Bio-based resin vacuum bag film and preparation method thereof

Abstract

The invention discloses a bio-based resin vacuum bag film and a preparation method thereof. The bio-based resin vacuum bag film comprises the following raw materials: 100 parts of bio-based resin and 10-15 parts of core-shell particles, the bio-based resin is prepared by taking pyromellitic dianhydride, bio-based pentamethylene diamine and C12 diamine as monomers through polymerization and imidization reaction; the core of the core-shell particle is a polysiloxane elastomer, the shell of the core-shell particle is polymethyl methacrylate, and an epoxy group is grafted on the shell layer of the polymethyl methacrylate; the core-shell particles are dispersed in the bio-based resin after the bio-based resin is prepared into polyamide acid and before imidization, and the specific bio-based main chain structure, the reactive core-shell particles and the specific adding time are tightly matched, so that the obtained bio-based vacuum bag film has high heat resistance, high flexibility and high airtight reliability.

Description

Technical Field

[0001] This application relates to the utilization of recycled plastics, and in particular to a bio-based resin vacuum bag film and its preparation method. Background Technology

[0002] In the aerospace field, the manufacturing of composite components commonly employs autoclave or oven vacuum bag molding processes. In this process, the vacuum bag film serves as a crucial auxiliary material. Its function is to create a sealed negative pressure environment with the mold during the curing process. By applying uniform pressure, it ensures tight fiber arrangement, thorough resin impregnation, and the elimination of internal air bubbles in the composite component, thereby obtaining a high-quality structural part. Therefore, the performance of the vacuum bag film directly affects the success or failure of the component, and it must meet extremely stringent requirements: excellent high-temperature resistance, extremely high flexibility and elongation at break, and absolute airtightness.

[0003] Currently, the mainstream material for vacuum bag films used in this field is polyimide (PI), which is widely used due to its excellent heat resistance, mechanical strength, and chemical stability. However, traditional polyimide films also have significant limitations: Firstly, the rigid aromatic ring structure of its molecular chain results in inherent brittleness of the material, with typically low elongation at break. This brittleness makes the film highly susceptible to microcracks or ruptures due to bending and stretching when laid in molds with complex geometries such as deep cavities and sharp corners, leading to vacuum leaks and the scrapping of expensive components.

[0004] Secondly, the raw materials for existing high-performance polyimide films are almost entirely derived from non-renewable petroleum resources, which contradicts the global advocacy of green and sustainable development.

[0005] To improve the brittleness of polyimide, existing technologies typically employ the addition of toughening agents, such as introducing rubber elastomers or thermoplastic powders. However, these methods face new challenges when applied to high-temperature vacuum bag applications: most flexible toughening components have significantly lower heat resistance than the polyimide matrix, and are prone to degradation or volatilization during high-temperature curing, not only losing their toughening effect but also potentially contaminating the component surface. More importantly, there is often poor compatibility between the toughening agent and the polyimide matrix, resulting in weak interfacial bonding. Under high temperatures and stress, interfacial delamination easily occurs, becoming a leakage point for the vacuum bag and severely compromising its core airtightness requirement.

[0006] On the other hand, with the development of bio-based materials technology, attempting to partially replace petroleum-based monomers with biomass raw materials to synthesize polyimides has become a research trend. However, polyimide films prepared in this way usually face the dilemma of not being able to balance heat resistance and flexibility: the aliphatic segments introduced to increase the bio-based content often lower the glass transition temperature of the material, making it difficult to meet the requirements of high-temperature curing; while in order to ensure heat resistance, the brittleness of the material becomes more prominent.

[0007] Therefore, there is an urgent need in this field for a vacuum bag film that combines heat resistance, extremely high flexibility, reliable airtightness, green sustainability, and significant bio-based content, in order to meet the aerospace industry's production needs for complex composite material components and its green and sustainable production philosophy. Summary of the Invention

[0008] To meet the production needs of complex composite material components in aerospace and the production concept of green and sustainable development, a bio-based resin vacuum bag film and its preparation method are provided.

[0009] The first inventive objective of this invention is achieved through the following technical solution: A bio-based resin vacuum bag film, comprising the following parts by weight of raw materials: 100 parts of bio-based resin 10-15 parts of core-shell particles; The bio-based resin is prepared by polymerization and imidization reaction using pyromellitic dianhydride, bio-based pentanediamine, and C12 diamine as monomers. The core-shell particle has a core of polysiloxane elastomer and a shell of polymethyl methacrylate, wherein the polymethyl methacrylate shell is grafted with reactive functional groups, the reactive functional groups being epoxy groups. The core-shell particles are dispersed in the bio-based resin after polyamic acid is prepared and before imidization.

[0010] By adopting the above technical solution, using bio-based resin as the base material, and employing pyromellitic dianhydride, bio-based pentanediamine, and C... 12 The diamine is obtained by polymerization of three substances, and a flexible C is introduced. 12 Diamine achieves an alternating arrangement of "rigid segments" and "flexible segments" on the molecular chain. The rigid segments are responsible for high temperature resistance, while the flexible segments are responsible for high elasticity, thus overcoming the brittleness of traditional polyimide. Then, the core-shell particles used for toughening were specifically designed. The core innovation lies in the introduction of reactive epoxy functional groups into the shell layer and the precise control of the timing of addition and reaction. The core-shell particles are added and uniformly dispersed in the system during the polyamic acid precursor stage of the bio-based resin. During the subsequent imidization curing process at a higher temperature, before the polymethyl methacrylate shell undergoes thermal decomposition, the epoxy groups on its surface can undergo an in-situ chemical reaction with the abundant carboxyl groups on the polyamic acid molecular chain to form a strong covalent bond.

[0011] The pre-established strong interfacial chemical bonds solve the problem of weak interfaces that are easily generated in traditional physical blending. Even if the polymethyl methacrylate shell decomposes due to subsequent high-temperature treatment, the decomposition fragments are "anchored" in the forming three-dimensional polyimide network by covalent bonds. This not only prevents the formation of microscopic defects and leakage points, but also forms a strong and tough molecular-level transition layer.

[0012] The "bonding first, then decomposition" mechanism ensures that the vacuum bag film achieves excellent toughening effect without compromising its airtightness, meeting the stringent requirements of the aerospace field for high reliability of auxiliary materials.

[0013] In summary, the "specific bio-based main chain structure," "reactive core-shell particles," and "specific addition timing" in this application work closely together. The presence of the rigid dianhydride framework and chemical crosslinking points ensures the high-temperature resistance of the film. The flexible segments embedded in the bio-resin main chain fundamentally improve the mobility of the chain segments and endow the material with basic toughness. The core-shell particles, bonded by chemical reactions, act as efficient stress concentration points and energy absorbers. Under external force, they induce crazes and shear bands, consuming a large amount of energy. Their interaction greatly enhances the elongation at break of the film. As a result, the bio-based vacuum bag film has high heat resistance, high flexibility, and high airtight reliability.

[0014] Optionally, the raw materials may also include 1-5 parts of bio-based nanofibers, wherein the bio-based nanofibers are acetylated modified cellulose nanofibers.

[0015] By adopting the above technical solution, the introduction of acetylated modified cellulose nanofibers (Ac-CNF) achieves multi-dimensional improvement of the mechanical properties of thin films through their unique nano-reinforcement effect and interfacial interaction.

[0016] The role of acetylated modified cellulose nanofibers begins in the early stages of film formation: After acetylation treatment, the hydroxyl groups on the surface of cellulose nanofibers are partially replaced by hydrophobic acetyl groups, which significantly enhances their compatibility with polyamic acid solution. This allows for uniform dispersion at the nanoscale under mechanical stirring and ultrasonic action, avoiding performance defects caused by agglomeration. Crucially, acetylation significantly improves the intrinsic thermal stability of cellulose nanofibers, enabling them to withstand subsequent high-temperature imidization processes without thermal degradation. As an effective nano-reinforcing phase, it is stably retained in the final polyimide matrix, which is the fundamental prerequisite for it to play a subsequent reinforcing and toughening role. After film formation, the core function of acetylated modified cellulose nanofibers (Ac-CNF) is fully realized: Ac-CNF with extremely high specific strength and modulus can effectively hinder the propagation of microcracks, force cracks to deflect or branch, consume a large amount of fracture energy, and thus simultaneously improve the elongation at break and strength of the material. Some of the hydroxyl groups retained on the Ac-CNF surface can form effective hydrogen bond interactions with the polar groups on the polyimide chain, ensuring efficient stress transfer from the matrix to the reinforcing fiber.

