Chitosan-based polymer composite aerogel, preparation method and application

Abstract

The application provides a chitosan-based polymer composite aerogel, a preparation method and application; the preparation method of the chitosan-based polymer composite aerogel comprises the following steps: homogenizing phosphate ester functionalized boron nitride nanosheets in water to obtain a suspension; mixing the suspension, chitosan powder and iron salt to form a composite gel; and drying to obtain the chitosan-based polymer composite aerogel; and the mass ratio of the chitosan, the phosphate ester functionalized boron nitride nanosheets and the iron salt is 1:0.5-2.5:0.08-0.3. The application utilizes the coordination crosslinking of iron ions and chitosan molecular chains and the chelation of phosphate groups on the surface of boron nitride nanosheets to construct a ternary crosslinking hierarchical network structure, and a low-density, high-specific-strength composite aerogel is prepared, which can realize efficient flame retardation through a triple synergistic mechanism of physical barrier, free radical capture of phosphorus elements and iron ion catalysis carbonization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite materials, and particularly relates to a chitosan-based polymer composite aerogel, a preparation method and application. BACKGROUND

[0002] Flame spread and toxic smoke diffusion caused by flammable materials are the core inducements of casualties. Although the organic flame retardant in the traditional flame-retardant material system can delay combustion, the pyrolysis process is easy to release carcinogenic gas; although the inorganic flame-retardant filler is more environmentally friendly, the addition amount needs to exceed 60% to reach the standard, which will seriously deteriorate the mechanical properties of the material. Biomass aerogel provides a new idea for constructing environmentally friendly flame-retardant materials due to its three-dimensional porous structure and intrinsic charring ability; among them, the modified chitosan aerogel not only exhibits unique self-extinguishing characteristics, but also effectively alleviates the unsustainable problem of petroleum-based materials due to its biodegradability.

[0003] Chinese invention patent CN113234256B discloses a preparation method of a double-crosslinked flame-retardant composite aerogel, which significantly improves the flame-retardant grade by synergistic crosslinking of nanocellulose and chitosan while maintaining biodegradability; however, the flame-retardant efficiency of pure bio-based aerogel is difficult to meet the stringent fireproof standard, which is mainly limited by the insufficient stability of the carbon layer structure and the self-supporting ability at high temperature. Although the introduction of inorganic nano-SiO2 reinforcing phase can improve this defect, such as Chinese invention patent CN111635554B discloses a preparation method and application of gelatin / hydroxyethyl cellulose-SiO2 composite aerogel, the nano-SiO2 composite technology proposed by it realizes the improvement of flame-retardant performance through interface optimization, but the mechanical properties under low density conditions still need to be optimized.

[0004] Therefore, it is necessary to provide a chitosan-based polymer composite aerogel, a preparation method and application, to solve the technical problem of how to obtain a low-density chitosan-based polymer composite aerogel with excellent flame-retardant efficiency and mechanical properties. SUMMARY

[0005] The main purpose of the present application is to provide a chitosan-based polymer composite aerogel, a preparation method and application, which aims to solve the above technical problem of how to obtain a chitosan-based polymer composite aerogel with excellent flame-retardant efficiency and mechanical properties.

[0006] To achieve the above purpose, the present application provides a preparation method of a chitosan-based polymer composite aerogel, comprising the steps of:

[0007] S1, providing chitosan powder, phosphate functionalized boron nitride nanosheet and iron salt;

[0008] The phosphonate functionalized boron nitride nanosheet is obtained by mixing boron nitride powder with an added liquid and then performing liquid-phase assisted ball milling treatment, and then collecting the phosphonate functionalized boron nitride nanosheet; the added liquid contains an organic phosphonate, and the organic phosphonate includes one or more of inositol hexaphosphate, phosphoglycerate, glucose phosphate, and ascorbic acid phosphate.

[0009] S2, homogenizing the phosphonate functionalized boron nitride nanosheet in water to obtain a suspension; mixing the suspension, the chitosan powder, and the iron salt and then standing to obtain a composite gel; and drying to obtain a chitosan-based high-molecular composite aerogel; the mass ratio of the chitosan, the phosphonate functionalized boron nitride nanosheet, and the iron salt is 1:0.5-2.5:0.08-0.3.

[0010] Further, the mass ratio of the boron nitride powder and the organic phosphonate is 1:2-10.

[0011] Further, in the added liquid, the mass percentage of the organic phosphonate is 25-65%.

[0012] Further, the phosphonate functionalized boron nitride nanosheet has a thickness distribution of 1-2.5 nm, a lateral size of 0.6-0.8 μm, and 3-5 layers.

[0013] Further, the mass percentage of the chitosan powder and the suspension is 1-3%.

[0014] Further, the iron salt includes one or more of ferric chloride, ferric nitrate, and ferric sulfate.

[0015] Further, the stirring speed for the homogenization treatment is 8000-15000 rpm.

[0016] The suspension, the chitosan powder, and the iron salt are mixed at a rotation speed of 300-500 rpm for 2-6 h.

[0017] Further, the ball milling rotation speed for the liquid-phase assisted ball milling treatment is 200-500 rpm, and the ball milling time is 8-40 h.

[0018] The liquid-phase assisted ball milling treatment is performed in a ball milling tank containing grinding balls, and the mass ratio of the grinding balls to the boron nitride powder is 50-100:1.

[0019] In the step S1, the process of collecting the phosphonate functionalized boron nitride nanosheet includes centrifuging to collect the upper mixed liquid after the liquid-phase assisted ball milling treatment, filtering and washing, and drying to obtain the phosphonate functionalized boron nitride nanosheet.

[0020] The application further provides a chitosan-based polymer composite aerogel prepared by the preparation method of the chitosan-based polymer composite aerogel.

[0021] The application further provides application of the chitosan-based polymer composite aerogel in fire resistance.

