Chitosan-based polymer composite aerogel, preparation method and application

Abstract

The invention provides chitosan-based polymer composite aerogel as well as a preparation method and application thereof. The preparation method of the chitosan-based polymer composite aerogel comprises the following steps: homogenizing phosphate functionalized boron nitride nanosheets in water to obtain a suspension; mixing the suspension liquid, chitosan powder and ferric salt to form composite gel; and drying to obtain the chitosan-based polymer composite aerogel. The mass ratio of the chitosan to the phosphate functionalized boron nitride nanosheet to the iron salt is 1: (0.5 to 2.5): (0.08 to 0.3). According to the preparation method disclosed by the invention, a ternary cross-linked hierarchical network structure is constructed by utilizing coordination cross-linking of iron ions and chitosan molecular chains and a chelation effect of phosphate ester groups on the surfaces of boron nitride nanosheets, so that the composite aerogel with low density and high specific strength is prepared; efficient flame retardance can be achieved through a triple synergistic mechanism of a physical barrier, free radical capture of phosphorus elements and catalytic char formation of iron ions.

Description

Technical Field

[0001] This invention belongs to the field of composite materials, and particularly relates to a chitosan-based polymer composite aerogel, its preparation method, and its application. Background Technology

[0002] The spread of flames and toxic fumes caused by flammable materials are the core causes of casualties. While organic flame retardants in traditional flame-retardant material systems can delay combustion, their pyrolysis process easily releases carcinogenic gases. Inorganic flame-retardant fillers, although more environmentally friendly, require an addition of over 60% to meet standards, which severely degrades the material's mechanical properties. Biomass aerogels, with their three-dimensional porous structure and intrinsic char-forming ability, offer a new approach to constructing environmentally friendly flame-retardant materials. Among them, chitosan aerogels, after modification, not only exhibit unique self-extinguishing properties but also effectively alleviate the unsustainability problem of petroleum-based materials due to their biodegradability.

[0003] Chinese invention patent CN113234256B discloses a method for preparing a double-crosslinked flame-retardant composite aerogel, which significantly improves the flame retardant rating while maintaining biodegradability through the synergistic crosslinking of nanocellulose and chitosan. However, the flame retardant efficiency of pure bio-based aerogels is difficult to meet stringent fire protection standards, mainly due to insufficient stability of their char layer structure and self-supporting ability at high temperatures. Although introducing inorganic nano-SiO2 reinforcing phases can improve this deficiency, as Chinese invention patent CN111635554B discloses a method for preparing and applying a gelatin / hydroxyethyl cellulose-SiO2 composite aerogel, the proposed nano-SiO2 composite technology achieves improved 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, its preparation method, and its 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 of the Invention

[0005] The main objective of this invention is to provide a chitosan-based polymer composite aerogel, its preparation method, and its application, aiming to solve the aforementioned 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 objectives, the present invention provides a method for preparing chitosan-based polymeric composite aerogels, comprising the following steps: S1 provides chitosan powder, phosphate-functionalized boron nitride nanosheets, and iron salts; The method for obtaining the phosphate-functionalized boron nitride nanosheets includes: mixing boron nitride powder with an external liquid and then performing liquid-phase assisted ball milling, and then collecting the phosphate-functionalized boron nitride nanosheets; the external liquid contains an organic phosphate ester, which includes one or more of inositol hexaphosphate, phosphoglycerate, glucose phosphate, and ascorbate phosphate. S2, the phosphate-functionalized boron nitride nanosheets are homogenized in water to obtain a suspension; the suspension, chitosan powder, and iron salt are mixed and allowed to stand to obtain a composite gel; after drying, a chitosan-based polymer composite aerogel is obtained; the mass ratio of chitosan, phosphate-functionalized boron nitride nanosheets, and iron salt is 1:0.5-2.5:0.08-0.3.

[0007] Furthermore, the mass ratio of the boron nitride powder to the organophosphate ester is 1:2-10.

[0008] Furthermore, in the added liquid, the organic phosphate ester accounts for 25-65% by mass.

[0009] Furthermore, the phosphate-functionalized boron nitride nanosheets have a thickness distribution of 1-2.5 nm, a lateral dimension of 0.6-0.8 μm, and 3-5 layers.

[0010] Furthermore, the mass percentage of the chitosan powder and the suspension is 1-3%.

[0011] Furthermore, the iron salt includes one or more of ferric chloride, ferric nitrate, and ferric sulfate.

[0012] Furthermore, the homogenization process employs a stirring speed of 8000-15000 rpm; The suspension, chitosan powder, and iron salt are mixed at a speed of 300-500 rpm for 2-6 hours.

[0013] Furthermore, the ball milling process using liquid-phase assisted ball milling involves a milling speed of 200-500 rpm and a milling time of 8-40 h. The liquid-phase assisted ball milling process is carried out in a ball milling jar, which is filled with 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: after completing the liquid-phase assisted ball milling treatment, centrifuging to collect the upper mixture, and then filtering and drying to obtain the phosphate-functionalized boron nitride nanosheets.

[0014] 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.

[0015] The present invention also provides an application of chitosan-based polymeric composite aerogels as described above in flame retardancy.

