High-performance sandwich wind power blade core material and preparation method thereof

Abstract

The invention relates to the field of wind power blade materials, and particularly discloses a high-performance sandwich wind power blade core material and a preparation method thereof.The high-performance sandwich wind power blade core material comprises a balsa wood base material and PET plates located on the two sides of the balsa wood base material, and the balsa wood base material comprises balsa wood located in the middle and modified balsa wood plates located between the balsa wood and the PET plates; the modified Basa wood board is prepared by carrying out modification pretreatment on Basa wood powder and then carrying out hot press molding, wherein the modification pretreatment comprises the steps of carrying out vacuum dipping treatment on the Basa wood powder in a modification solution and then carrying out dipping treatment in a silane coupling agent solution; the preparation method of the sandwich wind power blade core material comprises the following steps that the PET plate, the modified Basa wood plate, the Basa wood plate, the modified Basa wood plate and the PET plate are sequentially stacked, the interfaces of the plates are coated with an epoxy resin adhesive, then hot pressing and cooling demolding are conducted, and the sandwich wind power blade core material is prepared.

Description

Technical Field

[0001] This application relates to the field of wind turbine blade materials, and more specifically, it relates to a high-performance sandwich wind turbine blade core material and its preparation method. Background Technology

[0002] With the booming development of the wind power industry, wind turbine blades, as the core power components of wind turbine generators that convert wind energy into mechanical energy, directly affect the power generation efficiency and operational reliability of wind turbine generators. As the wind power industry continues to pursue larger, more efficient, and lower-cost wind turbine generators, wind turbine blades face the dual challenges of lightweighting and high strength, which places higher demands on the performance of the blade core material.

[0003] Currently, wind turbine blade core materials mainly include three types: balsa wood, PVC foam, and PET foam. Balsa wood, due to its low density and high specific strength, is often used in load-bearing parts such as the blade root. PET foam, on the other hand, is widely used in the blade midsection and leading edge due to its excellent closed-cell structure, weather resistance, and recyclability. In the manufacturing process of wind turbine blades, they are typically made by composite molding of core material and fiber reinforcement material. When the core material and fiber reinforcement material are placed in a mold using a vacuum pump to create a negative pressure environment, resin is drawn into the mold under negative pressure and impregnates the fiber reinforcement material and core material. The resin fills the pores between the fibers and the microstructure of the core material surface. After the resin cures, the fiber reinforcement material, core material, and resin form a unified whole.

[0004] However, single materials face significant bottlenecks in performance balance. Specifically, balsa wood, as a natural porous material, has an internal capillary closed-cell structure that easily retains moisture during vacuum infusion, becoming the main cause of bubble defects during resin curing. This leads to a decrease in interlayer shear strength of the blades and an increased risk of explosive polymerization and delamination. While traditional PET foam can avoid moisture interference, its mechanical properties are insufficient. Its compressive modulus and impact resistance are lower than those of balsa wood, making it difficult to completely replace the function of wood core materials in mechanical load-bearing and failing to meet the requirements of high strength and high stability of wind turbine blades under complex operating conditions.

[0005] Therefore, providing a sandwich wind turbine blade core material that can eliminate bubble defects during vacuum infusion and has better mechanical properties is of great significance for the application of wind turbine blades. Summary of the Invention

[0006] In order to eliminate bubble defects during vacuum infusion and to achieve better mechanical properties, this application provides a high-performance sandwich wind turbine blade core material and its preparation method.

[0007] In a first aspect, this application provides a high-performance sandwich wind turbine blade core material, employing the following technical solution:

[0008] A high-performance sandwich wind turbine blade core material includes a balsa wood substrate and PET boards on both sides of the balsa wood substrate. The balsa wood substrate includes balsa wood in the middle and modified balsa wood board between the balsa wood and the PET board.

[0009] The modified balsa wood board is made by hot pressing balsa wood powder after modification pretreatment. The modification pretreatment includes vacuum impregnation of balsa wood powder in a modification liquid and then impregnation in a silane coupling agent solution. The modification liquid contains at least lignin sulfonate, epichlorohydrin modified lignin and poly(N-isopropylacrylamide).

[0010] By adopting the above technical solution, the core material in this application uses a sandwich structure with wood in the middle and PET boards on both sides. The outer PET foam layer can effectively isolate the balsa wood from direct contact with the resin system, blocking the moisture migration path and fundamentally eliminating air bubble defects during vacuum infusion. The middle balsa wood layer fully utilizes its high specific strength to provide core mechanical support for the blade, ensuring that the blade can bear various loads during operation. The symmetrical coating structure of the inner and outer PET layers further improves the overall shear resistance and interface stability of the core material, enhancing the reliability and durability of the blade. This not only retains the mechanical performance advantages of wood core materials but also avoids their hygroscopic defects, while promoting the green transformation of wind turbine blade manufacturing through the recyclable characteristics of PET foam.

[0011] However, the difference in expansion coefficients between balsa wood and PET foam board easily leads to thermal stress concentration. During subsequent processing or use, high temperatures or temperature changes can cause interface debonding, affecting the later mechanical properties of the sandwich core. Therefore, the balsa wood substrate in this application includes the balsa wood core and a modified balsa wood board sandwiched between the balsa wood and the PET board. The modified balsa wood board is formed by hot pressing modified balsa wood powder, serving as an intermediate buffer. More specifically, the balsa wood powder is first vacuum impregnated with a modifying liquid. The poly(N-isopropylacrylamide) in the modifying liquid has a certain thermal responsiveness; its volume changes reversibly with temperature. When the temperature rises, the poly(N-isopropylacrylamide) shrinks, absorbing some of the stress caused by the difference in thermal expansion coefficients between balsa wood and PET board. When the temperature decreases, it expands, releasing some stress. This dynamic stress regulation mechanism can effectively reduce stress accumulation at the interface and prevent interface debonding.

