A controllable method for interlaminar toughening of composite materials

Abstract

This invention discloses a controllable interlaminar toughening method for composite materials. The method first mixes a thermosetting resin matrix with a prepolymerization degree of 10-60% with a toughening medium to form a film, which is then laminated with a fiber fabric to create a toughened prepreg tape. The toughened prepreg tape is then laid up and cured to obtain a toughened composite material. This method proposes a controllable interlaminar toughening technology for composite materials, utilizing the controllable solubility of the toughening medium in the thermosetting resin matrix to achieve the enrichment of the toughening medium in the interlaminar layers. This allows the composite material to possess good toughness and interfacial properties with a relatively low amount of toughening medium added. The technology is simple, offers controllable performance, and has a high level of technological maturity.

Description

Technical Field

[0001] This invention is a controllable method for interlaminar toughening of composite materials, belonging to the field of preparation technology of thermosetting resin-based composite materials. Background Technology

[0002] The widespread use of resin-based composite materials in the main load-bearing components of aircraft has brought increasing attention to the damage tolerance and durability of composite materials, with the impact resistance of composite laminates being a key performance characteristic of structural components. Most composite materials are made by laying and pressing single-layer fiber fabrics together, with a specific layup angle between each layer. The load is transferred between the layers by the resin matrix. Due to the low toughness of the matrix, composite materials often suffer from interlaminar matrix cracking and delamination under impact loads. These internal damages severely degrade the mechanical properties of the laminate and significantly reduce its structural strength. Therefore, improving the toughness and enhancing the impact resistance of composite materials has always been a key research focus in the field of composite materials.

[0003] Interlayer toughening is an effective method for toughening composite materials. Toughening agents are mostly rubber, thermoplastic resin, etc. Although these toughening agents have good toughening effects, their Young's modulus is lower than that of the resin matrix. Their large addition will inevitably affect the Young's modulus of the resin matrix, and thus affect the compressive properties of the composite material. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a controllable interlaminar toughening method for composite materials. This method improves the effective enrichment of toughening media in the interlaminar layers of composite fiber fabric by increasing the prepolymerization degree of the thermosetting resin matrix. It achieves interlaminar toughening of composite materials without increasing or with a low content of toughening media, while maintaining the strength and interface quality of the composite material without reduction.

[0005] In the controllable interlaminar toughening method of composite materials described in the technical solution of the present invention, a thermosetting resin matrix with a prepolymerization degree of 10-60% is first mixed with a toughening medium to form a film, which is then compounded with a fiber fabric to form a toughening prepreg tape. After the toughening prepreg tape is laid up, it is cured and molded to obtain a toughened composite material.

[0006] In practice, the thermosetting resin matrix with prepolymerization degree is composed of a mixture of thermosetting resin monomers and a curing agent.

[0007] Furthermore, the thermosetting resin monomer is an epoxy monomer, a bismaleimide monomer, or a polyimide monomer.

[0008] Furthermore, the molar ratio of the thermosetting resin monomer to the curing agent is 100:20 to 80.

[0009] Furthermore, the prepolymerization temperature of the thermosetting resin matrix is ​​30–100°C lower than the curing temperature of the composite material, and the prepolymerization time is 20–200 min.

[0010] In practice, the toughening medium is powdered polyethersulfone, polyetherimide, polyetheretherketone, or thermoplastic polyimide.

[0011] Furthermore, a non-reactive film-forming agent is added simultaneously with the toughening medium, and the molar ratio of the toughening medium to the non-reactive film-forming agent is 5-60:1-20.

[0012] The steps of the controllable interlaminar toughening method for composite materials are as follows:

[0013] Step 1: Mix 100 moles of thermosetting resin monomer with 20-80 moles of curing agent for prepolymerization. The prepolymerization temperature is 30-100°C lower than the curing temperature of the composite material, and the prepolymerization time is 20-200 min.

[0014] The thermosetting resin monomer is an epoxy monomer, a bismaleimide monomer, or a polyimide monomer;

[0015] Step 2: Add 5 to 60 moles of toughening medium and 1 to 20 moles of non-reactive film-forming agent to the prepolymerized thermosetting resin matrix, mix evenly, and then form a film.

[0016] The toughening medium is powdered polyethersulfone, polyetherimide, polyetheretherketone, or thermoplastic polyimide;

[0017] Step 3: Combine the adhesive film obtained in Step 2 with the fiber fabric to form a toughened prepreg tape;

[0018] Step 4: After laying up the toughened prepreg tape, cure it to obtain the toughened composite material.

