High-hardness and bend-resistant organic-inorganic composite film, and preparation method and application thereof

Abstract

This invention discloses a high-hardness, flexurally resistant organic-inorganic composite membrane, its preparation method, and its applications, belonging to the field of organic-inorganic composite material technology. This invention uses calcium phosphate oligomers as an inorganic precursor and bacterial cellulose as an organic precursor. Through organic and inorganic blending and filtration followed by hot pressing, the calcium phosphate oligomers are induced to polymerize in situ within the bacterial cellulose organic network, forming an inorganic network. This allows for the construction of an interpenetrating organic framework inorganic network at the nanoscale, and reversible interfacial bonding sites are formed through the electrostatic interaction between calcium ions and hydroxyl groups. The inorganic network provides rigid support, requiring a larger load to deform under external forces, thereby improving the membrane's stiffness and hardness. During cyclic loading, the interfacial bonding points between the organic and inorganic networks can break and reform, achieving stress dissipation and redistribution, thus improving the membrane's flexural fatigue life.

Description

Technical Field

[0001] This invention relates to the field of organic-inorganic composite materials technology, specifically to a high-hardness, bend-resistant organic-inorganic composite membrane, its preparation method, and its application. Background Technology

[0002] Organic-inorganic composite materials have attracted much attention due to their ability to combine the superior properties of both organic and inorganic phases. Currently, introducing rigid inorganic phases into polymer matrices is a common strategy to improve material hardness. Specific technical approaches include filling the polymer matrix with inorganic nanoparticles such as silica, alumina, and calcium carbonate, or constructing composite materials containing inorganic nanosheets and nanofibers. However, these inorganic components are prone to agglomeration due to their inherent high surface energy and weak interactions with the organic matrix, forming interfacial defects. These defects easily lead to stress concentration under external forces, which in turn induces the formation and propagation of microcracks. Under cyclic loading, this process intensifies, ultimately reducing the flexural fatigue life of the material.

[0003] To overcome the aforementioned bottlenecks, existing technologies mainly focus on improving the dispersibility of inorganic fillers in organic matrices. Patent CN102086280A discloses a method of melt-blending calcium carbonate nanoparticles and a β-crystal nucleating agent with maleic anhydride-grafted polypropylene, followed by dilution and dispersion in a polypropylene matrix to improve particle dispersibility in the polymer matrix. This method can alleviate the agglomeration of inorganic particles and reduce interfacial defects, but the inorganic phase exists in the polymer matrix as dispersed particles, failing to form a three-dimensional stress transfer network. Therefore, it is difficult to achieve the same effect as organic double networks, which increase mechanical hardness and fatigue resistance through network interpenetration and sacrificial bond mechanisms.

[0004] Constructing organic-inorganic interpenetrating networks is a potential approach to solving the aforementioned problems. For example, invention patent CN103861153A discloses a method for preparing a three-dimensional network structure of carbon nanofiber composite β-phosphate, comprising: purifying bacterial cellulose and stirring it in a calcium nitrate solution, slowly adding diammonium hydrogen phosphate solution while controlling the pH value of the system, aging it for 12-24 hours after the reaction is complete, freeze-drying it, and then heating the dried material in an atmosphere furnace, wherein the freeze-drying temperature is -20 to -80℃ and the heating temperature is 850 to 1100℃, and after cooling, a composite material with a three-dimensional network structure and uniformly distributed β-phosphate on the carbon fibers is obtained. However, this method requires extreme preparation conditions and is prone to causing the network structure to collapse during the heating process.

[0005] Furthermore, in inorganic salt solutions, the formation of inorganic phases (especially inorganic ionic compounds) is typically dominated by classical nucleation-growth mechanisms, readily forming nanoparticles rather than growing into inorganic network structures under the control of organic networks. This makes it difficult to construct inorganic networks with interpenetrating organic frameworks at the nanoscale, thus limiting further improvements in the hardness of composite materials and restricting their flexural fatigue resistance.

[0006] Therefore, it is still necessary to explore a method for preparing composite materials that can achieve interpenetration of organic and inorganic networks at the nanoscale, in order to develop composite membrane materials with both high hardness and bending resistance. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention proposes a high-hardness, bend-resistant organic-inorganic composite membrane, its preparation method, and its application. By in-situ polymerization of ultra-small calcium phosphate oligomers in a bacterial cellulose nanofiber network, an organic-inorganic interpenetrating nanonetwork structure is constructed, achieving a synergistic effect of high hardness and high bend durability in the material.

