In-situ flow-guiding fiber and preparation method of composite material thereof

Abstract

The present invention discloses an in-situ flow-guiding fiber and a method for preparing a composite material thereof. The in-situ flow-guiding fiber comprises a carbon fiber fabric body and a flow-guiding component. The flow-guiding component is composed of fibers, and the fibers are entangled and crossed with each other and arranged in no specific orientation to form a mesh structure with holes. The flow-guiding component is attached to one side of the carbon fiber fabric body. The chemical structure of the flow-guiding component is aromatic polyamide, which is synthesized from aromatic diacyl chloride monomers and diamine monomers. The main chain of the flow-guiding component contains amide bonds, imidazole, and carbazole groups, and is grafted with epoxy groups. The flow-guiding component has a rough surface structure. By adjusting the proportion of diamine monomers and the amount of epoxy group grafting, in-situ flow-guiding fibers with different chemical structures are designed. Furthermore, the above-mentioned flow-guiding fibers are used to prepare a preform, and an in-situ flow-guiding fiber ply with a gradient flow-guiding effect is designed. The technical solution of the present invention can provide structural enhancement while realizing the flow guidance of resin inside the preform, thereby improving the resin penetration effect and uniformity of the liquid molding process.

Description

Technical Field

[0001] The present invention belongs to the field of resin-based carbon fiber composite materials, and more specifically, relates to a composite material liquid molding process. Background Art

[0002] With the continuous development of composite manufacturing technology, composite materials are increasingly used in the aerospace field, and their usage has become a major indicator of the advancement of aircraft. Compared with autoclave molding methods, liquid molding technologies such as VARI (vacuum-assisted resin infiltration) and RTM (resin transfer molding) offer advantages such as low manufacturing costs, high manufacturing efficiency, and high dimensional and surface accuracy, showing broad application prospects in composite molding technology.

[0003] The liquid molding process forms a preform by laying down dry fiber fabrics, unidirectional tape, and other materials. After the auxiliary materials are laid, the resin inlet and outlet runners are placed. The preform is then encapsulated in a vacuum bag or closed mold. Resin is then pressed into the bag or mold under vacuum conditions to fully saturate the preform. The injection and discharge ports are then closed, and the resin is heated to solidify. After cooling, the composite part is obtained.

[0004] The control of the resin impregnation process is one of the key points and difficulties in determining the quality of liquid molding process products. Since carbon fibers are arranged in an orderly manner in fabrics or unidirectional tapes, the fibers in the prepared preform are tightly stacked, and the carbon fiber surface is smooth and chemically inert. Therefore, the resin penetrates the preform very slowly. For large-sized and complex structures, it is easy for the resin penetration time to exceed the process window time before the resin gels, resulting in preform penetration defects, poor thickness uniformity and other problems. To address this problem, the method of using a flow-guiding medium to assist in penetration is commonly used in engineering applications. The flow-guiding medium is usually a woven fabric of materials such as polyethylene and nylon. It is usually used in conjunction with a demoulding medium and laid on the surface of the preform. The material is peeled off and discarded after curing and molding. Traditional flow-guiding media have the following defects:

[0005] 1. Indentations are left on the surface of the molded product, affecting the surface quality of the product.

[0006] 2. The diversion direction is single, and the diversion effect is only produced in the surface and in-plane directions. The effect on the resin penetration of the bottom layer and thickness direction is very limited, which can easily cause the difference in penetration effect between the upper and lower surfaces, and the resin infiltration of the bottom preform is insufficient.

[0007] 3. For structures with internal inserts, closed-cell foam cores, etc., the flow-guiding medium only improves the resin penetration of the preform above the inserts and foam cores. The resin below the inserts and foam cores is difficult to infiltrate, which is prone to dry spot defects. Summary of the Invention

[0008] To address the problems of difficult resin penetration of dry fiber preforms in liquid molding processes and unsatisfactory application effects of traditional flow-guiding media, the present invention discloses an in-situ flow-guiding fiber and composite material and a preparation method. The technical solutions of the present invention are as follows:

[0009] An in-situ flow-guiding fiber includes a carbon fiber fabric body and a flow-guiding component. The flow-guiding component is composed of fibers. The fibers are entangled and crossed with each other and arranged in no specific orientation to form a network structure with holes. The flow-guiding component is attached to one side of the carbon fiber fabric body. The flow-guiding component material is aromatic polyamide, which is prepared by polymerization reaction using aromatic diamine monomers and aromatic diacyl chloride monomers as raw materials.

[0010] The aromatic diamine monomer of the in-situ flow-guiding fiber material is selected from one or more of the following substances, including: 4,4'-diphenylenediamine, 4,4'-(9H-carbazole-2,7-diyl)diphenylamine, 4,4'-diaminobenzanilide, 5,3'-diamino-2-phenyl-benzimidazole, N,N'-bis(4-aminophenyl)-p-benzimidazole, 5,4'-diamino-2-phenyl-benzimidazole, 2,2'-m-phenylene-bis-5-aminobenzimidazole, and 2,2'-p-phenylene-bis-5-aminobenzimidazole. Among them, 4,4-diphenylenediamine cannot be selected alone and needs to be copolymerized with other diamine monomers.

[0011] The diversion component material aromatic polyamide has an epoxy side group on its molecular chain, and the epoxy side group is grafted on the benzene ring of the aromatic diacid chloride unit.

[0012] The diversion component fiber is treated by chemical etching to form a rough surface. The chemical etchant used contains one of the following components: acetic anhydride, fluorine gas, and CaCl2 / ethanol solution, wherein the mass fraction of CaCl2 is 3%-8%.

