High-flame-retardant fireproof biomass composite aerogel as well as preparation method and application thereof

Abstract

The invention discloses high-flame-retardant fireproof biomass composite aerogel as well as a preparation method and application thereof, and belongs to the technical field of thermal insulation materials. The preparation method comprises the following steps: by taking the sea grass as a base material, extracting sea grass cellulose, and matching with chitosan (CS), phytic acid (PA) and kaolin (IM) to construct a ternary synergistic system. Wherein the sea grass cellulose provides a skeleton structure, the chitosan forms a condensed-phase flame-retardant barrier through a charring effect, the phytic acid releases phosphorus free radicals to inhibit gas-phase combustion, and the kaolin serves as an inorganic filler to enhance the physical barrier property. The material has excellent flame-retardant and heat-insulating properties, light weight characteristics and environmental friendliness, and meets the application requirements in the fields of building heat preservation, electronic fire prevention, new energy battery flame-retardant layers and the like.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant materials technology, specifically relating to a highly flame retardant and fireproof biomass composite aerogel, its preparation method, and its application. Background Technology

[0002] Aerogels are lightweight nanomaterials with a three-dimensional porous network structure. Due to their ultra-low density, high porosity, and excellent thermal insulation properties, they show broad application prospects in building insulation, fire protection of electronic equipment, and safety protection of new energy batteries. Cellulose aerogels, as a type of aerogel, are prepared from cellulose. Cellulose is widely available, renewable, and relatively inexpensive, making cellulose aerogels promising for future applications.

[0003] With the increasing global demand for green and sustainable development, the development of low-cost, high-performance, and environmentally friendly bio-based flame-retardant gels has become a research hotspot. Cellulose, as a widely available, renewable, and relatively low-cost natural polymer material, has become one of the ideal raw materials for preparing aerogels due to its unique physical and chemical properties. Cellulose aerogels not only possess excellent thermal insulation properties but also offer significant advantages in terms of environmental protection.

[0004] However, existing cellulose aerogels also have some drawbacks. On the one hand, pure cellulose aerogels have poor mechanical properties and are prone to breakage in practical applications, affecting their performance and lifespan. On the other hand, their flame-retardant properties are limited, making it difficult to meet stringent fire protection requirements when exposed to high temperatures or open flames. Traditional aerogel materials are mostly made from silicon-based or synthetic polymers. Although they have excellent performance, they suffer from high costs, complex preparation processes, and poor environmental friendliness. In addition, existing flame-retardant gels mostly rely on halogen-based or phosphorus-based flame retardants, which, while effectively inhibiting combustion, easily release toxic gases at high temperatures, posing potential hazards to the environment and human health.

[0005] Peat moss contains high-purity cellulose and has a naturally porous structure, exhibiting excellent biodegradability, making it an ideal raw material for preparing aerogels. However, aerogels prepared directly from peat moss cellulose still have shortcomings in terms of mechanical strength and flame retardant properties, limiting their widespread application in practice. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] This invention uses seaweed cellulose as a matrix and modifies it by introducing chitosan, phytic acid and kaolin. The amino groups of chitosan form a hydrogen bond network with the hydroxyl groups of cellulose, which significantly improves the mechanical properties. Phytic acid, as a bio-based flame retardant, promotes char formation during pyrolysis and effectively isolates heat and oxygen. The layered structure of kaolin further blocks the spread of flame and synergistically improves the flame retardant efficiency.

[0009] To address the aforementioned technical problems, this invention provides a method for preparing a highly flame-retardant and fire-resistant biomass composite aerogel. The preparation process includes the following key stages: Phytic acid-chitosan in situ complexation: the abundant phosphate groups in phytic acid undergo hydrogen bonding and electrostatic interaction with the amino and hydroxyl groups of chitosan, thus initially constructing a dynamic prepolymer with flame retardant potential.

[0010] Multi-component cross-linking and kaolin composites allow phytic acid-chitosan complexes to further coordinate and hydrogen bond with the hydroxyl groups on the cellulose surface, resulting in kaolin composite modification and initial interfacial integration between components.

[0011] Glutaraldehyde covalent crosslinking and freeze-molding: Glutaraldehyde is added as a covalent crosslinking agent, in which a Schiff base reaction occurs between the amino groups in chitosan molecules and the aldehyde groups in glutaraldehyde, forming a stable covalent crosslinking network. Finally, freeze-drying yields an aerogel material with a three-dimensional porous structure.

[0012] Specifically, the preparation steps include: Cellulose extracted from seaweed was added to deionized water to obtain a seaweed cellulose suspension; Kaolin was added to the seaweed cellulose suspension and mixed evenly to obtain a KL / CL solution; Phytic acid is dissolved in deionized water to obtain PA solution; Add chitosan to the PA solution and heat and stir in a water bath at 50℃~100℃ until the chitosan is completely dissolved to obtain a CS / PA solution. The water bath temperature is preferably 60℃~80℃; The CS / PA solution and KL / CL solution were mixed and mechanically stirred. After adding the crosslinking agent and stirring for another 1 minute, a mixed slurry was obtained. The mixed slurry is immediately poured into a mold and frozen with liquid nitrogen until a white frost appears on the sample surface, which is the wet gel. The wet gel is then freeze-dried to obtain a highly flame-retardant and fireproof biomass composite aerogel.

