Preparation method of cellulose ester-based asymmetric porous membrane capable of enhancing solvent steam response performance through heat treatment

Abstract

The invention belongs to the technical field of functional membrane materials, and provides a preparation method of a cellulose ester-based asymmetric porous membrane capable of enhancing solvent steam response performance through heat treatment, cellulose is subjected to esterification modification by fatty acyl chloride containing C = C double bonds, and the cellulose ester-based asymmetric porous membrane is prepared by taking the cellulose ester-based asymmetric porous membrane as a construction unit and combining a cationic surfactant benzalkonium chloride. Self-assembly is realized in a tetrahydrofuran solution through a slow volatilization process of a solvent, and a novel membrane material with an asymmetric porous structure is successfully constructed; the membrane shows obvious pore size difference at the top and the bottom, the pore size at the top is 0.6-4.9 microns, the pore size at the bottom is mainly concentrated in a range of 0.8-1.5 microns, an asymmetric structure with double-sided pore size difference is formed, and after the prepared asymmetric porous membrane is treated at the temperature of 50-130 DEG C, the cyclohexane steam response performance of the prepared asymmetric porous membrane is remarkably enhanced, and rapid bending response can be realized within 0.6 s; in other common organic solvent steam such as ethanol, acetone, tetrahydrofuran, methanol and the like, observable deformation response can be generated within 7s.

Description

Technical Field

[0001] This invention belongs to the field of functional membrane materials technology, and particularly relates to a method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance through heat treatment. Background Technology

[0002] With the widespread application of smart responsive materials in sensors, actuators, wearable devices, and environmental monitoring, the development of functional membrane materials that respond to external stimuli (such as temperature, humidity, light, pH, and solvent vapor) has become a research hotspot. Among them, solvent vapor responsive materials, due to their reversible morphological, dimensional, or mechanical property changes in response to specific organic solvent vapors, show significant application potential in gas sensing, controlled release, and intelligent separation.

[0003] Asymmetric porous membranes, due to the pore size gradient or structural density differences along their thickness, possess unique mass transfer regulation capabilities, enabling selective permeation, directional transport, and interfacial reaction control. They are widely used in membrane separation, biosensing, smart actuation, and flexible devices. In recent years, natural polymer materials have gradually become an important direction in membrane material research due to their renewability, environmental friendliness, and functional tunability. Among them, cellulose and its nanostructure derivatives (such as cellulose nanocrystals and cellulose nanofibers) exhibit significant advantages in functional membrane construction due to their high specific surface area, good mechanical properties, abundant hydroxyl active sites, and wide availability, non-toxicity, and biodegradability. By modifying the surface of cellulose-based materials with hydrophobic or functional chemicals, their interfacial properties can be regulated, endowing them with specific responsive behaviors and enabling responses to external environmental stimuli (such as temperature, pH, light, and solvents).

[0004] Currently, some studies have attempted to modify cellulose hydrophobically using esterification, grafting, and other methods to improve its stability in organic environments or achieve responsive performance. However, most modification methods suffer from insufficient structural control precision, poor membrane uniformity, or limited response sensitivity. This is particularly true in the construction of asymmetric porous membranes, where efficient and controllable preparation methods are still lacking. Therefore, there is an urgent need to develop a functional membrane preparation technology that is structurally tunable, exhibits excellent responsiveness, and is environmentally friendly, to meet the application needs of high-performance solvent vapor response materials in smart devices and environmental fields. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance through heat treatment. This method aims to solve the problems of uncontrollable structure, insufficient response performance, and poor biodegradability of existing responsive membrane materials, especially the lack of efficient and controllable preparation strategies for constructing asymmetric porous membranes with well-defined structures and rapid responses.

[0006] The objective of this invention is achieved as follows:

[0007] A method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response through heat treatment. The method involves esterifying a fatty acyl chloride containing double bonds with cellulose nanocrystals to obtain a modified cellulose material with both hydrophobic and flexible properties. Using this material as a building block, and with the assistance of the cationic surfactant benzalkonium chloride, the membrane self-assembles in a tetrahydrofuran solution through a slow solvent evaporation process. After annealing, a novel membrane material with an asymmetric porous structure that enhances solvent vapor response through heat treatment is constructed.