[0022] The principle that the chitosan-based polymer composite aerogel has excellent fire resistance in the application at least includes:

[0023] 1. Phosphate-functionalized boron nitride nanosheets (PBNNS) construct a multi-level synergistic fire-retardant system in the aerogel. The phosphate-functionalized boron nitride nanosheets form a continuous and dense barrier layer through directional arrangement to inhibit the diffusion of heat and oxygen. The phosphate groups on the surface of the nanosheets release phosphorus-containing free radicals at high temperatures to quench the gas-phase chain reaction. Meanwhile, the synergistic effect of iron ions and phosphate groups catalyzes the crosslinking of chitosan to form a high-graphitized carbon layer, realizing physical-chemical dual-effect barrier.

[0024] 2. The phosphate is modified on the surface of BN through liquid-phase assisted ball milling treatment in a P-O-B covalent bond, realizing synchronous exfoliation and functionalization and improving the monolayer dispersibility in the chitosan network of PBNNS. 3+ Through the double bridging effect and the coordination of chitosan Form a rigid coordination network; and the phosphate groups on the surface of PBNNS are chelated to construct a “chitosan-Fe 3+ -PBNNS” three-dimensional interpenetrating network, significantly enhancing the interface bonding density and thermal stability.

[0025] 3. The rigid layers of phosphate-functionalized boron nitride nanosheets are embedded in the pore wall skeleton, and the P-O-Fe bonding and physical interpenetration strengthen the porous structure; the connected pores maintained by the crosslinked network guide the directional migration of combustion products, promoting the formation of a continuous and expanded carbon layer. This structure resists thermal stress deformation, inhibits secondary ignition by prolonging the oxygen diffusion path, realizes self-supporting carbonization and long-acting fire-retardant synergy.

[0026] Compared with the prior art, the application at least has the following advantages:

[0027] The application obtains a low-density chitosan-based polymer composite aerogel with excellent fire-retardant efficiency and mechanical properties, which brings significant beneficial effects in improving fire-retardant performance, enhancing mechanical properties, optimizing inorganic-organic interface compatibility, environmental protection and sustainability, and application prospects.

[0028] The present application is based on the synergistic effect of phosphate functionalized boron nitride nanosheets cross-linked with iron ions to construct an aerogel triple flame-retardant system; wherein the phosphate functionalized boron nitride nanosheets form a dense physical barrier to inhibit heat / oxygen diffusion, the phosphate component captures free radicals in the gas phase, and the iron ion catalyzes the cross-linking of chitosan to form a high-graphitized carbon layer, realizing long-term condensate phase barrier; the present application significantly improves the flame-retardant performance of aerogels, enabling them to maintain stability for a longer period of time in high-temperature and flame environments.

[0029] In the present application, phosphate functionalized boron nitride nanosheets act as rigid reinforcing phases, playing a significant reinforcing role in composite aerogels; at the same time, the dynamic coordination bond between iron ions and chitosan hydroxyl / amino groups, and the chelation effect between iron ions and boron nitride nanosheet phosphate groups, further enhance the stability of the structure, enabling the composite aerogel to maintain good shape stability and mechanical properties when subjected to external forces, thereby broadening its range of application in actual flame-retardant applications.

[0030] The present application simultaneously realizes efficient exfoliation and surface phosphatization modification of boron nitride, with its phosphate groups covalently bonded to chitosan molecular chains, significantly improving the dispersion uniformity and interfacial bonding strength of boron nitride nanosheets in the chitosan three-dimensional network; this optimization avoids the performance decline caused by inorganic-organic phase separation, ensuring the stability of the overall performance of the composite aerogel.

[0031] The present application uses a water-phase ball-milling nanosheet-iron ion cross-linking composite gel process, with no strong acid / alkali and organic solvent involved throughout the process, resulting in a composite aerogel with low bulk density, high specific strength, and low smoke density; the present application has less impact on the environment during preparation and use, can replace traditional harmful environmental materials such as halogen-containing flame retardants, and conforms to the current green and environmentally friendly development trend, having wide application prospects in the fields of building insulation, new energy battery fire prevention, industrial heat protection, etc. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from the structures shown in these drawings without creative labor.

[0033] Figure 1(a) is a scanning electron microscope image of the boron nitride powder in Example 1 of the present application, (b) is a scanning electron microscope image of the solid-phase product in the first step in Comparative Example 1, (c) is a scanning electron microscope image of the PBNNS in Example 1 of the present application, and (d) is a transmission scanning electron microscope image of the PBNNS in Example 1 of the present application;

[0034] Figure 2 (a) is an atomic force microscope image, and (b) is a size-thickness curve graph of the PBNNS in Example 1 of the present application;

[0035] Figure 3 (a) is an infrared spectrum of the boron nitride powder BN and the boron nitride nanosheet PBNNS in Example 1 of the present application;

[0036] Figure 4 (a) is a scanning electron microscope image of the aerogel CSA in Comparative Example 2, (b) is a scanning electron microscope image of the aerogel BN / CS-Fe 3+ in Comparative Example 3, (c) is a scanning electron microscope image of the aerogel PBNNS / CSA in Comparative Example 4, and (d) is a scanning electron microscope image of the aerogel PBNNS / CS-Fe 3+ in Example 1 of the present application;

[0037] Figure 5 (a) is an infrared spectrum of the aerogel prepared in Example 1 and Comparative Example 2 of the present application;

[0038] Figure 6 (a) is an XPS full spectrum of the composite aerogel prepared in Example 1 of the present application, (b) is an N1s high-resolution spectrum, (c) is a B 1s high-resolution spectrum, and (d) is a Fe 2p high-resolution spectrum;

[0039] Figure 7 (a) is a thermogravimetric decomposition curve, and (b) is a differential thermal decomposition curve of the aerogel prepared in Example 1 and Comparative Example 2 of the present application;

[0040] Figure 8 (a) is a vertical combustion experiment graph of the aerogel CSA in Comparative Example 2, (b) is a vertical combustion experiment graph of the aerogel PBNNS / CS-Fe 3+ in Example 1 of the present application, (c) is a vertical combustion experiment graph of the aerogel BN / CS-Fe 3+ in Comparative Example 3.

[0041] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present application.

[0043] In addition, the technical solutions in each embodiment of the present application can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it. When the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope of the present application.

[0044] When the embodiments give a numerical range, it should be understood that, unless otherwise stated by the present application, each numerical range and any number between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present application are consistent with the mastery of the prior art by those skilled in the art and the description of the present application. Any method, equipment and material of the prior art similar or equivalent to the method, equipment and material described in the embodiments of the present application can also be used to realize the present application.