[0012] The addition of epichlorohydrin-modified lignin and lignin sulfonate introduces sulfonic acid groups and epoxy groups, respectively. The negatively charged sulfonic acid groups can electrostatically interact with the cations in the balsa wood substrate and the polar groups on the PET surface, thereby enhancing the interfacial bonding between the two. Moreover, lignin sulfonate can improve the wettability of the wood surface, which not only helps the penetration and adhesion of the modified liquid, but also facilitates the penetration of resin in the subsequent vacuum infusion process, improving the adhesion with the PET substrate. The introduction of epoxy groups can undergo ring-opening reactions with the carboxyl or hydroxyl groups in the PET sheet to form covalent bonds, thereby improving the interfacial bonding between the balsa wood substrate and the PET sheet and alleviating the subsequent debonding phenomenon caused by the difference in the thermal expansion coefficients of the two.

[0013] Ultimately, in this application, modified balsa wood is used as an intermediate buffer layer between the balsa wood and the PET board. This can alleviate the interface debonding caused by the difference in their thermal expansion coefficients. Furthermore, the modification treatment of balsa wood powder helps to improve the interfacial bonding between the balsa wood and the PET board, further alleviating the subsequent debonding phenomenon and ensuring the stability of subsequent mechanical properties. In addition, the outer PET board also solves the bubble defect of balsa wood during the vacuum infusion process, resulting in a core material with better mechanical properties.

[0014] Optionally, the modified liquid comprises the following raw materials in parts by weight:

[0015] 20-30 parts maleic anhydride modified polypropylene, 5-12 parts lignin sulfonate, 10-20 parts epichlorohydrin modified lignin, 5-10 parts poly(N-isopropylacrylamide) and 10-20 parts ethanol, 20-30 parts xylene, 5-10 parts water and 3-8 parts Tween.

[0016] By adopting the above technical solution, the addition of maleic anhydride-modified polypropylene allows it to penetrate the pores and surface of balsa wood powder during impregnation. The anhydride groups can chemically bond with active groups such as hydroxyl groups in the balsa wood substrate, and the anhydride groups can also react with polar groups such as carboxyl and hydroxyl groups on the surface of the PET sheet, thus forming a strong chemical bond between the balsa wood substrate and the PET sheet, enhancing the interfacial bonding strength. Furthermore, the maleic anhydride-modified polypropylene acts as a bridge; its polar portion is well-compatible with the PET sheet, while its non-polar portion is even more compatible with the balsa wood substrate, reducing the interfacial tension. This improved compatibility allows the subsequently infused resin to better wet the interface, filling the tiny gaps between the interfaces and forming a denser and more uniform structure. This helps maintain the interfacial bonding performance during subsequent processing or use under high temperatures or temperature changes, improving the overall interfacial bonding strength and mechanical properties of the core material.

[0017] Optionally, the modified liquid is prepared by the following method:

[0018] After mixing ethanol and water, poly-N-isopropylacrylamide and lignin sulfonate were added to prepare a preliminary mixture.

[0019] A mixture was prepared by mixing xylene with maleic anhydride-modified polypropylene and stirring.

[0020] Epichlorohydrin was added to the initial mixture to modify lignin. After stirring, Tween was added, and then the mixture was stirred to obtain the modified solution.

[0021] Optionally, the epichlorohydrin-modified lignin is prepared by the following method:

[0022] After mixing lignin and acetone at a mass ratio of 1:(2-3), the pH was adjusted to 7.5-8.5, and epichlorohydrin was added under stirring. The mixture was heated to 60-70℃ and reacted for 2-3 hours. Then, the mixture was centrifuged, washed and dried to obtain epichlorohydrin-modified lignin. The mass ratio of epichlorohydrin to lignin was 1:(3-4).

[0023] By adopting the above technical solution, lignin and epichlorohydrin react in an organic solvent under alkaline conditions. Epichlorohydrin reacts with the phenolic hydroxyl groups in lignin to introduce epoxy groups into lignin. The epoxy groups have high reactivity and can form chemical bonds with functional groups such as carboxyl and hydroxyl groups on the surface of PET boards. They can also crosslink with cellulose and hemicellulose in balsa wood substrates, further improving the bonding strength between wood and PET boards. In addition, this application adds more epichlorohydrin to modify lignin, improving the hydrophobicity of lignin, thereby alleviating the hygroscopicity of balsa wood substrates and improving its hygroscopic expansion phenomenon. This, in turn, improves the debonding phenomenon caused by the difference in expansion properties between balsa wood boards and PET boards.

[0024] Optionally, the modified balsa wood board is prepared by the following method:

[0025] 1) First, vacuum impregnate the balsa wood powder in the modification liquid for 30-40 minutes, then depressurize it to normal pressure, let it stand for 10-20 minutes, filter it, and dry it to obtain pretreated balsa wood powder.

[0026] 2) The pretreated balsa wood powder is impregnated in an impregnation solution containing aminosilane coupling agent for 60-90 minutes at an impregnation temperature of 40-50℃, then filtered and dried to obtain modified balsa wood powder.

[0027] 3) A wood flour mixture is prepared by mixing modified balsa wood flour with nano-silica and powdered phenolic resin;

[0028] 4) The wood flour mixture is first pre-pressed under a pressure of 1-2 MPa for 5-10 minutes, and then hot-pressed under a pressure of 5-10 MPa and a temperature of 150-180℃. After cooling, it is demolded to obtain modified balsa wood boards. The thickness of the modified balsa wood boards is 1 / 4-1 / 5 of the balsa wood substrate.

[0029] By adopting the above technical solution, balsa wood powder is first impregnated with a modified liquid, and then impregnated in an aminosilane coupling agent solution. The aminosilane coupling agent can form chemical bonds with the hydroxyl groups on the wood surface, and at the same time form a coupling agent molecular layer on the wood surface. When the wood board is bonded to the PET board, the organic groups in the coupling agent molecular layer can interact with the molecules on the PET board surface, enhancing the bonding strength between the wood and the PET board and improving the interfacial performance of the entire core material.

[0030] Ultimately, this application first chemically modifies balsa wood powder, then hot-presses it to produce modified balsa wood boards, which serve as a connecting bridge between the intermediate main substrate balsa wood and the PET board. This improves the surface properties of the balsa wood substrate, enhances its bonding strength with the PET board, improves the mechanical properties and stability of the entire core material, and alleviates subsequent debonding.