[0016] The principle behind the excellent flame-retardant properties of the chitosan-based polymer composite aerogel in this invention includes at least the following: 1. Phosphate-functionalized boron nitride nanosheets (PBNNS) construct a multi-level synergistic flame retardant system in aerogels; the phosphate-functionalized boron nitride nanosheets form a continuous and dense barrier layer through directional arrangement, inhibiting the diffusion of heat and oxygen; the phosphate groups on their surface release phosphorus-containing free radicals at high temperatures to quench gas-phase chain reactions; at the same time, the synergistic effect of iron ions and phosphate groups catalyzes the cross-linking of chitosan to form a highly graphitized carbon layer, achieving a dual physical-chemical barrier.

[0017] 2. Liquid-phase assisted ball milling is used to modify the BN surface with phosphate esters via POB covalent bonds, achieving simultaneous exfoliation and functionalization, and improving the monolayer dispersion in the PBNNS chitosan network; Fe 3+ Through a dual bridging effect with chitosan A rigid coordination network is formed; chelation with phosphate groups on the PBNNS surface constructs "chitosan-Fe 3+ -PBNNS" three-dimensional interpenetrating network significantly enhances interface bonding density and thermal stability.

[0018] 3. The rigid layers of phosphate-functionalized boron nitride nanosheets are embedded in the pore wall framework, and the porous structure is strengthened by PO-Fe bonding and physical interpenetration. The interconnected pores maintained by the cross-linked network guide the directional migration of combustion products, promoting the formation of a continuous expanding char layer. This structure resists thermal stress deformation, and by extending the oxygen diffusion path, it inhibits secondary ignition, achieving a synergistic effect of self-supporting char formation and long-term flame retardancy.

[0019] Compared with the prior art, the present invention has at least the following advantages: This invention yields a low-density chitosan-based polymeric composite aerogel with excellent flame retardant efficiency and mechanical properties, which brings significant benefits in terms of improving flame retardant performance, enhancing mechanical properties, optimizing inorganic-organic interface compatibility, environmental protection and sustainability, and application prospects.

[0020] This invention constructs a triple flame-retardant aerogel system based on the synergistic effect of phosphate-functionalized boron nitride nanosheets and iron ion crosslinking. 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, blocking chain combustion reactions; and iron ions catalyze the crosslinking of chitosan to form a highly graphitized carbon layer, achieving long-term condensed phase barrier. This invention significantly improves the flame-retardant properties of the aerogel, enabling it to maintain stability for a longer period under high temperature and flame conditions.

[0021] In this invention, phosphate-functionalized boron nitride nanosheets serve as a rigid reinforcing phase, playing a significant reinforcing role in the composite aerogel. Simultaneously, the dynamic coordination bonds between iron ions and the hydroxyl / amino groups of chitosan, as well as the chelation with the phosphate groups of the boron nitride nanosheets, further enhance the structural stability, enabling the composite aerogel to maintain good shape stability and mechanical properties under external forces, thereby broadening its application range in practical flame retardant applications.

[0022] This invention simultaneously achieves efficient boron nitride exfoliation and surface phosphating modification. Its phosphate groups are covalently bonded to chitosan molecular chains, which significantly improves the dispersion uniformity and interfacial bonding strength of boron nitride nanosheets in the chitosan three-dimensional network. This optimization avoids the performance degradation caused by inorganic-organic phase separation and ensures the overall stability of the composite aerogel.

[0023] This invention employs an aqueous ball-milled nanosheet-iron ion crosslinking composite gel process, with no strong acids / alkalis or organic solvents involved in the entire process. The resulting composite aerogel exhibits low bulk density, high specific strength, and low smoke density. This invention has minimal environmental impact during preparation and use, and can replace traditional halogenated flame retardants and other harmful environmental materials. It aligns with the current trend of green and environmentally friendly development and has broad application prospects in building insulation, fire protection for new energy batteries, and industrial thermal protection. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1The images shown are electron microscope images of boron nitride powder in Example 1 of the present invention, solid product in step 1 of Comparative Example 1, and PBNNS in Example 1; (a) is a scanning electron microscope image of boron nitride powder in Example 1, (b) is a scanning electron microscope image of solid product in step 1 of Comparative Example 1, (c) is a scanning electron microscope image of PBNNS in Example 1, and (d) is a transmission scanning electron microscope image of PBNNS in Example 1. Figure 2 The images shown are atomic force microscopy (AFM) images and dimension-thickness curves of the PBNNS in Embodiment 1 of the present invention; (a) is an AFM image, and (b) is a dimension-thickness curve. Figure 3 The infrared spectra of boron nitride powder (BN) and boron nitride nanosheets (PBNNS) in Example 1 of this invention are shown below. Figure 4 Scanning electron microscope images of the aerogels prepared in Example 1 and Comparative Examples 2-4 of this invention; (a) is the CSA aerogel in Comparative Example 2, and (b) is the BN / CS-Fe aerogel in Comparative Example 3. 3+ (c) is the aerogel PBNNS / CSA in Comparative Example 4, and (d) is the aerogel PBNNS / CS-Fe in Example 1. 3+ ; Figure 5 The infrared spectra of the aerogels prepared in Example 1 and Comparative Example 2 of this invention are shown below. Figure 6 XPS analysis images of the composite aerogel prepared in Example 1 of this invention: (a) is the full XPS spectrum, (b) is the N1s high-resolution image, (c) is the B1s high-resolution image, and (d) is the Fe2p high-resolution image. Figure 7 Thermogravimetric decomposition curves and differential thermal decomposition curves of the aerogels prepared in Example 1 and Comparative Example 2 of this invention are shown; (a) is the thermogravimetric decomposition curve, and (b) is the differential thermal decomposition curve. Figure 8 The figures show vertical combustion experiments of the aerogels prepared in Example 1 and Comparative Examples 2-3 of this invention; (a) is the aerogel CSA in Comparative Example 2, and (b) is the aerogel PBNNS / CS-Fe in Example 1. 3+ (c) is the aerogel BN / CS-Fe in Comparative Example 3. 3+ .

