Lignin-hydroxyapatite / biomass-based composite aerogel and preparation and application thereof

Abstract

The application discloses lignin-hydroxyapatite / biomass-based composite aerogel and preparation and application thereof. In the application, hydroxyapatite is dispersed in a weak alkali solution, then sodium lignosulfonate and sodium alginate are added, and after uniform stirring, a gluconolactone solution is added dropwise, a hydrogel is formed after being poured into a mold, and the hydrogel is frozen by liquid nitrogen or a refrigerator, and then the composite aerogel is obtained by freeze-drying. In the application, sodium alginate is used as a base material, and lignin is introduced as a carbonization agent and a structure reinforcing agent, and the organic / inorganic composite aerogel is prepared by using the combination of the slow release of hydroxyapatite and the use of gluconolactone, so that the heat preservation performance, mechanical performance and smoke suppression performance of the composite aerogel can be significantly improved. The prepared aerogel is subjected to hydrophobic modification, so that the application field of the aerogel is greatly widened. The prepared aerogel has the characteristics of low thermal conductivity, high porosity, high strength and high flame retardancy, and simultaneously opens up a new way for resource utilization of lignin.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant and heat-insulating material preparation, specifically relating to a lignin-hydroxyapatite / biomass-based composite aerogel and its preparation and application. Background Technology

[0002] With the continuous advancement of science and technology and rapid social development, industrialization is accelerating, and population density is rising rapidly, leading to a continuous increase in energy consumption. Against this backdrop, resource conservation and addressing energy shortages have become crucial measures for achieving sustainable development. Thermal insulation materials effectively reduce heat loss and improve energy utilization efficiency, and are widely used in building wall insulation, cold chain transportation, underground pipelines, and new energy vehicles. However, most thermal insulation materials are petroleum-based, non-renewable, and their combustion produces large amounts of toxic and harmful gases, severely polluting the environment and threatening human health and safety. Aerogels, due to their excellent performance and promising applications, have gradually gained public attention and become a hot research topic in the field of thermal insulation in recent years. Biomass aerogels, in particular, have attracted increasing interest from researchers due to their wide availability of raw materials, non-toxicity, environmental friendliness, renewability, and low cost. However, their flammability limits their application in flame retardant and insulation fields; therefore, research on flame retardant properties of biomass aerogels is of great significance.

[0003] Alginic acid is a byproduct of extracting iodine and mannitol from brown algae such as kelp or Sargassum. It is an important component of seaweed and other algae, mainly found in the cell wall, where it plays a supporting and reinforcing role. Alginic acid chains have numerous hydroxyl groups, and due to the strong hydrogen bonds between chains, it exhibits poor water solubility, making it unsuitable for use. Therefore, alginic acid is generally neutralized into salts, most commonly its sodium salt. Alginates are composed of β-D-mannuronic acid (M block) and α-L-guluronic acid (G block) randomly arranged through 1,4-glycosidic bonds. The G segment has a certain rigidity and can stably bind to divalent metal ions, while the M segment has a certain flexibility and hardly participates in ionic cross-linking. The gelling ability and molecular properties of alginate can be expressed by the M / G ratio. Currently, commercially available alginates are only derived from algae. Brown algae and other algae resources in rivers and oceans are abundant, and alginate substances exist in large quantities in nature. Therefore, sodium alginate (SA) is a cheap and readily available raw material.

[0004] Lignin is the most abundant aromatic polymer in nature, with wide-ranging sources and huge production volumes. Every year, a large amount of lignin byproducts are generated from pulp and paper manufacturing and the bioethanol industry. The vast majority of these lignin byproducts are simply incinerated or discharged into rivers and oceans, resulting in extremely low lignin utilization, environmental pollution, and resource waste. Lignin's chemical structure contains abundant carbon atoms, which can be used as fillers in some materials, significantly improving their mechanical properties. Furthermore, it provides a carbon source during combustion, forming a protective carbon layer. As an aromatic polymer, lignin's rigid structure can also enhance the mechanical properties of aerogels. In conclusion, lignin has great application potential in the field of biomass aerogels.