[0008] The method for preparing the above-mentioned heat-treated cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response is characterized by the following specific steps:

[0009] Step 1: The cellulose is pre-dried and then dispersed in anhydrous pyridine. A uniform suspension is formed by magnetic stirring. Fatty acyl chloride is slowly added under light-protected conditions while maintaining a constant temperature. The reaction time is controlled within 0.5 h to 10 h to obtain the reaction system.

[0010] Step 2: Pour the reaction system into excess ethanol to precipitate the product, then centrifuge the precipitated product and dry the lower precipitate. After drying, disperse it in tetrahydrofuran to obtain a dispersion.

[0011] Step 3: Repeat step 2 5 to 10 times to obtain a dispersion of fatty acyl chloride acylated cellulose dissolved in tetrahydrofuran;

[0012] Step 4: Adjust the mass concentration of the dispersion of fatty acyl chloride acylated cellulose dissolved in tetrahydrofuran to 2 mg / mL to 30 mg / mL, and after magnetic stirring, obtain a uniform fatty acyl chloride acylated cellulose solution.

[0013] Step 5: Weigh out the appropriate amount of benzalkonium chloride according to the range of 10% to 80% of the mass of fatty acyl chloride acylated cellulose, add it to the fatty acyl chloride acylated cellulose solution, and continue to stir magnetically to obtain a uniform fatty acyl chloride acylated cellulose / benzalkonium chloride mixture.

[0014] Step 6: Slowly pour the 10-30 mg / mL fatty acyl chloride acylated cellulose / benzalkonium chloride mixture into a glass petri dish or flat mold, and loosely cover it with a glass lid or aluminum foil to keep the system under limited ventilation, thereby slowing down the solvent evaporation rate and controlling the ambient temperature and relative humidity. After the solvent has completely evaporated, a dry film with a thickness of about 20-80 μm is obtained.

[0015] Step 7: Use a knife to make a circumference around the edge of the glass culture dish or mold, then add ethanol and soak repeatedly to fully remove unreacted or unbound benzalkonium chloride from the membrane. Then take out the membrane and rinse it with 90% to 100% ethanol 2 to 3 times, followed by heat treatment to obtain a cellulose ester-based asymmetric porous membrane with enhanced response performance after heat treatment.

[0016] The above-mentioned method for preparing cellulose ester-based asymmetric porous membranes with enhanced solvent vapor response performance through heat treatment, wherein the fatty acyl chloride in step 1 is an unsaturated fatty acyl chloride with a fatty chain length of 6 to 16; the cellulose pre-drying treatment involves placing the cellulose sample in a vacuum drying oven at a temperature of 60℃ to 80℃ for vacuum drying for ≥24 hours.

[0017] The preferred unsaturated fatty acyl chloride with a fatty chain length of 6 to 16 is 10-undecenoyl chloride.

[0018] The above-described method for preparing cellulose ester-based asymmetric porous membranes with solvent vapor response,

[0019] The magnetic stirring speed in step 1 is 200 r / min to 800 r / min;

[0020] The constant temperature is 50℃~100℃;

[0021] The molar ratio of dehydrated glucose units to 10-undecenoyl chloride in the cellulose is 1:1 to 6.

[0022] The above-mentioned method for preparing cellulose ester-based asymmetric porous membranes with enhanced solvent vapor response performance through heat treatment, wherein the cellulose in step 1 is at least one of cellulose nanocrystals, cellulose nanofibers, microcrystalline cellulose, bleached chemical pulp of coniferous wood or bleached chemical pulp of broadleaf wood.

[0023] The anhydrous pyridine is anhydrous pyridine and anhydrous N,N-dimethylacetamide in a volume ratio of 1:0 to 20.

[0024] The above-described method for preparing cellulose ester-based asymmetric porous membranes with enhanced solvent vapor response through heat treatment.

[0025] The centrifugation speed for separating the product in step 2 is 5000 r / min to 10000 r / min;

[0026] The centrifugation time is 5 min to 20 min;

[0027] The reaction temperature during centrifugation is 10℃~30℃.

[0028] The above-described method for preparing cellulose ester-based asymmetric porous membranes with enhanced solvent vapor response through heat treatment.