[0031] Optionally, in the preparation of modified balsa wood boards, in step 1), the mass ratio of balsa wood powder to modification liquid is 1:(4-5), the impregnation temperature is 45-60℃, and the impregnation is carried out under the conditions of -0.08-(-0.1) MPa.

[0032] In step 2), the mass ratio of pretreated balsa wood powder to impregnation solution is 1:(6-8), and the impregnation solution is obtained by mixing aminosilane coupling agent and ethanol solution at a mass ratio of 1:(3-4), and the ethanol solution is obtained by mixing ethanol and water at a volume ratio of 1:(0.8-1).

[0033] In step 3), the mass ratio of modified balsa wood powder to nano silica and powdered phenolic resin is 1:(0.1-0.2):(0.02-0.05).

[0034] By adopting the above technical solution, this application uses modified balsa wood flour as the main raw material, and also adds a small amount of nano-silica and powdered phenolic resin. Powdered phenolic resin acts as a wood flour hardener, which helps the wood flour to bond together and form balsa wood boards with better mechanical properties. Nano-silica, as a filler, not only helps to improve mechanical properties, but more importantly, the difference in thermal expansion coefficient between the grain direction and the cross direction of balsa wood is huge, and the difference in thermal expansion coefficient between PET and balsa wood is also large, resulting in obvious anisotropy. Nano-silica has a low thermal expansion coefficient. When it is added to the modified balsa wood board between PET board and balsa wood, it can act as a transition buffer layer, improve the overall thermal expansion coefficient of the modified balsa wood board, alleviate the difference in thermal expansion coefficient between PET board and balsa wood, and form a stress buffer layer to absorb and disperse the stress caused by the difference in thermal expansion coefficient, avoid local stress concentration, and thus alleviate the subsequent debonding caused by the difference in thermal expansion coefficient, affecting mechanical properties and stability.

[0035] Optionally, the PET sheet is made from the following parts by weight of raw materials:

[0036] 40-60 parts PET granules, 1-5 parts silane coupling agent modified nano silica, 0.5-3 parts tetramethyltetravinylcyclotetrasiloxane monomer, 3-8 parts polyether block amide, 0.8-3 parts 1,4-naphthalenedicarboxylic acid, 0.1-0.5 parts initiator, and 0.1-0.3 parts AC foaming agent.

[0037] By adopting the above technical solutions, the PET board preparation in this application uses PET particles as the substrate and adds nano-silica. Its extremely low coefficient of thermal expansion can effectively reduce the coefficient of thermal expansion of the PET board, while enhancing the rigidity of the material. Tetramethyltetravinylcyclotetrasiloxane monomer can form a siloxane network structure, improving the heat resistance and dimensional stability of PET, and also has a low thermal expansion capacity. When the temperature changes, its molecular structure can effectively reduce intermolecular stretching and deformation, thereby inhibiting volume change, and further reducing the debonding of PET board from balsa wood due to thermal expansion deformation. Polyether block amide has good flexibility and can play a buffering and stress dispersion role at the interface. When thermal stress is generated between balsa wood and PET board due to the difference in coefficient of thermal expansion, the highly elastic material can absorb and disperse these stresses through its own deformation, thereby reducing stress concentration at the interface and reducing the risk of interface debonding. Naphthalic acid monomer can improve the thermal stability coefficient of PET and further reduce the coefficient of thermal expansion.

[0038] Ultimately, this application addresses two main issues. First, by improving the raw material of PET sheets, its coefficient of thermal expansion is reduced, making it closer to that of balsa wood. Second, by using modified balsa wood as a buffer layer between balsa wood and PET sheets, the anisotropy of balsa wood is controlled, the difference in their coefficients of thermal expansion is buffered, and the chemical bonding between balsa wood and PET sheets is enhanced, further reducing debonding and improving interfacial bonding, thereby ensuring the stability of their mechanical properties.

[0039] Optionally, the PET sheet is prepared by the following method:

[0040] Raw material pretreatment: Disperse nano-silica in an ethanol aqueous solution, add silane coupling agent, heat to 55-65℃ and stir for 40-60 min, filter and dry to obtain silane coupling agent modified nano-silica;

[0041] The initiator was dissolved in xylene and then mixed evenly with polyether block amide to obtain a pre-dispersed mixture;

[0042] Feeding: The raw materials are extruded and granulated through a twin-screw extruder to obtain modified PET granules;

[0043] Hot pressing: The modified PET granules are first pre-dried at 100-110℃ for 2-3 hours, and then hot-pressed at 270-280℃ and 5-10MPa to obtain PET sheets.

[0044] By adopting the above technical solution, the nano-silica is first treated with a silane coupling agent before being added, which improves the compatibility between nano-silica and PET, helps it to be evenly dispersed, plays a better role, and improves the interfacial compatibility between nano-silica and PET.

[0045] Optionally, in the feeding step, the specific operation is as follows: first, PET granules are added to the main feed port of the twin-screw extruder and melted. Then, silane coupling agent modified nano-silica and 1,4-naphthalenedicarboxylic acid are added to the side feed port in the middle section of the melting section. The remaining raw materials are injected into the homogenization section, extruded, water-cooled, and pelletized to obtain modified PET granules.

[0046] Optionally, during the feeding step, the temperature of the feeding section is 240-250℃, the temperature of the melting section is 260-270℃, the temperature of the homogenization section is 275-285℃, the temperature of the die head is 270-280℃, and the screw speed is 200-300rpm.

[0047] Secondly, this application provides a method for preparing a high-performance sandwich wind turbine blade core material, employing the following technical solution:

[0048] A method for preparing a high-performance sandwich wind turbine blade core material includes the following steps:

[0049] The core material of the sandwich wind turbine blade is obtained by stacking PET board, modified balsa wood board, balsa wood, modified balsa wood board and PET board in sequence, with epoxy resin adhesive (50-80g / m²) applied at the interface of the boards. Then, it is hot-pressed at 120-130℃ and 5-8MPa for 20-30 minutes, cooled and demolded.

[0050] By adopting the above technical solution, the method provided in this application is simple, convenient, and easy to industrialize.