[0013] In a preferred embodiment of the preparation method described in this invention, the mass concentration of cellulose in the KL / CL solution is 1.5~2.5wt%.

[0014] In a preferred embodiment of the preparation method described in this invention, the mass concentration of kaolin in the KL / CL solution is 1~3wt%.

[0015] In a preferred embodiment of the preparation method described in this invention, the mass concentration of phytic acid in the CS / PA solution is 50~60wt%.

[0016] In a preferred embodiment of the preparation method described in this invention, the mass concentration of chitosan in the CS / PA solution is 1.5~2.5 wt%.

[0017] In a preferred embodiment of the preparation method described in this invention, the crosslinking agent is glutaraldehyde.

[0018] In a preferred embodiment of the preparation method described in this invention, the mass concentration of the crosslinking agent in the mixed slurry is 0.36~2.1wt%.

[0019] In a preferred embodiment of the preparation method described in this invention, the mixing volume ratio of the CS / PA solution to the KL / CL solution is 4:10.

[0020] Another object of the present invention is to provide a highly flame-retardant and fire-resistant biomass composite aerogel, which has the following characteristics: (i) Using cellulose extracted from seaweed as a three-dimensional framework, chitosan as a dynamic network matrix, phytic acid as a flame retardant-crosslinking bifunctional component, kaolin as a physical barrier enhancer, and glutaraldehyde as a covalent crosslinking bridge, an aerogel structure was synergistically constructed. (ii) The high flame retardant and fireproof biomass composite aerogel is prepared by constructing a dynamic prepolymer with flame retardant potential through in-situ complexation of phytic acid and chitosan, and then by adding glutaraldehyde to achieve covalent cross-linking. (iii) The mass ratio of phytic acid to chitosan is 50~60:1.5~2.5, and the mass ratio of kaolin to cellulose is 1~3:1.5~2.5.

[0021] The high flame-retardant and fireproof biomass composite aerogel of the present invention uses cellulose extracted from seaweed as a three-dimensional framework, chitosan as a dynamic network matrix, phytic acid as a flame-retardant-crosslinking bifunctional component, kaolin as a physical barrier reinforcing agent, and glutaraldehyde as a covalent crosslinking bridge to construct a high-strength and high-flame-retardant integrated aerogel structure through multiple mechanisms.

[0022] Kaolin, with its abundant Al–OH / Si–OH groups embedded in the cellulose framework, significantly enhances the surface roughness of the aerogel and introduces flame-retardant active sites. Subsequently, hydrogen bonds assemble between the cellulose molecular chains and chitosan, and the disordered growth of ice crystals during freezing forms the initial pore framework. The aldehyde group (–CHO) of glutaraldehyde reacts with the amino group (–NH2) of chitosan to form a carbon-nitrogen double bond. The aldehyde group (–CHO) in glutaraldehyde reacts with the hydroxyl group (-OH) of cellulose to form a hemiacetal or acetal. Finally, phytic acid, rich in phosphate groups (-PO4), forms a pore structure. 3- It forms a dense interpenetrating structure by covalently coordinating with the hydroxyl groups (-OH) of cellulose and the amino groups (-NH2) of chitosan, thereby reducing the pore size and increasing the porosity.

[0023] The resulting aerogel not only exhibits a limiting oxygen index (LOI) as high as 90%, far exceeding that of similar bio-based materials (typically LOI < 30%), but also achieves a UL-94 V-0 rating during vertical burning. Furthermore, after being burned at 1300℃ for 30 minutes, the material retains its flame-retardant effect and has a self-extinguishing time of < 1 second, demonstrating excellent fire-resistant performance. Moreover, the highly flame-retardant biomass composite aerogel achieves an extremely low peak heat release rate (pHRR, 7.26 kW·m³). -2 The breakthroughs in the material design, including the total heat of release (THR, 3.37 MJ / m²), are attributed to the ingenious utilization of the synergistic effect of multiple components, providing a novel solution for the application of bio-based aerogels in fields with high safety requirements.

[0024] Another objective of this invention is to provide the application of the highly flame-retardant and fireproof biomass composite aerogel in the preparation of building insulation, electronic fireproofing, and flame-retardant layers for new energy batteries.

[0025] Beneficial effects of this invention: (1) This invention achieves significant improvements in flame retardancy, heat insulation, mechanical properties, and environmental friendliness of seaweed cellulose-based aerogel through raw material innovation and ternary synergistic system design. Among them, the ternary synergistic flame retardant mechanism (phytic acid, chitosan, and kaolin) achieves a limiting oxygen index (LOI) of up to 90% through the synergistic effect of gas-phase free radical quenching, condensed phase expanded carbon layer barrier, and physical barrier high-temperature resistant inorganic layer. In addition, the vertical burning performance reaches UL94V-0 level (t1=t2=0s), and the self-extinguishing time of butane spray gun at 1300℃ is less than 1 second, demonstrating excellent flame retardant performance.

[0026] (2) The aerogel prepared by this invention achieves a comprehensive improvement in thermal insulation and mechanical properties. The three-dimensional porous network structure of the aerogel gives it a low heat release rate and excellent thermal insulation performance. In terms of mechanical properties, load-bearing tests show that the aerogel can withstand a load of more than 2487 times its own weight, and the deformation does not exceed 2%, which combines high strength and high toughness to meet the needs of various application scenarios.

