CN113637234B - Elastic cellulose aerogel and preparation method and application thereof - Google Patents

Abstract

The invention relates to an elastic cellulose aerogel and a preparation method and application thereof, and the preparation method comprises the following steps: (1) Freezing the nano cellulose suspension liquid by liquid nitrogen, and then carrying out freeze drying to obtain the submicron cellulose fiber; (2) Dispersing the submicron cellulose fiber in water, freezing for the second time, and then freezing and drying to obtain the elastic cellulose aerogel; the elastic cellulose aerogel is subjected to surface modification by adopting a silane compound through a chemical vapor deposition method to obtain the super-hydrophobic elastic cellulose aerogel, and the super-hydrophobic elastic cellulose aerogel is applied to the field of oil-water separation. The elastic cellulose aerogel obtained by the method has good rebound resilience and shape recovery performance under normal temperature and cold environment, and also has low heat conduction coefficient, the super-hydrophobic elastic cellulose aerogel obtained by surface modification shows super-strong separation performance in oil-water separation, and the adsorption capacity to chloroform can reach about 489 times of the self-mass.

Description

A kind of elastic cellulose airgel and its preparation method and application

technical field

The invention relates to the technical field of polymer materials, in particular to an elastic cellulose airgel and its preparation method and application.

Background technique

As the lightest solid material, aerogels have been widely used in thermal regulation, energy harvesting and storage, sensors, environmental remediation, and biomedicine. Such diverse applications of aerogels are attributed to their numerous advantages, including low density, high porosity, high specific surface area, low thermal conductivity, and biocompatibility. Among the various physical properties of aerogels, mechanical properties are an important factor limiting the application of aerogels. A lot of efforts have been made to improve the mechanical properties of aerogels, mainly focusing on improving the compression resistance and elasticity of organic aerogels and inorganic aerogels, among which aerogels with high resilience and rapid shape recovery properties Glues have also been further investigated because the ability to recover shape quickly from large compressive strains is extremely important for their applications in electrical signal sensing, water treatment, heat and sound insulation, air filtration, and energy storage.

Biologically derived natural polymers, especially cellulose, have attracted great interest as raw materials for the preparation of aerogels due to their wide sources and easy processability. Conventional cellulose airgel synthesis requires a large amount of solvent for the dissolution regeneration process. Recently, nanocellulose, especially cellulose nanofibers, has been widely used to construct aerogels with high specific surface area and excellent mechanical properties. Due to the high specific surface area and abundant polar functional groups, ultralight cellulose aerogels can be conveniently prepared by freeze-drying nanofibrous suspensions, showing excellent structural integrity. Although nanocellulose airgel has good compressibility and can compress more than 90% of the strain without breaking, the compressed airgel generally has poor resilience and cannot recover from the compressed state. The reason for the lack of resilience is due to the inelastic microstructure and strong hydrogen bonds formed between adjacent cellulose fibers during compression. Nanocellulose aerogels prepared by a single freezing method have unsatisfactory resilience properties due to their anisotropic elasticity in the axial direction.

Contents of the invention

Aiming at the technical problem of conventional airgel having poor resilience and being unable to recover from a compressed state, an elastic cellulose airgel and its preparation method and application are provided. The elastic cellulose airgel prepared by the invention has lower density and thermal conductivity, and better elasticity and shape recovery under normal temperature and cold environment.

In order to achieve the above object, the present invention is realized through the following technical solutions:

A preparation method of elastic cellulose airgel, comprising the steps of:

(1) The nanocellulose suspension is frozen with liquid nitrogen, and then freeze-dried to obtain submicron cellulose fibers;

(2) Dispersing the submicron cellulose fibers in water for secondary freezing, and then freeze-drying to obtain the elastic cellulose airgel.

Further, the nanocellulose suspension described in step (1) is to centrifuge 0.2wt% of the nanocellulose dispersion to remove the precipitate and collect the upper suspension, the centrifugation speed is 3000-800rpm, and the centrifugation time is 5 -10 min, dilute the upper suspension to obtain a nanocellulose suspension with a concentration of 0.05 wt%.

Still further, the TEMPO/NaClO oxidation system is used to oxidize the natural pulp for 20 minutes to 5 hours to obtain the nanocellulose dispersion liquid. During the oxidation treatment process, NaOH solution is used to control the pH of the oxidation system to be 9.8-10.5. After the treatment, use a dialysis bag for dialysis for one week, and then process it with a cell pulverizer for 25 minutes to obtain nanocellulose, and after dilution, obtain a 0.2wt% nanocellulose dispersion; the mass ratio of the TEMPO, the NaClO, and the pulp is 1:(1.4-5):1.

