Preparation of flame-retardant recyclable compressible recoverable degradable chitosan aerogel and infrared camouflage application of flame-retardant recyclable compressible recoverable degradable chitosan aerogel

Abstract

The invention discloses preparation of flame-retardant recyclable compressible recoverable degradable chitosan aerogel and infrared camouflage application of the flame-retardant recyclable compressible recoverable degradable chitosan aerogel, and belongs to the technical field of aerogel materials. The preparation method of the aerogel comprises the following steps: (1) mixing and stirring chitosan and water to obtain a chitosan solution, then adding phosphorus / nitrogen-containing bridged organosiloxane and tetraethyl orthosilicate into the chitosan solution, and then stirring to obtain white uniform turbid liquid; and (2) heating and curing the white suspension, then precooling, and finally freeze-drying to obtain the flame-retardant recyclable compressible recoverable degradable chitosan aerogel. The aerogel provided by the invention is a chitosan-based aerogel material integrating flame retardance, heat insulation, cyclic compression, recycling, degradation and other properties, has good heat insulation performance, can effectively shield infrared radiation, and has great application prospects in infrared camouflage.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel materials, and particularly to the preparation of flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel and its infrared camouflage application. Background Art

[0002] Chitosan (CS) is prepared by partial deacetylation of chitin. It is a polysaccharide linked by β-1,4-glycosidic bonds and has a structure similar to cellulose. However, due to the rich amino groups in its molecules, chitosan exhibits stronger chemical activity and can form covalent cross-links with active groups such as carboxyl and hydroxyl groups, showing great potential in modification. With these characteristics, chitosan has been widely used in many fields such as packaging films, photoelectrocatalysis, drug delivery, and antibacterial materials. At the same time, aerogel is one of the most promising lightweight thermal insulation materials. By replacing the liquid in the hydrogel with air under supercritical conditions while retaining the original continuous three-dimensional structure and the volume of the solid network, it has excellent properties such as superporosity, low density, high specific surface area, and low thermal conductivity. Especially in the field of thermal insulation, due to the high porosity and low thermal conductivity of aerogel, its thermal insulation effect is remarkable, and it is mainly applied in fields such as building wall and pipeline insulation. Therefore, chitosan-based aerogel has the characteristics of wide source, low cost, and good biocompatibility, and at the same time has properties such as thermal insulation and toughness, becoming a hot topic in materials science.

[0003] However, pure chitosan aerogel has problems such as insufficient flame retardancy and poor resilience when subjected to large external forces, which severely limit its practical applications. Generally, the improved method is to introduce small molecule flame retardants such as Al(OH)3 and Mg(OH)2 into chitosan aerogel and utilize the heat dehydration characteristics of the two to improve the flame retardant performance of chitosan. However, the improvement of the flame retardant effect is still limited, and with the increase of the amount of flame retardant, it has a certain impact on the mechanical properties of chitosan aerogel, and the preparation process of this method usually has more steps. In addition, the treatment of chitosan aerogel after abandonment is also a technical focus, and most of the relevant research on chitosan aerogel does not explore this point. Summary of the Invention

[0004] Technical Problem

[0005] Chitosan aerogel is a material with broad prospects, but it needs to be modified to solve the problems of poor flame retardant effect, poor resilience, low mechanical properties, and recycling.

[0006] Technical Content

[0007] The object of the present invention is to provide a method for preparing a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel and its application in infrared camouflage, aiming to solve the problems of insufficient flame retardancy and poor cyclic compression performance of chitosan aerogel, and to provide a new method for the application of infrared camouflage. The operation of the present invention is simple, the conditions are easy to control, and the obtained chitosan-based aerogel has remarkable flame retardancy, heat insulation and cyclic compression performance, and has application prospects in infrared camouflage.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel, comprising the following steps:

[0009] (1) Mix chitosan and water and stir to obtain a chitosan solution, then add a phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate to the chitosan solution, and then stir to obtain a white and uniform suspension;

[0010] (2) Heat and cure the white and uniform suspension, then pre-cool, and finally freeze-dry to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0011] Further, the deacetylation degree of the chitosan in step (1) is > 95%.

