Nano-cellulose fibril filter material composite filter film as well as preparation method and application of nano-cellulose fibril filter material composite filter film

Abstract

The invention relates to a preparation method of a nano-cellulose fibril filter material composite filter film, which comprises the following steps: adding nano-silica particles into a nano-cellulose fibril aqueous solution to prepare a nano-cellulose fibril suspension, the nano-cellulose fibril aqueous solution contains 1-1.5% by mass of nano-cellulose fibril, and the nano-silica particles are added into the nano-cellulose fibril aqueous solution to prepare the nano-cellulose fibril suspension. The mass of the nano silicon dioxide is 1%-8% of the absolute dry mass of the nano cellulose fibrils; laminating the nanocellulose fibril suspension and a filter base material for multiple times by adopting a vacuum filtration method or a centrifugal dehydration method or a papermaking method to prepare a wet nanocellulose fibril / filter base material composite filter film; and carrying out drying treatment on the obtained wet nano cellulose fibril / filter base material composite filter film. The nano cellulose fibril filter material composite filter film prepared by the method is applied to the field of heterogeneous substance filtration. According to the invention, fine particles are efficiently captured on the premise of accurately regulating and controlling the aperture.

Description

Technical Field

[0001] The invention belongs to the technical field of novel paper-based nanomaterials, and particularly relates to a nano-cellulose fibril filter material composite filter film and a preparation method and application thereof. Background Art

[0002] Against the backdrop of rapid development of science, technology and economy, membrane separation technology has gradually become the core means of material separation and purification due to its high efficiency, environmental protection and sustainability. Compared with traditional separation technology, membrane separation technology has shown extensive application potential in many fields such as petrochemicals, metallurgy, electronics, bioengineering, and medical care due to its advantages such as no need for phase change, low energy consumption, high efficiency, simple technology, and continuous operation at room temperature. Especially when dealing with the separation of heterogeneous substances, membrane separation technology has become a key tool for solving complex separation problems due to its unique advantages.

[0003] Microfiltration membrane and ultrafiltration membrane, as the two core forces in the field of membrane separation technology, have shown powerful functions in the separation and purification process, but the preparation of their existing membrane materials is highly dependent on petroleum-based polymer materials. Such materials not only come from non-renewable petroleum resources, but are also difficult to degrade in the natural environment, posing a long-term burden on the environment. In addition, the preparation process of petroleum-based polymer materials consumes a lot of energy. From raw material extraction to processing and molding, each step is accompanied by a significant carbon footprint, which runs counter to the current global pursuit of green and low-carbon development concepts. More importantly, although petroleum-based polymer membrane materials can effectively filter particles of different sizes according to the pore size, their inherent material properties limit their performance in certain specific application scenarios. For example, existing materials still face challenges in the efficient capture of fine particles. In order to break through this bottleneck, scientists began to seek membrane materials that can efficiently capture fine particles under the premise of precise control of pore size. Summary of the invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a composite filter membrane of nano-cellulose fibril filter material and its preparation method and application. This composite filter membrane not only adjusts the pore size of the filter element filter membrane through nano-silicon dioxide, so that the composite filter membrane has a precisely controllable filtering performance, but also exhibits excellent adsorption and grasping capabilities by virtue of its nano-cellulose fibril's brooming characteristics and rich hydroxyl groups, significantly improving the filtering efficiency for fine particles. At the same time, its high production efficiency, simple preparation process and low cost make this new membrane material occupy a favorable position in the market competition.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The first invention object provided by the present invention is to provide a method for preparing a nanocellulose fibril / filter substrate composite filter membrane, comprising the following steps:

[0007] Nanocellulose fibril aqueous solution was prepared by enzymatic hydrolysis combined with mechanical treatment;

[0008] Adding nano-silicon dioxide particles to a nano-cellulose fibril aqueous solution to prepare a nano-cellulose fibril suspension containing nano-silicon dioxide particles, wherein the mass percentage of the nano-cellulose fibrils in the nano-cellulose fibril aqueous solution is 1% to 1.5%, and the mass of the nano-silicon dioxide is 1% to 8% of the absolute dry mass of the nano-cellulose fibrils in the nano-cellulose fibril aqueous solution;

[0009] The nanocellulose fibril suspension and the filter substrate are stacked multiple times to prepare a wet nanocellulose fibril / filter substrate composite filter membrane, wherein the concentration of the nanocellulose fibril suspension is 0.5% to 6%;

[0010] The wet nanocellulose fibril / filter substrate composite filter membrane obtained above is dried.