[0019] In the above technical solution, the controllable interlaminar toughening method for composite materials refers to adjusting the toughness of the composite material according to the requirements of the composite product. This is achieved by adjusting the prepolymerization degree of the thermosetting resin matrix. The higher the toughness of the composite material, the lower its rigidity. The prepolymerization degree of the thermosetting resin matrix is ​​controlled by the prepolymerization time; the prepolymerization degree increases with the extension of the prepolymerization time. In this invention, the prepolymerization time is selected as 20–200 min, thereby controlling the prepolymerization degree between 10–60%. Studies have shown that if the prepolymerization degree of the thermosetting resin matrix is ​​below 10%, the effect on interlaminar toughening of the composite material is not significant. If the prepolymerization degree of the thermosetting resin matrix is ​​above 60%, the crosslinking of the thermosetting resin matrix is ​​too high, making it difficult to mix uniformly with the toughening medium and failing to achieve good interlaminar toughening.

[0020] Based on the aforementioned control of the prepolymerization degree of the thermosetting resin matrix, the technical solution of this invention simultaneously achieves controllable solubility of the toughening medium in the thermosetting resin matrix and enrichment of the toughening medium in the interlayer. The method involves mixing a thermoplastic toughening medium into a resin matrix with a certain degree of prepolymerization, then combining it with fibers to form a high-toughness prepreg, which is then cured to achieve interlayer toughening. This interlayer toughening is achieved through two mechanisms: firstly, utilizing the filtering effect of the fibers on the toughening medium, low-viscosity resin molecules penetrate into the fiber interior, thereby enriching the toughening medium in particulate form between the fiber layers; secondly, during the heating and molding process, the interlayer thermosetting resin matrix gradually dissolves or swells the toughening medium. As the curing reaction proceeds, the solubility parameters of the thermosetting and thermoplastic resins change, leading to phase separation between the layers and achieving interlayer toughening of the composite material.

[0021] The study found that changes in the initial prepolymerization degree of the thermosetting resin affected the distribution of the resin matrix both between and within the interlayers of the interlayer toughened composite material. Figure 1 As shown, with the increase of the initial resin prepolymerization degree, the thermosetting resin's ability to dissolve the toughening medium decreases, and the amount of interlaminar toughening medium propagating into the interlaminar layers decreases, leading to an increase in interlaminar thickness and a greater enrichment of the interlaminar toughening medium. With the increase in interlaminar thickness, interlaminar cracks can absorb more energy during propagation, exhibiting higher interlaminar fracture toughness. Therefore, by extending the prepolymerization time to increase the prepolymerization degree of the resin system, the solubility of the toughening medium in the resin matrix can be reduced, effectively achieving the enrichment of the thermoplastic medium in the interlaminar layers. Based on the above measures, a low toughening medium content can achieve a good toughening effect. Attached Figure Description

[0022] Figure 1 Schematic diagram showing the effect of prepolymerization degree on the microstructure of interlaminar toughened composite materials Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the embodiments:

[0024] In this embodiment, the steps for preparing the controllable composite material using the method of the present invention are as follows:

[0025] Step 1: Preparation of toughened adhesive film

[0026] 80 molar parts of S500M and 20 molar parts of E54 epoxy resin monomers were dissolved in 54 molar parts of DDS at 120℃, and then kept at 120℃ for 30 minutes to obtain epoxy resin masterbatch. This masterbatch was then mixed with 6 molar parts of non-reactive film-forming agent PEK-C at 60℃, and 33 molar parts of toughening medium LPI-P were added to the resin matrix in powder form. The mixture was further homogenized using a three-roll mill, and then coated onto a film using a film-forming machine. LPI-P is soluble in S500M but insoluble in E54.

[0027] S500M is a trifunctional epoxy resin, triglycidyl-m-aminophenol, produced by Nantong Haojin Chemical Co., Ltd., with the chemical formula shown below:

[0028]

[0029] The E54 epoxy resin monomer is an industrial-grade bisphenol A glycidyl ether type epoxy resin produced by Wuxi Lanxing Chemical Plant, with an epoxy value of 0.54. Its chemical formula is shown below:

[0030]

[0031] The DDS is industrial-grade 4,4-diaminodiphenyl sulfone produced by Suzhou Yinsheng Chemical Co., Ltd., with the chemical formula shown below:

[0032]

[0033] The toughening medium LPI-P is a linear thermoplastic polyimide in the form of irregularly shaped particles;

[0034] The non-reactive film-forming agent PEK-C is phenolphthalein polyarylether ketone;

[0035] Step 2: Preparation of toughened composite laminate

[0036] The adhesive film obtained in step one was prepared into a high-toughness unidirectional prepreg using a hot-melt prepreg process. The areal density of carbon fiber CCF800H in the single-layer prepreg was (145±4) g / m², and the resin mass content was (35±2)%. After the prepreg was laid in the standard required layup sequence, it was sealed in a vacuum bag and formed into a composite laminate using an autoclave molding process. Curing process: vacuum was applied at room temperature with a vacuum degree of not less than 0.095 MPa, pressure was applied at 0.6 MPa, and the temperature was increased to 180°C at a heating rate of 1°C / min to 1.5°C / min, held for 120 min, and naturally cooled to below 60°C before being removed from the autoclave to obtain the composite laminate. The carbon fiber volume fraction of the composite laminate was (56±2)%, and the CAI performance was 283 MPa.