[0013] The method for preparing a composite material product based on the above-mentioned in-situ flow-guiding fiber comprises the following steps:

[0014] Step 1: Preparation of polyamide solution: Aromatic diamine monomers and aromatic diacyl chloride monomers are used to synthesize polyamide solution in an organic solvent; the aromatic diamine monomers used include 4,4'-diphenylenediamine, 4,4'-(9H-carbazole-2,7-diyl)diphenylamine, 4,4'-diaminobenzanilide, 5,3'-diamino-2-phenyl-benzimidazole, N,N'-bis(4-aminophenyl)dicarboxamide, 5,4'-diamino-2-phenyl-benzimidazole , 2,2'-m-phenylene-bis-5-aminobenzimidazole, 2,2'-p-phenylene-bis-5-aminobenzimidazole or one or more thereof, wherein 4,4'-biphenylenediamine cannot be selected alone and needs to be copolymerized with other diamine monomers, and three polyamide solutions are prepared according to different proportions of 4,4'-biphenylenediamine and other diamine monomers, and the molar fractions of 4,4'-biphenylenediamine monomer in all diamine monomers are a, b, and c, respectively, wherein 100%>a>b>c≥0%;

[0015] Step 2: Preparation of in-situ flow-guiding fibers: The polyamide solution from step 1 is used for spinning. During the spinning process, a polyethylene plate is used as a base, and the polyamide fibers are sprayed onto the base, followed by drying to remove residual solvent. The resulting polyamide fibers are post-treated in different ways to obtain flow-guiding components, which are then laid on one side of the carbon fiber fabric body to obtain three types of in-situ flow-guiding fibers, in which the molar fractions of 4,4'-diphenylenediamine monomer to the total diamine monomer substances are a, b, and c;

[0016] Step 3: Prepare a reinforcement material preform using in-situ flow-guiding fibers: Lay the preform in layers, wherein the number of layers is ≥ 3 and is divided into three ply groups along the thickness direction: a bottom layer group, a middle layer group, and an upper layer group. In-situ flow-guiding fibers having a molar fraction of c, b, and a of 4,4'-biphenylenediamine monomer to the total diamine monomers are used to prepare the reinforcement material preforms of the bottom layer group, the middle layer group, and the upper layer group, respectively.

[0017] Step 4: Encapsulate the reinforcement material preform in a vacuum bag or a closed mold, and allow the epoxy resin prepolymer to infiltrate the reinforcement material preform under vacuum;

[0018] Step 5: De-molding after curing to obtain a composite material product.

[0019] In step 2, after drying to remove the residual solvent, the polyamide fiber is post-treated. The specific process of post-treatment is as follows:

[0020] Step 1: Transfer the three substrates with polyamide fibers into an appropriate amount of anhydrous AlCl3 and dichloromethane mixture and treat them under ultrasonic conditions at 40°C for a period of time;

[0021] Step 2: Prepare three groups of epichlorohydrin with different masses, where the ratio of epichlorohydrin mass to polyamide fiber mass is d, e, and f, respectively, wherein 10% ≥ d> e> f ≥ 2%, and add the three groups of epichlorohydrin accounting for d, e, and f of the polyamide fiber mass to the polyamide fiber mixture with the molar fractions of 4,4'-diphenylenediamine monomer substance c, b, and a in step 1, respectively, and soak at 40° C. for 2-4 hours;

[0022] Step 3: Take out the polyamide fiber, wash it with acetone and distilled water, and then dry it to remove the residual solvent;

[0023] Step 4: Peel the polyamide fibers from the polyethylene backing.

[0024] In step 2, after drying to remove the residual solvent, the polyamide fiber is post-treated. The specific process of post-treatment is as follows:

[0025] Step 1: transferring the dried polyamide fiber to an etchant for a period of time, wherein the etchant comprises one of the following components: acetic anhydride, fluorine gas, and a CaCl2 / ethanol solution, wherein the mass fraction of CaCl2 is 3% to 8%;

[0026] Step 2: Take out the polyamide fiber, wash it with acetone and distilled water, and dry it to remove the residual solvent.

[0027] The technical solution of the present invention has the following advantages:

[0028] 1. It can realize resin diversion in the plane and thickness direction. The diversion effect is evenly distributed in each layer of the preform, which helps to promote full and low-defect infiltration of thick, insert-containing, and closed-cell sandwich structure preforms, thereby improving the stability of product manufacturing quality.

[0029] 2. The flow-guiding component interacts with the matrix resin through hydrogen bonding and chemical cross-linking, which can provide a reinforcing effect. Moreover, the flow-guiding component is part of the composite material and is placed inside the product to avoid surface indentations.

[0030] 3. Strong designability. The location and area of ​​the guide fibers can be flexibly designed according to the product structure and layering scheme, so as to achieve precise control of the resin penetration process and improve the thickness uniformity of different areas of the product, such as Example 5. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 -The chemical structure of the diamine monomer selected in the present invention

[0032] Figure 2 -Schematic diagram of grafting epoxy groups onto the benzene ring of some diacid chloride units of aromatic polyamide

[0033] Figure 3- Schematic diagram of the preparation of preforms using in-situ flow-guiding fibers with different 4,4'-diphenylenediamine ratios

[0034] Figure 4 - Schematic diagram of the preparation of preforms using in-situ flow-guiding fibers with different epichlorohydrin contents

[0035] Figure 5 - Schematic diagram of the working principle of traditional diversion network

[0036] Figure 6 -Schematic diagram of the in-situ flow-guiding fiber structure

[0037] Figure 7 -Grafting reaction formula of epichlorohydrin and aromatic polyamide

[0038] Figure 8 - Schematic diagram of the preparation of the preform of the control group of Example 5

[0039] Figure 9 - Thickness measurement of product in Example 5: (a) blank sample; (b) control sample

