Aluminum hydroxide flame-retardant modified pyridoxal phosphate cross-linked chitosan aerogel material and preparation method thereof

Abstract

The invention discloses an aluminum hydroxide flame-retardant modified pyridoxal phosphate cross-linked chitosan aerogel material and a preparation method thereof, and belongs to the technical field of biomass aerogel materials.The chitosan aerogel material is prepared from chitosan (CS), pyridoxal phosphate (P5P) and aluminum hydroxide (ATH). According to a feeding sequence of chitosan, aluminum hydroxide and pyridoxal phosphate, the chitosan aerogel material prepared by a method of heating and dissolving, standing and defoaming, in-situ curing and gelling, pre-freezing and vacuum freeze-drying is V-0 level according to a vertical combustion test, the limit oxygen index is greater than 80%, and the chitosan aerogel material has excellent mechanical property and flame retardant property and is suitable for industrial production. According to GB 8624-2012 Classification for Combustion Performance of Building Materials and Products, the modified chitosan aerogel can meet the requirements of A1 grade on a non-combustible furnace test.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass aerogel materials, and in particular relates to an aluminum hydroxide flame-retardant modified pyridoxal phosphate cross-linked chitosan aerogel material and a preparation method thereof. Background Art

[0002] Aerogel, a three-dimensional mesh material with a high specific surface area and high porosity, has the advantages of low density and low thermal conductivity. However, most aerogels are primarily composed of inorganic or petroleum-based organic matter, making their preparation process quite complex. The raw materials and the resulting aerogel are also non-degradable, requiring further processing to protect the environment and improve economic efficiency. Compared to inorganic aerogels, biomass aerogels are highly reusable, significantly reducing economic losses. Furthermore, the greatest advantage of biomass aerogels is their self-degradability without causing secondary environmental pollution.

[0003] At present, the preparation method of biomass chitosan aerogel is mainly the sol-gel method, which usually requires the use of certain chemical reagents as cross-linking agents. Among them, chitosan aerogel often uses aldehydes such as glutaraldehyde, formaldehyde and o-phthalaldehyde as cross-linking agents, which have certain toxicity. Pyridoxal phosphate is an activated form of vitamin B6. It plays an irreplaceable role in life activities. Because of its antiviral effect, it is used in medical treatment and is approved for human use as a food supplement. The chemical formula of pyridoxal phosphate is C8H 10 NO6P. The aldehyde group of pyridoxal phosphate can undergo a Schiff base reaction with the amino groups on chitosan. Its negatively charged phosphate groups also provide electrostatic interactions during the gelation process of chitosan aerogel. Aluminum hydroxide (ATH) is a widely used inorganic filler with excellent flame retardancy and smoke suppression capabilities. It is non-toxic and produces no secondary pollution. Aluminum hydroxide has excellent chemical stability and is not easily reacted with other substances or decomposed. This allows it to remain stable in the material for a long time, maintaining the durability of its flame retardant properties. Summary of the Invention

[0004] The present invention aims to provide a chemically cross-linked chitosan composite flame-retardant modified aerogel material and its preparation method. The present invention uses aluminum hydroxide as a flame retardant, uses pyridoxal phosphate to chemically cross-link chitosan, and introduces flame retardant elements to prepare the chitosan biomass aerogel material.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] In one aspect of the present invention, a flame-retardant aluminum hydroxide-modified pyridoxal phosphate cross-linked chitosan aerogel is proposed. According to an embodiment of the present invention, the raw materials for preparing the biomass chitosan aerogel include: chitosan (CS), pyridoxal phosphate (P5P), and aluminum hydroxide (ATH). The flame-retardant biomass chitosan aerogel material prepared can be represented by CS / P5P / ATH. Depending on the usage content, such as the CS concentration is maintained at 3% of the acetic acid solution, P5P is 1% of the acetic acid concentration, and ATH is 4% of the mass of the acetic acid solution, the composite aerogel prepared by this ratio can be abbreviated as CS3P1A4. The raw materials used for the biomass aerogel prepared by the present invention have the following technical characteristics:

[0007] The biomass matrix described in the present invention utilizes chitosan, which is prepared by deacetylation or enzymatic degradation of chitin in an alkaline environment. Chitosan is a biopolymer found in the exoskeletons of crustaceans and insects, as well as fungi. Therefore, chitosan is the second most abundant biomass-derived polysaccharide on Earth. It is low-cost and sustainable, with good biocompatibility, biodegradability, and a high degree of polymerization. As a biomass-based polymer, chitosan possesses numerous hydroxyl groups and highly reactive amino groups on its backbone, which serve as active sites for chemical modification and cross-linking with aldehydes, making it the matrix material for aerogels.

[0008] The cross-linking agent introduced above can react the aldehyde group of pyridoxal phosphate with the amino group on chitosan to form a Schiff base reaction. At the same time, its negatively charged phosphate group provides electrostatic interaction with the biomass aerogel precursor chitosan during the gelation process. The chemical formula of pyridoxal phosphate is C8H 10 NO6P, its structural formula is as follows:

[0009]

[0010] The solid flame retardant aluminum hydroxide is a widely used inorganic filler with good flame retardancy and smoke suppression capabilities.

[0011] In addition, the present invention provides a method for preparing aluminum hydroxide flame-retardant modified pyridoxal phosphate cross-linked chitosan aerogel. According to an embodiment of the present invention, the method comprises:

[0012] (1) First, 4.5 g of chitosan (CS) and 0.75 g of pyridoxal phosphate were added to 100 mL and 50 mL of acetic acid solution (1 wt% HAc), respectively, and heated at 150 r / min and 85 °C for 1 h to dissolve until a uniform transparent sol liquid was obtained;

[0013] (2) Add 3 g of ATH to the dissolved chitosan solution at a speed of 150 r / min and stir for 20 min to fully mix;

[0014] (3) adding the completely dissolved pyridoxal phosphate solution to the chitosan solution and continuing stirring at the same speed as in (2) for 1 h until the mixture is evenly dispersed to form a sol-liquid mixture;

[0015] (4) Pour the sol liquid mixture into a standard mold, let it stand for degassing for 1 hour, cool to room temperature, place it in a liquid nitrogen freezer for 0.5 hours, and freeze it in a vacuum freeze dryer for 24 hours;

[0016] (5) The mold containing the completely frozen gel sample was placed in a vacuum freeze-drying environment (10 Pa, -45°C) and freeze-dried for 144 h to obtain CS / P5P / ATH aerogel.

[0017] In the method for preparing the aluminum hydroxide flame-retardant modified pyridoxal phosphate cross-linked chitosan aerogel according to the embodiment of the present invention, the influence of the mechanical stirring speed during the dissolution process is considered, and the stirring speed is preferably 50 to 300 r / min to reduce the introduction of bubbles during the mechanical stirring process. Considering the influence of the stirring temperature during the dissolution process, the stirring temperature is preferably 50 to 90°C. If the temperature is too low, the dissolution rate is slow and the sol viscosity is high; if the temperature is too high, the evaporation loss of water increases, and the high sol ratio causes insufficient dissolution.

[0018] The static degassing process used in the present invention can use a vibration table to accelerate physical degassing, or a vacuum static degassing method can be used. The degassing time is not less than 0.5 hours and not more than 3 hours. If the time is too short, the degassing effect is insufficient. If the time is too long, the viscosity of the gel increases after the temperature is lowered, and the cross-linking reaction of pyridoxal phosphate further increases the viscosity of the gel until it loses fluidity, making it impossible to perform static physical degassing.

[0019] According to the preparation method of the embodiment of the present invention, the order of adding chitosan, aluminum hydroxide and pyridoxal phosphate is followed, and the process of heating for dissolution - standing for degassing - in-situ solidification of gel - pre-freezing - vacuum freeze drying is carried out to ensure that a qualified biomass chitosan composite aerogel sample is prepared.