[0027] (3) This invention uses water-based solvents and freeze-drying process to achieve zero VOCs (volatile organic compounds), has biocompatibility, does not pollute the environment, fills the gap in sustainability of bio-based flame retardant gels, and meets the requirements of green development.

[0028] (4) This invention adopts a green preparation process, which simplifies the process steps and reduces energy consumption. At the same time, the raw materials used are inexpensive and readily available, which greatly reduces production costs, improves the market competitiveness of the product, and provides an economical and feasible solution for the high-value utilization of biomass resources and the sustainable development of the fire safety field. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments 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 these drawings without creative effort. Wherein: Figure 1 This is a flowchart illustrating the preparation process of the CN-CA aerogel obtained in Example 1 of the present invention.

[0030] Figure 2 Fourier transform infrared (FTIR) spectra of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention.

[0031] Figure 3 The thermogravimetric (TGA) and differential (DTG) plots of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown.

[0032] Figure 4 This is a comparison chart of the limiting oxygen index tests of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0033] Figure 5 The image shows a comparison of vertical combustion tests of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention.

[0034] Figure 6 This is a comparison chart of cone calorimetry tests of CN-CA aerogel and CA aerogel prepared in Example 1 and Comparative Example 2 of the present invention.

[0035] Figure 7 This is a load-bearing test diagram of the CN-CA aerogel prepared in Example 1 of the present invention.

[0036] Figure 8 XPS spectra of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention. Detailed Implementation

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0039] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0040] Unless otherwise specified, all raw materials used in this invention are commercially available. The sources of the raw materials used in specific embodiments are as follows: Chitosan (CS) (Jieshikai, medium viscosity, 200-400 mPa.s); Phytic acid (PA) (Aladdin, 70% by mass); Kaolin (KL) (Comio reagent, analytical grade); Glutaraldehyde (photorecovered, mass fraction 50%).

[0041] The extraction method for cellulose from seaweed extract is as follows: Seaweed obtained from Guizhou is mechanically crushed for 1 minute to obtain raw seaweed residue; Add 10 g of seaweed residue to a 2 wt% NaOH solution (500 mL) and stir at 80 °C for 1 h to remove hemicellulose; Wash the seaweed residue with deionized water, then mix it with 2 wt% NaClO2 solution (500 mL), and adjust the pH of the solution to 4-6 with acetic acid as an adjuster. Stir magnetically for 1 hour in an 80℃ water bath. Finally, the filter was filtered, and the filter residue was washed with deionized water until neutral and dried at 80°C for 12 h. The residue was then mechanically pulverized to obtain the final seaweed cellulose, which was used in the specific embodiment.

[0042] The abbreviations and full names in this invention are as follows: Chitosan (CS), phytic acid (PA), kaolin (KL), cellulose (CL) Since flame retardancy is a complex, multi-dimensional characteristic involving factors such as the ease of ignition, flame propagation, heat release, smoke production, and self-extinguishing ability, multiple indicators are needed for comprehensive evaluation from different perspectives. The limiting oxygen index reflects the ease of ignition, self-extinguishing time and flame retardant time demonstrate the material's sustained resistance to flames, PHRR and THR characterize the thermal hazard of the material in a fire, the thermogravimetric maximum decomposition rate indicates the material's thermal stability, and load-bearing capacity assesses the structural integrity of the material in a fire. The materials prepared in the embodiments and comparative examples of this invention were tested for performance using the following methods: Limiting Oxygen Index (LOI) Test: Obtain the limiting oxygen index (LOI) according to ASTM D2863-97; Vertical burning test: Refer to GB / T2408 to obtain the self-extinguishing time and evaluate the UL-94 rating. The non-self-extinguishing result in this application means that the sample failed to self-extinguish during the test until it was completely burned. Cone calorimetry test: Refer to ISO 5660-1 to obtain the peak heat release rate (PHRR) and total heat release rate (THR); Thermogravimetric analysis (TGA): Obtains the maximum thermogravimetric decomposition rate; Load-bearing capacity test: compared to its own weight; Flame retardant time test: Record the time from when the material is ignited until it completely loses its flame retardant barrier function and can no longer effectively insulate heat, and obtain the flame retardant time.

[0043] Example 1 This embodiment provides a method for preparing a highly flame-retardant and fire-resistant biomass composite aerogel, specifically as follows: 1) Add 2g of cellulose extracted from seaweed to deionized water to obtain a seaweed cellulose suspension with a concentration of 2wt%. Add 3g of kaolin to the seaweed cellulose suspension and mix well to obtain a KL / CL solution. 2) Dissolve 78.57 mL of phytic acid solution (70% by mass) in 21.43 mL of deionized water and mix thoroughly to obtain a uniform, transparent, pale yellow 55 wt% PA solution. Add 2 g of chitosan to the PA solution and heat and stir continuously at 80°C in a water bath until the chitosan is completely dissolved to obtain a yellow viscous CS / PA solution. The concentration of chitosan in the CS / PA solution is 2 wt%. 3) Mix CS / PA solution and KL / CL solution at a ratio of 4:10, stir mechanically for 30 min, add 1 wt% glutaraldehyde and continue stirring for 1 min to obtain a mixed slurry; The mixed slurry was immediately poured into a mold and frozen with liquid nitrogen until a white frost appeared on the sample surface, which yielded a wet gel. The wet gel was then freeze-dried at -50°C for 48 hours to obtain the high flame-retardant and fireproof biomass composite aerogel of this embodiment, denoted as CN-CA.