[0040] Explanation of the numbers in the figure: 1-carbon fiber fabric body; 2-flow-guiding component; 3-reinforcement material preform; 4-vacuum bag; 5-polyamide solution, wherein the amount fraction of 4,4'-biphenylenediamine in all diamine monomer substances is a; 6-polyamide solution, wherein the amount fraction of 4,4'-biphenylenediamine in all diamine monomer substances is b; 7-polyamide solution, wherein the amount fraction of 4,4'-biphenylenediamine in all diamine monomer substances is c; 8-in-situ flow-guiding fiber, wherein the amount fraction of 4,4'-biphenylenediamine in all diamine monomer substances is a; 9-in-situ flow-guiding fiber, wherein the amount fraction of 4,4'-biphenylenediamine in all diamine monomer substances is b; 10-in-situ flow-guiding fiber, wherein the amount fraction of 4,4'-biphenylenediamine in all diamine monomer substances is c; 11-bottom layer group; 12-middle layer group; 13-upper layer group; 14-epichlorohydrin (C3H5ClO), Its mass accounts for d% of the fiber mass; 15-epichlorohydrin (C3H5ClO), its mass accounts for e% of the fiber mass; 16-epichlorohydrin (C3H5ClO), its mass accounts for f% of the fiber mass; 17-in-situ flow-guiding fiber, wherein the mass of epichlorohydrin (C3H5ClO) added accounts for d% of the fiber mass; 18-in-situ flow-guiding fiber, wherein the mass of epichlorohydrin (C3H5ClO) added accounts for e% of the fiber mass; 19-in-situ flow-guiding fiber, wherein the mass of epichlorohydrin (C3H5ClO) added accounts for f% of the fiber mass; 20-traditional flow-guiding net; 21-resin "channel" formed between the traditional flow-guiding net and the vacuum bag; 22-flow-guiding component, wherein the amount fraction of 4,4'-diphenylenediamine in the total diamine monomer substances is 90%; 23-flow-guiding component, wherein the amount fraction of 4,4'-diphenylenediamine in the total diamine monomer substances is 0% DETAILED DESCRIPTION

[0041] like Figure 1-9 As shown, an in-situ flow-guiding fiber includes a carbon fiber fabric body 1 and a flow-guiding component 2. The flow-guiding component 2 is composed of fibers. The fibers are entangled and crossed with each other and arranged in no specific orientation to form a network structure with holes. The flow-guiding component 2 is attached to one side of the carbon fiber fabric body 1. The chemical structure of the flow-guiding component 2 is aromatic polyamide, which is prepared by polymerization reaction using aromatic diamine monomers and aromatic diacyl chloride monomers as raw materials.

[0042] The aromatic diamine monomer for preparing the in-situ flow-guiding fiber is selected from one or more of the following substances, including: 4,4'-diphenylenediamine, 4,4'-(9H-carbazole-2,7-diyl)diphenylamine, 4,4'-diaminobenzanilide, 5,3'-diamino-2-phenyl-benzimidazole, N,N'-bis(4-aminophenyl)-p-benzimidazole, 5,4'-diamino-2-phenyl-benzimidazole, 2,2'-m-phenylene-bis-5-aminobenzimidazole, and 2,2'-p-phenylene-bis-5-aminobenzimidazole. Among them, 4,4'-diphenylenediamine cannot be selected alone and needs to be copolymerized with other monomers.

[0043] The guiding component 2 material of the in-situ guiding fiber is an aromatic polyamide molecular chain with an epoxy group side group, and the side group is grafted on the benzene ring of the aromatic diacid chloride unit.

[0044] The fibers of the flow-guiding component 2 are chemically etched to form a rough surface. The chemical etchant comprises one of the following components: acetic anhydride, fluorine gas, and a CaCl2 / ethanol solution, wherein the mass fraction of CaCl2 is 3% to 8%.

[0045] The method for preparing a composite material product using the above-mentioned in-situ flow-guiding fiber comprises the following steps:

[0046] Step 1: Preparation of polyamide solution 5: Aromatic diamine monomers and aromatic diacyl chloride monomers are used to synthesize polyamide solution 5 in an organic solvent; the aromatic diamine monomers include 4,4'-diphenylenediamine, 4,4'-(9H-carbazole-2,7-diyl)diphenylamine, 4,4'-diaminobenzanilide, 5,3'-diamino-2-phenyl-benzimidazole, N,N'-bis(4-aminophenyl)-4-dicarboxamide, 5,4'-diamino-2-phenyl-benzimidazole, 2,2'-m-phenylene-bis-5-aminobenzimidazole, and 2,2'-p-phenylene-bis-5-aminobenzimidazole, among which 4,4'-diphenylenediamine cannot be selected alone and needs to be copolymerized with other diamine monomers. Three polyamide solutions 5, 6, and 7 were prepared according to different ratios of 4,4'-diphenylenediamine to other diamine monomers, and the molar fractions of 4,4'-diphenylenediamine monomer to the total diamine monomers were a, b, and c, respectively, where 100%>a>b>c≥0%;

[0047] Step 2: Prepare in-situ flow-guiding fibers: Spin the three polyamide solutions from step 1. During the spinning process, use a polyethylene plate as a base plate, spray the polyamide fibers onto the base plate, and then dry to remove the residual solvent. Post-process the obtained polyamide fibers in different ways to obtain three flow-guiding components 2. Lay the flow-guiding components 2 on one side of the carbon fiber fabric body 1 to obtain three in-situ flow-guiding fibers 8, 9, and 10 (such as Figure 3 As shown), wherein the amount fractions of 4,4'-diphenylenediamine monomer in the total diamine monomer substance are a, b, and c;

[0048] Step 3: Prepare the reinforcement preform using in-situ flow-guiding fibers 3: Figure 3 As shown, the preform is layered, wherein the number of layers is ≥3, and is divided into three layer groups along the thickness direction: a bottom layer group 11, a middle layer group 12, and an upper layer group 13. In-situ flow-guiding fibers 10, 9, and 8, in which the molar fractions of 4,4'-biphenylenediamine monomer to the total diamine monomer substance are c, b, and a, are selected respectively to prepare the bottom layer group 11, the middle layer group 12, and the upper layer group 13 reinforcement material preforms;

[0049] Step 4: Encapsulate the reinforcement material preform 3 in a vacuum bag 4 or a closed mold, and allow the epoxy resin prepolymer to infiltrate the reinforcement material preform 3 under vacuum.