[0026] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0029] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0030] This invention provides a method for preparing chitosan-based polymeric composite aerogels, comprising the following steps: S1 provides chitosan powder, phosphate-functionalized boron nitride nanosheets, and iron salts.

[0031] It should be noted that the high specific surface area and strong van der Waals forces of boron nitride nanosheets easily lead to irreversible stacking and re-aggregation within biopolymer matrices (such as chitosan and cellulose), causing localized defects and stress concentrations in the barrier network, significantly weakening the macroscopic mechanical properties of the aerogel. More importantly, the poor interfacial compatibility between inorganic boron nitride nanosheets and the organic matrix results in a substantial reduction in flame-retardant synergy efficiency, making it difficult for traditional composite aerogels to achieve a synergistic effect of flame retardant and mechanical properties while maintaining ultra-low density. Therefore, improving the dispersion stability and interfacial compatibility of boron nitride nanosheets is crucial for constructing boron nitride-enhanced biomass-based aerogels with high flame-retardant properties.

[0032] In this invention, the method for obtaining the phosphate-functionalized boron nitride nanosheets includes: 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.

[0033] In this invention, the boron nitride powder is microscopically granular. The process of collecting the phosphate-functionalized boron nitride nanosheets in this invention includes: after completing the liquid-phase assisted ball milling treatment, centrifuging to collect the upper mixture, filtering, washing, and drying to obtain the phosphate-functionalized boron nitride nanosheets; the centrifugation speed can be 3000-5000 rpm, and the centrifugation time can be 4-6 min; the filtering can be done by rinsing with water and isopropanol, and the drying method can be vacuum drying.

[0034] In this invention, the external liquid contains an organic phosphate ester, which includes one or more of inositol hexaphosphate, phosphoglycerate, glucose phosphate, and ascorbate phosphate; preferably, it includes one or more of inositol hexaphosphate and phosphoglycerate; the mass ratio of the boron nitride powder to the organic phosphate ester is 1:2-10, more preferably 1:2-4, 1:2-3, 1:8-10, or 1:9-10.

[0035] In the additive solution of the present invention, the organic phosphate ester accounts for 25-65% by mass, further 30-65% or 30-50% or 25-35% or 45-55%; the additive solution is composed of the organic phosphate ester and water.

[0036] In this invention, the phosphate-functionalized boron nitride nanosheets have a thickness distribution of 1-2.5 nm, a lateral dimension of 0.6-0.8 μm, and 3-5 layers; their edges exhibit a serrated ultrathin nanosheet layered structure formed by phosphate etching.

[0037] In this invention, the iron salt includes one or more of ferric chloride, ferric nitrate, and ferric sulfate; more specifically, ferric chloride.

[0038] In this invention, the liquid-phase assisted ball milling process uses a ball milling speed of 200-500 rpm and a milling time of 8-40 hours, more specifically 30-40 hours. The liquid-phase assisted ball milling process is carried out in a milling jar containing grinding balls with a size of 6 mm or 12 mm. The ball-to-powder ratio in this invention refers to the mass ratio of grinding balls to boron nitride powder; this ratio can be 50-100:1. During the specific operation of the liquid-phase assisted ball milling process, the milling direction is reversed every 2 hours, with a 30-minute pause after each reversal.

[0039] Specifically, in this invention, the boron nitride powder is uniformly mixed with the added liquid and placed in a ball mill jar. Then, grinding balls of appropriate size and quantity are loaded for liquid-phase assisted ball milling. Afterward, the collected mixture is centrifuged to remove the lower layer of large pieces of boron nitride. The upper layer of mixture is washed and filtered with water and isopropanol. Finally, it is vacuum dried to obtain phosphate-functionalized boron nitride nanosheets.

[0040] S2, the phosphate-functionalized boron nitride nanosheets are homogenized in water to obtain a suspension; the suspension, chitosan powder, and iron salt are mixed and allowed to stand to obtain a composite gel; after drying, a chitosan-based polymeric composite aerogel is obtained, denoted as PBNNS / CS-Fe. 3+ The drying method can be vacuum freeze drying.

[0041] In this invention, the mass ratio of chitosan, phosphate-functionalized boron nitride nanosheets, and iron salt is 1:0.5-2.5:0.08-0.3, further, it is 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.