[0020] In summary, the biomass chitosan composite aerogel prepared by the preparation method of the aluminum hydroxide flame retardant modified pyridoxal phosphate cross-linked chitosan aerogel in the present invention passes the vertical combustion test V-0 level, has a limiting oxygen index of 83%, has excellent mechanical properties and flame retardant properties, and according to the non-combustible furnace test of the "GB 8624 Building Exterior Wall Insulation Materials" CS3P1A16 aerogel can meet the A1 level.

[0021] In some embodiments of the present invention, in step (1), the stirring speed is 50-300 r / min, and the stirring speed should not be too high to reduce excessive bubbles introduced during the stirring process.

[0022] In some embodiments of the present invention, in step (1), the stirring temperature is 50-90°C. If the temperature is too low, the dissolution rate is slow and the sol viscosity is high; if the temperature is too high, the evaporation loss of water increases and the high sol ratio causes insufficient dissolution.

[0023] In some embodiments of the present invention, in step (2), the solid flame retardant ATH is added slowly at a rate of 1 g / min to avoid agglomeration caused by all-at-once addition.

[0024] In some embodiments of the present invention, the static degassing process in step (3) can be accelerated by a vibration table or a vacuum static degassing method, and the degassing time is not less than 0.5 hours and not more than 3 hours. If the time is too short, the degassing effect is insufficient. If the time is too long, the viscosity of the gel increases after the temperature is lowered, and the cross-linking reaction of pyridoxal phosphate further increases the viscosity of the gel until it loses fluidity, making it impossible to perform static physical degassing.

[0025] In some embodiments of the present invention, in step (4), the pre-freezing medium is liquid nitrogen, and the pre-freezing time is 15 to 45 minutes, preferably 20 to 30 minutes, so that the sample can be completely frozen.

[0026] In some embodiments of the present invention, in step (5), the vacuum degree of the vacuum degassing is not higher than 40 Pa, and the vacuum drying time is not less than 72 hours.

[0027] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0029] Figure 1 are infrared spectra of (a) CS, P5P, ATH, CS3A4, CS3P1, and CS3P1A4, and (b) infrared spectra of CS3P1, CS3P1A2, CS3P1A4, CS3P1A6, CS3P1A12, and CS3P16 aerogels according to embodiments of the present invention;

[0030] Figure 2 (a) Axial photograph, (b) axial SEM image, and (c) EDS element distribution map of CS3P1, CS3P1A2, CS3P1A4, CS3P1A6, CS3P1A12, and CS3P16 aerogels;

[0031] Figure 3(a) radial photographs, (b) radial SEM images, and (c) EDS element distribution maps of CS3P1, CS3P1A2, CS3P1A4, CS3P1A6, CS3P1A12, and CS3P16 aerogels;

[0032] Figure 4 are the (a) density, (b) volume shrinkage, (c) porosity, and (d) thermal conductivity of CS3P1, CS3P1A2, CS3P1A4, CS3P1A6, CS3P1A12, and CS3P16 aerogels;

[0033] Figure 5 (a) Stress-strain curves, (b) compression modulus and specific modulus of CS3P1, CS3P1A2, CS3P1A4, CS3P1A6, CS3P1A12, and CS3P16 aerogels;

[0034] Figure 6 are the LOI values and UL-94 ratings of CS aerogels and CS composite aerogels;

[0035] Figure 7 (a) Digital photos, (b) SEM photos, and (c) EDS elemental composition maps of CS3P1, CS3A4, CS3P1A2, CS3P1A4, CS3P1A6, CS3P1A12, and CS3P1A16 aerogels after cone calorimetry testing. DETAILED DESCRIPTION

[0036] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0037] The invention discloses an aluminum hydroxide flame-retardant modified pyridoxal phosphate cross-linked chitosan aerogel. The raw materials for preparing the biomass chitosan aerogel include chitosan (CS), pyridoxal phosphate (P5P) and aluminum hydroxide (ATH).

