Cellulose-based foam material and method for its production and use

Abstract

This invention discloses a cellulose-based foam material, its preparation method, and its applications, belonging to the field of foam materials. The invention first synthesizes a TESPA crosslinking agent with both crosslinking and flame-retardant functions using a phosphorus-containing dichlorophosphorus source monomer and 3-aminopropyltriethoxysilane. Carboxymethyl cellulose and bacterial cellulose are then mixed and dispersed in water, and TESPA is added for crosslinking and toughening. Sodium caseinate is then added for mechanical foaming, followed by pressing and drying to obtain a three-dimensional porous foam. This invention relies on the synergistic effect of the TESPA covalent crosslinking network and the bacterial cellulose nanoframework to inhibit cell collapse, resulting in a finished product with a porosity exceeding 80%. The introduction of phosphorus through TESPA imparts halogen-free flame-retardant properties to the material. The natural cellulose substrate is completely degraded in soil within 60 days, exhibiting low thermal conductivity, high compressive strength, and good cell compatibility. This process is simple, energy-efficient, and easily scalable. The resulting foam can be used in mid-to-far-infrared camouflage, flame-retardant insulation, environmentally friendly thermal insulation packaging, and biodegradable materials.

Description

Technical Field

[0001] This invention belongs to the field of foam materials, specifically relating to a cellulose-based foam material, its preparation method, and its application. Background Technology

[0002] With increasingly stringent global environmental requirements and dwindling petrochemical reserves, fully biodegradable biomass porous foam materials have become a core research and development direction in fields such as thermal insulation packaging, flame retardant insulation, and mid-to-far infrared camouflage. Cellulose, as the most abundant natural polymer, possesses advantages such as renewability, low cost, biocompatibility, and complete soil degradation. Among them, carboxymethyl cellulose (CMC) has good water solubility and excellent film-forming and adhesive properties, while bacterial cellulose (BC) is a nanoscale fiber network with outstanding crystallinity and mechanical strength, making it an ideal raw material for preparing high-performance foams.

[0003] Existing cellulose-based foam preparation processes have significant shortcomings. Mainstream freeze-drying and supercritical drying methods involve high equipment investment, long production cycles, and huge energy consumption, making it difficult to achieve continuous industrial production. During freeze-drying, water molecules can quickly condense into solid ice, and the ice crystals support the pores, making it easy to prepare complete porous aerogel structures. However, in room temperature and pressure drying systems, water molecules only evaporate slowly, without rigid ice crystals supporting the pore walls. Systems that only use mechanical foaming lack effective cross-linking support structures, and the pores are prone to shrinkage and collapse during drying, resulting in a significant decrease in porosity and a severe reduction in thermal insulation and buffering performance. At the same time, pure cellulose foam has a low limiting oxygen index, a large heat release during combustion, and its flame retardant properties cannot meet the requirements for safe use. For example, patent CN121873422 A discloses a flame-retardant bacterial cellulose foam material, which improves the material's mechanical and flame-retardant properties through phosphorus and nitrogen-containing dual organosilicon modification. However, this method requires pre-freezing and long-term freeze-drying after molding to maintain the integrity of the pores.

[0004] To circumvent the shortcomings of freeze-drying, patent CN 118420969 A proposes a method for preparing cellulose foam by atmospheric pressure drying. This method uses Pickering emulsion combined with ultraviolet light curing, and drying can be completed by heating at room temperature, eliminating the need for low-temperature vacuum equipment. However, this technical route is lengthy, requiring the step-by-step preparation of cellulose microgels, oil-in-water Pickering emulsions, and photocurable precursors. The multi-step emulsification and photocuring processes place stringent requirements on the control of equipment shear power and ultraviolet light source parameters. It also requires acrylic photopolymerization monomers, special photoinitiators, and crosslinking agents. The variety of raw materials and the complexity of formula control result in a low production error tolerance, and the overall process is still not simple or efficient enough.