[0029] The magnetic stirring speed in both step 4 and step 5 is 200 r / min to 800 r / min;

[0030] The magnetic stirring time is 5 min to 2 h.

[0031] The above-described method for preparing cellulose ester-based asymmetric porous membranes with enhanced solvent vapor response through heat treatment.

[0032] The controlled ambient temperature in step 6 is 10℃~50℃;

[0033] The controlled relative humidity is 30% to 90%;

[0034] The settling time is 3 days.

[0035] The above-described method for preparing cellulose ester-based asymmetric porous membranes with enhanced solvent vapor response through heat treatment.

[0036] The soaking time in step 7 is 0.5h to 2h;

[0037] The heat treatment temperature is 50℃~130℃, and the heat treatment time is 10min~40min.

[0038] The cellulose ester-based asymmetric porous membrane prepared by the method described above

[0039] The membrane exhibits a difference in pore size at the top and bottom, with the top pore size ranging from 0.6 to 4.9 μm and the bottom pore size mainly concentrated in the range of 0.8 to 1.5 μm, forming an asymmetric pore structure with a multi-scale gradient distribution; the thickness is 20-80 μm, the response time to cyclohexane vapor is ≤0.1s, and the response time to ethanol, acetone, tetrahydrofuran, and methanol vapor is ≤7s.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] This invention modifies cellulose nanocrystals by esterifying a fatty acyl chloride (10-undecenoyl chloride) containing C=C double bonds with cellulose nanocrystals to obtain a modified cellulose material with both hydrophobic and flexible properties. Using this material as a building block, and with the assistance of the cationic surfactant benzalkonium chloride, a novel membrane material with an asymmetric porous structure is successfully constructed through a slow solvent evaporation process in tetrahydrofuran solution. The membrane exhibits a significant difference in pore size between the top and bottom, with the top pore size ranging from 0.6 to 4.9 μm, while the bottom pore size is mainly concentrated in the range of 0.8 to 1.5 μm, forming an asymmetric porous structure with multi-scale distribution. This unique structural design not only facilitates the directional permeation and diffusion of solvent vapors but also enhances the membrane's deformation directionality and response sensitivity under swelling conditions. The prepared asymmetric porous membrane, after being treated at temperatures ranging from 50 to 130°C, exhibits significantly enhanced responsiveness to cyclohexane vapors, achieving a rapid bending response within 0.1 seconds. In other common organic solvent vapors such as ethanol, acetone, tetrahydrofuran, and methanol, observable deformation responses can also be observed within 7 seconds. This rapid response characteristic is primarily attributed to the synergistic effect of the membrane's asymmetric microstructure and hydrophobic functional groups. The introduced double bond structure endows the material with excellent flexibility and a tunable functional interface, while benzalkonium chloride induces microphase separation during membrane formation. The membrane material is simple to prepare under mild conditions, and the resulting membrane exhibits good stability and repeatability, making it suitable for constructing novel intelligent actuators, flexible sensing elements, and solvent-responsive transmission systems. It holds broad application prospects in soft robotics, environmental monitoring, and smart wearables. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 The images show the tetrahydrofuran solution of 10-undecenoyl cellulose prepared in step 2① of Example 1 and the mixture after adding benzalkonium chloride.

[0044] Figure 2 The dry film obtained in step 2③ of Example 1;

[0045] Figure 3 Electron micrograph of the cellulose ester-based asymmetric porous membrane prepared with 10% benzalkonium chloride obtained in Example 7;

[0046] Figure 4 This is an electron microscope image of the cellulose ester-based asymmetric porous membrane prepared with 20% benzalkonium chloride obtained in Example 7;

[0047] Figure 5 This is an electron microscope image of the cellulose ester-based asymmetric porous membrane prepared with 50% benzalkonium chloride obtained in Example 7;

[0048] Figure 6 This is an electron microscope image of the cellulose ester-based asymmetric porous membrane after heat treatment at 60°C in step three of Example 1.

[0049] Figure 7 This is an electron microscope image of the cellulose ester-based asymmetric porous membrane after heat treatment at 80°C in step three of Example 1.

[0050] Figure 8 This is an electron microscope image of the cellulose ester-based asymmetric porous membrane after heat treatment at 100°C in step three of Example 1.