[0005] Currently, there are still some problems with using biomass-based aerogels as thermal insulation materials: mechanical properties and flame retardant properties cannot be simultaneously achieved, toxic and harmful flame retardants are used, and they are prone to moisture absorption and softening. Therefore, it is necessary to design an aerogel with wide application scenarios, simple process, low cost, and excellent flame retardant and thermal insulation properties. Summary of the Invention

[0006] To address the common problems of flammability, insufficient mechanical properties, and moisture absorption and softening in biomass-based aerogels, and to improve the various properties of aerogels and broaden their application scenarios, the primary objective of this invention is to provide a method for preparing lignin-hydroxyapatite / biomass-based composite aerogels.

[0007] This invention utilizes an in-situ release method, employing a composite system of hydroxyapatite (HAP) and glucono-delta-lactone (GDL). Sodium alginate serves as the gel matrix, lignin as a structural reinforcing agent and macromolecular char-forming agent, and hydroxyapatite as a crosslinking agent and flame retardant, releasing calcium and phosphorus sources. A flame-retardant biomass composite aerogel is obtained through simple freeze-drying. The aerogel is then hydrophobically modified to form a superhydrophobic aerogel. Both sodium alginate and lignin are abundant and widely available biomass resources, and the preparation method is simple and easy for large-scale production. Compared to traditional in-situ release methods, the hydroxyapatite (HAP) and glucono-delta-lactone (GDL) composite system does not generate gas or create small pores within the gel, thus improving the overall performance of the aerogel and showing promising application prospects in thermal insulation and heat preservation.

[0008] Another objective of this application is to provide a lignin-hydroxyapatite / biomass-based composite aerogel prepared by the above method.

[0009] Another object of the present invention is to provide the application of the above-mentioned lignin-hydroxyapatite / biomass-based composite aerogel.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for preparing a lignin-hydroxyapatite / biomass-based composite aerogel includes the following steps:

[0012] (1) Mix hydroxyapatite, lignin, sodium alginate and alkaline solution evenly to obtain a composite solution;

[0013] (2) Add the calcium ion regulator solution dropwise to the composite solution in step (1), mix evenly, let stand to gel, freeze dry, and obtain sodium alginate / lignin / hydroxyapatite composite aerogel.

[0014] (3) Hydrophobic modification of sodium alginate / lignin / hydroxyapatite composite aerogel was carried out by chemical vapor deposition to obtain hydrophobic lignin-hydroxyapatite / biomass-based composite aerogel.

[0015] Preferably, the alkaline solution in step (1) is at least one of sodium hydroxide solution and potassium hydroxide solution; the concentration of the alkaline solution is 0.03 to 0.06 mol / L; more preferably 0.05 mol / L.

[0016] Preferably, the ratio of hydroxyapatite to alkaline solution in step (1) is 0.3-0.9 g: 80 mL; more preferably, it is 0.9 g: 80 mL.

[0017] Preferably, the composite solution in step (1) is obtained by the following method: adding hydroxyapatite to an alkaline solution, mixing evenly, adding lignin and sodium alginate, and mixing evenly again to obtain the composite solution.

[0018] More preferably, after the hydroxyapatite is added to the alkaline solution, it is mixed evenly using a homogenizer at 40–60°C.

[0019] More preferably, after adding lignin and sodium alginate, the mixture is stirred at 40-60°C for 1-2 hours to ensure uniform mixing.

[0020] Preferably, the lignin in step (1) is at least one of alkali lignin, enzymatically hydrolyzed lignin, lignin sulfonate and solvent lignin; more preferably, it is lignin sulfonate, and most preferably sodium lignin sulfonate.

[0021] Preferably, the mass ratio of sodium alginate to lignin in step (1) is 1:0.5 to 1, more preferably 1:1; the mass ratio of hydroxyapatite to sodium alginate is 0 to 0.3:1, wherein the mass ratio of hydroxyapatite is not 0; even more preferably, the mass ratio of hydroxyapatite to sodium alginate is 0.1 to 0.3:1; most preferably 0.3:1.

[0022] Preferably, the concentration of the calcium ion regulator solution in step (2) is (0.02-0.06) g / mL; more preferably, it is 0.04 g / mL.

[0023] Preferably, the mass ratio of calcium ion regulator to hydroxyapatite in step (2) is 8:(2-9), more preferably 8:9 or 8:2.25.

[0024] Preferably, the calcium ion regulator in step (2) is at least one of gluconolactone, gluconic acid and lactic acid; more preferably, it is gluconolactone.

[0025] Preferably, the time for mixing evenly in step (2) is 3 to 10 minutes, more preferably 5 minutes.

[0026] Preferably, the static gel in step (2) is formed in a mold.