[0045] The present application provides a preparation method of chitosan-based high molecular composite aerogel, comprising the steps of:

[0046] S1, providing chitosan powder, phosphate functionalized boron nitride nanosheet and iron salt.

[0047] It should be noted that the high specific surface area and strong van der Waals force of boron nitride nanosheet easily lead to irreversible stacking and reaggregation in the biological polymer (such as chitosan, cellulose) matrix, causing local defects and stress concentration in the barrier network, significantly weakening the macro mechanical properties of the aerogel. More importantly, the poor interfacial compatibility between inorganic boron nitride nanosheet and organic matrix leads to a significant reduction in flame-retardant synergistic efficiency, making it difficult for traditional composite aerogels to achieve synergistic enhancement of flame-retardant performance and mechanical properties while maintaining ultra-low density. Therefore, improving the dispersion stability and interfacial compatibility of boron nitride nanosheet is the key to constructing boron nitride reinforced biomass-based aerogel with efficient flame-retardant performance.

[0048] In the present application, the phosphate functionalized boron nitride nanosheet is obtained by mixing boron nitride powder with an external liquid and then performing liquid phase assisted ball milling treatment, and then collecting the phosphate functionalized boron nitride nanosheet.

[0049] In the application, the boron nitride powder is in a granular form in microcosm. In the application, the process for collecting the phosphate functionalized boron nitride nanosheets comprises: after the liquid phase assisted ball milling is completed, the upper mixed solution is collected by centrifugation, and the phosphate functionalized boron nitride nanosheets are obtained after filtration and drying; the speed of centrifugation can be 3000-5000 rpm, and the time of centrifugation can be 4-6 min; the filtration can be washing the filter with water and isopropanol, and the drying method can be vacuum drying.

[0050] In the application, the external solution contains organic phosphates, and the organic phosphates include one or more of inositol hexaphosphate, glycerophosphate, glucose phosphate and ascorbic acid phosphate; preferably one or more of inositol hexaphosphate and glycerophosphate; the mass ratio of the boron nitride powder to the organic phosphates is 1:2-10, further 1:2-4 or 1:2-3 or 1:8-10 or 1:9-10.

[0051] In the external solution of the application, the mass percentage of the organic phosphates is 25-65%, further 30-65% or 30-50% or 25-35% or 45-55%; the external solution is composed of the organic phosphates and water.

[0052] In the application, the thickness distribution of the phosphate functionalized boron nitride nanosheets is 1-2.5 nm, the lateral size is 0.6-0.8 μm, and the number of layers is 3-5 layers; the edges present a sawtooth-shaped ultra-thin nanosheet layered structure etched by phosphates.

[0053] In the application, the iron salt includes one or more of ferric chloride, ferric nitrate and ferric sulfate; further ferric chloride.

[0054] In the application, the liquid phase assisted ball milling adopts a ball milling speed of 200-500 rpm and a ball milling time of 8-40 h, further 30-40 h; the liquid phase assisted ball milling is carried out in a ball milling tank, the ball milling tank is loaded with grinding balls, and the size of the grinding balls is 6 mm or 12 mm; the ball powder ratio in the application refers to the mass ratio of the grinding balls to the boron nitride powder; the ball powder mass ratio of the grinding balls to the boron nitride powder can be 50-100:1. In the specific operation of the liquid phase assisted ball milling in the application, the ball milling direction is reversed every 2 h, and each reversal stops working for 30 min.

[0055] Specifically, in the application, the boron nitride powder and the external solution are uniformly mixed and then put into a ball milling tank, and then corresponding size and number of grinding balls are loaded for the liquid phase assisted ball milling; then, the collected mixed solution is centrifuged to remove the lower large piece bulk boron nitride, and the upper mixed solution is washed and filtered with water and isopropanol; finally, the phosphate functionalized boron nitride nanosheets are obtained by vacuum drying.

[0056] S2, homogenizing the phosphate functionalized boron nitride nanosheet in water to obtain a suspension; mixing the suspension, the chitosan powder and the iron salt and standing to obtain a composite gel; drying to obtain a chitosan-based polymer composite aerogel, denoted as PBNNS / CS-Fe 3+ The drying mode can be vacuum freeze drying.

[0057] In the present application, the mass ratio of the chitosan, the phosphate functionalized boron nitride nanosheet and the iron salt is 1:0.5-2.5:0.08-0.3, further 1:1.5-2.5:0.08-0.3, or 1:1.5-2:0.08-0.3, or 1:1.5-2:0.1-0.15, or 1:1.8-2.5:0.08-0.3, or 1:1.8-2.2:0.1-0.15, or 1:1.8-2.2:0.08-0.12, or 1:1.3-1.7:0.1-0.2, or 1:1.4-1.6:0.14-0.16.

[0058] In the present application, the mass percentage of the chitosan powder and the suspension is 1-3%, further 1.5-2.5%, further 2-2.5%.

[0059] In the present application, the stirring speed for the homogenization is 8000-15000 rpm, further 12000-15000 rpm; the rotation speed for mixing the suspension, the chitosan powder and the iron salt is 300-500 rpm, further 400-500 rpm, and the mixing time is 2-6 h, further 3-6 h, further 3-4 h or 5-6 h.

[0060] The present application is a full aqueous phase preparation process; in the preparation method of the present application, the use of acid, base and organic solvent is avoided, and further, the use of acetic acid is avoided. Specifically, in the step S1 and the step S2, the use of acid, base and organic solvent is not performed. For example, in the step S1, only water phase ball milling is performed; in the step S2, only the chitosan powder, the phosphate functionalized boron nitride nanosheet, the iron salt and water are used.

[0061] The present application synchronously realizes the boron nitride sheet layer dissociation and surface functionalization modification by using specific phosphate, and obtains phosphate-based covalently modified boron nitride nanosheet; compared with triphenyl phosphate (TPP) ball milling modified boron nitride which can only obtain agglomerated broken particles; the present application modifies the boron nitride surface through P-O-B covalent bond, inhibits the re-stacking of nanosheet and improves the single-layer dispersibility of the nanosheet in chitosan solution.