[0005] Furthermore, existing research has reported on CMC / BC composite systems, but all of them suffer from incompatibility between the product form and process route and the present invention. Patent CN 101530749 A utilizes a fermentation system to synthesize CMC / BC composite materials in situ, producing a dense film, and the post-processing still relies on freeze-drying, which cannot yield a high-porosity foam structure and is unsuitable for heat insulation and buffering applications. Patent CN 115975228 A also uses a fermentation in-situ composite process to prepare CMC / BC composite membranes, producing a dense sheet material without a three-dimensional interconnected porous network, suitable only for the medical film field. Its application direction and microstructure differ greatly from the high-porosity foam product of the present invention and are therefore not of reference value.

[0006] In summary, existing technologies either rely on energy-intensive freeze-drying, involve complex processes and raw material systems, or can only produce dense films. They cannot simultaneously solve the technical problems of foam drying collapse, insufficient flame retardancy, high production costs, and scalable production. Therefore, developing foam materials with extremely simple processes, ambient pressure drying throughout, high strength, low thermal conductivity, halogen-free flame retardancy, and complete biodegradability has significant industrial value. Summary of the Invention

[0007] Technical issues Existing cellulose-based porous materials rely on energy-intensive freeze drying, and even if they can be prepared under normal pressure, the process is cumbersome.

[0008] Technical solution To address the aforementioned technical problems, this invention provides a biodegradable cellulose-based foam material, its preparation method, and its applications. This material utilizes a phosphorus-containing siloxane crosslinking agent (TESPA) to form a crosslinked network support structure between the foam pore walls, preventing foam breakage and collapse during drying. Combined with mechanical foaming and atmospheric pressure drying techniques, a foam material with a stable three-dimensional porous network structure is prepared, exhibiting excellent flame retardant properties, low thermal conductivity, and complete biodegradability.

[0009] To achieve the above objectives, the technical solution provided by the present invention is as follows: The first objective of this invention is to provide a method for preparing cellulose-based foam materials, wherein the method can prepare cellulose-based foam materials by drying under normal pressure, and the method includes the following steps: (1) Raw material mixing: Carboxymethyl cellulose (CMC) and bacterial cellulose (BC) are added to water and stirred to form a cellulose mixture; (2) Crosslinking and toughening: Add phosphorus-containing bridging siloxane crosslinking agent to the cellulose mixture and stir evenly to obtain a precursor solution; (3) Foaming and molding: Sodium caseinate (SC) is added to the precursor solution, stirred and dissolved, and then mechanically foamed by high-speed stirring to obtain wet foam; (4) Drying and shaping: The wet foam obtained in step (4) is dried to obtain a cellulose-based foam material with a three-dimensional porous structure.

[0010] In one embodiment, carboxymethyl cellulose in step (1) can be replaced by sodium carboxymethyl cellulose, or a mixture of both can be used.

[0011] In one embodiment, the degree of substitution of carboxymethyl cellulose or sodium carboxymethyl cellulose is 0.6 to 0.8, and the viscosity is 200-500 mPa·s.

[0012] In one embodiment, bacterial cellulose is cellulose synthesized by microorganisms such as Acetic Acid Bacteria, Agrobacterium, Rhizobium, and Micrococcus; it has a diameter of 40-120 nm and a length greater than 10 μm.

[0013] In one embodiment, bacterial cellulose is a freeze-dried powdered solid.

[0014] In one implementation, the mass ratio of CMC to BC in step (1) is 4:2~4.

[0015] In one implementation, the mass ratio of CMC to BC in step (1) is 4:2, 4:3 or 4:4.

[0016] In one embodiment, the CMC concentration in the cellulose mixture in step (1) is 0.5~10wt%.

[0017] In one embodiment, the preparation method of the phosphorus-containing bridged siloxane crosslinking agent in step (2) is as follows: Under nitrogen protection, phosphorus source monomers containing phosphorus dichloride are dissolved in an organic solvent, and then 3-aminopropyltriethoxysilane is added. The mixture is heated to react, and after the reaction is completed, the solvent is removed by rotary evaporation to obtain the phosphorus-containing bridged siloxane crosslinking agent.

