Preparation method of temperature and humidity synergistic response type carbon dioxide regulation and control aerogel

Abstract

The invention discloses a preparation method of temperature and humidity synergistic response type carbon dioxide regulation aerogel, and belongs to the field of functional materials. The method sequentially comprises the following steps: polymerizing N-isopropylacrylamide in a nanocellulose dispersion liquid to form first temperature-sensitive network hydrogel; immersing the wet gel into alkali liquor containing polyethyleneimine and a quaternary ammonium salt modifier, and carrying out synchronous in-situ grafting to construct a second network and a third network, so as to obtain three-network interpenetrating wet gel; carrying out integral hydrophobic modification by using a methyl trimethoxy silane alcohol solution in a wet gel state, and integrating an antibacterial agent; and finally, carrying out programmed cooling freezing and freeze drying to obtain the three-dimensional porous aerogel. According to the method, through sequential construction and synchronous grafting, uniform and stable compounding of a functional network is ensured, wet gel state overall hydrophobic treatment is combined, and the product has high hydrophobicity, excellent structural stability and a temperature and humidity synergistic response type CO2 regulation and control function and is suitable for the fields of fruit and vegetable preservation and the like.

Description

Technical Field

[0001] This invention relates to the field of functional materials preparation technology, specifically to a method for synthesizing a smart aerogel with a complex interpenetrating network structure. More specifically, this invention relates to a method for preparing a smart aerogel capable of preserving fruits and vegetables and possessing dual-response temperature and humidity control and synergistic carbon dioxide regulation functions through sequential steps and a simultaneous in-situ grafting process. Background Technology

[0002] With the ever-increasing demands on the performance of smart materials, the precise control of the structure and functional integration of materials at the nano or micro scale has become a core challenge in the fabrication process. For smart aerogels designed for use in dynamically changing environments, their performance is highly dependent on the uniformity of distribution, binding strength, and synergistic relationship of functional components (such as responsive units and adsorption sites) in the three-dimensional network.

[0003] Existing methods for preparing cellulose-based functional materials, such as the one-pot method for preparing cellulose-based porous materials by crosslinking epoxy-functionalized polyethyleneimine (PEI) and epichlorohydrin as reported in Chinese patent publication CN115845810B, or the blending-freeze-drying method described in the article "Quaternized Chitosan / PVA Aerogels for Reversible CO2 Capture," while simple in process, are prone to uneven distribution of functional components, phase separation, or weak binding forces (such as physical adsorption). Under long-term use or cyclic stress, these methods are susceptible to functional degradation or structural damage. Especially for composite materials requiring the integration of multiple responsive and adsorption functions, traditional one-step or simple blending methods struggle to achieve stable and uniform interpenetration and coupling between functional networks.

[0004] Furthermore, existing processes often fail to adequately consider the harshness of the end-use environment of the materials. For example, the preservation environment for fruits and vegetables requires aerogels to be exposed to near-saturated high humidity conditions for extended periods. Hydrophilic aerogels prepared by conventional methods will experience pore collapse under such conditions due to capillary forces. Although some literature uses post-treatment to achieve surface hydrophobicity, this method is difficult to uniformly and thoroughly modify the complex pores inside the material, and cannot fundamentally solve the stability problem.

[0005] Therefore, there is an urgent need to develop a new preparation method that can: 1) construct a stable interpenetrating network framework in a stepwise and orderly manner; 2) accurately and uniformly anchor multiple functional groups on the network framework at the molecular level in a covalent manner; and 3) achieve effective hydrophobic protection of the overall structure (including internal pores) during the material forming process, thereby preparing a smart aerogel material with stable structure, synergistic function, and strong environmental tolerance. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings of existing preparation techniques and provide a new method for efficiently and reliably preparing structurally stable and functionally synergistic smart aerogels. The aerogels prepared by this method can precisely respond to changes in temperature and humidity in the fruit and vegetable preservation environment, achieving intelligent dynamic control of carbon dioxide concentration.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for preparing a temperature and humidity synergistically responsive carbon dioxide-regulated aerogel, characterized by comprising the following sequential steps:

[0009] S1. Constructing the first temperature-sensitive network: In an aqueous dispersion of nanocellulose with a concentration of 0.5wt% to 3.0wt%, N-isopropylacrylamide monomer, crosslinking agent, and initiator are added, and a polymerization reaction is carried out at 55°C to 65°C under nitrogen protection to form a primary hydrogel with poly(N-isopropylacrylamide) as the first network; wherein, the mass ratio of N-isopropylacrylamide monomer to nanocellulose is 1:1 to 10:1;

[0010] S2. Simultaneous in-situ construction of the second and third networks: The primary hydrogel is immersed in an aqueous sodium hydroxide solution containing an amino compound and a quaternary ammonium salt modifier, and reacted for 4 to 8 hours at 40°C to 60°C and pH 9 to 11, so that the amino compound and quaternary ammonium salt groups are simultaneously covalently grafted in situ onto the nanocellulose skeleton in the primary hydrogel, forming a three-network wet gel with an interpenetrating structure.

[0011] S3. Overall hydrophobicity and functional integration: The three-network wet gel is immersed in an alcohol solution of hydrophobic modifier, and an antibacterial agent is added during or after the immersion process;

[0012] S4. Directional freeze-drying molding: The wet gel treated in step S3 is subjected to programmed cooling and then freeze-dried to obtain a three-dimensional porous bulk aerogel.

[0013] Preferably, in step S1, the crosslinking agent is N,N'-methylenebisacrylamide, and its amount is 0.5% to 2% of the mass of the N-isopropylacrylamide monomer; the initiator is ammonium persulfate, and its amount is 0.5% to 3% of the mass of the N-isopropylacrylamide monomer.

[0014] Preferably, in step S2, the amino compound is polyethyleneimine with a weight-average molecular weight of 600 to 10,000; the quaternary ammonium salt modifier is 2,3-epoxypropyltrimethylammonium chloride; and the ratio of the total number of moles of amino groups in the amino compound to the sum of the number of moles of the quaternary ammonium salt modifier to the number of moles of hydroxyl groups in the nanocellulose is 0.2:1 to 2.0:1.

[0015] Preferably, in step S3, the hydrophobic modifier is methyltrimethoxysilane, the alcohol solution is an ethanol solution with a concentration of 10 vol% to 20 vol%, the volume ratio of the alcohol solution to the mass of the triple network wet gel is (10-50) mL / g, the soaking time is 0.5 to 2 hours, and the antibacterial agent is cinnamon essential oil or vanillin, with a loading of 1% to 5% of the total weight of the aerogel.

[0016] Preferably, in step S4, the programmed cooling freezing is performed at a rate not exceeding 5°C / min to -45°C to -55°C; the freeze-drying conditions are: cold trap temperature below -50°C, vacuum degree below 10Pa, and drying time of 40 to 56 hours.

[0017] More preferably, after step S4, step S5 is further included: heat-treating the aerogel at 100°C to 130°C for 0.5 to 1.5 hours to enhance network crosslinking.

[0018] The beneficial effects of this invention include:

[0019] 1. "Sequential Construction and Synchronous Grafting" Ensures Precise Functional Integration and Synergy: This invention adopts a strategy of "first constructing a stable temperature-sensitive network template, then simultaneously grafting adsorption and humidity-sensitive functions." The initially formed poly(N-isopropylacrylamide) / cellulose primary network provides a pre-existing, well-ordered three-dimensional reaction field. In step S2, polyethyleneimine (amine group) and quaternary ammonium salt modifier undergo synchronous in-situ covalent grafting within this network, ensuring that the two functional molecules are uniformly and firmly fixed on the cellulose backbone and naturally form a structure that interpenetrates with the first network. This process avoids the steric hindrance and uneven distribution that may be caused by stepwise grafting, and also eliminates the phase separation problem caused by physical blending. It is the technological basis for achieving efficient synergy of the "temperature-humidity-adsorption" ternary network within the material.