[0017] Ac-CNF, in synergy with reactive core-shell particles, jointly constructs a multi-scale composite network of "rigid nanofiber reinforcement" and "flexible microparticle toughening". Ac-CNF reduces the stress burden on the core-shell particles by bearing part of the load and inhibiting crack propagation, enabling the entire system to withstand greater stress without breaking. Ultimately, this allows the film to exhibit excellent structural integrity and durability under extreme conditions such as complex mold bonding and vacuum negative pressure.

[0018] Optional: The raw materials may also include 0.2-1 parts of aminated modified boron nitride nanosheets.

[0019] By adopting the above technical solution, boron nitride nanosheets are two-dimensional nanomaterials with extremely high in-plane thermal conductivity and excellent electrical insulation. After being modified by amylation on its surface, they can be uniformly dispersed in polyimide solution, thereby improving the thermal conductivity of the film without damaging its electrical insulation properties, promoting the rapid and uniform diffusion of heat during the resin curing process in the mold, and thus optimizing the temperature field inside the component. Furthermore, regarding the bio-resin and bio-based nanofibers of this application, the amino groups on the surface of boron nitride nanosheets can also chemically react with the carboxyl groups of polyamic acid, and even with functional groups such as epoxy groups on the shell of bio-based nanofibers or core-shell particles. This makes the boron nitride nanosheets no longer an isolated composite system, but rather firmly integrated into the existing reinforcing and toughening network system through chemical bonds. From a structural material to a "thermo-mechanical integrated" material, it improves thermal conductivity while playing a role in crack deflection and inhibition, making a positive contribution to the strength and modulus of the film. It promotes mutual development with bio-based nanofibers and core-shell particles, enabling the film to have high toughness, high strength, and high thermal conductivity.

[0020] Optionally, a portion of the bio-based nanofibers may be used directly as a raw material component, while the other portion may be used as a modifier to react with aminated boron nitride nanosheets to prepare cellulose nanofiber-grafted boron nitride nanosheets as a raw material component.

[0021] By adopting the above technical solution, a portion of bio-based nanofibers are covalently grafted onto the surface of boron nitride nanosheets as "surface modifiers" to form a new hybrid functional unit (CNF-g-BNNS) of "cellulose nanofiber grafted boron nitride nanosheets". In CNF-g-BNNS, cellulose nanofibers grafted onto the surface of boron nitride nanosheets effectively prevent the face-to-face stacking and aggregation of boron nitride nanosheets through steric hindrance, enabling them to achieve excellent monodispersity in solvents and polymer matrices. When dispersed in organic solvents, the acetylated cellulose nanofibers exhibit high compatibility with the solvent, and the compatibility of the boron nitride nanosheets grafted with cellulose nanofibers also increases, thus enhancing their dispersibility. Cellulose nanofibers extending from the surface of boron nitride nanosheets can overlap with adjacent boron nitride nanosheets or CNF-g-BNNS hybrid functional units, thereby constructing a continuous three-dimensional thermally conductive network connected by covalent bonds within the composite material. The thermal conductivity is significantly higher than that of individually dispersed random systems. The strong chemical bonds between cellulose nanofibers and boron nitride nanosheets allow stress to be effectively transferred from boron nitride nanosheets to high-strength cellulose nanofibers and vice versa. Therefore, the hybrid functional unit of "cellulose nanofiber grafted boron nitride nanosheets" (CNF-g-BNNS) can more effectively induce toughening mechanisms such as crack deflection and fiber pull-out, while improving the strength, modulus and toughness of the film. Thus, the hybrid functional unit "cellulose nanofiber grafted boron nitride nanosheets" (CNF-g-BNNS) solves the common problems of difficult dispersion and weak interface of multi-component nanomaterials, and constructs an efficient three-dimensional thermally conductive-reinforcing network, further improving the strength, toughness and thermal conductivity of the film.

[0022] Optional: The degree of acetylation substitution of the bio-based nanofibers is 1.8.

[0023] By adopting the above technical solution, each glucose unit of cellulose has 3 reactive hydroxyl groups. When the degree of substitution is 1.8, the cellulose nanofibers have sufficient dispersion stability in the polyamic acid organic solution, avoiding agglomeration, while retaining a certain number of hydroxyl groups. These hydroxyl groups can form strong hydrogen bonds with the carboxyl or amide groups on the polyamic acid chain, thereby constructing a strong physical crosslinking point between the cellulose nanofibers and the bio-based resin, resulting in a film with superior performance.

[0024] Optional: The ratio of the thickness of the core-shell particle shell to the diameter of the core is 1:10-1:5.

[0025] By adopting the above technical solution, when the thickness of the core-shell particle shell is in a ratio of 1:10 to 1:5 to the diameter of the core, the shell thickness is sufficient to ensure the uniform dispersion of particles in the early stage of processing and to provide sufficient reaction sites to achieve strong interfacial chemical bonding. It is also sufficient to almost completely decompose in the later stage of imidization, thereby minimizing its role as an "inert layer" in hindering toughening and resulting in a better toughening effect.

[0026] The second objective of this invention is achieved through the following technical solution: A method for preparing a bio-based resin vacuum bag film includes the following steps: S1: Under nitrogen protection, bio-based pentamethylenediamine, C 12 Diamine dissolves in an organic solvent to form a diamine solution; S2: Add phenyltetracarboxylic dianhydride in batches to the diamine solution under stirring to carry out a polycondensation reaction and obtain a polyamic acid solution. S3: Add the remaining raw materials to the polyamic acid solution and disperse them evenly to obtain the composite film-forming solution; S4: The film-forming liquid is cast onto a flat surface and dried by a temperature gradient of 80-150℃ to form a film; S5: The film is heated to undergo imidization treatment, and after cooling, a bio-based resin vacuum bag film is obtained.

[0027] By adopting the above technical solution, it is ensured that the reactive functional groups of the core-shell particles have sufficient time and a suitable temperature window to complete the chemical reaction with the polyamic acid solution before the polymethyl methacrylate shell decomposes, resulting in a high-strength, high-toughness, and high-airtightness bio-based resin vacuum bag film.

[0028] Optional: The imidization treatment in S5 is as follows: first, treat at 200℃ for 30 min, then treat at 280℃ for 20 min, with a heating rate of 2-5℃ / min.

[0029] By adopting the above technical solution, the unique mechanism of action of the core-shell particles and bio-based resin in this application leads to two challenges in the preparation process: "the time window for interfacial chemical reactions" and "the controllable removal of volatile byproducts." The reaction between the reactive functional groups on the shell of the core-shell particles and the carboxyl groups of polyamic acid requires sufficient time and appropriate temperature to complete. If the temperature rises too quickly, it will spike to the violent decomposition temperature of polymethyl methacrylate before the reaction is fully completed, which will lead to shell decomposition, insufficient interfacial chemical reaction, weak interfacial bonding, and a significant reduction in toughening effect. The imidization process itself produces water, and the decomposition of the polymethyl methacrylate shell also produces small molecule gases. If the temperature rises too quickly, volatile substances will be produced rapidly, forming a high internal vapor pressure. They cannot diffuse out of the film in time, and microbubbles or micropores are easily formed inside the film. This is a fatal defect for vacuum bag films that require absolute airtightness. The temperature program here is controlled in two stages, 200℃ and 280℃, with a heating rate of 2-5℃ / min. This is designed to ensure that the reactive functional groups of the core-shell particles complete a full interfacial chemical reaction with the polyamic acid and that the reaction byproducts are released smoothly, thus guaranteeing that the final film achieves both high toughness and high airtightness.

