Nanofiber and nanomesh composite double network structure membrane and preparation method thereof

Abstract

This invention provides a dual-network structure membrane composed of nanofibers and nanomesh, and its preparation method. The dual-network structure membrane includes a porous substrate and a dual-network structure loaded on the surface of the porous substrate. The dual-network structure is composed of nanofibers and a low-molecular-weight gel nanomesh. This invention first loads a nanofiber network onto the surface of the porous substrate, and then assembles a low-molecular-weight gel in situ into the nanofiber network. Utilizing the strong interaction between the nanofibers and the low-molecular-weight gel, the low-molecular-weight gel self-assembles on the nanofibers to form a loose yet stable nano-network structure. This enhances mechanical properties while avoiding increasing the packing density and air resistance of the nanofiber network. As a result, the dual-network structure membrane composed of nanofibers and nanomesh exhibits excellent air filtration performance and has promising application prospects in the fields of air filtration and protection.

Description

Technical Field

[0001] This invention relates to the field of air filter membrane material technology, and in particular to a dual-network structure membrane composed of nanofibers and nanomesh and its preparation method. Background Technology

[0002] As people's requirements for the filtration efficiency, rate, quality, and service life of air filtration materials continue to increase, traditional single-type fiber materials are no longer sufficient to meet application requirements. Therefore, composite technology has been introduced into the processing of high-performance air filtration materials, leading to the development of composite air filtration materials. An invention patent (application number CN 202111158435.5) discloses an organic-inorganic hybrid multi-level structure air filtration and protection material. This material is obtained by dispersing micro-nano-sized inorganic particles in a nanofiber suspension, mixing them evenly, and then coating the mixture onto the surface of a porous nonwoven fabric substrate. The micro-nano-sized particles and nanofibers form a nanofiber hybrid network structure on the nonwoven fabric surface, improving the porosity, specific surface area, and surface roughness of the nanofiber membrane, and also endowing the air filtration and protection material with bactericidal and disinfecting properties. However, this air filtration and protection material combines inorganic ions with nanofibers, resulting in poor bonding between the two. In subsequent applications, inorganic particles may detach, affecting the material's filtration efficiency and protective quality.

[0003] Existing research utilizes gradient-structured composite filter media made from fiber layers of varying diameters. This involves combining fiber webs of different diameters, resulting in varying pore sizes and distributions across different layers, as well as varying fiber thicknesses, thus achieving stepped filtration of particles of different sizes. A patent application (CN 202010283439.5) discloses a multi-scale structured plant fiber air filter material, its preparation method, and its applications. This air filter material is formed by overlapping various plant fibers of different diameters. Internally, it mainly comprises three layers: a micron-scale plant fiber layer, a submicron-scale plant fiber layer, and a nano-scale plant fiber layer, forming a gradient pore structure that provides good filtration and retention capabilities for particles and bacteria of different sizes in the air. However, this material suffers from weak interlayer interaction, poor mechanical properties, and high packing density and resistance after multiple layers of coating, affecting its filtration efficiency.

[0004] In view of this, it is necessary to design an improved dual-network structure membrane composed of nanofibers and nanomesh and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-network structure membrane composed of nanofibers and nanomesh and its preparation method. By utilizing the strong interaction between nanofibers and low molecular weight gel, and by controlling the diameter of the nanofibers and the concentration of the low molecular weight gel solution, the two are self-assembled to form a dual-network structure composed of nanofibers and nanomesh. This dual-nano-network structure membrane has good air filtration efficiency and low air filtration resistance, and has good application prospects in the field of air filtration and protection.

[0006] To achieve the above-mentioned objectives, the present invention provides a dual-network structure membrane composed of nanofibers and nanomesh, comprising a porous substrate and a dual-network structure loaded on the surface of the porous substrate, wherein the dual-network structure is composed of nanofibers and low molecular weight gel nanomesh.

[0007] As a further improvement of the present invention, the diameter of the nanofiber is 100-1000 nm; preferably 800-1000 nm.

[0008] As a further improvement of the present invention, the low molecular weight gel nanonet is a nanonet formed by sorbitol nucleating agent.

[0009] As a further improvement of the present invention, the nanofiber is one or more of ethylene-vinyl alcohol copolymer nanofiber, polyester nanofiber, polyacrylonitrile nanofiber, polyamide nanofiber, and polyolefin nanofiber; preferably ethylene-vinyl alcohol copolymer nanofiber.

