Template-based bio-based microporous membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of waterproof and moisture permeable membrane materials, and particularly relates to a bio-based microporous membrane based on a template and a preparation method and application thereof, and the preparation method comprises the following steps: dispersing one of polybenzimidazole, aminated PI and carboxylated PBO and modified CNF into a DMF / water system; performing electrostatic spinning on the high-viscosity spinning solution; carrying out low-temperature vacuum drying treatment on the modified nanofiber self-supporting framework; coating and filling the bio-based polyurethane resin into the bio-based microporous membrane template, and carrying out negative pressure adsorption until the filling is uniform; and carrying out gradient drying on the bio-based wet membrane to obtain the bio-based microporous membrane. Compared with the prior art, the problems that in the prior art, the mechanical property or stability of bio-based polyurethane is insufficient, and a nanofiber reinforcing technology is difficult to combine with the bio-based polyurethane are solved. A nanofiber self-supporting framework with a stable structure is prepared through an electrostatic spinning technology, and then the nanofiber self-supporting framework is compounded with bio-based polyurethane to form a microporous membrane layer with waterproof and moisture permeable functions.

Description

Technical Field

[0001] This invention belongs to the technical field of waterproof and breathable membrane materials, specifically relating to a template-based bio-based microporous membrane, its preparation method, and its application. Background Technology

[0002] In recent years, with increasing global emphasis on environmental protection and sustainable development, the application of bio-based materials in industrial manufacturing has become a research hotspot. Among them, bio-based polyurethane (BPU) is considered an ideal alternative to traditional synthetic polymer materials due to its renewable and biodegradable raw materials and mechanical properties similar to traditional petroleum-based polyurethane, especially in the field of footwear materials. However, bio-based polyurethane still faces significant technical bottlenecks in practical applications, particularly in terms of high-temperature resistance and abrasion resistance, which severely restricts its promotion in the composite hot-pressing process of footwear materials.

[0003] In footwear manufacturing, composite hot pressing technology is widely used for bonding soles and uppers, laminating multi-layer materials, and molding three-dimensional structures. This process typically requires materials to maintain dimensional stability, resistance to deformation, and interfacial bonding strength under high temperatures (150~200 ℃) and high pressures (5~15 MPa). Furthermore, as everyday wearable items, footwear materials must withstand long-term mechanical stresses such as friction and bending, thus requiring extremely high abrasion resistance and fatigue resistance. While traditional petroleum-based polyurethane can meet these performance requirements, its raw materials are non-renewable, and its production process generates high carbon emissions, contradicting global carbon reduction goals.

[0004] Bio-based polyurethane is synthesized from vegetable oils (such as castor oil and soybean oil), lignin, or starch through the reaction of polyols with isocyanates. Despite its significant environmental advantages, its high-temperature resistance and abrasion resistance are generally poor due to the molecular structure characteristics of bio-based raw materials (such as low branching and insufficient rigid segments). Specifically: Insufficient high-temperature resistance: Bio-based polyurethane has a lower glass transition temperature (Tg) and thermal decomposition temperature, making it prone to softening, adhesion, and even degradation during hot pressing, leading to decreased composite interface strength or delamination. Abrasion resistance defects: The hardness and crosslinking density of bio-based polyurethane are usually lower than those of petroleum-based products, making it prone to surface wear and crack propagation during dynamic friction, shortening the lifespan of footwear materials.

[0005] To improve the performance of bio-based polyurethane, researchers have proposed various modification strategies, but all have significant limitations: Blending modification: Adding petroleum-based polyurethane or engineering plastics (such as TPU) improves mechanical properties, but sacrifices the bio-based content of the material (usually below 50%), significantly reducing its environmental value. Crosslinking agent reinforcement: Introducing isocyanate crosslinking agents or nanofillers (such as silica, carbon nanotubes) can increase the material's hardness, but excessive crosslinking can lead to embrittlement, and the dispersion of nanofillers is difficult to control. High-temperature resistant coating: Coating the surface of bio-based polyurethane with a high-temperature resistant coating (such as silicone resin) can temporarily improve heat resistance, but the interfacial compatibility between the coating and the substrate is poor, leading to easy peeling after long-term use.