[0038] The inventors found that the biomass chitosan composite aerogel prepared by the preparation method of the aluminum hydroxide flame-retardant modified pyridoxal phosphate cross-linked chitosan aerogel in this application passed the vertical combustion test V-0 level, with a limiting oxygen index of 83%, and has excellent mechanical properties and flame retardant properties. According to the non-combustible furnace test of the "Building Exterior Wall Thermal Insulation Materials Specified in GB 8624", the CS3P1A16 aerogel can meet the A1 level.

[0039] The following embodiments of the present invention are described in detail. It should be noted that the following embodiments are illustrative and are intended only to explain the present invention and are not to be construed as limiting the present invention. In addition, unless otherwise expressly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0040] The raw materials and auxiliary agents used in the examples of the present invention are shown in the following table.

[0041] Table 1 Raw materials used in the present invention

[0042]

[0043] Comparative Example 1

[0044] The biomass chitosan composite aerogel was prepared according to the formula shown in Table 2. The specific preparation steps of Comparative Example 1 are as follows:

[0045] (1) First, 4.5 g of chitosan (CS) and 1.5 g of pyridoxal phosphate were added to 100 mL and 50 mL of acetic acid solution (1 wt% HAc), respectively, and heated at 150 r / min and 85 °C for 1 h to dissolve until a uniform transparent sol liquid was obtained;

[0046] (2) adding the completely dissolved pyridoxal phosphate solution to the chitosan solution, and continuing to stir at the same stirring speed as step (1) for 1 h until the mixture is evenly dispersed to form a sol-liquid mixture;

[0047] (3) Pour the sol liquid mixture into a standard mold, let it stand for degassing for 1 hour, cool to room temperature, place it in a liquid nitrogen freezer for 0.5 hours, and freeze it in a vacuum freeze dryer for 24 hours;

[0048] (4) The mold containing the completely frozen gel sample was placed in a vacuum freeze-drying environment (10 Pa, -45°C) and freeze-dried for 144 h to obtain CS / P5P / ATH aerogel.

[0049] Comparative Example 2

[0050] The biomass chitosan composite aerogel was prepared according to the formula shown in Table 2. The specific preparation steps of Comparative Example 2 are as follows:

[0051] (1) First, 4.5 g of chitosan (CS) was added to 150 mL of acetic acid solution (1 wt% HAc) and heated at 150 r / min and 85 °C for 1 h until a uniform and transparent sol liquid was obtained;

[0052] (2) Add 6 g of ATH to the dissolved chitosan solution at a speed of 150 r / min and stir for 20 min to obtain a sol mixture;

[0053] (3) Pour the sol liquid mixture into a standard mold, let it stand for degassing for 0.5 h, cool to room temperature, place it in a liquid nitrogen freezer for pre-freezing for 0.5 h, and freeze it in a vacuum freeze dryer for 24 h;

[0054] (4) The mold containing the completely frozen gel sample was placed in a vacuum freeze-drying environment (10 Pa, -45°C) and freeze-dried for 120 h to obtain CS / P5P / ATH aerogel.

[0055] Examples 1 to 5

[0056] The biomass chitosan composite aerogel was prepared according to the formula shown in Table 2. The specific preparation steps of Examples 1 to 5 are as follows:

[0057] (1) First, 4.5 g of chitosan (CS) and 1.5 g of pyridoxal phosphate were added to 100 mL and 50 mL of acetic acid solution (1 wt% HAc), respectively, and heated at 150 r / min and 85 °C for 1 h to dissolve until a uniform transparent sol liquid was obtained;

[0058] (2) Add 3 g of ATH to the dissolved chitosan solution at a speed of 150 r / min and stir for 20 min to fully mix;

[0059] (3) adding the completely dissolved pyridoxal phosphate solution to the chitosan solution, and continuing to stir at the same stirring speed as in step (2) for 1 h until the mixture is evenly dispersed to form a sol-liquid mixture;

[0060] (4) Pour the sol liquid mixture into a standard mold, let it stand for degassing for 1 hour, cool to room temperature, place it in a liquid nitrogen freezer for 0.5 hours, and freeze it in a vacuum freeze dryer for 24 hours;

[0061] (5) The mold containing the completely frozen gel sample was placed in a vacuum freeze-drying environment (10 Pa, -45°C) and freeze-dried for 144 h to obtain CS / P5P / ATH aerogel.