[0012] Further, the concentration of chitosan in the chitosan solution in step (1) is 0.2 - 5 wt%.

[0013] Preferably, the concentration of chitosan in the chitosan solution in step (1) is 0.5 - 2 wt%.

[0014] Specifically, optionally, the concentration of chitosan in the chitosan solution in step (1) is 0.5.

[0015] Further, acetic acid can also be added to the chitosan solution in step (1); the concentration of the added acetic acid in the chitosan solution is 0.1 - 3 wt%.

[0016] Further, the phosphorus / nitrogen bridged organosiloxane in step (1) is prepared by heating and reacting hexachlorocyclotriphosphazene and γ-aminopropyl silanetriol in a protective gas atmosphere.

[0017] Further, the protective gas includes nitrogen or noble gas.

[0018] Further, the specific preparation process of the phosphorus / nitrogen bridged organosiloxane is as follows:

[0019] In a nitrogen environment, take hexachlorocyclotriphosphazene and γ-aminopropyl silanetriol, mix them in a mass ratio of 1:3.5 - 4, then stir and react at 45 - 55 °C for 20 - 40 min, and then raise the temperature to 75 - 85 °C and continue to react for 2 - 4 h to obtain the phosphorus / nitrogen bridged organosiloxane.

[0020] Further, the mass ratio of the phosphorus / nitrogen bridged organosiloxane to chitosan described in step (1) is 0.3 to 1.5:1.

[0021] Preferably, the mass ratio of the phosphorus / nitrogen bridged organosiloxane to chitosan described in step (1) is 0.5 to 1:1.

[0022] Further, the mass ratio of tetraethyl orthosilicate to chitosan described in step (1) is 0.2 to 1.5:1.

[0023] Preferably, the mass ratio of tetraethyl orthosilicate to chitosan described in step (1) is 0.3 to 1:1.

[0024] Specifically and optionally, the mass ratio of chitosan, phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate in step (1) is 1:1:0.3, 1:0.5:0.3 or 1:1:1.

[0025] Further, in step (1), the phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate need to be added dropwise to the chitosan solution.

[0026] Further, in step (1), tetraethyl orthosilicate is added after an interval of 10 to 30 minutes after adding the phosphorus / nitrogen bridged organosiloxane.

[0027] Further, the stirring time in step (1) is 30 to 50 minutes.

[0028] Further, the temperature for heat curing in step (2) is 60 to 80 °C, and the time is 40 to 60 minutes.

[0029] Further, the temperature for pre-cooling in step (2) is -78 to -5 °C, and the time is 12 to 48 hours.

[0030] Further, the temperature for freeze-drying in step (2) is -80 to -70 °C; the freeze-drying time is 48 to 72 hours.

[0031] The present invention provides a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared according to the above method.

[0032] The application of the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel provided by the present invention in the field of thermal insulation materials and / or infrared camouflage materials.

[0033] The present invention has the following beneficial effects:

[0034] (1) By introducing phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate into chitosan aerogel, the present invention can effectively improve the flame retardancy of the aerogel material. Firstly, the phosphorus / nitrogen bridged organosiloxane contains phosphorus and nitrogen elements, and tetraethyl orthosilicate contains silicon element. Secondly, the phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate will hydrolyze in the chitosan solution to generate compounds containing a large number of hydroxyl groups, which can combine with the amino or hydroxyl groups in the chitosan molecule by covalent bonds or hydrogen bonds to form crosslinking points between chitosan molecules, thereby improving the elastic recovery ability of the aerogel. This method has simple steps and rapid preparation, and can be mass-produced in batches. At the same time, the chitosan-based aerogel prepared by the present invention also has good heat insulation performance and resilience performance. It is an aerogel integrating flame retardancy, heat insulation, cyclic compression degradation and other properties, and can effectively shield infrared radiation, showing great application prospects in infrared camouflage.