[0027] Preferably, the settling time of the gel in step (2) is 3 to 6 hours.

[0028] Preferably, before freeze-drying in step (2), the gel is refrigerated at -20 to -30°C for more than 12 hours or frozen with liquid nitrogen to ensure that the gel is completely frozen.

[0029] Preferably, the freeze-drying temperature in step (2) is -50°C to room temperature, and the time is 12 to 48 hours, more preferably 48 hours.

[0030] Preferably, the modifier used for hydrophobic modification in step (3) is at least one of methyltrichlorosilane and methyltrimethoxysilane; more preferably, it is methyltrichlorosilane.

[0031] Preferably, the ratio of the modifier used in the hydrophobic modification in step (3) to the sodium alginate / lignin / hydroxyapatite composite aerogel is 1 mL: 2-3 g.

[0032] Preferably, the hydrophobic modification time in step (3) is 6 to 24 hours; more preferably, it is 12 hours.

[0033] A lignin-hydroxyapatite / biomass-based composite aerogel was prepared by the above method.

[0034] The above-mentioned lignin-hydroxyapatite / biomass-based composite aerogel is used in the field of flame retardant and heat insulation.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] 1. This invention is based on an in-situ release method, which yields large quantities of inexpensive raw materials and has a simple preparation process. Gluconolactone is added to a uniformly mixed system of hydroxyapatite and sodium alginate, stimulating the insoluble hydroxyapatite to release calcium ions. Because the hydroxyapatite is uniformly dispersed in the mixed system during preparation, each sodium alginate chain can bind an equal amount of calcium ions. Furthermore, compared to traditional in-situ release methods, this method does not generate gas and avoids creating pores in the hydrogel that could disrupt the overall structure, thus providing better thermal insulation.

[0037] 2. The aerogel obtained by this invention possesses excellent mechanical properties, thermal insulation properties, and lightweight properties, while also exhibiting excellent smoke suppression performance. As a flame-retardant and heat-insulating material, it demonstrates superior overall performance. The phosphate group in hydroxyapatite acts as a phosphorus-based flame retardant, effectively enhancing the flame-retardant effect of the aerogel.

[0038] 3. In this invention, lignin has a large number of rigid phenylpropane units and a high carbon content. Introducing it into aerogel can effectively improve the mechanical properties of the aerogel, greatly help the formation of the carbon layer, and will not affect the overall lightweight and smoke suppression properties of the aerogel. At the same time, it opens up new ways for the resource utilization of lignin and realizes the transformation of waste into treasure.

[0039] 4. The hydrophobically modified aerogel of this invention will not absorb moisture and deliquesce due to excessive air humidity, thus broadening the application scenarios of aerogel; the constructed flame-retardant aerogel will provide valuable data and reference for the design of such aerogels in the future. Attached Figure Description

[0040] Figure 1 This invention relates to the design concept of sodium alginate / sodium lignosulfonate / hydroxyapatite composite aerogel.

[0041] Figure 2 This is a schematic diagram illustrating the flow properties of Comparative Example 1, Comparative Example 3, and Example 3.

[0042] Figure 3 SEM images of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 3.

[0043] Figure 4 A schematic diagram of the aerogel used to support the flower in Example 3 and a schematic diagram of the weight compression in Example 3.

[0044] Figure 5 The thermogravimetric curves are for Comparative Example 2, Comparative Example 3, and Example 3.

[0045] Figure 6 This is a schematic diagram of human body weight-bearing in Example 3.

[0046] Figure 7 The stress-strain curves are for Comparative Example 2, Comparative Example 3, and Example 3.

[0047] Figure 8 Thermal conductivity diagrams for Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Example 2, and Example 3.

[0048] Figure 9 Infrared camera images of the heating plates of Comparative Example 3 and Example 3 after heating.

[0049] Figure 10 This is a schematic diagram of vertical combustion for Comparative Example 4 and Example 4.

[0050] Figure 11 The contact angle diagram and dye immersion state diagram are for Example 3 (before hydrophobic modification) and Example 6 (after hydrophobic modification).

[0051] Figure 12 The thermal conductivity is compared between Comparative Example 5, Comparative Example 6, Example 5, and Example 7.

[0052] Figure 13 This is a comparison chart of the cumulative smoke production of Comparative Example 2 and Example 3.

