Bacterial cellulose thermoplastic polymer composite foamed material, and its preparation and application

Abstract

The application discloses a bacterial cellulose thermoplastic polymer composite foaming material and a preparation method and application thereof, and relates to the technical field of bacterial cellulose thermoplastic polymer composite foaming materials. The preparation method comprises the following steps: after surface activation treatment, foaming and poring microspheres are subjected to static fermentation culture in a strain culture solution, the liquid surface of the strain culture solution is 1-5 mm higher than the accumulation surface of the foaming and poring microspheres, and the fermentation product is purified and dried to obtain a bacterial cellulose-foaming and poring microsphere composite with a microporous structure; the bacterial cellulose-foaming and poring microsphere composite is further heated and immersed in a melt of a thermoplastic polymer material to obtain the bacterial cellulose thermoplastic polymer composite foaming material after cooling; wherein the foaming and poring microspheres are of a core-shell structure, the core is a foaming agent, and the shell is a thermoplastic polymer material. The material is environment-friendly and has excellent mechanical properties, and can be widely applied to fields of porous foaming materials, such as building heat insulation, sound insulation materials and cushion packaging materials.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and relates to a bacterial cellulose thermoplastic polymer composite foam material, its preparation method and application. Background Technology

[0002] Porous materials, due to their unique pore structure, have a wide range of applications across various industries, offering functions such as lightweighting, cushioning, sound insulation, and heat insulation. Taking packaging as an example, polystyrene (PS) foam cushioning packaging materials, widely used in the packaging of household appliances, precision instruments, computers, and electronic components, are high-molecular-weight chemical compounds. This packaging waste cannot be biodegraded or fully recycled. With the integration of global trade and the increasing emphasis placed on environmental issues by various countries, the application of these non-biodegradable and non-recyclable cushioning packaging materials will face increasing restrictions and will eventually be phased out.

[0003] Cellulose fiber porous materials possess excellent biodegradability and environmental compatibility. They are completely degradable and can be recycled for use as animal feed or as fertilizer in soil. Therefore, their waste does not pollute the environment, and the production process itself does not pollute the atmosphere or the environment. Furthermore, cellulose is one of the most abundant natural polymers and a renewable organic resource. Therefore, in recent years, with increasing global attention to environmental pollution, cellulose porous buffer materials have become a hot research and development area worldwide.

[0004] Existing research indicates that the ideal structure of a cellulose fiber-based porous buffer material should be a three-dimensional network structure. The strength of this structure depends on the strength of the fiber bundles themselves and the bonding strength between the fiber bundles. Furthermore, this "three-dimensional network" structure requires the addition of reinforcing agents and other chemical substances to improve its strength to meet the requirements of industrial applications. Bacterial cellulose is a natural source of cellulose fibers, possessing a natural three-dimensional network structure; it is also currently the only nanocellulose fiber that can be mass-produced.

[0005] Specifically, bacterial cellulose is a biopolymer obtained by bacterial fermentation, composed of glucose linked by β-1,4-glycosidic chains, and possesses unique physical and chemical properties. Bacterial cellulose has a natural three-dimensional nanonetwork structure, consisting of 40-60 nanometer-thick fiber bundles composed of microfibers with a diameter of 3-4 nanometers, interwoven to form a well-developed, ultra-fine network structure. It exhibits high tensile strength and elastic modulus; excellent air permeability, water absorption, and water permeability; exceptional water retention; and high wet strength.

[0006] The preparation of bacterial cellulose-based porous materials has always been a research hotspot. Chinese invention patent CN106191165A discloses a method of preparing stable foam using a foaming agent and stabilizer, followed by co-culturing bacteria with the foam to obtain a bacterial cellulose foam material. However, this method suffers from difficulty in controlling the foam stabilization time, and the fermentation time is relatively short (10-12 hours), making it difficult to obtain foam materials with good mechanical properties and controllable pore structure. Chinese invention patent CN102276876A discloses a method of immersing normally cultured bacterial cellulose in a foaming solution to obtain a bacterial cellulose porous material. However, this method utilizes simple gas foaming expansion to create pores, which faces problems such as difficulty in controlling the pore size structure, small pore size, uneven pore size distribution, and poor mechanical strength.

