High-strength corrosion-resistant PVDF-based composite material and preparation method thereof

Abstract

The invention discloses a preparation method of a high-strength corrosion-resistant PVDF-based composite material, and belongs to the technical field of composite materials. The method mainly comprises the following steps: (1) preparing surface nanocrystallization carbon fibers with SiO2 nano layers on the surfaces through alkali liquor activation, silanization and in-situ growth processes; (2) preparing fluorine-containing modified graphene oxide; (3) mixing the filler with PVDF resin, introducing a VDF monomer for in-situ polymerization, and constructing a chemical bonding interface; (4) respectively preparing outer layer slurry rich in nano TiO2, middle layer slurry rich in surface nanocrystallization carbon fibers and inner layer slurry rich in SiO2 coated Al2O3 core-shell nanoparticles by quantitatively supplementing specific filler; and (5) carrying out gradient tape casting, segmented drying, hot press molding and annealing treatment to prepare the composite material. The problems that a traditional PVDF material is weak in interface bonding and corrosion resistance and strength are difficult to consider at the same time are solved, and the prepared material has excellent mechanical strength and strong acid corrosion resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite material preparation, and particularly relates to a preparation method of a high-strength corrosion-resistant PVDF-based composite material. BACKGROUND

[0002] Polyvinylidene fluoride (PVDF) is a semi-crystalline fluoropolymer, which has excellent chemical corrosion resistance, high temperature resistance, oxidation resistance and unique piezoelectric properties, and is widely used in chemical corrosion-resistant equipment, ocean engineering and new energy components. However, pure PVDF resin has defects such as insufficient mechanical strength, poor creep resistance, and swelling or stress cracking in high-strength acid and strong alkali environment for long-term use, which limits its further application in extreme harsh environments.

[0003] Filling modification is a common means to improve the comprehensive performance of PVDF. Carbon fiber (CF) is often used as a reinforcing filler due to its high specific strength and modulus, but the surface of carbon fiber is chemically inert and has low surface energy, and the interface compatibility between the polar PVDF matrix is poor, which leads to weak interfacial bonding force and difficult load transfer. At high filling amount, it is easy to agglomerate, which reduces the material performance. Graphene oxide (GO) has a large specific surface area and rich functional groups, but it is difficult to disperse in organic matrix. The composite material prepared by traditional physical blending method only has weak van der Waals force between the filler and the matrix, and there are many interface defects, and a single filler often cannot meet the multiple requirements of strength, toughness and corrosion resistance. In addition, the existing single-layer homogeneous structure design is difficult to balance the contradiction between surface corrosion resistance and core high bearing capacity. Therefore, it is necessary to explore a new preparation method of high-strength corrosion-resistant PVDF-based composite material. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a high-strength corrosion-resistant PVDF-based composite material. The preparation method disclosed in the present application combines functional gradient structure design through multi-level interface modification and in-situ polymerization technology, and the prepared PVDF composite material has excellent mechanical strength and corrosion resistance.

[0005] The preparation method of the high-strength corrosion-resistant PVDF-based composite material disclosed in the present application comprises the following steps: S1 preparation of surface nano-carbon fiber

[0006] The carbon fiber is activated by treating in 10wt% NaOH solution at 80℃ for 30min, washed with deionized water until neutral, then added into the aqueous solution of 3-aminopropyltriethoxysilane in ethanol, adjusted pH to 4.5-5.0, stirred at 60℃ for 4h, washed and dried after reaction; then added into the aqueous solution of tetraethyl orthosilicate (TEOS) in ethanol, adjusted pH to 9-10 by adding ammonia, in-situ grown at 60℃ for 4-6h, washed and dried after reaction, to prepare the surface-nanofiber carbon fiber with 5-20nm thick SiO2 nanolayer on the surface;

[0007] Preparation of S2 fluorine-containing modified graphene oxide

[0008] The graphene oxide is dispersed in anhydrous DMF, added with perfluorooctyltriethoxysilane, reacted at 80℃ for 6h under nitrogen protection, washed with ethanol and vacuum dried after reaction, to prepare the fluorine-containing modified graphene oxide;

[0009] Preparation of S3 in-situ polymerized slurry

[0010] The surface-nanofiber carbon fiber, fluorine-containing modified graphene oxide and SiO2@Al2O3 core-shell nanoparticles with particle size of 20-50nm are ultrasonically dispersed in a mixed solvent, added with PVDF resin to be dissolved by stirring at 60℃, then added with VDF monomer and initiator, in-situ polymerized in a high-pressure reaction kettle at 95-105℃ for 3-4h, concentrated under reduced pressure after reaction, to prepare the in-situ polymerized slurry;

