 minutes;

[0163] S4, Pressure Vulcanization

[0164] Cover with a film, pressurize to 5 MPa, and maintain the temperature and pressure at 110℃ for 0.5 hours;

[0165] S5, two-stage vulcanization

[0166] Depressurize, adjust the temperature to 105℃, and keep warm for 5 hours to obtain the superhydrophobic modified polyurethane leather product.

[0167] Comparative Example 1

[0168] The polyionic liquid brush grafted with SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 1, and the rest was the same as in Example 2.

[0169] Comparative Example 2

[0170] The polyionic liquid brush grafted with SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 2, and the rest was the same as in Example 2.

[0171] Comparative Example 3

[0172] The polyionic liquid brush grafted with SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 3, and the rest was the same as in Example 2.

[0173] Comparative Example 4

[0174] The polyionic liquid brush grafted with SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 4, and the rest was the same as in Example 2.

[0175] Comparative Example 5

[0176] The chain extender in Example 2 was replaced with diethyltoluenediamine, and the rest was the same as in Example 2.

[0177] Comparative Example 6

[0178] The chain extender in Example 2 was replaced with PPG-400, and the rest was the same as in Example 2.

[0179] Comparative Example 7

[0180] The SiO2 used in the polyionic liquid brush grafting of SiO2 in Example 2 was replaced with SiO2 with a particle size of 100-150 nm, and the rest was the same as in Example 2.

[0181] Comparative Example 8

[0182] In Example 2, the raw material 2-bromoethanol used for grafting SiO2 onto the polyionic liquid was replaced with bromoethane to obtain a hydroxyl-free ionic liquid monomer. The rest of the process was the same as in Example 2.

[0183] Comparative Example 9

[0184] The injection volume of the coating slurry in Example 2 was changed to 800 g / m. 2 The rest is the same as in Example 2.

[0185] Comparative Example 10

[0186] The S4 step and the pressure vulcanization process in Example 2 are omitted; the rest is the same as in Example 2.

[0187] Comparative Example 11

[0188] The S5 and second-stage vulcanization processes in Example 2 are omitted, and the rest is the same as in Example 2.

[0189] Comparative Example 12

[0190] In Example 2, the high-NCO polyurethane in the soft polyurethane inner layer is replaced with the same low-NCO polyurethane as the rigid functional outer layer, and the rest is the same as in Example 2.

[0191] III. Performance Testing

[0192] The leathers of Examples 1-3 and Comparative Examples 1-12 were subjected to the following performance tests:

[0193] 1. Static water contact angle

[0194] Referring to ASTM D7334, "Standard Practice for Evaluating Surface Wettability by Contact Angle Measurement", a flat, clean, and defect-free sample (2cm × 5cm) is cut from the finished leather product, equilibrated in a standard laboratory environment (typically 23±2℃ and 50±10% relative humidity), and tested using a contact angle measuring instrument.

[0195] 2. Hardness

[0196] Outer layer (hard): ASTM D2240, using a Type D hardness tester. Hold the Type D hardness tester perpendicular to the outer surface of the leather, apply sufficient force to ensure the indenter foot is in full contact with the sample, and read the stable hardness value within 1 second.

[0197] Inner layer (soft): ASTM D2240, using a Type A hardness tester. Inner layer hardness (Shore A): Carefully peel or cut away the hard functional outer layer with a sharp blade to expose the soft inner layer surface. Measure the hardness with a Type A hardness tester perpendicular to the inner layer surface.

[0198] Each hardness was measured at least 5 times at different locations on the sample, and the average value was taken. The hardness gradient difference ΔShoreA was calculated as follows: the surface hardness (Shore D) was converted to an approximate Shore A value, and then the measured Shore A value of the inner layer was subtracted.

[0199] 3. Antibacterial rate

[0200] Refer to the testing standard: ISO 22196 "Measurement of antimicrobial activity of plastics and other nonporous surfaces", which is the most commonly used and recognized standard for surface antimicrobial activity.

[0201] Prepare sterile samples (5cm × 5cm). The test bacteria are *Escherichia coli* and *Staphylococcus aureus* to verify broad-spectrum antibacterial activity.

[0202] Inoculation: Add a certain concentration of bacterial solution (100 μL) to the sample surface, cover with a sterile covering film to ensure that the bacterial solution is in uniform contact with the sample.

[0203] Culture: The inoculated samples were cultured in a constant temperature and humidity chamber (35℃, >90% RH) for 24 hours.

[0204] Elution and Counting: After incubation, bacteria on the sample surface were eluted with a neutralizing solution, diluted, and spread onto agar plates. An untreated control sample (e.g., ordinary polyurethane leather) was also prepared.