[0050] Step 5: De-molding after curing to obtain a composite material product.

[0051] In step 2, after drying to remove residual solvent, post-processing is performed. The specific process is as follows:

[0052] Step 1: Transfer the three substrates with polyamide fibers into an appropriate amount of anhydrous AlCl3 and dichloromethane mixture and treat them under ultrasonic conditions at 40°C for a period of time;

[0053] Step 2: If Figure 4 As shown, three groups of epichlorohydrin 14, 15, and 16 of different masses are prepared, and the ratio of the mass of epichlorohydrin to the mass of polyamide fiber is d, e, and f, respectively, wherein 10% ≥ d> e> f ≥ 2%, and the three groups of epichlorohydrin 14, 15, and 16 accounting for the mass d, e, and f of the polyamide fiber are added to the polyamide fiber mixture having the molar fractions of 4,4'-diphenylenediamine monomer substance c, b, and a in step 1, respectively, and soaked at 40° C. for 2-4 hours;

[0054] Step 3: Take out the polyamide fiber, wash it with acetone and distilled water, and then dry it to remove the residual solvent;

[0055] Step 4: Peel the polyamide fibers from the polyethylene backing.

[0056] In step 2, after drying to remove the residual solvent, the polyamide fiber is post-treated. The specific process of post-treatment is as follows:

[0057] Step 1: transferring the dried polyamide fiber to an etchant for a period of time, wherein the etchant comprises one of the following components: acetic anhydride, fluorine gas, and a CaCl2 / ethanol solution, wherein the mass fraction of CaCl2 is 3% to 8%;

[0058] Step 2: Take out the polyamide fiber, wash it with acetone and distilled water, and dry it to remove the residual solvent.

[0059] The following provides five examples for detailed description of the preparation process.

[0060] Example 1:

[0061] The specific process for preparing polyamide fibers with different main chain chemical structures is as follows:

[0062] (1) Preparation of polyamide solution: 4,4'-diphenylenediamine (BPDA), 2,2'-p-phenylene-bis-5-aminobenzimidazole (BPABI) and terephthaloyl chloride were used as monomers to synthesize four groups of polyamide solutions in N-methylpyrrolidone, with the molar fraction of BPDA in the diamine monomer being 10%, 50%, 80% and 100%.

[0063] (2) Preparation of in-situ flow-guiding fibers: Spinning was performed using the flow-guiding component polymer solution in step (1), with polyethylene as the base plate, and the flow-guiding component fibers were sprayed onto the base plate, followed by drying to remove residual solvent, and labeled as flow-guiding component-10% BPDA, flow-guiding component-50% BPDA, flow-guiding component-80% BPDA, and flow-guiding component-100% BPDA.

[0064] (3) Select a portion of the diversion component - 50% BPDA, transfer the bottom plate with the diversion component to an appropriate amount of anhydrous AlCl3 and dichloromethane mixture, and treat it under ultrasonic conditions at 40°C for a period of time.

[0065] (4) The diversion component mixture in step (3) was divided into three groups, and epichlorohydrin (C3H5ClO) with a fiber mass fraction of 10%, 5%, and 2% was added, respectively. The mixture was immersed at 40°C for 4 hours and marked as diversion component-50% BPDA-2% epoxy group, diversion component-50% BPDA-5% epoxy group, and diversion component-50% BPDA-10% epoxy group.

[0066] (5) The diversion component in step (4) is washed with acetone and distilled water, and dried to remove residual solvent.

[0067] (6) A portion of the diversion component-80% BPDA was selected and transferred to an acetic anhydride solution for treatment for a period of time, and then washed with distilled water, dried, and marked as the diversion component-80% BPDA-acetic anhydride.

[0068] The contact angles of the epoxy resin prepolymers were measured using a dynamic contact angle analyzer using the aforementioned flow-distribution components and carbon fiber fabrics. The results are shown in Table 1. The contact angle of the flow-distribution component was significantly smaller than that of the carbon fiber fabric. The contact angle gradually decreased with increasing proportions of 2,2'-p-phenylene-bis-5-aminobenzimidazole (BPABI) monomer. Furthermore, as the amount of epichlorohydrin added increased, the epoxy group content increased and the contact angle decreased. This indicates that the flow-distribution component is more easily wetted by the epoxy resin prepolymer than the carbon fiber fabric. Chemical structure design, including the introduction of imidazole, carbazole, and epoxy groups, can enhance the interaction between the flow-distribution component and the epoxy resin prepolymer, improving the wetting effect. After treatment with acetic anhydride, the surface of the flow-distribution component forms a rough structure, which reduces the contact angle and further enhances the resin wetting effect.

[0069] Table 1 Resin contact angles of carbon fiber fabrics and flow-guiding components

[0070]

[0071]

[0072] Example 2:

[0073] Preparation of diversion components with different epoxy side group contents, the specific process is as follows:

[0074] (1) Preparation of polyamide solution: 4,4'-benzenediamine (BPDA), 4,4'-diaminobenzanilide (DABA) and terephthaloyl chloride were used as monomers to synthesize polyamide solution in N-methylpyrrolidone, with BPDA accounting for 50% of the molar fraction of the diamine monomer.

[0075] (2) Preparation of the diversion component: Spinning the polyamide solution in step (1) with polyethylene as the base, spraying the polyamide fibers onto the base, and then drying to remove the residual solvent inside the polyamide fibers. Select a portion of the polyamide fibers and mark them as blank samples, and perform the treatment of the remaining fibers in step (3).