[0008] A method for preparing a high-hardness, bend-resistant organic-inorganic composite membrane includes the following steps: (1) Prepare calcium phosphate oligomers as precursors and add them to bacterial cellulose aqueous dispersion to form a mixture; (2) The mixture is filtered to form a membrane and then subjected to hot pressing to obtain an organic-inorganic composite membrane.

[0009] This invention utilizes calcium phosphate oligomers as an inorganic precursor and bacterial cellulose as an organic template. Through organic-inorganic blending and filtration followed by hot pressing, the calcium phosphate oligomers are induced to polymerize in situ within the bacterial cellulose organic network, forming an inorganic network. This results in the construction of an interpenetrating organic framework inorganic network at the nanoscale, with reversible interfacial bonding sites formed through electrostatic interactions between calcium ions and hydroxyl groups. The inorganic network provides rigid support, requiring a greater load to deform the composite membrane under external forces, thereby improving the membrane's stiffness and hardness. During cyclic loading, the interfacial bonding points between the organic and inorganic networks can break and reform, achieving stress dissipation and redistribution, thus improving the membrane's flexural fatigue life.

[0010] Preferably, the process of preparing calcium phosphate oligomers in step (1) includes: A calcium source is dissolved in an organic solvent to form a calcium source solution. A capping agent and phosphoric acid are added sequentially to the calcium source solution to react and prepare a colloid. The colloid is redispersed in an organic solvent and concentrated to obtain calcium phosphate oligomers.

[0011] Preferably, the calcium source is one of calcium chloride, calcium nitrate, and calcium bromide; The terminator is one of triethylamine, tripropylamine, and tripentylamine; The organic solvent is one of ethanol, n-propanol, and n-butanol.

[0012] More preferably, the molar ratio of calcium ions in the calcium source to phosphorus in the phosphoric acid is 1~3.5:1; The molar ratio of the capping agent to calcium ions in the calcium source is 10~25:1.

[0013] By limiting the above molar ratio, ultra-small calcium phosphate oligomers with high reactivity can be obtained, providing a suitable inorganic precursor for subsequent in-situ polymerization in an organic network to form an inorganic network structure.

[0014] More preferably, the molar ratio of calcium ions to phosphorus in phosphoric acid is 1~2:1; and the molar ratio of the capping agent to calcium ions in the calcium source is 15~22:1.

[0015] Preferably, the size of the calcium phosphate oligomer is 1~1.5 nm.

[0016] The calcium phosphate oligomers in the aforementioned size range exhibit high reactivity and can bind tightly to bacterial cellulose, which is beneficial for the regulation of subsequent inorganic ion polymerization behavior and thus promotes the formation of inorganic networks.

[0017] Preferably, the bacterial cellulose has a diameter of 30-60 nm and an aspect ratio of 500-1000.

[0018] Bacterial cellulose of this size and aspect ratio serves as the basis for an organic network, which is conducive to the formation of a three-dimensional nanofiber network structure. On the one hand, this three-dimensional nanofiber network structure can induce inorganic ionic oligomers to polymerize in situ within the network to form an inorganic network. On the other hand, its high specific surface area also provides sufficient interfacial binding sites.

[0019] Preferably, the concentration of the bacterial cellulose aqueous dispersion in step (1) is 1~3 mg / mL.

[0020] Preferably, the mixing temperature in step (1) is 15~40℃ and the mixing time is 12~72 h to ensure that the calcium phosphate oligomers and bacterial cellulose nanofibers are mixed evenly.

[0021] Preferably, the hot pressing temperature in step (2) is 40~100°C, the hot pressing pressure is 0.2~5 MPa, and the hot pressing time is 10~120 min.

[0022] During the drying and hot-pressing process, the calcium phosphate oligomers obtained by vacuum filtration are connected and polymerized through ionic bonds, gradually generating an inorganic phase of calcium phosphate with a three-dimensional network structure. This phase interpenetrates with the bacterial cellulose organic network, forming a composite membrane with an organic-inorganic interpenetrating network structure.

[0023] The present invention also provides a high-hardness, bend-resistant organic-inorganic composite membrane prepared by the preparation method described above.