[0044] Figure 1 This is a schematic diagram illustrating the preparation and application of the high flame-retardant and fire-resistant biomass composite aerogel in this embodiment.

[0045] Measurements showed that the CN-CA aerogel prepared in this embodiment had a limiting oxygen index (LOI) as high as 90%, far exceeding that of similar bio-based materials (typically LOI < 30%). It achieved a UL-94 V-0 rating during vertical burning. After being burned at 1300℃ for 30 minutes, the material still exhibited flame-retardant properties and a self-extinguishing time of < 1 second, demonstrating excellent fire-resistant performance. Furthermore, the highly flame-retardant biomass composite aerogel achieved an extremely low peak heat release rate (pHRR, 7.26 kW·m³). -2 The total heat of release (THR, 3.37 MJ / m²), maximum thermogravimetric decomposition rate: 2.14 % / min, load-bearing capacity (compared to its own weight) 2487 times, and flame retardant time of 1800 s are all breakthroughs achieved by the ingenious use of the synergistic effect of multiple components in material design, providing a brand-new solution for the application of bio-based aerogels in fields with high safety requirements.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is that PA is omitted in step 2), and 2 g of chitosan powder and 1 g of acetic acid are directly dissolved in deionized water and stirred until the chitosan is completely dissolved to obtain a CS solution with a concentration of 2wt%. The remaining preparation processes were the same as in Example 1, and the KL-CA aerogel of this comparative example was obtained.

[0047] Comparative Example 2 The difference between this comparative example and Example 1 is that kaolin is not added in step 1) and PA is omitted in step 2). Instead, 2 g of chitosan powder and 1 g of acetic acid are directly dissolved in deionized water and stirred until the chitosan is completely dissolved. The rest of the preparation process is the same as in Example 1, and the CA aerogel of this comparative example is obtained.

[0048] Figure 2 The Fourier transform infrared (FTIR) spectra of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown in the figures. As can be seen from the figures, at 3460 cm⁻¹... -1 and 2930 cm -1 The wide bonds at these points correspond to -OH and CH bonds, respectively. 1320 cm -1 1160 cm -1 and 904 cm -1 The peak at 1000 cm⁻¹ belongs to the -OH, CO, and glycosidic bonds in cellulose. -1 The peaks around 1500 cm⁻¹ are attributed to the P=O bonds in phytic acid. -1 The peaks appearing on the left and right are attributed to the Schiff base bond (C=N) formed by the reaction between chitosan and glutaraldehyde. (A Schiff base is a class of organic compounds containing an imine bond (C=N). Its formation process involves the condensation reaction of an aldehyde or ketone with a primary amine to generate an imine containing a carbon-nitrogen double bond, while simultaneously losing one molecule of water.) This indicates that phytic acid and chitosan have successfully cross-linked with cellulose.

[0049] Figure 3The thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTG) plots of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown. As can be seen from the figures, the first decomposition process involves a slight mass loss at approximately 100°C, attributed to the loss of water of crystallization in CN-CA and CA aerogels, with the water of crystallization evaporating as water vapor, causing weight loss. Furthermore, CN-CA aerogel exhibits an additional peak at approximately 180°C on the DTG curve, which can be attributed to the decomposition of PA. The decomposition of PA produces phosphoric acid or metaphosphoric acid, catalyzing... The dehydration of the carbohydrate backbone of the aerogel serves as a carbon source, forming a char layer. This thermally stable char layer acts as a fire barrier, limiting the transfer of combustion heat and combustible volatiles to the aerogel matrix, thereby enhancing its fire resistance. The second decomposition process is weight loss around 300°C, common to CN-CA, KL-CA, and CA aerogels, attributed to the decomposition of chitosan and cellulose in the components. At this temperature, residual char degrades, generating low-molecular-weight and volatile components that volatilize, leading to weight loss. The third decomposition process is weight loss at around 600°C, attributed to the complete collapse and disintegration of the aerogel structure. Throughout the decomposition process, CN-CA aerogel exhibits a higher maximum decomposition temperature compared to KL-CA and CA aerogels, but its maximum decomposition rate is reduced to 2.14% / min, lower than the 5.13% / min of CA aerogel. This is because the introduction of phytic acid and kaolin, two flame retardants, promotes catalytic char formation in the aerogel, reducing the decomposition rate and improving its thermal stability. During heating, phytic acid promotes the dehydration and carbonization of cellulose and chitosan. With the synergistic effect of kaolin, a stable expanded carbon layer forms on the aerogel surface, isolating combustible gases and heat from external exchange, thus delaying aerogel decomposition and reducing its decomposition rate, exhibiting condensed-phase flame-retardant properties. TGA data clearly demonstrate the synergistic effect between the CN-CA aerogel components and the excellent thermal stability it imparts to the material.