[0205] Calculation: Count the number of colonies (CFU) formed in the eluent of the control and experimental groups. Antibacterial rate calculation formula:

[0206] (1 - Average colony count in experimental group / Average colony count in control group) × 100%

[0207] An antibacterial rate >99% (i.e., a decrease in logarithm greater than 2) indicates potent antibacterial activity. The experiment must be repeated at least three times to ensure reproducibility.

[0208] The test results are shown in Table 1 below:

[0209] Table 1. Effects of different formulations and process parameters on leather properties

[0210]

[0211] Data Analysis:

[0212] 1. The influence of leather base formulation:

[0213] As shown in Table 1, Example 2 exhibits the best overall performance with all parameters in the middle range. The PIL-g-SiO2 formulation and synthesis conditions used in Example 2 resulted in a moderate grafting rate and highly reactive hydroxyl groups, achieving optimal dispersion, anchoring, and gradient formation. The process parameters (such as holding time and pressure) were also the most balanced, thus yielding the highest WCA, an ideal hardness gradient (ΔShoreA>30), and a perfect interface.

[0214] The performance of Examples 1 and 3 remained excellent, demonstrating the rationality of the formulation range. Example 1, using a low-NCO outer layer and the low SiO2 / PIL content of Preparation Example 1, resulted in slightly lower surface hardness and WCA than the baseline due to fewer crosslinkable points and roughness building units on the surface. Example 3, using a high-NCO outer layer and the high SiO2 / PIL content of Preparation Example 3, achieved the highest surface hardness, but the inner layer was also relatively hard due to the high NCO content, resulting in a stiffer overall leather feel and slightly less flexibility than Example 2.

[0215] The NCO content and PIL-g-SiO2 dosage of the outer layer together determine the surface hardening density and micro / nano roughness. The NCO content of the inner layer determines the crosslinking density and hardness of the inner layer. Fine-tuning is required based on the final application (e.g., shoe materials require flexibility, table mats require stiffness). Example 2 represents the optimal balance between flexibility and stiffness.

[0216] 2. Effect of PIL-g-SiO2 synthesis parameters

[0217] In Comparative Example 1, without pH adjustment, WCA and surface hardness decreased significantly, and the gradient worsened. Under neutral conditions (pH approximately 7), the hydrolysis rate of the silane coupling agent (MPS) was extremely slow, and the hydrolysis products readily self-condensed to form dimers or polymers instead of reacting with the hydroxyl groups on the SiO2 surface. This resulted in extremely low grafting efficiency of MPS on the SiO2 surface. The subsequent polyionic liquid brushing resulted in insufficient grafting, significantly reducing its dispersibility and anchoring ability, with performance falling between that of fully modified and unmodified products.

[0218] In Comparative Example 2, the absence of 2-bromoethanol resulted in a significant decrease in WCA, hardness, and antibacterial rate. The lack of 2-bromoethanol means that the ionic liquid monomer cannot be synthesized. The actual process involved directly polymerizing the 1-vinylimidazolium monomer onto the SiO2 surface. 1-Vinylimidazolium is a neutral molecule, and its polymerization product does not contain quaternary ammonium salt cations, thus resulting in the loss of antibacterial properties. Simultaneously, the polymer brush lacks hydroxyl groups (-OH), preventing the anchoring reaction and leading to accelerated sedimentation and a poor gradient structure. Furthermore, the hydrophobicity of the neutral poly(1-vinylimidazolium) brush is inferior to that of the quaternary ammonium salt-type polyionic liquid, also contributing to the decrease in WCA.

[0219] Comparative Example 3, lacking 1-vinylimidazolium and 2-bromoethanol, completely lost its superhydrophobic and antibacterial properties, and the hardness gradient disappeared. This comparative example actually only used MPS-modified SiO2. MPS only provides a double bond and a flexible chain, without introducing a polyionic liquid brush. Therefore, the material lacks the antibacterial properties of quaternary ammonium salts, and the surface roughness comes only from the original SiO2 particles, making it impossible to construct an effective micro / nano composite structure. The WCA only reaches 108°, exhibiting hydrophilicity. Simultaneously, lacking the steric hindrance and anchoring effect of the PIL brush, SiO2 has poor dispersion and rapid sedimentation in PU, failing to form a gradient.

[0220] Comparative Example 4, lacking unmodified SiO2, exhibited the worst performance. Compared to Comparative Example 3, the absence of MPS led to more severe SiO2 agglomeration. Unmodified SiO2 readily agglomerates in polyurethane systems due to van der Waals forces and rapidly settles. The results are consistent with previous analyses: ① Agglomerates cannot form a uniform micro / nano rough structure, resulting in low WCA; ② Rapid settling leads to a lack of surface SiO2 (low hardness), while a large amount of SiO2 sinks into the inner layer, forming "hard spots" (abnormally increased inner layer hardness), completely destroying the gradient structure and inner layer elasticity. This comparison strongly demonstrates the irreplaceable nature of PIL-g-SiO2 modification.