[0006] In recent years, nanofiber composites have become a research hotspot in materials science due to their unique structure-property relationship. Nanofiber membranes prepared by electrospinning possess high specific surface area, three-dimensional interconnected pores, and tunable mechanical properties, making them suitable as functional skeletons to reinforce polymer matrices. For example, high-temperature resistant nanofibers such as polyimide (PI) and aramid (Nomex) have been used to improve the thermal stability of composite materials. Their decomposition temperatures are generally above 300 °C, effectively resisting the high-temperature environment of hot-pressing processes. Structural reinforcement mechanisms: The three-dimensional network of nanofibers can improve the wear resistance of composite materials through stress transfer and crack deflection mechanisms. Simultaneously, their porous structure facilitates resin impregnation, forming an interpenetrating network (IPN) structure.

[0007] However, although waterproof and breathable membranes prepared by traditional pure electrospinning technology possess certain porosity and breathability due to their micro-nano fiber structure, they still have significant defects in practical applications. First, their hydrostatic performance is generally low, mainly due to the uneven pore size distribution and loose structure of the fiber membrane: the random stacking of electrospun fibers easily forms local large-sized pores (>5 μm), and the lack of gradient or dense structural design allows liquid water to penetrate the membrane layer at relatively low pressure, making it difficult to meet the high hydrostatic pressure (≥150 kPa) requirements of high-performance outdoor footwear waterproof fabrics. Second, insufficient mechanical properties are another bottleneck. Pure electrospun nanofiber membranes rely solely on physical entanglement between fibers, resulting in low cross-linking density and a lack of chemical bonding, leading to low tensile strength (usually <5 MPa) and elongation at break. This makes them prone to structural damage under the high pressure environment of hot pressing processes in footwear or during dynamic bending during wear. Furthermore, the abrasion resistance is a particularly prominent defect. The nanofibers, with their small diameter (100-500 nm) and high surface energy, are prone to surface defects due to fiber breakage or peeling during friction, accelerating the wear process. The lack of reinforced interfacial bonding or abrasion-resistant fillers in traditional processes further exacerbates the rapid failure of the film layer under repeated friction on shoe soles. These issues not only limit its application in high-end functional footwear materials but also force the industry to continue relying on adding fluorinated hydrophobic agents or composite lamination processes to compensate for performance shortcomings, leading to increased production costs and decreased environmental friendliness.

[0008] Furthermore, existing nanofiber reinforcement technologies mostly focus on petroleum-based systems, and face two major challenges when directly applied to bio-based polyurethanes: (1) The interfacial compatibility between nanofibers and bio-based resins is poor, which can easily lead to phase separation.

[0009] (2) Traditional impregnation process makes it difficult to achieve uniform filling of bio-based resin in the self-supporting framework of nanofibers, and the porosity control is not precise, which affects the final performance.

[0010] In the prior art, CN115920675B discloses a polybenzimidazole nanofiber membrane for use in medical mask filter materials, as well as its preparation and modification methods. The polybenzimidazole nanofiber membrane is composed of polybenzimidazole nanofibers in a cross-linked state, with the cross-points bonded together by polybenzimidazole to form an adhesive structure. The nanofiber membrane has a dumbbell-shaped pore size distribution structure. The preparation method of the polybenzimidazole nanofiber membrane includes the following steps: preparing a spinning solution, preparing an adhesive solution, preparing the nanofiber membrane layer, impregnation and adhesion, and post-treatment. For example, CN109853135B discloses a core-shell structured nanofiber membrane of polybenzimidazole-coated polyimide nanofibers. The preparation method involves first obtaining a polyamic acid nanofiber membrane from a polyamic acid solution via electrospinning, followed by high-temperature cyclization to obtain a polyimide nanofiber membrane. The polyimide nanofiber membrane is then etched with an alkaline solution, and the etched membrane is placed in an oven with a dilute polybenzimidazole solution for constant-temperature intermittent immersion treatment, followed by gradient-heating treatment. However, these existing technologies, ultimately applied in fields such as masks and battery separators, emphasize single properties such as structural strength and filtration efficiency. In the footwear industry, however, properties such as water resistance, moisture permeability, and mechanical stability need to be considered simultaneously, making direct application of existing technologies difficult.