[0011] S4: forming of the gradient structure composite material

[0012] A) respectively prepare the outer layer slurry, the middle layer slurry and the inner layer slurry: the outer layer slurry is part of the in-situ polymerized slurry prepared in step S3, and added with nano-TiO2, the added amount of nano-TiO2 is 5-10wt% of the solid content in the part of the slurry; the middle layer slurry is part of the in-situ polymerized slurry prepared in step S3, and supplemented with the surface-nanofiber carbon fiber, the supplemented amount is 10-20wt% of the solid content in the part of the slurry; the inner layer slurry is part of the in-situ polymerized slurry prepared in step S3, and supplemented with the SiO2@Al2O3 core-shell nanoparticles, the supplemented amount is 3-5wt% of the solid content in the part of the slurry;

[0013] B) gradient flow casting method is adopted to flow cast the inner layer, the middle layer and the outer layer on the carrier in sequence, each layer is partially dried after flow casting, and finally completely dried by sectional temperature rising, to prepare the three-layer composite dry film;

[0014] C) The three-layer composite dry film was hot-pressed at 195-210℃ and 15-20MPa for 8-15 minutes, cooled under pressure, and then annealed at 170℃ for 1 hour to prepare a high-strength and corrosion-resistant PVDF-based composite material.

[0015] In S3, the volume ratio of ethanol to water in the ethanol-water solution of 3-aminopropyltriethoxysilane is 4:1. In S1, the volume ratio of ethanol to water in the ethanol-water solution of TEOS is 6:1. The drying in S1 is performed at 60°C for 2 hours (after silanization) and at 100°C for 12 hours (after in-situ growth). In S1, alkaline activation increases the surface roughness and oxygen-containing functional groups of the carbon fibers, APTES silanization introduces amino active sites, and then TEOS undergoes hydrolysis and condensation to grow a dense SiO2 nanolayer in situ on the carbon fiber surface. This nanolayer not only serves as a physical barrier but also provides an anchor point for subsequent bonding with the PVDF matrix.

[0016] Specifically, in S2 above, the mass-to-volume ratio of graphene oxide to perfluorooctyltriethoxysilane is 1:2, in g / mL. The anhydrous DMF in S2 needs to be dehydrated using anhydrous MgSO4. In S2, the graphene oxide is fluorinated using perfluorooctyltriethoxysilane, introducing low surface energy fluorocarbon chains that exhibit excellent compatibility with the PVDF matrix, solving the problem of difficult GO dispersion and simultaneously imparting excellent hydrophobicity to the material.

[0017] Specifically, the mixed solvent mentioned in S3 is a mixture of DMF and NMP in a volume ratio of 7:3. The amount of VDF monomer added in S3 is 5-8% of the PVDF resin mass, and the initiator is azobisisobutyronitrile (AIBN), added at 0.3% of the VDF monomer mass. The vacuum concentration mentioned in S3 controls the solid content to 35-45%. In S3, VDF monomer is introduced for in-situ polymerization. The monomer polymerizes in-situ on the surface of the filler (especially nano-sized carbon fibers and modified GO with abundant active sites) to generate PVDF molecular chains, forming a chemically bonded PVDF transition layer (5-10 nm thick). This solves the problem of weak interfacial bonding in traditional physical mixing, achieving a strong bond between the filler, transition layer, and matrix.

[0018] Specifically, the viscosity of the intermediate layer slurry in S4 is controlled at 20000-22000 mPa·s, and the viscosity of the outer layer slurry is controlled at 25000-27000 mPa·s. The gap between the inner layer casting blades in S4 is 50-100 μm, the gap between the intermediate layer casting blades is 1500-3000 μm, and the gap between the outer layer casting blades is 80-150 μm. The partial drying program in S4 is as follows: inner layer 60℃×5min+80℃×5min, intermediate layer 60℃×10min+80℃×10min+100℃×10min, outer layer 60℃×5min+80℃×8min. The hot pressing in S4 employs staged pressurization: increasing to 5 MPa in the first minute, increasing to 10 MPa in the second minute, and increasing to the target pressure of 15-20 MPa in the third minute.