[0030] In summary, this application has at least the following beneficial effects: 1. By using a "rigid-flexible" block molecular design, while ensuring the high heat resistance of the film above 260℃, the synergistic toughening of long-chain diamine and reactive core-shell particles increases the elongation at break to over 120%, solving the problem of the difficulty in achieving high strength, high toughness and high heat resistance simultaneously. 2. A "chemical bonding interface" and a "multi-scale reinforcement network" were constructed, in which reactive core-shell particles are firmly bonded to the matrix through chemical bonds, eliminating interface delamination; composite nanocellulose and boron nitride nanosheets further improved the mechanical and thermal management properties, ensuring the high reliability of the vacuum bag under extreme working conditions; 3. The core components use bio-based raw materials, which significantly improves the sustainability of the product. At the same time, the precise and controllable preparation process ensures the stable production of high-performance films, providing the aerospace field with a new material that combines excellent comprehensive performance with environmental value. Detailed Implementation

[0032] Raw material: Sodium bicarbonate, commercially available product, analytical grade, purity 99.5%; Sodium dodecyl sulfate, analytical grade, purity 99%; Glacial acetic acid, commercially available product, analytical grade, purity 99.5%; Acetic anhydride, commercially available product, analytical grade, purity 99.5%. Concentrated sulfuric acid, 96.7 wt% concentration; Anhydrous ethanol, commercially available product, 99.7% purity. Anhydrous toluene, commercially available product, 99.5% purity. N-Methylpyrrolidone, market product, electronic grade, ≥99.9%, water content <0.005%; Potassium persulfate, commercially available product, 99.5% purity. Dodecylbenzenesulfonic acid, commercially available product, purity 98.5 wt%. Ammonia solution, concentration 26.5 wt%; Nonylphenol polyoxyethylene ether, OP-10, is a commercially available product with an HLB value of 13.8. Anti-caking agent, nano-silica, hydrophilic, specific surface area 200±25m² / g, Evonik AEROSIL200; Pyromellitic dianhydride, commercially available product, electronic grade, 99.5% purity. Bio-based pentanediamine, commercially available bio-based product 1,5-pentanediamine, purity 99.5%; C 12 Diamine, commercially available product 1,12-dodecaneamine, Zhengzhou Alpha Chemical Co., Ltd., purity 99.5%; Microcrystalline cellulose, particle size 50μm, commercially available product of Anhui Shanhe Pharmaceutical Excipients Co., Ltd. Octamethylcyclotetrasiloxane, industrial grade, 98.0% purity, commercially available product from Dow Chemical. Methyl methacrylate, a commercially available product after processing, with an original purity of 99.0 wt%, is subjected to vacuum distillation to remove polymerization inhibitors before use; Glycidyl methacrylate, a commercially available product after processing, with an original purity of 97.5 wt%, is subjected to vacuum distillation to remove polymerization inhibitors before use; Boron nitride nanosheets, content (%): 99.9%, thickness 20~40nm, sheet diameter 1-3μm, average specific surface area 30m². 2 / g, commercially available flake-shaped nano boron nitride from Beijing Deco Island Gold Technology Co., Ltd.; APTES, 3-aminopropyltriethoxysilane, a commercially available product with a purity of 98.5%; EDC, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride, with a purity of 98.5%, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. NHS, N-hydroxysuccinimide, purity 99.5%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. The compound emulsifier is prepared by mixing sodium dodecyl sulfate and nonylphenol polyoxyethylene ether (OP-10) in a mass ratio of 1:1. Both sodium dodecyl sulfate and nonylphenol polyoxyethylene ether (OP-10) are commercially available chemically pure reagents, which are mixed on-site according to the specified ratio. MES buffer is 2-(N-morpholino)ethanesulfonic acid (MES) buffer, 0.1 mol / L, pH=5.5, prepared using MES raw materials according to standard methods.

[0033] Preparation Example 1 The core-shell particle has a polysiloxane elastomer core and a polymethyl methacrylate shell. The ratio of the shell thickness to the core diameter is 1:8.

[0034] The outer diameter of a core-shell particle is the sum of the core diameter and twice the shell thickness.

[0035] The polymethyl methacrylate shell is grafted with reactive functional groups, which are epoxy groups.

[0036] The specific preparation process is as follows: T1: Mix 60kg deionized water, 0.4kg compound emulsifier and 0.02kg sodium bicarbonate, stir at 200rpm, then add 12.5kg octamethylcyclotetrasiloxane, and continue stirring at 350rpm for 61min to pre-emulsify and obtain a pre-emulsion. The pre-emulsion was heated to 78℃, and 1.1 kg of 10 wt% dodecylbenzenesulfonic acid aqueous solution was added dropwise at a constant rate of 350 rpm for 50 min. After the addition was completed, the reaction was continued at 78℃ for 8 h. After the reaction was completed, the emulsion was cooled to below 40℃, neutralized with ammonia water to pH=7, filtered and redispersed to obtain a seed emulsion with a solid content of 10 wt% and a seed particle diameter of 160±4 nm. T2: Add 0.4 kg sodium dodecyl sulfate to 15 kg deionized water and stir to dissolve. Add a mixture of 11.9 kg methyl methacrylate and 0.24 kg glycidyl methacrylate monomers while stirring at 800 rpm. Continue shearing and emulsifying for 30 min to obtain a shell monomer pre-emulsion. T3: Heat the seed emulsion to 75°C under nitrogen protection, add the initial initiator solution prepared by dissolving 0.05 kg potassium persulfate in 1 kg deionized water, maintain the temperature and stir at 200 rpm, and simultaneously and uniformly add the shell monomer pre-emulsion and the added initiator solution (prepared by dissolving 0.07 kg potassium persulfate in 3 kg deionized water) using a metering pump for 3 hours; T4: After the addition is complete, raise the reactor temperature to 80℃ and continue the reaction for 1.5 hours to allow the monomers to react fully. After the reaction is complete, cool to below 30℃ and adjust the pH to 7 with ammonia to obtain a dispersion. Use vacuum concentration to concentrate the dispersion to a solid content of 25%. Add 0.1 kg of anti-caking agent to the concentrated dispersion, disperse at high speed for 30 min until uniformly mixed, and then spray dry. The spray drying inlet temperature is 170℃, the feed rate is 20 L / h, and the outlet temperature is 90±5℃. Pass the collected powder through a 100-mesh vibrating screen to remove large agglomerates, and then stir and cool in a cooling stirred tank to below 40℃ to obtain core-shell particles with a particle size of 200±2 nm.

[0037] Preparation Example 2 The core-shell particles differ from those in Preparation Example 1 in the preparation of the shell monomer pre-emulsion: 0.4 kg of sodium dodecyl sulfate was added to 15 kg of deionized water and stirred to dissolve. 12.14 kg of methyl methacrylate was added while stirring at 800 rpm, and shear emulsification was continued for 30 min to obtain the shell monomer pre-emulsion.

[0038] Preparation Example 3 The core-shell particles consist of a polysiloxane elastomer core and a polymethyl methacrylate shell, with the shell thickness to core diameter ratio being 1:15. The preparation process differs from Preparation Example 1 in steps T2 and T3, as detailed below.

[0039] T2: Add 0.21 kg sodium dodecyl sulfate to 15 kg deionized water and stir to dissolve. Add a mixture of 6.34 kg methyl methacrylate and 0.13 kg glycidyl methacrylate monomers while stirring at 800 rpm. Continue shearing and emulsifying for 30 min to obtain a shell monomer pre-emulsion. T3: Heat the seed emulsion to 75°C under nitrogen protection, add the initial initiator solution prepared by dissolving 0.02 kg potassium persulfate in 1 kg deionized water, maintain the temperature and stir at 200 rpm, and use a metering pump to simultaneously and uniformly add the shell monomer pre-emulsion and the added initiator solution (prepared by dissolving 0.03 kg potassium persulfate in 3 kg deionized water) for 3 hours.