[0010] As a further improvement of the present invention, the porous substrate is a nonwoven porous substrate.

[0011] This invention also provides a method for preparing a dual-network structure membrane composed of nanofibers and nanomesh, comprising the following steps:

[0012] S1. Disperse nanofibers in solvent I to obtain a nanofiber suspension, and load the nanofiber suspension onto the surface of a porous substrate to obtain a nanofiber membrane;

[0013] S2. The low molecular weight gel is neutralized with solvent II and dissolved at a certain temperature to obtain a low molecular weight gel solution; the concentration of the low molecular weight gel solution is 0.02wt% to 0.5wt%.

[0014] S3. Load the low molecular weight gel solution prepared in step S2 onto the surface of the nanofiber membrane in step S1. After solvent II evaporates, the dual-network structure membrane composed of nanofibers and nanonets is obtained.

[0015] As a further improvement of the present invention, in step S2, the dissolution temperature of the low molecular weight gel is 60-120°C.

[0016] As a further improvement of the present invention, in step S2, the low molecular weight gel is a sorbitol nucleating agent.

[0017] As a further improvement of the present invention, in step S1, the concentration of the nanofiber suspension is 0.5wt% to 2wt%.

[0018] As a further improvement of the present invention, in step S1, solvent I is a mixed solvent of isopropanol and water, wherein the ratio of isopropanol to water is (30:70) to (70:30); in step S2, solvent II used to prepare the low molecular weight gel solution is one or more of methanol, ethanol, isopropanol, n-propanol, n-octanol, acetophenone, chloroform, toluene, and benzene.

[0019] As a further improvement of the present invention, in step S1 or step S2, the loading method of the nanofiber suspension or the low molecular weight gel solution includes one of spin coating, spray coating, blade coating or impregnation adsorption.

[0020] The beneficial effects of this invention are:

[0021] 1. This invention provides a dual-network structure membrane composed of nanofibers and nanomesh, and its preparation method. The membrane includes a porous substrate and a dual-network structure loaded on the surface of the porous substrate. The dual-network structure is composed of nanofibers and a low-molecular-weight gel nanomesh. This invention utilizes the strong interaction between nanofibers and the low-molecular-weight gel, and by controlling the diameter of the nanofibers and the concentration of the low-molecular-weight gel solution, the two self-assemble to form a dual-network structure composed of nanofibers and nanomesh. This dual-nanonetwork structure membrane exhibits good mechanical properties, high air filtration efficiency, and low air filtration resistance, showing promising application prospects in the fields of air filtration and protection.

[0022] 2. This invention first loads a nanofiber network onto the surface of a porous substrate, then assembles a low-molecular-weight gel in situ within the nanofiber network. Because the nanofiber network is characterized by its ultrafine fibers, small pore size, and high porosity, the low-molecular-weight gel, after loading, forms strong connections between the nanofibers, resulting in a layered and stably connected dual-network structure. This leads to the final membrane material possessing high mechanical properties. This invention uses sorbitol as a nucleating agent, and by controlling its concentration, it allows the solvent to evaporate, forming an ultrafine fiber network on the nanofiber surface. Furthermore, sorbitol has numerous surface-active groups, resulting in strong interactions with the abundant CH bonds on the nanofiber surface. It can self-assemble between the nanofibers to form a loose network structure, enhancing mechanical properties while avoiding increased nanofiber network density and resistance, which would negatively impact the membrane material's filtration performance. The resulting layered and interconnected dual-network membrane exhibits both excellent mechanical properties and air filtration performance.

[0023] 3. The preparation method of the dual-network structure membrane composed of nanofibers and nanomesh provided by the present invention is simple and easy to implement, has low preparation cost, and is suitable for large-area preparation; moreover, the prepared dual-network structure membrane has a wide range of applications. Its high porosity and stable cavity structure provide a large number of channels for airflow, while the unique dual-network structure further improves its filtration efficiency, better meeting the needs of actual production and application. Attached Figure Description

[0024] Figure 1 These are electron microscope images at different magnifications of the dual-network structure membrane composed of nanofibers and nanomesh prepared in Example 1 of this invention.