[0024] The organic-inorganic composite membrane prepared by the above method is composed of bacterial cellulose and calcium phosphate, both of which are environmentally friendly components. Bacterial cellulose can be degraded by enzymes such as cellulase, and calcium phosphate can be degraded by acidic solutions. Therefore, in an acidic buffer solution containing cellulase, the composite membrane of this invention can be completely degraded within a few hours, exhibiting good degradability and being more environmentally friendly than traditional petroleum-based polymer plastics.

[0025] Preferably, based on the total solid mass of the organic-inorganic composite membrane, the mass fraction of calcium phosphate is 72-80 wt%, and the mass fraction of bacterial cellulose is 20-28 wt%.

[0026] Within the above-mentioned mass fraction range, the inorganic phase can form an inorganic network under the regulation of the organic nanofiber template. The stiffness and hardness of the prepared composite membrane material can reach a high level, while maintaining good bending durability, so that the material achieves a better balance between high hardness and high bending cycle durability.

[0027] The present invention also provides the application of the aforementioned organic-inorganic composite membrane in the preparation of bending strain sensors.

[0028] Preferably, the preparation of the bending strain sensor includes: dispersing conductive filler in an aqueous solution containing carboxymethyl cellulose to prepare a conductive coating, coating the conductive coating on the surface of the organic-inorganic composite membrane, drying to form a conductive path, and bonding wires to both ends of the conductive path and connecting it to an electrochemical workstation.

[0029] Preferably, when the bending strain sensor is used, the relative distance and contact state between the conductive fillers change when the organic-inorganic composite membrane undergoes cyclic bending deformation, resulting in a repeatable change in the resistance of the conductive network. By monitoring the change in resistance or current signal with the degree of bending, the bending strain can be detected.

[0030] Compared with the prior art, the present invention has the following beneficial effects: (1) By successfully constructing an organic-inorganic interpenetrating network structure at the nanoscale, the present invention increases the volume fraction of the organic-inorganic interface, effectively avoiding the problems of inorganic nanoparticle agglomeration and stress concentration in traditional particle-filled systems, and enabling external forces to be transmitted and dispersed in multiple directions through the three-dimensional interpenetrating network, thereby preventing the initiation and propagation of cracks in the material during cyclic bending.

[0031] (2) The composite membrane of the present invention achieves a combination of high hardness and high flexural cycle life on a macroscopic scale, overcoming the contradiction between improving hardness and flexural durability in traditional inorganic nanoparticle-filled composite materials. This material can withstand 20,000 bends without breaking when the bending radius is 5 mm.

[0032] (3) The material of the present invention is composed of naturally derived bacterial cellulose and calcium phosphate, which can be completely degraded within hours in the presence of an acidic buffer solution containing cellulase. This property makes it a promising alternative to traditional petroleum-based electronic substrate materials and suitable for the field of green electronic devices. Attached Figure Description

[0033] Figure 1 The mechanism diagram of the organic-inorganic composite membrane provided by the present invention.

[0034] Figure 2 Transmission electron microscopy image of the organic-inorganic composite film prepared in Example 1.

[0035] Figure 3 The hardness and modulus of the organic-inorganic composite membrane prepared in Example 1.

[0036] Figure 4 Optical photographs of the organic-inorganic composite film prepared in Example 1 when it undergoes torsion and bending deformation.

[0037] Figure 5 Images and force-cycle curves of the organic-inorganic composite membrane prepared in Example 1 during cyclic bending tests.

[0038] Figure 6 Optical photographs and mass changes of the organic-inorganic composite membrane prepared in Example 1 during its degradation process.

[0039] Figure 7 The organic-inorganic composite film prepared in Example 1 is used as a substrate material for electronic devices. The curve of current change with the number of cycles during periodic cyclic bending is shown. Detailed Implementation

[0040] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art.

[0041] All raw materials were purchased from the market. Among them, bacterial cellulose was purchased from Guilin Qihong Technology Co., Ltd., with product number BCY00809.

[0042] The hardness test method for the composite film in this embodiment is as follows: The sample is fixed on a sample stage, and the surface hardness and Young's modulus of the sample are tested using a nanoindenter. The instrument is equipped with a Berkovich tip (tip radius approximately 20 nm). Before each test, calibration is performed using a silica standard, and thermal drift is corrected to below 0.05 nm / s. During the test, the maximum load is set to 10 mN, and the holding time is 2 s. The applied load force and the depth of indentation into the sample are continuously recorded by computer.