[0062] In the process of compositing phosphate-functionalized boron nitride nanosheets (PBNNS) with chitosan, this invention utilizes a dual crosslinking mechanism triggered by iron salts: on the one hand, iron ions coordinate with the hydroxyl and amino groups of the chitosan molecular chains to form a three-dimensional network framework; on the other hand, Fe... 3+ It chelates with the phosphate groups on the surface of PBNNS to construct "chitosan-Fe 3+ The ternary cross-linked structure of "PBNNS" significantly enhances interfacial bonding density and mechanical strength. The aerogel obtained in this invention possesses excellent flame retardancy through a three-tiered synergistic flame-retardant mechanism: the physical barrier effect of PBNNS, the capture of phosphorus gas-phase free radicals, and the catalytic char formation by iron ions in the condensed phase. Based on green chemical processes, this invention overcomes the bottlenecks in the flammability and mechanical properties of biomass aerogels. It is environmentally friendly and can replace traditional halogen-containing flame-retardant materials, showing promising applications in precision equipment thermal protection management and industrial flame retardancy, and is suitable for building fire protection and thermal management equipment protection.

[0063] The present invention also provides a chitosan-based polymeric composite aerogel, which is prepared by any of the chitosan-based polymeric composite aerogel preparation methods described above.

[0064] The properties of the chitosan-based polymeric composite aerogel described in this invention include one or more of the following: a density of 0.0364-0.0610 g / cm³. 3 The compressive modulus ranges from 0.681 to 1.819 MPa, the maximum compressive strength ranges from 0.702 to 1.55 MPa, and the specific modulus ranges from 18.47 to 35.54 MPa·cm. 3 / g, specific strength is 18.16-26.69 MPa·cm 3 / g.

[0065] Alternatively, the properties of the chitosan-based polymeric composite aerogel described in this invention may include one or more of the following: a density of 0.0482-0.0610 g / cm³. 3 The compressive modulus is 1.118-1.819 MPa, the maximum compressive strength is 1.06-1.55 MPa, and the specific modulus is 18.47-35.54 MPa·cm. 3 / g, specific strength is 21.15-26.69 MPa·cm 3 / g.

[0066] Alternatively, the properties of the chitosan-based polymeric composite aerogel described in this invention may include one or more of the following: a density of 0.0482-0.0581 g / cm³. 3 The compressive modulus is 1.713-1.819 MPa, the maximum compressive strength is 1.06-1.55 MPa, and the specific modulus is 30.50-35.54 MPa·cm. 321.99-26.69 MPa·cm 3 21.99-26.69 MPa·cm

[0067] Alternatively, the performance of the chitosan-based polymer composite aerogel in the application includes one or more of the following: the density is 0.0576-0.0581 g / cm 3 1.757-1.819 MPa, the maximum compressive strength is 1.43-1.55 MPa, and the specific modulus is 30.50-31.31 MPa·cm 3 24.83-26.69 MPa·cm 3 24.83-26.69 MPa·cm

[0068] As a preferred case, the maximum thermal decomposition temperature of the chitosan-based polymer composite aerogel is 508-538℃, the maximum thermal decomposition rate is -0.8 to -0.5% / ℃, and the pyrolysis mass at 800℃ is 57-59%.

[0069] The application also provides a chitosan-based polymer composite aerogel as described above for use in flame retardation, which not only has excellent mechanical properties under the condition of maintaining low density, but also can efficiently retard flame; the application includes the use of the chitosan-based polymer composite aerogel for preparing other flame-retardant materials, or the use of the chitosan-based polymer composite aerogel as a flame-retardant material in flame-retardant engineering.

[0070] The following is a specific example of the application:

[0071] Example 1

[0072] Step 1: Obtain boron nitride nanosheets: uniformly mix boron nitride powder (BN) with an additional liquid (the additional liquid is composed of inositol hexaphosphate and water, and the mass fraction of inositol hexaphosphate is 50%) and place it in a ball mill tank, the mass ratio of boron nitride powder to inositol hexaphosphate is 1:10; then load zirconia balls (Φ=6 mm) with a ball-to-powder mass ratio of 50 for liquid-assisted ball milling, the ball milling speed is 200 rpm, the ball milling direction is reversed every 2 h, and the ball milling time is 40 h.

[0073] After ball milling, the collected mixed liquid is centrifuged at 4000 rpm for 5 min to remove large pieces of bulk BN; the upper mixed liquid is washed and filtered with a large amount of water and isopropanol; finally, the solid-phase product obtained after washing and filtering is vacuum dried at 80℃ to obtain inositol hexaphosphate-modified boron nitride nanosheets, which are denoted as PBNNS in this embodiment.

[0074] Step 2, preparation of aerogel: the prepared boron nitride nanosheets were homogenized in deionized water at 12000 rpm to form a uniform suspension, then chitosan powder was added, the mass percentage of chitosan powder and suspension was 2wt%, the mass ratio of chitosan powder and boron nitride nanosheets was 1:2; then ferric chloride was added, the mass percentage of ferric chloride and suspension was 0.2wt%, after mixing and stirring at 500 rpm for 6 h, a uniform composite gel was obtained by standing; finally, vacuum freeze-drying was performed to obtain a chitosan-based polymer composite aerogel, which is denoted as PBNNS / CS-Fe in this embodiment. 3+ .

[0075] Comparative Example 1

[0076] In this comparative example, compared with Example 1, only the inositol hexaphosphate is adjusted to triphenyl phosphate (TPP), and the other conditions are the same as those in Example 1.

[0077] In this comparative example, the solid-phase product in Step 1 is agglomerated and fragmented, so the preparation of aerogel is not performed.

[0078] Comparative Example 2

[0079] In this comparative example, compared with Example 1, Step 1 is not performed, and in the preparation of aerogel in Step 2, the boron nitride nanosheets (PBNNS) are omitted, and the suspension is adjusted to deionized water, and the other conditions are the same as those in Example 1.

[0080] The aerogel prepared in this comparative example is denoted as CSA.