[0050] Figure 4 This is a bar chart comparing the limiting oxygen index (LOI) of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Examples 1, 1, and 2 of this invention with that of other flame-retardant materials. The limiting oxygen index (LOI) is the volume fraction of oxygen at which a polymer can just sustain combustion in a mixture of oxygen and nitrogen. It is an index characterizing the combustion behavior of a material. Materials with a high LOI are difficult to burn. Generally, an LOI < 22% is considered flammable, an LOI between 22% and 27% is considered combustible, and an LOI > 27% is considered flame-retardant. The test results show that the LOI of CN-CA aerogel is as high as 90%, classifying it as a flame-retardant material. This is significantly higher than the LOI of CA aerogel (21%), indicating that CN-CA aerogel exhibits excellent flame-retardant properties.

[0051] Figure 5 This image shows a comparison of vertical combustion tests of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Examples 1, 1, and 2 of this invention. During combustion, chitosan and phytic acid in CN-CA aerogel form a dense carbonized layer on the surface of the aerogel. The carbonized layer effectively prevents the flame from spreading, and the aerogel remains unburned after two ignitions, demonstrating excellent flame retardant properties. Compared to CA aerogel, CN-CA aerogel achieved a test result of t1=t2=0s, reaching the V-0 rating of UL-94, while CA aerogel did not extinguish after ignition, lacking self-extinguishing ability, and the flame even burned the clamping device, indicating that CN-CA aerogel possesses excellent flame retardant ability and self-extinguishing performance.

[0052] Figure 6 Figure 1 shows a comparison of cone calorimetry results of CN-CA aerogel and CA aerogel prepared in Example 1 and Comparative Example 2 of this invention. Figure 2(a) shows the comparison curves of HRR, SPR, THR, TSP, TSR, and EHC of CN-CA aerogel and CA aerogel. Figure 3(g) shows CN-CA aerogel after cone calorimetry test. Figure 4(j) shows CA aerogel after cone calorimetry test. Figure 5(hi) shows the scanning and mapping diagram of CN-CA aerogel after cone calorimetry test. Figure 6(kl) shows the scanning diagram of CA aerogel after cone calorimetry test.

[0053] from Figure 6 It can be seen that the peak heat release rate (PHRR) of CN-CA aerogel decreases with the addition of phytic acid and kaolin. The PHRR decreases from 40.07 kW / m 2 Reduced to 7.26 kW / m 2 The total heat release rate (THR) increased from 6.49 MJ / m³. 2 It continuously decreased to 3.37 MJ / m 2 The above results indicate that the addition of phytic acid and kaolin significantly reduces heat release and enables the formation of a stable carbon layer during combustion. CN-CA aerogel releases non-combustible gases CO2 and H2O during combustion, which dilutes the combustible gases and inhibits the reactions required to sustain combustion. Phytic acid releases free radicals such as HPO·, PO·, and HPO2· during combustion. These free radicals react with high-energy OH· and H· free radicals, generating in the early stages of combustion and thus interrupting the chain reaction crucial for continuous combustion. Simultaneously, phytic acid, as an excellent acid source, combines with chitosan as a foaming agent and carbon source to form a foaming system that creates a protective char layer in the condensed phase, protecting the aerogel. This highly stable char layer, acting as a low thermal conductivity coating on the surface, prevents heat transfer to the aerogel skeleton, thus combining gas-phase and condensed-phase flame retardancy to achieve flame retardancy in fires.

[0054] Figure 7 This is a load-bearing test diagram of the CN-CA aerogel prepared in Example 1 of the present invention. Figure 7 (ac) CN-CA aerogel standing on a real flower, (df) CN-CA aerogel standing on a paper flower, (g) CN-CA aerogel bearing a 1000g weight. Tests show that the CN-CA aerogel samples, under load on real flower petals and ultra-thin paper flower substrates, did not cause visible deformation of the substrates, confirming that the material density reaches an ultra-lightweight level. Quasi-static compression tests show that the material maintains its structural integrity even when subjected to loads thousands of times its own weight. This property gives the flame-retardant and heat-insulating aerogel good mechanical strength and stability in practical applications.

[0055] Figure 8 XPS spectra of CN-CA aerogel, KL-CA aerogel, and CA aerogel prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown. XPS elemental analysis reveals that the figures show the XPS-fitted spectra of CN-CA aerogel, KL-CA aerogel, and CA aerogel. The wide-scan full spectrum of CN-CA aerogel exhibits six characteristic peaks. Besides the peaks of 532.80 eV (O1s), 400.35 eV (N1s), and 285.81 eV (C1s) which are consistent with those of CA aerogel, three new peaks are added: 135.12 eV (P2p), 102.96 eV (Si2p), and 74.73 eV (Al2p), directly confirming the successful introduction of kaolin and phytic acid into the aerogel system.