[0042] In this invention, the mass percentage of the chitosan powder and the suspension is 1-3%, more specifically 1.5-2.5%, more specifically 2-2.5%.

[0043] In this invention, the homogenization process uses a stirring speed of 8000-15000 rpm, more specifically 12000-15000 rpm; the mixing speed of the suspension, the chitosan powder, and the iron salt is 300-500 rpm, more specifically 400-500 rpm, and the mixing time is 2-6 h, more specifically 3-6 h, more specifically 3-4 h, or 5-6 h.

[0044] This invention is a fully aqueous preparation process. In the preparation method of this invention, the use of acids, alkalis, and organic solvents is avoided; furthermore, the use of acetic acid is avoided. Specifically, in steps S1 and S2, no acids, alkalis, or organic solvents are used. For example, in step S1, ball milling is performed only in the aqueous phase; in step S2, only the chitosan powder, the phosphate-functionalized boron nitride nanosheets, the iron salt, and water are used.

[0045] This invention utilizes a specific phosphate ester to simultaneously achieve the dissociation of boron nitride sheets and surface functionalization modification, obtaining phosphate ester-covalently modified boron nitride nanosheets. Compared to the ball milling modification of boron nitride with triphenyl phosphate (TPP), which only yields agglomerated fragments, this invention modifies the surface of boron nitride through POB covalent bonds, inhibiting the re-stacking of nanosheets and improving their monolayer dispersion in chitosan solution.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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. 3 / g, specific strength is 21.99-26.69 MPa·cm 3 / g.

[0051] Alternatively, the properties of the chitosan-based polymeric composite aerogel described in this invention include one or more of the following: a density of 0.0576-0.0581 g / cm³. 3 The compressive modulus is 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 / g, specific strength is 24.83-26.69 MPa·cm 3 / g.

[0052] As a preferred example, 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%.

[0053] The present invention also provides an application of chitosan-based polymeric composite aerogel as described above in flame retardancy, which not only has excellent mechanical properties while maintaining low density, but also can effectively retard flames; the application includes using the chitosan-based polymeric composite aerogel to prepare other flame retardant materials, or using the chitosan-based polymeric composite aerogel as a flame retardant material in flame retardant engineering.

[0054] The following are specific examples of the present invention: Example 1 Step 1, Obtaining boron nitride nanosheets: Boron nitride powder (BN) was uniformly mixed with an external liquid (the external liquid consisted of inositol hexaphosphate and water, with inositol hexaphosphate accounting for 50% by mass) and placed in a ball mill jar. The mass ratio of boron nitride powder to inositol hexaphosphate was 1:10. Then, zirconia balls (Φ=6 mm) with a ball-powder mass ratio of 50 were loaded and subjected to liquid-phase assisted ball milling. The ball milling speed was 200 rpm, and the ball milling direction was reversed every 2 hours. Each time the ball milling direction was reversed, the milling was stopped for 30 minutes. The total ball milling time was 40 hours.

[0055] After ball milling, the collected mixture was centrifuged at 4000 rpm for 5 min to remove large pieces of BN; the upper mixture was washed and filtered with a large amount of water and isopropanol; finally, the solid product obtained after washing and filtration was vacuum dried at 80℃ to obtain boron nitride nanosheets modified with inositol hexaphosphate, which are referred to as PBNNS in this example.

[0056] Step 2, preparation of the aerogel: The prepared boron nitride nanosheets were homogenized in deionized water at 12000 rpm to form a uniform suspension. Then, chitosan powder was added, with a chitosan powder to suspension mass percentage of 2 wt% and a chitosan powder to boron nitride nanosheet mass ratio of 1:2. Next, ferric chloride was added, with a ferric chloride to suspension mass percentage of 0.2 wt%. The mixture was stirred at 500 rpm for 6 h and then allowed to stand to obtain a uniform composite gel. Finally, the chitosan-based polymeric composite aerogel was obtained by vacuum freeze-drying, which is denoted as PBNNS / CS-Fe in this example. 3+ .

[0057] Comparative Example 1 Compared to Example 1, this comparative example only changed inositol hexaphosphate to triphenyl phosphate (TPP), while all other conditions were the same as in Example 1.

[0058] In this comparative example, the solid product in step 1 was agglomerated fragments, therefore no aerogel was prepared.

[0059] Comparative Example 2 Compared to Example 1, this comparative example omits step 1, and in step 2, the preparation of the aerogel is done without boron nitride nanosheets (PBNNS), and the suspension is adjusted to deionized water. Other conditions are the same as in Example 1.

[0060] The aerogel prepared in this comparative example is denoted as CSA.

[0061] Comparative Example 3 Compared to Example 1, this comparative example did not perform step 1, and in step 2, the boron nitride nanosheets were changed to boron nitride powder (BN) in the preparation of the aerogel. Other conditions were the same as in Example 1.

[0062] The aerogel prepared in this comparative example is designated as BN / CS-Fe. 3+ .

[0063] Comparative Example 4 Compared to Example 1, in the preparation of the aerogel, ferric chloride was omitted, and the deionized water used for high-speed homogenization was adjusted to a 2 vol% acetic acid solution (for dissolving chitosan). Other conditions were the same as in Example 1.