[0011] Preferably, the method for preparing the nanocellulose fibril aqueous solution comprises the following steps:

[0012] Soaking the cellulose raw material in water for at least 12 hours to fully swell the cellulose raw material and obtain a cellulose slurry having a cellulose content of 5% to 10%;

[0013] The cellulose slurry prepared above is broken up, and cellulase is added thereto, and then enzymatically treated at a temperature of 40°C to 60°C and a pH of 5.4 to 6.0 for 40min to 60min, and water is added to prepare an enzymatic reaction slurry, wherein the amount of cellulase added is 1000U / g to 2000U / g;

[0014] 1 g to 2 g of a silane coupling agent is added to the enzymatic reaction slurry and then ground to prepare a nanocellulose fibril aqueous solution.

[0015] Preferably, the cellulose raw material is any one of bacterial cellulose, bleached hardwood pulp, bleached softwood pulp, cotton pulp, hemp pulp, bleached straw pulp or bleached bamboo pulp.

[0016] Preferably, the filter substrate is one of filter paper or filter cloth.

[0017] Preferably, the mesh number of the filter cloth is 300-500 meshes, and the mesh number of the filter paper is 100-200 meshes.

[0018] Preferably, the drying treatment includes rolling and hot pressing, and the nanocellulose fibril / filter substrate composite filter membrane obtained by vacuum filtration, centrifugal dehydration, or papermaking is rolled at 50°C to 80°C to remove excess moisture, and then placed in a hot pressing drying at a temperature of 80°C to 100°C.

[0019] Preferably, the centrifugal speed during the centrifugal dehydration treatment is 10000rpm~25000rpm, the centrifugal time is 5min~10min, and the vacuum degree during the vacuum filtration treatment is 0.08MPa~0.1MPa, and the vacuum filtration time is 30min~90min.

[0020] Preferably, when vacuum filtration is performed, a nanocellulose fibril filter cake is obtained, and the nanocellulose fibril film has a quantitative value of 30 g / m 2 When making paper, the pulp used for papermaking is consistent with the nanocellulose fiber pulp, and the paper pulp sheet weight is 50g / m 2 The basis weight of the nanocellulose filament film sheet is 30g / m 2 .

[0021] The second inventive object of the present invention is to provide a method for preparing a nanocellulose fibril / filter substrate composite filter membrane to obtain a nanocellulose fibril / filter substrate composite filter membrane.

[0022] The third inventive object of the present invention is the application of nanocellulose fibril / filter substrate composite filter membrane in the field of heterogeneous material filtration, the filtration retention rate of the nanocellulose fibril / filter substrate composite filter membrane is greater than 99.99%, and when the filter substrate is filter paper, the PM0.3 outlet one-time filtration rate of the nanocellulose fibril / filter paper composite filter membrane reaches more than 99.9%, and the air resistance is less than 160Pa.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention adjusts the pore size of the filter element filter membrane through nano-silicon dioxide to achieve precise control of the filtration accuracy, thereby improving the filtration efficiency of the filter element and meeting various filtration requirements;

[0025] The nanocellulose fibrils prepared by the enzymatic hydrolysis method combined with the mechanical treatment method have unique fibril-forming properties, which endow the nanocellulose fibril / filter substrate composite filter membrane material with excellent filtration performance. With the fibril-forming properties and rich hydroxyl groups of the nanocellulose fibrils, it exhibits excellent adsorption and grasping capabilities; further, by controlling the morphology of the nanocellulose fibrils with fibril-forming properties, the amount of nano-silica added, and the hierarchical composite method with ordinary filter materials (i.e., by carefully considering the aspect ratio of the nanocellulose fibril morphology, the content and size of nano-silica particles, combined with surface modification and cutting-edge nanomaterial technologies), the filtration performance of the composite filter membrane material is adjusted to meet the requirements of ultrafiltration membrane or microfiltration membrane, significantly improving the filtration efficiency for fine particles, so that it can efficiently capture and filter out fine particles.