[0007] Therefore, in practical applications, there is an urgent need to find a method for foaming that maintains the original three-dimensional structure of bacterial cellulose and can be combined with appropriate materials to improve the mechanical strength of the foamed material in order to meet the requirements of various industrial applications. Summary of the Invention

[0008] The first objective of this invention is to provide a method for preparing a bacterial cellulose thermoplastic polymer composite foam material; the second objective of this invention is to provide the bacterial cellulose thermoplastic polymer composite foam material prepared by this method; and the third objective of this invention is to provide the application of the bacterial cellulose thermoplastic polymer composite foam material in building insulation, sound insulation materials, or cushioning packaging materials.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] On one hand, the present invention provides a method for preparing a bacterial cellulose thermoplastic polymer composite foam material, which includes the following steps:

[0011] The surface of foamed porous microspheres was activated using biopolymer compounds;

[0012] The surface-activated foamed porous microspheres were statically fermented in the bacterial culture medium. The liquid level of the bacterial culture medium was 1-5 mm higher than the surface of the foamed porous microspheres. After purification and drying, the fermentation product was used to obtain a bacterial cellulose-foamed porous microsphere composite with a microporous structure. The composite was further heated and impregnated in the melt of a thermoplastic polymer material. After cooling, a bacterial cellulose thermoplastic polymer composite foam material was obtained.

[0013] The foamed porous microspheres have a core-shell structure, with the core being a foaming agent and the outer shell being a thermoplastic polymer material.

[0014] This invention creatively combines the pore-forming agent method with the foaming method. First, utilizing the spatial occupancy effect of foamed porous microspheres, the microspheres and bacterial culture medium are placed together in a fermentation vessel for static fermentation. Before fermentation, the surface of the foamed porous microspheres is activated to enhance the affinity between the bacterial strain and the microsphere surface. During static fermentation, the liquid level of the bacterial culture medium is 1–5 mm higher than the surface of the foamed porous microspheres. This design ensures that the bacterial cellulose hydrogelatinizer generated during fermentation can encapsulate the microspheres. After freeze-drying or critical carbon dioxide drying of the fermentation product, a bacterial cellulose-foamed porous microsphere complex with a microporous structure is formed. When the dried fermentation product is immersed in the thermoplastic polymer melt, due to the high temperature of the melt, during this process: (1) the external thermoplastic polymer melt enters the system through the micropores of the bacterial cellulose; (2) the foamed porous microspheres of the present invention have a core-shell structure, with a core of foaming agent and a shell of thermoplastic polymer material; due to heat conduction, the thermoplastic polymer on the shell of the foamed porous microspheres gradually melts and enters the microporous bacterial cellulose covering its surface; (3) the foaming agent in the core of the foamed porous microspheres generates a large amount of gas under the action of heat, forming foam. After final cooling, a bacterial cellulose thermoplastic polymer composite foamed material with a porous structure is obtained. The method of the present invention can obtain a porous composite porous foamed material while maintaining the original three-dimensional structure of bacterial cellulose nanofibers, which significantly improves the mechanical properties of the composite material. It can be widely used as a porous foamed material in the fields of building insulation, sound insulation materials, and cushioning packaging materials.

[0015] In the above preparation method, preferably, the foaming agent includes one or more of 2,2'-azobisisobutyronitrile, benzenesulfonyl hydrazine, p-toluenesulfonyl hydrazine, N,N'-dimethyl-N,N'-dinitrosoterephthalamide, 1,3-benzenedisulfonyl hydrazine, 3,3'-disulfonyl hydrazine diphenyl sulfone, azoaminobenzene, 4,4'-oxobisbenzenesulfonyl hydrazine, azodicarboxamide, and barium azodicarbonate, but is not limited thereto. The foaming agent used in this invention is in powder form, has a specific gravity greater than water, and decomposes upon heating to release gas.