[0019] Specifically, the high-strength corrosion-resistant PVDF-based composite material described in S4 above, by weight, is composed of the following raw materials: 100 parts PVDF resin, 18-25 parts surface-nanosized carbon fiber, 0.5-2 parts fluorine-modified graphene oxide, and 2-4 parts core-shell nanoparticles. The high-strength corrosion-resistant PVDF-based composite material described in S4 has a three-layer gradient structure: an outer layer with a thickness of 8-15 μm, an inner layer with a thickness of 5-12 μm, and a middle layer as the main layer. The outer layer is rich in TiO2 nanoparticles, forming a dense shielding layer that enhances corrosion resistance and weather resistance; the middle layer utilizes the synergistic reinforcement of carbon fiber and GO to serve as the main load-bearing layer; the inner layer is rich in SiO2@Al2O3 core-shell particles, enhancing adhesion and blocking the penetration of corrosive media.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The preparation method of the high-strength and corrosion-resistant PVDF-based composite material of the present invention adopts a dual-phase synergistic reinforcement strategy of "combining rigidity and flexibility". The SiO2 nanolayer (5-20nm) grown in situ on the surface of carbon fibers not only repairs the surface defects of the fibers, but also significantly increases the specific surface area and mechanical interlocking force; fluorine-modified graphene oxide, with its flexible two-dimensional structure and the similar compatibility principle of fluorocarbon chains, fills the gap between the fibers and the matrix, and induces PVDF to form a denser crystalline phase during the in-situ polymerization process. The synergy of the two results in a 70-82% increase in tensile strength and a 320-353% increase in flexural modulus of the composite material compared to pure PVDF, while maintaining good processing performance even with high filler content.

[0022] 2. This invention introduces VDF monomer in-situ polymerization technology to construct a chemically bonded PVDF transition layer in-situ on the surface of inorganic fillers, transforming the traditional physical interface into a chemical interface, which significantly improves the interfacial shear strength.

[0023] 3. This invention utilizes a gradient casting process to construct a three-layer gradient structure, achieving targeted functional optimization. The outer dense corrosion-resistant layer effectively resists strong acid and alkali corrosion, the inner core-shell structure reinforcement layer improves impermeability, and the middle high-strength load-bearing layer ensures overall mechanical properties. Tests show that after immersion in 98% sulfuric acid for 2000 hours, the material retains over 92% of its tensile strength, solving the problem of traditional homogeneous materials struggling to balance surface corrosion resistance and internal high strength. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements, and equivalents included within the scope of the claims.

[0025] PVDF resin: Kynar® 720, powder, average particle size 5μm.

[0026] Carbon fiber: T700 grade, 5mm chopped length, 7μm monofilament diameter.

[0027] Graphene oxide (GO): sheet diameter 3-8μm, thickness 0.8-1.2nm, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0028] SiO2@Al2O3 core-shell nanoparticles: purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a core of SiO2 particles (approximately 30nm in diameter) and a shell of Al2O3 (approximately 5nm in thickness), and a purity of 99.9%.

[0029] VDF monomer: Vinylidene fluoride gas, purity ≥99.9%.

[0030] Nano TiO2: Rutile type, average particle size 20nm, hydrophobic treatment.

[0031] All other reagents were of analytical grade.

[0032] Example 1

[0033] The preparation method of the high-strength and corrosion-resistant PVDF-based composite material described in Example 1 consists of the following steps:

[0034] (1) Preparation of surface-grown carbon fibers: Carbon fibers were activated by treatment in 10wt% NaOH solution at 80℃ for 30 min, washed with deionized water until neutral, and then added to an ethanol-water solution of 3-aminopropyltriethoxysilane (APTES) (volume ratio ethanol:water = 4:1). The pH was adjusted to 4.7, and the reaction was stirred at 60℃ for 4 h. After washing, the carbon fibers were dried at 60℃ for 2 h. Subsequently, the carbon fibers were dispersed in an ethanol-water solution of tetraethyl orthosilicate (TEOS) (volume ratio ethanol:water = 6:1), and ammonia was added dropwise to adjust the pH to 9.5. The reaction was carried out at 60℃ for 5 h. After the reaction, the carbon fibers were washed with ethanol and dried at 100℃ for 12 h. SEM analysis showed that the SiO2 nanolayers grown in situ on the carbon fiber surface were uniform in thickness, with an average thickness of about 12 nm.