[0018] In one embodiment, the phosphorus source monomer containing phosphorus dichloride includes one or more of phosphorus oxychloride, methylphosphonodichloride, phenylphosphonodichloride, and ethyl dichloroacetate.

[0019] In one embodiment, the molar ratio of the phosphorus-containing dichloro phosphorus source monomer to 3-aminopropyltriethoxysilane is 1:2~5.

[0020] In one embodiment, the organic solvent is tetrahydrofuran.

[0021] In one embodiment, the heating reaction is first carried out at 40-50°C for 0.5-1 hour, and then at 70-80°C for 4-7 hours.

[0022] In one embodiment, the mass ratio of CMC to phosphorus-containing bridging siloxane crosslinking agent in step (2) is 4:5~15.

[0023] In one embodiment, the mass ratio of CMC to phosphorus-containing bridging siloxane crosslinking agent in step (2) is 4:5~10.

[0024] In one embodiment, the amount of SC added in step (3) is 1 to 5 wt% of the precursor solution mass.

[0025] In one embodiment, the amount of SC added in step (3) is 1 to 3 wt% of the precursor solution mass.

[0026] In one embodiment, the high-speed stirring speed in step (3) is 1000~2000 r / min, and the foaming time is 10~20 min.

[0027] In one embodiment, the drying temperature in step (4) is 50~80 °C, the time is 5~10 hours, and the pressure is 90~110 kPa.

[0028] A second objective of this invention is to provide a cellulose-based foam material prepared by the above method.

[0029] The third objective of this invention is to provide applications of the aforementioned cellulose-based foam materials in the fields of mid- and far-infrared camouflage, flame retardant insulation, and thermal insulation packaging.

[0030] Beneficial effects (1) The preparation process is simple and energy-saving, and easy to scale up for industrial production: This invention adopts a mechanical foaming combined with atmospheric pressure and low temperature drying molding process, which abandons the high energy consumption and high equipment investment processes such as freeze drying and supercritical drying that traditional cellulose foam relies on. It does not require vacuum refrigeration or high-pressure supercritical supporting equipment, which greatly reduces the energy consumption of equipment purchase, production operation and processing cycle; the overall preparation process only includes five integrated processes: crosslinking agent synthesis, cellulose dispersion, crosslinking toughening, mechanical foaming and atmospheric pressure drying. Compared with the existing technology, it does not require multiple complex molding operations such as Pickering emulsion and ultraviolet curing. The raw material system is simple and the process error tolerance is high. It can realize continuous batch production and effectively solve the industry problems of high production cost, limited production capacity and difficulty in mass production of the existing technology.

[0031] (2) Synergistic effect of each component to achieve foam structure stability and halogen-free flame retardancy: The phosphorus-bridged siloxane of this invention has the dual functions of cross-linking enhancement and halogen-free flame retardancy. Its siloxane group and cellulose hydroxyl group condense to form a covalent rigid network, which supports the foam pores and prevents drying collapse. The phosphorus unit catalyzes the carbonization of the substrate and blocks heat and oxygen transfer, giving the material excellent flame retardant properties. The CMC and BC binary compound system complement each other. CMC constructs a continuous aqueous matrix, and BC provides a nanofiber entanglement skeleton, providing a stable substrate for foaming and molding. Sodium caseinate macromolecular foam stabilizer is selected to construct a high-strength interfacial film at the gas-liquid interface to avoid the coarsening and collapse of bubbles. The three work together to solve the defects of low porosity, poor flame retardancy and easy collapse of foam pores in ordinary silane and small molecule surfactant systems, and obtain a stable high-porosity three-dimensional interconnected porous structure to meet the requirements of room temperature and pressure drying.