[0011] In summary, the temperature and abrasion resistance defects of existing bio-based polyurethanes severely restrict their application in the footwear material field, while traditional modification methods often sacrifice environmental friendliness, making it difficult to meet future market demands. Summary of the Invention

[0012] This invention aims to address the problems of insufficient mechanical properties or stability of bio-based polyurethane in existing technologies, and the difficulty in effectively combining it with nanofiber reinforcement technology. To this end, this invention proposes a template-based microporous bio-based membrane structure, which uses electrospinning technology to prepare a structurally stable modified nanofiber self-supporting framework, which is then composited with bio-based polyurethane to form a microporous membrane layer with both waterproof and breathable functions.

[0013] The objective of this invention is achieved through the following technical solution: The first aspect of this invention discloses a method for preparing a template-based bio-based microporous membrane, comprising the following steps: (1) One of polybenzimidazole (PBI), amino-modified polyimide (PI) and carboxylated poly(p-phenylenebenzodioxazole) (PBO) is uniformly dispersed with modified cellulose nanofibers (CNF) in a DMF / water system to prepare a high-viscosity spinning solution; (2) Electrospinning is performed on the high viscosity spinning solution prepared in step (1) to prepare a modified nanofiber self-supporting skeleton. (3) The modified nanofiber self-supporting skeleton prepared in step (2) is subjected to low-temperature vacuum drying to obtain a bio-based microporous membrane template. (4) The bio-based polyurethane resin is coated and filled into the bio-based microporous membrane template obtained in step (3), and the negative pressure adsorption is applied until the filling is uniform to obtain a bio-based wet membrane. (5) The bio-based wet membrane obtained in step (4) is subjected to gradient drying to obtain the bio-based microporous membrane.

[0014] Preferably, in step (1), The high-viscosity spinning solution has a viscosity of 10,000~30,000 cP and comprises: (a) One of polybenzimidazole (PBI), amino-modified polyimide (PI), and carboxylated poly(p-phenylenebenzodioxazole) (PBO), in a content of 10-20 wt% based on the total weight of the high-viscosity spinning solution; (b) Cellulose nanofibers (CNF) treated with a silane coupling agent at a content of 1–1.6 wt% based on the total weight of the high-viscosity spinning solution; (c) A DMF / water system constructed with dimethylformamide (DMF) and deionized water (85:15~95:5) was supplemented to a total volume of 100 wt% of the high viscosity spinning solution.

[0015] Preferably, in step (2), The electrospinning parameters are as follows: (a) Flow rate: 0.05~0.20 mL / h; (b) Voltage: 15~30 kV; (c) Needle-collecting plate distance: 10~25 cm; (d) Ambient humidity: 30~60% RH; (e) Temperature: 15~30 ℃.

[0016] Preferably, in step (2), The modified nanofiber self-supporting skeleton has a porosity of 70-95% and a pore size distribution of 100-5000 nm, and has a three-dimensional interconnected network structure.

[0017] Preferably, in step (3), The temperature for the low-temperature vacuum drying is 30~70 ℃.

[0018] Preferably, in step (4), The bio-based polyurethane resin contains at least 60% bio-based content.

[0019] Preferably, in step (4), The coating and filling process is a slot coating, which is combined with negative pressure adsorption to achieve uniform filling of bio-based polyurethane resin in the bio-based microporous membrane template. The coating and filling temperature is 40~100 ℃, and the negative pressure value of the negative pressure adsorption is 0.05~0.5MPa.

[0020] Preferably, in step (5), The gradient drying process consists of two stages: i) First stage: temperature 80~110 ℃; ii) Second stage: temperature is 120~150 ℃.

[0021] The second aspect of this invention discloses a template-based bio-based microporous membrane, which is prepared using any of the preparation methods described above; The bio-based microporous membrane has a moisture permeability ≥8000 g / m³. 2 • 24 h, hydrostatic pressure ≥150 kPa.

[0022] The third aspect of this invention discloses the application of a template-based bio-based microporous membrane as described above in the field of footwear materials.