[0043] The test method for the bending durability of the composite membrane in the embodiment is as follows: the prepared composite membrane is cut into strips with a width of 12 mm and a thickness of 60 µm, and cyclically bent on a universal testing machine with a bending radius of 5 mm and a loading speed of 1000 mm / min.

[0044] Example 1 The method for preparing the organic-inorganic composite membrane in this embodiment is as follows: calcium phosphate oligomers are added as inorganic precursors to an aqueous dispersion of bacterial cellulose to form a homogeneous mixture; during filtration and subsequent hot pressing, the calcium phosphate oligomers are induced to polymerize in situ within the bacterial cellulose network, constructing an inorganic calcium phosphate network interpenetrating with bacterial cellulose nanofibers. Specifically: (1) Preparation of calcium phosphate oligomers: 5.88 g of calcium chloride dihydrate was dissolved in 800 mL of anhydrous ethanol to obtain a transparent calcium source solution. 88.97 mL of triethylamine was added under stirring, and after mixing evenly, a phosphoric acid ethanol solution (1.98 mL of phosphoric acid dissolved in 40 mL of ethanol) was added. The mixture was stirred at room temperature for 12 h to ensure complete reaction. After the reaction, the mixture was centrifuged at 8000 rpm for 10 min, and the colloid was collected and washed three times with ethanol to remove excess triethylamine. The washed colloid was redispersed in ethanol, and the solid content was adjusted to obtain calcium phosphate oligomers with a mass concentration of approximately 10 mg / mL. The size of the prepared calcium phosphate oligomers was approximately 1.17 nm.

[0045] Preparation of a high-hardness, bend-resistant organic-inorganic composite membrane: 40 mL of the above-mentioned high-concentration calcium phosphate oligomer was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, and 50 mL of a bacterial cellulose aqueous dispersion with a mass concentration of 2 mg / mL was added. The mixture was magnetically stirred at room temperature for 2 days to allow the calcium phosphate oligomers to fully mature, resulting in a light blue homogeneous mixture. The mixture was then poured onto an aqueous filter membrane and vacuum filtered to form a membrane. The membrane was then placed in a flatbed hot press and hot-pressed at 60℃ and 1 MPa for 60 min to obtain an organic-inorganic composite membrane with a thickness of approximately 60 μm.

[0046] like Figure 1 The diagram illustrates the principle of preparing an organic-inorganic composite membrane. Calcium phosphate oligomers polymerize in situ within organic nanofibers to form an inorganic network, which then interpenetrates with the organic nanofiber network, thus creating an organic-inorganic interpenetrating double network.

[0047] like Figure 2 As shown, the inorganic components did not exhibit obvious aggregation, but rather displayed the characteristics of a network structure. Figure 2 (See Figure A in the diagram). Furthermore, after selectively dissolving and removing the calcium phosphate phase under acidic conditions, retained bacterial cellulose nanofibers (…) were observed. Figure 2 Figure B in the figure illustrates the presence of an organic-inorganic dual-network structure in the original material. The composite membrane prepared in this embodiment contains 77.5 wt% calcium phosphate and 22.5 wt% bacterial cellulose.

[0048] like Figure 3 As shown, nanoindentation tests were performed on the composite membrane prepared in Example 1. The results showed that the composite membrane had a hardness of 0.74 GPa and a modulus of 17.72 GPa. These mechanical properties are significantly better than those of pure bacterial cellulose membranes and composite membranes prepared by simple blending of hydroxyapatite nanoparticles and bacterial cellulose.

[0049] like Figure 4 As shown, the composite membrane prepared in Example 1 exhibits excellent flexibility and can withstand helical torsion and bending deformation without breaking at room temperature.

[0050] like Figure 5 Figure A in the middle and Figure 5 As shown in Figure B, after the composite membrane prepared in Example 1 was subjected to 20,000 cycles of bending with a bending radius of 5 mm, the mechanical properties of the composite membrane did not change significantly, indicating that it has good resistance to bending fatigue.