[0025] Figure 2 The images shown are electron microscope images of the nanofiber and nanomesh composite double network structure films prepared in Examples 1 and 6-7 of this invention; where (a) is Example 6, (b) is Example 1, and (c) is Example 7. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0028] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] A dual-network structure membrane composed of nanofibers and nanomesh comprises a porous substrate and a dual-network structure loaded on the surface of the porous substrate. The dual-network structure is composed of nanofibers and a low-molecular-weight gel nanomesh. By utilizing the strong interaction between the nanofibers and the low-molecular-weight gel, and controlling the diameter of the nanofibers and the concentration of the low-molecular-weight gel solution, the two self-assemble to form a dual-network structure composed of nanofibers and nanomesh. This dual-nano-network structure membrane exhibits high air filtration efficiency and low air filtration resistance, showing promising application prospects in the fields of air filtration and protection.

[0030] Specifically, the diameter of the nanofibers is 100–1000 nm; preferably 800–1000 nm. The low molecular weight gel nanonetwork is a nanonetwork formed by sorbitol nucleating agent. The diameter of the nanofibers is related to the porosity of the nanofiber network structure and also affects the subsequent loading of the low molecular weight gel nanonetwork, so it needs to be limited. In addition, the low molecular weight gel nanonetwork has an important influence on the fiber diameter and network structure formation of the gel nanonetwork, and can play a role in regulating the balance between porosity, packing density and resistance of the layered double network structure.

[0031] In some specific embodiments, the nanofibers are one or more selected from ethylene-vinyl alcohol copolymer nanofibers, polyester nanofibers, polyacrylonitrile nanofibers, polyamide nanofibers, and polyolefin nanofibers; preferably, they are ethylene-vinyl alcohol copolymer nanofibers. The strong interaction between the ethylene-vinyl alcohol copolymer nanofibers and the low molecular weight gelling sorbitol nucleating agent is beneficial for the stable formation of the dual-network structure.

[0032] In some specific implementations, the porous substrate is a nonwoven porous substrate.

[0033] A method for preparing a dual-network structure membrane composed of nanofibers and nanomesh includes the following steps:

[0034] S1. Disperse nanofibers in solvent I to obtain a nanofiber suspension. Load the nanofiber suspension onto the surface of a porous substrate to obtain a nanofiber membrane. The concentration of the nanofiber suspension is 0.5wt% to 2wt%.

[0035] S2. Neutralize the low molecular weight gel with solvent II and dissolve it at a certain temperature to obtain a low molecular weight gel solution; the concentration of the low molecular weight gel solution is 0.02wt% to 0.5wt%.

[0036] S3. Load the low molecular weight gel solution prepared in step S2 onto the surface of the nanofiber membrane in step S1. After solvent II evaporates, a dual-network structure membrane composed of nanofibers and nanonets is obtained.

[0037] This invention first loads a nanofiber network onto the surface of a porous substrate, then assembles a low-molecular-weight gel in situ within the nanofiber network. Because the nanofiber network possesses ultra-fine fibers, small pore size, and high porosity, the loaded low-molecular-weight gel forms strong connections between the nanofibers, resulting in a layered and stably connected dual-network structure. This leads to the final membrane material exhibiting high mechanical properties. This preparation method is simple to implement, has low production costs, and is suitable for large-area fabrication. Furthermore, the resulting dual-network membrane has a wide range of applications; its high porosity and stable cavity structure provide numerous channels for airflow, while the unique dual-network structure further enhances its filtration efficiency, better meeting the needs of practical production and applications.

[0038] Specifically, in step S2, the dissolution temperature of the low molecular weight gel is 60–120°C. The low molecular weight gel is a sorbitol nucleating agent. This invention selects sorbitol as a nucleating agent and, by controlling its concentration, allows it to form an ultrafine fiber network on the surface of nanofibers after solvent evaporation. Furthermore, sorbitol has numerous surface-active groups, resulting in strong interactions with the abundant CH bonds on the nanofiber surface. This allows it to self-assemble between nanofibers to form a loose network structure, avoiding increased nanofiber network density and air filtration resistance, thus preventing adverse effects on membrane material filtration performance. The resulting layered and interconnected double-network structure membrane possesses both excellent mechanical properties and air filtration performance.

[0039] In some specific embodiments, in step S1, solvent I is a mixed solvent of isopropanol and water, wherein the ratio of isopropanol to water is (30:70) to (70:30); in step S2, solvent II used to prepare the low molecular weight gel solution is one or more of methanol, ethanol, isopropanol, n-propanol, n-octanol, acetophenone, chloroform, toluene, and benzene.

[0040] In some specific embodiments, in step S1 or step S2, the loading method of the nanofiber suspension or low molecular weight gel solution includes one of spin coating, spray coating, blade coating or impregnation adsorption.