[0076] (3) The polyamide fiber prepared in step (2) is transferred to an appropriate amount of anhydrous AlCl3 and dichloromethane mixture and treated under ultrasonic conditions at 40°C for a period of time.

[0077] (4) The diversion component mixture in step (3) was divided into 5 groups, and epichlorohydrin (C3H5ClO) with a polyamide fiber mass fraction of 20%, 10%, 5%, 2%, and 1% was added, respectively. The mixture was immersed at 40°C for 4 hours and marked as diversion component-20% epoxy group, diversion component-10% epoxy group, diversion component-5% epoxy group, diversion component-2% epoxy group, and diversion component-1% epoxy group.

[0078] (5) The diversion component fiber in step (4) is repeatedly washed with acetone and distilled water, and dried to remove residual solvent.

[0079] The C, O, N, and Cl content of the samples was determined using X-ray photoelectron spectroscopy (XPS). The results are shown in Table 2. Compared to the blank sample, the treated sample showed an increase in the O / C ratio, confirming the successful grafting of epoxy groups onto the polyamide backbone. The O / C ratio of the diversion component (1% epoxy group) showed no significant change, indicating no significant impact on the diversion component's performance. The O / C ratio of the diversion component (20% epoxy group) showed no increase compared to the diversion component (10% epoxy group), indicating that the grafting reaction essentially reached saturation when the epichlorohydrin (C3H5ClO) addition reached 10% of the fiber weight due to grafting steric hindrance and the difficulty of grafting in crystalline regions.

[0080] Table 2 Element content of flow-guiding fibers with different epoxy group grafting amounts

[0081]

[0082] Example 3:

[0083] The laminate product, with a size of 3200mm*450mm, is made of 90 layers of carbon fiber fabric. The preparation process is as follows:

[0084] (1) Preparation of three groups of polyamide solutions: 4,4'-benzyl diamine (BPDA), 5,3'-diamino-2-phenyl-benzimidazole (MAP-ABI) and terephthaloyl chloride were used as monomers to synthesize three groups of polyamide solutions in N-methylpyrrolidone, with the molar fractions of BPDA in the diamine monomers being 90%, 30% and 10%, respectively.

[0085] (2) Preparation of in-situ flow-guiding fibers: The polyamide solution in step (1) is used for spinning, and the polyethylene is used as a base plate. The polyamide fibers are sprayed onto the base plate, and then dried to remove the residual solvent inside.

[0086] (3) A portion of polyamide fibers containing 30% of the molar fraction of BPDA in the diamine monomer was reserved, and the remaining three groups of substrates with polyamide fibers were transferred to an appropriate amount of anhydrous AlCl3 and dichloromethane mixture and treated under ultrasonic conditions at 40°C for a period of time.

[0087] (4) Add 2%, 5%, and 10% of the fiber mass fraction of epichlorohydrin (C3H5ClO) to the mixed solution in which the molar fraction of BPDA in the diamine monomer substance is 90%, 30%, and 10%, respectively, and soak at 40°C for 2-4 hours.

[0088] (5) Take out the polyamide fiber, wash it with acetone and distilled water, and dry it to remove the residual solvent.

[0089] (6) The polyamide fiber with a BPDA content of 30% of the diamine monomer reserved in step (3) and the three groups of polyamide fibers prepared in step (5) were peeled off from the polyethylene base plate and transferred to the surface of one side of the carbon fiber fabric, and were marked as blank guide fiber, 90% BPDA-2% C3H5ClO, 30% BPDA-5% C3H5ClO, and 10% BPDA-10% C3H5ClO, respectively.

[0090] (7) The reinforcement material preform layer is divided into a bottom layer group, a middle layer group, and an upper layer group along the thickness direction, and each layer contains 10 layers of carbon fiber fabric.

[0091] (8) A preform was prepared using the in-situ flow-guiding fibers prepared in step (6). The bottom, middle, and upper layers were composed of 10% BPDA-10% C3H5ClO, 30% BPDA-5% C3H5ClO, and 90% BPDA-2% C3H5ClO in-situ flow-guiding fibers, respectively, and these were labeled as control samples. A preform was prepared using a blank flow-guiding fiber, labeled as a blank sample.

[0092] (9) The control sample and the blank sample reinforced material preforms in step 8 are encapsulated in a vacuum bag, and an injection port is set. The resin penetrates along the width direction with a penetration distance of 450 mm. Under the action of vacuum, the epoxy resin prepolymer is infiltrated into the reinforced material preform.

[0093] (10) After curing, demoulding is performed to obtain composite materials of blank sample and control sample.

[0094] Table 3 summarizes the resin penetration of the blank and control samples. The upper layer resin penetration rates of the two groups of samples were similar, but the lower layer resin penetration rate of the blank sample was significantly slower than that of the control sample. The lower layer of the control sample had a similar penetration rate to the upper layer, and the overall flow front was relatively uniform, with no evidence of resin encapsulating air. The surface quality of the control sample was good, and the nondestructive testing met the acceptance criteria. The upper layer of the blank sample penetrated faster, but when the lower layer was not fully penetrated, the upper layer resin penetrated the lower preform in the opposite direction, forming an air encapsulation approximately 30 mm from the resin riser. Dry spots were present in this area after curing, and no ultrasonic reflection signal was detected during nondestructive testing.