Further, the concentration of the submicron cellulose fibers dispersed in water in step (2) is controlled to be 0.2wt%-2wt%; preferably, the concentration is controlled to be 0.2wt%-0.6wt%.

Further, the temperature of liquid nitrogen freezing described in step (1) is -196°C, and the time is 1-2h; the temperature of secondary freezing described in step (2) is frozen for 3h in a refrigerator with a temperature of -20°C; step The freeze-drying described in (1) and step (2) is carried out by a freeze dryer at -55 to -45° C. for 48 hours, and the freezing pressure is 0.02-1 Pa.

Another aspect of the present invention provides the elastic cellulose airgel prepared by the above preparation method.

The third aspect of the present invention provides the application of the elastic cellulose airgel prepared by the above preparation method on water-absorbing materials or on heat-insulating materials.

The fourth aspect of the present invention provides the application of the elastic cellulose airgel prepared by the above preparation method, and the elastic cellulose airgel is modified by chemical vapor deposition using silane compounds to obtain superhydrophobic elastic cellulose airgel glue, applying the superhydrophobic elastic cellulose airgel to the field of oil-water separation.

Further, in the chemical vapor deposition method, the elastic cellulose airgel is placed above the stainless steel grid, and two containers respectively containing water and the silane compound are placed side by side under the stainless steel grid, and then React at 70-90° C. for 5-7 hours in a closed vacuum state to prepare superhydrophobic elastic cellulose airgel.

Still further, the amount of the elastic cellulose airgel, the silane compound, and the water is (20-25) mg: (1-2) mL: 0.5 mL; the silane compound is methyl Trimethoxysilane or Dimethicone.

Beneficial technical effects:

The invention assembles the elastic cellulose airgel through the double freezing method of liquid nitrogen freezing and low-temperature refrigerator freezing, and then obtains the superhydrophobic elastic cellulose airgel through surface modification. The elastic cellulose aerogel of the present invention has a density of 2-20 mg/cm ³ , and has good shape recovery, good resilience and superelasticity in both normal and extremely cold environments (-196°C); and Low thermal conductivity, only 0.023W/m K, has good heat insulation and infrared shielding properties; in addition, the superhydrophobic elastic cellulose airgel obtained after surface modification shows super strong separation in oil-water separation Performance, the adsorption capacity of chloroform can reach about 489 times its own mass. The material of the invention can be used in the fields of high water absorption material, heat insulation material, oil-water separation and the like.

Description of drawings

Fig. 1 is the SEM topography figure that embodiment 1 makes, and wherein a represents nano-cellulose suspension, b represents submicron cellulose fiber, c, d represent elastic cellulose aerogel; Scale bar among abd figure is 500nm , The scale bar in c is 500 μm.

Fig. 2 is the elastic stress-strain curve diagram of the elastic cellulose airgel prepared in Example 1.

Figure 3 is the FTIR curve of the superhydrophobic elastic cellulose airgel of Application Example 1, wherein a represents the elastic cellulose airgel of Example 2, and b represents the superhydrophobic elastic cellulose airgel of Application Example 1.

Fig. 4 is a time-dependent graph of the water contact angle of the superhydrophobic elastic cellulose airgel of Application Example 1.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. The following description of at least one exemplary embodiment is merely illustrative in nature and in no way taken as limiting the invention, its application or uses. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The numerical values set forth in these examples do not limit the scope of the invention unless specifically stated otherwise. Techniques and methods known to those of ordinary skill in the related art may not be discussed in detail, but under appropriate circumstances, the techniques and methods should be regarded as a part of the specification. In all examples shown and discussed herein, any specific values should be construed as exemplary only, and not as limitations. Therefore, other examples of the exemplary embodiment may have different values.

Example 1

A preparation method of elastic cellulose airgel, comprising the steps of:

(1) Put the 0.05wt% nanocellulose suspension into liquid nitrogen at -196°C for liquid nitrogen freezing for 1 hour, then place it in a freeze dryer with a temperature of -55°C and a pressure of 0.02Pa for 48 hours, Obtain submicron cellulose fibers;

(2) Disperse the submicron cellulose fibers in water with a vortex mixer to prepare a dispersion with a concentration of 0.2 wt%. After stirring evenly, place it in a refrigerator at -20°C for secondary freezing for 3 hours, and then place it at temperature Freeze-drying in a freeze dryer at -55°C and a pressure of 0.02Pa for 48 hours to obtain elastic cellulose airgel.