[0032] (3) The finished material has excellent comprehensive physical and chemical properties, is green and biodegradable and has good biocompatibility: The material of the present invention has a high porosity three-dimensional interconnected porous network, which seals static air inside and has a low thermal conductivity, thus having excellent heat insulation capabilities; the cellulose nanofiber network and the TESPA covalent cross-linked network work together to toughen the material, resulting in high compressive strength and good buffering and load-bearing performance; and all the substrates are made of natural renewable cellulose, which does not contain petrochemical components that are difficult to degrade, and can be completely degraded within 60 days when buried in natural soil environment. At the same time, it has excellent cell compatibility and belongs to environmentally friendly biomass functional materials. Attached Figure Description

[0033] Figure 1 A scanning electron microscope (SEM) cross-sectional image of the cellulose-based foam material prepared in Example 1; Figure 2 The pore size distribution curve of the cellulose-based foam material prepared in Example 1 is shown. Figure 3 The heat release rate (HRR) curve of the cellulose-based foam material prepared in Example 1; Figure 4 The image shows the compressive stress-strain curve of the cellulose-based foam material prepared in Example 1. Figure 5 The graph shows the 60-day degradation performance of the cellulose-based foam material prepared in Example 1. Figure 6 Comparative diagrams of the foam materials prepared in Example 1, Comparative Example 4, Comparative Example 5, Comparative Example 6, and Comparative Example 7; Detailed Implementation The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The specific embodiments described below further illustrate the present invention.

[0034] The testing method involved in this invention 1. Scanning Electron Microscopy (SEM) Test: After the sample is sliced ​​and sputtered with gold, the microstructure and pore structure of the material are observed using a scanning electron microscope.

[0035] 2. Porosity testing: The porosity and pore size distribution of the material are tested using the mercury intrusion porosimetry method.

[0036] 3. Flame retardant performance test: The heat release rate (HRR) of the material was tested using a micro calorimeter (MCC).

[0037] 4. Compression performance test: The compressive strength and compressive modulus of the material are tested using a universal testing machine.

[0038] 5. Thermal conductivity test: The thermal conductivity of the material is tested using a thermal constant analyzer.

[0039] 6. Degradation performance test: The material is buried in natural soil and periodically removed to test the weight loss rate.

[0040] The raw materials involved in this invention 1. Raw materials and reagents Carboxymethyl cellulose (sodium carboxymethyl cellulose), degree of substitution 0.7, viscosity 200-500 mPa·s, analytical grade; Bacterial cellulose (BC): lyophilized powder, 50-100 nm in diameter and greater than 20 μm in length; Phosphorus oxychloride (POCl3): analytical grade; 3-Aminopropyltriethoxysilane (APTES): Analytical grade; Tetrahydrofuran (THF): analytical grade; Sodium caseinate (SC): analytical grade.

[0041] 2. Synthesis method of TESPA: Under nitrogen protection, 0.04 mol of phosphorus oxychloride was dissolved in 100 mL of tetrahydrofuran, and then 0.12 mol of 3-aminopropyltriethoxysilane was added dropwise to the solution at 45 °C. After reacting for 30 min, the temperature was raised to 75 °C and the reaction was continued for 5 h to obtain a light yellow solution. The THF solvent was removed by rotary evaporation under vacuum at 60 °C to obtain a light yellow viscous liquid product, namely tris[N-(3-triethoxysilylpropyl)]phosphamide (TESPA).

[0042] Example 1 A method for preparing a cellulose-based foam material includes the following: (1) Synthesis of TESPA: Same as above.

[0043] (2) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.3 g of bacterial cellulose and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0044] (3) Crosslinking and toughening: Add 0.7 g TESPA to the dispersion obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0045] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain dense wet foam.

[0046] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain cellulose-based foam material.

[0047] Example 2 A method for preparing a cellulose-based foam material includes the following: (1) Synthesis of TESPA: Same as above.