[0064] The aerogel prepared in this comparative example is denoted as PBNNS / CSA.

[0065] Example 2 Compared to Example 1, this embodiment only changes inositol hexaphosphate to phosphoglycerate, while other conditions remain the same as in Example 1.

[0066] Example 3 Compared to Example 1, this embodiment only changes inositol hexaphosphate to glucose phosphate, while other conditions remain the same as in Example 1.

[0067] Example 4 Compared to Example 1, this embodiment only changes inositol hexaphosphate to ascorbic acid phosphate, while other conditions remain the same as in Example 1.

[0068] Example 5 Step 1, Obtaining boron nitride nanosheets: Boron nitride powder (BN) was uniformly mixed with an external liquid (composed of phosphoglycerate and water, with phosphoglycerate accounting for 30% by mass) and placed in a ball mill jar. The mass ratio of boron nitride powder to phosphoglycerate was 1:2. Then, zirconia balls (Φ=12 mm) with a ball-powder mass ratio of 100 were loaded into the jar for liquid-phase assisted ball milling. The ball milling speed was 200 rpm, and the milling direction was reversed every 2 hours. The milling was stopped for 30 minutes after each reversal. The total milling time was 40 hours.

[0069] After ball milling, the collected mixture was centrifuged at 4000 rpm for 5 min to remove large pieces of BN; the upper mixture was washed and filtered with a large amount of water and isopropanol; finally, the solid product obtained after washing and filtration was vacuum dried at 80℃ to obtain boron nitride nanosheets modified with phosphoglycerate.

[0070] Step 2, preparation of aerogel: The prepared boron nitride nanosheets were homogenized in deionized water at 15000 rpm to form a uniform suspension. Then, chitosan powder was added, with a mass percentage of 2 wt% of chitosan powder to suspension and a mass ratio of 1:1.5 between chitosan powder and boron nitride nanosheets. Next, ferric sulfate was added, with a mass percentage of 0.3 wt% of ferric sulfate to suspension. After stirring at 400 rpm for 3 h, the mixture was allowed to stand to obtain a uniform composite gel. Finally, the mixture was freeze-dried under vacuum to obtain a chitosan-based polymer composite aerogel.

[0071] Example 6 Step 1, Obtaining boron nitride nanosheets: Boron nitride powder (BN) was uniformly mixed with an external liquid (the external liquid consisted of glucose phosphate and water, with glucose phosphate accounting for 65% by mass) and placed in a ball mill jar. The mass ratio of boron nitride powder to glucose phosphate was 1:5. Then, zirconia balls (Φ=6 mm) with a ball-powder mass ratio of 80 were loaded and subjected to liquid-phase assisted ball milling. The ball milling speed was 200 rpm, and the milling direction was reversed every 2 hours. The milling was stopped for 30 minutes each time the direction was reversed. The total milling time was 40 hours.

[0072] After ball milling, the collected mixture was centrifuged at 4000 rpm for 5 min to remove large pieces of BN; the upper mixture was washed and filtered with a large amount of water and isopropanol; finally, the solid product obtained after washing and filtration was vacuum dried at 80℃ to obtain glucose phosphate modified boron nitride nanosheets.

[0073] Step 2, preparation of aerogel: The prepared boron nitride nanosheets were homogenized in deionized water at 10,000 rpm to form a uniform suspension. Then, chitosan powder was added, with a mass percentage of 2 wt% for chitosan powder to suspension and a mass ratio of 1:1 for chitosan to boron nitride nanosheets. Next, ferric nitrate was added, with a mass percentage of 0.3 wt% for ferric nitrate to suspension. The mixture was stirred at 300 rpm for 2 h and then allowed to stand to obtain a uniform composite gel. Finally, the mixture was freeze-dried under vacuum to obtain a chitosan-based polymer composite aerogel.

[0074] Example 7 Step 1, Obtaining boron nitride nanosheets: Boron nitride powder (BN) was uniformly mixed with an external liquid (the external liquid consisted of ascorbate phosphate and water, with ascorbate phosphate accounting for 60% by mass) and placed in a ball mill jar. The mass ratio of boron nitride powder to ascorbate phosphate was 1:6. Then, zirconia balls (Φ=12 mm) with a ball-powder mass ratio of 100 were loaded for liquid-phase assisted ball milling. The ball milling speed was 200 rpm, and the ball milling direction was reversed every 2 hours. Each time the ball milling direction was reversed, the milling was stopped for 30 minutes. The total ball milling time was 40 hours.

[0075] After ball milling, the collected mixture was centrifuged at 4000 rpm for 5 min to remove large pieces of BN; the upper mixture was washed and filtered with a large amount of water and isopropanol; finally, the solid product obtained after washing and filtration was vacuum dried at 80℃ to obtain ascorbic acid phosphate modified boron nitride nanosheets.

[0076] 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, with a mass percentage of 2 wt% of chitosan powder to suspension and a mass ratio of 1:0.5 of chitosan to boron nitride nanosheets. Next, ferric chloride was added, with a mass percentage of 0.5 wt% of ferric chloride to suspension. The mixture was stirred at 500 rpm for 4 h and then allowed to stand to obtain a uniform composite gel. Finally, the mixture was freeze-dried under vacuum to obtain a chitosan-based polymer composite aerogel.