[0051] To evaluate the degradation performance of the composite membrane prepared in this embodiment, it was subjected to degradation experiments in an acidic buffer solution containing cellulase. Optical photographs of the degradation process are shown below. Figure 6Figure A shows that the composite membrane decomposes into fragments after 3 hours and completely decomposes after 5 hours, indicating that the material is biodegradable. The corresponding changes in material weight percentage over time are shown in Figure [Figure Number]. Figure 6 As shown in Figure B, the composite membrane degrades rapidly at the beginning of the degradation process, but the rate slows down in the latter half, with almost 100% weight loss after 5 hours. The weight loss results are consistent with... Figure 6 The results in Figure A are consistent with the observation that the composite membrane disappeared after 5 hours in the cellulase solution. These results indicate that the composite membrane is a green and biodegradable material.

[0052] As can be seen from this embodiment, by using ultra-small calcium phosphate oligomers to polymerize in situ in bacterial cellulose networks, an organic-inorganic interpenetrating network structure can be constructed at the nanoscale, thereby achieving a synergy of high hardness and high bending durability on a macroscopic scale.

[0053] This invention relates to the application of a high-hardness, bend-resistant organic-inorganic composite membrane in a bending strain sensor.

[0054] Electrode preparation: 0.2 g carbon black, 0.1 g carboxymethyl cellulose, and 14 mL deionized water were added to a 50 mL beaker, and a uniformly dispersed conductive slurry was obtained by ultrasonic treatment. The composite film prepared in Example 1 was cut into strips of 60 mm × 12 mm. The conductive slurry was uniformly coated onto one side of the composite film using a scraping method. The strips were dried at 105 °C for 90 min, and the coating-drying process was repeated three times to obtain a uniform and continuous conductive layer. Copper wires were bonded to both ends of the film sample coated with the conductive layer using conductive adhesive to serve as electrodes. Wires were then led out to obtain the bending strain sensor.

[0055] Bending sensing performance test: The above sensor was clamped on a universal testing machine and subjected to periodic bending-recovery at a set bending radius and bending speed, while the current change was recorded in real time using an electrochemical workstation.

[0056] like Figure 7 As shown, the sensor can generate stable and repeatable current response signals at different bending speeds. After 20,000 bending-recovery cycles, the signal amplitude remains essentially unchanged, indicating that the composite material of this invention can still stably monitor bending strain over a long period of time while serving as an electronic substrate and protective layer.

[0057] Example 2 Example 2 is the same as Example 1, except that: when preparing the composite membrane, 30 mL of calcium phosphate oligomer with a mass concentration of about 10 mg / mL is used to prepare the organic-inorganic composite membrane.

[0058] The prepared organic-inorganic composite membrane contained 73 wt% calcium phosphate and had a hardness of 0.60 GPa.

[0059] Example 3 Example 3 is the same as Example 1, except that: when preparing the composite membrane, 50 mL of calcium phosphate oligomer with a mass concentration of about 10 mg / mL is used to prepare the organic-inorganic composite membrane.

[0060] The prepared organic-inorganic composite membrane contained 79.2 wt% calcium phosphate and had a hardness of 0.72 GPa.

[0061] Example 4 Example 4 is the same as Example 1, except that when synthesizing calcium phosphate oligomers, the ratio of phosphoric acid to ethanol solution is adjusted to dissolve 1.37 mL of phosphoric acid in 40 mL of ethanol.

[0062] The prepared calcium phosphate oligomers had a size of 1.45 nm, and the prepared organic-inorganic composite membrane had a hardness of 0.62 GPa.

[0063] Example 5 Example 5 is the same as Example 1, except that the amount of triethylamine added is 55.75 mL when synthesizing calcium phosphate oligomers.

[0064] The prepared calcium phosphate oligomers had a size of 1.36 nm, and the prepared organic-inorganic composite membrane had a hardness of 0.64 GPa.

[0065] Example 6 Example 6 is the same as Example 1, except that the hot pressing temperature is adjusted to 80°C.

[0066] The hardness of the prepared organic-inorganic composite membrane is 0.66 GPa.

[0067] Comparative Example 1 (Nanoparticle Composite) 0.4 g of hydroxyapatite powder was added to 50 mL of bacterial cellulose aqueous dispersion with a mass concentration of 2 mg / mL, and magnetically stirred for 2 days at room temperature to obtain a white mixture. The mixture was then poured onto an aqueous filter membrane and vacuum filtered to form a membrane. The membrane was then placed in a flatbed hot press and hot-pressed at 60 °C and 1 MPa for 60 min to obtain a composite membrane as a control.