[0020] 2. "Overall hydrophobicity in the wet gel state" provides excellent environmental stability: This invention innovatively performs silanization hydrophobic treatment in the wet gel state before freeze-drying. At this time, the alcohol solution of the hydrophobic modifier (methyltrimethoxysilane) can fully wet and modify all surfaces of the entire three-dimensional network, including the inner walls of the deepest pores, thanks to its excellent permeability. After subsequent drying and molding, the material achieves uniform and durable superhydrophobicity from the inside out, fundamentally overcoming the common problem of structural instability of aerogels in high humidity applications.

[0021] 3. Optimized hierarchical pore structure through "directional freeze-drying": By controlling the freezing rate (≤5℃ / min), ice crystals are induced to grow slowly along a specific direction, thereby forming a well-oriented macroporous template in the gel. After freeze-drying, these ice crystals sublimate, leaving behind hierarchical pores with good interconnectivity and concentrated pore size distribution, which is conducive to rapid gas diffusion and mass transfer, and improves adsorption kinetics performance.

[0022] 4. Strong process controllability, conducive to scale-up production: The reaction conditions in each step are mild and the parameters are well-defined, requiring no special or expensive equipment. The process scale-up path from gram-level preparation in the laboratory to large-scale production is clear, with good repeatability, and has good industrialization prospects. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification, but do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a schematic diagram of the process flow for the preparation method of the present invention.

[0025] Figure 2 This is a comparison chart showing the performance retention rate of aerogels prepared using the method of the present invention (Example 1) and Comparative Example 1 (physical blending method) in five adsorption-desorption cycle tests.

[0026] Figure 3 This is a comparison chart showing the volume retention of aerogels that were not hydrophobically treated (Comparative Example 2) and those that were hydrophobically treated by the method of the present invention (Example 1) after being placed in a high humidity environment (RH 93%) for different times.

[0027] Figure 4 The images show a comparison of scanning electron microscope (SEM) images of the examples and comparative samples. (a) shows the microstructure of sample F from Example 1; (b) shows the pore structure of sample H from Example 2 (freezing rate 1℃ / min); (c) shows the pore structure of sample G from Example 2 (freezing rate 10℃ / min); and (d) shows the microstructure of sample I from Comparative Example 1, where phase separation regions are visible. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solution of the present invention, the preparation method of the present invention will be described in detail below with reference to specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the reagents used are all available from commercial sources.

[0029] Example 1: Preparation method of aerogel

[0030] This embodiment details the process flow and parameter control of the preparation method described in this invention.

[0031] S1: Construction of the first temperature-sensitive network: In a three-necked flask containing 100 g of 1.5 wt% nanocellulose suspension, add 5.0 g of N-isopropylacrylamide and 0.05 g of N,N'-methylenebisacrylamide, and bubble with nitrogen to remove oxygen for 30 minutes. Heat the mixture to 60°C in a water bath, and quickly add 0.05 g of ammonium persulfate (dissolved in 1 mL of water). Stir the reaction at 60°C under nitrogen protection for 2 hours to obtain a homogeneous and elastic primary hydrogel.

[0032] S2: Simultaneous in-situ construction of the second and third networks: Prepare 200 mL of an aqueous solution containing 8.0 g of polyethyleneimine (weight-average molecular weight approximately 600) and 2.0 g of 2,3-epoxypropyltrimethylammonium chloride, and adjust the pH to 10.5 with NaOH. Immerse the monolithic hydrogel obtained in step S1 into this solution and place it in a constant temperature shaker at 50°C, shaking at 60 rpm for 6 hours. After the reaction is complete, rinse thoroughly with plenty of deionized water until neutral to obtain a robust three-network wet gel.

[0033] S3: Overall hydrophobicity and functional integration: Transfer the wet gel (approximately 20 g) to 150 mL of 15 vol% methyltrimethoxysilane in ethanol. Simultaneously add 0.10 g of cinnamon essential oil microcapsules. Soak at room temperature for 1 hour, gently agitating several times during this period.