[0035] (2) The flame-retardant, recyclable, compressible and degradable chitosan aerogel in the present invention can be dissolved in aqueous solutions such as dilute acetic acid or dilute hydrochloric acid and then freeze-dried again to become a complete aerogel. The re-shaped aerogel still has good flame retardancy, heat insulation, cyclic compression and other properties. And because the chitosan aerogel of the present invention also has good biodegradability, it can be completely degraded within two weeks in moist soil. Brief Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, it is necessary to briefly introduce the drawings used in the embodiments. It should be clear that the following drawings are only related diagrams of some embodiments of the present invention. Based on these embodiments of the present invention, all other embodiments that can be obtained by those of ordinary skill in the art without creative work are within the protection scope of the present invention.

[0037] Figure 1 It is a schematic diagram of the thermogravimetric test curve of the flame-retardant, recyclable, compressible and degradable chitosan aerogel prepared in Example 1 of the present invention.

[0038] Figure 2 It is the stress-strain curves of the flame-retardant, recyclable, compressible and degradable chitosan aerogel prepared in Example 1 of the present invention and the pure chitosan aerogel prepared in Comparative Example 1 under different compression loads.

[0039] Figure 3 It is the stress-strain curves of the flame-retardant, recyclable, compressible and degradable chitosan aerogel prepared in Example 1 of the present invention and the pure chitosan aerogel prepared in Comparative Example 1 under 30% and 50% constant strain for 1000 compression-rebound cycles.

[0040] Figure 4This is the cyclic compression process diagram of the flame-retardant, recyclable, compressible, and degradable chitosan aerogel prepared in Example 1 of the present invention.

[0041] Figure 5 This is the flowchart for the recycling and utilization of the flame-retardant, recyclable, compressible, and degradable chitosan aerogel prepared in Example 1 of the present invention in the discarded state.

[0042] Figure 6 This is the flowchart for the natural degradation of the flame-retardant, recyclable, compressible, and degradable chitosan aerogel prepared in Example 1 of the present invention in the soil.

[0043] Figure 7 This is the infrared thermal imaging diagram of the flame-retardant, recyclable, compressible, and degradable chitosan aerogel prepared in Example 1 of the present invention. From top to bottom, they are the infrared thermal imaging diagrams of the hot stage surface, the car model, and the house model. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] Raw material sources

[0046] Chitosan (>95% deacetylated) was purchased from Shanghai Macklin Biochemical Co., Ltd.; the phosphorus / nitrogen bridged organosiloxane was formed by heating and reacting hexachlorocyclotriphosphazene and γ-aminopropyl silanetriol in an oil bath. The specific synthesis steps are as follows: First, weigh 4.2 g of hexachlorocyclotriphosphazene and 16.0 g of γ-aminopropyl silanetriol, and place a 50 mL three-necked flask (previously dried in an oven) in the oil bath. Then add the rotor and hexachlorocyclotriphosphazene to the three-necked flask, connect the three-necked flask to a nitrogen cylinder, set the initial heating temperature to 22 °C, turn on the magnetic stirrer, and dropwise add γ-aminopropyl silanetriol. After completion, raise the temperature of the oil bath to 50 °C, and after half an hour, raise the temperature to 80 °C and continue the reaction for 3 hours. The whole process needs to be carried out under a nitrogen atmosphere. Finally, a light yellow phosphorus / nitrogen bridged organosiloxane is obtained; both hexachlorocyclotriphosphazene and γ-aminopropyl silanetriol were purchased from Shanghai Titan Scientific Co., Ltd.

[0047] Example 1

[0048] Add 0.5 g of chitosan, 0.5 g of acetic acid and 99 mL of deionized water into a reaction device, and stir magnetically until the chitosan is completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution is 0.5 wt%, and the concentration of acetic acid is 0.5 wt%; transfer the chitosan solution to a three-necked flask and stir mechanically at a speed of 900 r / min. Weigh 0.5 g of phosphorus / nitrogen bridged organosiloxane and add it dropwise to the chitosan solution, stir mechanically for 20 min, then weigh 0.15 g of tetraethyl orthosilicate and add it dropwise to the chitosan solution, and stir mechanically for 40 min until a uniform and stable white suspension is formed.