[0081] Comparative Example 3

[0082] In this comparative example, compared with Example 1, Step 1 is not performed, and in the preparation of aerogel in Step 2, the boron nitride nanosheets are adjusted to boron nitride powder (BN), and the other conditions are the same as those in Example 1.

[0083] The aerogel prepared in this comparative example is denoted as BN / CS-Fe 3+ .

[0084] Comparative Example 4

[0085] In this comparative example, compared with Example 1, in the preparation of aerogel, ferric chloride is omitted, and the deionized water used for high-speed homogenization is adjusted to a 2vol% acetic acid solution (used for dissolving chitosan), and the other conditions are the same as those in Example 1.

[0086] The aerogel prepared in this comparative example is denoted as PBNNS / CSA.

[0087] Example 2

[0088] Compared with Example 1, only the inositol hexaphosphate is adjusted to be glycerophosphate, and other conditions are the same as those in Example 1.

[0089] Example 3

[0090] Compared with Example 1, only the inositol hexaphosphate is adjusted to be glycerophosphate, and other conditions are the same as those in Example 1.

[0091] Example 4

[0092] Compared with Example 1, only the inositol hexaphosphate is adjusted to be glycerophosphate, and other conditions are the same as those in Example 1.

[0093] Example 5

[0094] Step 1: Obtain boron nitride nanosheets: uniformly mix boron nitride powder (BN) and an additional liquid (the additional liquid is composed of glycerophosphate and water, and the mass percentage of glycerophosphate is 30%) and place them in a ball mill tank. The mass ratio of boron nitride powder to glycerophosphate is 1:2. Then, load zirconia balls (Φ=12 mm) with a ball-to-powder mass ratio of 100 into the ball mill tank for liquid-assisted ball milling treatment. The rotation speed is 200 rpm, the milling direction is reversed every 2 h, and the ball milling time is 40 h.

[0095] After ball milling, the collected mixed liquid is centrifuged at 4000 rpm for 5 min to remove large pieces of bulk BN. The upper mixed liquid is washed and filtered with a large amount of water and isopropanol. Finally, the solid-phase product obtained after washing and filtering is vacuum dried at 80°C to obtain glycerophosphate-modified boron nitride nanosheets.

[0096] Step 2: Prepare aerogel: the prepared boron nitride nanosheets are homogenized in deionized water at a high speed of 15000 rpm to form a uniform suspension. Then, add chitosan powder, and the mass percentage of chitosan powder to the suspension is 2wt%. The mass ratio of chitosan powder to boron nitride nanosheets is 1:1.5. Then, add ferric sulfate, and the mass percentage of ferric sulfate to the suspension is 0.3wt%. After stirring at 400 rpm for 3 h, a uniform composite gel is obtained by standing. Finally, vacuum freeze-drying is performed to obtain a chitosan-based high-molecular composite aerogel.

[0097] Example 6

[0098] Step 1, obtaining boron nitride nanosheets: boron nitride powder (BN) and an added liquid (the added liquid is composed of glucose phosphate and water, and the mass percentage of glucose phosphate is 65%) are uniformly mixed and then placed in a ball mill tank, the mass ratio of boron nitride powder to glucose phosphate is 1:5; then zirconia balls (Φ=6 mm) with a ball-to-powder mass ratio of 80 are loaded for liquid-phase-assisted ball milling treatment, the ball milling speed is 200 rpm, the ball milling direction is reversed every 2 h, and the ball milling time is 40 h.

[0099] After ball milling, the collected mixed liquid is centrifuged at 4000 rpm for 5 min to remove large pieces of bulk BN; the upper mixed liquid is washed and filtered with a large amount of water and isopropanol; finally, the solid-phase product obtained after washing and filtering is vacuum dried at 80°C to obtain glucose phosphate-modified boron nitride nanosheets.

[0100] Step 2, preparation of aerogel: the prepared boron nitride nanosheets are homogenized in deionized water at a high speed of 10000 rpm to form a uniform suspension, then chitosan powder is added, the mass percentage of chitosan powder to the suspension is 2wt%, and the mass ratio of chitosan to boron nitride nanosheets is 1:1; then ferric nitrate is added, the mass percentage of ferric nitrate to the suspension is 0.3wt%, and the uniform composite gel is obtained after stirring at 300 rpm for 2 h and standing; finally, the chitosan-based high-molecular composite aerogel is obtained by vacuum freeze-drying.

[0101] Example 7

[0102] Step 1, obtaining boron nitride nanosheets: boron nitride powder (BN) and an added liquid (the added liquid is composed of ascorbic acid phosphate and water, and the mass percentage of ascorbic acid phosphate is 60%) are uniformly mixed and then placed in a ball mill tank, the mass ratio of boron nitride powder to ascorbic acid phosphate is 1:6; then zirconia balls (Φ=12 mm) with a ball-to-powder mass ratio of 100 are loaded for liquid-phase-assisted ball milling treatment, the ball milling speed is 200 rpm, the ball milling direction is reversed every 2 h, and the ball milling time is 40 h.

[0103] After ball milling, the collected mixed liquid is centrifuged at 4000 rpm for 5 min to remove large pieces of bulk BN; the upper mixed liquid is washed and filtered with a large amount of water and isopropanol; finally, the solid-phase product obtained after washing and filtering is vacuum dried at 80°C to obtain ascorbic acid phosphate-modified boron nitride nanosheets.

[0104] Step 2, preparation of aerogel: the prepared boron nitride nanosheets were homogenized in deionized water at 8000 rpm to form a uniform suspension, then chitosan powder was added, the mass percentage of chitosan powder and suspension was 2wt%, the mass ratio of chitosan and boron nitride nanosheets was 1:0.5; then ferric chloride was added, the mass percentage of ferric chloride and suspension was 0.5wt%, after stirring at 500 rpm for 4 h, a uniform composite gel was obtained by standing; finally, vacuum freeze-drying was performed to obtain a chitosan-based polymer composite aerogel.

[0105] Analysis Example 1

[0106] (1) Electron microscope analysis was performed on the boron nitride powder (original boron nitride BN) in Example 1, the solid-phase product in Step 1 of Comparative Example 1, and PBNNS in Example 1:

[0107] As shown in (a) of Figure 1 , the original boron nitride exhibited irregular large aggregate, the surface was relatively smooth and accompanied by micron-level layered crystal structure accumulation.