[0023] The working principle of this invention is as follows: A high-temperature resistant three-dimensional nanofiber self-supporting framework was constructed by electrospinning with a high-viscosity spinning solution. This framework was then used as a template to allow bio-based polyurethane resin to uniformly permeate and cure under negative pressure. The reactive groups on the fiber surface formed an interfacial chemical bond with the resin, jointly constructing a stable microporous composite network structure. This enabled the membrane material to maintain excellent moisture permeability and structural stability while retaining high hydrostatic pressure. The template primarily served to provide structural support, pore constraint, and guide the wetting path.

[0024] (1) Electrospinning of high-viscosity spinning solution forms a three-dimensional nanofiber self-supporting skeleton with self-supporting ability: In electrospinning, the spinning solution forms a Taylor cone under a high electric field, generating a continuous jet. The higher viscosity of the spinning solution increases the molecular chain entanglement density, thereby improving the stability of the jet and preventing breakage, shrinkage, or bead-like defects during stretching, resulting in fibers with uniform diameter and continuity. The DMF / water dual-solvent system undergoes rapid evaporation and induced phase separation during jet flight, allowing the fibers to solidify and shape in the air. The resulting fibers are randomly stacked on a collecting plate, forming a three-dimensional interconnected porous network structure with a porosity of 70–95% and a pore size range of 100–5000 nm. Due to the high thermal stability of the framework material, this network structure can maintain its original morphology and provide stable support during subsequent film formation.

[0025] (2) The nanofiber self-supporting framework serves as a template to provide pore structure constraints and dimensional stability: The aforementioned three-dimensional interconnected porous network structure acts as a template in this invention. On one hand, the three-dimensional channels formed between the fibers provide geometric constraints for the penetration, distribution, and curing of the bio-based polyurethane resin, enabling the subsequently formed microporous structure to possess controllable pore size and continuity. On the other hand, the high-temperature resistant fibers themselves have high rigidity, providing necessary dimensional stability during coating, negative pressure adsorption, and drying processes to prevent structural collapse or channel deformation, thereby ensuring the uniformity of the final microporous structure. This solution eliminates the need for traditional substrates (such as PET, PTFE, or fabrics) as film-forming support layers to complete the resin coating and curing process, improving process flexibility and eliminating problems such as substrate peeling.

[0026] (3) Bio-based polyurethane resin can directly penetrate into the interior of the self-supporting skeleton under negative pressure adsorption: Bio-based polyurethane resin fills the pores of the self-supporting nanofiber framework under negative pressure adsorption. The negative pressure adsorption creates a pressure difference, allowing the high-viscosity resin to penetrate deep into the three-dimensional network, reducing the formation of blind pores or bubbles. Heating and coating further reduce the resin viscosity and improve its flowability, enabling uniform spreading and complete wetting of the resin between the fibers. Because the pore size is in the nanometer to micrometer range, capillary action and interfacial wetting further promote the directional spreading of the resin along the fiber surface, resulting in a continuous distribution of the resin phase within the fiber network, thus providing a good structural foundation for subsequent curing.

[0027] (4) The interface reaction and the confined curing process together form a stable microporous composite structure: High-temperature nanofibers (PBI, amino-modified PI, carboxylated PBO, and silane-modified CNF) contain reactive groups such as amino, hydroxyl, epoxy, or siloxy groups on their surface. These groups can react with isocyanate groups (-NCO) or hydroxyl groups (-OH) in bio-based polyurethanes to form urea bonds, urethane bonds, or Si-OC bonds. This creates a chemical bond at the fiber-resin interface, allowing the resin phase to adhere firmly to the fiber surface, improving interfacial stability, and reducing the risk of delamination during drying and use.