[0049] Pour the obtained white suspension into a mold and place it in an electrothermal constant temperature air blast drying oven at 60 °C for 30 min for curing. Then, pre-freeze the cured dispersion with liquid nitrogen or a refrigerator. The pre-freezing temperature is -78 to -5 °C, and the time is 12 to 48 h. Finally, place the pre-frozen sample in a freeze dryer for freeze drying. The freeze drying temperature is -76 °C, and the time is 48 to 72 h to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0050] Example 2

[0051] Add 1 g of chitosan, 0.5 g of acetic acid and 98.5 mL of deionized water into a reaction device, and stir magnetically until the chitosan is completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution is 1 wt%, and the concentration of acetic acid is 0.5 wt%; transfer the chitosan solution to a three-necked flask and stir mechanically at a speed of 900 r / min. Weigh 1 g of phosphorus / nitrogen bridged organosiloxane and add it dropwise to the chitosan solution, stir mechanically for 20 min, then weigh 0.3 g of tetraethyl orthosilicate and add it dropwise to the chitosan solution, and stir mechanically for 40 min until a uniform and stable white suspension is formed.

[0052] Pour the obtained white suspension into a mold and place it in an electrothermal constant temperature air blast drying oven at 60 °C for 30 min for curing. Then, pre-freeze the cured dispersion with liquid nitrogen or a refrigerator. The pre-freezing temperature is -78 to -5 °C, and the time is 12 to 48 h. Finally, place the pre-frozen sample in a freeze dryer for freeze drying. The freeze drying temperature is -76 °C, and the time is 48 to 72 h to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0053] Example 3

[0054] Add 2 g of chitosan, 0.5 g of acetic acid and 97.5 mL of deionized water into a reaction device, and stir magnetically until the chitosan is completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution is 2 wt%, and the concentration of acetic acid is 0.5 wt%; transfer the chitosan solution to a three-necked flask and stir mechanically at a speed of 900 r / min. Weigh 2 g of phosphorus / nitrogen bridged organosiloxane and add it dropwise to the chitosan solution, stir mechanically for 20 min, then weigh 0.6 g of tetraethyl orthosilicate and add it dropwise to the chitosan solution, and stir mechanically for 40 min until a uniform and stable white suspension is formed.

[0055] Put the obtained white suspension into a mold and place it in an electrothermal constant temperature air blast drying oven at 60 °C for 30 min for curing. Then, pre-freeze the cured dispersion with liquid nitrogen or a refrigerator, with the pre-freezing temperature being -78 to -5 °C and the time being 12 to 48 h. Finally, place the pre-frozen sample in a freeze dryer for freeze drying, with the freeze drying temperature being -76 °C and the time being 48 to 72 h to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0056] Example 4

[0057] Add 0.5 g of chitosan, 0.5 g of acetic acid and 99 mL of deionized water into a reaction device, and stir magnetically until the chitosan is completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution is 0.5 wt%, and the concentration of acetic acid is 0.5 wt%; transfer the chitosan solution to a three-necked flask and stir mechanically at a speed of 900 r / min. Weigh 0.25 g of phosphorus / nitrogen bridged organosiloxane and add it dropwise to the chitosan solution, stir mechanically for 20 min, then weigh 0.15 g of tetraethyl orthosilicate and add it dropwise to the chitosan solution, and stir mechanically for 40 min until a uniform and stable white suspension is formed.

[0058] Put the obtained white suspension into a mold and place it in an electrothermal constant temperature air blast drying oven at 60 °C for 30 min for curing. Then, pre-freeze the cured dispersion with liquid nitrogen or a refrigerator, with the pre-freezing temperature being -78 to -5 °C and the time being 12 to 48 h. Finally, place the pre-frozen sample in a freeze dryer for freeze drying, with the freeze drying temperature being -76 °C and the time being 48 to 72 h to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0059] Example 5

[0060] 0.5 g of chitosan, 0.5 g of acetic acid and 99 mL of deionized water were added to a reaction device, and magnetically stirred until the chitosan was completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution was 0.5 wt%, and the acetic acid concentration was 0.5 wt%; the chitosan solution was transferred to a three-necked flask and mechanically stirred at a speed of 900 r / min. 0.5 g of phosphorus / nitrogen bridged organosiloxane was weighed and added dropwise to the chitosan solution, and mechanically stirred for 20 min. Then, 0.5 g of tetraethyl orthosilicate was weighed and added dropwise to the chitosan solution, and mechanically stirred for 40 min until a uniform and stable white suspension was formed.