[0035] (2) Preparation of fluorine-modified graphene oxide: Graphene oxide was dispersed in anhydrous DMF dried with MgSO4, and perfluorooctyltriethoxysilane (FOTES to GO mass ratio of 2:1) was added. The reaction was carried out at 80°C for 6 h under nitrogen protection, and the mixture was washed and dried to obtain fluorine-modified graphene oxide (F-GO).

[0036] (3) Preparation of in-situ polymerization slurry

[0037] Surface-grown carbon fibers, F-GO, and SiO2@Al2O3 core-shell nanoparticles prepared in S1 were ultrasonically dispersed in a DMF / NMP (7:3) mixed solvent. PVDF resin was added and dissolved at 60℃. VDF monomer (6.5% of the PVDF mass) and AIBN initiator were added. In-situ polymerization was carried out in a high-pressure reactor at 100℃ for 3.5 h. After the reaction, the mixture was concentrated under reduced pressure to control the solid content of the slurry to 40%.

[0038] (4) Molding of gradient structure composite materials

[0039] a) Slurry preparation: Outer layer slurry: Take 100g of base slurry, add 3.0g of nano-TiO2, and adjust the viscosity to 26000mPa·s. Intermediate layer slurry: Take 500g of base slurry, add 30g of surface-nanosized carbon fibers prepared by S1, and adjust the viscosity to 21000 mPa·s. Inner layer slurry: Take 100g of base slurry, add 1.6g of SiO2@Al2O3 core-shell nanoparticles.

[0040] b) Gradient Casting: The following layers are sequentially cast on a PET substrate: Inner layer: 75 μm doctor blade gap, dried in sections at 60℃ / 80℃. Middle layer: 2250 μm doctor blade gap, dried in sections at 60℃ / 80℃ / 100℃. Outer layer: 115 μm doctor blade gap, dried in sections at 60℃ / 80℃. Finally, the layers are completely dried using a programmed temperature rise process to obtain a three-layer dry film.

[0041] c) Hot pressing and annealing: The dry film is laminated and hot-pressed at 202℃ and 17.5MPa for 11 min. It is then cooled to 60℃ under pressure and demolded. Finally, the sheet is placed in an oven and annealed at 170℃ for 1 hour.

[0042] Example 2

[0043] The preparation method of the high-strength and corrosion-resistant PVDF-based composite material described in Example 2 consists of the following steps:

[0044] (1) The preparation steps of the surface nanofibers are the same as in Example 1, except that the pH of silanization is adjusted to 4.5, the pH of in-situ growth is adjusted to 9.0, and the reaction time is 4h. The thickness of the SiO2 nanolayer is measured to be about 5.5nm.

[0045] (2) Preparation of fluorine-modified graphene oxide, the steps are the same as in Example 1.

[0046] (3) Preparation of in-situ polymerization slurry: The steps are the same as in Example 1, except that: the amount of VDF monomer added is 5%, the polymerization temperature is 95℃, and the reaction time is 3h. The solid content is concentrated under reduced pressure to 35%.

[0047] (4) Molding of gradient structure composite materials

[0048] a) Slurry preparation: The amount of nano-TiO2 added to the outer layer slurry is 5wt%; the amount of surface nano-sized carbon fiber added to the middle layer slurry is 10wt%; and the amount of SiO2@Al2O3 core-shell nanoparticles added to the inner layer slurry is 3wt%. The viscosity of the outer layer slurry is controlled at 25000 mPa·s, and the viscosity of the middle layer slurry is controlled at 20000 mPa·s.

[0049] b) Gradient casting: inner layer scraper gap 50μm, middle layer scraper gap 1500μm, outer layer scraper gap 80μm.

[0050] c) Hot pressing and annealing: The hot pressing conditions were 195°C, 15MPa, and 8min; the annealing conditions were the same as in Example 1.

[0051] Example 3

[0052] The preparation method of the high-strength and corrosion-resistant PVDF-based composite material described in Example 3 consists of the following steps:

[0053] (1) The preparation steps of the surface nanofibers are the same as in Example 1, except that: the pH of silanization is adjusted to 5.0, the pH of in-situ growth is adjusted to 10.0, and the reaction time is 6h. The thickness of the SiO2 nanolayer is about 19.5nm.

[0054] (2) Preparation of fluorine-modified graphene oxide, the steps are the same as in Example 1.