[0016] In the above preparation method, preferably, the thermoplastic polymer material includes one or more of polycaprolactone (PCL), polyurethane (PU), polybutylene succinate (PBS), polylactic acid (PLA), polyhydroxybutyrate (PHA), nylon (PA), and polypropylene terephthalate (PTT), but is not limited thereto. The thermoplastic polymer material used in this invention is a biodegradable thermoplastic polymer material.

[0017] In the above preparation method, preferably, the particle size of the foamed porous microspheres is 200-5000 μm; wherein the mass of the foaming agent accounts for 1-30 wt% of the mass of the foamed porous microspheres.

[0018] In the above preparation method, preferably, the preparation method of the foamed porous microspheres includes:

[0019] Thermoplastic polymer materials are processed into thermoplastic hollow microsphere shell structures using existing template methods or microfluidic methods. Then, a foaming agent is injected into the hollow interior of the microsphere shell structure using microneedles, resulting in core-shell structured foamed porous microspheres. The preparation process of the hollow microsphere shell structure of this invention is a conventional operation in the field.

[0020] In the above preparation method, preferably, the biopolymer compound includes one or more of gelatin, hyaluronic acid, alginate, pectin and silk protein, but is not limited thereto.

[0021] In the above preparation method, preferably, the process of activating the surface of the foamed porous microspheres with a biopolymer compound includes:

[0022] Prepare an aqueous solution of biological macromolecules by dissolving them in water.

[0023] Foamed porous microspheres were immersed in an aqueous solution of a biopolymer compound, removed and air-dried to uniformly coat the surface of the foamed porous microspheres with a layer of biopolymer compound.

[0024] Since the outer shell of the foamed porous microspheres is a thermoplastic polymer, it generally has poor affinity with the bacterial strain. This invention creatively uses a special immersion method to coat the surface of the foamed porous microspheres with a layer of biopolymer that has good affinity and compatibility with the fermentation strain, thereby activating and modifying the surface of the foamed porous microspheres. This method ensures that the bacterial cellulose fibers have a high surface density on the foamed porous microspheres. When heated and foamed, under the dual action of the foaming gas and the high-density bacterial cellulose fibers, the porous structure will not collapse due to the melting of the outer shell of the foamed porous microspheres.

[0025] In the above preparation method, preferably, the concentration of the aqueous solution of the biopolymer compound is 0.5-3 wt%.

[0026] The immersion time can be controlled between 1 and 5 minutes. The immersion temperature can be controlled at room temperature.

[0027] In the above preparation method, preferably, the bacterial culture medium is composed of a bacterial strain capable of fermenting to obtain bacterial cellulose and a fermentation culture medium;

[0028] The bacterial strains capable of fermenting to obtain bacterial cellulose include one or more of Acetobacter xylinum, Rhizobium, Micrococcus occulta, Pseudomonas, Achromobacterium, Alcaligenes, Aerobacterium, and nitrogen-fixing bacteria. The culture medium for these strains is a conventional culture medium used in the art for obtaining bacterial cellulose.

[0029] In the above preparation method, preferably, the process of static fermentation culture of the surface-activated foamed porous microspheres in the bacterial culture medium includes:

[0030] The surface-activated foamed porous microspheres were placed in a petri dish, and the bacterial culture solution was poured into the petri dish until the liquid level of the bacterial culture solution was 1-5 mm higher than the surface of the foamed porous microspheres. Static culture was carried out for 1-7 days at a fermentation temperature of 30-40℃.

[0031] There is no special limitation on the stacking height of the foamed microspheres; it can be set conventionally according to actual needs. In addition, the height difference of 1-5 mm is to ensure that the foamed microspheres will not be exposed due to the evaporation of the culture medium under normal fermentation conditions, and to ensure that all the foamed microspheres are incorporated into the bacterial cellulose fermentation product.