[0051] In summary, this application has the following beneficial effects:

[0052] 1. In this application, on the one hand, the coefficient of thermal expansion of PET sheet is reduced by improving the raw material of PET sheet, making it closer to that of balsa wood. On the other hand, the modified balsa wood board between balsa wood and PET sheet is used as a buffer transition layer. This controls the anisotropy of balsa wood and buffers the difference in the coefficient of thermal expansion between the two. It also enhances the chemical bonding between balsa wood and PET sheet, further reducing the debonding of the two in the later stage and improving the interfacial bonding force, thereby ensuring the stability of its mechanical properties.

[0053] 2. In this application, the core material uses a sandwich structure with wood in the middle and PET sheets on both sides. The outer PET foam effectively isolates the balsa wood from direct contact with the resin system, blocking moisture migration paths and fundamentally eliminating air bubble defects during vacuum infusion. The middle balsa wood layer fully utilizes its high specific strength to provide core mechanical support for the blade, ensuring that the blade can withstand various loads during operation. The symmetrical coating structure of the inner and outer PET layers further enhances the overall shear resistance and interfacial stability of the core material, improving the reliability and durability of the blade. This not only retains the mechanical performance advantages of wood core materials but also avoids their hygroscopic defects. At the same time, the recyclable nature of PET foam promotes the green transformation of wind turbine blade manufacturing.

[0054] 3. In this application, the balsa wood powder undergoes vacuum impregnation treatment with a modifying liquid. The poly(N-isopropylacrylamide) in the modifying liquid exhibits a certain degree of thermal responsiveness, with its volume reversibly changing with temperature. When the temperature rises, the poly(N-isopropylacrylamide) shrinks, absorbing some of the stress caused by the difference in thermal expansion coefficients between balsa wood and PET board; when the temperature decreases, it expands, releasing some stress. This dynamic stress regulation mechanism can effectively reduce stress accumulation at the interface and prevent interface debonding. Detailed Implementation

[0055] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0056] The following preparation examples illustrate the preparation of epichlorohydrin-modified lignin.

[0057] Preparation Example 1

[0058] After mixing lignin and acetone at a mass ratio of 1:2.5, the pH was adjusted to 8, and epichlorohydrin was added under stirring. The mixture was heated to 65°C and reacted for 2.5 hours. Then, the mixture was centrifuged, washed, and dried to obtain epichlorohydrin-modified lignin. The mass ratio of epichlorohydrin to lignin was 1:3.5.

[0059] Preparation Example 2

[0060] Lignin and acetone were mixed at a mass ratio of 1:2, the pH was adjusted to 7.5, and epichlorohydrin was added under stirring. The mixture was heated to 60°C and reacted for 3 hours. After centrifugation, washing and drying, epichlorohydrin-modified lignin was obtained. The mass ratio of epichlorohydrin to lignin was 1:3.

[0061] Preparation Example 3

[0062] Lignin and acetone were mixed at a mass ratio of 1:3, the pH was adjusted to 8.5, and epichlorohydrin was added under stirring. The mixture was heated to 70°C and reacted for 2 hours. After centrifugation, washing and drying, epichlorohydrin-modified lignin was obtained. The mass ratio of epichlorohydrin to lignin was 1:4.

[0063] The balsa wood powder used in the following examples can be commercially available balsa wood powder, or it can be balsa wood powder recovered after crushing and separating balsa wood from waste wind turbine blades, or it can be balsa wood powder scraps generated during the processing of balsa wood boards. In the following examples, the balsa wood powder used is balsa wood powder scraps generated during the cutting, drilling, or milling of balsa wood boards.

[0064] In the following examples, the maleic anhydride-modified polypropylene used was maleic anhydride-modified PP from Dongguan Taotao Plastic Raw Materials Co., Ltd.

[0065] Sodium lignosulfonate is selected as the lignosulfonate.

[0066] The powdered phenolic resin used is solid phenolic resin of model HY555 from Shengwanjia New Materials (Shandong) Co., Ltd.

[0067] The epoxy resin adhesive used is from Shandong Kebang Chemical Co., Ltd.

[0068] The PET granules used are DuPont grade FR530 polyester granules from Xinhongshou Plastics (Suzhou) Co., Ltd.

[0069] The polyether block amide selected is Wanhua PEBA 4012 polyether block amide from Dongguan Yanxi Plastic Raw Materials Co., Ltd.

[0070] The tetramethyltetravinylcyclotetrasiloxane monomer used is the vinyl cyclone V4 from Zhongshan Dixin Chemical Co., Ltd.

[0071] Example 1

[0072] A method for preparing a high-performance sandwich wind turbine blade core material includes the following steps:

[0073] S1. Preparation of modified balsa wood boards, specifically including the following steps:

[0074] 1) Preparation of modified solution:

[0075] 15 kg of ethanol and 8 kg of water were mixed, and then 8 kg of poly-N-isopropylacrylamide and 8 kg of lignin sulfonate were added to prepare the initial mixture.

[0076] 25 kg of xylene and 25 kg of maleic anhydride-modified polypropylene were mixed and stirred to obtain a mixture.

[0077] Add 15 kg of epichlorohydrin-modified lignin prepared in Preparation Example 1 to the initial mixture, stir, add 5 kg of Tween 60, then add the mixture and stir to obtain the modified solution.

[0078] Balsa wood powder was first vacuum impregnated in a modified liquid for 35 minutes at a temperature of 55°C and under a pressure of -0.09 MPa. Then the pressure was released to atmospheric pressure, allowed to stand for 15 minutes, filtered, and dried to obtain pretreated balsa wood powder.

[0079] 2) The impregnation solution is prepared by mixing aminosilane coupling agent KH-550 with ethanol solution at a mass ratio of 1:3.5, and the ethanol solution is prepared by mixing ethanol and water at a volume ratio of 1:0.9.

[0080] Then, the pretreated balsa wood powder obtained in step 1) is impregnated in the prepared impregnation solution for 70 minutes at an impregnation temperature of 45°C, then filtered and dried to obtain modified balsa wood powder.