[0051] Figure 9 This is a photograph of the response behavior of the cellulose ester-based asymmetric porous membrane with enhanced response performance after heat treatment at 60°C in step three of Example 1 in a cyclohexane vapor environment.

[0052] Figure 10 This is a photograph of the response behavior of the cellulose ester-based asymmetric porous membrane with enhanced response performance after heat treatment at 80°C in step three of Example 1 in a cyclohexane vapor environment.

[0053] Figure 11 This is a photograph of the response behavior of the cellulose ester-based asymmetric porous membrane with enhanced response performance after heat treatment at 100°C in step three of Example 1, in a cyclohexane vapor environment. Detailed Implementation

[0054] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0055] A method for preparing a cellulose ester-based asymmetric porous membrane with solvent vapor response is disclosed. The method involves esterifying cellulose nanoparticles with a fatty acyl chloride containing double bonds to obtain a modified cellulose material with both hydrophobic and flexible properties. Using this modified cellulose material as a building block, and with the assistance of the cationic surfactant benzalkonium chloride, the membrane material undergoes self-assembly induced in a tetrahydrofuran solution to construct a novel membrane material with an asymmetric porous structure.

[0056] The specific steps are as follows:

[0057] Step 1: The cellulose is pre-dried and then dispersed in anhydrous pyridine. A uniform suspension is formed by magnetic stirring. Fatty acyl chloride is slowly added under light-protected conditions while maintaining a constant temperature. The reaction time is controlled within 0.5 h to 10 h to obtain the reaction system.

[0058] Step 2: Pour the reaction system into excess ethanol to precipitate the product, then centrifuge the precipitated product and dry the lower precipitate. After drying, disperse it in tetrahydrofuran to obtain a dispersion.

[0059] Step 3: Repeat step 2 5 to 10 times to obtain a dispersion of fatty acyl chloride acylated cellulose dissolved in tetrahydrofuran.

[0060] Step 4: Adjust the mass concentration of the dispersion of fatty acyl chloride acylated cellulose dissolved in tetrahydrofuran to 2 mg / mL to 30 mg / mL, and after magnetic stirring, obtain a homogeneous fatty acyl chloride acylated cellulose solution.

[0061] Step 5: Weigh out the appropriate amount of benzalkonium chloride according to the range of 10% to 80% of the mass of fatty acyl chloride acylated cellulose, add it to the fatty acyl chloride acylated cellulose solution, and continue to stir magnetically to obtain a uniform fatty acyl chloride acylated cellulose / benzalkonium chloride mixture.

[0062] Step 6: Slowly pour the 10-30 mg / mL fatty acyl chloride acylated cellulose / benzalkonium chloride mixture into a glass petri dish or flat mold, and loosely cover it with a glass lid or aluminum foil to keep the system under limited ventilation, thereby slowing down the solvent evaporation rate and controlling the ambient temperature and relative humidity. After the solvent has completely evaporated, a dry film with a thickness of about 20-80 μm is obtained.

[0063] Step 7: Use a knife to make a circumference around the edge of the glass culture dish or mold, then add ethanol and soak repeatedly to fully remove unreacted or unbound benzalkonium chloride from the membrane. Then take out the membrane and rinse it with 90% to 100% ethanol 2 to 3 times, followed by heat treatment to obtain a cellulose ester-based asymmetric porous membrane with enhanced response performance after heat treatment.

[0064] In the above-mentioned method for preparing a cellulose ester-based asymmetric porous membrane with solvent vapor response, the fatty acyl chloride in step 1 is an unsaturated fatty acyl chloride with a fatty chain length of 6 to 16; the cellulose pre-drying treatment is to place the cellulose sample in a vacuum drying oven at a temperature of 60℃ to 80℃ for vacuum drying for ≥24h.

[0065] In the above-mentioned method for preparing a cellulose ester-based asymmetric porous membrane with solvent vapor response, the unsaturated fatty acyl chloride with a fatty chain length of 6 to 16 is preferably 10-undecenoyl chloride.