[0026] 2. As a renewable resource derived from nature, nanocellulose fibrils reduce production costs. In addition, nanocellulose fibrils not only have excellent biocompatibility and degradability, but also exhibit unique physical and chemical properties, such as high specific surface area, good mechanical strength and adjustable pore structure, which make them ideal candidate materials for building efficient filtration systems. By cleverly combining nanocellulose fibrils with appropriate filter matrix materials, composite filter membranes that are both environmentally friendly and can achieve efficient filtration of fine particles can be prepared.

[0027] 3. The performance of customized composite filtration membrane materials can better meet the diverse demands for filtration performance in multiple industries, from petrochemicals to biomedicine.

[0028] 4. Through continuous innovation and exploration, the present invention provides a method for preparing a nanocellulose fibril / filter substrate composite filter membrane. The preparation process is simple and efficient, and the cost of materials and equipment required is relatively low. This not only makes it possible to achieve large-scale production, but also greatly reduces production costs, thereby accelerating the commercialization of membrane separation technology. This significant advantage makes the nanocellulose fibril / filter substrate composite filter thin material more competitive in the market and provides efficient and environmentally friendly separation solutions for all walks of life.

[0029] 5. The nanocellulose fibril / filter substrate composite filter thin material provided by the present invention can be applied in the field of heterogeneous material filtration, which not only injects new vitality into the development and application of membrane separation technology. Moreover, its excellent performance and wide application prospects also provide strong support for all walks of life, and play a key role in promoting sustainable development and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a SEM image of nanocellulose fibrils prepared using coniferous wood bleached pulp as raw material in Comparative Example 1.

[0031] Figure 2 This is a surface SEM image of the nanocellulose fibril film in Comparative Example 1 of the present invention.

[0032] Figure 3 This is a cross-sectional SEM image of the nanocellulose fibril film in Comparative Example 1 of the present invention.

[0033] Figure 4 This is a front SEM image of the nanocellulose fibril film in Example 1 of the present invention.

[0034] Figure 5 This is a front SEM image of the nanocellulose fibril film to which 6% nano-silicon dioxide particles are added in Example 8 of the present invention.

[0035] Figure 6 This is a cross-sectional SEM image of the nanocellulose fibril film that was vacuum dried at room temperature and added with 1% nano-silica particles in Example 12 of the present invention.

[0036] Figure 7 This is a SEM image of regenerated nanocellulose fibrils obtained by infiltrating and dispersing the nanocellulose film after filtration and adsorption in Example 9 of the present invention using water. DETAILED DESCRIPTION

[0037] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified.

[0038] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any numerical value between the two endpoints can be selected. Since the steps and methods used are the same as those in Examples 1-4, in order to avoid redundancy, the present invention describes a preferred embodiment, but the present invention is not limited thereto, but can also be specifically implemented in other ways within the scope of the technical solution defined in the attached claims.

[0039] The inventors found that although existing membrane materials, especially microfiltration membranes and ultrafiltration membranes based on petroleum-based polymer materials, have been widely used in many fields, their preparation process is complex, energy consumption is high, and the filtration efficiency for fine particles is limited. In response to these pain points, the present invention proposes an innovative nanocellulose fibril filter material composite filter membrane and a preparation method thereof. By introducing the ingenious combination of nanocellulose fibrils and nano-silicon dioxide particles, not only the precise control of the filtration pore size is achieved, but also the unique brooming structure of nanocellulose fibrils and the powerful adsorption and grasping ability brought by the rich hydroxyl groups are fully utilized, thereby significantly improving the filtration efficiency for fine particles. This inventive concept not only overcomes the limitations of traditional membrane materials, but also provides a new solution for the efficient and environmentally friendly separation of heterogeneous substances.