[0040] Preparation Example 4 The core-shell particles consist of a polysiloxane elastomer core and a polymethyl methacrylate shell, with the shell thickness to core diameter ratio being 1:10. The preparation process differs from Preparation Example 1 in steps T2 and T3, as detailed below.

[0041] T2: Add 0.32 kg of sodium dodecyl sulfate to 15 kg of deionized water and stir to dissolve. Add a mixture of monomers consisting of 9.52 kg of methyl methacrylate and 0.19 kg of glycidyl methacrylate while stirring at 800 rpm. Continue shearing and emulsifying for 30 min to obtain a shell monomer pre-emulsion. T3: Heat the seed emulsion to 75°C under nitrogen protection, add the initial initiator solution prepared by dissolving 0.03 kg potassium persulfate in 1 kg deionized water, maintain the temperature and stir at 200 rpm, and use a metering pump to simultaneously and uniformly add the shell monomer pre-emulsion and the added initiator solution (prepared by dissolving 0.05 kg potassium persulfate in 3 kg deionized water) for 3 hours.

[0042] Preparation Example 5 The core-shell particles consist of a polysiloxane elastomer core and a polymethyl methacrylate shell, with the shell thickness to core diameter ratio being 1:5. The preparation process differs from Preparation Example 1 in steps T2 and T3, as detailed below.

[0043] T2: Add 0.64 kg of sodium dodecyl sulfate to 15 kg of deionized water and stir to dissolve. Add a mixture of monomers consisting of 19.03 kg of methyl methacrylate and 0.39 kg of glycidyl methacrylate while stirring at 800 rpm. Continue shearing and emulsifying for 30 min to obtain a shell monomer pre-emulsion. T3: Heat the seed emulsion to 75°C under nitrogen protection, add the initial initiator solution prepared by dissolving 0.06 kg potassium persulfate in 1 kg deionized water, maintain the temperature and stir at 200 rpm, and use a metering pump to simultaneously and uniformly add the shell monomer pre-emulsion and the added initiator solution (prepared by dissolving 0.1 kg potassium persulfate in 3 kg deionized water) for 3 hours.

[0044] Preparation Example 6 The core-shell particles consist of a polysiloxane elastomer core and a polymethyl methacrylate shell, with the shell thickness to core diameter ratio being 1:4. The preparation process differs from Preparation Example 1 in steps T2 and T3, as detailed below.

[0045] T2: Add 0.8 kg sodium dodecyl sulfate to 15 kg deionized water and stir to dissolve. Add a mixture of monomers consisting of 23.79 kg methyl methacrylate and 0.49 kg glycidyl methacrylate while stirring at 800 rpm. Continue shearing and emulsifying for 30 min to obtain a shell monomer pre-emulsion. T3: Heat the seed emulsion to 75°C under nitrogen protection, add the initial initiator solution prepared by dissolving 0.08 kg potassium persulfate in 1 kg deionized water, maintain the temperature and stir at 200 rpm, and simultaneously and uniformly add the shell monomer pre-emulsion and the added initiator solution (prepared by dissolving 0.12 kg potassium persulfate in 3 kg deionized water) using a metering pump for 3 hours.

[0046] Preparation Example 7 The bio-based nanofibers are acetylated cellulose nanofibers with a degree of substitution of 1.8. The specific preparation method is as follows: 200g of microcrystalline cellulose was dispersed in 10L of deionized water and pre-dispersed at 10000 rpm for 30min using a high-speed shear disperser to fully wet the cellulose and obtain a pre-dispersed suspension. The pre-dispersed suspension was circulated 10 times under 80 MPa pressure by a high-pressure homogenizer to obtain a translucent to milky white cellulose nanofiber suspension (CNF suspension), with the aspect ratio of the cellulose nanofibers controlled at 80:1. Take 100g of the CNF suspension prepared above (based on oven-dry cellulose), and add dropwise a mixture of 300mL glacial acetic acid and 150mL acetic anhydride while cooling in an ice-water bath and stirring continuously. Control the dropping rate to keep the system temperature below 10℃. After the addition was complete, 5 mL of concentrated sulfuric acid was added as a catalyst, the reaction system was heated to 60 °C, and the reaction was carried out at a constant speed for 4 h to carry out acetylation modification. After the reaction is complete, the reaction solution is quickly poured into the ice-water mixture (volume ratio of reaction solution to ice-water mixture is 1:10) to terminate the reaction; The modified cellulose nanofibers were collected using a vacuum filtration device and repeatedly washed with deionized water until the filtrate was neutral. The wet filter cake after washing was redispersed in anhydrous ethanol for solvent replacement. This process was repeated three times to remove the water inside the fibers. The sample after ethanol replacement was freeze-dried (-50℃, vacuum degree <10Pa) for 48 hours to obtain a fluffy white powder product, which is the surface acetylated modified cellulose nanofiber (Ac-CNF).

[0047] Preparation Example 8 Bio-based nanofibers are unmodified cellulose nanofibers. The specific preparation method is as follows: 200g of microcrystalline cellulose was dispersed in 10L of deionized water and pre-dispersed at 10000rpm for 30min using a high-speed shear disperser to fully wet the cellulose and obtain a pre-dispersed suspension. The pre-dispersed suspension was circulated 10 times under 80 MPa pressure by a high-pressure homogenizer to obtain a translucent to milky white cellulose nanofiber suspension (CNF suspension), with the aspect ratio of the cellulose nanofibers controlled at 80:1. Cellulose nanofibers were collected using a vacuum filtration device and repeatedly washed with deionized water until the filtrate was neutral. The wet filter cake after washing was redispersed in anhydrous ethanol for solvent replacement. This process was repeated three times to remove the water inside the fibers. The sample after ethanol replacement was freeze-dried (-50℃, vacuum degree <10Pa) for 48 hours to obtain a fluffy white powder product, which is unmodified cellulose nanofiber.

[0048] Preparation Example 9 The bio-based nanofibers are acetylated cellulose nanofibers with a degree of substitution of 1.5. The specific preparation method is as follows: 200g of microcrystalline cellulose was dispersed in 10L of deionized water and pre-dispersed at 10000rpm for 30min using a high-speed shear disperser to fully wet the cellulose and obtain a pre-dispersed suspension. The pre-dispersed suspension was circulated 10 times under 80 MPa pressure by a high-pressure homogenizer to obtain a translucent to milky white cellulose nanofiber suspension (CNF suspension), with the aspect ratio of the cellulose nanofibers controlled at 80:1. Take 100g of the CNF suspension prepared above (based on oven-dried cellulose), and add dropwise a mixture of 250mL glacial acetic acid and 125mL acetic anhydride while cooling in an ice-water bath and stirring continuously. Control the dropping rate to keep the system temperature below 10℃. After the addition was complete, 3 mL of concentrated sulfuric acid was added as a catalyst, and the reaction system was heated to 60 °C. The reaction was carried out at a constant speed for 2.5 h to carry out acetylation modification. After the reaction is complete, the reaction solution is quickly poured into the ice-water mixture (volume ratio of reaction solution to ice-water mixture is 1:10) to terminate the reaction; The modified cellulose nanofibers were collected using a vacuum filtration device and repeatedly washed with deionized water until the pH of the filtrate was 7. The wet filter cake after washing was redispersed in anhydrous ethanol for solvent replacement. This process was repeated three times to remove the water inside the fibers. The sample after ethanol replacement was freeze-dried (-50℃, vacuum degree <10Pa) for 48 hours to obtain a fluffy white powder product, which is the surface acetylated modified cellulose nanofiber (Ac-CNF).