[0066] In the above-mentioned method for preparing a cellulose ester-based asymmetric porous membrane with solvent vapor response, the magnetic stirring speed in step 1 is 200 r / min to 800 r / min; the constant temperature is 50℃ to 100℃; and the molar ratio of dehydrated glucose units in cellulose to 10-undecenoyl chloride is 1:1 to 6.

[0067] In the above-mentioned method for preparing a heat-treated enhanced cellulose ester-based asymmetric porous membrane with solvent vapor response, the cellulose in step 1 is at least one of cellulose nanocrystals, microcrystalline cellulose, bleached softwood pulp, or bleached broadwood pulp; the anhydrous pyridine is anhydrous pyridine and anhydrous N,N-dimethylacetamide in a volume ratio of 1:0 to 20.

[0068] In the above-mentioned method for preparing a heat-treated enhanced cellulose ester-based asymmetric porous membrane with solvent vapor response, the centrifugation speed of the product in step 2 is 5000 r / min to 10000 r / min; the centrifugation time is 5 min to 20 min; and the reaction temperature during centrifugation is 10℃ to 30℃.

[0069] The method for preparing the above-mentioned heat-treated enhanced cellulose ester-based asymmetric porous membrane with solvent vapor response is characterized in that the magnetic stirring speed in steps 4 and 5 is 200 r / min to 800 r / min; and the magnetic stirring time is 5 min to 2 h.

[0070] In the above-described method for preparing a heat-treated enhanced cellulose ester-based asymmetric porous membrane with solvent vapor response, the controlled ambient temperature in step 6 is 10℃~50℃; the controlled relative humidity is 30%~90%; and the settling time is 3 days.

[0071] The above-described method for preparing heat-treated enhanced cellulose ester-based asymmetric porous membranes with solvent vapor responsiveness

[0072] The soaking time in step 7 is 0.5h to 2h;

[0073] The heat treatment temperature is 50℃~130℃, and the heat treatment time is 10min~40min.

[0074] The cellulose ester-based asymmetric porous membrane prepared by the method described above is characterized in that...

[0075] The membrane exhibits a difference in pore size at the top and bottom, with the top pore size ranging from 0.6 to 4.9 μm and the bottom pore size mainly concentrated in the range of 0.8 to 1.5 μm, forming an asymmetric pore structure with a multi-scale gradient distribution; the thickness is 20-80 μm, the response time to cyclohexane vapor is ≤0.1s, and the response time to ethanol, acetone, tetrahydrofuran, and methanol vapor is ≤7s.

[0076] The same group of compounds in the fatty acyl chloride can also achieve the purpose of this invention, such as various unsaturated acyl chlorides with different chain lengths, such as 12-dodecenoyl chloride and oleoyl chloride, but 10-undecenoyl chloride has the best implementation effect.

[0077] 10-Undecenoyl chloride is an unsaturated aliphatic acyl chloride compound containing C=C double bonds and a medium-to-long carbon chain structure, exhibiting good hydrophobicity and flexibility. Introducing it into the molecular structure of cellulose allows for effective modification of cellulose segments through esterification, not only regulating its polarity and self-assembly behavior but also introducing dynamically responsive groups into the material. This enables the resulting material to undergo reversible deformation or controllable structural changes in response to specific organic solvent vapors, expanding its application potential in smart responsive materials.

[0078] The specific embodiments of the present invention will be described in detail below:

[0079] Example 1

[0080] Step 1: Synthesis of 10-undecenoyl cellulose;

[0081] ① Weigh the dried cellulose nanocrystals, dry them in a vacuum drying oven at 60℃ for 24 hours, and then cool them to room temperature for later use; put the dried cellulose into anhydrous pyridine, adjust the magnetic stirring speed to 600 r / min, and form a uniformly dispersed suspension; under light-protected conditions, slowly add 10-undecenoyl chloride to the suspension at a molar ratio of 1:3 (relative to the dehydrated glucose units in cellulose), while maintaining the reaction temperature at 80℃ and the reaction time at 6 hours.

[0082] ② After the reaction is complete, slowly pour the reaction system from step ① into 5 times the volume of anhydrous ethanol to precipitate the product; centrifuge at 8000 r / min for 5 min at 10℃ and collect the precipitate; redissolve the obtained product in tetrahydrofuran, sonicate for 10 min and repeat the precipitation and washing process for a total of 6 times to finally obtain a tetrahydrofuran dispersion of 10-undecenoyl acylated cellulose.