[0041] Example 1

[0042] This embodiment provides a dual-network structure membrane composed of nanofibers and nanomesh and its preparation method, including a porous substrate and a dual-network structure loaded on the surface of the porous substrate. The dual-network structure is composed of nanofibers and a low molecular weight gel nanomesh. The specific preparation method includes the following steps:

[0043] S1. Ethylene-vinyl alcohol copolymer nanofibers are dispersed in a mixed solvent of isopropanol and water (volume ratio of isopropanol and water is 50:50) to obtain a nanofiber suspension. The nanofiber suspension is then loaded onto the surface of a porous substrate by spraying to obtain a nanofiber membrane. The concentration of the nanofiber suspension is 1 wt%.

[0044] S2. The sorbitol nucleating agent is neutralized with n-propanol and dissolved at 80°C to obtain a sorbitol nucleating agent solution; the concentration of the sorbitol nucleating agent solution is 0.09 wt%.

[0045] S3. The sorbitol nucleating agent solution prepared in step S2 is loaded onto the surface of the nanofiber membrane in step S1 by spraying. After solvent II evaporates, a dual-network structure membrane composed of nanofibers and nanonets is obtained.

[0046] Please see Figure 1 The image shows electron microscope (EM) images of the nanofiber and nanomesh composite dual-network structure membrane prepared in Example 1 at different magnifications. As can be seen from the images, the membrane material exhibits a distinct dual-network structure, with interconnected ultrafine fibers forming between the nanofibers. This indicates that the sorbitol nucleating agent self-assembles between the nanofibers to form a loose network structure, enabling the dual-network structure membrane to possess both excellent mechanical and filtration properties.

[0047] Examples 2-5

[0048] Examples 2-5 provide a dual-network structure membrane composed of nanofibers and nanomesh and its preparation method. Compared with Example 1, the difference is that the concentrations of the sorbitol nucleating agent solutions in Examples 2-5 are 0.08wt%, 0.1wt%, 0.2wt%, and 0.4wt%, respectively; the rest are roughly the same as in Example 1 and will not be repeated here.

[0049] Comparative Example 1

[0050] Comparative Example 1 provides a nanofiber network structure membrane and its preparation method. Compared with Example 1, the difference is that only step S1 is performed to obtain the nanofiber membrane. The rest is roughly the same as Example 1, and will not be described again here.

[0051] The performance of the membrane materials prepared in Examples 1-5 and Comparative Example 1 was tested, including filtration efficiency and pressure drop. The results are shown in the table below.

[0052] Table 1 shows the performance tests of the membrane materials prepared in Examples 1-5 and Comparative Example 1.

[0053] Sorbitol concentration Filtration efficiency (%) Pressure drop (Pa) Example 1 0.09wt% 99.04±0.17 291.67±20.23 Example 2 0.08wt% 95.55±0.30 176.33±4.51 Example 3 0.1wt% 99.12±0.27 333.33±26.01 Example 4 0.2wt% 92.69±1.74 123.33±4.93 Example 5 0.4wt% 91.09±0.53 100.33±3.06 Comparative Example 1 0％ 89.287±0.66 105±1.73

[0054] Table 1 shows that the concentration of the sorbitol nucleating agent solution affects both the filtration efficiency and pressure drop of the membrane material. With increasing concentration, the filtration efficiency initially increases and then decreases; similarly, the pressure drop also initially increases with increasing sorbitol concentration, then decreases. Both filtration efficiency and pressure drop reach their maximum when the sorbitol concentration is 0.1 wt%. The optimal concentration is 0.08 wt%, exhibiting high filtration efficiency and relatively low pressure drop. Comparative Example 1 shows that the filtration efficiency and pressure drop of a single nanofiber membrane are both low.

[0055] Examples 6-7

[0056] Examples 6 and 7 respectively provide a dual-network structure membrane composed of nanofibers and nanomesh and its preparation method. Compared with Example 1, the difference is that the concentration of sorbitol nucleating agent solution in Examples 6 and 7 is 0.08wt% and 0.1wt% respectively, and the loading method is immersion instead of spraying; the rest is roughly the same as Example 1, and will not be repeated here.

[0057] Please see Figure 2 The figures show electron micrographs of the nanofiber and nanomesh composite double-network structure membranes prepared in Examples 1 and 6-7; where (a) is Example 6, (b) is Example 1, and (c) is Example 7. As can be seen from the figures, membrane materials with a distinct double-network structure were also prepared by loading nanofibers or low molecular weight gels using the immersion method, and interconnected ultrafine fibers were formed between the nanofibers.