[0062] Table 2 Formula for preparing biomass chitosan composite aerogel samples of the present invention

[0063]

[0064] The beneficial effects of the present invention are demonstrated below through specific test examples. The performance test and characterization of the aluminum hydroxide flame retardant modified pyridoxal phosphate cross-linked chitosan aerogel of the present invention are as follows:

[0065] (1) Morphological and structural analysis

[0066] Fourier transform infrared (FTIR) spectroscopy of the aerogels was characterized using a Nicolet iS50 spectrometer (Thermo Fisher Scientific, Ltd., China) in attenuated total reflectance (ATR) mode. Spectra were recorded from 400 to 4000 cm -1 within the wavenumber range.

[0067] The sample surface was sprayed with gold powder, and the morphology and structure of the aerogel were observed using a Quattro S environmental scanning electron microscope (Thermo Fisher Scientific (China) Co., Ltd.) at an accelerating voltage of 20 kV. The sample micro-region composition, element types and contents were analyzed by surface scanning using an energy dispersive spectrometer (EDS).

[0068] (2) Basic physical properties test

[0069] The mass and size of the aerogel were measured using an electronic balance and a vernier caliper, and the density of the aerogel was obtained by calculation.

[0070] The ethanol displacement method was used to measure the mass of the test block, which was recorded as m0, and the total weight of ethanol and the test block was recorded as m1. The test block was immersed in anhydrous ethanol and placed in a vacuum dryer until no bubbles were generated. After taking out the test block, the mass of ethanol was measured and recorded as m2. The porosity of the aerogel was obtained by calculation.

[0071] Porosity (%) = (m1-m2-m0) / (m1-m2)×100%

[0072] The shrinkage of the aerogel was calculated using the ratio of the volume V0 of the gel before freeze-drying to the volume V1 of the aerogel after drying.

[0073] Volume shrinkage (%) = (V0-V1) / V0×100%

[0074] The thermal conductivity of the aerogel samples was obtained by using the transient plane source method at ambient temperature using sfmitDRE-2C (Xiangtan Instrument Co., Ltd., China) and taking the average value at different points on the sample surface.

[0075] (3) Mechanical properties

[0076] Compression tests were conducted on 30 mm x 30 mm x 15 mm specimens using an electronic universal testing machine (CMT5105, SASCK Co., Ltd., China) according to ISO 12817-2013. A preload of 5 N was applied to the specimens, compressing them to 80% of their thickness. The force was applied parallel to the radial direction. The compression modulus was calculated from the slope of the initial linear region of the stress-strain curve. Each specimen was repeated three times.

[0077] (4) Flame retardant properties

[0078] According to GB / T 2406.2-2009, the limiting oxygen index (LOI) value was tested using an HC-2C oxygen index meter (Jiangning Analytical Instrument Co., Ltd., China), and the size of all samples was 100 mm × 10 mm × 10 mm.

[0079] The vertical burning test (UL-94) was carried out according to GB / T 8333-2008 using a CZF-3 horizontal vertical burning tester (Jiangning Analytical Instrument Co., Ltd., China). The size of all samples was 100 mm × 10 mm × 10 mm.

[0080] Combustion behavior was determined according to ISO 5660 using a Vouch 6810 cone calorimeter at 50 kW / m 2 The measurements were performed under a radiation power of 1000 nm. The dimensions of all samples were 100 mm × 100 mm × 15 mm.