[0083] Step 2: Preparation of asymmetric porous membranes;

[0084] ① Adjust the tetrahydrofuran dispersion of 10-undecenoyl cellulose prepared in steps ① and ② to a concentration of 20 mg / mL, and stir at 400 r / min for 30 min on a magnetic stirrer to form a homogeneous solution; weigh benzalkonium chloride according to 50% of the mass of 10-undecenoyl cellulose, add it to the above solution, and continue stirring for 1 h to obtain a homogeneous 10-undecenoyl cellulose / benzalkonium chloride mixture. Figure 1 The image shown is a photograph of the prepared tetrahydrofuran solution of 10-undecenoyl acylated cellulose and the mixture after adding benzalkonium chloride.

[0085] ② Slowly pour 10 mL of the mixture from step ②① into a glass petri dish with an inner diameter of 90 mm, cover the mouth of the dish to create a semi-closed environment, and let it stand at 22℃ and approximately 50% relative humidity for 3 days to allow the solvent to slowly evaporate and form a film; the resulting dry film thickness is approximately 59 μm. Figure 2 As shown.

[0086] ③ Immerse the dried membrane from step ② in ethanol for 0.5 hours each time, repeating three times to remove unbound or residual benzalkonium chloride; then remove the membrane, rinse it twice with 90% ethanol, and dry it in a 100℃ oven for 30 minutes to finally obtain a heat-treated cellulose ester-based asymmetric porous membrane with enhanced responsiveness, such as... Figure 8 As shown.

[0087] Step 3: Response performance testing;

[0088] The asymmetric porous membranes prepared in step 2③ were placed in different solvent vapor environments (cyclohexane, ethanol, acetone, tetrahydrofuran, and methanol), and their deformation response behavior was recorded using a camera.

[0089] This embodiment involves dispersing 10-undecenoyl cellulose in tetrahydrofuran to form a stable solution, and adding benzalkonium chloride at 20% by mass to form a homogeneous mixture. Under controlled conditions, the mixture is slowly volatilized and solidified into a film. After ethanol washing and heat treatment at 100°C, a structurally stable asymmetric porous membrane with significantly enhanced responsiveness is successfully constructed. The prepared membrane exhibits typical asymmetric microporous hierarchy characteristics, with a thickness of approximately 59 μm. The pore size distribution at the top is mainly concentrated between 0.6 and 4.8 μm, while the pore size at the bottom is mainly concentrated between 0.8 and 1.0 μm. After heat treatment at 100°C, the structural stability and interfacial gradient of the membrane are further enhanced, resulting in a significant rapid response capability in organic solvent vapors. In a cyclohexane vapor environment, the membrane can undergo rapid bending deformation within 0.6 s, such as... Figure 11As shown in the figure, significant deformation response can also be achieved within 7 seconds in other solvent vapors such as ethanol, acetone, and methanol. This rapid response behavior is mainly attributed to the flexible molecular chain and dynamic interface regulation capability brought about by the double bond structure carried by 10-undecenoyl acylated cellulose; the micro-phase separation and pore network structure induced by benzalkonium chloride; and the stable gradient pore structure and synergistically enhanced interface driving capability formed by the membrane after heat treatment. This method has a simple process and mild operating conditions. The obtained porous membrane has significant advantages in terms of structural regulation, response performance, and environmental adaptability. It is suitable for multiple application scenarios such as solvent vapor response driving, intelligent deformable materials, flexible sensors, and environmental response systems, and shows good application prospects in the fields of soft robots, intelligent devices, and material response control.

[0090] Example 2

[0091] The difference between this embodiment and Example 1 is that the 10-undecenoyl chloride mentioned in step 1① is at least one of the unsaturated fatty acyl chlorides with a fatty chain length of 6 to 16, and the rest is the same as in Example 1.

[0092] Example 3

[0093] The difference between this embodiment and Example 1 or Example 2 is that the cellulose mentioned in step 1① is at least one of microcrystalline cellulose, cellulose nanofibers, bleached chemical pulp of coniferous wood or bleached chemical pulp of broadleaf wood, while the others are the same as in Example 1 or Example 2.