[0028] (5) A stable microporous structure with water-blocking and moisture-permeable properties is formed by a restricted curing mechanism: During the gradient drying process, the resin cures in a confined state within the three-dimensional fiber channels: (a) the continuous polyurethane phase forms a water-blocking structure at the narrow points of the channels, increasing the resistance to liquid water penetration; (b) the presence of incompletely filled interconnected micropores allows water vapor to diffuse along the channels, thereby maintaining high moisture permeability; and (c) the self-supporting fiber skeleton provides thermal stability and mechanical support, enabling the microporous structure to maintain its three-dimensional morphology during curing. The resulting microporous composite structure combines water resistance, moisture permeability, and mechanical stability.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses one of polybenzimidazole (PBI), amino-modified polyimide (PI), or carboxylated poly(p-phenylenebenzodioxazole) (PBO) along with high-temperature resistant polymers such as silane-modified cellulose nanofibers (CNF) as electrospinning skeleton materials. These materials exhibit high thermal stability, maintaining their three-dimensional pore structure without collapse during subsequent coating, negative pressure adsorption, and drying processes. This overcomes the defects of traditional cellulose-based nanofibers, which are prone to deformation under high temperatures or solvent environments, thus improving the temperature resistance and chemical stability of the template. Furthermore, the obtained nanofiber self-supporting skeleton possesses excellent self-supporting capabilities, maintaining structural integrity without additional substrate support, providing an independent template for subsequent resin coating and filling.

[0030] (2) The three-dimensional nanofiber self-supporting framework formed by electrospinning in this invention has a large number of reactive groups such as amino, hydroxyl or siloxy groups, which can chemically bond with the functional groups in bio-based polyurethane. Compared with the traditional method that relies solely on physical adsorption, this invention significantly improves the interfacial bonding strength through chemical coupling, thereby avoiding interfacial delamination after film formation and improving the overall stability and reliability of the composite film structure.

[0031] (3) The present invention performs low-temperature vacuum drying and pre-fixation on the self-supporting skeleton of nanofibers after electrospinning, which can effectively prevent the skeleton from shifting or deforming during the coating or negative pressure adsorption stage, so that its three-dimensional pore structure remains stable throughout the film formation process, which helps to ensure the uniformity and controllability of the final microporous structure.

[0032] (4) This invention utilizes the synergistic effect of heated coating and filling (40~100 ℃) and negative pressure adsorption (0.05~0.5 MPa) to reduce the viscosity of high-viscosity bio-based polyurethane under heating conditions while simultaneously creating a pressure gradient through negative pressure to penetrate deep into the pores of the skeleton. This measure effectively avoids the problems of blind holes, bubbles, or incomplete local filling that occur in traditional impregnation methods, and significantly improves the uniformity of resin filling and film quality.

[0033] (5) Through systematic research and comparative analysis of various coating methods such as slit coating, blade coating, and dip-and-roll coating, this invention has determined that the slit coating structure combined with negative pressure flow control can achieve better resin flow control and thickness uniformity in the wide direction. This method significantly improves the distribution accuracy and film formation stability of the casting liquid on the skeleton surface, effectively avoiding the problems of large flow fluctuations, local thickness deviations, and insufficient coating consistency that are common in traditional blade coating or uncontrolled flow dipping processes.

[0034] (6) The electrospun nanofiber self-supporting skeleton of the present invention has a porosity of 70-95% and a pore size range of 100-5000 nm. Combined with the confined curing effect of resin within the skeleton, the resulting composite membrane forms a microporous structure with both water-blocking and moisture-permeable functions. The microporous structure can prevent liquid water from permeating while retaining gas diffusion pathways, thereby enabling the membrane to maintain high hydrostatic pressure capability while still having good moisture permeability.

[0035] (7) The nanofiber self-supporting skeleton constructed in this invention has good self-supporting ability and structural integrity, and can be directly coated or filled with resin without additional substrate support. This characteristic allows the nanofiber self-supporting skeleton itself to be used as a film-forming template, which simplifies the process and avoids problems such as interface separation, dimensional instability or subsequent peeling difficulties caused by dependence on additional substrates in traditional technologies, thereby improving process flexibility and film-forming stability.

[0036] (8) The high-temperature resistant nanofiber self-supporting skeleton used in this invention provides necessary mechanical support during the film forming and subsequent high-temperature processing (such as hot pressing of shoe materials), preventing the film from collapsing or becoming uneven in thickness under thermal stress, thereby improving the thermal stability and reliability of the overall structure. At the same time, the formed microporous structure also helps to maintain waterproof and breathable performance.