Wherein the obtaining method of nano-cellulose suspension in step (1): 1. adopt TEMPO/NaClO oxidation system to carry out oxidation treatment 2h to natural paper pulp, in oxidation treatment process, adopt NaOH solution to control oxidation system pH to be 10, after oxidation treatment finishes , after one week of dialysis using a dialysis bag, nanocellulose was obtained after being treated with a cell pulverizer for 25 minutes, and after dilution, a 0.2wt% nanocellulose dispersion was obtained; the mass ratio of the TEMPO, the NaClO, and the pulp was 1 :1.6:1; ②Put 0.2wt% nanocellulose dispersion in a centrifuge tube, centrifuge through a high-speed centrifuge, the centrifuge speed is 5000r/min, and the centrifugation time is 10 minutes. After the centrifugation, remove the bottom of the centrifuge tube The white precipitate, the upper suspension was collected, and the upper suspension was diluted to obtain a nanocellulose suspension with a concentration of 0.05 wt%.

The elastic cellulose airgel that has been finally prepared by the submicron cellulose fiber prepared in step (1) in this embodiment is observed by electron microscope, as shown in Figure 1, wherein a represents the nanocellulose suspension, and b represents the submicron cellulose aerogel. Micron cellulose fibers, c and d represent elastic cellulose airgel; the scale bar in abd is 500nm, and the scale in c is 500μm. As can be seen from Figure 1, the width of cellulose in the original nanocellulose suspension in Figure 1a is 3-5nm, and the length is at least 500nm; Figure 1b obtained continuous submicron cellulose fibers after liquid nitrogen freezing, and the fiber width is about 100-200nm; Figure 1c and Figure 1d are the aerogels obtained after liquid nitrogen freezing and secondary freezing in the refrigerator. It can be seen that after liquid nitrogen freezing and low-temperature refrigerator secondary freezing, the microscopic morphology of the airgel shows Honeycomb structure.

The elastic cellulose airgel prepared in this example is subjected to a stress-strain test. The test is to place the prepared cylindrical airgel (21mm in diameter, 23mm in height) on an Instron 3345 material testing system, and use 2KN pressure measurement The element compresses the airgel to a strain of 60 percent. The results are shown in Figure 2. It can be seen from Figure 2 that the cyclic compressive stress-strain curve of the airgel in this example shows good elastic behavior after 50 cycles, and the airgel can almost return to its original size after compression. After 50 times, the unrecoverable strain is only 3.8%, and the resilience is good. The ultimate stress remains at 0.542kPa, which is close to the first cycle, indicating that the airgel structure is well maintained.

The elastic airgel prepared by the present invention has better resilience, which can be attributed to the existence of submicron fibers. During the liquid nitrogen freezing process, nano-scale cellulose fibers (3-5nm in diameter) can be assembled into submicron cellulose fibers with a diameter of 100-200nm, and the submicron cellulose fibers are dispersed in water to form a dispersion and then frozen in the refrigerator (- 20°C), due to the growth of larger ice crystals at a low freezing rate, a honeycomb structure with large pores of several hundred micrometers (as shown in Figure 1c) is formed, transforming from nanofibers (3-5 nm in diameter) to In the process of submicron fibers (diameter 100-200nm), due to the significant reduction in surface area, and the submicron cellulose assembly into the airgel process no longer forms a film structure, inhibiting the hydrogen bonding between adjacent cellulose, The honeycomb structure formed by the interconnected submicrometer fiber network provides excellent elastic behavior and exhibits excellent flexibility and foldability.

Example 2

A preparation method of elastic cellulose airgel, comprising the steps of:

(1) Put 0.05wt% nanocellulose suspension into liquid nitrogen at -196°C for 2 hours, then place it in a freeze dryer with a temperature of -55°C and a pressure of 0.2Pa for 48 hours, Obtain submicron cellulose fibers;

(2) Disperse the submicron cellulose fibers in water with a vortex mixer to prepare a dispersion with a concentration of 0.2 wt%. After stirring evenly, place it in a refrigerator at -20°C for secondary freezing for 3 hours, and then place it at temperature Freeze-drying in a freeze dryer at -55°C and a pressure of 0.2 Pa for 48 hours to obtain elastic cellulose airgel.

Example 3

The preparation method of the elastic cellulose airgel of this embodiment is the same as that of Example 2, except that in step (2), the submicron cellulose fibers are dispersed in water to prepare a dispersion with a concentration of 0.4 wt%. .

Example 4

The preparation method of the elastic cellulose airgel of this embodiment is the same as that of Example 2, except that in step (2), the submicron cellulose fibers are dispersed in water to prepare a dispersion with a concentration of 0.6 wt%. .