[0034] S4: Directional freeze-drying molding: The gel is placed in a programmed cooling freezer and cooled from 25°C to -50°C at a rate of 2°C / min, and held for 24 hours. Then it is transferred to the freeze dryer chamber pre-cooled to -55°C and dried under a vacuum of <5Pa for 48 hours.

[0035] S5: Post-crosslinking treatment: The dried aerogel was heat-treated in a 120℃ forced-air oven for 1 hour, and after cooling, the final product (denoted as sample F) was obtained. Structural characterization and performance testing of this sample showed that: firstly, it possesses a three-dimensional structure formed by the interpenetration of a poly(N-isopropylacrylamide) thermosensitive network, an adsorption network grafted with polyethyleneimine, and a humidity-responsive network grafted with quaternary ammonium salt groups. Figure 4a) Secondly, its porosity is 92% and its static water contact angle is 148°; thirdly, its adsorption capacity for carbon dioxide at 4℃ and 93% relative humidity is not less than 0.96 mmol / g, and its adsorption capacity change rate is 30% under alternating conditions of 4℃ and 15℃.

[0036] The above results fully demonstrate that the preparation method provided by the present invention can successfully and reproducibly obtain intelligent aerogels with the aforementioned three-dimensional interpenetrating network structure, high hydrophobicity, and temperature and humidity synergistic response carbon dioxide regulation function.

[0037] Example 2: Comparison of Process Parameter Optimization

[0038] Change the freezing rate in step S4: Prepare sample G (freezing rate 10℃ / min) and sample H (freezing rate 1℃ / min), and the remaining steps are the same as in Example 1.

[0039] Characterization results: SEM showed that the pore structure of sample H (slow-frozen) was small, uniform, and interconnected. Figure 4 b); The pore structure of sample G (rapidly frozen) is large and disordered. Figure 4 c). Nitrogen adsorption tests showed that the mesopore volume (2-50 nm) of sample H was approximately 35% larger than that of sample G. In CO2 adsorption kinetic tests, the time required for sample H to reach 90% saturation adsorption was approximately 40% shorter than that for sample G. This demonstrates that slow programmed cooling is beneficial for forming a more regular pore structure that is more conducive to gas transport.

[0040] Comparative Example 1: One-pot physical blending method

[0041] 100g of nanocellulose suspension, 5g of N-isopropylacrylamide, 0.05g of N,N'-methylenebisacrylamide, 8g of polyethyleneimine (weight average molecular weight approximately 600), and 2g of 2,3-epoxypropyltrimethylammonium chloride were mixed uniformly in one step. After deoxygenation, 0.05g of ammonium persulfate was added, and polymerization was carried out at 60°C for 2 hours. Subsequent hydrophobic and freeze-drying steps were the same as in Example 1, yielding Sample I.

[0042] Performance comparison: such as Figure 2 As shown, in the temperature and humidity cycling test under simulated preservation conditions, sample F (using the method of this invention) maintained a CO2 adsorption capacity change rate of over 98% after 5 cycles. However, sample I (using the physical blending method) began to decline in performance after the 3rd cycle, and the retention rate was only 72% after the 5th cycle. SEM showed obvious phase separation regions within sample I. Figure 4 d). This demonstrates that the stepwise synchronous grafting process of the present invention has significant advantages in constructing stable, uniform, and durable functional networks.

[0043] Comparative Example 2: No pre-hydrophobic treatment

[0044] The preparation process is the same as in Example 1, but the hydrophobic treatment in step S3 is completely omitted. The three-network wet gel obtained in S2 is directly freeze-dried to obtain sample J.