[0037] (9) This invention uses polyurethane resin with high bio-based content and introduces modified cellulose nanofibers as a reinforcing phase, which improves the performance of the membrane structure while reducing the dependence on petrochemical raw materials. The process has no fluorination treatment step, which is in line with the technical trend of green manufacturing and sustainable development. Attached Figure Description

[0038] Figure 1 The image shows a SEM image of the bio-based microporous membrane prepared in Example 1.

[0039] Figure 2 SEM image of the bio-based microporous membrane prepared for Comparative Example 1.

[0040] Figure 3 SEM image of the bio-based microporous membrane prepared for Comparative Example 2. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0042] Unless otherwise specified, the reagents used in the following examples are all commercially available products, and the methods used are all well-known in the art.

[0043] This invention provides a template-based coating method for preparing bio-based microporous membranes, which can be mass-produced through the synergistic design of modified nanofiber self-supporting framework and bio-based polyurethane resin.

[0044] A template-based coating method for preparing bio-based microporous membranes comprises the following steps: (1) Preparation of high viscosity spinning solution and formation of nanofiber self-supporting skeleton precursor: any one of polybenzimidazole (PBI), amino-modified polyimide (PI) and carboxylated poly(p-phenylenebenzodioxazole) (PBO) is dispersed with modified cellulose nanofibers (CNF) in a DMF / water system to obtain a high viscosity micro-swelling spinning solution; the spinning solution is electrospun to obtain a modified nanofiber self-supporting skeleton; (2) Drying and template formation of nanofiber self-supporting framework: The obtained nanofiber self-supporting framework precursor was dried under low temperature vacuum conditions to form a bio-based microporous membrane template. (3) Casting solution filling: The pre-prepared bio-based polyurethane resin casting solution is applied to the template through a coating device, and a negative pressure is applied under the action of a suction device to make the casting solution uniformly enter the template channel, thereby obtaining a preliminary bio-based wet film. (4) Wet film stabilization treatment: The obtained bio-based wet film is subjected to necessary static or pre-drying to stabilize the filling structure and provide conditions for final film formation; (5) Gradient drying and membrane formation: The stabilized wet membrane is subjected to gradient drying treatment to cure the bio-based polyurethane in the template, and finally obtains a bio-based microporous membrane based on the template. In one embodiment of the present invention, in step (1), the modified nanofiber self-supporting framework comprises any of the following high-temperature resistant nanofibers: polybenzimidazole (PBI), amino-modified polyimide (PI) nanofibers, and carboxylated poly(p-phenylenebenzodioxazole) (PBO) nanofibers treated with an aminosilane coupling agent. One of the above nanofibers and cellulose nanofibers (CNF) treated with a silane coupling agent are dispersed together in a DMF / water mixture to form a high-viscosity micro-swelling spinning solution, and the nanofiber self-supporting framework precursor is obtained by electrospinning.

[0045] In one embodiment of the present invention, the nanofiber self-supporting skeleton precursor obtained in step (1) is pre-fixed by low-temperature vacuum drying and hot pressing before entering the casting liquid filling step, so as to improve the structural stability of the skeleton and prevent structural displacement during the subsequent negative pressure filling process.

[0046] In one embodiment of the present invention, the coating device and the matching suction device used to apply the bio-based polyurethane casting liquid in step (3) have a controllable heating function, and their working temperature range is 40~100 ℃, so as to reduce the viscosity of the bio-based polyurethane casting liquid system and improve its penetration and flowability in the nanofiber channels.

[0047] In one embodiment of the present invention, the coating device in step (3) works in conjunction with the negative pressure adsorption mechanism to achieve precise control of the amount of casting liquid applied and the penetration rate, thereby ensuring the uniformity of the casting film.

[0048] In one embodiment of the present invention, the negative pressure applied by the suction device in step (3) is in the range of 0.05~0.5 MPa. Through the synergistic effect of thermally induced diffusion and negative pressure adsorption, the high viscosity polyurethane casting liquid can achieve bubble-free and uniform filling in the nanofiber microporous structure.

[0049] In one embodiment of the present invention, after the casting liquid is filled in step (5), the wet film is subjected to structural stabilization treatment by gradient drying. The gradient drying temperature atmosphere is in two stages (first stage: 80~110 ℃, second stage: 120~150 ℃) to gradually release the solvent and reduce the interfacial stress, thereby ensuring the structural fixation and uniform curing of the polyurethane system inside the nanofiber self-supporting skeleton.