[0049] Preparation Example 10 Cellulose nanofibers with surface acetylation modification and a degree of substitution of 2. The specific preparation method is as follows: 200g of microcrystalline cellulose was dispersed in 10L of deionized water and pre-dispersed at 10000rpm for 30min using a high-speed shear disperser to fully wet the cellulose and obtain a pre-dispersed suspension. The pre-dispersed suspension was circulated 10 times under 80 MPa pressure by a high-pressure homogenizer to obtain a translucent to milky white cellulose nanofiber suspension (CNF suspension), with the aspect ratio of the cellulose nanofibers controlled at 80:1. Take 100g of the CNF suspension prepared above (based on oven-dried cellulose), and add dropwise a mixture of 400mL glacial acetic acid and 200mL acetic anhydride while cooling in an ice-water bath and stirring continuously. Control the dropping rate to keep the system temperature below 10℃. After the addition was complete, 8 mL of concentrated sulfuric acid was added as a catalyst, the reaction system was heated to 60 °C, and the reaction was carried out at a constant speed for 5 h to carry out acetylation modification. After the reaction is complete, the reaction solution is quickly poured into the ice-water mixture (volume ratio of reaction solution to ice-water mixture is 1:10) to terminate the reaction; The modified cellulose nanofibers were collected using a vacuum filtration device and repeatedly washed with deionized water until the filtrate was neutral. The wet filter cake after washing was redispersed in anhydrous ethanol for solvent replacement. This process was repeated three times to remove the water inside the fibers. The sample after ethanol replacement was freeze-dried (-50℃, vacuum degree <10Pa) for 48 hours to obtain a fluffy white powder product, which is the surface acetylated modified cellulose nanofiber (Ac-CNF).

[0050] Preparation Example 11 The specific preparation process of aminated boron nitride nanosheets is as follows: Add 50g of commercially available boron nitride nanosheets to a reaction vessel, add 3L of anhydrous toluene, stir and mix at 200rpm to wet the boron nitride nanosheets, turn on a high-speed disperser, and shear and disperse at 2800rpm for 30min to obtain a uniform boron nitride nanosheet / toluene suspension. Turn on the jacket of the reactor and heat it to 110°C. Azeotropically dehydrate it under reflux for 1 hour, and then cool it to room temperature. Under stirring at 200 rpm and nitrogen protection, 500 mL of APTES was added dropwise to the reactor. After the addition was complete, 5 mL of glacial acetic acid was added as a catalyst. The reaction system was heated to 110 °C and refluxed for 24 hours. During the reaction, water and ethanol were continuously separated using a water separator. After the reaction was completed, heating was stopped and the mixture was allowed to cool naturally to room temperature. Filter the reaction mixture and collect the solid product. Use anhydrous ethanol as a washing agent to re-pulverize and disperse the filter cake, and then filter it again. Repeat this process until the filtrate is clear and transparent and neutral when tested with pH paper. The washed filter cake was placed in an 80℃ vacuum drying oven and dried for 24 hours until constant weight was achieved. The dried block product was then ground in a mortar and passed through a 300-mesh sieve to obtain a loose, dry white powder, which is the surface-aminated boron nitride nanosheet (BNNS-NH2).

[0051] Preparation Example 12 The specific preparation process of boron nitride nanosheets is as follows: Add 50g of commercially available boron nitride nanosheets to a reaction vessel, add 3L of anhydrous toluene, stir and mix at 200rpm to wet the boron nitride nanosheets, turn on a high-speed disperser, and shear and disperse at 2800rpm for 30min to obtain a uniform boron nitride nanosheet / toluene suspension. Turn on the jacket of the reactor and heat it to 110°C. Azeotropically dehydrate it under reflux for 1 hour, and then cool it to room temperature. Filter the mixture and collect the solid product. Use anhydrous ethanol as a washing agent to re-pulverize and disperse the filter cake, and then filter it again. Repeat this process until the filtrate is clear and transparent and the pH test paper shows that it is neutral. The washed filter cake was placed in an 80℃ vacuum drying oven and dried for 24 hours until constant weight was achieved. The dried block product was then ground in a mortar and passed through a 300-mesh sieve to obtain boron nitride nanosheets.

[0052] Preparation Example 13 The preparation method of cellulose nanofiber-grafted boron nitride nanosheets (CNF-g-BNNS) is as follows: Weigh 5.0 g of BNNS-NH2 prepared in Preparation Example 11 and disperse it in 1000 mL of MES buffer to obtain a uniform and stable BNNS-NH2 suspension. Weigh 2.5g of the Ac-CNF prepared in Preparation Example 7, disperse it in 500mL of MES buffer, sonicate for 15min to obtain a uniform Ac-CNF suspension, add 1.0g of EDC and 0.5g of NHS to the Ac-CNF suspension under continuous mechanical stirring, and activate the reaction at room temperature for 1h. The activated Ac-CNF suspension was added dropwise to the BNNS-NH2 suspension under stirring at 800 rpm. After the addition was complete, the mixture was transferred to a constant temperature water bath and reacted at 40°C for 20 h. During this process, the carboxyl groups on the activated Ac-CNF reacted with the amino groups on the surface of BNNS-NH2 to undergo amidation. After the reaction was completed, the reaction mixture was centrifuged at 12,000 rpm for 20 min, the precipitate was collected, the precipitate was redispersed with deionized water and centrifuged again, and the washing process was repeated 5 times to remove unreacted EDC, NHS, byproducts and physically adsorbed Ac-CNF. The final pure precipitate was freeze-dried (-50℃, vacuum degree <10Pa, 48h) to obtain a fluffy white to light gray flocculent solid, which is the hybrid functional unit of cellulose nanofiber grafted boron nitride nanosheets (CNF-g-BNNS).

[0053] Example 1 A bio-based resin vacuum bag film, the raw materials of which are bio-based resin, core-shell particles, bio-based nanofibers and aminated boron nitride nanosheets.

[0054] The bio-based resin consists of pyromellitic dianhydride, bio-based pentanediamine, and C. 12 Diamines are prepared by polymerization and imidization of monomers, including pyromellitic dianhydride, bio-based pentanediamine, and C. 12 The diamine molar ratio is 50:45.8:4.2. The bio-based pentamethylenediamine is 1,5-pentanediamine, C 12 The diamine is 1,12-dodecylamine.

[0055] The core-shell particles were prepared in Preparation Example 1, the bio-based nanofibers were prepared in Preparation Example 7, and the aminated modified boron nitride nanosheets were prepared in Preparation Example 11.

[0056] The specific preparation method is as follows: Under nitrogen protection and stirring at 200 rpm, 3.199 kg (31.363 mol) of bio-based pentanediamine and 0.575 kg of C were added. 12 Diamine (2.875 mol) was dissolved in 26.5 kg of N-methylpyrrolidone to obtain a diamine solution; Maintaining 0℃ and nitrogen protection, the stirring speed was increased to 300 rpm. 7.465 kg of pyromellitic dianhydride (34.243 mol) powder was divided into 15 batches. One batch of pyromellitic dianhydride powder was added to the diamine solution every 4 min for feeding and mixing. After the addition was completed, the temperature was raised to 5℃ and the reaction was continued for 8 h to obtain a polyamic acid solution. 1.2 kg of core-shell particles, 0.3 kg of bio-based nanofibers, and 0.06 kg of aminated modified boron nitride nanosheets were added to a polyamic acid solution and dispersed at high speed to obtain a uniform, light yellow, opalescent composite film-forming solution without visible particles. Using a precision slit casting machine, the composite film-forming solution was coated onto a mirror-finished stainless steel belt running at a uniform speed (8.0 m / min). The wet film thickness was controlled at 650 μm. Then, the film was dried by a three-stage gradient temperature increase: 80℃ for 8 min, 120℃ for 8 min, and 150℃ for 8 min, to obtain a film with a thickness of 110 μm and a solvent residue of 16 ± 1 wt%. The adhesive film was peeled off and transferred, and then sent to an oven for imidization and final film formation. The temperature was increased from room temperature to 200°C at a rate of 3°C / min, and then kept at 200°C for 30 min. The temperature was then increased from 200°C to 280°C at a rate of 3°C / min, and then kept at 280°C for 20 min. After the treatment, the film was cooled to below 50°C in the oven, removed and wound up to obtain a bio-based resin vacuum bag film with a thickness of 75±3μm.