[0056] Further fitting of the C, N, and O peaks revealed that for CA and CN-CA aerogels, peak fitting of the C element showed five peak components in the C1s spectrum: the C=C peak at 284.8 eV, the C=N peak at approximately 285.45 eV, confirming the cross-linking between chitosan and glutaraldehyde to form Schiff base bonds, consistent with the C=N peak at 1400 cm⁻¹ in the FT-IR spectrum; the C=O peak at approximately 288.92 eV, attributed to the aldehyde group in glutaraldehyde; and the CO peak at approximately 286.62 eV, attributed to the CO bond in chitosan and cellulose. The characteristic C-OH peak at 287.93 eV originates from the hydroxyl groups in chitosan and cellulose. The peak area in CN-CA aerogel is significantly smaller than that in CA and KL-CA aerogels, directly demonstrating the cross-linking reaction between phytic acid and chitosan, consuming a large number of hydroxyl groups, consistent with the peak area at 3460 cm⁻¹ in the FT-IR spectrum. The weakening of the hydroxyl stretching vibration peak at cm⁻¹ corroborates each other, jointly revealing that the cross-linking reaction increased the cross-linking density of the components.

[0057] The N1s fitted spectrum of CA aerogel can be divided into peaks at 402.25, 400.48, 399.48, and 398.69 eV, which are attributed to NH, NC, -NH2, and CN=C, respectively. The first three groups are derived from chitosan, and the last can be attributed to the linkage between chitosan and glutaraldehyde. A new peak at 400.25 eV appears in CN-CA aerogel and is identified as a PN bond, while the infrared 500 cm⁻¹... -1 The PN vibration peak at the position also indicates that phytic acid and chitosan have undergone cross-linking. Fitting the C, O, and N elements revealed that the peak values ​​for the same functional groups in the CA aerogel and CN-CA aerogel shifted towards lower peak values. These slight shifts may be attributed to the addition of kaolinite and phytic acid. Further fitting of Si2p and Al2p showed that the fitted results were consistent with the chemical bonds of kaolinite itself, and no new chemical bonds appeared, indicating that kaolinite was merely physically covering the aerogel surface without undergoing a chemical reaction. This judgment was confirmed in the O1s spectrum, where the Si-O-Si bond at 532.76 eV and the Al-O bond at 531.51 eV both originated from kaolinite, and the P=O bond at 533.39 eV originated from phytic acid. Combined with Fourier transform infrared spectroscopy, the XPS fitting results were consistent with the FTIR results, confirming the successful loading of kaolinite into the aerogel. In addition to the Si2p and Al2p peaks, a new peak was detected at 135.12 eV (P2p) in the broad-scan full spectrum of CN-CA aerogel, proving that phosphorus (P) has been introduced into the aerogel surface. The P2p spectrum can be decomposed into three peaks at 134.74, 135.55, and 136.27 eV, which can be attributed to PN, P=O, and PO / POC bonds, respectively. The PN bond indicates that phytic acid and chitosan have undergone cross-linking; at the same time, the peak at 136.27 eV also proves that a covalent bond has formed between the phosphorus atom of phytic acid and the oxygen atom of cellulose, resulting in a POC bond. The FT-IR spectrum at 1700 cm⁻¹... -1 The POC vibration peak at 135.55 eV confirms this. The P=O fitting peak at 135.55 eV is attributed to phosphate in phytic acid. In summary, the XPS analysis results are highly consistent with the FTIR characteristic peak information, jointly confirming that kaolin and phytic acid have been successfully loaded into the aerogel system.

[0058] Example 2 The difference between this embodiment and Example 1 is that the concentration of chitosan in the CS / PA solution in step 2) is adjusted to 1wt%, 1.5wt%, 2.5wt%, and 3wt%, while the rest of the preparation process is the same as in Example 1, thus obtaining the CN-CA aerogel of this embodiment.

[0059] The properties of aerogels prepared with different chitosan concentrations in Example 1, Comparative Example 1, and Example 2 were measured, and the comparison results are shown in Table 1.

[0060] Table 1

[0061] As can be seen from the table above, adjusting the amount of chitosan powder added during the preparation of the CS / PA solution has a significant impact on the performance of CN-CA aerogel. This is because excessive chitosan will cover the flame-retardant active sites of phytic acid and weaken the catalytic char formation effect of phosphoric acid. However, insufficient chitosan will cause phytic acid to be unable to be fully anchored on the framework, resulting in early decomposition upon heating and loss of the flame-retardant function of the condensed phase. According to the results in the table above, when the mass percentage of chitosan in the mixed solution system in this invention is 1.5~2.5wt%, the material exhibits a higher limiting oxygen index and a lower thermal decomposition rate.

[0062] Example 3 The difference between this embodiment and Example 1 is that the concentration of PA solution in the CS / PA solution in step 2) is adjusted to 30wt%, 50wt%, 55wt%, 60wt%, and 70wt%, while the rest of the preparation process is the same as in Example 1, thus obtaining the CN-CA aerogel of this embodiment.

[0063] The properties of the aerogels prepared with different PA concentrations in Example 3 were measured, and the results compared with those of Example 1 and Comparative Example 1 are shown in Table 2.

[0064] Table 2

[0065] As shown in the table above, adjusting the PA solution concentration significantly affects the performance of CN-CA aerogel. This is because insufficient phytic acid leads to insufficient char source, resulting in a loss of the thermal barrier due to the reduced char content; while excessive phytic acid causes acidic hydrolysis of cellulose chains and chitosan, leading to the formation of a brittle char layer, loss of barrier function, and a significant reduction in flame retardant effect; and the absence of PA solution results in a precipitous drop in flame retardant performance due to the lack of cross-linking to form a three-dimensional network. Based on the results in the table, the optimal technical effect can be obtained when the PA solution concentration in this invention is 50wt%~60wt%.