[0077] Analysis example 1 (1) Electron microscopy analysis was performed on the boron nitride powder (original boron nitride BN) in Example 1, the solid product of step 1 in Comparative Example 1, and the PBNNS in Example 1: See Figure 1As shown in part (a), the original boron nitride exhibits irregular bulk aggregates with relatively smooth surfaces and micron-scale layered crystal structures.

[0078] See Figure 1 As shown in part (b), the solid product obtained in step 1 of Comparative Example 1 is boron nitride that is not a nano-thin layer. The boron nitride only becomes smaller under mechanical action, but it is not exfoliated into the morphology of boron nitride nanosheets, and there is obvious particle aggregation.

[0079] See Figure 1 As shown in section (c), the inositol hexaphosphate modified boron nitride nanosheets (PBNNS) in Example 1 exhibit an exfoliated sheet structure with a significantly reduced thickness and a rougher surface due to the mechanochemical process, resulting in certain defect structures; at the same time, weak aggregation is retained due to van der Waals interactions.

[0080] See Figure 1 As shown in section (d), the inositol hexaphosphate-modified boron nitride nanosheets (PBNNS) in Example 1 exhibit a thin two-dimensional nanosheet layer structure with approximately 3-5 layers. These results demonstrate that inositol hexaphosphate, due to its multidentate chelating ability, strong intercalation capacity, and electrostatic stability, can efficiently exfoliate pristine boron nitride into ultrathin nanosheets.

[0081] (2) Atomic force microscopy (AFM) analysis was performed on the PBNNS in Example 1: See Figure 2 As shown, Figure 2 The AFM thickness profile and corresponding thickness dimensions of PBNNS are shown, and the results quantitatively demonstrate the exfoliation efficiency of the ball milling process. The main thickness distribution is 1-2.5 nm, and the lateral dimension is about 0.6-0.8 μm. These microstructures indicate that controllable exfoliation is achieved while realizing edge-specific chemical modification, effectively solving the problems of size control and stability in the production of boron nitride nanosheets.

[0082] (3) Fourier transform infrared spectroscopy (FTIR) analysis was performed on the boron nitride powder (original boron nitride BN) in Example 1 and the PBNNS in Example 1: See Figure 3 As shown, the original boron nitride (BN) was at 1374. and 779 The characteristic in-plane stretching vibration of BN and bending vibration of BNB are shown at the locations respectively.

[0083] For the PBNNS in Example 1, after ball milling treatment with inositol hexaphosphate, the area of ​​the BN stretching vibration peak increased, and at 1642 A new characteristic peak appeared at 2920, corresponding to the BOP stretching vibration, confirming that inositol hexaphosphate is anchored to the BN surface through coordination; in addition, at 2920 CH stretching vibration peak (methylene) and 3420 The broadened OH vibration peak (hydrogen bond) further verifies the construction of the organic-inorganic interface, indicating that the chemical functionalization of BN nanosheets is achieved through BOP covalent bonding and van der Waals synergy.

[0084] Analysis example 2 (1) Structural chemical properties analysis of the aerogel materials prepared in Example 1 and Comparative Examples 2-4: See Figure 4 As shown in part (a), the aerogel CSA in Comparative Example 2 exhibits an irregular porous structure with a wide pore size distribution (approximately 10-150 μm) and uneven pore wall thickness (1-5 μm). Local pore wall collapse is visible in this structure. Although the pore wall surface is relatively smooth, it is accompanied by obvious wrinkling texture, which is presumably caused by the shrinkage of polymer chains during solvent evaporation.

[0085] See Figure 4 As shown in section (b), the aerogel BN / CS-Fe in Comparative Example 3 3+ Its porous structure contains a large number of boron nitride particles aggregated on the surface of the pore walls, and the porous structure formed after freeze-drying is in a disordered state.

[0086] See Figure 4 As shown in section (c), the surface morphology of the aerogel PBNNS / CSA in Comparative Example 4 indicates that PBNNS has a certain guiding effect on the aerogel structure. The formation of an ordered pore structure was observed, but the interlayer spacing between the pores was relatively large, which may be due to the insufficient cross-linking between polymer molecular chains.

[0087] See Figure 4 As shown in section (d), the aerogel PBNNS / CS-Fe in Example 1 3+ The microstructure exhibits typical hierarchical porous network characteristics: the main pores have relatively uniform pore size (20-50 μm), and a large number of submicron-sized through pores (500 nm-2 μm) are embedded in the pore walls; in this system, PBNNS nanosheets are uniformly dispersed in the chitosan framework as nucleation sites and are partially encapsulated by the chitosan layer. This structure effectively inhibits volume shrinkage during the freeze-drying process.

[0088] More importantly, in Example 1, under the cross-linking of iron salt ions, a large number of tortuous polymer fiber filaments are entangled in the porous structure of the composite aerogel. This multiple cross-linking effect enriches the pore size hierarchy of the material and significantly enhances the compactness and stability of the overall structure.