[0057] Comparative Example 1 A bio-based resin vacuum bag film, differing from Example 1 in that it uses an equimolar amount of bio-based pentanediamine instead of C. 12 diamine.

[0058] Bio-based resin polymerization raw materials do not contain C 12 The ratio of diamine, pyromellitic dianhydride, and bio-based pentanediamine is 50:50.

[0059] During the preparation process, the diamine solution was prepared by dissolving 3.203 kg of bio-based pentanediamine in 4000 g of N-methylpyrrolidone under nitrogen protection at 0 °C and stirring at 200 rpm.

[0060] Comparative Example 2 A bio-based resin vacuum bag film, which differs from Example 1 in that the core-shell particles were prepared in Preparation Example 2, and its shell has no reactive functional groups.

[0061] Comparative Example 3 A bio-based resin vacuum bag film, the raw materials of which are bio-based resin, core-shell particles, bio-based nanofibers and aminated boron nitride nanosheets.

[0062] The bio-based resin consists of pyromellitic dianhydride, bio-based pentanediamine, and C. 12 Diamines are prepared by polymerization and imidization of monomers, including pyromellitic dianhydride, bio-based pentanediamine, and C. 12 The diamine molar ratio is 50:45.8:4.2. The bio-based pentamethylenediamine is 1,5-pentanediamine, C 12 The diamine is 1,12-dodecylamine.

[0063] The core-shell particles were prepared in Preparation Example 1, the bio-based nanofibers were prepared in Preparation Example 7, and the aminated modified boron nitride nanosheets were prepared in Preparation Example 11.

[0064] The specific preparation method is as follows: Under nitrogen protection at 0℃ and stirring at 200 rpm, 3.199 kg (31.363 mol) of bio-based pentanediamine and 0.575 kg of C were added. 12 Diamine (2.875 mol) was dissolved in 26.5 kg of N-methylpyrrolidone to obtain a diamine solution; Maintaining 0℃ and nitrogen protection, the stirring speed was increased to 300 rpm. 7.465 kg of pyromellitic dianhydride (34.243 mol) powder was divided into 15 batches. One batch of pyromellitic dianhydride powder was added to the diamine solution every 4 min for feeding and mixing. After the addition was completed, the temperature was raised to 5℃ and the reaction was continued for 8 h to obtain a polyamic acid solution. Using a precision slit casting machine, a polyamic acid solution was coated onto a mirror-finished stainless steel strip running at a uniform speed (8.0 m / min). The wet film thickness was precisely controlled to 650 μm through the gap of the slit die. Then, the film was dried by a three-stage gradient temperature increase, holding at 80℃ for 8 min, 120℃ for 8 min, and 150℃ for 8 min, to obtain a film with a thickness of 110 μm and a solvent residue of 16 ± 1 wt%. The adhesive film was peeled off and transferred, and then sent to an oven for imidization and final film formation. The temperature was increased from room temperature to 200°C at a rate of 3°C / min in the oven, and then kept at 200°C for 30 min. The temperature was then increased from 200°C to 280°C at a rate of 3°C / min, and then kept at 280°C for 20 min. After the treatment, the film was cooled to below 50°C in the oven to obtain a polyimide film. The polyimide film was crushed by a crusher and then ground into resin powder with a uniform particle size of 80 mesh. 10 kg of resin powder was mixed with 1.2 kg of core-shell particles, 0.3 kg of bio-based nanofibers, and 0.06 kg of aminated modified boron nitride nanosheets at high speed until uniform. The mixture was then sintered and blended in a high-viscosity state under nitrogen protection at 300 °C and hot-pressed to form a film with a thickness of 75 ± 3 μm. The area with an intact center was then cut to obtain the film.

[0065] Example 2 A bio-based resin vacuum bag film, which differs from Example 1 in that the amount of bio-based nanofibers used is 0, and no bio-based nanofibers are used in the raw materials.

[0066] Comparative Example 4 A bio-based resin vacuum bag film, which differs from Example 1 in that the bio-based nanofibers were prepared in Preparation Example 8.

[0067] Example 3 A bio-based resin vacuum bag film differs from Example 1 in that the amount of aminated boron nitride nanosheets is 0, and aminated boron nitride nanosheets are not used in the raw materials.

[0068] Comparative Example 5 A bio-based resin vacuum bag film, which differs from Example 1 in that it replaces the aminated modified boron nitride nanosheets with the same mass as the boron nitride nanosheets prepared in Example 12.

[0069] Example 4 A bio-based resin vacuum bag film differs from Example 1 in that it uses cellulose nanofiber-grafted boron nitride nanosheets (CNF-g-BNNS) from Preparation Example 13 instead of aminated boron nitride nanosheets. The amount of cellulose nanofiber-grafted boron nitride nanosheets (CNF-g-BNNS) is 1.5 times the mass of aminated boron nitride nanosheets (0.09 kg), and the original 0.3 kg of bio-based nanofibers is changed to 0.27 kg.

[0070] Example 5 A bio-based resin vacuum bag film, which differs from Example 1 in that the cellulose nanofibers were prepared in Preparation Example 9.

[0071] Example 6 A bio-based resin vacuum bag film, which differs from Example 1 in that the cellulose nanofibers were prepared in Preparation Example 10.

[0072] Example 7 A bio-based resin vacuum bag film, which differs from Example 1 in that the core-shell particles were prepared in Preparation Example 3.

[0073] Example 8 A bio-based resin vacuum bag film, which differs from Example 1 in that the core-shell particles were prepared in Preparation Example 4.

[0074] Example 9 A bio-based resin vacuum bag film, which differs from Example 1 in that the core-shell particles were prepared in Preparation Example 5.

[0075] Example 10 A bio-based resin vacuum bag film, which differs from Example 1 in that the core-shell particles were prepared in Preparation Example 6.

[0076] Example 11 A bio-based resin vacuum bag film, which differs from Example 1 in that when the film is peeled off and sent into the oven for imidization and final film formation, the heating rate is 1°C / min.

[0077] Example 12 A bio-based resin vacuum bag film, which differs from Example 1 in that when the film is peeled off and sent into the oven for imidization and final film formation, the heating rate is 2°C / min.

[0078] Example 13 A bio-based resin vacuum bag film, which differs from Example 1 in that when the film is peeled off and sent into the oven for imidization and final film formation, the heating rate is 5°C / min.

[0079] Example 14 A bio-based resin vacuum bag film, which differs from Example 1 in that when the film is peeled off and sent into the oven for imidization and final film formation, the heating rate is 6°C / min.

[0080] Comparative Example 6 A bio-based resin vacuum bag film, which differs from Example 1 in that when the film is peeled off and sent into the oven for imidization and final film formation, the heating rate is 8°C / min.

[0081] Example 15 A bio-based resin vacuum bag film differs from Example 1 in the amount of raw materials used: 1.0 kg of core-shell particles, 0.5 kg of bio-based nanofibers, and 0.1 kg of aminated modified boron nitride nanosheets, while the rest are the same.

[0082] Example 16 A bio-based resin vacuum bag film differs from Example 1 in the amount of raw materials used: 1.52 kg of core-shell particles, 0.1 kg of bio-based nanofibers, and 0.02 kg of aminated modified boron nitride nanosheets, while the other components remain the same.

[0083] The toughness, high temperature resistance, thermal conductivity and air tightness of the films obtained from Examples 1-16, Comparative Examples 1-6 and commercially available PI films (DuPont Kapton) were tested. The test results are shown in the table below.

[0084] Toughness: Elongation at break and tensile strength were tested according to ASTM D882.

[0085] High temperature resistance: The glass transition temperature of the film is tested according to ASTM E1545. The higher the glass transition temperature of the film, the better the high temperature resistance.