[0221] 3. The Influence of Chain Extenders on Inner Layer Design

[0222] Comparative Example 5 used the amine chain extender DETDA, resulting in a failed process with an excessively hard inner layer. The reaction rate of DETDA with NCO is extremely fast (seconds), far exceeding that of BDO (minutes). Upon addition, the system viscosity increases dramatically and instantaneously, making controlled stirring, titration, and molding impossible. The material rapidly gels within the reactor, leading to processing failure. Even with forced molding, the resulting urea bonds have high strength and modulus, causing the inner layer to be as hard as plastic (>Shore A85), completely losing the soft lining function required for leather.

[0223] Comparative Example 6, using PPG-400 chain extender, showed low hardness in both the inner and outer layers, resulting in a softer overall product. PPG, with a molecular weight of 400, is a flexible long-chain molecule with lower reactivity than BDO. Its participation in chain extension effectively introduces longer flexible segments into the molecular chain, disrupting the ability of BDO to form regular hard segment micro-regions. This leads to slow establishment of the cross-linking network strength, resulting in generally lower modulus and hardness in the final product, failing to meet the hardness requirements for leather surfaces.

[0224] In Comparative Example 12, the inner layer used low-NCO polyurethane, which was too soft, resulting in a limp and unsupported overall product. The core function of the inner layer is to provide support and elasticity. Low-NCO polyurethane means its molecular chains are short, its functionality is low, and its cross-linking density after curing is very low, forming a soft and weak gel network. Such an inner layer cannot support the outer layer, causing the entire leather product to resemble a limp lump of dough, lacking shape and having no practical value. This demonstrates that a "soft inner layer" is not necessarily better the softer it is, but rather needs to have a supporting strength that matches the "hard outer layer."

[0225] 4. Influence of leather preparation process parameters

[0226] Comparative Example 7, using large-particle-size SiO2 (100-150 nm), showed a significant decrease in surface roughness (WCA) and surface hardness. The micro / nano secondary roughness structures required for superhydrophobicity necessitate the construction of small-sized nanoparticles (20-50 nm in the original scheme). When the particle size increases to 100-150 nm, the number of particles at the same volume fraction decreases sharply, making it difficult to form sufficiently fine nanostructures, leading to a reduction in surface roughness and consequently, a decrease in WCA. Simultaneously, larger particles exhibit a stronger tendency to settle under gravity, which is detrimental to gradient formation and surface enrichment, thus resulting in lower surface hardness.

[0227] Comparative Example 8, using bromoethane (without hydroxyl groups), showed a decrease in surface hardness and gradient effect. This comparison directly verifies the crucial role of the hydroxyl anchoring mechanism. Replacing 2-bromoethanol with bromoethane resulted in an ionic liquid monomer without hydroxyl groups. While its polymer brush still provides steric hindrance to improve dispersion, it lacks the crucial "holding point" of covalent anchoring with the gel layer's -NCO. This causes the SiO2 particles to fail to anchor properly during sedimentation, leading to a faster sedimentation rate, a shorter and steeper gradient transition zone, and a reduced amount of SiO2 enriched on the surface, resulting in insufficient surface hardness.

[0228] The coating amount of 800 g / m² in Comparative Example 9 was too high, resulting in excessively high surface properties, but also increased brittleness of the product. While an excessively thick functional outer layer (thickness > 2 mm) brought extremely high surface hardness and WCA, it caused two problems: (1) the overall flexibility of the leather decreased significantly, making it prone to cracking when bent; (2) the modulus difference between the outer and inner layers was too large, making the interface prone to peeling under stress. This indicates that the coating amount needs to be within an optimal range to balance surface properties and overall mechanical properties.

[0229] Comparative Example 10, without pressure vulcanization, resulted in a product with numerous bubbles, lack of density, and decreased performance. Pressure vulcanization serves three purposes: ① suppressing bubbles (the reaction may produce CO2 or cause residual solvent evaporation); ② increasing density; ③ promoting interfacial fusion between the two layers. Without pressure, the product contains numerous bubbles, leading to strength degradation. Furthermore, the SiO2 gradient initially formed during the post-coating heat treatment stage is disrupted by slight material flow under pressureless conditions.

[0230] Comparative Example 11, with the two-stage vulcanization omitted, showed acceptable initial performance, but deteriorated after standing. Two-stage vulcanization is a post-curing process that allows residual -NCO groups to fully react. Omitting this step results in an incomplete cross-linking network and the presence of unreacted monomers or oligomers within the product. This leads to the following during standing: ① dimensional shrinkage; ② surface stickiness (small molecule migration); ③ long-term degradation of mechanical properties. This demonstrates that two-stage vulcanization is crucial for achieving stable and final performance.