Example 5

The preparation method of the elastic cellulose airgel of this embodiment is the same as that of Example 2, except that in step (2), the submicron cellulose fibers are dispersed in water to prepare a dispersion with a concentration of 0.8 wt%. .

The aerogels prepared in Examples 2-5 all have honeycomb microstructure morphology.

Comparative example 1

Preparation of traditional cellulose gel:

(1) Use TEMPO/NaClO to oxidize the natural pulp for 2 hours. In the oxidation treatment process, use NaOH solution to control the pH of the oxidation system to be 10. After dialysis with a dialysis bag for one week, nanofibers are obtained after being treated with a cell pulverizer for 25 minutes. Element, after dilution, obtain the nanocellulose dispersion liquid of 0.4wt%; The mass ratio of described TEMPO, described NaClO, described pulp is 1:1.6:1.

(2) Place the 0.4wt% nanocellulose dispersion in step (1) in a refrigerator at -20°C for 3 hours to obtain 0.4wt% frozen nanocellulose;

(3) The 0.4wt% frozen nanocellulose in step (2) was frozen in a freeze dryer at -55° C. for 48 hours, and the freezing pressure was 0.2 Pa.

Comparative example 2

The preparation method of the cellulose airgel of this comparative example is: put 0.5wt% nanocellulose suspension into liquid nitrogen at -196°C for liquid nitrogen freezing for 5 minutes, and then place it at a temperature of -91°C and a pressure of 0.6 Carry out freeze-drying 72h in the freeze-drying machine of Pa, obtain cellulose aerogel.

The airgel prepared in Examples 1-4 and Comparative Examples 1-2 were tested for porosity, density, thermal conductivity and resilience, and the test results are shown in Table 1. The test method for the rebound rate at room temperature is: use a weight of 200g to compress the airgel with a diameter of 21mm x height of 23mm to 80% of the original height, and calculate the rebound height of the airgel after removing the weight of 200g. The percentage of the height of the size is the rebound rate after the initial compression. On this basis, 50 cycles of compression and rebound are performed, and the percentage of the height of the airgel rebound after removing the 200g weight after 50 cycles is calculated as the percentage of the original size height is It is the compression rebound rate after 50 cycles. The test method of compression resilience at -196°C is to place the airgel in liquid nitrogen, compress the airgel to 80% of its original size, remove the force, and observe the resilience.

The airgel performance that table 1 embodiment 1-4 and comparative example 1-2 make

It can be seen from Table 1 that the airgel prepared by the method of the present invention has a well-developed pore structure and a very small density, and has good shape recovery and better resilience in normal and extremely cold environments (-196°C). , with superelasticity; and low thermal conductivity, only 0.023-0.028W/m·K, with good heat insulation and infrared shielding properties. It can be used in the fields of super absorbent materials and heat insulation materials.

Application example 1

The elastic cellulose airgel prepared in Example 2 is used to modify the surface of the elastic cellulose airgel by using methyltrimethoxysilane (abbreviated as MTMS) by chemical vapor deposition to obtain superhydrophobic elastic cellulose airgel Glue; wherein the chemical vapor deposition method is to place 22mg of the elastic cellulose airgel above the stainless steel grid, and place side by side below the stainless steel grid are respectively equipped with 0.5mL water and 1mL methyltrimethoxysilane Two containers (the size of the stainless steel mesh needs to cover the surface area of the two containers) were reacted at 80° C. for 6 hours in a closed vacuum state to prepare superhydrophobic elastic cellulose airgel.

The FTIR test was carried out on the prepared superhydrophobic elastic cellulose airgel, and the test results are shown in Fig. 3 respectively. Since cellulose aerogels are hydrophilic, they can be easily redispersed in water with gentle agitation. Therefore, in order to improve the stability and hydrophobicity of elastic cellulose aerogels, superhydrophobic elastic cellulose aerogels can be obtained by vapor deposition of MTMS under vacuum at 80 °C for 6 h. FTIR spectroscopy confirmed the successful modification of the silane. The characteristic peaks at 3328cm ^-1 , 1598cm ^-1 and 1032cm ^-1 are all OH stretching vibrations, C=O/C=C stretching vibrations and CO stretching vibrations, all appearing in elastic cellulose airgel (the product of Example 2) and superhydrophobic elastic cellulose airgel (the product of this application example). In addition to having the typical spectral features of unmodified cellulose aerogels, the superhydrophobic elastic cellulose aerogels obtained by MTMS modified elastic cellulose aerogels have a peak of 1262 cm ^-1 in Si- _CH3 and Si-O-Si , 776cm ^-1 , 798cm ^-1 all appear characteristic peaks.