[0086] Thermal conductivity: The thermal diffusivity was determined according to GB / T 22588. The thermal conductivity was calculated by combining the specific heat capacity and density of the sample. The higher the thermal conductivity, the better the thermal conductivity.

[0087] Air tightness: Refer to ASTM D4991 to test the leakage rate. The lower the leakage rate, the better the air tightness.

[0088] Table 1. Results of toughness and high temperature resistance tests in Examples 1-16 and Comparative Examples 1-6

[0089] Table 2. Results of thermal conductivity and airtightness tests for Examples 1-16 and Comparative Examples 1-6

[0090] By combining Tables 1 and 2 and comparing Example 1 with Comparative Examples 1-3, it can be seen that: The elongation at break and tensile strength of Example 1 are significantly greater than those of Comparative Examples 1-3 and commercially available PI films. In particular, the elongation at break of Example 1 is greater than 120%. The toughness of Example 1 is significantly improved compared with Comparative Examples 1-3 and commercially available PI films. At the same time, the glass transition temperature of Example 1 is the highest and greater than 260°C, which is maintained at a high level and meets the requirements of 200-230°C for curing temperature of aerospace impregnating resin. The leakage rate of Example 1 is lower than that of commercially available PI films and Comparative Examples 2-3, especially compared to Comparative Examples 2-3, which is three orders of magnitude lower. This verifies that the core-shell particles used for toughening in this application are specifically designed. The core innovation lies in the introduction of reactive epoxy functional groups into the shell layer and the precise control of the timing of addition and reaction. The core contribution to ensuring the airtightness of the vacuum bag is that the core-shell particles are added and uniformly dispersed in the system at the polyamic acid stage of the bio-based resin precursor. During the subsequent imidization curing process at a programmed temperature, before the polymethyl methacrylate shell layer undergoes thermal decomposition, the epoxy groups on its surface can undergo in-situ chemical reaction with the abundant carboxyl groups on the polyamic acid molecular chain to form a strong covalent bond. This fundamentally solves the problem of weak interfaces that are easily generated in traditional physical blending. Even if the polymethyl methacrylate shell layer decomposes due to subsequent high-temperature treatment, its decomposition fragments are "anchored" in the forming three-dimensional polyimide network by covalent bonds. This not only prevents the formation of microscopic defects and leakage points, but also forms a strong and tough molecular-level transition layer.

[0091] Therefore, this application uses bio-based resin as the base material and employs pyromellitic dianhydride, bio-based pentanediamine, and C 12 The three diamines are polymerized to achieve an alternating arrangement of "rigid segments" and "flexible segments" on the molecular chain. Then, the toughening core-shell particles are modified for the substrate polyimide and dispersed in polyamic acid. The epoxy groups of the shell react chemically with the carboxyl groups on the precursor polyamic acid molecular chain to form a strong chemical bond. The close cooperation of "specific bio-based main chain structure", "reactive core-shell particles" and "specific addition timing" fundamentally improves the mobility of chain segments and endows the material with basic toughness. The core-shell particles, which are chemically bonded, act as efficient stress concentration points and energy absorbers. Under the action of external force, they induce crazes and shear bands, consuming a large amount of energy. They combine with each other to greatly improve the elongation at break of the film. The resulting bio-based vacuum bag film has high heat resistance, high flexibility and high airtight reliability.

[0092] Comparing Examples 1, 2, and 4, it can be seen that the bio-based nanofibers in the film raw material of Example 1 are acetylated modified cellulose nanofibers, the film raw material of Example 2 does not contain bio-based nanofibers, and the bio-based nanofibers in the film raw material of Comparative Example 4 are unmodified cellulose nanofibers. The test results show that the tensile strength and tensile breaking rate of Example 1 are significantly better than those of Example 2, indicating that the toughness of Example 1 is superior to that of Example 2. On the other hand, regarding Comparative Example 4, which uses unmodified cellulose nanofibers, these fibers decompose during the subsequent imidization process and cannot be stably retained. Therefore, its tensile strength and tensile breaking rate are even worse than those of Example 2, and the leakage rate increases while the airtightness decreases.

[0093] It can be seen that the introduction of acetylated modified cellulose nanofibers (Ac-CNF) has achieved multi-dimensional improvement of the mechanical properties of thin films through its unique nano-reinforcement effect and interfacial interaction.

[0094] The role of acetylated modified cellulose nanofibers begins in the early stages of film formation: After acetylation, the hydroxyl groups on the CNF surface are partially replaced by hydrophobic acetyl groups, which significantly enhances its compatibility with polyamic acid solution. This allows for uniform dispersion at the nanoscale under mechanical stirring and ultrasonic treatment, avoiding performance defects caused by agglomeration. Crucially, acetylation significantly improves the intrinsic thermal stability of cellulose nanofibers, enabling them to withstand subsequent high-temperature imidization processes without thermal degradation. As an effective nano-reinforcing phase, it is stably retained in the final polyimide matrix, which is the fundamental prerequisite for it to play a subsequent reinforcing and toughening role. After film formation, the core function of acetylated modified cellulose nanofibers is fully realized: Ac-CNF with extremely high specific strength and modulus can effectively hinder the propagation of microcracks, force cracks to deflect or branch, consume a large amount of fracture energy, and thus simultaneously improve the elongation at break and strength of the material. Some of the hydroxyl groups retained on the Ac-CNF surface can form effective hydrogen bond interactions with the polar groups on the polyimide chain, ensuring efficient stress transfer from the matrix to the reinforcing fiber.

[0095] Ac-CNF, in synergy with reactive core-shell particles, jointly constructs a multi-scale composite network of "rigid nanofiber reinforcement" and "flexible microparticle toughening". Ac-CNF reduces the stress burden on the core-shell particles by bearing part of the load and inhibiting crack propagation, enabling the entire system to withstand greater stress without breaking. Ultimately, this allows the film to exhibit excellent structural integrity and durability under extreme conditions such as complex mold bonding and vacuum negative pressure.

[0096] Comparing Example 1, Example 3, and Comparative Example 5, it can be seen that: The elongation at break, tensile strength, and thermal conductivity of Example 1 were greater than those of Example 3, indicating that the addition of aminated modified boron nitride nanosheets provided enhanced thermal conductivity and additional strengthening effects. The additional strengthening effect is due to... After being modified by amylation, boron nitride nanosheets can be uniformly dispersed in polyimide solution, thereby improving the thermal conductivity of the film without damaging its electrical insulation properties, promoting the rapid and uniform diffusion of heat during the resin curing process in the mold, and thus optimizing the temperature field inside the component. Regarding the bio-resin and bio-based nanofibers of this application, the amino groups on the surface of boron nitride nanosheets can also chemically react with the carboxyl groups of polyamic acid, and even with functional groups such as epoxy groups on the shell of bio-based nanofibers or core-shell particles. This makes the aminated boron nitride nanosheets no longer an isolated composite system, but rather firmly integrated into the existing reinforcing and toughening network system through chemical bonds. From a structural material to a "thermo-mechanical integrated" material, it improves thermal conductivity while playing a role in crack deflection and inhibition, making a positive contribution to the strength and modulus of the film. It promotes mutual development with bio-based nanofibers and core-shell particles, giving the film high toughness, high strength, and high thermal conductivity.

[0097] The elongation at break and tensile strength of Example 1 are greater than those of Comparative Example 5, the leakage rate of Example 1 is less than that of Comparative Example 5, and the tensile fracture rate and tensile strength of Example 3 are greater than those of Comparative Example 5. This is because the unmodified boron nitride nanosheets in Comparative Example 5 lack surface functional groups and are prone to agglomeration in the matrix, forming stress concentration points, which slightly reduces the performance.

[0098] Example 4 of this application is a new optimization scheme based on Example 1. It uses a partial acetylated cellulose nanofiber to covalently graft amino-modified boron nitride nanosheets onto the surface to "pre-assemble" a new hybrid functional unit (CNF-g-BNNS) of "cellulose nanofiber grafted boron nitride nanosheets".