[0032] The culture dish used in the fermentation process of this invention has a height of 10-50 cm. It is a glass or metal container with an open top and a foot at the bottom edge, with a foot height of 0.5-1 cm. The bottom of the fermentation culture dish has a porous mesh design, and a thin film of silica is placed on the bottom surface. Since the strains that can ferment to obtain bacterial cellulose are all aerobic bacteria, they need to consume oxygen during the fermentation process to produce bacterial cellulose. Under normal circumstances, if the liquid level in the culture system is too high, bacterial cellulose can only form on the upper surface of the culture dish. The purpose of the culture dish design in this invention is to increase the oxygen content at the bottom of the fermentation culture dish during static culture, so that the bacterial cellulose at the bottom can grow normally.

[0033] In the above preparation method, preferably, the process of purifying and drying the fermentation product includes:

[0034] The fermentation product was repeatedly pressed and immersed in anhydrous ethanol and hydrogen peroxide to wash away the residue of the culture medium and obtain the purified product. Then, the purified product was freeze-dried or critical carbon dioxide dried to obtain a bacterial cellulose-foamed pore microsphere complex with a microporous structure.

[0035] The microporous structure consists of bacterial cellulose nanofibers of 20–50 nm in diameter, with an average pore size of 1–10 μm. The purified product is freeze-dried or subjected to critical carbon dioxide drying to form the microporous structure.

[0036] In the above preparation method, preferably, the process of further heating and impregnating the bacterial cellulose-foamed porous microsphere composite in the melt of a thermoplastic polymer includes:

[0037] The bacterial cellulose-foamed porous microsphere composite was heated to 60–220°C. When the foaming agent in the foamed porous microspheres began to release gas, the bacterial cellulose-foamed porous microsphere composite was immersed in a thermoplastic polymer melt (the melt temperature of which is determined by the melting temperature of the material itself). After immersion for 10–30 minutes, it was removed and kept at 60–220°C for 20–30 minutes. Then, it was gradually cooled to room temperature to obtain a bacterial cellulose thermoplastic polymer composite foam material with a porous structure.

[0038] In the above preparation method, preferably, the thermoplastic polymer material is the same material as the thermoplastic polymer material in the foamed porous microspheres.

[0039] On the other hand, the present invention also provides a bacterial cellulose thermoplastic polymer composite foam material, which is prepared by the above-described preparation method.

[0040] Preferably, the bacterial cellulose thermoplastic polymer composite foam material has a pore size of 0.5 to 6 mm and the pores are interconnected.

[0041] Furthermore, the present invention also provides the application of the above-mentioned bacterial cellulose thermoplastic polymer composite foam material in building insulation, sound insulation materials, or cushioning packaging materials. For example, the bacterial cellulose thermoplastic polymer composite foam material can be filled into building materials to produce high-performance sound-insulating and heat-insulating building materials; the bacterial cellulose thermoplastic polymer composite foam material can be filled into cushioning packaging materials to produce high-performance cushioning packaging materials.

[0042] The beneficial effects of this invention are:

[0043] This invention employs a preparation method combining a pore-forming agent method and a foaming method. While maintaining the three-dimensional network structure of bacterial cellulose, it produces a bacterial cellulose thermoplastic polymer composite foam material with controllable and uniform pore size. Furthermore, the introduction of thermoplastic polymer materials significantly improves the mechanical properties of the porous composite material. The bacterial cellulose thermoplastic polymer composite foam material prepared by this invention is an environmentally friendly foam material and can be widely used as a porous foam material in fields such as building insulation, soundproofing materials, and cushioning packaging materials. Attached Figure Description

[0044] Figure 1 This is a 50x electron microscope image of the bacterial cellulose thermoplastic polymer composite foam material prepared in Example 4 of the present invention.