The obtained superhydrophobic elastic cellulose airgel was tested for water contact angle, and the contact angle changes with time are shown in Fig. When contacting with water for the first time, the water contact angle is 164°, and after 7s, the water contact angle gradually decreases to 157°, and tends to be stable. It has good superhydrophobicity and certain self-cleaning ability.

The superhydrophobic elastic cellulose airgel prepared in this application example is applied to oil-water separation, and the oily solvent is selectively removed from water. The data of oil-water separation performance are shown in Table 2. Oil-water separation performance test method: soak the superhydrophobic elastic cellulose airgel in water mixed with oily solvent to absorb the oily solvent, the weight of the superhydrophobic elastic cellulose airgel after absorbing the oily solvent and the weight of the dry airgel The ratio represents the weight gain (wt%) to evaluate the oil-water separation performance.

Table 2 Oil-water separation performance

As can be seen from Table 2, the superhydrophobic elastic cellulose airgel obtained by modifying the elastic cellulose aerogel of the present invention with low surface energy shows a higher adsorption capacity to most oil solvents, and has a higher adsorption capacity to chloroform, The weight gains of pump oil and rapeseed oil after adsorption reached 48886%, 25765%, and 23416%, respectively. The superhydrophobic elastic cellulose airgel of the present invention can absorb most oil solvents at 159-489 times its own weight, and has better oil-water separation effect.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (8)

1. a preparation method of elastic cellulose airgel, is characterized in that, comprises the steps: (1) The nanocellulose suspension is frozen in liquid nitrogen, and then freeze-dried to obtain submicron cellulose fibers; The nanocellulose suspension is obtained by centrifuging 0.2wt% of the nanocellulose dispersion to remove the precipitate and collecting the upper suspension, and diluting the upper suspension to obtain a nanocellulose suspension with a concentration of 0.05wt%; The nanocellulose dispersion is obtained by using a TEMPO/NaClO oxidation system to oxidize the natural pulp for 20 minutes to 5 hours. During the oxidation treatment, NaOH solution is used to control the pH of the oxidation system to be 9.8-10.5. After the oxidation treatment is completed, After adopting dialysis bags for dialysis for one week, the cell pulverizer is processed to obtain nanocellulose, and after dilution, a 0.2wt% nanocellulose dispersion is obtained; the mass ratio of the TEMPO, the NaClO, and the pulp is 1:(1.4 -5):1; The freezing temperature of the liquid nitrogen is -196°C and the time is 1-2h; (2) Disperse the submicron cellulose fibers in water for secondary freezing, and then freeze-dry to obtain elastic cellulose airgel; the concentration of the submicron cellulose fibers dispersed in water is controlled to 0.2wt %～2wt%; the temperature of the secondary freezing adopts a refrigerator with a temperature of -20° C. for 3 hours. 2. The preparation method of a kind of elastic cellulose airgel according to claim 1, characterized in that, the centrifugation speed is 5000rpm, and the centrifugation time is 10min; the treatment time of the cell pulverizer is 25min. 3. the preparation method of a kind of elastic cellulose airgel according to claim 1 is characterized in that, the freeze-drying described in step (1) and step (2) adopts the freeze-drying machine of-55～-45 ℃ Freeze for 48 hours, and the freezing pressure is 0.02-1Pa. 4. The elastic cellulose airgel prepared by the preparation method according to any one of claims 1-3. 5. The application of the elastic cellulose airgel prepared by the preparation method according to any one of claims 1-3 on a water-absorbing material or on a heat-insulating material. 6. An application of elastic cellulose airgel, characterized in that, said elastic cellulose airgel is prepared according to the preparation method described in any one of claims 1-3, by chemical vapor deposition using silanes The compound modifies the surface of the elastic cellulose airgel to obtain a superhydrophobic elastic cellulose airgel, and the superhydrophobic elastic cellulose airgel is applied to the field of oil-water separation. 7. The application according to claim 6, characterized in that, the chemical vapor deposition method is to place the elastic cellulose aerogel above the stainless steel grid, and place side by side below the stainless steel grid to be filled with water respectively. react with two containers of the silane compound in a sealed vacuum state at 70-90° C. for 5-7 hours to prepare superhydrophobic elastic cellulose airgel. 8. application according to claim 6, is characterized in that, the consumption of described elastic cellulose airgel, described silane compound, described water is (20-25) mg: (1-2) mL: 0.5 mL; the silane compound is methyltrimethoxysilane or polydimethylsiloxane.

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