[0081] 3) The modified balsa wood flour obtained in step 2) is mixed with nano silica and powdered phenolic resin at a mass ratio of 1:0.1:0.03 to obtain a wood flour mixture;

[0082] 4) The wood flour mixture is first pre-pressed at a pressure of 1.5 MPa for 8 minutes, then hot-pressed at a pressure of 8 MPa and a temperature of 160℃, and then demolded after cooling to obtain modified balsa wood boards. The thickness of the modified balsa wood boards is 1 / 5 of that of the balsa wood substrate.

[0083] In step 1), the mass ratio of balsa wood powder to modified liquid is 1:4.5; in step 2), the mass ratio of pretreated balsa wood powder to impregnation liquid is 1:7.

[0084] S2. Preparation of PET plates: The specific steps are as follows:

[0085] Raw material pretreatment: Nano-silica was dispersed in an ethanol-water solution at a mass ratio of 2.5 times (ethanol to water in a mass ratio of 1:1), and silane coupling agent KH-550 was added. The mixture was heated to 60°C and stirred for 50 min, then filtered and dried to obtain silane coupling agent modified nano-silica. The amount of silane coupling agent KH-550 added was 5 wt% of the nano-silica.

[0086] 0.3 kg of initiator, specifically dicumyl peroxide (DCP), was dissolved in xylene at a mass ratio of 1, and then mixed evenly with polyether block amide to obtain a pre-dispersed mixture.

[0087] Feeding: The following additives are added in a twin-screw extruder for melt extrusion: 50 kg PET granules, 3 kg silane coupling agent modified nano-silica, 1.5 kg tetramethyltetravinylcyclotetrasiloxane monomer, 5 kg polyether block amide, 1.5 kg 1,4-naphthalenedicarboxylic acid, 0.3 kg initiator, and 0.2 kg AC foaming agent. The more specific feeding sequence is as follows:

[0088] First, PET granules are added to the main feed port of a twin-screw extruder and melted. Then, silane coupling agent modified nano-silica and 1,4-naphthalenedicarboxylic acid are added to the side feed port in the middle section of the melting section. The remaining raw materials are injected into the homogenization section, extruded, water-cooled, and pelletized to obtain modified PET granules.

[0089] The parameters of the twin-screw extruder are as follows: feeding section temperature 245℃, melting section temperature 265℃, homogenization section temperature 280℃, die head temperature 275℃, and screw speed 250rpm.

[0090] Hot pressing: The modified PET granules were first pre-dried at 105℃ for 2.5h, and then hot-pressed at 275℃ and 8MPa to obtain PET sheets.

[0091] S3. PET board, modified balsa wood board, balsa wood, modified balsa wood board and PET board are stacked in sequence, and epoxy resin adhesive (60g / m²) is applied to the interface of the boards. Then, after hot pressing at 125℃ and 6MPa for 25min, the core material of the sandwich wind turbine blade is obtained after cooling and demolding.

[0092] Example 2

[0093] A method for preparing a high-performance sandwich wind turbine blade core material includes the following steps:

[0094] S1. Preparation of modified balsa wood boards, specifically including the following steps:

[0095] 1) Preparation of modified solution:

[0096] 10 kg of ethanol and 5 kg of water were mixed, and then 5 kg of poly(N-isopropylacrylamide) and 5 kg of lignin sulfonate were added to prepare a preliminary mixture.

[0097] 20 kg of xylene and 20 kg of maleic anhydride-modified polypropylene were mixed and stirred to obtain a mixture.

[0098] 10 kg of epichlorohydrin-modified lignin prepared in Preparation Example 2 was added to the initial mixture, and after stirring, 3 kg of Tween 60 was added. Then, the mixture was added and stirred to obtain the modified solution.

[0099] Balsa wood powder was first vacuum impregnated in a modified liquid for 30 minutes at a temperature of 60°C and under a pressure of -0.08 MPa. Then the pressure was released to atmospheric pressure, allowed to stand for 10 minutes, filtered, and dried to obtain pretreated balsa wood powder.

[0100] 2) The impregnation solution is prepared by mixing aminosilane coupling agent KH-550 with ethanol solution at a mass ratio of 1:3, and the ethanol solution is prepared by mixing ethanol and water at a volume ratio of 1:0.8.

[0101] Then, the pretreated balsa wood powder obtained in step 1) is impregnated in the prepared impregnation solution for 60 minutes at an impregnation temperature of 50°C, then filtered and dried to obtain modified balsa wood powder.

[0102] 3) The modified balsa wood flour obtained in step 2) is mixed with nano silica and powdered phenolic resin at a mass ratio of 1:0.1:0.02 to obtain a wood flour mixture;

[0103] 4) The wood flour mixture is first pre-pressed at a pressure of 1 MPa for 10 minutes, then hot-pressed at a pressure of 5 MPa and a temperature of 180℃, and then demolded after cooling to obtain modified balsa wood boards. The thickness of the modified balsa wood boards is 1 / 4 of the balsa wood substrate.

[0104] In step 1), the mass ratio of balsa wood powder to modified liquid is 1:4; in step 2), the mass ratio of pretreated balsa wood powder to impregnation liquid is 1:6.

[0105] S2. Preparation of PET plates: The specific steps are as follows:

[0106] Raw material pretreatment: Nano-silica was dispersed in an ethanol-water solution at a mass ratio of 2:1 (ethanol to water in a mass ratio of 1:0.8), silane coupling agent KH-550 was added, the mixture was heated to 55°C and stirred for 60 min, filtered and dried to obtain silane coupling agent modified nano-silica. The amount of silane coupling agent KH-550 added was 3 wt% of the nano-silica.

[0107] 0.1 kg of initiator, specifically dicumyl peroxide (DCP), was dissolved in xylene at a mass ratio of 1, and then mixed evenly with polyether block amide to obtain a pre-dispersed mixture.

[0108] Feeding: The following additives are added in a twin-screw extruder for melt extrusion: 40 kg PET granules, 1 kg silane coupling agent modified nano-silica, 0.5 kg tetramethyltetravinylcyclotetrasiloxane monomer, 3 kg polyether block amide, 0.8 kg 1,4-naphthalenedicarboxylic acid, 0.1 kg initiator, and 0.1 kg AC foaming agent. The more specific feeding sequence is as follows:

[0109] First, PET granules are added to the main feed port of a twin-screw extruder and melted. Then, silane coupling agent modified nano-silica and 1,4-naphthalenedicarboxylic acid are added to the side feed port in the middle section of the melting section. The remaining raw materials are injected into the homogenization section, extruded, water-cooled, and pelletized to obtain modified PET granules.