[0108] As shown in (b) of Figure 1 , the solid-phase product obtained in Step 1 of Comparative Example 1 was non-nanosheet boron nitride, the boron nitride only became finer under mechanical action, but did not peel off into the morphology of boron nitride nanosheets, and there was obvious particle agglomeration.

[0109] As shown in (c) of Figure 1 , the inositol hexaphosphate modified boron nitride nanosheets (PBNNS) in Example 1 exhibited a peeled sheet structure, the thickness was significantly reduced and the mechanical chemical process resulted in a relatively rough surface, producing certain defect structures; at the same time, weak agglomeration was retained due to van der Waals interaction.

[0110] As shown in (d) of Figure 1 , the inositol hexaphosphate modified boron nitride nanosheets (PBNNS) in Example 1 showed a relatively thin two-dimensional nanosheet structure, with about 3-5 layers. The above results show that inositol hexaphosphate can efficiently exfoliate the original boron nitride into ultrathin nanosheets due to its multidentate chelation, strong intercalation ability and electrostatic stabilization.

[0111] (2) Atomic force microscope (AFM) analysis was performed on PBNNS in Example 1:

[0112] As shown in Figure 2 , the inositol hexaphosphate modified boron nitride nanosheets (PBNNS) in Example 1 showed a relatively thin two-dimensional nanosheet structure, with about 3-5 layers. The above results show that inositol hexaphosphate can efficiently exfoliate the original boron nitride into ultrathin nanosheets due to its multidentate chelation, strong intercalation ability and electrostatic stabilization. Figure 2The AFM thickness profile and corresponding thickness dimension of PBNNS are shown, and the results quantitatively demonstrate the exfoliation efficiency of the ball milling process, with the main thickness distribution being 1-2.5 nm and the lateral dimension being about 0.6-0.8 μm; these microstructures indicate that controlled exfoliation is achieved while achieving edge-specific chemical modification, effectively solving the problems of size control and stability in the production of boron nitride nanosheets.

[0113] (3) Fourier transform infrared spectroscopy (FTIR) analysis of the boron nitride powder in Example 1 (original boron nitride BN) and PBNNS in Example 1:

[0114] As shown in Figure 3 , the original boron nitride BN shows its characteristic in-plane B-N stretching vibration and B-N-B bending vibration at 1374 and 779 , respectively.

[0115] For PBNNS in Example 1, after myo-inositol hexaphosphate ball milling treatment, the B-N stretching vibration peak area increases, and a new characteristic peak appears at 1642 , corresponding to B-O-P stretching vibration, confirming that myo-inositol hexaphosphate is anchored on the BN surface through coordination; in addition, the C-H stretching vibration peak (methylene) at 2920 and the broadened O-H vibration peak (hydrogen bond) at 3420 further verify the construction of the organic-inorganic interface; it is shown that the chemical functionalization of BN nanosheets is achieved through B-O-P covalent bonding and van der Waals cooperative effect.

[0116] Analysis Example 2

[0117] (1) Structural and chemical property analysis of the aerogel materials prepared in Example 1 and Comparative Examples 2-4:

[0118] As shown in Figure 4 part (a), the aerogel CSA in Comparative Example 2 presents an irregular porous structure with a wide pore size distribution (about 10-150 μm) and uneven pore wall thickness (1-5 μm); local pore wall collapse can be seen in this structure, and although the pore wall surface is relatively smooth, it is accompanied by obvious shrinkage texture, which is speculated to be caused by the shrinkage of polymer chains during solvent evaporation.

[0119] As shown in Figure 4 part (b), the aerogel BN / CS-Fe 3+ in Comparative Example 3 has a large number of agglomerates of boron nitride particles accumulated on the pore wall surface, and the entire porous structure formed after freeze-drying is in a disordered state.

[0120] As shown in Figure 4As shown in part (c) of FIG. 1, the aerogel PBNNS / CSA in Comparative Example 4 has a surface morphology indicating that the PBNNS has a certain guiding effect on the structure of the aerogel, and the formation of an ordered pore structure is observed, but the interlayer spacing between the channels is large, which may be due to the fact that the crosslinking between the polymer molecular chains is not tight enough.

[0121] Referring to Figure 4 part (d) of FIG. 1, the aerogel PBNNS / CS-Fe in Example 1 has a surface morphology as shown in FIG. 1d. 3+ The microstructure exhibits typical characteristics of a hierarchical porous network: the main channel has a relatively uniform pore size (20-50 μm), and a large number of submicron through-holes (500 nm-2 μm) are embedded in the pore wall; in this system, the PBNNS nanosheets are uniformly dispersed in the chitosan framework as nucleation sites and are partially embedded by the chitosan layer, and this structure effectively inhibits the volume shrinkage during freeze-drying.

[0122] More importantly, in Example 1, under the crosslinking of iron salt ions, there are a large number of twisted polymer fiber filaments in the porous structure of the composite aerogel, and this multiple crosslinking effect enriches the pore size hierarchy of the material and significantly enhances the compactness and stability of the overall structure.

[0123] (2) Fourier transform infrared spectroscopy (FTIR) analysis was performed on the aerogel materials prepared in Example 1 and Comparative Example 2:

[0124] Referring to Figure 5 FIG. 2, the characteristic peaks of the aerogel CSA in Comparative Example 2 mainly include C=O stretching vibration (about 1650-1680 ) and N–H bending vibration (1520-1580 ), indicating the presence of amide I and II bands.

[0125] The aerogel PBNNS / CS-Fe in Example 1 has a surface morphology as shown in FIG. 1d. 3+ In the composite aerogel, after the introduction of polyphosphate-doped BN nanosheets, the O-H / N-H peak at 3420 is significantly broadened and red-shifted, indicating that the phosphoric acid group forms a hydrogen bond network with the polar group of chitosan; at the same time, the amide bond characteristic peak intensity at 1650 and 1550 is weakened, which is due to the interaction between the protonated amino group of chitosan and the phosphoric acid group; it is worth noting that the B–N stretching vibration peak near 1300 confirms the presence of BN nanosheets; it is shown that the composite aerogel constructs a multi-scale interface crosslinking network through hydrogen bonding, electrostatic interaction and covalent bonding, which lays a chemical foundation for the mechanical enhancement and flame retardant functionalization of the material.