[0048] (2) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.2 g of bacterial cellulose and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0049] (3) Crosslinking and toughening: Add 0.7 g TESPA to the dispersion obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0050] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain dense wet foam.

[0051] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain cellulose-based foam material.

[0052] Example 3 A method for preparing a cellulose-based foam material includes the following: (1) Synthesis of TESPA: Same as above.

[0053] (2) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.4 g of bacterial cellulose and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0054] (3) Crosslinking and toughening: Add 0.7 g TESPA to the dispersion obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0055] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain dense wet foam.

[0056] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain cellulose-based foam material.

[0057] Example 4 A method for preparing a cellulose-based foam material includes the following: (1) Synthesis of TESPA: Same as above.

[0058] (2) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.3 g of bacterial cellulose and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0059] (3) Crosslinking and toughening: Add 0.6 g TESPA to the dispersion obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0060] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain dense wet foam.

[0061] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain cellulose-based foam material.

[0062] Example 5 A method for preparing a cellulose-based foam material includes the following: (1) Synthesis of TESPA: Same as above.

[0063] (2) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.3 g of bacterial cellulose and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0064] (3) Crosslinking and toughening: Add 0.7 g TESPA to the dispersion obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0065] (4) Foaming and molding: Add 1% (about 0.214 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain dense wet foam.

[0066] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain cellulose-based foam material.

[0067] Results Analysis 1 The performance of the cellulose-based foam materials prepared in Examples 1-5 was tested, and the results are shown in Table 1: Table 1 Performance Tests of Cellulose-Based Foam Materials

[0068] The results showed that the cellulose-based foam materials prepared in each embodiment all possessed a high-porosity three-dimensional network structure and excellent comprehensive properties. Example 1 exhibited the best performance, while Examples 2-5 maintained good foam structures under different formulations. Figures 1-5 As shown, the foam material forms a uniform, interconnected three-dimensional network. Figure 1 The pore size is mainly macroporous. Figure 2 Low heat release rate ( Figure 3 Excellent compression performance at different compression ratios ( Figure 4 It can be completely degraded within 60 days. Figure 5 ).

[0069] Comparative Example 1 A method for preparing a cellulose-based foam material (using microcrystalline cellulose instead of bacterial cellulose) includes the following: (1) Synthesis of TESPA: Same as above.

[0070] (2) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.3 g of microcrystalline cellulose and continue stirring at 300 r / min for 2 h to make the microcrystalline cellulose evenly dispersed.

[0071] (3) Crosslinking and toughening: Add 0.7 g TESPA to the solution obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0072] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain wet foam.

[0073] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain the foam material.

[0074] Comparative Example 2 A method for preparing a cellulose-based foam material (using 1,2-bis(triethoxysilyl)ethane instead of TESPA) includes the following: (1) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.3 g of bacterial cellulose and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0075] (2) Crosslinking and toughening: Add 0.7 g of 1,2-bis(triethoxysilyl)ethane to the dispersion obtained in step (1) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0076] (3) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (2), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain dense wet foam.

[0077] (4) Drying and shaping: Pour the wet foam obtained in step (3) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain cellulose-based foam material.

[0078] Comparative Example 3 A method for preparing a cellulose-based foam material (using sodium dodecyl sulfate instead of sodium caseinate) includes the following: (1) Synthesis of TESPA: Same as above.

[0079] (2) Raw material mixing: Dissolve 0.4 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, then add 0.3 g of bacterial cellulose and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0080] (3) Crosslinking and toughening: Add 0.7 g TESPA to the dispersion obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0081] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium dodecyl sulfate by weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain dense wet foam.

[0082] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain cellulose-based foam material.

[0083] Comparative Example 4 A method for preparing a cellulose-based foam material (adding only carboxymethyl cellulose) includes the following: (1) Synthesis of TESPA: Same as above.

[0084] (2) Raw material mixing: Dissolve 0.7 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, and continue stirring at 300 r / min for 2 h to make the carboxymethyl cellulose evenly dispersed.