[0095] Table 3 Resin penetration distance of Example 3

[0096]

[0097]

[0098] Example 4:

[0099] The foam sandwich panel has a flat plate structure and dimensions of 1500mm*800mm. It uses a 30mm thick closed-cell foam core with 30 layers of carbon fiber fabric laid on the top and bottom of the core. The preparation process is as follows:

[0100] (1) Preparation of polyamide solution: 4,4'-diphenylenediamine (BPDA), N,N'-bis(4-aminophenyl)-p-dicarboxamide (APTA) and terephthaloyl chloride were used as monomers to synthesize three groups of polyamide solutions in N-methylpyrrolidone, with BPDA accounting for 10%, 50% and 90% of the molar fraction of the diamine monomer.

[0101] (2) Preparation of the diversion component: The polyamide solution in step (1) is used for spinning, and polyethylene is used as a base plate. The diversion component fibers are sprayed onto the base plate, and then dried to remove the residual solvent.

[0102] (3) The flow-guiding component is peeled off from the base plate and attached to one side of the carbon fiber fabric body to obtain in-situ flow-guiding fibers with BPDA content of 10%, 50%, and 90% of diamine monomer, respectively.

[0103] (4) The preform was divided into a bottom layer group, a middle layer group, and an upper layer group, each group having 10 layers. A reinforced material preform was prepared using the in-situ flow-guiding fibers and foam core prepared in step (3). The upper layer group had a BPDA ratio of 90%, the middle layer group had a BPDA ratio of 50%, and the bottom layer group had a BPDA ratio of 10%, which was labeled as a control sample. At the same time, a preform was prepared using untreated carbon fiber fabric, which was labeled as a blank sample.

[0104] (5) The reinforced material preform prepared in step (4) is encapsulated in a vacuum bag, an injection port is set, and the resin is infiltrated along the width direction with a penetration distance of 800 mm. Under the action of vacuum, the epoxy resin prepolymer is infiltrated into the reinforced material preform 3.

[0105] (6) After curing, demoulding is performed to obtain composite materials of blank sample and control sample.

[0106] Table 4 shows the resin penetration of the sample of Example 4. The blank sample penetration rate is significantly slower than that of the control sample. The penetration rate under the core of the blank sample is significantly slower than that on the core, and the penetration uniformity is poor. In contrast, the penetration rate under the core of the control sample is slightly slower than that on the core. The overall flow front is more uniform, and there is no resin wrapped in air (Table 4). Continue to extend the time, and the preform on the core of the blank sample will eventually complete resin penetration, but there are still large penetration defects under the core. The preform is cured and demoulded. The surface quality of the control sample product is good, and the non-destructive testing meets the acceptance criteria, while there are large-scale dry spots visible to the naked eye under the blank sample core.

[0107] Table 4 Resin penetration distance of Example 4

[0108]

[0109] Example 5:

[0110] The composite U-shaped leading edge product, measuring 1200mm*320mm*300mm, is constructed with 12 layers of carbon fiber fabric. The manufacturing process is as follows:

[0111] (1) Preparation of polyamide solution: 4,4'-diphenylenediamine (BPDA), 5,3'-diamino-2-phenyl-benzimidazole (MAP-ABI) and terephthaloyl chloride were used as monomers to synthesize two sets of polyamide solutions in N-methylpyrrolidone, with BPDA accounting for 0% and 90% of the molar fraction of the diamine monomer.

[0112] (2) Preparation of a flow-guiding component: The polyamide solution prepared in step (1) was used for spinning, and the polyamide fibers were sprayed onto a polyethylene substrate, followed by drying to remove residual solvent. The flow-guiding component was peeled off the substrate to prepare a blank flow-guiding component and a control flow-guiding component.

[0113] (3) A flow-guiding component containing BPDA accounting for 90% of the molar fraction of the diamine monomer is attached to one side of the carbon fiber fabric body to obtain a blank in-situ flow-guiding fiber. The carbon fiber fabric is divided into two equal parts along the width direction ( Figure 8 ), two parts of the carbon fiber fabric body were attached with the guiding components 23 and 22 with the molar fraction of BPDA accounting for 0% and 90% of the diamine monomer on one side respectively, to obtain the control in-situ guiding fiber.

[0114] (4) Using the blank in-situ flow-guiding fiber in step (3) to prepare a blank reinforcement material preform, and using the control in-situ flow-guiding fiber to prepare a control reinforcement material preform ( Figure 8 ), using concave die forming.

[0115] (5) The reinforced material preform prepared in step (4) is encapsulated in a vacuum bag. Injection nozzles are respectively set at the top of the die along the long side of the part, the injection nozzle is set on the side close to the diversion component 22, and the riser is set on the side close to the diversion component 23. The resin penetrates along the width direction, the penetration distance is 664mm, and the epoxy resin prepolymer is infiltrated into the reinforced material preform under the action of vacuum.

[0116] (6) After curing, demoulding is performed to obtain composite materials of blank sample and control sample.

[0117] Table 5 summarizes the resin penetration distance of the blank and control samples in Example 5. The resin penetrated from the sprue to the bottom of the U-shaped part (approximately 330 mm) in 720 seconds, with the control sample slightly faster than the blank. The resin penetrated from the bottom of the U-shaped part to the riser in 940 seconds, a process that was slower due to the resin needing to overcome gravity. The control sample had a faster penetration rate during this stage than the blank sample. This indicates that increasing the imidazole content in the flow-inducing component can enhance the interaction between the preform and the resin, leading to faster resin penetration. This layering method can shorten the difference in resin penetration rates between the two stages. The figure records the thickness measurements of the two groups of samples, which have a theoretical thickness of 3.06 mm. Both groups of samples showed a thicker thickness at the sprue than at the riser, due to the longer resin infiltration time of the preform at the sprue. The maximum thickness difference between the relative positions of the sprue and riser for the blank sample was 0.16 mm, while the maximum thickness difference between the relative positions of the sprue and riser for the control sample was 0.06 mm. In comparison, the control sample exhibited better thickness uniformity.