[0094] Example 4

[0095] The difference between this embodiment and one of Examples 1 to 3 is that the cellulose drying in step 1① is specifically vacuum drying in a vacuum drying oven at a temperature of 60℃~80℃ for a vacuum drying time of ≥24h. The rest is the same as in Examples 1 to 3.

[0096] Example 5

[0097] The difference between this embodiment and one of Examples 1 to 4 is that the reaction solvent system described in step 1① is anhydrous pyridine and anhydrous N,N-dimethylacetamide (volume ratio of 1:5), while the rest is the same as in Examples 1 to 4.

[0098] Example 6

[0099] The difference between this embodiment and any one of Examples 1 to 5 is that the concentration of the 10-undecenoyl acylated cellulose tetrahydrofuran solution in step two ① is 5-20 mg / mL; otherwise, it is the same as Examples 1 to 5.

[0100] Example 7

[0101] The difference between this embodiment and any one of Examples 1 to 6 is that the benzalkonium chloride added in step two ① is 5% to 80% by mass of 10-undecenoyl acylated cellulose, and the rest is the same as in Examples 1 to 6.

[0102] like Figure 3 and Figure 4 As shown, Figure 3 Electron micrograph of the cellulose ester-based asymmetric porous membrane prepared with 10% benzalkonium chloride; Figure 4 Electron micrograph of the cellulose ester-based asymmetric porous membrane prepared from the obtained 20% benzalkonium chloride; Figure 5 Electron microscopy images of the cellulose ester-based asymmetric porous membrane prepared with 50% benzalkonium chloride. It can be observed that both the number and size of pores in the porous membrane increase with increasing benzalkonium chloride content. This may be because benzalkonium chloride may lead to more microphase separation regions, thus increasing the number of pores. The asymmetric two-sided pore structure is related to the difference in evaporation rates between the top and bottom surfaces, and the resulting concentration effect, surface tension changes, and temperature gradients. During film formation, the top surface is directly exposed to air, while the bottom surface is in contact with the substrate. The solvent evaporation rate at the top surface is typically higher than that at the bottom. In this process, solvent evaporation from the top surface leads to an increase in solution concentration there, causing a change in surface tension. This change in surface tension encourages the solution to flow from the bottom surface to the top surface, resulting in a structure where the top pore size is larger than that at the bottom. Simultaneously, solvent evaporation leads to a temperature gradient, causing temperature differences between the top and bottom surfaces, further affecting the separation process and pore structure formation.

[0103] Example 8

[0104] The difference between this embodiment and one of Examples 1 to 7 is that the volume percentage of the ethanol solution in step two ① is 70% to 90%, while the rest is the same as in Examples 1 to 7.

[0105] Example 9

[0106] The difference between this embodiment and any one of Examples 1 to 8 is that: the diameter of the glass culture dish used in step 2② is 60-90 mm; the concentration in step 2① is 5-20 mg / mL; the volume taken in step 2② is 5-10 mL; the rest is the same as in Examples 1 to 8.

[0107] Example 10

[0108] The difference between this embodiment and one of Examples 1 to 9 is that the relative humidity in step 2③ is 30-90%, while the rest is the same as in Examples 1 to 9.

[0109] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance through heat treatment, characterized in that, This method involves esterifying fatty acyl chlorides containing C=C double bonds with cellulose to obtain modified cellulose materials with both hydrophobic and flexible properties. Using these modified cellulose materials as building blocks, and with the assistance of the cationic surfactant benzalkonium chloride, the materials undergo a slow solvent evaporation process in a tetrahydrofuran solution to achieve self-assembly, thus constructing a novel membrane material with an asymmetric porous structure.