[0089] (2) Fourier transform infrared spectroscopy (FTIR) analysis was performed on the aerogel materials prepared in Example 1 and Comparative Example 2: See Figure 5 As shown, the characteristic peaks of the aerogel CSA in Comparative Example 2 mainly include the C=O stretching vibration (approximately 1650-1680). ) and N–H bending vibrations (1520-1580) This indicates the presence of amide I and II bands.

[0090] Aerogel PBNNS / CS-Fe of Example 1 3+ In the composite aerogel, after introducing polyphosphate-doped BN nanosheets, 3420 The OH / NH peak at 1650°C showed significant broadening and red shift, indicating that the phosphate groups formed a hydrogen bond network with the polar chitosan groups; simultaneously, at 1650°C... and 1550 The weakening of the characteristic peak intensity of the amide bond at 1300 is attributed to the interaction between the protonated amino groups of chitosan and the phosphate groups; notably, at 1300... The nearby B–N stretching vibration peaks confirmed the presence of BN nanosheets, indicating that the composite aerogel constructs a multi-scale interfacial cross-linked network through hydrogen bonding, electrostatic interactions, and covalent bonding, laying a chemical foundation for the mechanical enhancement and flame-retardant functionalization of the material.

[0091] (3) High-resolution X-ray photoelectron spectroscopy (XPS) analysis was performed on the aerogel material prepared in Example 1: See Figure 6 As shown, the aerogel PBNNS / CS-Fe in Example 1 3+ The sample is mainly composed of C, N, O, B, and a trace amount of Fe. The N1s spectrum exhibits a triplet characteristic, with the peak at 398.1 eV attributed to BN bonds in the h-BN lattice, the peak at 399.2 eV corresponding to amide I nitrogen (C-NH-C) in chitosan, and the peak at 401.3 eV originating from newly formed BNC bonds. This indicates covalent grafting of BN nanosheet edge defect sites with chitosan molecular chains. The B1s spectrum shows a bimodal structure, mainly including a BN bond at 190.4 eV and a newly appearing BOP bond characteristic peak at 191.3 eV, consistent with FTIR results, indicating that boron atoms are bound to polyphosphate acids through coordination bonds. Fe 2p spectral analysis shows that the binding energy of the Fe 2p3 / 2 main peak is located at 711.2 eV, indicating the presence of Fe in the sample. 3+ The signal mainly comes from It exhibits two chemical environments: Fe and Fe–OH. The spin orbital splitting peak Fe2p1 / 2 is located at 725.2 eV, with an energy difference of approximately 14 eV between it and the main peak, further confirming that Fe… 3+ The chemical state of.

[0092] Therefore, Example 1 not only enhances the interfacial compatibility between BN nanosheets and chitosan through BOP bonds, but its free phosphate groups also form an ionic crosslinking network with chitosan amino and iron ions, synergistically inducing the formation of a hierarchical porous structure in the aerogel, thus realizing the interfacial coupling between BN nanosheets and the chitosan matrix; this chemical synergistic effect is beneficial to improving the mechanical strength and thermal stability of the composite aerogel.

[0093] Analysis example 3 Mechanical properties of the aerogels prepared in Examples 1-7 and Comparative Examples 2-4 were analyzed: The mechanical properties of the aerogels prepared in Examples 1-7 and Comparative Examples 2-4 are shown in Table 1. The composite aerogel (PBNNS / CS-Fe) obtained in Example 1 under iron salt ion crosslinking... 3+ The improved mechanical properties are mainly attributed to the use of PBNNS nanosheets as the reinforcing phase in the pore walls of the cured aerogel. The multi-layered pore structure constructed through multiple cross-linking and chelation of iron salt ions significantly increases the compressive modulus of the pore walls. This indicates that the strengthening effect dominated by the nano-reinforcing phase significantly enhances the mechanical properties of the material. This effect is attributed to the role of PBNNS in the chitosan-Fe... 3+ The unique feature formed in the gel matrix is ​​a three-dimensional network structure.

[0094] As shown in Table 1, compared to the aerogel in Comparative Example 2 (density 0.0311 g / cm³), 3 Specific strength 16.17 MPa·cm 3 / g), the aerogels in each embodiment maintained a low density (0.0364-0.0610 g / cm³). 3 At the same time, the maximum compressive strength is increased to 0.702-1.55 MPa. The modified BN nanosheets in Examples 1-4 serve as a better modifier, effectively enhancing interfacial interactions and further improving the mechanical properties of chitosan-based composite aerogels.

[0095] Generally, the specific modulus (compressive modulus / density) of aerogel blocks reflects the stiffness per unit density, while the specific strength (maximum compressive strength / density) reflects the load-bearing capacity per unit density. Higher values ​​indicate that the material is lighter and stronger. In Example 1, the specific strength of the aerogel was significantly increased to a maximum of 26.69 MPa·cm. 3 / g; the aerogel in Example 5 exhibited the best specific modulus, reaching 35.54 MPa·cm. 3 / g indicates that the optimal mechanical properties of the chitosan-based composite aerogel can be improved through compositional ratio adjustment and inorganic reinforcement modification. In contrast, the BN / CS-Fe in Comparative Example 3... 3+ Due to the lack of nanosheets and particle aggregation, even when the amount of boron nitride powder added was the same as that of nanosheets in Example 1, the specific modulus was only 18.51 MPa·cm³ / g. In Comparative Example 4, the lack of iron ion crosslinking in PBNNS / CSA resulted in insufficient pore support, and the specific strength was only 18.77 MPa·cm³ / g. Furthermore, Comparative Example 4 required the addition of external acid and could not achieve full aqueous phase treatment.