[0110] The parameters of the twin-screw extruder are as follows: feeding section temperature 240℃, melting section temperature 260℃, homogenization section temperature 275℃, die head temperature 270℃, and screw speed 200rpm.

[0111] Hot pressing: The modified PET granules were first pre-dried at 100℃ for 3 hours, and then hot-pressed at 270℃ and 10MPa to obtain PET sheets.

[0112] S3. PET board, modified balsa wood board, balsa wood, modified balsa wood board and PET board are stacked in sequence, and epoxy resin adhesive (50g / m²) is applied to the interface of the boards. Then, after hot pressing at 120℃ and 5MPa for 30min, the core material of the sandwich wind turbine blade is obtained after cooling and demolding.

[0113] Example 3

[0114] A method for preparing a high-performance sandwich wind turbine blade core material includes the following steps:

[0115] S1. Preparation of modified balsa wood boards, specifically including the following steps:

[0116] 1) Preparation of modified solution:

[0117] 20 kg of ethanol and 10 kg of water were mixed, and then 10 kg of poly-N-isopropylacrylamide and 12 kg of lignin sulfonate were added to prepare the initial mixture.

[0118] 30 kg of xylene and 30 kg of maleic anhydride-modified polypropylene were mixed and stirred to obtain a mixture.

[0119] 20 kg of epichlorohydrin-modified lignin prepared in Preparation Example 3 was added to the initial mixture, and after stirring, 8 kg of Tween 60 was added. Then, the mixture was added and stirred to obtain the modified solution.

[0120] Balsa wood powder was first vacuum impregnated in a modified liquid for 40 minutes at a temperature of 45°C and under a pressure of -0.1 MPa. Then the pressure was released to atmospheric pressure, allowed to stand for 20 minutes, filtered, and dried to obtain pretreated balsa wood powder.

[0121] 2) The impregnation solution is prepared by mixing aminosilane coupling agent KH-550 with ethanol solution at a mass ratio of 1:4, and the ethanol solution is prepared by mixing ethanol and water at a volume ratio of 1:1.

[0122] Then, the pretreated balsa wood powder obtained in step 1) is impregnated in the prepared impregnation solution for 90 minutes at an impregnation temperature of 40°C, then filtered and dried to obtain modified balsa wood powder.

[0123] 3) The modified balsa wood flour obtained in step 2) is mixed with nano silica and powdered phenolic resin at a mass ratio of 1:0.2:0.05 to obtain a wood flour mixture;

[0124] 4) The wood flour mixture is first pre-pressed at a pressure of 2MPa for 5 minutes, then hot-pressed at a pressure of 10MPa and a temperature of 150℃, and then demolded after cooling to obtain modified balsa wood boards. The thickness of the modified balsa wood boards is 1 / 5 of the balsa wood substrate.

[0125] In step 1), the mass ratio of balsa wood powder to modified liquid is 1:5; in step 2), the mass ratio of pretreated balsa wood powder to impregnation liquid is 1:8.

[0126] S2. Preparation of PET plates: The specific steps are as follows:

[0127] Raw material pretreatment: Nano-silica was dispersed in an ethanol-water solution at a mass ratio of 3:1.2 (ethanol to water in a mass ratio of 1:1.2), and silane coupling agent KH-550 was added. The mixture was heated to 65°C and stirred for 40 min, then filtered and dried to obtain silane coupling agent modified nano-silica. The amount of silane coupling agent KH-550 added was 8 wt% of the nano-silica.

[0128] 0.5 kg of initiator, specifically dicumyl peroxide (DCP), was dissolved in xylene at a mass ratio of 1, and then mixed evenly with polyether block amide to obtain a pre-dispersed mixture.

[0129] Feeding: The following additives are added to a twin-screw extruder for melt extrusion: 60 kg PET granules, 5 kg silane coupling agent modified nano-silica, 3 kg tetramethyltetravinylcyclotetrasiloxane monomer, 8 kg polyether block amide, 3 kg 1,4-naphthalenedicarboxylic acid, 0.5 kg initiator, and 0.3 kg AC foaming agent. The more specific feeding sequence is as follows:

[0130] First, PET granules are added to the main feed port of a twin-screw extruder and melted. Then, silane coupling agent modified nano-silica and 1,4-naphthalenedicarboxylic acid are added to the side feed port in the middle section of the melting section. The remaining raw materials are injected into the homogenization section, extruded, water-cooled, and pelletized to obtain modified PET granules.

[0131] The parameters of the twin-screw extruder are as follows: feeding section temperature 250℃, melting section temperature 270℃, homogenization section temperature 285℃, die head temperature 280℃, and screw speed 300rpm.

[0132] Hot pressing: The modified PET granules were first pre-dried at 110℃ for 2 hours, and then hot-pressed at 280℃ and 5MPa to obtain PET sheets.

[0133] S3. PET board, modified balsa wood board, balsa wood, modified balsa wood board and PET board are stacked in sequence, and epoxy resin adhesive (80g / m²) is applied to the interface of the boards. Then, after hot pressing at 130℃ and 8MPa for 20min, the core material of the sandwich wind turbine blade is obtained after cooling and demolding.

[0134] Example 4

[0135] A method for preparing a high-performance sandwich wind turbine blade core material differs from the method in Example 1 in that, in step S2, the PET sheet is directly prepared by using PET granules and AC foaming agent as raw materials and hot pressing in Example 1.

[0136] Example 5

[0137] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that tetramethyltetravinylcyclotetrasiloxane monomer is not added in the feeding step of step S2.

[0138] Example 6

[0139] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that polyether block amide is not added in the feeding step of step S2.

[0140] Example 7

[0141] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that maleic anhydride-modified polypropylene is not added to the modification liquid in step S1.

[0142] Example 8

[0143] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that nano-silica is not added in step S1 3).