[0085] (3) Crosslinking and toughening: Add 0.7 g TESPA to the solution obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0086] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain wet foam.

[0087] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain the foam material.

[0088] Comparative Example 5 A method for preparing a cellulose-based foam material (adding only bacterial cellulose) includes the following: (1) Synthesis of TESPA: Same as above.

[0089] (2) Raw material mixing: Dissolve 0.7 g of bacterial cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a 2% solution, and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0090] (3) Crosslinking and toughening: Add 0.7 g TESPA to the solution obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0091] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain wet foam.

[0092] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain the foam material.

[0093] Comparative Example 6 A method for preparing a cellulose-based foam material (adjusting the amount of carboxymethyl cellulose and bacterial cellulose) includes the following: (1) Synthesis of TESPA: Same as above.

[0094] (2) Raw material mixing: Dissolve 0.3 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a solution, add 0.4 g of bacterial cellulose, and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0095] (3) Crosslinking and toughening: Add 0.7 g TESPA to the solution obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0096] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain wet foam.

[0097] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain the foam material.

[0098] Comparative Example 7 A method for preparing a cellulose-based foam material (adjusting the amount of carboxymethyl cellulose and bacterial cellulose) includes the following: (1) Synthesis of TESPA: Same as above.

[0099] (2) Raw material mixing: Dissolve 0.5 g of carboxymethyl cellulose in 20 mL of water, stir at 300 r / min for 2 h to prepare a solution, add 0.2 g of bacterial cellulose, and continue stirring at 300 r / min for 2 h to make the bacterial cellulose evenly dispersed.

[0100] (3) Crosslinking and toughening: Add 0.7 g TESPA to the solution obtained in step (2) and stir at 100 r / min for 3 h to make the components mix evenly and undergo crosslinking reaction.

[0101] (4) Foaming and molding: Add 2% (about 0.428 g) of sodium caseinate by total weight to the mixed precursor solution obtained in step (3), stir at 100 r / min for half an hour until completely dissolved, then adjust the speed to 1500 r / min and stir for 15 min to obtain wet foam.

[0102] (5) Drying and shaping: Pour the wet foam obtained in step (4) into a mold and dry it in an oven at 60 ℃ under normal pressure (98~102kPa) for 8 h to obtain the foam material.

[0103] Results Analysis 2 The performance of the cellulose-based foam materials prepared in Example 1 and Comparative Examples 1-3 was tested, and the results are shown in Table 2: Table 2 Performance Tests of Cellulose-Based Foam Materials

[0104] Comparative Example 1 shows that when microcrystalline cellulose (MCC) is used to replace bacterial cellulose (BC), micron-sized MCC particles cannot form an entangled network structure of nanofibers. The foam pore walls almost completely collapse during the drying process, and the porosity is only 20.0%, highlighting the indispensability of the BC nanofiber skeleton in foam molding. Comparative Example 2 shows that although BTSE can form a certain cross-linked structure (porosity 72%) after replacing TESPA with 1,2-bis(triethoxysilyl)ethane (BTSE), its molecules do not contain phosphorus and its LOI is only 18.5%, which allows it to burn continuously in air. This indicates that the flame-retardant effect of phosphorus in TESPA in Example 1 is irreplaceable.

[0105] Comparative Example 3 verified the irreplaceable role of sodium caseinate (SC) in achieving high-stability foam molding. When replaced by sodium dodecyl sulfate (SDS), the small-molecule SDS could not form a stable interfacial film at the gas-liquid interface, resulting in bubble coalescence and coarsening. The porosity after drying was only 56.0%, highlighting the key role of SC's unique protein structure in stable foam molding.