[0081] (5) Combustion performance of building materials and products

[0082] According to GB / T 5464, the test method for the non-combustibility of building materials, the samples were tested in a building material non-combustibility test furnace. The pre-treatment temperature was 23±2℃ and the humidity was 50±5%. The samples were treated for no less than 48 hours until the weight was constant. The sample was cylindrical and the volume was (76±8) cm. 3 , diameter (45±2)mm, height (50±3)mm.

[0083] The performance test results of the aluminum hydroxide flame retardant modified pyridoxal phosphate cross-linked chitosan aerogel of the present invention are as follows:

[0084] like Figure 1 As shown, infrared spectrum Figure 1 (a) For ATH, at 3615 cm -1 、3519cm -1 、3423cm -1 A clear absorption peak can be observed at 1017cm, which is caused by the stretching vibration of the OH bond in the aluminum hydroxide molecule, reflecting the formation of hydrogen bonds and the existence of intermolecular interactions. -1 The characteristic peaks near the 630-780 cm-1 are attributed to the stretching vibration of the Al-O bond. This vibration corresponds to the vibration mode of the bond between aluminum and oxygen and is one of the important indicators for determining the presence of aluminum hydroxide. -1 Several strong absorption peaks can be observed in the range of , which are also attributed to the stretching vibration of Al-O bonds. Figure 1 (b) It can be found that with the increase of ATH addition, the 3400 cm -1 、1017cm-1 and 630-780cm -1 The corresponding absorption peak intensity gradually increases, indicating that the number of Al-O bonds in the aerogel sample increases, resulting in an increase in the absorption intensity corresponding to this vibration mode. -1 and 1629cm -1 The corresponding NH and C=N bond absorption peaks weakened, mainly because the mass ratio and concentration of CS / P5P in the aerogel decreased with the increase of ATH. These results indicate that the main force in the aerogel comes from the hydrogen bonds between aluminum hydroxide and chitosan.

[0085] like Figure 2 and Figure 3 As shown, by observing the actual picture of aerogel, refer to Figure 2 (a) and Figure 3 (a), it can be found that with the increase in the amount of ATH added, the color of the aerogel gradually changes from dark yellow to light yellow. This is because aluminum hydroxide itself is a white or nearly white substance, and it has a pigment effect when added to aerogel. With the increase in the amount of aluminum hydroxide added, its white or nearly white properties may cover or mix the original dark yellow of the aerogel, making the overall color lighter, and the addition of aluminum hydroxide particles will change the optical properties of the aerogel. In addition, aluminum hydroxide particles may increase the aerogel's absorption and scattering of light, thereby changing its color. With the increase in the amount of aluminum hydroxide added, the aerogel may absorb and scatter more light, causing its color to become lighter. From Figure 2 (b) and Figure 3 In (b), it can be observed that ATH is attached to the surface of the aerogel's pore structure. As the amount of ATH added increases, the pore size of the aerogel gradually becomes smaller. By observing CS3P1A12 and CS3P1A16, it can be found that when too much ATH is added, the aerogel pore structure is spindle-shaped, similar to the structure of pure chitosan aerogel. This indicates that the Schiff base reaction is inhibited. The reason may be that ATH is wrapped around the CS surface, forming a barrier, making it difficult for the NH2 on the chitosan to fully react with the aldehyde group on the P5P. Figure 2 In (c), the element distribution of the aerogel can be observed. As the ATH content increases, the nitrogen and phosphorus elements in the aerogel are approximately 0 wt%. By observing the radial microstructure of the aerogel, Figure 3 (b) It can be found that the addition of ATH reduces the pore size of the aerogel and affects the formation of a regular step-like shape of the aerogel. This further illustrates that excessive addition of ATH will disrupt the reaction between CS and P5P.

