NL2027080B1

NL2027080B1 - Method for preparing nanocellulose/polyvinyl alcohol reinforced chitosan aerogel

Info

Publication number: NL2027080B1
Application number: NL2027080A
Authority: NL
Inventors: Xiong Shixian; E Dianyu; Zhang Sizhao; Li Zhengquan; Xiao Qi; Zou Ruiping; Ding Feng
Original assignee: Univ Jiangxi Sci & Technology; Ganjiang New Area Abler Particle Tech Research Institute Co Ltd
Priority date: 2020-04-09
Filing date: 2020-12-09
Publication date: 2023-07-21
Also published as: NL2027080A; CN111320787A

Abstract

The present disclosure provides a method for preparing a nanocellulose (NC)/polyvinyl alcohol (PVA) reinforced chitosan (CTS) aerogel. NC and linear polymer PVA are used to reinforce a CTS aerogel, so that an enhanced and crosslinked fine skeleton is formed in a chemical gelling process, and an NC/PVA reinforced CTS aerogel is obtained after drying with supercritical carbon dioxide (sc—C02). The NC/PVA reinforced CTS aerogel obtained by the method of the present disclosure hasarelativelylowshrinkagerateandoutstandingcompressive strength.

Description

METHOD FOR PREPARING NANOCELLULOSE/POLYVINYL ALCOHOL

REINFORCED CHITOSAN AEROGEL

TECHNICAL FIELD

The present disclosure relates to the technical field of organic aerogels, and in particular to a method for preparing a nanocellulose (NC) /polyvinyl alcohol (PVA) reinforced chitosan (CTS) aerogel.

BACKGROUND

CTS, as the second largest natural polymer material in nature right next to cellulose, 1s the only biorenewable alkaline polysaccharide polymer. It can be obtained by deacetylation of chitin and has many advantages such as availability from abundant sources, excellent biocompatibility, environmental degradability, high drug activity and strong antibacterial ability. It is widely used in food, textile and chemical industries, environmental protection and other fields. Thus, researches on development and application of CTS may have great significance.

It iswell known that, aerogels may be applied in many fields, such as adsorption, catalysis, heat insulation, and drug release. In view of this, synthesis of CTS aerogel is particularly important. At present, preparation of CTS aerogels generally relies on two mechanisms. A first mechanism is based on physical principles, in which an aerogel is formed from a CTS solution through actions of, for example, hydrogen bonds in an alkaline environment. A second mechanism is based on chemical principles, in which an aerogel is formed from chemical crosslinking reactions between CTS in a solution and genipin, citric acid, glyoxal, acetaldehyde and the like.

However, the CTS aerogels in the prior art are generally prepared with a high shrinkage rate (referring to shrinkage from final gel to aerogel, where the final gel is a gel obtained after completion of aging, the same below) and poor compressive performance. How to efficiently inhibit sharp shrinkage

(typically reaching 80% of a final hydrogel volume after drying and extraction with supercritical carbon dioxide (sc~C0;)) and improve compressive strength is a long-term unanswered issue for biomass aerogel.

SUMMARY

An objective of the present disclosure is to provide a method for preparing an NC/PVA-reinforced CTS aerogel, which solves the technical problem that the CTS aerogels obtained in the prior art have a high shrinkage rate and poor compressive performance.

In the present disclosure, NC/linear PVA chains are physically entangled/chemically crosslinked to form a large number of fixed and crosslinked network sheets. Dehydration and condensation reactions between resorcinol and crosslinker further enhance the network structure. An obtained

NC/PVA-reinforced CTS aerogel has a relatively low shrinkage rate and outstanding compressive strength.

The present disclosure provides a method for preparing an

NC/PVA-reinforced CTS aerogel, including the following steps:

Step l: Preparation of NC/PVA reinforced CTS hydrogel. This step is implemented by mixing an NC solution and a PVA solution homogeneously to obtain a homogeneous NC/PVA solution, dissolving CTS in an ethanol-water solvent to obtain a CTS solution, adding the homogeneous NC/PVA solution into the CTS solution, stirring uniformly, adding 10-40 mL of resorcinol solution, stirring to achieve homogeneity, adding a crosslinker solution, stirring and allowing to stand still to obtain an NC/PVA reinforced CTS hydrogel.

Step 2: Aging. This step is implemented by aging the NC/PVA reinforced CTS hydrogel to obtain a mature NC/PVA reinforced

CTS hydrogel.

Step 3: Replacement of organic solvent. This step is implemented by replacing the ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel with an organic solvent for 1-7 d;

Step 4: Drying to obtain an NC/PVA reinforced CTS aerogel.