[0061] The obtained white suspension was filled into a mold and placed in an electrothermal constant temperature blast drying oven at 60 °C for 30 min for curing. Then, the cured dispersion was pre-frozen with liquid nitrogen or a refrigerator, the pre-freezing temperature was -78 to -5 °C, and the time was 12 to 48 h. Finally, the pre-frozen sample was freeze-dried in a freeze dryer, the freeze-drying temperature was -76 °C, and the time was 48 to 72 h to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0062] Example 6

[0063] 0.5 g of chitosan, 0.5 g of acetic acid and 99 mL of deionized water were added to a reaction device, and magnetically stirred until the chitosan was completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution was 0.5 wt%, and the acetic acid concentration was 0.5 wt%; the chitosan solution was transferred to a three-necked flask and mechanically stirred at a speed of 900 r / min. 1 g of phosphorus / nitrogen bridged organosiloxane was weighed and added dropwise to the chitosan solution, and mechanically stirred for 20 min. Then, 1 g of tetraethyl orthosilicate was weighed and added dropwise to the chitosan solution, and mechanically stirred for 40 min until a uniform and stable white suspension was formed.

[0064] The obtained white suspension was filled into a mold and placed in an electrothermal constant temperature blast drying oven at 60 °C for 30 min for curing. Then, the cured dispersion was pre-frozen with liquid nitrogen or a refrigerator, the pre-freezing temperature was -78 to -5 °C, and the time was 12 to 48 h. Finally, the pre-frozen sample was freeze-dried in a freeze dryer, the freeze-drying temperature was -76 °C, and the time was 48 to 72 h to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0065] Example 7

[0066] 0.5 g of chitosan, 0.5 g of acetic acid and 99 mL of deionized water were added to a reaction device, and magnetically stirred until the chitosan was completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution was 0.5 wt%, and the acetic acid concentration was 0.5 wt%; the chitosan solution was transferred to a three-necked flask and mechanically stirred at a speed of 900 r / min. 1.5 g of phosphorus / nitrogen bridged organosiloxane was weighed and added dropwise to the chitosan solution, and mechanically stirred for 20 min. Then, 1.5 g of tetraethyl orthosilicate was weighed and added dropwise to the chitosan solution, and mechanically stirred for 40 min until a uniform and stable white suspension was formed.

[0067] The obtained white suspension was loaded into a mold and placed in an electrothermal constant temperature blast drying oven at 60 °C for 30 min for curing. Then, the cured dispersion was pre-frozen with liquid nitrogen or a refrigerator, the pre-freezing temperature was -78 to -5 °C, and the time was 12 to 48 h. Finally, the pre-frozen sample was freeze-dried in a freeze dryer, the freeze-drying temperature was -76 °C, and the time was 48 to 72 h to obtain a flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel.

[0068] Comparative Example 1

[0069] 0.5 g of chitosan, 0.5 g of acetic acid and 99 mL of deionized water were added to a reaction device, and magnetically stirred until the chitosan was completely dissolved to obtain a chitosan solution, where the mass fraction of the chitosan aqueous solution was 0.5 wt%, and the acetic acid concentration was 0.5 wt%; the obtained chitosan solution was loaded into a mold and placed in an electrothermal constant temperature blast drying oven at 60 °C for 30 min for curing. Then, the cured chitosan solution was pre-frozen with liquid nitrogen or a refrigerator, the pre-freezing temperature was -78 to -5 °C, and the time was 12 to 48 h. Finally, the pre-frozen sample was freeze-dried in a freeze dryer, the freeze-drying temperature was -76 °C, and the time was 48 to 72 h to obtain a pure chitosan aerogel.

[0070] In order to verify the flame-retardant and heat-insulating properties of the aerogel products in the above Examples 1-7 and Comparative Example 1. The axial and radial thermal conductivities and the anisotropy values, and the limiting oxygen index of the aerogels in each example and comparative example were measured. The test results are shown in Table 1 below.