[0086] like Figure 4 As shown in Figure 2, the density, volume shrinkage, porosity and thermal conductivity of CS / P5P / ATH aerogel. Figure 4As can be seen in (a), the density of aerogel increases significantly with the increase of ATH addition, and the density of CS3P1A16 is as high as 0.2596g / cm3. Figure 4 (b) It can be found that with the increase of ATH addition, the volume shrinkage of aerogel decreases significantly. The volume shrinkage of CS3P1A16 is 2.85%, which is 71.6% lower than that of CS3P1. This shows that the addition of ATH is beneficial to maintain the dimensional stability of the aerogel structure. Figure 4 (c) It can be clearly seen that with the increase of ATH addition, the porosity of the aerogel decreases significantly. Combined with the SEM results, this is mainly due to the fact that ATH particles adhere to the surface of the aerogel and occupy the space in the pores, resulting in a decrease in porosity. Figure 4 (d) shows that the thermal conductivity of the aerogel gradually increases with increasing ATH addition, with CS3P1A16 aerogel having the highest thermal conductivity, reaching 0.1038 W / (m·K). The addition of inorganic fillers increases thermal conductivity, consistent with previous research. The thermal conductivity of air is relatively low, ranging from 0.025 to 0.0267 W / (m·K). Generally speaking, the higher the porosity, the lower the thermal conductivity of the aerogel. However, since ATH occupies a portion of the aerogel's pores, the reduction in porosity leads to a significant increase in the aerogel's thermal conductivity. Furthermore, thermal conductivity is closely related to the solid-phase heat transfer of the aerogel. The thermal conductivity of ATH is approximately 10-30 W / (m·K). The high thermal conductivity of ATH enhances solid-phase conduction, leading to an increase in the thermal conductivity of the CS / P5P / ATH aerogel.

[0087] like Figure 5 As shown, the stress-strain curve of the composite aerogel initially rises very slowly, then rises sharply, exhibiting ideal compressive strength. This behavior is consistent with traditional porous foam materials. In such materials, when the applied stress causes large strain, the aerogel's cellular structure collapses and forms a tightly contracted network skeleton. Figure 5 (b) Comparison of the compression moduli of CS3P1A2, CS3P1A2, CS3P1A4, CS3P1A4, CS3P1A12, and CS3P1A16 aerogels: 6.485 MPa, 3.424 MPa, 6.876 MPa, 4.210 MPa, and 10.291 MPa, respectively. CS3P1A16 has the highest compression modulus, a 146.9% increase compared to CS3P1's 4.168 MPa, demonstrating the best mechanical properties. However, because CS3P1A16 has a density approximately four times that of CS3P1, its specific modulus decreases by 48.7%.

[0088] like Figure 6As shown in Figure 2, the combustion behavior of the aerogels was first evaluated by the limiting oxygen index (LOI) and vertical burning test (UL-94). Comparative examples include pure CS aerogel (CS3), aerogel with only P5P added (CS3P1), aerogel with only ATH added (CS3A4), and CS / P5P / ATH composite aerogels with different ATH addition amounts. Figure 6 This shows that all aerogels can achieve the UL-94 V-0 rating. By comparison, it can be found that ATH and P5P can further enhance the flame retardant effect of chitosan aerogels. The LOI value of CS3A4 is 67.3%, which is lower than the 78.3% of CS3P1. This is equivalent to the LOI value of adding 4 parts of ATH being lower than that of adding 1 part of P5P, which shows that the flame retardant effect of P5P is significantly better than that of ATH. When both ATH and P5P are added together to prepare the CS3P1A4 aerogel, the LOI value is 85.0%, indicating that the two have a synergistic flame retardant effect. Interestingly, when a small amount of ATH is added, the LOI value of CS3P1A2 is lower than that of CS3P1.

[0089] like Figure 7 As shown in the figure, in order to better explore the flame retardant mechanism of aerogel condensed phase, SEM test was carried out on the carbon residue of aerogel. Figure 7 (a) The carbon residue of the CS / P5P / ATH aerogel is significantly different from that of the pure CS / P5P aerogel, with the color gradually transitioning from dark black to off-white. This is mainly because after the CS / P5P / ATH aerogel is burned, the ATH in the aerogel thermally decomposes into Al2O3, a white solid. Figure 7 (b) shows that as the amount of ATH increases, the particles on the surface of the carbon residue become more dense. Figure 7 It was observed in (c) that the carbon residue contained relatively few C, N and P elements, while Al and O elements accounted for a large proportion. It can be considered that a large amount of Al2O3 was generated and covered on the surface of the aerogel.