Further, the method may include: preparation of NC/PVA reinforced CTS hydrogel which is implemented by preparing a 1-5 wt% homogeneous mixed solution of NC solution and PVA solution, dissolving CTS in an ethanol-water solvent to obtain a 6-16 g/L CTS solution, adding a homogeneous NC/PVA solution into the CTS solution, stirring uniformly, adding 10-40 mL of 1-10 wt% resorcinol solution, stirring to achieve homogeneity, adding a solution of crosslinker in ethanol, stirring and allowing to stand still to obtain an NC/PVA reinforced CTS hydrogel; aging the NC/PVA reinforced CTS hydrogel to obtain a mature

NC/PVA reinforced CTS hydrogel, replacing the ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel with an organic solvent for 1-7 d, and drying to obtain an NC/PVA reinforced CTS aerogel, where the ethanol-water solvent is obtained by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of (10-40): (60-90).

Further, the drying may be drying with sc-CO0:; at 40-60°C and 15-20 MPa.

Further, the solution of crosslinker may have a concentration of 2-12 wt% and the crosslinker may be any one of genipin, formaldehyde, acetaldehyde, glyoxal, succinaldehyde, glutaraldehyde, o-phthalaldenyde, isophthalaldehyde and terephthalaldehyde, or any combination thereof.

Further, the aging the NC/PVA reinforced CTS hydrogel may be carried out by raising a starting temperature of 10-40°C to 60-80°C at a rate of 10°C/d and then holding a temperature for 1-3 d.

Further, the organic solvent may be any one of methanol, ethanol, isopropanol, tert-butanol, acetone, benzyl alcohol and n-hexane, or any combination thereof.

Technical effects: 1. According to the method for preparing an NC/PVA reinforced CTS aerogel, an NC/PVA reinforced CTS aerogel may be obtained. 2. According to the method for preparing an NC/PVA reinforced CTS aerogel, a gel is formed under control at a low

CTS substrate concentration (below 16 g/L) and a low crosslinker concentration (below 12 wt%). 3. According to the method for preparing an NC/PVA reinforced CTS aerogel, a gel is formed at a low CTS substrate concentration (below 16 g/L) and a low crosslinker concentration (below 12 wt$) in an alcohol/water binary solvent system. NC and linear polymer PVA are used to reinforce a CTS aerogel, so that an enhanced and crosslinked fine skeleton is formed in a chemical gelling process, and an NC/PVA reinforced

CTS aerogel is obtained after drying with sc-CO:. The NC/PVA reinforced CTS aerogel obtained by the method of the present disclosure has a relatively low shrinkage rate and outstanding compressive strength. 4. The method for preparing an NC/PVA-reinforced CTS aerogel provided by the present disclosure includes easily available and environmentally friendly raw materials and a simple preparation route which is easy to implement, with low requirements for equipment. Therefore, it is suitable for industrial production.

For details, please refer to the following descriptions of various embodiments proposed in the method for preparing an

NC/PVA reinforced CTS aerogel according to the present disclosure, which will make the above and other aspects of the present disclosure obvious.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic flowchart of the method for preparing an NC/PVA-reinforced CTS aerogel provided by the present disclosure.

DETAILED DESCRIPTION

The following contents describe implementations of the present disclosure through specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification. The present disclosure can also be implemented or applied through other different embodiments.

Based on different viewpoints and applications, various modifications or amendments can be made to various details of the specification without departing from the spirit of the 5 present disclosure.

The accompany drawings constituting a part of the application provide further understanding of the present disclosure. The schematic embodiments of the disclosure and description thereof are intended to be illustrative of the present disclosure and do not constitute an undue limitation of the present disclosure.

Referring to FIG.1, the present disclosure provides a method for preparing an NC/PVA reinforced CTS aerogel, including the following steps: step 1): preparation of NC/PVA reinforced CTS hydrogel: preparing a 1-2.5 wt% homogeneous mixed solution of NC solution and PVA solution, dissolving CTS in an ethanol-water solvent to obtain a 6-16 g/L CTS solution, adding a homogeneous NC/PVA solution into the CTS solution, stirring uniformly, adding 10-40 mL of 1-10 wt% resorcinol solution, stirring to achieve homogeneity, adding a solution of crosslinker in ethanol, stirring and allowing to stand still to obtain an NC/PVA reinforced CTS hydrogel; step 2): aging the NC/PVA reinforced CTS hydrogel to obtain a mature NC/PVA reinforced CTS hydrogel, replacing the ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel with an organic solvent for 1-3 d, and drying to obtain an NC/PVA reinforced CTS aerogel, where the ethanol-water solvent is obtained by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of (10-40): (60-90).