[0071] Table 1 Heat-insulating and flame-retardant properties of the aerogel samples in Examples 1-7 and Comparative Example 1

[0072]

[0073] As can be seen from Table 1 above, for Examples 1 - 7, whether it is the axial thermal conductivity or the radial thermal conductivity, they are all less than that of Comparative Example 1, indicating that each group of examples has good heat insulation effect. However, due to the addition of excessive phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate in Example 6 and Example 7, the pores in the aerogel are reduced instead. Therefore, the heat insulation effect of Example 6 and Example 7 is inferior to that of Examples 1 - 5. In addition, Examples 1 - 7 start to burn between the oxygen index of 38% - 44%, exceeding the national flame retardant standard limit oxygen index of 27%, and being much greater than the pure chitosan limit oxygen index of Comparative Example 1, showing excellent flame retardant effect.

[0074] Example 8

[0075] The aerogel after 1000 compression - rebound cycles is used as waste aerogel. Then, 1 g of waste aerogel, 98 mL of deionized water, and 1 g of acetic acid are weighed and mechanically stirred for 1.5 hours to obtain a white homogeneous dispersion. Then, the obtained dispersion is loaded into a mold and placed in an electro - thermal constant - temperature forced - air drying oven at 60 °C for 30 min for curing. Then, the cured dispersion is pre - frozen using liquid nitrogen or a refrigerator, with the pre - freezing temperature being - 78 °C to - 5 °C and the time being 12 h to 48 h. Finally, the pre - frozen sample is freeze - dried in a freeze - dryer, with the freeze - drying temperature being - 76 °C and the time being 48 h to 72 h, to obtain a new flame - retardant, recyclable by compression, recoverable, and degradable chitosan aerogel.

[0076] To verify that the recycled flame - retardant, recyclable by compression, recoverable, and degradable chitosan aerogel prepared in Example 8 still has good flame - retardant, heat - insulation, and mechanical properties, the new flame - retardant, recyclable by compression, recoverable, and degradable chitosan aerogel obtained in Example 8 is subjected to 1000 compression - rebound cycles and then recycled as described above. After that, compression - rebound cycles and recycling are carried out again to obtain flame - retardant, recyclable by compression, recoverable, and degradable chitosan aerogels with recycling times of 2 times, 5 times, 10 times, and 20 times respectively. The limiting oxygen index LOI value, thermal conductivity, and compression modulus value in the radial direction are measured and compared with those of Example 1. The results are shown in Table 2 below:

[0077] Table 2

[0078]

[0079] As can be seen from the above table, even after 20 times of recycling, the flame - retardant, recyclable by compression, recoverable, and degradable chitosan aerogel still has excellent heat - insulation, flame - retardant, and mechanical properties, and the limiting oxygen index LOI value is still much higher than the national flame retardant standard limit oxygen index of 27%, indicating its excellent recycling performance.

[0080] Figure 1Schematic diagram of the thermogravimetric test curves of the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared in Example 1 of the present invention and the pure chitosan aerogel prepared in Comparative Example 1. From Figure 1 It can be seen that the weight of the aerogel prepared in Example 1 remains 43%, while the weight of the aerogel prepared in Comparative Example 1 only remains 25%. The thermal stability of the aerogel in the example is greatly improved.

[0081] Figure 2 Stress-strain curves of the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared in Example 1 of the present invention and the pure chitosan aerogel prepared in Comparative Example 1 under different compression loads. From Figure 2 It can be seen that the aerogel prepared in Comparative Example 1 will have a large strain under a very small stress, while the aerogel in Example 1 will have a large strain under a relatively large stress, with a larger Young's modulus and better mechanical properties.

[0082] Figure 3 Stress-strain curves of the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared in Example 1 of the present invention and the pure chitosan aerogel prepared in Comparative Example 1 during 1000 compression and rebound cycles under 30% and 50% constant strain. From Figure 3 It can be seen that the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared in Example 1 has good elastic recovery performance, maintains a relatively high Young's modulus and good mechanical properties even after 1000 cycles of cyclic compression, whether under 30% or 50% constant strain.