[0144] Comparative Example 1

[0145] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that step S1 is not performed. In step S3, PET board, balsa wood and PET board are stacked in sequence, that is, no modified balsa wood board is placed between the PET board and the balsa wood, and the thickness of the balsa wood is the same as the sum of the thickness of the balsa wood and the modified balsa wood boards on both sides in Example 1. The rest of the operation is the same as in Example 1.

[0146] Comparative Example 2

[0147] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that step 1) is not performed in step S1, and balsa wood powder is directly added to the impregnation liquid in step 2), that is, the balsa wood powder is not subjected to vacuum impregnation treatment with modified liquid.

[0148] Comparative Example 3

[0149] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that poly-N-isopropylacrylamide is not added to the modification solution in step S1.

[0150] Comparative Example 4

[0151] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that lignin sulfonate is not added to the modification solution in step S1.

[0152] Comparative Example 5

[0153] A method for preparing a high-performance sandwich wind turbine blade core material is carried out according to the method in Example 1, except that epichlorohydrin-modified lignin is not added to the modification liquid in step S1.

[0154] Performance testing

[0155] The compressive strength of the core materials prepared in the above embodiments and comparative examples was tested according to the method of ISO-844, and the shear strength of the core materials prepared in the above embodiments and comparative examples was tested according to ASTM C-273 to characterize the interfacial bonding strength of the prepared core materials.

[0156] In addition, the core materials prepared in the above embodiments and comparative examples were heated to 105°C and 95%RH humidity in an environment of 25°C and 50%RH humidity and held for 2 hours, and then reduced to the initial conditions to complete one damp heat cycle. After 100 damp heat cycles, the core materials were taken out and left to stand for 24 hours. The compressive strength and shear strength after damp heat cycles were then tested according to the above method. The test results are shown in Table 1 below.

[0157] Table 1:

[0158] Performance testing Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Initial compressive strength / MPa 18.3 17.5 18.1 16.1 16.8 17.1 17.3 Initial shear strength / MPa 6.8 6.2 6.5 5.3 5.8 6.0 6.2 Compressive strength after damp heat cycling / MPa 17.9 17.1 17.7 14.5 15.6 15.8 16.2 Shear strength after damp heat cycling / MPa 6.6 5.8 6.1 4.4 5.2 5.3 5.6 Performance testing Example 8 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 — Initial compressive strength / MPa 17.8 8.9 9.9 10.5 11.6 11.8 — Initial shear strength / MPa 6.1 1.8 2.1 2.6 3.1 3.2 — Compressive strength after damp heat cycling / MPa 16.9 5.2 6.8 8.5 9.9 10.4 — Shear strength after damp heat cycling / MPa 5.5 0.8 1.4 1.9 2.4 2.7 —

[0159] Referring to the test results in Table 1 above, the core materials prepared in Examples 1-3 of this application have good shear strength, good interfacial bonding between the balsa wood board and the PET board, and maintain good mechanical properties and shear strength after hydrothermal cycling. The interfacial bonding strength remains good after hydrothermal cycling, with minimal interfacial debonding. In contrast, when the PET board and balsa wood are directly composited without modified balsa wood board, the mechanical properties and shear strength decrease significantly after hydrothermal cycling, the interfacial bonding strength decreases significantly, and the interfacial debonding is more severe. Furthermore, in contrast, when the balsa wood powder is not vacuum impregnated with a modifying liquid during the preparation of the modified balsa wood board between the PET board and the intermediate balsa wood, the initial shear strength decreases, and both the mechanical properties and shear strength decrease significantly after hydrothermal cycling, with a significant decrease in interfacial bonding strength.

[0160] Combining the test results of Example 1 and Comparative Examples 3-5, it can be seen that when no poly-N-isopropylacrylamide, lignin sulfonate, or epichlorohydrin-modified lignin is added to the modified solution, its initial shear strength is lower than that of Example 1, and its compressive strength and shear strength after wet heat cycling treatment are also significantly lower. However, it is better than Example 2. It can be seen that the modified solution treatment significantly improves the interfacial bonding strength between PET board and balsa wood board, thereby ensuring the stability of its mechanical properties. At the same time, poly-N-isopropylacrylamide, lignin sulfonate, or epichlorohydrin-modified lignin in the modified solution play an important role in the above process.

[0161] Furthermore, combining the test results of Examples 1 and 4, it can be seen that in Example 4, when the PET board raw material consisted only of PET particles without the addition of other siloxane monomers or other substances, the initial shear strength was reduced, and the compressive and shear strengths were significantly reduced after wet heat cycling. This shows that the addition of silica and siloxane monomers to the PET particles can significantly improve the interfacial bonding between the PET particles and balsa wood. This is because the aforementioned substances can alleviate the thermal expansion coefficient of the PET board, thereby reducing the debonding phenomenon caused by the difference in thermal expansion coefficients between the PET board and the balsa wood. Combining the test results of Examples 5-6, when polyether block amide and tetramethyltetravinylcyclotetrasiloxane monomers were not added during the preparation of the PET board, its compressive and shear strengths were significantly reduced after wet heat cycling. The addition of polyether block amide, as a toughness buffer layer, can absorb the stress caused by the inconsistent deformation at the interface due to the difference in thermal expansion coefficients. The addition of tetramethyltetravinylcyclotetrasiloxane monomer, with the introduction of its siloxane groups, reduces the thermal expansion coefficient of the PET board, improves its heat resistance and dimensional stability, and inhibits volume changes under temperature changes, thereby inhibiting the debonding of the interface between the two.

[0162] Combining the test results from Examples 1 and 7, when maleic anhydride-modified polypropylene was not added to the modified solution, its initial mechanical properties, shear strength, and properties after wet heat treatment were all reduced. The addition of maleic anhydride-modified polypropylene helps to improve the interfacial compatibility between PET and balsa wood board, thereby improving the interfacial bonding strength between the two. Combining the test results from Example 8, when preparing modified balsa wood board, the addition of nano-silica serves two purposes: firstly, as nanoparticles, it improves the mechanical interfacial bonding between the two; secondly, it acts as a thermal expansion buffer, alleviating the interfacial debonding phenomenon caused by the difference in thermal expansion coefficients between the two, and improving mechanical stability.