[0040] A corresponding nanocellulose fibril / filter substrate composite filter membrane material is prepared according to a method for preparing a nanocellulose fibril / filter substrate composite filter membrane, thereby improving the filtration efficiency of fine particles.

[0041] Application of nanocellulose fibril / filter substrate composite filter membrane in the field of heterogeneous material filtration

[0042] A method for preparing a nanocellulose fibril / filter substrate composite filter membrane, characterized in that it comprises the following steps:

[0043] Nanocellulose fibril aqueous solution was prepared by enzymatic hydrolysis combined with mechanical treatment;

[0044] Adding nano-silicon dioxide particles to a nano-cellulose fibril aqueous solution to prepare a nano-cellulose fibril suspension containing nano-silicon dioxide particles, wherein the mass percentage of the nano-cellulose fibrils in the nano-cellulose fibril aqueous solution is 1%, and the mass of the nano-silicon dioxide is 1% to 8% of the absolute dry mass of the nano-cellulose fibrils in the nano-cellulose fibril aqueous solution;

[0045] The nanocellulose fibril suspension and the filter substrate are stacked multiple times by vacuum filtration, centrifugal dehydration or papermaking to prepare a nanocellulose fibril / filter substrate composite filter membrane;

[0046] The nanocellulose fibril / filter substrate composite filter membrane obtained above is dried.

[0047] Specifically, the method for preparing the nanocellulose fibril aqueous solution comprises the following steps:

[0048] Soaking the cellulose raw material in water for at least 12 hours to fully swell the cellulose raw material and obtain a cellulose slurry having a cellulose content of 5% to 10%;

[0049] The cellulose slurry prepared above is broken up, and cellulase is added thereto, and then enzymatically treated at a temperature of 40°C to 60°C and a pH of 5.4 to 6.0 for 40min to 60min, and water is added to prepare an enzymatic reaction slurry, wherein the amount of cellulase added is 1000U / g to 2000U / g;

[0050] 1 g to 2 g of a silane coupling agent is added to the enzymatic reaction slurry and then ground to prepare a nanocellulose fibril aqueous solution.

[0051] Specifically, the cellulose raw material is any one of bacterial cellulose, bleached hardwood pulp, bleached softwood pulp, cotton pulp, hemp pulp, bleached straw pulp or bleached bamboo pulp.

[0052] Specifically, the filter substrate is one of filter paper or filter cloth.

[0053] Specifically, the mesh number of the filter cloth is 300-500 meshes, and the mesh number of the filter paper is 20-200 meshes. The mesh number is limited here in order to select filter cloth and filter paper with appropriate mesh numbers, so as to limit the escape of water.

[0054] Specifically, the drying treatment includes rolling and hot pressing, wherein the nanocellulose fibril / filter substrate composite filter membrane obtained by vacuum filtration, centrifugal dehydration, or papermaking is rolled at 50°C to 80°C to remove excess water, and then placed in a hot press drying at a temperature of 80°C to 100°C. The rolling temperature and hot pressing given here are for drying the water.

[0055] Specifically, the centrifugal speed during the centrifugal dehydration process is 10000rpm to 25000rpm, the centrifugal time is 5min to 10min, and the vacuum degree during the vacuum filtration process is 0.08MPa to 0.1MPa, and the vacuum filtration time is 30min to 90min. Matching the vacuum degree and the filtration time is conducive to removing moisture.

[0056] There are no mandatory requirements for centrifugation speed and duration. You can first use slow centrifugation to remove excess water, and then increase the centrifugation speed to remove more water. The duration is mainly to ensure that more water is thrown out to improve the efficiency of subsequent hot pressing.