2. The method for preparing a heat-treated enhanced cellulose ester-based asymmetric porous membrane with solvent vapor response properties according to claim 1, characterized in that, The specific steps are as follows: Step 1: The cellulose is pre-dried and then dispersed in anhydrous pyridine. A uniform suspension is formed by magnetic stirring. Fatty acyl chloride is slowly added under light-protected conditions while maintaining a constant temperature. The reaction time is controlled within 0.5 h to 10 h to obtain the reaction system. Step 2: Pour the reaction system into excess ethanol to precipitate the product, then centrifuge the precipitated product and dry the lower precipitate. After drying, disperse it in tetrahydrofuran to obtain a dispersion. Step 3: Repeat step 2 5 to 10 times to obtain a dispersion of fatty acyl chloride acylated cellulose dissolved in tetrahydrofuran; Step 4: Adjust the mass concentration of the dispersion of fatty acyl chloride acylated cellulose dissolved in tetrahydrofuran to 2 mg / mL to 30 mg / mL, and after magnetic stirring, obtain a uniform fatty acyl chloride acylated cellulose solution. Step 5: Weigh out the appropriate amount of benzalkonium chloride according to the range of 10% to 80% of the mass of fatty acyl chloride acylated cellulose, add it to the fatty acyl chloride acylated cellulose solution, and continue to stir magnetically to obtain a uniform fatty acyl chloride acylated cellulose / benzalkonium chloride mixture. Step 6: Slowly pour the 10-30 mg / mL fatty acyl chloride acylated cellulose / benzalkonium chloride mixture into a glass petri dish or flat mold, and loosely cover it with a glass lid or aluminum foil to keep the system under limited ventilation, thereby slowing down the solvent evaporation rate and controlling the ambient temperature and relative humidity. After the solvent has completely evaporated, a dry film with a thickness of about 20-80 μm is obtained. Step 7: Use a knife to make a circumference around the edge of the glass culture dish or mold, then add ethanol and soak repeatedly to fully remove unreacted or unbound benzalkonium chloride from the membrane. Then take out the membrane and rinse it with 90% to 100% ethanol 2 to 3 times, followed by heat treatment to obtain a cellulose ester-based asymmetric porous membrane with enhanced response performance after heat treatment.

3. The method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance after heat treatment according to claim 2, characterized in that, The fatty acyl chloride mentioned in step 1 is an unsaturated fatty acyl chloride with a fatty chain length of 6 to 16; the cellulose pre-drying treatment is to place the cellulose sample in a vacuum drying oven at a temperature of 60℃ to 80℃ for vacuum drying for ≥24 hours. The preferred unsaturated fatty acyl chloride with a fatty chain length of 6 to 16 is 10-undecenoyl chloride.

4. The method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance after heat treatment according to claim 3, characterized in that, The constant temperature mentioned in step 1 is 50℃~100℃; The molar ratio of dehydrated glucose units to 10-undecenoyl chloride in the cellulose is 1:1 to 6.

5. The method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance after heat treatment according to claim 2, characterized in that, The cellulose mentioned in step 1 is at least one of cellulose nanocrystals, cellulose nanofibers, microcrystalline cellulose, bleached chemical pulp of coniferous wood or bleached chemical pulp of broadleaf wood; The anhydrous pyridine is anhydrous pyridine and anhydrous N,N-dimethylacetamide in a volume ratio of 1:0 to 20.

6. The method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance after heat treatment according to claim 2, characterized in that, The centrifugation time in step 2 is 5 min to 30 min; The reaction temperature during centrifugation is 10℃~30℃.

7. The method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance after heat treatment according to claim 2, characterized in that, The magnetic stirring time in both step 4 and step 5 is 5 min to 2 h.

8. The method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance after heat treatment according to claim 2, characterized in that, The controlled ambient temperature in step 6 is 10℃~50℃; The controlled relative humidity is 30% to 90%; The settling time is 3 days.

9. The method for preparing a cellulose ester-based asymmetric porous membrane with enhanced solvent vapor response performance after heat treatment according to claim 2, characterized in that, The soaking time in step 7 is 0.5h to 2h; The heat treatment temperature is 50℃~130℃, and the heat treatment time is 10min~40min.

10. A cellulose ester-based asymmetric porous membrane prepared by the method described in claim 1, characterized in that, The membrane exhibits a difference in pore size at the top and bottom, with the top pore size ranging from 0.6 to 4.9 μm and the bottom pore size mainly concentrated in the range of 0.8 to 1.5 μm, forming an asymmetric structure with a difference in pore size between the two sides; the thickness is 20-80 μm, the response time to cyclohexane vapor is ≤0.1s, and the response time to ethanol, acetone, tetrahydrofuran, and methanol vapor is ≤7s.

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