[0126] (3) High-resolution X-ray photoelectron spectroscopy (XPS) analysis was performed on the aerogel material prepared in Example 1:

[0127] Referring to Figure 6 Figure 2, the aerogel PBNNS / CS-Fe 3+ mainly includes C, N, O, B and weak Fe elements; wherein, the N1s spectrum presents a triplet feature, the B-N bond in the h-BN lattice is attributed to 398.1 eV, the type I amide nitrogen (C-NH-C) in chitosan is corresponded to 399.2 eV, and the newly generated B-N-C bond is derived from 401.3 eV, which indicates the covalent grafting of the BN nanosheet edge defect sites and the chitosan molecular chain; the B1s spectrum distribution shows a double-peak structure, mainly including the B-N bond at 190.4 eV and the newly appeared B-O-P bond characteristic peak at 191.3 eV, which is consistent with the FTIR result, indicating that the boron atom is combined with the polyphosphate acid through a coordination bond; the Fe 2p spectrum analysis shows that the binding energy of the Fe 2p3 / 2 main peak is located at 711.2 eV, indicating that there is Fe 3+ in the sample. The signal mainly comes from and Fe–OH two chemical environments. The spin-orbit splitting satellite peak Fe2p1 / 2 is located at 725.2 eV, and the energy difference between the main peak and the satellite peak is about 14 eV, which further confirms the chemical state of Fe 3+ .

[0128] Therefore, Example 1 not only enhances the interfacial compatibility of the BN nanosheet and chitosan through the B-O-P bond, but also forms an ionic crosslinking network with the chitosan amino group and iron ions, which synergistically induces the aerogel to form a hierarchical pore structure, realizing the interfacial coupling of the BN nanosheet and the chitosan matrix; this chemical synergistic effect is beneficial to improve the mechanical strength and thermal stability of the composite aerogel.

[0129] Analysis Example 3

[0130] The mechanical property analysis of the aerogels prepared in Examples 1-7 and Comparative Examples 2-4 was performed:

[0131] Referring to Table 1, the mechanical property analysis of the aerogels prepared in Examples 1-7 and Comparative Examples 2-4 shows that the composite aerogel (PBNNS / CS-Fe 3+ ) obtained in Example 1 under the crosslinking of iron salt ions has good mechanical property improvement, which is mainly due to the PBNNS nanosheet as a reinforcing phase to solidify the pore wall of the aerogel; the multiple crosslinking chelation of the iron salt ions constructs a multi-level pore structure, which greatly improves the compression modulus of the pore wall; this indicates that the strengthening effect of the nano-reinforcing phase significantly enhances the mechanical properties of the material, and this effect is attributed to the PBNNS in the chitosan-Fe 3+The unique formed in the gel matrix is a three-dimensional network structure.

[0132] As can be seen from Table 1, compared with the aerogel in Comparative Example 2 (density 0.0311 g / cm 3 , specific strength 16.17 MPa·cm 3 / g), the aerogels in each of the examples have a maximum compressive strength of 0.702-1.55 MPa while maintaining a low density (0.0364-0.0610 g / cm 3 / g), and the modified BN nanosheets in Examples 1-4 serve as a better modifier, effectively enhancing the interfacial interaction and further improving the mechanical properties of the chitosan-based composite aerogel.

[0133] In general, the specific modulus (compressive modulus / density) of the aerogel block reflects the stiffness per unit density, and the specific strength (maximum compressive strength / density) reflects the carrying capacity per unit density, and a higher value indicates that the material is lighter and more tough; the specific strength of the aerogel in Example 1 is significantly improved to a maximum of 26.69 MPa·cm 3 / g; the aerogel in Example 5 exhibits the best specific modulus, as high as 35.54 MPa·cm 3 / g, indicating that the material can improve the optimal mechanical properties of the chitosan-based composite aerogel through composition ratio adjustment and inorganic reinforcement modification. In contrast, in Comparative Example 3, the BN / CS-Fe 3+ , due to the absence of nanosheets and the aggregation of particles, even if the amount of BN powder added is the same as that in Example 1, the specific modulus is only 18.51 MPa·cm³ / g; in Comparative Example 4, the lack of iron ion crosslinking in PBNNS / CSA leads to insufficient support for the pores, and the specific strength is only 18.77 MPa·cm³ / g, and Comparative Example 4 requires an external acid solution and cannot be processed in an all-aqueous phase.

[0134] In summary, the PBNNS / CS-Fe 3+ The excellent properties of the aerogel are derived from the synergistic effect of three aspects: PBNNS nanosheets as a reinforcing phase to solidify the pore walls, iron ion crosslinking to construct a multi-level porous structure and enhance the modulus of the pore walls, and an optimized ratio of BN to chitosan to achieve high specific modulus and specific strength at low density, ultimately forming a stable three-dimensional network structure and significantly improving the overall mechanical properties of the material.

[0135] Table 1 Density and mechanical physical parameters of the aerogels prepared in Examples 1-7 and Comparative Examples 2-4

[0136]

[0137] Analysis Example 4

[0138] Thermal stability analysis was performed on the aerogels prepared in Example 1 and Comparative Example 2:

[0139] See Figure 7 As shown, the thermal decomposition behavior of the aerogels prepared in Example 1 and Comparative Example 2 was compared, and the heat resistance and reinforcement properties of the PBNNS / CSA composite material were quantitatively analyzed.

[0140] The thermal decomposition process of the chitosan aerogel CSA in Comparative Example 2 can be divided into three stages: the first stage is around 75℃, mainly due to the desorption of physically adsorbed water; the second stage, the main decomposition stage, has a maximum decomposition rate at 253.7℃, corresponding to the thermal cleavage of glycosidic bonds and side chain functional groups in the chitosan molecular chain; the third stage has a second decomposition peak at 435.9℃ and 540.1℃, which can be attributed to the further breakage and recombination of aromatic carbon ring structures in the previous cleavage residue, as well as the slow oxidation and graphitization process of the final carbonaceous residue, indicating that the chitosan aerogel has poor thermal stability at high temperatures.