[0066] Example 4 The difference between this embodiment and Example 1 is that the mass concentration of glutaraldehyde in the mixed slurry system in step 3) is adjusted to 0.36wt%, 0.5wt%, 1.5wt%, and 2.1wt%, respectively. The rest of the preparation process is the same as in Example 1, and the CN-CA aerogel of this embodiment is obtained.

[0067] The properties of the aerogels prepared with different glutaraldehyde concentrations in Example 4 were measured, and the results compared with those of Example 1 and Comparative Example 1 are shown in Table 3.

[0068] Table 3

[0069] As shown in the table above, adjusting the amount of glutaraldehyde significantly affects the performance of CN-CA aerogel. When the dosage deviates from the optimal value (1.4 g, 1 wt%), the heat release rate of the material increases sharply and it loses its self-extinguishing ability. When the amount of glutaraldehyde is insufficient, the aldehyde groups cannot undergo a Schiff base reaction with sufficient amino groups on the chitosan molecular chain, resulting in insufficient cross-linking of the formed three-dimensional network. This loose structure cannot effectively fix and disperse phytic acid molecules, thus losing its key role in catalytic carbonization. When the amount of glutaraldehyde is excessive, the excess aldehyde groups, after completing the cross-linking with the chitosan amino groups, will further react with the phosphate groups of phytic acid. This side reaction consumes the active groups in phytic acid that catalyze carbonization, leading to the loss of its catalytic activity and inability to self-extinguish. According to the results in the table above, the optimal technical effect can be obtained when the amount of glutaraldehyde in this invention is 1 wt%.

[0070] Example 5 The difference between this embodiment and Example 1 is that the concentration of cellulose in the KL / CL solution in step 1) is adjusted to 1wt%, 1.5wt%, 2.5wt%, and 3wt%, while the rest of the preparation process is the same as in Example 1, thus obtaining the CN-CA aerogel of this embodiment.

[0071] The properties of the aerogels prepared with different cellulose concentrations in Example 5 were measured, and the results compared with those of Example 1 and Comparative Example 1 are shown in Table 4.

[0072] Table 4

[0073] As shown in the table above, adjusting the cellulose content significantly affects the performance of CN-CA aerogel. This is because excessive cellulose disrupts the uniformity of the chitosan-phytic acid crosslinking network, leading to a harder and more brittle material. The brittle structure is prone to collapse in real fire conditions, failing to achieve optimal long-term thermal insulation. Insufficient cellulose weakens the role of the three-dimensional network framework, causing the aerogel structure to deform easily and significantly reducing its load-bearing capacity. Insufficient cellulose also reduces the "carbon source" for synergistic char formation, preventing the formation of a stable and dense char layer with phytic acid and chitosan. Based on the results in the table, the optimal technical effect is achieved when the cellulose solution concentration in this invention is between 1.5 wt% and 2.5 wt%.

[0074] Comparative Example 3 The difference between this comparative example and Example 1 is that step 3) omits the PA / CS solution and directly adds glutaraldehyde to the KL / CL solution. The rest of the preparation process is the same as in Example 1, and the KL aerogel of this comparative example is obtained.

[0075] Comparative Example 4 The difference between this comparative example and Example 1 is that the PA solution in step 2) is replaced with a phosphoric acid solution with an equal number of phosphorus moles. The rest of the preparation process is the same as in Example 1, and the aerogel of this comparative example is obtained.

[0076] Comparative Example 5 The difference between this comparative example and Example 1 is that in step 2), the PA solution is replaced with an equal mass of tannic acid solution, while the rest of the preparation process is the same as in Example 1, and the aerogel of this comparative example is obtained.

[0077] The performance of the aerogels prepared in each comparative example was tested and compared with that of Example 1 and Comparative Example 1. The comparison results are shown in Table 5.

[0078] Table 5

[0079] As shown in the table above, the total heat release (THR) and self-extinguishing time data strongly confirm the sophisticated synergistic flame-retardant effect between the seaweed cellulose-chitosan-phytic acid ternary system in this invention. This effect is not a simple superposition of the functions of each component. Example 1 exhibits the lowest THR (3.37 MJ / m²) and instantaneous self-extinguishing (0 s), thanks to the complete synergistic effect. Phytic acid, upon heating, catalyzes the dehydration of cellulose and chitosan, serving as a carbon source and forming a char layer. This thermally stable char layer acts as a fire barrier, limiting the transfer of combustion heat and combustible volatiles to the aerogel matrix, thereby enhancing its fire resistance. Kaolin, as a physical barrier, is firmly embedded in the char layer formed by the former two components, making it denser and more stable, effectively isolating heat and oxygen. This, combined perfectly with the three-dimensional framework of seaweed cellulose, constitutes a highly efficient gas-solid synergistic flame-retardant system.