[0055] (3) The preparation steps of the in-situ polymerization slurry are the same as in Example 1, except that: the amount of VDF monomer added is 8%, the polymerization temperature is 105℃, and the reaction time is 4h. The solid content is concentrated under reduced pressure to 45%.

[0056] (4) Molding of gradient structure composite materials

[0057] a) Slurry preparation: The amount of nano-TiO2 added to the outer layer slurry is 10wt%; the amount of surface nano-sized carbon fiber added to the middle layer slurry is 20wt%; and the amount of SiO2@Al2O3 core-shell nanoparticles added to the inner layer slurry is 5wt%. The viscosity of the outer layer slurry is controlled at 27000 mPa·s, and the viscosity of the middle layer slurry is controlled at 22000 mPa·s.

[0058] b) Gradient casting: inner layer scraper gap 100μm, middle layer scraper gap 3000μm, outer layer scraper gap 150μm.

[0059] c) Hot pressing and annealing: The hot pressing conditions were 210°C, 20MPa, and 15min; the annealing conditions were the same as in Example 1.

[0060] Comparative Example 1

[0061] The preparation method of the high-strength corrosion-resistant PVDF-based composite material described in Comparative Example 1 does not involve the separate preparation in step a) of S4. The basic slurry prepared in S3 (containing only the initially added filler, without any targeted replenishment) is directly used for casting and hot pressing. The remaining conditions are the same as in Example 1.

[0062] Comparative Example 2

[0063] The preparation method of the high-strength and corrosion-resistant PVDF-based composite material described in Comparative Example 2 does not involve in-situ polymerization. In step S3, no VDF monomer or initiator is added; only physical mixing is performed. The remaining formulation amounts and processes are the same as in Example 1.

[0064] Comparative Example 3: The preparation method of the high-strength corrosion-resistant PVDF-based composite material described in Comparative Example 3 does not involve annealing. In step c) of S4, after hot pressing and annealing, the material is directly tested after cooling without undergoing annealing treatment at 170℃ for 1 hour.

[0065] The high-strength and corrosion-resistant PVDF-based composite materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. Tensile strength was tested according to GB / T 1040.2 standard; interlaminar shear strength (ILSS) was tested according to ASTM D2344 standard; corrosion resistance was tested by measuring the tensile strength retention rate after immersion in 98% H2SO4 (60℃) for 2000 h. The test results are shown in Table 1.

[0066] Table 1. Performance test results of high-strength and corrosion-resistant PVDF-based composite materials

[0067] Item Tensile Strength (MPa) Flexural Modulus (GPa) Interlaminar Shear Strength (MPa) H2SO4 soak retention Example 1 82.5 10.4 108 94.5% Example 2 79.2 10.6 101 93.5% Example 3 77.6 9.6 98 92.2% Comparative Example 1 68.5 8.2 95 86.0% Comparative Example 2 64.0 7.5 76 84.5% Comparative Example 3 67.3 7.8 90 89.0%

[0068] As shown in Table 1, the composite materials prepared in Examples 1-3 all exhibited excellent performance.