[0068] The hardness of the resulting composite membrane was 0.14 GPa. When tested at a bending radius of 5 mm, the composite membrane broke after 35 bends.

[0069] Comparative Example 2 Comparative Example 2 is the same as Example 1, except that the amount of triethylamine added is 5.58 mL when preparing calcium phosphate oligomers.

[0070] The obtained calcium phosphate nanoparticles have a size of 23.78 nm, and the prepared organic-inorganic composite film has a hardness of 0.29 GPa.

[0071] Comparative Example 3 Comparative Example 3 is the same as Example 1, except that: when preparing the composite membrane, 10 mL of calcium phosphate oligomer with a mass concentration of about 10 mg / mL was used to prepare the organic-inorganic composite membrane.

[0072] The prepared organic-inorganic composite membrane contained 34.2 wt% calcium phosphate and had a hardness of 0.34 GPa.

[0073] Comparative Example 4 Comparative Example 4 is the same as Example 1, except that the hot pressing temperature is adjusted to 120°C.

[0074] The hardness of the prepared organic-inorganic composite membrane is 0.40 GPa.

[0075] Comparative Example 5 Comparative Example 5 is the same as Example 1, except that calcium phosphate oligomers are not prepared. The test results for modulus and hardness are as follows: Figure 3 As shown, this invention successfully constructs an organic-inorganic interpenetrating network structure at the nanoscale, thereby increasing the volume fraction of the organic-inorganic interface. This allows external forces to be transmitted and dispersed in multiple directions through the three-dimensional interpenetrating network, thus preventing the initiation and propagation of cracks in the material during cyclic bending.

[0076] The above embodiments illustrate that the high-hardness, bend-resistant organic-inorganic composite film of the present invention can not only serve as a high-hardness protective structural material for electronic devices, but also, by introducing a conductive layer on the surface, construct bend-resistant electronic devices with strain sensing function.

[0077] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-hardness, bend-resistant organic-inorganic composite membrane, characterized in that, Includes the following steps: (1) Prepare calcium phosphate oligomers as precursors and add them to bacterial cellulose aqueous dispersion to form a mixture; (2) The mixture is filtered to form a membrane and then subjected to hot pressing to obtain an organic-inorganic composite membrane.

2. The preparation method according to claim 1, characterized in that, The process of preparing calcium phosphate oligomers in step (1) includes: A calcium source is dissolved in an organic solvent to form a calcium source solution. A capping agent and phosphoric acid are added sequentially to the calcium source solution to react and prepare a colloid. The colloid is redispersed in an organic solvent and concentrated to obtain calcium phosphate oligomers.

3. The preparation method according to claim 2, characterized in that, The calcium source is one of calcium chloride, calcium nitrate, and calcium bromide; The terminator is one of triethylamine, tripropylamine, and tripentylamine; The organic solvent is one of ethanol, n-propanol, and n-butanol.

4. The preparation method according to claim 2, characterized in that, The molar ratio of calcium ions in the calcium source to phosphorus in the phosphoric acid is 1~3.5:1; The molar ratio of the capping agent to calcium ions in the calcium source is 10~25:

1.

5. The preparation method according to claim 1, characterized in that, The size of calcium phosphate oligomers is 1~1.5 nm; Bacterial cellulose has a diameter of 30-60 nm and an aspect ratio of 500-1000.

6. The preparation method according to claim 1, characterized in that, The mixing temperature in step (1) is 15~40℃ and the mixing time is 12~72 h.

7. The preparation method according to claim 1, characterized in that, The hot pressing temperature in step (2) is 40~100°C, the hot pressing pressure is 0.2~5 MPa, and the hot pressing time is 10~120 min.

8. The high-hardness, bend-resistant organic-inorganic composite membrane prepared by the preparation method according to any one of claims 1-7.

9. The high-hardness, bend-resistant organic-inorganic composite membrane according to claim 8, characterized in that, Based on the total solid mass of the organic-inorganic composite membrane, the mass fraction of calcium phosphate is 72-80 wt%, and the mass fraction of bacterial cellulose is 20-28 wt%.

10. The application of the high-hardness, bend-resistant organic-inorganic composite membrane according to claim 9 in the preparation of a bending strain sensor.

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