[0118] Table 5 Resin penetration distance of Example 5

[0119] Sample Time / s 195 531 720 862 1106 1458 1660 Blank sample Penetration distance / mm 126 258 328 392 475 536 664 Control sample Penetration distance / mm 131 266 338 389 469 519 647

[0120] The principles of the present invention are as follows:

[0121] The process of transferring liquid resin prepolymer into the preform consists of three stages:

[0122] (1) Wetting stage: Wetting is the interaction between the resin prepolymer and the preform, transforming from a solid / gas interface to a solid / liquid interface. The wetting process follows Young's equation (Equation 1). If θ < 90°, the solid surface is more easily wetted by the liquid, resulting in spontaneous wetting. In addition, increasing the surface roughness of the material facilitates material wetting.

[0123] γ SG -γSL =γ LG cosθ (Equation 1)

[0124] Where: γ SG —solid / gas interfacial tension; γ SL —solid / liquid interfacial tension; γ LG —Liquid / gas interfacial tension.

[0125] (2) Diffusion stage: For the liquid molding VARI process, the main driving forces for the diffusion of the resin prepolymer inside the preform are the external vacuum pressure and the capillary osmotic pressure of the preform itself. Under the external vacuum pressure, the relationship between the liquid flow rate and the pressure difference in the porous medium follows Darcy's law (Equation 2). The factors affecting the permeability K are relatively complex, including the size, shape, and number of pores inside the preform, the interaction between the preform and the resin prepolymer, and the layup angle.

[0126]

[0127] Where: ū is the volume flow rate; K is the permeability of the porous medium; μ is the fluid viscosity; △P is the pressure gradient (for liquid molding processes, it refers to the pressure difference between the resin injection and the riser)

[0128] There is a certain tension between the resin prepolymer and the preform, and the preform has pores and channels within it, which exert capillary osmotic pressure on the resin prepolymer. Factors influencing this process include the number and size of the pores and their surface energy. The capillary osmotic pressure of the preform itself follows the following relationship (Equation 3):

[0129]

[0130] Where: Q is the volume flow rate of the fluid (m3 / s); V is the linear velocity of the fluid (m / s); γ LG —Liquid-gas interfacial tension (N / m), θ—solid / liquid contact angle; R—capillary equivalent radius (m); η—liquid viscosity.

[0131] (3) Saturation stage: All pores inside the preform are filled with resin prepolymer, and the resin penetration reaches saturation.

[0132] Traditional induction mesh 20, with its grid-like structure, introduces multiple resin "channels" 21 (pictured) between the preform and the vacuum bag. This works by increasing the number and size of pores in the preform's surface, thereby increasing preform permeability. These "channels" are distributed in the in-plane direction and promote resin penetration only in that direction. For thick structures with inserts and closed-cell foam cores, the mesh loses its effect on the underlying preform, resulting in differential resin penetration between the upper and lower layers and poor resin infiltration of the underlying preform. Furthermore, traditional induction meshes are prone to leaving indentations on the surface, resulting in suboptimal surface quality.

[0133] The technical solution of the present invention is as follows:

[0134] 1. Consider the influence of the chemical structure of the diversion component on the wetting and diffusion stages during the resin penetration process, such as Figure 6 As shown, an aromatic polyamide fiber with a backbone containing amide bonds, imidazole, and carbazole structures was designed as the flow-guiding component 2, attached to one side of the carbon fiber fabric body 1. Advantageously, the amide bonds impart strong polarity to the flow-guiding component, and the hydrogen atoms in the -NH- group can form hydrogen bonds with the oxygen atoms in the epoxy resin prepolymer, facilitating resin wetting of the flow-guiding component. Experimental results from Example 1 show that the resin contact angle of the aromatic polyamide film is much smaller than that of the carbon fiber fabric, and the contact angle decreases with increasing amide bonds, imidazole, and carbazole structures.

[0135] 2. The traditional guide net 20 is used as an auxiliary material. The guide effect only affects the surface preform and is discarded after curing. It is easy to cause indentations on the surface of the workpiece. In comparison, the technical solution provided by the present invention can introduce guide fibers into each layer of the preform, which helps to uniformly penetrate the resin. In order to avoid the adverse effects of the guide component fibers on the performance of the composite material, the aromatic polyamide fibers with amide bonds, imidazole, and carbazole structures designed by the present invention have high strength and modulus. As a guide component, it can also be present in the composite body as a reinforcing material, producing an "in-situ guide" effect. In order to further enhance the interaction between the guide component and the resin and strengthen the "guide + reinforcement" effect, the present invention designs epoxy structure side groups on the main chain of the guide component 2 molecules. This solution uses Friedel-Crafts alkylation reaction to achieve the grafting reaction of epichlorohydrin and aromatic polyamide. Due to the steric effect of the benzene ring, the hydrogen activity on the amide bond is relatively poor, and grafting is relatively difficult. There are a large number of benzene rings on the aramid main chain, and the steric effect of the hydrogen atoms on the benzene ring is not obvious. The reaction process is shown in FIG. Figure 7 . The introduction of epoxy structure side groups makes the polarity of the guide fiber and the epoxy resin more matched, the interaction is stronger, and the resin wetting effect of the guide component is better. On the other hand, the epoxy groups on the side groups of the guide component fibers can participate in the resin curing reaction, forming chemical crosslinks between the guide component fibers and the resin, further exerting a reinforcing effect. Example 2 confirms the feasibility of the grafting reaction. At the same time, the present invention also optimizes the amount of epichlorohydrin added in the grafting reaction. According to Example 2, the amount of epichlorohydrin added is more than 2% of the fiber mass fraction, the grafting modification effect is more obvious, and when the addition amount reaches 10%, the grafting reaction tends to saturation. Therefore, the optimal addition amount of epichlorohydrin is 2%-10% of the fiber mass fraction.