[0045] Figure 2 This is a 200x electron microscope image of the bacterial cellulose thermoplastic polymer composite foam material prepared in Example 1 of the present invention. Detailed Implementation

[0046] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0047] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0048] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0049] Example:

[0050] The following embodiments provide a method for preparing a bacterial cellulose thermoplastic polymer composite foam material, which includes the following steps:

[0051] 1. Preparation of foamed porous microspheres:

[0052] In the following embodiments, the foamed porous microspheres have a core-shell structure, with a foaming agent as the core and a thermoplastic polymer material as the outer shell. The preparation method of these foamed porous microspheres is as follows: The thermoplastic polymer material is processed into a thermoplastic hollow microsphere shell structure using existing template methods or microfluidic methods (conventional methods in the art). Then, a foaming agent is injected into the hollow interior of the microsphere shell structure using microneedles to obtain core-shell structured foamed porous microspheres. Table 1 shows the parameters used in preparing the foamed porous microspheres in each embodiment, including the foaming agent, thermoplastic polymer material, microsphere particle size, and dosage.

[0053] Table 1:

[0054]

[0055] 2. Activation treatment of the surface of foamed porous microspheres using biopolymers, specifically including:

[0056] The foamed porous microspheres of Examples 1 to 9 were immersed in a 2wt% gelatin aqueous solution for 5 minutes, and then naturally dried to obtain a layer of gelatin uniformly covering the surface of the foamed porous microspheres.

[0057] 3. Static fermentation culture:

[0058] The foamed porous microspheres after surface activation treatment in Examples 1-9 were placed in petri dishes. The bacterial culture solution was poured into the petri dishes until the liquid level of the bacterial culture solution was 5 mm higher than the surface of the foamed porous microspheres. Static fermentation was carried out for 7 days, and the fermentation temperature was controlled at 30℃.

[0059] The fermentation process used a 50cm high metal petri dish with an open top and 1cm high feet at the bottom edge. The bottom of the dish featured a porous mesh design and a thin silica film on its surface. The culture medium consisted of *Acetobacter xylinum* strain capable of fermenting to obtain bacterial cellulose and a fermentation medium. The *Acetobacter xylinum* strain concentration was approximately 1×10⁻⁶. 6 The fermentation medium was a conventional fermentation medium in the field.

[0060] 4. Purification and drying of fermentation products:

[0061] The fermentation products obtained in Examples 1-9 were immersed in anhydrous ethanol and hydrogen peroxide, respectively, and repeatedly pressed for 3-5 minutes. Then, they were washed in distilled water 3-5 times. This process was repeated 3-7 times to remove the residual culture medium and obtain purified products. The purified products were then freeze-dried at -20°C for 24 hours to obtain bacterial cellulose-foamed porous microsphere complexes with microporous structures corresponding to Examples 1-9. The microporous structure is composed of bacterial cellulose nanofibers of 20-50 nm with an average pore size of 1-10 μm.

[0062] 5. Melt treatment of thermoplastic polymer materials:

[0063] The bacterial cellulose-foamed porous microsphere composites prepared in Examples 1 to 9 were placed in an oven at the high-temperature treatment temperatures corresponding to Examples 1 to 9 in Table 1. When the foaming agent in the foamed porous microspheres began to release gas, the bacterial cellulose-foamed porous microsphere composites were then immersed in the melt of the respective thermoplastic polymer materials corresponding to Examples 1 to 9 in Table 1 for 10 minutes. After being removed, they were placed in the oven at the corresponding high-temperature treatment temperatures of Examples 1 to 9 for 20 minutes and then allowed to cool naturally to room temperature in the oven. The bacterial cellulose thermoplastic polymer composite foam materials of Examples 1 to 9 were obtained. The porous diameter of the bacterial cellulose thermoplastic polymer composite foam materials was 0.5 to 6 mm, and the pores were interconnected.