[0057] The nanocellulose fibril filter cake was obtained by vacuum filtration, and the quantitative content of the nanocellulose fibril film was 30 g / m 2 When making paper, the pulp used for papermaking is consistent with the nanocellulose fiber pulp, and the paper pulp sheet weight is 50g / m 2 The basis weight of the nanocellulose filament film sheet is 30g / m 2 .

[0058] The filtration retention rate of the nanocellulose fibril / filter substrate composite filter membrane is greater than 99.99%. When the filter substrate is filter paper, the PM0.3 outlet primary filtration rate of the nanocellulose fibril / filter paper composite filter membrane reaches more than 99.9%, and the air resistance is less than 160Pa.

[0059] The technical solution of the present invention is further illustrated below in the form of specific examples.

[0060] Example 1

[0061] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane provided in Example 1 has the following specific preparation steps:

[0062] (1) Preparation of nanocellulose fibrils: 100 g of bleached softwood pulp was soaked in pure water for no less than 12 hours to prepare a 10% slurry, and the pulp was dispersed for 30 minutes. Cellulase was added to the reactor containing the cellulose pulp at a ratio of 5 mg / g, and the enzymatic hydrolysis reaction was carried out at a pH of 5.4 and a temperature of 40°C for 40 minutes to prepare a slurry with a concentration of 1%. Then, 1 g of methyltrimethoxysilane was added to the slurry with a concentration of 1%, and the slurry was ground using an ultrafine mill until nanocellulose fibrils were obtained, and water was added to correct the concentration of the nanocellulose fibrils to 1%;

[0063] (2) Nanocellulose fibril suspension doped with nanosilica: nanosilica particles are added to the nanocellulose fibril aqueous solution prepared above to obtain a nanocellulose fibril suspension, wherein the amount of nanosilica particles added is 1% of the absolute dry mass of the nanocellulose fibrils;

[0064] (3) Wet nanocellulose fibril film: The nanocellulose fibril suspension prepared above was vacuum filtered to obtain a nanocellulose fibril filter cake. The nanocellulose fibril film had a weight of 30 g / m 2 , the nanocellulose fibril filter cake was placed between two layers of 300-mesh filter cloth;

[0065] (4) Nanocellulose fibril / filter cloth composite filter membrane: The wet nanocellulose fibril / filter cloth composite filter membrane prepared above was rolled at 50° C. to press out excess water, and finally hot-pressed and dried at 105° C. to obtain a nanocellulose fibril / filter cloth composite filter membrane;

[0066] Example 2

[0067] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 2 is similar to that in Example 1, except that the coniferous bleached wood pulp is replaced by any one of bacterial cellulose, broad-leaved bleached wood pulp, cotton pulp, hemp pulp, bleached straw pulp or bleached bamboo pulp.

[0068] Example 3

[0069] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 3 is similar to that in Example 1, except that the added amount of cellulase is replaced by any one of 0 mg / g, 1 mg / g, 2 mg / g, 3 mg / g, 4 mg / g, 6 mg / g, 7 mg / g or 8 mg / g.

[0070] Example 4

[0071] The method for preparing a nanocellulose fibril / filter cloth composite filter membrane given in this Example 4 is similar to that in Example 1, except that the pH value of the cellulose enzymatic hydrolysis reaction is replaced by any one of 5.6, 5.8 or 6.0.

[0072] Example 5

[0073] The method for preparing a nanocellulose fibril / filter cloth composite filter membrane given in this Example 5 is similar to that in Example 1, except that the cellulose enzymatic hydrolysis temperature is replaced by any one of 45°C, 50°C, 55°C, and 60°C.

[0074] Example 6

[0075] The method for preparing a nanocellulose fibril / filter cloth composite filter membrane given in Example 6 is similar to that in Example 1, except that the cellulose enzymatic hydrolysis time of 40 min is replaced by any one of 45 min, 50 min, 55 min, and 60 min.