Herein, the ethanol-water solvent refers to a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio, which is abbreviated as ethanol-water solvent hereinafter. The NC/PVA reinforced CTS hydrogel refers to a binary solution system formed by dissolving CTS in a mixed solution of ethanol and 2 wt% acetic acid aqueous solution in a volume ratio, which is abbreviated as NC/PVA reinforced CTS hydrogel hereinafter. NC and linear polymer PVA are used to reinforce a CTS aerogel, so that an enhanced and crosslinked fine skeleton is formed in a chemical gelling process, and an NC/PVA reinforced CTS aerogel is obtained after drying with sc-CO:. The NC/PVA reinforced CTS aerogel obtained by the method of the present disclosure has a relatively low shrinkage rate and outstanding compressive strength. Other unspecified parameters and operations in the method can be determined with reference to an existing method for preparing a CTS aerogel. For example, for specific operations, the section of specific method can be referred to.

Preferably, the drying may be drying with sc-CO: at 40-60°C and 15-20 MPa.

Preferably, the solution of crosslinker may have a concentration of 2-12 wt% and the crosslinker may be any one of genipin, formaldehyde, acetaldehyde, glyoxal, succinaldehyde and glutaraldehyde, or any combination thereof.

Preferably, the aging the NC/PVA reinforced CTS hydrogel may be carried out by raising a starting temperature of 10-40°C to 60-80°C at a rate of 10°C/d and then holding a temperature for 1-3 d. Aging under these conditions can increase proportion of reinforced and crosslinked fine skeleton formed in an obtained gel, so that a finally obtained NC/PVA reinforced CTS aerogel has a relatively low shrinkage rate and outstanding compressive strength.

Preferably, the organic solvent may be any one of ethanol, isopropanol, tert-butanol and n-hexane, or any combination thereof.

Specifically, the present disclosure provides a method for preparing an NC/PVA-reinforced CTS aerogel, including the following steps: step {1}: preparing a 1-5 wt% homogeneous mixed solution of NC solution and PVA solution, dissolving CTS in an ethanol-water solvent to obtain a CTS solution, adding a homogeneous NC/PVA solution into the CTS solution, stirring uniformly, adding 10-40 mL of 1-10 wt% resorcinol solution,

stirring to achieve homogeneity, adding a solution of crosslinker in ethanol, stirring and allowing to stand still to obtain an NC/PVA reinforced CTS hydrogel; where a binary solvent system is formed by mixing ethanol and 2 wt& acetic acid aqueous solution in a volume ratio of (10-40): (60-90), the CTS solution has an initial concentration of 6-16 g/L, the solution of crosslinker has a concentration of 2-12 wt%, the crosslinker may be any one of genipin, formaldehyde, acetaldehyde, glyoxal, succinaldehyde and glutaraldehyde, or any combination thereof, and a temperature is as low as 5-15°C; step (2): placing an initially obtained NC/PVA reinforced

CTS hydrogel in a thermostat aging tank, aging by raising a starting temperature of 10-40°C to 60-80°C at a rate of 10°C/d and then holding a temperature for 1-3 d to obtain a mature

NC/PVA reinforced CTS hydrogel; step (3): replacing the ethanol-water solvent in the mature

NC/PVA reinforced CTS hydrogel with a specific organic solvent for 1-3 dto obtain a CTS gel with organic solvent, and finally drying with sc-CO: at a certain temperature and pressure to obtain an NC/PVA reinforced CTS aerogel; where the specific organic solvent 1s one of ethanol, tert-butanol, and isopropanol or any combination thereof, and the certain temperature and pressure is 40-60°C and 15-20 MPa respectively.

Materials and instruments used in the following embodiments are all commercially available.

Example 1

A 1 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 10:90 to obtain a 7 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 10 mL of 2 wt& resorcinol solution was added and stirred to achieve homogeneity. Finally, a 3 wt% solution of crosslinker in formaldehyde was added at a temperature as low as 5°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 70°C at a rate of 10°C/d and then holding a temperature for 2 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with an ethanol solvent for 3d to obtain an NC/PVA reinforced CTS alcohol gel. Finally, drying with sc-CO: was carried out at 40°C and 16 MPa to obtain an NC/PVA reinforced CTS aerogel. The CTS aerogel was tested for shrinkage rate and compressive strength. Results were shown in Table 1.

