Preparation method of a highly elastic bacterial cellulose / KH560 composite aerogel

Abstract

The invention discloses a preparation method of a highly elastic bacterial cellulose / KH560 composite aerogel, which includes: fully mixing KH560, acetic acid and a bacterial cellulose aqueous dispersion evenly, and then standing to form a hydrogel; then performing a freezing treatment on the hydrogel to make it freeze and solidify as a whole; then performing a drying treatment to sublime the solid ice into water vapor, thereby obtaining the bacterial cellulose / KH560 composite aerogel; then performing a heat treatment on the bacterial cellulose / KH560 composite aerogel to reinforce the aerogel skeleton, thereby obtaining the highly elastic bacterial cellulose / KH560 composite aerogel. The preparation process of the invention is simple, and there is no residue of auxiliary agents in the aerogel, and it does not need to be washed and can be directly applied to the water environment for dye adsorption; the prepared composite aerogel has ultra-high compression and rebound performance and anti-fatigue performance, and at the same time has a low thermal conductivity and is suitable for use as a clothing thermal insulation material. Therefore, the composite aerogel is a multifunctional and multi-purpose material.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a preparation method of a highly elastic bacterial cellulose / KH560 composite aerogel. Background Art

[0002] Cellulose is rich in reserves and can be rapidly regenerated, making it an ideal material to replace petrochemical products. Aerogels prepared from cellulose as the base material have good application prospects in the fields of adsorption, separation, catalysis, sensors, thermal insulation, tissue engineering, etc. Cellulose aerogels with low density and low thermal conductivity are lightweight and warm, making them very suitable as thermal insulation layers for clothing. However, cellulose aerogels have poor mechanical properties, making it difficult to meet the requirements of mechanical processing such as cutting and shearing, and inevitably facing complex conditions such as collision, extrusion, and bending during wearing, thus posing extremely high requirements for the mechanical properties of aerogels. In addition, when aerogels are used for water treatment, not only are there certain requirements for their strength, but more importantly, the aerogels themselves should not contain harmful additives.

[0003] Crosslinking, especially chemical crosslinking, is currently the most effective method to improve the mechanical properties of cellulose aerogels. However, general chemical crosslinking steps are cumbersome, the process is lengthy, and the conditions are harsh. In addition, after many crosslinking reactions, the aerogels will contain a large amount of chemical additives, which need to be washed repeatedly and redried, undoubtedly increasing energy consumption and causing pollution. Therefore, finding a simple and green crosslinking method is of great significance for the preparation of aerogels. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a preparation method of a highly elastic bacterial cellulose / KH560 composite aerogel.

[0005] The technical solution for the present invention to solve the above technical problem is to provide a preparation method of a highly elastic bacterial cellulose / KH560 composite aerogel, which is characterized in that the method comprises the following steps:

[0006] (1) Mix KH560, acetic acid, and the bacterial cellulose aqueous dispersion thoroughly, and then let it stand to form a hydrogel;

[0007] (2) Subject the hydrogel to a freezing treatment to freeze it solid; then perform a drying treatment to sublime the solid ice into water vapor, and obtain the bacterial cellulose / KH560 composite aerogel;

[0008] (3) Subject the bacterial cellulose / KH560 composite aerogel to a heat treatment to reinforce the aerogel skeleton and obtain the highly elastic bacterial cellulose / KH560 composite aerogel.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0010] (1) The preparation process of the present invention is simple, and there is no residue of auxiliaries in the aerogel. It does not need to be washed and can be directly applied to the water environment for dye adsorption.

[0011] (2) The composite aerogel prepared by the present invention has ultra-high compression and rebound performance and fatigue resistance, and at the same time has a low thermal conductivity, and is suitable for use as a clothing thermal insulation material.

[0012] (3) The composite aerogel prepared by the present invention can be used as a high-strength aerogel substrate, and can be further functionally processed according to requirements, and then applied to different fields. Therefore, the composite aerogel is a promising multi-functional and multi-purpose material. Description of the Drawings

[0013] Figure 1 It is a low-magnification SEM image of the highly elastic composite aerogel prepared in Example 1 of the present invention;

[0014] Figure 2 It is a high-magnification SEM image of the highly elastic composite aerogel prepared in Example 1 of the present invention;

[0015] Figure 3 It is a nuclear magnetic resonance image of silicon element of the highly elastic composite aerogel prepared in Example 1 of the present invention;