[0231] 5. Summary

[0232] This series of experiments, through meticulously designed comparisons, comprehensively and profoundly verified the scientific validity and necessity of each step in the technical solution of the superhydrophobic gradient polyurethane leather described in this invention, from multiple dimensions including raw material synthesis (PIL-g-SiO2), formulation design (chain extender, NCO content) to process flow (coating amount, pressurization, vulcanization). The core conclusion is that the synergistic slow-sinking mechanism of the polyionic liquid brush—"steric hindrance + chemical anchoring"—combined with carefully matched polyurethane chemical reaction kinetics and step-by-step processing technology, is key to achieving multi-functional integration of hardness gradient from the outside to the inside, superhydrophobicity, and antibacterial properties. Deviation from any step will lead to a significant decrease in the final product's performance or even failure.

[0233] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A superhydrophobic modified polyurethane leather, characterized in that, It includes a flexible polyurethane inner layer and a rigid functional outer layer, wherein the rigid functional outer layer contains polyionic liquid brush-grafted SiO2 to form a gradient structure in which the SiO2 content decreases from the outside to the inside. The flexible polyurethane inner layer comprises the following components in parts by weight: 100 parts high NCO polyurethane, 5-8 parts chain extender; The rigid functional outer layer comprises the following components in parts by weight: 100 parts of polyionic liquid grafted with SiO2, 20-30 parts of low-NCO polyurethane, and 1.5-2 parts of chain extender; The high-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 15-20%. The low-NCO polyurethane is an NCO-terminated polyurethane prepolymer with an NCO content of 3-5%. The chain extender is 1,4-butanediol; The synthesis steps of the polyionic liquid brush grafted SiO2 are as follows: 1) Preparation of silane-modified SiO2 Nano-sized SiO2 particles with a particle size of 20-50 nm and γ-methacryloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water. The pH of the mixed solution was adjusted to 3-5 using hydrochloric acid. Then, the solution was heated to 50-70℃ and stirred for 6-12 h. After centrifugation, the solution was washed several times with ethanol and dried to obtain silane-modified SiO2. 2) Preparation of ionic liquid monomers: 1-Vinylimidazole and 2-bromoethanol were stirred at 80°C for 12-36 h to obtain an ionic liquid monomer solution; 3) Synthesis of SiO2 grafted onto polyionic liquid brushes: In an ionic liquid monomer solution, silane-modified SiO2, azobisisobutyronitrile, and acetone are added, with the amount of acetone accounting for 30% of the total weight of the system. The mixture is heated to 70-80℃ and refluxed for 8-12 hours. Finally, it is vacuum dried at 80℃ to obtain a white powder, thus obtaining polyionic liquid brush-grafted SiO2.

2. The superhydrophobic modified polyurethane leather according to claim 1, characterized in that, The polyionic liquid brush-grafted SiO2 comprises the following raw materials in parts by weight: 5-20 parts of nano-SiO2 particles, 1-5 parts of γ-methacryloyloxypropyltrimethoxysilane, 10-50 parts of 1-vinylimidazolium, 10-70 parts of 2-bromoethanol, and 0.05-0.1 parts of azobisisobutyronitrile.

3. A method for preparing superhydrophobic modified polyurethane leather according to any one of claims 1-2, characterized in that, Includes the following steps: S1. Preparation of gel layer Heat the high-NCO polyurethane to 80°C, and add the chain extender slowly and evenly over 30-60 seconds while stirring at a high speed of 500-800 rpm. Maintain temperature and stirring, and titrate every 1-2 minutes until NCO% drops to 7±1%; When the NCO% drops to 7±1% and the viscosity reaches 20,000 - 40,000 mPa·s, the reaction should be stopped immediately, and the material should be quickly injected into a mold preheated to 100-105℃. The injection process should be completed within 1-2 minutes. S2. Preparation of coating slurry The coating slurry is prepared by brush-grafting SiO2, low-NCO polyurethane, and chain extender with polyionic liquid at high speed of 500-800 rpm and mixing at room temperature. S3, Apply gradient layer After the gel layer is injected into the mold, continue to keep it at 100-105℃ for 1-2 minutes. The coating slurry is then poured onto the surface of the gel layer and kept at 100-105℃ for 4-5 minutes; the pouring amount of the coating slurry in S3 is 400-450 g / m³. 2 The thickness of the resulting gradient layer is 0.5-1 mm; S4, Pressure Vulcanization Cover with a film, pressurize to 1-5 MPa, and maintain the temperature and pressure at 110℃ for 0.5-1 h; S5, two-stage vulcanization: Depressurize, adjust the temperature to 100-105℃, and keep warm for 5-10 hours to obtain the superhydrophobic modified polyurethane leather product.

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