[0053] Figure 14 This is a comparison chart of the cumulative smoke production of Comparative Example 5, Comparative Example 6, Example 5, and Example 7. Detailed Implementation

[0054] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0055] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0056] Example 1

[0057] 0.3 g of hydroxyapatite powder (HAP) was weighed and added to 80 mL of 0.05 mol / L NaOH solution at 50 °C. After homogenization, 3 g of sodium lignin sulfonate (LS) was weighed and dissolved in the hydroxyapatite solution. Then, 3 g of sodium alginate (SA) was added and stirred continuously for 1.5 h until the solution was completely mixed. 0.8 g of glucono delta-lactone (GDL) was weighed and dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for about 4–5 min until the solution was homogenized. The mixture was then poured into a cylindrical mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then dried in a vacuum freeze dryer at -50 °C for 48 h to obtain the S3L3H0.3G0.8 composite aerogel.

[0058] Example 2

[0059] 0.6 g of hydroxyapatite powder (HAP) was weighed and added to 80 mL of 0.05 mol / L NaOH solution at 50 °C. After homogenization, 3 g of sodium lignin sulfonate (LS) was weighed and dissolved in the hydroxyapatite solution. Then, 3 g of sodium alginate (SA) was added and stirred continuously for 1.5 h until the solution was completely mixed. 0.8 g of glucono delta-lactone (GDL) was weighed and dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for about 4–5 min until the solution was homogenized. The mixture was then poured into a cylindrical mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then dried in a vacuum freeze dryer at -50 °C for 48 h to obtain the S3L3H0.6G0.8 composite aerogel.

[0060] Example 3

[0061] 0.9 g of hydroxyapatite powder (HAP) was added to 80 mL of 0.05 mol / L NaOH solution at 50 °C and homogenized using a homogenizer. Then, 3 g of sodium lignosulfonate (LS) was dissolved in the hydroxyapatite solution by stirring. Next, 3 g of sodium alginate (SA) was added, and the mixture was stirred continuously for 1.5 h until the solution was completely homogenized. 0.8 g of glucono delta-lactone (GDL) was dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for approximately 4–5 min until the solution was homogenized. The mixture was then poured into a cylindrical mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then dried in a vacuum freeze dryer at -50 °C for 48 h to obtain the S3L3H0.9G0.8 composite aerogel.

[0062] Example 4

[0063] 0.9 g of hydroxyapatite powder (HAP) was added to 80 mL of 0.05 mol / L NaOH solution at 50 °C and homogenized using a homogenizer. Then, 3 g of sodium lignin sulfonate (LS) was weighed and dissolved in the hydroxyapatite solution, followed by the addition of 3 g of sodium alginate (SA). The mixture was stirred continuously for 1.5 h until the solution was completely homogenized. 0.8 g of glucono delta-lactone (GDL) was weighed and dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for approximately 4–5 min until the solution was homogenized. The mixture was then poured into a 1×1×10 cm long strip mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel is formed, it is placed in a refrigerator at -30℃ for 24 hours and then placed in a vacuum freeze dryer at -50℃ for 48 hours to obtain a 1×1×10cm long strip of S3L3H0.9G0.8 composite aerogel.

[0064] Example 5

[0065] 0.45 g of hydroxyapatite powder (HAP) was added to 80 mL of 0.05 mol / L NaOH solution at 50 °C and homogenized using a homogenizer. Then, 3 g of sodium lignosulfonate (LS) was dissolved in the hydroxyapatite solution by stirring. Next, 3 g of sodium alginate (SA) was added, and the mixture was stirred continuously for 1.5 h until the solution was completely homogenized. 0.8 g of glucono delta-lactone (GDL) was dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for approximately 4–5 min until the solution was homogenized. The mixture was then poured into a cylindrical mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then dried in a vacuum freeze dryer at -50 °C for 48 h to obtain the S3L3H0.45G0.8 composite aerogel.

[0066] Example 6

[0067] 0.9 g of hydroxyapatite powder (HAP) was added to 80 mL of 0.05 mol / L NaOH solution at 50 °C and homogenized using a homogenizer. Then, 3 g of sodium lignosulfonate (LS) was dissolved in the hydroxyapatite solution by stirring. Next, 3 g of sodium alginate (SA) was added, and the mixture was stirred continuously for 1.5 h until the solution was completely homogenized. 0.8 g of glucono delta-lactone (GDL) was dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for approximately 4–5 min until the solution was homogenized. The mixture was then poured into a cylindrical mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then dried in a vacuum freeze dryer at -50 °C for 48 h to obtain the S3L3H0.9G0.8 composite aerogel. Then, 1 mL of methyltrichlorosilane was placed in a bottle, and 2 g of aerogel was placed in a beaker. After sealing, a bottle-within-a-bottle device was formed and placed in a fume hood for 12 hours. After completion, it was taken out and placed in a vacuum oven to remove excess methyltrichlorosilane, and silane-modified S3L3H0.9G0.8 composite aerogel was obtained.