[0064] Figure 1 This is an electron micrograph of the bacterial cellulose thermoplastic polymer composite foam material prepared in Example 4 of the present invention. Figure 1As can be seen, the average pore size of the porous material is 2.5 mm, and interconnected pores are clearly visible on the pore walls in the figure. Furthermore, the external thermoplastic polymer melt has fused with the bacterial cellulose nanofibers into a unified whole, making the nanofibers virtually invisible. Mechanical strength measurements of this bacterial cellulose thermoplastic polymer composite foam material showed a tensile strength of 80 MPa and a modulus of 600 MPa. In contrast, a pure bacterial cellulose membrane (prepared by soaking the fermentation product in a 3 wt%–6 wt% sodium hydroxide solution, cooking for 1–3 hours, then washing with distilled water until neutral and drying) had a tensile strength of 40 MPa and a modulus of approximately 300 MPa. Therefore, the bacterial cellulose thermoplastic polymer composite foam material of this invention exhibits superior mechanical properties.

[0065] Figure 2 This is an electron micrograph of the bacterial cellulose thermoplastic polymer composite foam material prepared in Example 1 of the present invention. Figure 2 As can be seen, the average pore size is 530 μm, and interconnected pores are clearly visible on the pore walls. Furthermore, the external thermoplastic polymer melt has fused with the bacterial cellulose nanofibers, making the nanofibers virtually invisible. Mechanical strength measurements of this bacterial cellulose thermoplastic polymer composite foam material showed a tensile strength of 200 MPa and a modulus of 800 MPa. In contrast, the pure bacterial cellulose membrane had a tensile strength of approximately 40 MPa and a modulus of approximately 300 MPa. Therefore, the bacterial cellulose thermoplastic polymer composite foam material of this invention exhibits superior mechanical properties.

Claims

1. A method for preparing a bacterial cellulose thermoplastic polymer composite foam material, comprising the following steps: The surface of foamed porous microspheres was activated using biopolymer compounds; The surface-activated foamed porous microspheres were statically fermented in the bacterial culture medium. The liquid level of the bacterial culture medium was 1-5 mm higher than the surface of the foamed porous microspheres. After purification and drying, the fermentation product was used to obtain a bacterial cellulose-foamed porous microsphere composite with a microporous structure. The composite was further heated and impregnated in the melt of a thermoplastic polymer material. After cooling, a bacterial cellulose thermoplastic polymer composite foam material was obtained. The foamed porous microspheres have a core-shell structure, with the core being a foaming agent and the outer shell being a thermoplastic polymer material.

2. The preparation method according to claim 1, wherein, The foaming agent includes one or more of 2,2'-azobisisobutyronitrile, benzenesulfonyl hydrazine, p-toluenesulfonyl hydrazine, N,N'-dimethyl-N,N'-dinitrosoterephthalamide, 1,3-benzene disulfonyl hydrazine, 3,3'-disulfonyl hydrazine diphenyl sulfone, azoaminobenzene, 4,4'-oxobisbenzenesulfonyl hydrazine, azodicarboxamide, and barium azodicarboxate.

3. The preparation method according to claim 1, wherein, The thermoplastic polymer material includes one or more of polycaprolactone, polyurethane, polybutylene succinate, polylactic acid, polyhydroxybutyrate, nylon, and polypropylene terephthalate.

4. The preparation method according to any one of claims 1 to 3, wherein, The particle size of the foamed porous microspheres is 200–5000 μm; wherein the mass of the foaming agent accounts for 1–30 wt% of the mass of the foamed porous microspheres.

5. The preparation method according to any one of claims 1 to 3, wherein, The method for preparing the foamed porous microspheres includes: Thermoplastic polymer materials are processed into thermoplastic hollow microsphere shell structures using existing template methods or microfluidic methods. Then, a foaming agent is injected into the hollow interior of the microsphere shell structure using microneedles to obtain core-shell structured foamed porous microspheres.

6. The preparation method according to claim 4, wherein, The method for preparing the foamed porous microspheres includes: Thermoplastic polymer materials are processed into thermoplastic hollow microsphere shell structures using existing template methods or microfluidic methods. Then, a foaming agent is injected into the hollow interior of the microsphere shell structure using microneedles to obtain core-shell structured foamed porous microspheres.