[0080] The THR of Comparative Examples 1, 2, and 3 increased sharply and they were unable to self-extinguish, demonstrating that without the core dynamic network of phytic acid-chitosan, the materials degenerate into ordinary combustibles. Compared to Example 1, Comparative Example 4, despite having the same phosphorus content, had a much higher THR (7.80 MJ / m²) and was also unable to self-extinguish. This indicates that the role of phytic acid is far more than simply "providing phosphorus." The multiple phosphate groups of phytic acid molecules cross-link with the amino groups of chitosan and the hydroxyl groups of cellulose, forming the basis for a stable and dense three-dimensional network. Small-molecule phosphate cannot construct this network; it can only provide gas-phase flame retardancy and cannot form a robust char barrier in the condensed phase, resulting in low flame retardant efficiency.

[0081] The effect of Comparative Example 5 was not as good as that of Example 1, further ruling out the possibility of other bio-based polyacids replacing phytic acid. Although tannic acid has a polyphenolic structure, it lacks the high-density phosphate groups unique to phytic acid. It cannot effectively catalyze the dehydration of carbohydrates to carbon, nor can it synergize with chitosan through phosphorus-nitrogen interactions. This again highlights the uniqueness of the chemical structure of phytic acid and its irreplaceable role in the system of this invention.

[0082] The superior flame-retardant properties of this invention (ultra-low THR and rapid self-extinguishing) are the inevitable result of a synergistic effect of "1+1+1>3" between the seaweed cellulose skeleton, the chitosan-phytic acid dynamic cross-linking network, and the kaolin physical barrier reinforcement. The absence of any key component or its replacement with a chemically incompatible substance will lead to the breakdown of this precise synergy, resulting in a sharp decline in material properties.

[0083] In summary, using Guizhou's unique seaweed as raw material, and through the ternary synergistic modification of chitosan-phytic acid-kaolin into a highly flame-retardant and fire-resistant biomass composite aerogel and its green preparation process, a multifunctional seaweed cellulose flame-retardant and heat-insulating aerogel material was prepared. This material possesses excellent flame-retardant and heat-insulating properties, lightweight characteristics, and environmental friendliness, meeting the application needs in fields such as building insulation, electronic fire protection, and flame-retardant layers for new energy batteries.

[0084] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a highly flame-retardant and fire-resistant biomass composite aerogel, characterized in that: include, Cellulose extracted from seaweed was added to deionized water to obtain a seaweed cellulose suspension; Kaolin was added to the seaweed cellulose suspension and mixed evenly to obtain a KL / CL solution; Phytic acid is dissolved in deionized water to obtain PA solution; Add chitosan to the PA solution and heat and stir in a water bath at 50℃~100℃ until the chitosan is completely dissolved to obtain a CS / PA solution. The CS / PA solution and KL / CL solution were mixed and mechanically stirred. After adding the crosslinking agent and stirring for another 1 minute, a mixed slurry was obtained. The mixed slurry is immediately poured into a mold and frozen with liquid nitrogen until a white frost appears on the sample surface, which is the wet gel. The wet gel is then freeze-dried to obtain a highly flame-retardant and fireproof biomass composite aerogel.

2. The preparation method of the high flame-retardant and fire-resistant biomass composite aerogel as described in claim 1, characterized in that: The mass concentration of cellulose in the KL / CL solution is 1.5~2.5wt%.

3. The preparation method of the high flame-retardant and fire-resistant biomass composite aerogel as described in claim 2, characterized in that: The mass concentration of kaolin in the KL / CL solution is 1~3wt%.

4. The preparation method of the high flame-retardant and fire-resistant biomass composite aerogel as described in claim 1, characterized in that: The phytic acid concentration in the CS / PA solution is 50~60wt%.

5. The preparation method of the high flame-retardant and fire-resistant biomass composite aerogel as described in claim 4, characterized in that: The mass concentration of chitosan in the CS / PA solution is 1.5~2.5wt%.

6. The preparation method of the high flame-retardant and fire-resistant biomass composite aerogel as described in claim 1, characterized in that: The crosslinking agent is glutaraldehyde.

7. The preparation method of the high flame-retardant and fire-resistant biomass composite aerogel as described in claim 6, characterized in that: The mass concentration of the crosslinking agent in the mixed slurry is 0.5~1.5wt%.

8. The preparation method of the high flame-retardant and fire-resistant biomass composite aerogel as described in claim 1, characterized in that: The mixing volume ratio of the CS / PA solution to the KL / CL solution is 4:

10.

9. The high flame-retardant and fire-resistant biomass composite aerogel as described in any one of claims 1 to 8, characterized in that: It has the following characteristics, (i) Using cellulose extracted from seaweed as a three-dimensional framework, chitosan as a dynamic network matrix, phytic acid as a flame retardant-crosslinking bifunctional component, kaolin as a physical barrier enhancer, and glutaraldehyde as a covalent crosslinking bridge, an aerogel structure was synergistically constructed. (ii) The high flame retardant and fireproof biomass composite aerogel is prepared by constructing a dynamic prepolymer with flame retardant potential through in-situ complexation of phytic acid and chitosan, and then by adding glutaraldehyde to achieve covalent cross-linking. (iii) The mass ratio of phytic acid to chitosan is 50~60:1.5~2.5, and the mass ratio of kaolin to cellulose is 1~3:1.5~2.

5.

10. The application of the high flame-retardant and fireproof biomass composite aerogel as described in claim 9 in the preparation of building insulation, electronic fireproofing and flame-retardant layers for new energy batteries.

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