[0068] Example 7

[0069] 0.45 g of hydroxyapatite powder (HAP) was added to 80 mL of 0.05 mol / L NaOH solution at 50 °C and homogenized using a homogenizer. Then, 3 g of sodium lignosulfonate (LS) was dissolved in the hydroxyapatite solution by stirring. Next, 3 g of sodium alginate (SA) was added, and the mixture was stirred continuously for 1.5 h until the solution was completely homogenized. 1.6 g of glucono delta-lactone (GDL) was dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for approximately 4–5 min until the solution was homogenized. The mixture was then poured into a cylindrical mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then freeze-dried in a vacuum freeze dryer at -50 °C for 48 h to obtain the S3L3H0.45G1.6 composite aerogel.

[0070] Comparative Example 1

[0071] Weigh 1.5g of sodium lignosulfonate (LS) and add it to 100mL of 0.05mol / L NaOH solution at 50℃. After stirring until dissolved, add 3g of sodium alginate (SA) and continue stirring for 1.5h to ensure complete mixing. Pour the mixture into a cylindrical mold and let it stand for 3h to form a hydrogel. After the hydrogel has solidified, freeze it with liquid nitrogen. Once frozen solid, dry it in a vacuum freeze dryer at -50℃ for 48h to obtain the S3L1.5 composite aerogel.

[0072] Comparative Example 2

[0073] Weigh 3g of sodium lignosulfonate (LS) and add it to 100mL of 0.05mol / L NaOH solution at 50℃. Stir until dissolved and homogeneous, then add 3g of sodium alginate (SA) and continue stirring for 1.5h to ensure complete mixing. Pour the mixture into a cylindrical mold and allow it to stand for 3h to form a hydrogel. After the hydrogel has solidified, freeze it with liquid nitrogen. Once frozen solid, place it in a vacuum freeze dryer at -50℃ for 48h to obtain the S3L3 composite aerogel.

[0074] Comparative Example 3

[0075] At 50℃, 3g of sodium alginate (SA) was added to 100mL of 0.05mol / L NaOH solution and stirred continuously for 1.5h to ensure complete mixing. The mixture was then poured into a cylindrical mold and allowed to stand for 3h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then dried in a vacuum freeze dryer at -50℃ for 48h to obtain S3 aerogel.

[0076] Comparative Example 4

[0077] At 50℃, 3g of sodium alginate (SA) was added to 100mL of 0.05mol / L NaOH solution and stirred continuously for 1.5h until the solution was completely mixed. The mixture was then poured into a 1×1×10cm long strip mold and allowed to stand for 3h to form a hydrogel. After the hydrogel solidified, it was frozen at -30℃ for 24 hours, and then freeze-dried at -50℃ for 48h to obtain a 1×1×10cm long strip S3 aerogel.

[0078] Comparative Example 5

[0079] 0.45 g of calcium carbonate powder (CaCO3) was added to 80 mL of 0.05 mol / L NaOH solution at 50 °C and homogenized using a homogenizer. Then, 3 g of sodium lignosulfonate (LS) was dissolved uniformly in the calcium carbonate solution, followed by the addition of 3 g of sodium alginate (SA). The mixture was stirred continuously for 1.5 h until completely homogeneous. 1.6 g of glucono-delta-lactone (GDL) was dissolved in 20 mL of deionized water. While stirring continuously, 20 mL of GDL solution was slowly added dropwise to the sodium alginate / lignin solution, stirring for approximately 4–5 min until homogeneous. The mixture was then poured into a mold and allowed to stand for 3 h to form a hydrogel. After the hydrogel solidified, it was frozen in liquid nitrogen and then freeze-dried in a vacuum freeze dryer at -50 °C for 48 h to obtain the S3L3(CaCO3)0.45G1.6 composite aerogel.