Addition of the NC solution greatly shortened distance between reactants. This improved chemical reaction progress between the reactants and increased entanglement of nanofibers of the NC, showing a synergistic effect which helped to form a self-reinforced structure reinforced by a sheet and a fiber-like material. Addition of NC caused the CTS aerogel to evolve from a network structure with a loose skeleton and large pores to a dense network structure with wide layers and small pores.

Example 2

A 2 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 20:80 to obtain a 15 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 15 mL of 3 wt% resorcinol solution was added and stirred to achieve homogeneity. Finally, a 4 wt% solution of crosslinker in acetaldehyde was added at a temperature as low as 6°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 75°C at a rate of 10°C/d and then holding a temperature for 1 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with a tert-butanol solvent for 2 d to obtain an NC/PVA reinforced CTS alcohol gel.

Finally, drying with sc-CO: was carried out at 40°C and 16 MPa to obtain an NC/PVA reinforced CTS aerogel. The CTS aerogel was tested for shrinkage rate and compressive strength. Results were shown in Table 1.

Example 3

A 3 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 20:80 to obtain a 10 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 20 mL of 4 wt% resorcinol solution was added and stirred to achieve homogeneity. Finally, a 5 wt% solution of crosslinker in glyoxal was added at a temperature as low as 5°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 75°C at a rate of 10°C/d and then holding a temperature for 1 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with an isopropanol solvent for 2 d to obtain an NC/PVA reinforced CTS alcohol gel.

Finally, drying with sc-C0;3 was carried out at 40°C and 18 MPa to obtain an NC/PVA reinforced CTS aerogel. The CTS aerogel was tested for shrinkage rate and compressive strength. Results were shown in Table 1.

Example 4

A 3 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 20:80 to obtain a 12 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 20 mL of 4 wt% resorcinol solution was added and stirred to achieve homogeneity. Finally, a 6 wt% solution of crosslinker in genipin was added at a temperature as low as 10°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 80°C at a rate of 10°C/d and then holding a temperature for 1 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with an ethanol solvent for2 dto obtain an NC/PVA reinforced CTS alcohol gel. Finally, drying with sc-CO: was carried out at 45°C and 15 MPa to obtain an NC/PVA reinforced CTS aerogel. The CTS aerogel was tested for shrinkage rate and compressive strength. Results were shown in Table 1.

Example 5

A 4 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 30:70 to obtain a 10 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 25 mL of 7 wt% resorcinol solution was added and stirred to achieve homogeneity. Finally, a 7 wt& solution of crosslinker in o-phthalaldehyde was added at a temperature as low as 5°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 75°C at a rate of 10°C/d and then holding a temperature for 1 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with an isopropanol solvent for 2 d to obtain an NC/PVA reinforced CTS alcohol gel.

Example 6

A 3 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt& acetic acid aqueous solution in a volume ratio of 40:60 to obtain a 14 g/L

CTS solution, A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 30 mL of 8 wt% resorcinol solution was added and stirred to achieve homogeneity. Finally, an 8 wt% solution of crosslinker in isophthalaldehyde was added at a temperature as low as 10°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 75°C at a rate of 10°C/d and then holding a temperature for 2 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with an isopropanol solvent for 3 d to obtain an NC/PVA reinforced CTS alcohol gel.

Finally, drying with sc-CO0: was carried out at 40°C and 16 MPa to obtain an NC/PVA reinforced CTS aerogel. The CTS aerogel was tested for shrinkage rate and compressive strength. Results were shown in Table 1.

Example 7

A 5 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 40:60 to obtain a 9 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 35 mL of 8 wt% resorcinol solution was added and stirred to achieve homogeneity. Finally, a 10 wt% solution of crosslinker in terephthalaldehyde was added at a temperature as low as 5°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 75°C at a rate of 10°C/d and then holding a temperature for 2 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with a tert-butanol solvent for 3 d to obtain an NC/PVA reinforced CTS alcohol gel.

Finally, drying with sc~C0; was carried out at 45°C and 19 MPa to obtain an NC/PVA reinforced CTS aerogel. The CTS aerogel was tested for shrinkage rate and compressive strength. Results were shown in Table 1.

Example 8

A 4 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 40:60 to obtain a 12 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 40 mL of 8 wt% resorcinol solution was added and stirred to achieve homogeneity. Finally, a 10 wt% solution of crosslinker in glutaraldehyde was added at a temperature as low as 5°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 75°C at a rate of 10°C/d and then holding a temperature for 2 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with a tert-butanol solvent for 3 d to obtain an NC/PVA reinforced CTS alcohol gel.