7. The preparation method according to claim 1, wherein, The biopolymers include one or more of gelatin, hyaluronic acid, alginate, pectin, and silk protein.

8. The preparation method according to claim 1 or 7, wherein, The process of activating the surface of foamed porous microspheres using biopolymers includes: Prepare an aqueous solution of biological macromolecules by dissolving them in water. Foamed porous microspheres were immersed in an aqueous solution of a biopolymer compound, removed and air-dried to uniformly coat the surface of the foamed porous microspheres with a layer of biopolymer compound.

9. The preparation method according to claim 8, wherein, The concentration of the aqueous solution of the biopolymer compound is 0.5–3 wt%. The immersion treatment time is 1 to 5 minutes.

10. The preparation method according to claim 1, wherein, The bacterial culture medium consists of a bacterial strain capable of fermenting to obtain bacterial cellulose and a fermentation medium. The bacterial strains capable of fermenting to obtain bacterial cellulose include one or more of Acetobacter xylinum, Rhizobium, Micrococcus occulta, Pseudomonas aeruginosa, Alcaligenes, Aerobacterium, and nitrogen-fixing bacteria.

11. The preparation method according to claim 1 or 10, wherein, The process of static fermentation culture of surface-activated foamed porous microspheres in bacterial culture medium includes: The surface-activated foamed porous microspheres were placed in a petri dish, and the bacterial culture solution was poured into the petri dish until the liquid level of the bacterial culture solution was 1-5 mm higher than the surface of the foamed porous microspheres. Static culture was carried out for 1-7 days at a fermentation temperature of 30-40℃.

12. The preparation method according to claim 1, wherein, The process of purifying and drying the fermentation product includes: The fermentation product was repeatedly pressed and immersed in anhydrous ethanol and hydrogen peroxide to wash away the residue of the culture medium and obtain the purified product. Then, the purified product was freeze-dried or critical carbon dioxide dried to obtain a bacterial cellulose-foamed pore microsphere complex with a microporous structure. Among them, the microporous structure is a microporous structure with an average pore size of 1-10 μm composed of bacterial cellulose nanofibers of 20-50 nm.

13. The preparation method according to claim 11, wherein, The process of purifying and drying the fermentation product includes: The fermentation product was repeatedly pressed and immersed in anhydrous ethanol and hydrogen peroxide to wash away the residue of the culture medium and obtain the purified product. Then, the purified product was freeze-dried or critical carbon dioxide dried to obtain a bacterial cellulose-foamed pore microsphere complex with a microporous structure. Among them, the microporous structure is a microporous structure with an average pore size of 1-10 μm composed of bacterial cellulose nanofibers of 20-50 nm.

14. The preparation method according to any one of claims 1, 12-13, wherein, The process of further heating and impregnating the bacterial cellulose-foamed porous microsphere composite in a melt of thermoplastic polymer includes: The bacterial cellulose-foamed porous microsphere composite was heated to 60–220°C. When the foaming agent in the foamed porous microspheres began to release gas, the bacterial cellulose-foamed porous microsphere composite was immersed in the melt of thermoplastic polymer material for 10–30 min. After immersion, it was removed and kept at 60–220°C for 20–30 min. Then, it was gradually cooled to room temperature to obtain a bacterial cellulose thermoplastic polymer composite foam material with a porous structure.

15. A bacterial cellulose thermoplastic polymer composite foam material, which is prepared by the preparation method described in any one of claims 1 to 14.

16. The bacterial cellulose thermoplastic polymer composite foam material according to claim 15, wherein, The porous pores of this bacterial cellulose thermoplastic polymer composite foam material are 0.5–6 mm in diameter and are interconnected.

17. The application of the bacterial cellulose thermoplastic polymer composite foam material according to claim 15 or 16 in building insulation, sound insulation or cushioning packaging materials.

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