[0050] In one embodiment of the present invention, the porosity of the modified nanofiber self-supporting framework is 70-95%, and the pore size distribution range is 100-5000 nm. Its three-dimensional interconnected pore structure can endow the resulting bio-based microporous membrane with high moisture permeability (moisture permeability ≥8000 g / m³). 2 • 24 h) and high water pressure resistance (static water pressure ≥ 150 kPa).

[0051] In one embodiment of the present invention, through gradient drying and subsequent final film formation process, a stable mechanical bond can be formed between the nanofibers and the polyurethane matrix, so that the interfacial bonding strength (QB / T 5655-2021) of the resulting film material reaches more than 5 MPa, the temperature resistance (ASTM D5721) reaches more than 180 ℃, and the wear resistance cycle (HG / T2874-1997) is ≥10000 times (load 1 N).

[0052] The following example is from Embodiment 1, but it does not mean that this solution can only be implemented under the specific parameter combination of Embodiment 1. It should be noted that this solution can be arbitrarily combined within the parameter range given above and achieve performance results that are equivalent to or substantially equivalent to Embodiment 1.

[0053] Example 1 Step 1: One of polybenzimidazole (PBI), amino-modified polyimide (PI), and carboxylated poly(p-phenylenebenzodioxazole) (PBO) (15 wt%) was dispersed with silane-modified CNF (1.2 wt%) in a DMF / water (92:8 mass ratio) mixed solvent. The mixture was stirred for 4 h until the system was homogeneous and transparent, and the viscosity of the spinning solution was 18,000 cP. A three-dimensional nanofiber self-supporting framework was prepared using an electrospinning device (voltage 20 kV, collection distance 18 cm). After drying (40 ℃, 2 h), the porosity was approximately 85%.

[0054] Step 2: Mix bio-based polyurethane resin PU (solid content 12 wt%, bio-based content 60%) with an appropriate amount of leveling agent and stir for 1 hour before use.

[0055] Step 3: Lay the nanofiber self-supporting skeleton on the adhesive application curtain, and control the flow rate (0.5 mL·cm) using a slit-type adhesive application device. -1 The PU application area is kept at 40 ℃ to reduce the viscosity of PU; then it enters the negative pressure chamber and is adsorbed at ~0.12 MPa for 60 s, so that the PU penetrates into the skeleton and forms a bubble-free and uniform filling.

[0056] Step 4: Gradient drying at 90 ℃ (for 5 min) and 135 ℃ (for 5 min) in sequence to obtain a complete microporous structure.

[0057] Comparative Example 1 Step 1: Prepare the modified nanofiber self-supporting framework according to the method in Example 1.

[0058] Step 2: Prepare bio-based polyurethane casting solution according to the method in Example 1.

[0059] Step 3: Fix the nanofiber self-supporting skeleton onto the surface of a glass substrate heated to 40°C, and apply the coating with a stainless steel scraper to a film thickness of 0.15 mm.

[0060] Step 4: Use the same gradient drying procedure as in Example 1.

[0061] Comparative Example 2 Step 1: Prepare the modified nanofiber self-supporting framework according to the method in Example 1.

[0062] Step 2: Prepare bio-based polyurethane casting solution according to the method in Example 1.

[0063] Step 3: Immerse the nanofiber self-supporting skeleton completely in the PU casting liquid for 10 seconds, and then squeeze the liquid through a pressure roller with a gap of 0.20 mm and a temperature of 40 ℃.

[0064] Step 4: Use the same gradient drying procedure as in Example 1.

[0065] SEM images of the bio-based microporous membranes prepared by Examples 1, 1, and 2 are shown below. Figures 1-3 As shown.

[0066] Performance testing: Table 1. Sample Performance The comparative results show that different coating methods affect the uniformity of resin distribution in the skeleton and the ability to maintain the three-dimensional pore structure. The slit coating combined with negative pressure adsorption used in Example 1 achieved optimal resin penetration and microporous structure integrity; the scraping method in Comparative Example 1 had slightly poorer flow control stability, resulting in uneven local filling; the dip-and-roll method in Comparative Example 2 easily introduced air bubbles under high viscosity resin and caused slight compression of the skeleton, resulting in a decrease in performance.