[0163] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-performance sandwich wind turbine blade core material, characterized in that, It includes a balsa wood substrate and PET sheets on both sides of the balsa wood substrate, wherein the balsa wood substrate includes balsa wood in the middle and modified balsa wood between the balsa wood and the PET sheet; The modified balsa wood board is made by hot pressing balsa wood powder after modification pretreatment. The modification pretreatment includes vacuum impregnation of balsa wood powder in a modification liquid and then impregnation in a silane coupling agent solution. The modification liquid contains at least lignin sulfonate, epichlorohydrin modified lignin and poly(N-isopropylacrylamide).

2. The high-performance sandwich wind turbine blade core material according to claim 1, characterized in that: Optionally, the modified liquid comprises the following raw materials in parts by weight: 20-30 parts maleic anhydride modified polypropylene, 5-12 parts lignin sulfonate, 10-20 parts epichlorohydrin modified lignin, 5-10 parts poly(N-isopropylacrylamide) and 10-20 parts ethanol, 20-30 parts xylene, 5-10 parts water and 3-8 parts Tween.

3. The high-performance sandwich wind turbine blade core material according to claim 2, characterized in that: The modified liquid is prepared by the following method: After mixing ethanol and water, poly-N-isopropylacrylamide and lignin sulfonate were added to prepare a preliminary mixture; A mixture was prepared by mixing xylene with maleic anhydride-modified polypropylene and stirring. Epichlorohydrin was added to the initial mixture to modify lignin. After stirring, Tween was added, and then the mixture was stirred to obtain the modified solution.

4. The high-performance sandwich wind turbine blade core material according to claim 1, characterized in that: The epichlorohydrin modified lignin is prepared by the following method: After mixing lignin and acetone at a mass ratio of 1:(2-3), the pH was adjusted to 7.5-8.5, and epichlorohydrin was added under stirring. The mixture was heated to 60-70℃ and reacted for 2-3 hours. Then, the mixture was centrifuged, washed and dried to obtain epichlorohydrin-modified lignin. The mass ratio of epichlorohydrin to lignin was 1:(3-4).

5. The high-performance sandwich wind turbine blade core material according to claim 1, characterized in that: The modified balsa wood board is prepared by the following method: 1) First, vacuum impregnate the balsa wood powder in the modification liquid for 30-40 minutes, then depressurize it to normal pressure, let it stand for 10-20 minutes, filter it, and dry it to obtain pretreated balsa wood powder. 2) The pretreated balsa wood powder is impregnated in an impregnation solution containing aminosilane coupling agent for 60-90 minutes at an impregnation temperature of 40-50℃, then filtered and dried to obtain modified balsa wood powder. 3) A wood flour mixture is prepared by mixing modified balsa wood flour with nano-silica and powdered phenolic resin; 4) The wood flour mixture is first pre-pressed under a pressure of 1-2 MPa for 5-10 minutes, and then hot-pressed under a pressure of 5-10 MPa and a temperature of 150-180℃. After cooling, it is demolded to obtain modified balsa wood boards. The thickness of the modified balsa wood boards is 1 / 4-1 / 5 of the balsa wood substrate.

6. The high-performance sandwich wind turbine blade core material according to claim 5, characterized in that: In the preparation of modified balsa wood boards, in step 1), the mass ratio of balsa wood powder to modification liquid is 1:(4-5), the impregnation temperature is 45-60℃, and the impregnation is carried out under the conditions of -0.08-(-0.1)MPa. In step 2), the mass ratio of pretreated balsa wood powder to impregnation solution is 1:(6-8), and the impregnation solution is obtained by mixing aminosilane coupling agent and ethanol solution at a mass ratio of 1:(3-4), and the ethanol solution is obtained by mixing ethanol and water at a volume ratio of 1:(0.8-1). In step 3), the mass ratio of modified balsa wood powder to nano silica and powdered phenolic resin is 1:(0.1-0.2):(0.02-0.05).

7. The high-performance sandwich wind turbine blade core material according to claim 1, characterized in that: The PET sheet is made from the following parts by weight of raw materials: 40-60 parts PET granules, 1-5 parts silane coupling agent modified nano silica, 0.5-3 parts tetramethyltetravinylcyclotetrasiloxane monomer, 3-8 parts polyether block amide, 0.8-3 parts 1,4-naphthalenedicarboxylic acid, 0.1-0.5 parts initiator, and 0.1-0.3 parts AC foaming agent.

8. The high-performance sandwich wind turbine blade core material according to claim 7, characterized in that: The PET sheet is obtained by the following method: Raw material pretreatment: Disperse nano-silica in an ethanol aqueous solution, add silane coupling agent, heat to 55-65℃ and stir for 40-60 min, filter and dry to obtain silane coupling agent modified nano-silica; The initiator was dissolved in xylene and then mixed evenly with polyether block amide to obtain a pre-dispersed mixture; Feeding: The raw materials are extruded and granulated through a twin-screw extruder to obtain modified PET granules; Hot pressing: The modified PET granules are first pre-dried at 100-110℃ for 2-3 hours, and then hot-pressed at 270-280℃ and 5-10MPa to obtain PET sheets.

9. The high-performance sandwich wind turbine blade core material according to claim 7, characterized in that: In the feeding step, the specific operation is as follows: First, PET granules are added to the main feed port of the twin-screw extruder and melted. Then, silane coupling agent modified nano-silica and 1,4-naphthalenedicarboxylic acid are added to the side feed port in the middle section of the melting section. The remaining raw materials are injected into the homogenization section, extruded, water-cooled, and pelletized to obtain modified PET granules.

10. The method for preparing the core material of the high-performance sandwich wind turbine blade as described in any one of claims 1-9, characterized in that: Includes the following steps: The core material of the sandwich wind turbine blade is prepared by stacking PET board, modified balsa wood board, balsa wood, modified balsa wood board and PET board in sequence, with epoxy resin adhesive applied at the interface of the boards. Then, it is hot-pressed at 120-130℃ and 5-8MPa for 20-30 minutes, cooled and demolded.