[0016] Figure 4 It is a stress-strain curve of the highly elastic composite aerogel prepared in Example 1 of the present invention compressed 50 times at 80% strain;

[0017] Figure 5 It is a graph showing the change of the adsorption amount of methylene blue adsorbed by the highly elastic composite aerogel prepared in Example 2 of the present invention with time;

[0018] Figure 6 It is a graph showing the change of the adsorption amount of methylene blue adsorbed by the highly elastic composite aerogel prepared in Example 2 of the present invention after 5 cycles of use;

[0019] Figure 7 It is a thermal conductivity graph of the highly elastic composite aerogels prepared in Examples 1, 2, 3, and 4 of the present invention. Detailed Embodiments

[0020] The following are specific embodiments of the present invention. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of the present invention.

[0021] The present invention provides a preparation method of a highly elastic bacterial cellulose / KH560 composite aerogel (hereinafter referred to as the method), which is characterized in that the method includes the following steps:

[0022] (1) Mix KH560 silane coupling agent (γ-glycidoxypropyltrimethoxysilane), acetic acid and bacterial cellulose aqueous dispersion thoroughly, and then let it stand to form a hydrogel;

[0023] Preferably, in step (1), the concentration of the bacterial cellulose aqueous dispersion is 0.2 - 2 wt% (preferably 0.2 - 1 wt%, more preferably 0.4 wt%).

[0024] Preferably, in step (1), the mass of KH560 is 50 - 500% (preferably 50 - 300%, more preferably 100%) of the solute mass of the bacterial cellulose aqueous dispersion, and the volume of acetic acid is 0.1 - 2% (preferably 0.1 - 1%, more preferably 1%) of the volume of the bacterial cellulose aqueous dispersion.

[0025] Preferably, in step (1), the standing temperature is 4 - 90 °C and the standing time is at least 1 h.

[0026] (2) Freeze the hydrogel to make it freeze and solidify as a whole; then dry it to sublime the solid ice into water vapor to obtain a bacterial cellulose / KH560 composite aerogel;

[0027] Preferably, in step (2), the freezing methods include slow freezing in a refrigerator and rapid freezing in liquid nitrogen, as well as other freezing methods from liquid to solid; among them, the temperature of slow freezing in a refrigerator is -4 - 80 °C and the freezing time is at least 2 h; the freezing time of rapid freezing in liquid nitrogen is at least 3 min.

[0028] Preferably, in step (2), the drying methods include vacuum freeze-drying and supercritical drying; the temperature of vacuum freeze-drying is at least -40 °C and the time is at least 6 h; supercritical drying uses carbon dioxide as the drying medium, and the temperature and pressure are the temperature (about 40 °C) and pressure (about 12 MPa) when carbon dioxide turns into the supercritical state.

[0029] (3) Heat-treat the bacterial cellulose / KH560 composite aerogel to reinforce the aerogel skeleton to obtain a highly elastic bacterial cellulose / KH560 composite aerogel (abbreviated as highly elastic composite aerogel).

[0030] Preferably, in step (3), the heat-treatment temperature is 90 - 150 °C (preferably 120 °C) and the time is 5 - 60 min (preferably 10 min).

[0031] Example 1

[0032] (1) Add KH560 and acetic acid to the bacterial cellulose aqueous dispersion with a concentration of 0.4 wt%, where the mass of KH560 is 200% of the solute mass of the bacterial cellulose aqueous dispersion, and the volume of acetic acid is 0.1% of the volume of the bacterial cellulose aqueous dispersion. After stirring evenly, let it stand at room temperature for 24 h to form a hydrogel;

[0033] (2) Put the hydrogel into the refrigerator for slow freezing until it is completely frozen and solidified; then place it in the freezer for vacuum freeze-drying to obtain the bacterial cellulose / KH560 composite aerogel;

[0034] (3) Heat-treat the bacterial cellulose / KH560 composite aerogel at 120 °C for 30 min to obtain the highly elastic bacterial cellulose / KH560 composite aerogel.

[0035] It can be seen from Figure 1 and Figure 2 that the highly elastic composite aerogel prepared in Example 1 presents two-scale structures. On the one hand, the aerogel is composed of a cellulose skeleton and micron-sized large cavities, and these large cavities are caused by the growth of ice crystals during the freezing process. On the other hand, the wall material of the cavity is composed of nanoscale cellulose fibers and KH560.