[0136] 3. A rough structure is designed on the surface of the diversion component fiber. Surface etching uses chemicals such as acids, alkalis, and halogen-containing compounds to hydrolyze the amide bonds on the surface of the aramid fiber, destroying the aggregated structure on the fiber surface, increasing the relative content of the amorphous area on the surface, and making the smooth aramid surface rough, thereby increasing the contact area with the resin. At the same time, the breaking of the amide bond also reduces the steric effect of the benzene ring, increases the active points on the fiber surface, and enables the resin to more effectively infiltrate the fiber.

[0137] 4. To address the problem that traditional diversion nets cannot divert fluid along the thickness direction, the present invention regulates the capillary osmotic pressure of the diversion component through chemical structure design to form a pressure gradient along the thickness direction. Specifically, the preparation method regulates the ratio of amide bond, imidazole and carbazole structures in the diversion component ( Figure 3 ). The density of epoxy groups grafted onto the diversion component fibers was regulated ( Figure 4 The higher the proportion of amide bonds, imidazoles, and carbazole structures, and the higher the amount of epoxy group grafting, the stronger the interaction between the flow-guiding component and the epoxy resin prepolymer, and the higher the surface energy. The above scheme utilizes this principle to design an in-situ flow-guiding fiber with a surface energy gradient. During the preparation of the reinforced material preform, the flow-guiding fiber with a larger surface energy is placed under the bottom layer or insert or sandwich structure, forming an osmotic pressure difference between the bottom layer and the surface layer, promoting the penetration of the resin prepolymer along the thickness direction. Example 3 confirms that this surface energy gradient design helps to uniformly penetrate the resin of the upper and lower layers of the preform.

Claims

1. A method for preparing a composite material of an in-situ flow-guiding fiber, characterized in that The following steps are involved: 1-1 Preparation of polyamide solution: Aromatic diamine monomer and aromatic diacyl chloride monomer are used to synthesize polyamide solution in an organic solvent; the aromatic diamine monomers used include 4,4'-diphenylenediamine, 4,4'-(9H-carbazole-2,7 One or more of the following: -diamino)diphenylamine, 4,4'-diaminobenzanilide, 5,3'-diamino-2-phenyl-benzimidazole, N,N'-bis(4-aminophenyl)-p-benzimidazole, 5,4'-diamino-2-phenyl-benzimidazole, 2,2'-m-phenylene-bis-5-aminobenzimidazole, and 2,2'-p-phenylene-bis-5-aminobenzimidazole are copolymerized, wherein 4,4'-biphenylenediamine cannot be selected alone and needs to be copolymerized with other diamine monomers, and three polyamide solutions are prepared according to different ratios of 4,4'-biphenylenediamine and other diamine monomers, and the molar fractions of 4,4'-biphenylenediamine monomer to all diamine monomers are a, b, and c, respectively, wherein 100%>a>b>c≥0%; 1-2 Preparation of in-situ flow-guiding fibers: The polyamide solution in step 1-1 is used for spinning. During the spinning process, a polyethylene plate is used as a base plate, and the polyamide fiber is sprayed onto the base plate. The residual solvent is then dried to remove the residual solvent. The resulting polyamide fiber is post-treated by different methods to obtain a flow-guiding component. The flow-guiding component is laid on one side of the carbon fiber fabric body to obtain three types of in-situ flow-guiding fibers, in which the molar fractions of 4,4'-diphenylenediamine monomer to the total diamine monomer substance are a, b, and c; 1-3 Preparing a reinforcement material preform using in-situ flow-guiding fibers: Laying the reinforcement material preform, wherein the number of layers is ≥3, and dividing it into three ply groups along the thickness direction: a bottom layer group, a middle layer group, and an upper layer group. In-situ flow-guiding fibers having a molar fraction of c, b, and a of 4,4'-biphenylenediamine monomer to the total diamine monomer substance are used to prepare the bottom layer group, the middle layer group, and the upper layer group of reinforcement material preforms, respectively; 1-4 Encapsulating the reinforcement material preform in a vacuum bag or a closed mold, and allowing the epoxy resin prepolymer to infiltrate the reinforcement material preform under vacuum; 1-5 After curing, demoulding is performed to obtain a composite material product.

2. The method for preparing a composite material of an in-situ flow-guiding fiber according to claim 1, characterized in that: After the drying described in step 1-2 to remove the residual solvent, the polyamide fiber is post-treated. The specific process of the post-treatment is as follows: 2-1 The three substrates with polyamide fibers were transferred to an appropriate amount of anhydrous AlCl3 and dichloromethane mixture and treated under ultrasonic conditions at 40°C for a period of time; 2-2 Prepare three groups of epichlorohydrin with different masses, where the ratio of epichlorohydrin mass to polyamide fiber mass is d, e, and f, respectively, where 10% ≥ d > e > f ≥ 2%, and add the three groups of epichlorohydrin with the mass fractions d, e, and f of the polyamide fiber to the polyamide fiber mixture with the mass fractions c, b, and a of the 4,4'-diphenylenediamine monomer in step 1-1, respectively, and soak at 40°C for 2-4 hours; 2-3 Take out the polyamide fiber, wash it with acetone and distilled water, and then dry it to remove the residual solvent; 2-4 Peel the polyamide fiber off the polyethylene substrate.

3. The method for preparing a composite material of an in-situ flow-guiding fiber according to claim 1, characterized in that: After the drying described in step 1-2 to remove the residual solvent, the polyamide fiber is post-treated. The specific process of the post-treatment is as follows: 3-1 Transferring the dried polyamide fiber to an etchant for a period of time, wherein the etchant comprises one of the following components: acetic anhydride, fluorine gas, and a CaCl2 / ethanol solution, wherein the mass fraction of CaCl2 is 3% to 8%; 3-2 Take out the polyamide fiber, wash it with acetone and distilled water, and dry it to remove the residual solvent.

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