[0141] Aerogel PBNNS / CS-Fe in Example 1 3+ It exhibits significantly different two-stage thermal behavior: its initial weight loss stage occurs at 91.1℃, slightly higher than that of chitosan aerogel, which is attributed to Fe 3+ The cross-linked structure enhances the material's water-binding capacity, thereby reducing free water desorption at low temperatures. The second stage involves two decomposition processes: the first, a sharp weight loss peak at 259.7℃ corresponds to the decomposition of the chitosan backbone and the organophosphate groups on the boron nitride surface; the second, slower weight loss occurs at 537.7℃. This gentler thermal decomposition facilitates the formation of a continuous, dense protective char layer, effectively inhibiting further combustion and thermal decomposition of the matrix. Furthermore, the excellent thermal stability of the boron nitride nanosheet framework at high temperatures plays a crucial supporting role in the overall high-temperature char retention of the material. These results indicate that the synergistic effect of the three-dimensional cross-linked network and the heat-resistant nano-reinforcing phase significantly improves the material's thermal stability and char-forming ability.

[0142] Analysis example 5

[0143] Flame retardant properties of the aerogels prepared in Example 1 and Comparative Examples 2-3 were analyzed:

[0144] See Figure 8 As shown, the vertical combustion experiment results indicate that the introduction of functionalized boron nitride nanosheets (PBNNS) significantly improves the flame retardant properties of chitosan aerogel.

[0145] In Comparative Example 2, the aerogel CSA continued to burn and produce a large amount of dense smoke (smoke density DS=89) 10 seconds after the first ignition, and it could not self-extinguish after a second ignition.

[0146] Aerogel PBNNS / CS-Fe in Example 1 3+ showed the best performance, which self-extinguished rapidly within 1.8 seconds after the first ignition, no flame spread after the second ignition, smoke density significantly reduced to 12, and formed a dense and expanded char layer, reaching the quasi-V-0 level of flame retardant standard.

[0147] Aerogel BN / CS-Fe in Comparative Example 3 3+ showed a transition performance, which had certain flame retardancy, self-extinguished within 2.9 seconds after the first ignition and no spread after the second ignition, but its smoke density (DS = 37) was much higher than that of Example 1, and the density of the char layer was insufficient.

[0148] The above comparison shows that functionalized boron nitride nanosheet not only plays a condensed phase flame retardant role by forming a dense physical barrier and catalyzing carbon formation, but also effectively suppresses smoke generation, and its synergistic flame retardant efficiency is much better than that of non-functionalized nanosheet, greatly improving the fire safety of bio-based materials; the flame retardant performance parameters of the aerogels prepared in Examples 1 and Comparative Examples 2-3 are shown in Table 2:

[0149] Table 2 Flame retardant performance parameters of aerogels prepared in Examples 1 and Comparative Examples 2-3

[0150]

[0151] Analysis Example 6

[0152] The thermal performance of the aerogels prepared in Examples 1-7 was analyzed:

[0153] Referring to Table 3, the pyrolysis behavior of the aerogels prepared in Examples 1-7 in air atmosphere was analyzed, and the flame retardant performance of the aerogels of the present application is closely related to the carbon formation ability at high temperature; among them, Example 1 showed the best flame retardant potential, with a char yield of more than 57%, and the thermal decomposition process was smooth, indicating that the material can form a stable and dense protective carbon layer at high temperature, effectively inhibiting the further combustion and thermal decomposition of the matrix.

[0154]

[0155] In the above technical solution of the present application, the above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made under the technical concept of the present application, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A method for preparing a chitosan-based polymer composite aerogel, characterized in that, The method comprises the steps of: S1, providing chitosan powder, phosphate functionalized boron nitride nanosheets, and iron salt; The phosphate functionalized boron nitride nanosheets are obtained by mixing boron nitride powder with an external liquid and then performing liquid-phase-assisted ball milling treatment, and then collecting the phosphate functionalized boron nitride nanosheets; the external liquid contains organic phosphates, and the organic phosphates include one or more of inositol hexaphosphate, glycerophosphate, glucose phosphate, and ascorbic acid phosphate; S2, homogenizing the phosphate functionalized boron nitride nanosheets in water to obtain a suspension; mixing the suspension, the chitosan powder, and the iron salt and then standing to obtain a composite gel; and drying to obtain a chitosan-based polymer composite aerogel; the mass ratio of the chitosan, the phosphate functionalized boron nitride nanosheets, and the iron salt is 1:0.5-2.5:0.08-0.

3.

2. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, The mass ratio of the boron nitride powder and the organic phosphates is 1:2-10.

3. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, In the external liquid, the mass percentage of the organic phosphates is 25-65%.

4. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, The phosphate functionalized boron nitride nanosheets have a thickness distribution of 1-2.5 nm, a lateral size of 0.6-0.8 μm, and 3-5 layers.

5. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, The mass percentage of the chitosan powder and the suspension is 1-3%.

6. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, The iron salt includes one or more of ferric chloride, ferric nitrate, and ferric sulfate.

7. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, The stirring speed for the homogenization treatment is 8000-15000 rpm; The mixing speed of the suspension, the chitosan powder, and the iron salt is 300-500 rpm, and the mixing time is 2-6 h.

8. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, The ball milling speed for the liquid-phase-assisted ball milling treatment is 200-500 rpm, and the ball milling time is 8-40 h; The liquid-phase-assisted ball milling treatment is performed in a ball milling tank containing grinding balls, and the mass ratio of the grinding balls to the boron nitride powder is 50-100:

1. In step S1, the process of collecting the phosphate functionalized boron nitride nanosheets includes centrifuging the upper mixed liquid after the liquid-phase-assisted ball milling treatment, and then filtering, washing, and drying to obtain the phosphate functionalized boron nitride nanosheets.

9. A chitosan-based polymer composite aerogel, characterized by, The chitosan-based polymer composite aerogel is prepared by the method of any one of claims 1-8.

10. The chitosan-based polymer composite aerogel of claim 9 for use in flame retardation.

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