[0080] Comparative Example 6

[0081] Under magnetic stirring at room temperature, 3g of sodium lignin sulfonate was weighed and added to 80mL of 0.05mol / L NaOH solution. After dissolving, 0.45g of calcium carbonate powder was uniformly dispersed in the lignin solution, followed by 3g of sodium alginate. The mixture was stirred for 5 hours to ensure complete mixing. 1.6g of glucono-delta-lactone was weighed and dissolved in 20mL of deionized water, gently shaken to ensure complete dissolution. While stirring, 20mL of glucono-delta-lactone solution was added dropwise to the sodium alginate / lignin solution. After stirring for another 1.5 minutes, the sol was poured into a mold and allowed to stand for 12 hours to form a hydrogel. The hydrogel was frozen at -20℃ for at least 24 hours until solid, and then freeze-dried at -50℃ for 48 hours to obtain S3L3(CaCO3)0.45G1.6 aerogel.

[0082] Example Effect Description

[0083] Figure 1 This demonstrates the design concept of the sodium alginate / sodium lignosulfonate / hydroxyapatite composite aerogel of the present invention.

[0084] Figure 2 This is a schematic diagram illustrating the flowability of Comparative Example 1, Comparative Example 3, and Example 3. Inverting the solution in the bottle verified the strong cross-linking behavior of the sol precursor. At certain concentrations, the S3 and S3L1.5 sols were very viscous and had poor flowability; when the bottle was inverted 180°, they flowed downwards along the bottle wall due to the lack of internal cross-linking. However, the prepared S3L3H0.9G0.8 composite hydrogel adhered firmly to the bottom of the bottle. These phenomena simply demonstrate that a cross-linking reaction had occurred inside the hydrogel.

[0085] Figure 3SEM images of Comparative Examples 1, 2, 3, and 3 are shown. It can be seen that the aerogels directionally frozen by liquid nitrogen all contain abundant porous structures, while the sodium alginate aerogel without sodium lignosulfonate mainly exhibits a sheet-like stacked porous structure with poor mechanical strength, soft pore walls, and is easily deformed by compression. With the addition of sodium lignosulfonate, the hydrogen bonding between macromolecules gradually strengthens, and sodium lignosulfonate becomes one of the structural components of the framework, providing strong support for the framework. Furthermore, the aerogel structure becomes more compact, manifested by a gradual decrease in pore size, a vertical pore structure in the measured aerogel cross-section, and a gradual increase in pore wall strength. After adding HAP, the composite aerogel exhibits an even denser porous honeycomb structure with interconnected pores.

[0086] Figure 4 The schematic diagrams of the aerogel in Example 3 for supporting flowers and the schematic diagram of the weight compression in Example 3 show that the composite aerogel can be placed on open flowers without deforming the flowers and can easily support the weight of a 500g weight, indicating that the prepared S3L3H0.9G0.8 composite aerogel has the characteristics of being lightweight and having high strength.

[0087] Figure 5 The thermogravimetric curves for Comparative Examples 2, 3, and 3 show that all samples exhibited similar three stages as temperature increased: the first weight loss stage mainly occurred between 50 and 100°C, possibly due to the high porosity and large specific surface area of ​​the samples, which easily adsorbed free water from the air; the evaporation of free water in the early stages of heating led to some mass loss. The second stage occurred between 200 and 300°C, which was the main weight loss stage, possibly due to the cracking of the sodium alginate / sodium lignosulfonate skeleton. At higher temperatures, the small molecules produced by the pyrolysis of the aerogel in the previous stage further degraded, forming the final char residue. The S3 aerogel began to decompose rapidly at around 200°C, reaching its maximum weight loss rate at around 250°C; when the temperature exceeded 900°C, only about 13% of the mass remained. Compared with the S3 aerogel, the composite aerogel with added LS showed a certain increase in the temperature at which the mass loss reached 10%, indicating that the addition of LS helps to improve the thermal stability of the material. After adding HAP, the maximum thermal degradation rate of the composite aerogel was significantly reduced and the temperature corresponding to the maximum pyrolysis rate was increased, as observed from the DTG curve. This indicates that HAP effectively improved the thermal stability of the aerogel.

[0088] Figure 6 This is a schematic diagram of human body load-bearing in Example 3, with 8 samples placed in each of the left and right images. It shows that the prepared S3L3H0.9G0.8 composite aerogel can withstand the weight of an adult without significant deformation, demonstrating its potential for practical application.