[0036] It can be seen from Figure 3 that the peak at a chemical shift of -58.3 ppm belongs to Si-O-Si, indicating that self-crosslinking has occurred between KH560. The peak at -67.3 ppm corresponds to C-O-Si, indicating that covalent crosslinking has occurred between KH560 and the hydroxyl groups of cellulose. These two crosslinking methods form a three-dimensional spatial network, providing a basis for the strong mechanical properties of the aerogel.

[0037] The sample for the stress-strain test is a cylindrical aerogel. It can be seen from Figure 4 that at a compressive strain of 80%, the elastic recovery rate is 86.5% after 50 compressions, and the sample has high elasticity. And the elastic loss occurs within 5 cycles. After 5 cycles, the elasticity of the aerogel is very stable, indicating that after the first few compressions, the unstable factors inside the aerogel have been fully eliminated, showing strong fatigue resistance.

[0038] Comparative Example 1

[0039] The difference between Comparative Example 1 and Example 1 is that KH560 was not added in step 1, specifically as follows:

[0040] (1) Add acetic acid to the bacterial cellulose aqueous dispersion with a concentration of 0.4 wt%, where the volume of acetic acid is 0.1% of the volume of the bacterial cellulose aqueous dispersion. After stirring evenly, let it stand at room temperature for 24 h to form a hydrogel;

[0041] (2) Place the hydrogel in the refrigerator for slow freezing until it is completely frozen and solidified; then place it in the freezer for vacuum freeze-drying to obtain bacterial cellulose aerogel;

[0042] (3) Heat-treat the bacterial cellulose aerogel at 120 °C for 30 min to obtain pure bacterial cellulose aerogel.

[0043] Example 2

[0044] (1) Add KH560 and acetic acid to the bacterial cellulose aqueous dispersion with a concentration of 0.4 wt%, where the mass of KH560 is 50% of the solute mass of the bacterial cellulose aqueous dispersion, and the volume of acetic acid is 0.1% of the volume of the bacterial cellulose aqueous dispersion. After stirring well, let it stand at room temperature for 24 h to form a hydrogel;

[0045] (2) Place the hydrogel in the refrigerator for slow freezing until it is completely frozen and solidified; then perform vacuum freeze-drying to obtain bacterial cellulose / KH560 composite aerogel;

[0046] (3) Heat-treat the bacterial cellulose / KH560 composite aerogel at 90 °C for 60 min to obtain bacterial cellulose / KH560 composite aerogel.

[0047] The composite aerogel prepared in Example 2 was used for the adsorption of cationic dye (methylene blue), as Figure 5 and Figure 6 shown. The adsorption rate of this aerogel within 60 min was significantly faster than that afterwards. After about 360 min, the adsorption reached equilibrium ( Figure 5 ). The cyclic use performance of this aerogel was investigated by using hydrochloric acid desorption, as Figure 6 shown. After 5 adsorption-desorption cycles, the adsorption capacity of this aerogel still remained above 80%, showing strong reusability.

[0048] Example 3

[0049] (1) Add KH560 and acetic acid to the bacterial cellulose aqueous dispersion with a concentration of 2 wt%, where the mass of KH560 is 500% of the solute mass of the bacterial cellulose aqueous dispersion, and the volume of acetic acid is 2% of the volume of the bacterial cellulose aqueous dispersion. After stirring well, let it stand at 90 °C for 1 h to form a hydrogel;

[0050] (2) Rapidly freeze the hydrogel with liquid nitrogen until it is completely frozen and solidified; then perform supercritical drying to obtain bacterial cellulose / KH560 composite aerogel;

[0051] (3) Heat-treat the bacterial cellulose / KH560 composite aerogel at 150 °C for 5 min to obtain a highly elastic bacterial cellulose / KH560 composite aerogel.

[0052] Example 4

[0053] (1) Add KH560 and acetic acid to a 0.8 wt% aqueous dispersion of bacterial cellulose, where the mass of KH560 is 100% of the solute mass of the aqueous dispersion of bacterial cellulose, and the volume of acetic acid is 0.1% of the volume of the aqueous dispersion of bacterial cellulose. After stirring well, let it stand at 4 °C for 48 h to form a hydrogel;

[0054] (2) Perform rapid freezing treatment of the hydrogel with liquid nitrogen to freeze it as a whole; then, after vacuum freeze-drying, obtain the bacterial cellulose / KH560 composite aerogel;

[0055] (3) Heat-treat the bacterial cellulose / KH560 composite aerogel at 120 °C for 30 min to obtain a highly elastic bacterial cellulose / KH560 composite aerogel.