[0076] Example 7

[0077] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 7 is similar to that in Example 1, except that the mass percentage of nanocellulose fibrils in the nanocellulose fibril aqueous solution is replaced by any one of 0.5%, 2%, 3%, 4%, 5% or 6%.

[0078] Example 8

[0079] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 8 is similar to that in Example 1, except that the added amount of nano-silicon dioxide particles is replaced by any one of 0.5%, 2%, 3%, 4%, 5%, 6%, 7% or 8% of the absolute dry mass of the nanocellulose fibrils.

[0080] Example 9

[0081] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 9 is similar to that in Example 1, except that the mass of added methyltrimethoxysilane can be replaced by any one of 0.5g, 1.5g, 2g, 3g, 4g or 5g.

[0082] Example 10

[0083] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 10 is similar to that in Example 1, except that the mass of methyltrimethoxysilane added can be replaced by any one of trimethylchlorosilane, lactic acid, sodium stearate, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, stearyltrimethylammonium chloride, benzyltrimethylammonium chloride, diallyldimethylammonium chloride, phenyltrimethylammonium chloride, and glycidyltrimethylammonium chloride.

[0084] Embodiment 11

[0085] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 11 is similar to that in Example 1, except that the nanocellulose fibril suspension is replaced by either a centrifugal or papermaking process, wherein the centrifugal treatment is performed at a centrifugal speed of 10000rpm to 25000rpm for 5min to 10min.

[0086] Example 12

[0087] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 12 is similar to that in Example 1, except that the mesh size of the filter cloth is replaced by any one of 350 mesh filter cloth, 400 mesh filter cloth, 450 mesh filter cloth or 500 mesh filter cloth.

[0088] Example 13

[0089] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 13 is similar to that in Example 1, except that the hot pressing drying temperature is replaced by any one of 80°C, 90°C, 100°C, 110°C or 120°C.

[0090] Embodiment 14

[0091] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in this Example 14 is similar to that in Example 1, except that the drying method of the nanocellulose fibril / filter cloth composite filter membrane is replaced by vacuum drying in a vacuum drying oven at room temperature, vacuum drying in a vacuum drying oven at 60°C, and freeze drying.

[0092] Embodiment 15

[0093] The preparation method of a nanocellulose fibril / filter cloth composite filter membrane given in Example 15 is similar to that in Example 1, except that the basis weight of the nanocellulose fibril membrane is 50 g / m 2 .

[0094] Comparative Example 1

[0095] A method for preparing a nanocellulose fibril / filter cloth composite filter membrane, the specific preparation steps are as follows:

[0096] (1) Preparation of nanocellulose fibrils: 100 g of bleached softwood pulp was soaked in pure water for no less than 12 hours to prepare a 10% slurry, and the pulp was dispersed for 30 minutes. Cellulase was added to a reactor containing cellulose pulp at a ratio of 5 mg / g, and enzymatic hydrolysis was carried out at a pH of 5.4 and a temperature of 40° C. for 40 minutes to prepare a slurry with a concentration of 1%. The slurry was ground using an ultrafine mill until nanocellulose fibrils were obtained, and water was added to correct the concentration of the nanocellulose fibrils to 1%;

[0097] (2) Nanocellulose fibril / filter cloth composite filter membrane: The nanocellulose fibril suspension in step (1) is vacuum filtered to obtain a nanocellulose fibril filter cake. The nanocellulose fibril film has a quantitative weight of 30 g / m 2 , the nanocellulose fibril filter cake was placed between two layers of 300-mesh filter cloth;

[0098] (3) Nanocellulose fibril / filter cloth composite filter membrane: The wet nanocellulose fibril / filter cloth composite filter membrane in step (2) is rolled at 50°C to squeeze out excess water, and finally hot-pressed and dried at 105°C to obtain a nanocellulose fibril / filter cloth composite filter membrane.

[0099] Experimental analysis

[0100] Morphology analysis:

[0101] In the detailed study of Comparative Example 1, the nanocellulose fibrils were carefully observed by scanning electron microscopy (SEM), and we significantly captured its unique fibrilization phenomenon (such as Figure 1 This characteristic morphology laid the foundation for subsequent experiments.