[0090] According to GB / T 5464-2010, Test Method for Non-combustibility of Building Materials, samples CS3P1A12 and CS3P1A16 were tested using a building material non-combustibility test furnace, and the data were obtained, as shown in Table 3.

[0091] Table 3 Data of the building material non-combustibility test furnace

[0092]

[0093] According to the GB 8624-2012 "Classification of Fire Performance of Building Materials and Products," CS3P1A16 aerogel meets the three key criteria specified in GB / T 5464 "Test Methods for Non-combustibility of Building Materials": 1) Temperature rise ≤ 30°C; 2) Mass loss ≤ 50%, and sustained combustion ≤ 20 seconds. This meets the criteria for Class A1 thermal insulation materials under this standard. To qualify as Class A1, aerogel must also meet the requirements of GB / T 14402 "Fire Performance of Building Materials and Products - Determination of Calorific Value." Therefore, at this time, we can only make a qualitative assessment, but there is a high probability that it will meet Class A1.

[0094] In summary, the biomass chitosan composite aerogel prepared by the preparation method of the aluminum hydroxide flame retardant modified pyridoxal phosphate cross-linked chitosan aerogel in the present invention passes the vertical combustion test V-0 level, has a limiting oxygen index of 83%, has excellent mechanical properties and flame retardant properties, and according to the non-combustible furnace test CS3P1A16 aerogel in GB 8624-2012 "Classification of Combustion Performance of Building Materials and Products" can meet the A1 level.

[0095] In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. In the absence of mutual contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples. Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and are not to be construed as limiting the present invention. Those skilled in the art may change, modify, replace, and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing aluminum hydroxide flame retardant modified pyridoxal phosphate cross-linked chitosan aerogel, characterized in that: include: (1) adding chitosan and pyridoxal phosphate into acetic acid solution respectively, and heating and dissolving them at a certain speed and temperature until a uniform transparent sol liquid is formed; (2) Adding solid flame retardant ATH to the dissolved chitosan solution and stirring at a certain speed until it is evenly dispersed; (3) adding the completely dissolved pyridoxal phosphate solution to the chitosan solution of step (2), and continuing to stir at the stirring speed of step (2) until the mixture is uniformly dispersed to form a sol-liquid mixture; (4) Pour the sol liquid mixture into a standard mold, let it stand for a period of time to degas, cool it to room temperature, place it in a liquid nitrogen freezer for pre-freezing, and freeze it completely in a vacuum freeze dryer; (5) The mold containing the completely frozen gel sample is placed in a vacuum freeze-drying environment for freeze-drying to obtain an aerogel.

2. The preparation method according to claim 1, characterized in that In step (1): the stirring speed is 50-300 r / min, and the stirring temperature is 50-90°C.

3. The preparation method according to claim 1, characterized in that In step (2): solid flame retardant ATH is added slowly at a rate of 1 g / min to avoid agglomeration caused by adding it all at once.

4. The preparation method according to claim 1, characterized in that In step (3): the static degassing process adopts a vibration table to accelerate physical degassing, or a vacuum static degassing method, and the degassing time is not less than 0.5h and not more than 3h.

5. The preparation method according to claim 1, characterized in that In step (4): the pre-freezing medium is liquid nitrogen, and the time is 15 to 45 minutes, preferably 20 to 30 minutes.

6. The preparation method according to claim 1, characterized in that In step (5): the vacuum degree of the vacuum degassing is not higher than 40 Pa, and the vacuum drying time is not less than 72 hours.

7. An aerogel, characterized in that The method is prepared according to any one of claims 1 to 6.

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