[0083] Figure 4 Process diagram of the cyclic compression of the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared in Example 1 of the present invention. The aerogel can be compressed by placing a 500 g weight on it, and due to the formation of cross-linking points between chitosan molecules by phosphorus / nitrogen bridged organosiloxane and tetraethyl orthosilicate, the aerogel has good elastic recovery performance and can return to the state before compression within 10 minutes.

[0084] Figure 5 Flow chart of the recycling of the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared in Example 1 of the present invention in the discarded state. Through this process, the discarded aerogel in the example can be reshaped, and the reshaped aerogel also has good heat insulation, flame retardancy and mechanical properties.

[0085] Figure 6 Flow chart of the natural degradation of the flame-retardant, recyclable, compressible, recoverable and degradable chitosan aerogel prepared in Example 1 of the present invention in the soil. From Figure 6 It can be seen that the aerogel prepared in this example can be completely degraded within 15 days in the soil.

[0086] Figure 7 The infrared thermal imaging diagrams of the flame-retardant, recyclable, compressible, and degradable chitosan aerogel prepared in Example 1 of the present invention on the surface of a hot stage and inside a house and a car model. From Figure 7 It can be seen that whether on the surface of the hot stage or inside the house and car models, the aerogel prepared by the present invention can effectively shield the infrared radiation emitted by objects and play a role in infrared camouflage.

[0087] The embodiments provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit the order of their execution. Obvious improvements made by those skilled in the art to the present invention in combination with the existing well-known common knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a flame-retardant, recyclable, compressible, recyclable and degradable chitosan aerogel, characterized in that: The following steps are involved: (1) mixing chitosan and water to obtain a chitosan solution, then adding phosphorus / nitrogen bridging organosiloxane and tetraethyl orthosilicate to the chitosan solution, and then stirring to obtain a white uniform suspension; the phosphorus / nitrogen bridging organosiloxane is prepared by heating hexachlorocyclotriphosphazene and γ-aminopropylsilanetriol under a protective gas atmosphere; the mass ratio of the phosphorus / nitrogen bridging organosiloxane to chitosan is 0.3 to 1.5:1; the mass ratio of the tetraethyl orthosilicate to chitosan is 0.2 to 1.5:1; (2) The white uniform suspension is heated and matured, then precooled, and finally freeze-dried to obtain a flame-retardant, recyclable, compressible, recyclable, and biodegradable chitosan aerogel.

2. The preparation method according to claim 1, characterized in that The chitosan solubility in the chitosan solution in step (1) is 0.2-5wt%.

3. The preparation method according to claim 1, characterized in that: The preparation process of the phosphorus / nitrogen bridged organosiloxane in step (1) is as follows: in a nitrogen environment, hexachlorocyclotriphosphazene and γ-aminopropylsilanetriol are mixed in a mass ratio of 1:3.5-4, and then stirred at 45-55° C. for 20-40 minutes, and then the temperature is raised to 75-85° C. and the reaction is continued for 2-4 hours to obtain a phosphorus / nitrogen bridged organosiloxane.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the phosphorus / nitrogen-containing bridging organosiloxane to chitosan in step (1) is 0.5 to 1:

1.

5. The preparation method according to claim 1, characterized in that: The mass ratio of tetraethyl orthosilicate to chitosan in step (1) is 0.3 to 1:

1.

6. The preparation method according to claim 1, characterized in that: The stirring time in step (1) is 30 to 50 minutes.

7. The preparation method according to claim 1, characterized in that: The heating and aging temperature in step (2) is 60 to 80° C. and the time is 40 to 60 minutes.

8. The preparation method according to claim 1, characterized in that: The precooling temperature in step (2) is -78 to -5°C for 12 to 48 hours; the freeze-drying temperature is -80 to -70°C; and the freeze-drying time is 48 to 72 hours.

9. A flame retardant, recyclable, compressible, recyclable and degradable chitosan aerogel, characterized in that: The chitosan aerogel is prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the flame retardant, recyclable, compressible, recyclable and degradable chitosan aerogel according to claim 9 in the field of thermal insulation materials and / or infrared camouflage materials.

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