[0069] The comparative examples and comparative examples further confirm the key roles of in-situ polymerization, gradient addition structure, and annealing process in improving material properties.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength, corrosion-resistant PVDF-based composite material, characterized in that: It consists of the following steps: Preparation of S1 surface nanofibers Carbon fibers were activated by treatment in 10wt% NaOH solution at 80℃ for 30 min, washed with deionized water until neutral, and then added to an ethanol-water solution of 3-aminopropyltriethoxysilane. The pH was adjusted to 4.5-5.0, and the reaction was stirred at 60℃ for 4 h. After the reaction, the fibers were washed and dried. Subsequently, the carbon fibers were added to an ethanol-water solution of tetraethyl orthosilicate, and ammonia was added to adjust the pH to 9-10. The reaction was carried out at 60℃ for 4-6 h for in-situ growth. After the reaction, the fibers were washed and dried to prepare surface nanofibers with a 5-20 nm thick SiO2 nanolayer. Preparation of S2 Fluorine-Modified Graphene Oxide Graphene oxide was dispersed in anhydrous DMF, perfluorooctyltriethoxysilane was added, and the reaction was carried out at 80°C for 6 hours under nitrogen protection. After the reaction was completed, the mixture was washed with ethanol and dried under vacuum to prepare fluorine-modified graphene oxide. Preparation of S3 in-situ polymerization slurry Surface-nanosized carbon fibers, fluorine-modified graphene oxide, and SiO2@Al2O3 core-shell nanoparticles with a particle size of 20-50 nm were ultrasonically dispersed in a mixed solvent. PVDF resin was added and stirred at 60 °C to dissolve. VDF monomer and initiator were then added, and the mixture was in-situ polymerized in a high-pressure reactor at 95-105 °C for 3-4 h. After the reaction was completed, the mixture was concentrated under reduced pressure to prepare an in-situ polymerized slurry. S4: Molding of Gradient Structure Composite Materials A) Prepare outer layer slurry, intermediate layer slurry, and inner layer slurry separately: The outer layer slurry is a portion of the in-situ polymerization slurry prepared in step S3, to which nano-TiO2 is added, with the amount of nano-TiO2 added being 5-10 wt% of the solid content of this portion of the slurry; The intermediate layer slurry is a portion of the in-situ polymerization slurry prepared in step S3, to which the surface nano-carbon fiber is added, with the amount added being 10-20 wt% of the solid content of this portion of the slurry; The inner layer slurry is a portion of the in-situ polymerization slurry prepared in step S3, to which SiO2@Al2O3 core-shell nanoparticles are added, with the amount added being 3-5 wt% of the solid content of this portion of the slurry; B) Using the gradient casting method, the inner layer, middle layer and outer layer are cast sequentially on the carrier. After each layer is cast, it is partially dried. Finally, it is completely dried by segmented heating to prepare a three-layer composite dry film. C) The three-layer composite dry film was hot-pressed at 195-210℃ and 15-20MPa for 8-15 minutes, cooled under pressure, and then annealed at 170℃ for 1 hour to prepare a high-strength and corrosion-resistant PVDF-based composite material.

2. The method for preparing the high-strength, corrosion-resistant PVDF-based composite material according to claim 1, characterized in that: The volume ratio of ethanol to water in the aqueous ethanol solution of 3-aminopropyltriethoxysilane described in S1 is 4:1; the volume ratio of ethanol to water in the aqueous ethanol solution of TEOS described in S1 is 6:

1.

3. The method for preparing a high-strength, corrosion-resistant PVDF-based composite material according to claim 1, characterized in that: The mass-to-volume ratio of graphene oxide to perfluorooctyltriethoxysilane in S2 is 1:2, in g / mL; the anhydrous DMF in S2 needs to be dehydrated by anhydrous MgSO4.

4. The method for preparing a high-strength, corrosion-resistant PVDF-based composite material according to claim 1, characterized in that: The mixed solvent mentioned in S3 is a mixture of DMF and NMP in a volume ratio of 7:3; the amount of VDF monomer added in S3 is 5-8% of the mass of PVDF resin, and the initiator is azobisisobutyronitrile (AIBN), which is added at 0.3% of the mass of VDF monomer; the vacuum concentration mentioned in S3 is to control the solid content to 35-45%.

5. The method for preparing a high-strength, corrosion-resistant PVDF-based composite material according to claim 1, characterized in that: The viscosity of the intermediate layer slurry in S4 is controlled at 20000-22000 mPa·s, and the viscosity of the outer layer slurry is controlled at 25000-27000 mPa·s.

6. The method for preparing a high-strength, corrosion-resistant PVDF-based composite material according to claim 1, characterized in that: The gap between the inner layer casting blades in S4 is 50-100 μm, the gap between the middle layer casting blades is 1500-3000 μm, and the gap between the outer layer casting blades is 80-150 μm. The partial drying program is as follows: inner layer 60℃×5min+80℃×5min, middle layer 60℃×10min+80℃×10min+100℃×10min, outer layer 60℃×5min+80℃×8min.

7. The method for preparing a high-strength, corrosion-resistant PVDF-based composite material according to claim 1, characterized in that: The hot pressing described in S4 adopts a staged pressurization method: the pressure is increased to 5 MPa in the first minute, to 10 MPa in the second minute, and to the target pressure of 15-20 MPa in the third minute.

8. The method for preparing a high-strength, corrosion-resistant PVDF-based composite material according to claim 1, characterized in that: The high-strength corrosion-resistant PVDF-based composite material described in S4c) is composed of the following raw materials by weight: 100 parts PVDF resin, 18-25 parts surface nano-sized carbon fiber, 0.5-2 parts fluorine-modified graphene oxide, and 2-4 parts core-shell nanoparticles.