[0102] Subsequently, the nanocellulose fibrils without special control were used as raw materials to further process and prepare nanocellulose films. When the surface of the film was analyzed by SEM, we found that it showed a highly dense structure with a smooth surface and no pore channels formed ( Figure 2 This directly reflects the lack of necessary structural regulation during the preparation process.

[0103] Further observation of the cross section of the film ( Figure 3 The SEM image also reveals the compactness of its internal structure, with closely connected layers and a lack of obvious pore structure, which further confirms that it is difficult to spontaneously form a filtration film with a micro-nano pore structure without precise control of the preparation process and film-forming process of nanocellulose fibrils. This discovery not only reveals the key role of structural control in the preparation of nanocellulose films, but also points out the direction for optimizing experiments.

[0104] In Example 1, a nanocellulose fibril film was successfully prepared by introducing 1 gram of methyltrimethoxysilane as a chemical modifier and adding 1% nano-silicon dioxide particles. The cross section of the film was analyzed by SEM ( Figure 4 The results showed that the film surface significantly showed the formation of nanopore structure. This finding preliminarily verified the effectiveness of chemical modification and nanoparticle regulation in promoting the generation of micro-nano voids.

[0105] In Example 8, the amount of nano-silicon dioxide particles added was increased to 6%. This adjustment brought about significant changes (such as Figure 5 The number and distribution of nanopores on the film surface increased significantly and can be seen almost everywhere, showing a more open and porous microstructure. This finding preliminarily verifies the effectiveness of chemical modification and nanoparticle regulation in promoting the generation of micro-nano voids.

[0106] Example 12 uses room temperature vacuum drying technology, and also adds 1% nano-silicon dioxide particles during the preparation process. Figure 6 As shown, the SEM image clearly reveals the looseness of the interlayer structure of the film under this condition, and many tiny gaps appear between the layers, forming unique interlayer nanochannels. This result not only shows that the drying method has a profound impact on the internal structure of the film, but also further confirms that by comprehensively regulating chemical modification, nanoparticle addition and drying process, a nanocellulose fibril filtration membrane with complex micro-nanostructure gaps can be accurately constructed. The experiment not only reveals the synergistic effect of chemical modification and nano-silica regulation in the preparation of nanocellulose fibril films, but also shows that by optimizing the preparation conditions, such as nanoparticle content and drying method, the micro-nano structure of the film can be effectively regulated, thereby preparing a nanocellulose fibril film with excellent filtration performance.

[0107] In Example 9, when 4 g of methyltrimethoxysilane was introduced as a modifier, the prepared composite filtration membrane exhibited excellent filtration performance, specifically, at 20 L / min, the filtration performance of PM 0.3The filtration efficiency is 99.8% and the filtration pressure drop is 175Pa. This significant improvement is mainly attributed to the ingenious layout of nanoparticles on the membrane surface and the deep effect of the modified chemicals, which together finely regulate the micro-nano structure of the membrane material. Specifically, these modification measures greatly increase the roughness of the fiber surface and effectively widen the gap spacing, forming a more complex and efficient capture network, thereby significantly enhancing the film's ability to capture and intercept particulate pollutants. In contrast, the composite filter membrane in Example 1, which has not undergone similar modification, has a dense and almost non-porous surface structure, resulting in the membrane having almost no effective filtration function and being unable to effectively intercept particulate pollutants. This sharp contrast highlights the key role of methyltrimethoxysilane modification in improving the performance of filtration membranes, and provides a strong practical basis and theoretical support for the development of high-efficiency air filtration materials.

[0108] like Figure 7 As shown, Figure 7 The nanocellulose film after filtration and adsorption in Example 9 of the present invention is dispersed by water to obtain regenerated nanocellulose fibrils. From the SEM image, it can be clearly observed that the surface of the nanocellulose fibrils grasps and adheres to the nanoparticles, indicating that the surface of the nanocellulose fibril film has a strong grasping ability.