[0067] In summary, this invention not only solves the material performance bottleneck in the composite hot-pressing process of shoe materials, but its microporous structure can also be extended to high-end applications such as breathable linings for sports shoes and waterproof and breathable membranes for outdoor shoes, demonstrating broad market potential. Furthermore, this design concept provides a universal solution for the high performance of bio-based materials, and is expected to drive the upgrading of the entire environmentally friendly materials industry.

[0068] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a template-based bio-based microporous membrane, characterized in that, Includes the following steps: (1) One of polybenzimidazole, amino-modified polyimide and carboxylated poly(p-phenylenebenzodioxazole) is uniformly dispersed with modified cellulose nanofibers in a DMF / water system to prepare a high-viscosity spinning solution; (2) Electrospinning the high-viscosity spinning solution obtained in step (1) to prepare a modified nanofiber self-supporting skeleton. (3) The modified nanofiber self-supporting skeleton prepared in step (2) is subjected to low-temperature vacuum drying to obtain a bio-based microporous membrane template. (4) The bio-based polyurethane resin is coated and filled into the bio-based microporous membrane template obtained in step (3), and the negative pressure adsorption is applied until the filling is uniform to obtain a bio-based wet membrane. (5) The bio-based wet membrane obtained in step (4) is subjected to gradient drying to obtain the bio-based microporous membrane.

2. The method for preparing a template-based bio-based microporous membrane according to claim 1, characterized in that, In step (1), The high-viscosity spinning solution has a viscosity of 10,000~30,000 cP and comprises: (a) One of polybenzimidazole, amino-modified polyimide, and carboxylated poly(p-phenylenebenzodioxazole), in a content of 10-20 wt% based on the total weight of the high-viscosity spinning solution; (b) Cellulose nanofibers treated with a silane coupling agent at a content of 1 to 1.6 wt% based on the total weight of the high-viscosity spinning solution; (c) DMF / water system, replenished to a total volume of 100 wt% for high viscosity spinning solution; wherein the weight ratio of DMF to deionized water is 85:15 to 95:

5.

3. The method for preparing a template-based bio-based microporous membrane according to claim 1, characterized in that, In step (2), The electrospinning parameters are as follows: (a) Flow rate: 0.05~0.20 mL / h; (b) Voltage: 15~30 kV; (c) Needle-collecting plate distance: 10~25 cm; (d) Ambient humidity: 30~60% RH; (e) Temperature: 15~30 ℃.

4. The method for preparing a template-based bio-based microporous membrane according to claim 1, characterized in that, In step (2), The modified nanofiber self-supporting skeleton has a porosity of 70-95% and a pore size distribution of 100-5000 nm, and has a three-dimensional interconnected network structure.

5. The method for preparing a template-based bio-based microporous membrane according to claim 1, characterized in that, In step (3), The temperature for the low-temperature vacuum drying is 30~70 ℃.

6. The method for preparing a template-based bio-based microporous membrane according to claim 1, characterized in that, In step (4), The bio-based polyurethane resin has a bio-based content of ≥60%.

7. The method for preparing a template-based bio-based microporous membrane according to claim 1, characterized in that, In step (4), The coating and filling process uses a slit-type method, combined with negative pressure adsorption, to achieve uniform filling of bio-based polyurethane resin in the bio-based microporous membrane template. The coating and filling temperature is 40~100 ℃, and the negative pressure value of the negative pressure adsorption is 0.05~0.5MPa.

8. The method for preparing a template-based bio-based microporous membrane according to claim 1, characterized in that, In step (5), The gradient drying process consists of two stages: i) First stage: temperature 80~110 ℃; ii) Second stage: temperature is 120~150 ℃.

9. A template-based bio-based microporous membrane, characterized in that, It was prepared by any one of the preparation methods described in claims 1 to 8; The bio-based microporous membrane has a moisture permeability ≥8000 g / m³. 2 • 24 h, hydrostatic pressure ≥150 kPa.

10. The application of the template-based bio-based microporous membrane as described in claim 9 in the field of footwear materials.

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