[0058] In summary, this invention provides a dual-network structure membrane composed of nanofibers and nanomesh, and its preparation method. The dual-network structure membrane includes a porous substrate and a dual-network structure loaded on the surface of the porous substrate. The dual-network structure is composed of nanofibers and a low-molecular-weight gel nanomesh. This invention first loads a nanofiber network onto the surface of the porous substrate, and then assembles a low-molecular-weight gel in situ into the nanofiber network. Because the nanofiber network has the characteristics of ultrafine fibers, small pore size, and high porosity, the low-molecular-weight gel, after loading, forms a strong connection between the nanofibers and can self-assemble to form a loose and stable dual-network structure. While enhancing mechanical properties, it avoids increasing the packing density and resistance of the nanofiber network, which would adversely affect the filtration performance of the membrane material. The resulting layered and interconnected dual-network structure membrane possesses both excellent mechanical properties and air filtration performance. This invention utilizes the strong interaction between nanofibers and low molecular weight gels, and by controlling the diameter of the nanofibers and the concentration of the low molecular weight gel solution, the two self-assemble to form a dual-network structure of nanofibers and nanomesh composites. This dual-nano-network structure membrane has high air filtration efficiency and low air filtration resistance, and has good application prospects in the field of air filtration and protection.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a dual-network structure membrane composed of nanofibers and nanomesh, characterized in that, The dual-network structure membrane composed of nanofibers and nanomesh includes a porous substrate and a dual-network structure loaded on the surface of the porous substrate. The dual-network structure is composed of nanofibers and low molecular weight gel nanomesh. The low molecular weight gel nanonet is a nanonet formed by sorbitol nucleating agent; The preparation method includes the following steps: S1. Disperse nanofibers in solvent I to obtain a nanofiber suspension, and load the nanofiber suspension onto the surface of a porous substrate to obtain a nanofiber membrane; S2. The low molecular weight gel is neutralized with solvent II and dissolved at a certain temperature to obtain a low molecular weight gel solution; the concentration of the low molecular weight gel solution is 0.02wt% to 0.5wt%; the low molecular weight gel is a sorbitol nucleating agent; S3. Load the low molecular weight gel solution prepared in step S2 onto the surface of the nanofiber membrane in step S1. After solvent II evaporates, the dual-network structure membrane composed of nanofibers and nanonets is obtained.

2. The method for preparing the dual-network structure membrane of nanofibers and nanomesh composites according to claim 1, characterized in that, The diameter of the nanofibers is 100–1000 nm.

3. The method for preparing the dual-network structure membrane of nanofibers and nanomesh composites according to claim 2, characterized in that, The diameter of the nanofibers is 800–1000 nm.

4. The method for preparing the dual-network structure membrane of nanofibers and nanomesh composites according to claim 1, characterized in that, The nanofibers are one or more of ethylene-vinyl alcohol copolymer nanofibers, polyester nanofibers, polyacrylonitrile nanofibers, polyamide nanofibers, and polyolefin nanofibers; the porous substrate is a nonwoven porous substrate.

5. The method for preparing the dual-network structure membrane of nanofibers and nanomesh composites according to claim 4, characterized in that, The nanofibers are ethylene-vinyl alcohol copolymer nanofibers.

6. The method for preparing the dual-network structure membrane of nanofibers and nanomesh composites according to claim 1, characterized in that, In step S2, the dissolution temperature of the low molecular weight gel is 60–120°C.

7. The method for preparing a dual-network structure membrane composed of nanofibers and nanomesh according to claim 1, characterized in that, In step S1, the concentration of the nanofiber suspension is 0.5 wt% to 2 wt%.

8. The method for preparing the dual-network structure membrane of nanofibers and nanomesh composites according to claim 1, characterized in that, In step S1, solvent I is a mixed solvent of isopropanol and water, wherein the ratio of isopropanol to water is (30:70) to (70:30); in step S2, solvent II used to prepare the low molecular weight gel solution is one or more of methanol, ethanol, isopropanol, n-propanol, n-octanol, acetophenone, chloroform, toluene, and benzene.

9. The method for preparing a dual-network structure membrane composed of nanofibers and nanomesh according to claim 1, characterized in that, In step S1 or step S3, the loading method of the nanofiber suspension or the low molecular weight gel solution includes one of spin coating, spray coating, blade coating or impregnation adsorption.

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