[0056] Test the density (mg / cm 3 ), porosity (%), specific surface area (m 2 / g), average pore diameter (nm), compression-elastic recovery rate (%), and Young's modulus (kPa) of the composite aerogels of Comparative Example 1 and Examples 1-4. The test results are shown in Table 1. The specific surface area and pore size distribution are obtained by testing the nitrogen adsorption-desorption curve of the aerogel with a microporous-specific surface area analyzer, calculating the specific surface area using the multi-point BET method, and calculating the pore size distribution using the BJH method. The elastic recovery rate is calculated from the results of the compression stress-strain test of the sample (compression strain is 80%, and the compression cycle is two times). The specific calculation method is that its value is the ratio of the height of the aerogel after compression to the initial height before compression.

[0057] Table 1

[0058]

[0059]

[0060] As can be seen from Table 1, as the amount of KH560 used increases, both the Young's modulus and the elastic recovery rate of the aerogel increase significantly. The elastic recovery rate of Comparative Example 1 is only 17.6%, and it hardly rebounds after compression. When the amount of KH560 used is 100%, the elastic recovery has reached more than 90%. And the Young's modulus also increases significantly, indicating that KH560 has an obvious strengthening effect on the BC aerogel.

[0061] The transient plane heat source method (TPS2500S) was used to measure the thermal conductivity of the composite aerogels prepared in Example 1, Example 2, Example 3 and Example 4. The specific results are as Figure 7 . The thermal conductivity of all composite aerogels is below 35 mW / mK. In particular, the thermal conductivity of Example 4 is as low as 29.66 mW / mK, approaching that of still air. Since the composite aerogel also has high mechanical properties, especially elasticity, it is suitable as a flexible thermal insulation material.

[0062] Matters not described in the present invention are applicable to the prior art.

Claims

1. A preparation method of a highly elastic bacterial cellulose / KH560 composite aerogel, characterized in that, The method comprises the following steps: (1) Mix KH560, acetic acid and bacterial cellulose aqueous dispersion thoroughly and evenly, and then let it stand to form a hydrogel; The concentration of the bacterial cellulose aqueous dispersion is 0.2 - 2 wt%; the mass of KH560 is 50 - 500% of the solute mass of the bacterial cellulose aqueous dispersion, and the volume of acetic acid is 0.1 - 2% of the volume of the bacterial cellulose aqueous dispersion; (2) Freeze the hydrogel to make it freeze and solidify as a whole; then perform a drying treatment to sublime the solid ice into water vapor, and obtain a bacterial cellulose / KH560 composite aerogel; (3) Perform a heat treatment on the bacterial cellulose / KH560 composite aerogel to strengthen the aerogel framework, and obtain a highly elastic bacterial cellulose / KH560 composite aerogel.

2. The preparation method of the highly elastic bacterial cellulose / KH560 composite aerogel according to claim 1, characterized in that, In step (1), the standing temperature is 4 - 90 °C, and the standing time is at least 1 h.

3. The preparation method of the highly elastic bacterial cellulose / KH560 composite aerogel according to claim 1, wherein, In step (2), the freezing treatment methods include slow freezing in a refrigerator and rapid freezing with liquid nitrogen.

4. The preparation method of the highly elastic bacterial cellulose / KH560 composite aerogel according to claim 3, wherein In step (2), the temperature for slow freezing in a refrigerator is -4 - 80 °C, and the freezing time is at least 2 h; the freezing time for rapid freezing with liquid nitrogen is at least 3 min.

5. The preparation method of the highly elastic bacterial cellulose / KH560 composite aerogel according to claim 1, characterized in that In step (2), the drying methods include vacuum freeze-drying and supercritical drying.

6. The preparation method of the highly elastic bacterial cellulose / KH560 composite aerogel according to claim 5, characterized in that, In step (2), the temperature for vacuum freeze-drying is at least -40 °C, and the time is at least 6 h.

7. The preparation method of the highly elastic bacterial cellulose / KH560 composite aerogel according to claim 5, wherein, In step (2), supercritical drying uses carbon dioxide as the drying medium, and the temperature and pressure are the temperature and pressure conditions when carbon dioxide turns into the supercritical state.

8. The preparation method of the highly elastic bacterial cellulose / KH560 composite aerogel according to claim 1, characterized in that, In step (3), the temperature for heat treatment is 90 - 150 °C, and the time is 5 - 60 min.

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