[0106] Comparative Example 4 shows that when only CMC is added without BC, the lack of BC nanofiber skeleton support causes the foam to almost completely collapse during drying, with a porosity of only 14%, highlighting the necessity of BC nanofibers in constructing foam structures. Comparative Example 5 shows that when only BC is added without CMC, BC is difficult to disperse evenly in water and cannot form a continuous and stable foam matrix. The porosity is only 25%, highlighting the indispensability of CMC as a dispersion matrix. Comparative Example 6 shows that when the mass ratio of CMC to BC is 3:4, the low CMC content leads to insufficient system viscosity, uneven BC dispersion, and severe foam structure collapse. Comparative Example 7 shows that when the mass ratio of CMC to BC is 5:2, the low BC content leads to insufficient nanofiber skeleton, weakened foam pore wall support, and foam collapse.

[0107] In summary, this invention is based on the construction of a three-dimensional porous network framework using mechanical foaming technology. It utilizes the covalent condensation reaction between a phosphorus-containing bridging siloxane crosslinking agent (TESPA) and cellulose hydroxyl groups to construct a pore wall reinforcement system, simultaneously achieving structural shaping and flame-retardant functionalization. Furthermore, the natural cellulose matrix ensures the complete biodegradability of the material. The above-mentioned technical means work together to successfully prepare a structurally stable, highly flame-retardant, and completely degradable cellulose-based foam material, effectively overcoming the technical defects of existing technologies, such as easy collapse of foam during drying, difficulty in balancing flame retardancy and mechanical properties, and insufficient biodegradability.

[0108] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a cellulose-based foam material, characterized in that, The method includes the following steps: (1) Raw material mixing: Carboxymethyl cellulose and bacterial cellulose are added to water and stirred to form a cellulose mixture; the mass ratio of carboxymethyl cellulose to bacterial cellulose is 4:2~4; (2) Crosslinking and toughening: Add phosphorus-containing bridging siloxane crosslinking agent to the cellulose mixture and stir evenly to obtain a precursor solution; (3) Foaming and molding: Sodium caseinate is added to the precursor solution, stirred and dissolved, and then mechanically foamed by high-speed stirring to obtain wet foam; (4) Drying and shaping: The wet foam obtained in step (4) is dried to obtain a cellulose-based foam material with a three-dimensional porous structure; the pressure during the drying process is 90~110 kPa; The preparation method of the phosphorus-containing bridged siloxane crosslinking agent in step (2) is as follows: Under nitrogen protection, phosphorus source monomers containing phosphorus dichloride are dissolved in an organic solvent, and then 3-aminopropyltriethoxysilane is added. The mixture is heated to react, and after the reaction is completed, the solvent is removed by rotary evaporation to obtain phosphorus-containing bridged siloxane crosslinking agent. The phosphorus source monomer containing phosphorus dichloride includes one or more of phosphorus oxychloride, methylphosphonodichloride, phenylphosphonodichloride, and ethyl dichloroacetate.

2. The preparation method according to claim 1, characterized in that, In step (1), the CMC concentration in the cellulose mixture is 0.5~10wt%.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the phosphorus source monomer containing phosphorus dichloride to 3-aminopropyltriethoxysilane is 1:2~5.

4. The preparation method according to claim 1, characterized in that, The heating reaction is carried out first at 40~50℃ for 0.5~1 hours, and then at 70~80℃ for 4~7 hours.

5. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of carboxymethyl cellulose to phosphorus-containing bridging siloxane crosslinking agent is 4:5~15.

6. The preparation method according to claim 1, characterized in that, In step (3), the amount of sodium caseinate added is 1 to 5 wt% of the precursor solution mass.

7. The preparation method according to claim 1, characterized in that, In step (3), the speed of high-speed stirring is 1000~2000 r / min, and the foaming time is 10~20 min.

8. The preparation method according to claim 1, characterized in that, In step (4), the drying temperature is 50~80℃ and the time is 5~10 hours.

9. A cellulose-based foam material, characterized in that, The cellulose-based foam material is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the cellulose-based foam material as described in claim 9 in the fields of mid- and far-infrared camouflage, flame retardant insulation, heat insulation packaging.

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