Example 9

A 4 wt% homogeneous mixed solution of NC solution and PVA solution was prepared. Then, CTS was dissolved in a binary solvent system formed by mixing ethanol and 2 wt% acetic acid aqueous solution in a volume ratio of 40:60 to obtain an 8 g/L

CTS solution. A homogeneous NC/PVA solution was added into the

CTS solution and stirred uniformly. 30 mL of 4 wt& resorcinol solution was added and stirred to achieve homogeneity. Finally, an 8 wt% solution of crosslinker in o-phthalaldehyde was added at a temperature as low as 5°C, stirred and allowed to stand still to obtain an NC/PVA reinforced CTS hydrogel. An initially obtained NC/PVA reinforced CTS hydrogel was placed in a thermostat aging tank, and aged by raising a starting temperature of 10°C to 75°C at a rate of 10°C/d and then holding a temperature for 1 d to obtain a mature NC/PVA reinforced CTS hydrogel. An ethanol-water solvent in the mature NC/PVA reinforced CTS hydrogel was replaced with an isopropanol solvent for 2 d to obtain an NC/PVA reinforced CTS alcohol gel.

Table 1: Shrinkage rate and compressive strength of NC/PVA reinforced CTS aerogels prepared in each Example strain (MPa) rate (%) 0.81 14.21 oe Los | azas 7.12

Those skilled in the art should understand that the scope of the present disclosure is not limited to the above embodiments, and several changes and modifications can be made without departing from the scope of the present disclosure as defined by the appended claims. Although the present disclosure is described in detail in the drawings and the description, such illustration and description is merely illustrative or schematic, rather than restrictive. The present disclosure is not limited to the disclosed embodiments.

Through reading the drawings, the description and the claims,

those skilled in the art can understand and implement variations of the disclosed embodiments when implementing the present disclosure. In the claims, the term "comprising" does not exclude other steps or elements, and the indefinite article "a" or "an" does not exclude a plurality. The fact that certain measures are cited in mutually different dependent claims does not mean that these measures cannot be combined. Any reference signs in the claims do not limit the scope of the present disclosure.

The above contents merely describe preferred embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modification, equivalent substitution and improvement without departing fromthe spirit and principle of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

CONCLUSIONS

A method for preparing a nanocellulose (NC)/polyvinyl alcohol (PVA)-enhanced chitosan-{(CTS)- airgel, comprising the following steps: step 1: preparing NC/PVA-enhanced CTS hydrogel : mixing an NC solution and a PVA solution homogeneously to obtain a homogeneous NC/PVA solution, dissolving CTS in an ethanol-water solvent to obtain a CTS solution, adding the homogeneous NC /PVA solution into the CTS solution, stirring uniformly, adding 10-40 mL of resorcinol solution, stirring to achieve homogeneity, adding cross-linking agent solution, stirring and standing still to achieve NC /PVA-enhanced CTS hydrogel; step 2: maturing: maturing the NC/PVA-enhanced CTS hydrogel to obtain a matured NC/PVA-enhanced CTS hydrogel; step 3: organic solvent replacement: replacing the ethanol-water solvent in the matured NC/PVA-enhanced CTS hydrogel with an organic solvent for 1-7 d; step 4: drying to obtain an NC/PVA reinforced CTS airgel.

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein the homogeneous NC/PVA solution has a concentration of 1-5% by weight.

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein the ethanol-water solvent is obtained by mixing ethanol and 2% by weight aqueous acetic acid solution in a volume ratio of (10-40 ): (60-90).

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein the CTS solution has a concentration of 6-16 g/L.

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein the cross-linking agent solution is obtained by dissolving a cross-linking agent in ethanol and has a concentration of 2-12% by weight .

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 5, wherein the cross-linking agent is one of genipin, formaldehyde, acetaldehyde, glyoxal, succinaldehyde, glutaraldehyde, o-phthalaldehyde, iso -phthalaldehyde, and terephthalaldehyde, or any combination thereof.

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein the resorcinol solution has a concentration of 1-10% by weight.

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein maturing of the NC/PVA-enhanced CTS hydrogel is carried out by an initial temperature of 10-40 2C to 60-80 2C at a rate of 5-10 2C/d and then maintain a temperature for 1-3 d.

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein the organic solvent is one of methanol, ethanol, isopropanol, tert-butanol, acetone, benzyl alcohol, and n-hexane, or any combination thereof.

The method for preparing an NC/PVA-enhanced CTS airgel according to claim 1, wherein the drying is drying with supercritical carbon dioxide {sc-CO:2) at 40-60 2C and 15-20 MPa. -0-0-0-