[0089] Figure 7For the stress-strain curves of Comparative Examples 2, 3, and 3, all aerogels exhibited similar characteristics during testing, with three characteristic stages: a linear deformation stage with low strain (0–5%), a plateau stage with gradually increasing stress at moderate strain (5–10%), and a densification stage with a sharp increase in stress at high strain (>50%). The compressive modulus of S3 aerogel was 0.69 MPa, while after adding an equal amount of sodium lignosulfonate, the compressive modulus of S3L3 aerogel increased to 2.7 MPa, an increase of approximately 3.9 times, indicating that the addition of sodium lignosulfonate as a structural reinforcing agent to sodium alginate aerogel can effectively improve the mechanical strength of the composite aerogel. The mechanical strength of the aerogel further increased after the addition of HAP, with the strength of the S3L3H0.9G0.8 composite aerogel reaching 6.34 MPa.

[0090] Figure 8 The figures show the thermal conductivity of Comparative Examples 1, 2, 3, 1, 2, and 3. The results indicate that the thermal conductivity of the material initially increases and then decreases with the increase of sodium lignosulfonate. This is because the addition of sodium lignosulfonate has a certain impact on the solid-phase thermal conductivity of the aerogel framework, enhancing heat transfer. However, due to the rigidity of lignin itself, the pore walls of the aerogel change from soft and tortuous to flat and orderly, reducing the gas-phase thermal conductivity of the aerogel pore structure. The effect of gas-phase thermal conductivity is greater than that of solid-phase thermal conductivity, ultimately resulting in a decrease in thermal conductivity, which is consistent with the results of scanning electron microscopy. Similarly, the addition of HAP also increases the bulk density of the material, leading to an increase in thermal conductivity, but it remains at a relatively low level, and the aerogel still exhibits good thermal insulation properties.

[0091] Figure 9 Infrared camera images of Comparative Example 3 and Example 3 after heating with a heating plate are shown. The aerogel was placed on a 200°C heating plate for heating experiments, and the temperature change on its surface was recorded using an infrared camera. The infrared heat distribution on the surface was observed to investigate the thermal insulation performance of the composite aerogel and the effect of its thickness on thermal insulation performance. The temperature of the aerogel surface first increased and then tended to stabilize. Compared with S3 aerogel, the final surface temperature of the S3L3H0.9G0.8 composite aerogel of the same height was 73°C after heating for 10 minutes, which is much lower than the 93°C of sodium alginate aerogel. These results indicate that the composite aerogel has excellent thermal insulation performance.

[0092] Figure 10This is a schematic diagram of vertical combustion of Comparative Example 4 and Example 4. As can be observed from the figure, neither gel produces dripping or open flame during combustion; however, the S3 aerogel carbonizes, shrinks, and spreads upwards during combustion. After adding HAP, the carbonization rate of S3L3H0.9G0.8 is further slowed down, and the gel deformation is relatively small. The addition of HAP is equivalent to the addition of a phosphorus-based flame retardant, which generates phosphorus and phosphorus-nitrogen free radicals at high temperatures. These free radicals can capture H· and OH· generated during combustion, terminating the chain reaction during combustion. This indicates that the addition of HAP significantly improves the fire resistance of sodium alginate aerogel.

[0093] Figure 11 The images show the contact angle and dye penetration diagrams for Examples 3 (before hydrophobic modification) and 6 (after hydrophobic modification). The results show that the water contact angle of the unmodified S3L3H0.9G0.8 aerogel was only 12.49°, while after hydrophobic modification, the water contact angle of the S3L3H0.9G0.8 composite aerogel reached 157°, and even after 5 days, it still reached 152°. Further analysis of the dye penetration state reveals that the dye penetrates into the interior of the unmodified composite aerogel, while after modification, the dye remains on the surface as droplets. After hydrophobic modification, the prepared aerogel can adapt to humid environments, greatly expanding the application range of aerogels.

[0094] Figure 12 The thermal conductivity of Comparative Examples 5, 6, 5, and 7 was compared. The results showed that the thermal conductivity values ​​for Example 5 < Comparative Example 5 < Comparative Example 6 < Comparative Example 7. The reduction in thermal conductivity significantly improves the thermal insulation performance. This may be attributed to the fact that the binary slow-release system of gluconolactone and hydroxyapatite, reacting with sodium alginate, results in a more uniform gel network without generating CO2 gas that could disrupt the integrity of the aerogel structure. The smaller and more uniform pore size also reduces gas-phase turbulence, lowers thermal conductivity, and improves thermal insulation performance.