[0045] Stability comparison: such as Figure 3 As shown, samples F and J were placed in an environment of 4°C and 93% RH. After 72 hours, sample J showed a volume shrinkage rate of 65%, severe structural collapse, and a decrease in adsorption capacity of over 60%; while sample F maintained a volume retention rate of over 95%, retained its morphology, and exhibited a performance retention rate of >95%. This comparison strongly demonstrates the indispensability of the "wet gel state overall hydrophobicity" process for ensuring the structural integrity and functional stability of materials under extreme high humidity environments.

[0046] The above description is merely a preferred embodiment of the method of the present invention. Any equivalent adjustments or modifications made to the process parameters (such as concentration, temperature, and time) by those skilled in the art, based on an understanding of the principles of the present invention, should be included within the scope of protection of the present invention. The scope of protection of the present invention should be defined by the claims.

Claims

1. A preparation method of a temperature and humidity synergistically responsive carbon dioxide regulation aerogel, characterized in that, Comprising the following sequential steps: S1. Constructing a first temperature-sensitive network: adding N-isopropyl acrylamide monomer, crosslinking agent and initiator into a nanocellulose water dispersion with a concentration of 0.5wt% to 3.0wt%, and performing polymerization reaction at 55℃ to 65℃ under nitrogen protection to form a primary hydrogel with poly(N-isopropyl acrylamide) as the first network; S2. Simultaneously constructing a second and a third network in situ: immersing the primary hydrogel as a whole into a sodium hydroxide aqueous solution containing an amino compound and a quaternary ammonium salt modifier, and performing reaction at 40℃ to 60℃ and pH value of 9 to 11 for 4 to 8 hours to enable the amino compound and the quaternary ammonium salt group to be simultaneously covalently grafted in situ on the nanocellulose skeleton within the primary hydrogel, thereby forming a three-network wet gel with interpenetrating structure; S3. Integrating hydrophobicity and functionality as a whole: immersing the three-network wet gel into an alcohol solution of a hydrophobic modifier, and adding an antibacterial agent during or after the immersion process; S4. Directional freeze-drying molding: performing programmed temperature reduction freezing on the wet gel treated in step S3, and then performing freeze-drying to obtain a three-dimensional porous block aerogel.

2. The production method according to claim 1, characterized by, In step S1, the mass ratio of the N-isopropyl acrylamide monomer to the nanocellulose is 1:1 to 10:1; the crosslinking agent is N,N'-methylenebisacrylamide, and the amount of the crosslinking agent is 0.5% to 2% of the mass of the N-isopropyl acrylamide monomer; and the initiator is ammonium persulfate, and the amount of the initiator is 0.5% to 3% of the mass of the N-isopropyl acrylamide monomer.

3. The preparation method according to claim 1, characterized in that, In step S2, the amino compound is polyethyleneimine with a weight average molecular weight of 600 to 10,000; the quaternary ammonium salt modifier is 2,3-epoxypropyltrimethylammonium chloride; and the ratio of the total moles of amine groups contained in the amino compound to the moles of the quaternary ammonium salt modifier to the moles of hydroxyl groups of the nanocellulose is 0.2:1 to 2.0:

1.

4. The method of claim 1, wherein, In step S3, the hydrophobic modifier is methyltrimethoxysilane, the alcohol solution is an ethanol solution with a concentration of 10vol% to 20vol%, the ratio of the volume of the alcohol solution to the mass of the three-network wet gel is (10-50)mL / g, the immersion treatment time is 0.5 to 2 hours, and the antibacterial agent is cinnamon essential oil or vanillin with a loading amount of 1% to 5% of the total weight of the aerogel.

5. The preparation method according to claim 1, characterized in that, In step S4, the programmed temperature reduction freezing is performed at a rate of not more than 5℃ / min to -45℃ to -55℃ and maintained for 24 to 48 hours, and the freeze-drying is performed under the conditions of a cold trap temperature lower than -50℃, a vacuum degree lower than 10Pa, and a drying time of 40 to 56 hours.

6. The method of claim 1, wherein, After step S4, step S5 is further included: performing heat treatment on the aerogel at 100℃ to 130℃ for 0.5 to 1.5 hours to strengthen network crosslinking.

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