[0096] In summary, PBNNS / CS-Fe 3+ The superior properties of aerogels stem from the synergistic effect of three aspects: PBNNS nanosheets act as a reinforcing phase to solidify the pore walls, iron ions crosslink to construct a multi-layered porous structure and enhance the pore wall modulus, and the optimized ratio of BN to chitosan achieves high specific modulus and specific strength at low density, ultimately forming a stable three-dimensional network structure that significantly improves the overall mechanical properties of the material.

[0097] Table 1. Density and mechanical and physical parameters of aerogels prepared in Examples 1-7 and Comparative Examples 2-4 Analysis example 4 Thermal stability analysis was performed on the aerogels prepared in Example 1 and Comparative Example 2: 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.

[0098] 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.

[0099] 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.

[0100] Analysis example 5 Flame retardant properties of the aerogels prepared in Example 1 and Comparative Examples 2-3 were analyzed: 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.

[0101] 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.

[0102] Aerogel PBNNS / CS-Fe in Example 1 3+ It exhibits superior performance, self-extinguishing rapidly within 1.8 seconds after initial ignition, with no flame spread upon secondary ignition, significantly reducing smoke density to 12, and forming a dense and expanded char layer, achieving the near-V-0 flame retardant standard.

[0103] Aerogel BN / CS-Fe in Comparative Example 3 3+ It exhibits transitional characteristics. Although it has certain flame retardancy, it self-extinguishes within 2.9 seconds after the first ignition and does not spread after the second ignition, but its smoke density (DS=37) is much higher than that of Example 1, and the density of the char layer is insufficient.

[0104] The above comparison shows that functionalized boron nitride nanosheets not only exert a condensed phase flame retardant effect by forming a dense physical barrier and catalyzing char formation, but also effectively suppress smoke generation. Their synergistic flame retardant efficiency is far superior to that of unfunctionalized nanosheets, greatly improving the fire safety of bio-based materials. The flame retardant performance parameters of the aerogels prepared in Example 1 and Comparative Examples 2-3 are shown in Table 2. Table 2 Flame retardant properties of the aerogels prepared in Example 1 and Comparative Examples 2-3 Analysis example 6 Thermal properties of the aerogels prepared in Examples 1-7 were analyzed: As shown in Table 3, the pyrolysis behavior of the aerogels prepared in Examples 1-7 in an air atmosphere was analyzed. The flame retardant properties of the aerogels of the present invention are closely related to their char-forming ability at high temperatures. Among them, Example 1 showed the best flame retardant potential, with a char residue rate of more than 57% and a slow thermal decomposition process, indicating that the material can form a stable and dense protective char layer at high temperatures, effectively inhibiting further combustion and thermal decomposition of the matrix.

[0105] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a chitosan-based polymeric composite aerogel, characterized in that, Including the following steps: S1 provides chitosan powder, phosphate-functionalized boron nitride nanosheets, and iron salts; The method for obtaining the phosphate-functionalized boron nitride nanosheets includes: mixing boron nitride powder with an external liquid and then performing liquid-phase assisted ball milling, and then collecting the phosphate-functionalized boron nitride nanosheets; the external liquid contains an organic phosphate ester, which includes one or more of inositol hexaphosphate, phosphoglycerate, glucose phosphate, and ascorbate phosphate. S2, the phosphate-functionalized boron nitride nanosheets are homogenized in water to obtain a suspension; the suspension, chitosan powder, and iron salt are mixed and allowed to stand to obtain a composite gel; after drying, a chitosan-based polymer composite aerogel is obtained; the mass ratio of chitosan, phosphate-functionalized boron nitride nanosheets, and 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 to the organophosphate is 1:2-10.

3. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, In the added liquid, the organic phosphate ester accounts for 25-65% by mass.

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 dimension 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 salts include 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 homogenization process uses a stirring speed of 8000-15000 rpm; The suspension, chitosan powder, and iron salt are mixed at a speed of 300-500 rpm for 2-6 hours.

8. The method for preparing chitosan-based polymeric composite aerogel according to claim 1, characterized in that, The liquid-phase assisted ball milling process uses a ball milling speed of 200-500 rpm and a ball milling time of 8-40 h. The liquid-phase assisted ball milling process is carried out in a ball milling jar, which is filled with 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: after completing the liquid-phase assisted ball milling treatment, centrifuging to collect the upper mixture, and then filtering and drying to obtain the phosphate-functionalized boron nitride nanosheets.

9. A chitosan-based polymeric composite aerogel, characterized in that, The chitosan-based polymeric composite aerogel was prepared using the preparation method described in any one of claims 1-8.

10. The application of the chitosan-based polymeric composite aerogel as described in claim 9 in flame retardancy.

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