[0109] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a nanocellulose fibril / filter substrate composite filter membrane, characterized in that: The steps include: Nanocellulose fibril aqueous solution was prepared by enzymatic hydrolysis combined with mechanical treatment; Adding nano-silicon dioxide particles to a nano-cellulose fibril aqueous solution to prepare a nano-cellulose fibril suspension containing nano-silicon dioxide particles, wherein the mass percentage of the nano-cellulose fibrils in the nano-cellulose fibril aqueous solution is 1% to 1.5%, and the mass of the nano-silicon dioxide is 1% to 8% of the absolute dry mass of the nano-cellulose fibrils in the nano-cellulose fibril aqueous solution; The nanocellulose fibril suspension and the filter substrate are stacked multiple times to prepare a wet nanocellulose fibril / filter substrate composite filter membrane, wherein the concentration of the nanocellulose fibril suspension is 0.5% to 6%; The wet nanocellulose fibril / filter substrate composite filter membrane obtained above is dried.

2. The method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to claim 1, characterized in that: The method for preparing a nanocellulose fibril aqueous solution comprises the following steps: Soaking the cellulose raw material in water for at least 12 hours to fully swell the cellulose raw material and obtain a cellulose slurry having a cellulose content of 5% to 10%; The cellulose slurry prepared above is broken up, and cellulase is added thereto, and then enzymatically treated at a temperature of 40°C to 60°C and a pH of 5.4 to 6.0 for 40min to 60min, and water is added to prepare an enzymatic reaction slurry, wherein the amount of cellulase added is 1000U / g to 2000U / g; 1 g to 2 g of a silane coupling agent is added to the enzymatic reaction slurry and then ground to prepare a nanocellulose fibril aqueous solution.

3. The method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to claim 2, characterized in that: The cellulose raw material is any one of bacterial cellulose, bleached broadleaf wood pulp, bleached coniferous wood pulp, cotton pulp, hemp pulp, bleached straw pulp or bleached bamboo pulp.

4. The method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to claim 1, characterized in that: The filter substrate is one of filter paper or filter cloth.

5. The method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to claim 4, characterized in that: The mesh number of the filter cloth is 300-500 meshes, and the mesh number of the filter paper is 100-200 meshes.

6. The method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to claim 1, characterized in that: The drying treatment includes rolling and hot pressing. The nanocellulose fibril / filter substrate composite filter membrane obtained by vacuum filtration, centrifugal dehydration, or papermaking is rolled at 50°C to 80°C to remove excess moisture, and then placed in a hot pressing drying at a temperature of 80°C to 100°C.

7. The method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to claim 6, characterized in that: The centrifugal speed during the centrifugal dehydration treatment is 10000rpm-25000rpm, and the centrifugal time is 5min-10min. During the vacuum filtration treatment, the vacuum degree is 0.08MPa-0.1MPa, and the vacuum filtration time is 30min-90min.

8. The method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to claim 6, characterized in that: The nanocellulose fibril filter cake was obtained by vacuum filtration, and the quantitative content of the nanocellulose fibril film was 30 g / m 2 When making paper, the pulp used for papermaking is consistent with the nanocellulose fiber pulp, and the paper pulp sheet weight is 50g / m 2 The basis weight of the nanocellulose filament film sheet is 30g / m 2 .

9. A nanocellulose fibril / filter substrate composite filter membrane prepared by the method for preparing a nanocellulose fibril / filter substrate composite filter membrane according to any one of claims 1 to 8.

10. Application of the nanocellulose fibril / filter substrate composite filter membrane as claimed in claim 9 in the field of heterogeneous material filtration, wherein the filtration retention rate of the nanocellulose fibril / filter substrate composite filter membrane is greater than 99.99%, and when the filter substrate is filter paper, the PM0.3 outlet primary filtration rate of the nanocellulose fibril / filter paper composite filter membrane reaches more than 99.9%, and the air resistance is less than 160Pa.

Images