[0099] In CNF-g-BNNS, bio-based nanofibers grafted onto the surface of boron nitride nanosheets effectively prevent the face-to-face stacking and aggregation of boron nitride nanosheets through steric hindrance, enabling them to achieve excellent monodispersity in solvents and polymer matrices. When dispersed in organic solvents, the acetylated cellulose nanofibers exhibit high compatibility with the solvent, and the compatibility of the boron nitride nanosheets grafted with cellulose nanofibers also increases accordingly, thus enhancing their dispersibility. Cellulose nanofibers extending from the surface of boron nitride nanosheets can overlap with adjacent boron nitride nanosheets or CNF-g-BNNS hybrid functional units, thereby constructing a continuous three-dimensional thermally conductive network connected by covalent bonds within the composite material. The thermal conductivity is significantly higher than that of individually dispersed random systems. The strong chemical bonds between cellulose nanofibers and boron nitride nanosheets allow stress to be effectively transferred from the boron nitride nanosheets to the high-strength cellulose nanofibers and vice versa. Therefore, the hybrid functional unit of "cellulose nanofiber-grafted boron nitride nanosheets" (CNF-g-BNNS) can more effectively induce toughening mechanisms such as crack deflection and fiber pull-out, while improving the strength, modulus, and toughness of the film. The test results showed that the elongation at break, tensile strength, and thermal conductivity of Example 4 were all further improved compared to the high levels of Example 1, and the glass transition temperature and leakage rate did not decrease. This verifies that the common problems of difficult dispersion and weak interface of multi-component nanomaterials have been solved, and a highly efficient three-dimensional thermally conductive-reinforced network has been constructed. The use of CNF-g-BNNS has resulted in a higher-performance bio-based resin vacuum film based on Example 1.

[0100] Comparing Examples 1 and 5-6, the difference lies in the degree of acetylation of the cellulose nanofibers. In the test results, Example 1 showed higher elongation at break and tensile strength than Examples 5-6. The glass transition temperature, from highest to lowest, was Example 5, Example 1, and Example 6. The thermal conductivity, from highest to lowest, was Example 6, Example 1, and Example 5. The leakage rate, from highest to lowest, was Example 1, Example 6, and Example 5. Therefore, in this application, a degree of acetylation of 1.8 in the bio-based nanofibers is preferred.

[0101] Comparing Examples 1 and 7-10, the difference lies in the ratio of the shell thickness to the core diameter. In the test results, the elongation at break, from highest to lowest, is as follows: Examples 1, 8, 9, 7, and 10; tensile strength, from highest to lowest, is as follows: Examples 1, 8, 9, 7, and 10; glass transition temperature, from highest to lowest, is as follows: Examples 7, 8, 1, 9, and 10; and leakage rate, from lowest to highest, is as follows: Examples 1, 8, 9, 7, and 10.

[0102] The reason is that the shell needs to be thick enough—to ensure that the particles can be stably dispersed during processing and to provide enough epoxy functional groups to react chemically with the matrix and form a strong initial interface bond; In addition, the shell layer should not be too thick—during the subsequent high-temperature imidization process, the polymethyl methacrylate shell layer needs to be able to decompose and volatilize almost completely. If the proportion is too high, a large amount of thermally unstable decomposition products will remain, forming a fragile "inert isolation layer" at the interface, which will hinder stress transfer, weaken the toughening effect, and increase the risk of porosity. Therefore, in this application, the shell thickness to core diameter ratio of the core-shell particles is preferably 1:10-1:5, which ensures that the shell can effectively fulfill its mission as a dispersion carrier and reaction platform before smoothly exiting, allowing the elastic nucleus to exert its toughening effect to the maximum extent, while ensuring the compactness of the film.

[0103] As mentioned above, the shell effect of the core-shell particles is also related to the decomposition and volatilization of the polymethyl methacrylate shell during the subsequent high-temperature imidization process. Therefore, comparing Examples 1, 11-14 and Comparative Example 6, the difference between Examples 1, 11-14 and Comparative Example 6 lies in the different heating rates during the imidization process.

[0104] The test results showed that as the heating rate increased, the tensile strength and tensile strength of the resulting film first increased and then decreased. Examples 1, 13, and 12 were greater than Examples 11, 16, and Comparative Example 6. However, as the heating rate increased, the leakage rate of the resulting film first decreased and then increased. Examples 1, 13, and 12 were less than Examples 11, 16, and Comparative Example 6. In particular, Comparative Example 6, which further increased the heating rate compared to Example 16, showed a significant increase in leakage rate. Therefore, considering the application requirements of the bio-based resin in this application, a heating rate of 2-5℃ / min is preferred for the imidization process.

[0105] In addition, this application also has other superior solutions during the research and development process, such as Examples 15-16. The elongation at break and tensile strength of Examples 15-16 are significantly greater than those of Comparative Examples 1-3 and commercially available PI films. The leakage rate of Examples 15-16 is less than that of Comparative Examples 2-3, while the glass transition temperature is greater than 260°C, maintained at a high level, meeting the requirements of 200-230°C for curing aerospace impregnating resins. Therefore, in this application, the mass percentage of bio-based resin vacuum bag film raw materials is controlled at 100 parts bio-based resin, 10-15 parts core-shell particles, 1-5 parts bio-based nanofibers, and 0.2-1 parts boron nitride nanosheets. The resulting bio-based resin vacuum bag film has high heat resistance, high flexibility, and high airtight reliability.

[0106] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of protection claimed by the present invention, they are protected by patent law.

Claims

1. A bio-based resin vacuum bag film, characterized in that, The raw materials include the following parts by weight: 100 parts of bio-based resin 10-15 parts of core-shell particles; Bio-based resins contain pyromellitic dianhydride, bio-based pentanediamine, and C 12 Diamine is prepared by polymerization and imidization of monomers; The core-shell particle has a core of polysiloxane elastomer and a shell of polymethyl methacrylate, wherein the polymethyl methacrylate shell is grafted with reactive functional groups, the reactive functional groups being epoxy groups. The core-shell particles are dispersed in the bio-based resin after polyamic acid is prepared and before imidization.

2. The bio-based resin vacuum bag film according to claim 1, characterized in that, The raw materials also include 1-5 parts of bio-based nanofibers, which are acetylated modified cellulose nanofibers.

3. The bio-based resin vacuum bag film according to claim 2, characterized in that, The raw materials also include 0.2-1 parts of aminated modified boron nitride nanosheets.

4. The bio-based resin vacuum bag film according to claim 3, characterized in that, One part of the bio-based nanofibers is used directly as a raw material component, and the other part is used as a modifier to react with aminated boron nitride nanosheets to prepare cellulose nanofiber grafted boron nitride nanosheets as a raw material component.

5. The bio-based resin vacuum bag film according to claim 2, characterized in that, The degree of acetylation substitution of the bio-based nanofibers is 1.

8.

6. The bio-based resin vacuum bag film according to claim 1, characterized in that, The ratio of the thickness of the shell to the diameter of the nucleus in a core-shell particle is 1:10 to 1:

5.

7. The method for preparing the bio-based resin vacuum bag film according to any one of claims 1-6, characterized in that, Includes the following steps: S1: Under nitrogen protection, bio-based pentamethylenediamine, C 12 Diamine dissolves in an organic solvent to form a diamine solution; S2: Add phenyltetracarboxylic dianhydride in batches to the diamine solution under stirring to carry out a polycondensation reaction and obtain a polyamic acid solution. S3: Add the remaining raw materials to the polyamic acid solution and disperse them evenly to obtain the composite film-forming solution; S4: The film-forming liquid is cast onto a flat surface and dried by a temperature gradient of 80-150℃ to form a film; S5: The film is heated to undergo imidization treatment, and after cooling, a bio-based resin vacuum bag film is obtained.

8. The method for preparing the bio-based resin vacuum bag film according to claim 7, characterized in that, The imidization treatment in S5 is as follows: first, treat at 200℃ for 30 min, then treat at 280℃ for 20 min, with a heating rate of 2-5℃ / min.

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