[0095] Figure 13 This is a comparison chart of the cumulative smoke production of Comparative Example 2 and Example 3. The results show that the smoke production was significantly reduced after adding hydroxyapatite to the binary slow-release system, demonstrating a good smoke suppression effect.

[0096] Figure 14 This is a comparison chart of the cumulative smoke production of Comparative Examples 5, 6, 5, and 7. The results show that the smoke production of Examples 5 and 7 is significantly lower than that of Comparative Examples 6 and 7, and Comparative Example 6 is also significantly lower than that of Comparative Example 7. Using water bath heating and homogenizer dispersion can effectively enhance the uniformity of hydroxyapatite within the gel, and hydroxyapatite has a better smoke-suppressing effect than calcium carbonate, thus playing a certain role in reducing smoke generation.

[0097] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a lignin-hydroxyapatite / biomass-based composite aerogel, characterized in that, Includes the following steps: (1) Mix hydroxyapatite, lignin, sodium alginate and alkaline solution evenly to obtain a composite solution; (2) Add the calcium ion regulator solution dropwise to the composite solution in step (1), mix evenly, let stand to gel, freeze dry, and obtain sodium alginate / lignin / hydroxyapatite composite aerogel. In step (1), the mass ratio of sodium alginate to lignin is 1:0.5-1; the mass ratio of hydroxyapatite to sodium alginate is 0-0.3:1, wherein the mass ratio of hydroxyapatite is not 0. The mass ratio of calcium ion regulator to hydroxyapatite in step (2) is 8:(2-9); In step (2), the calcium ion regulator is gluconolactone.

2. The preparation method according to claim 1, characterized in that, Hydrophobic modification of sodium alginate / lignin / hydroxyapatite composite aerogel was carried out by chemical vapor deposition to obtain hydrophobic lignin-hydroxyapatite / biomass-based composite aerogel.

3. The preparation method according to claim 1, characterized in that, The lignin in step (1) is at least one of alkali lignin, enzymatic hydrolyzed lignin, lignin sulfonate and solvent lignin.

4. The preparation method according to claim 1, characterized in that, The alkaline solution in step (1) is at least one of sodium hydroxide solution and potassium hydroxide solution; the concentration of the alkaline solution is 0.03 to 0.06 mol / L; In step (1), the ratio of hydroxyapatite to alkaline solution is 0.3–0.9 g: 80 mL; The concentration of the calcium ion regulator solution in step (2) is 0.02 to 0.06 g / mL.

5. The preparation method according to claim 2, characterized in that, The modifier used for the hydrophobic modification is at least one of methyltrichlorosilane and methyltrimethoxysilane; The ratio of the modifier used for hydrophobic modification to the sodium alginate / lignin / hydroxyapatite composite aerogel is 1 mL: 2-3 g. The hydrophobic modification time in step (3) is 6 to 24 hours.

6. The preparation method according to claim 1, characterized in that, The composite solution in step (1) is obtained by the following method: adding hydroxyapatite to an alkaline solution, mixing it evenly, adding lignin and sodium alginate, mixing it evenly again, and obtaining the composite solution; The hydroxyapatite was added to the alkaline solution and then homogenized using a homogenizer at 40–60 °C. After adding lignin and sodium alginate, the mixture is stirred at 40–60 °C for 1–2 h to ensure uniform mixing.

7. The preparation method according to claim 1, characterized in that, The time for mixing evenly in step (2) is 3 to 10 minutes; The gel is left to stand for 3 to 6 hours in step (2); Before freeze-drying in step (2), the gel should be refrigerated at -20 to -30 ℃ for more than 12 hours or frozen with liquid nitrogen to ensure that the gel is completely frozen. The freeze-drying process in step (2) involves drying at a temperature of -50°C to room temperature for 12 to 48 hours.

8. The preparation method according to claim 3, characterized in that, The lignin mentioned in step (1) is lignin sulfonate; The mass ratio of sodium alginate to lignin in step (1) is 1:1; The mass ratio of hydroxyapatite to sodium alginate in step (1) is 0.1–0.3:1; The mass ratio of calcium ion regulator to hydroxyapatite in step (2) is 8:9 or 8:2.

25.

9. A lignin-hydroxyapatite / biomass-based composite aerogel prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the lignin-hydroxyapatite / biomass-based composite aerogel according to claim 9 in the field of flame retardant and heat insulation.

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