[0037] Comparative Example

[0038] The preparation steps of the composite material in this comparative example are as follows:

[0039] Step 1: Preparation of toughened adhesive film

[0040] 80 molar parts of S500M and 20 molar parts of E54 epoxy resin monomers were dissolved in 54 molar parts of DDS at 120℃, and then kept at 120℃ for 0 min to obtain epoxy resin masterbatch. This masterbatch was then mixed with 6 molar parts of non-reactive film-forming agent PEK-C at 60℃, and 33 molar parts of toughening medium LPI-P were added to the resin matrix in powder form. The mixture was further homogenized using a three-roll mill, and then coated onto a film using a film-forming machine. Note that LPI-P is soluble in S500M but insoluble in E54.

[0041] Step 2: Preparation of toughened composite laminate

[0042] The adhesive film obtained in step one was prepared into a high-toughness unidirectional prepreg using a hot-melt prepreg process. The areal density of carbon fiber CCF800H in the single-layer prepreg was (145±4) g / ㎡, and the resin mass content was (35±2)%. After the prepreg was laid in the standard required layup sequence, it was sealed in a vacuum bag and formed into a composite laminate using an autoclave molding process. The curing process was as follows: vacuuming at room temperature with a vacuum degree of not less than 0.095 MPa, pressurizing at 0.6 MPa, heating to 180℃ at a heating rate of 1℃ / min~1.5℃ / min, holding at that temperature for 120 min, and naturally cooling to below 60℃ before being removed from the autoclave to obtain the composite laminate. The carbon fiber volume fraction of the composite laminate was (56±2)%, and the CAI performance was 212 MPa.

Claims

1. A controllable method for interlaminar toughening of composite materials, characterized in that, The method first mixes a thermosetting resin matrix with a prepolymerization degree of 10-60% with a toughening medium to form a film, which is then combined with a fiber fabric to form a toughened prepreg tape. After the toughened prepreg tape is laid up, it is cured to obtain a toughened composite material.

2. The controllable interlaminar toughening method for composite materials according to claim 1, characterized in that, The thermosetting resin matrix with a prepolymerization degree of 10-60% is composed of thermosetting resin monomers and curing agents.

3. The controllable interlaminar toughening method for composite materials according to claim 2, characterized in that, The thermosetting resin monomer is an epoxy monomer, a bismaleimide monomer, or a polyimide monomer.

4. The controllable interlaminar toughening method for composite materials according to claim 2, characterized in that, The molar ratio of the thermosetting resin monomer to the curing agent is 100. 20~80.

5. The controllable interlaminar toughening method for composite materials according to claim 2, characterized in that, The prepolymerization temperature of the thermosetting resin matrix is ​​30-100°C lower than the curing temperature of the composite material, and the prepolymerization time is 20-200 min.

6. The controllable interlaminar toughening method for composite materials according to claim 1, characterized in that, The toughening medium is powdered polyethersulfone, powdered polyetherimide, powdered polyetheretherketone, or powdered thermoplastic polyimide.

7. The controllable interlaminar toughening method for composite materials according to claim 1 or 6, characterized in that, A non-reactive film-forming agent is added along with the toughening medium, and the molar ratio of the toughening medium to the non-reactive film-forming agent is 5~60:1~20.

8. The controllable interlaminar toughening method for composite materials according to claim 7, characterized in that, The steps of this method are as follows: Step 1: Mix 100 moles of thermosetting resin monomer with 20-80 moles of curing agent for prepolymerization. The prepolymerization temperature is 30-100℃ lower than the curing temperature of the composite material, and the prepolymerization time is 20-200 min. The thermosetting resin monomer is an epoxy monomer, a bismaleimide monomer, or a polyimide monomer; Step 2: Add 5-60 moles of toughening medium and 1-20 moles of non-reactive film-forming agent to the prepolymerized thermosetting resin matrix, mix evenly, and then form a film. The toughening medium is powdered polyethersulfone, powdered polyetherimide, powdered polyetheretherketone, or powdered thermoplastic polyimide. Step 3: Combine the adhesive film obtained in Step 2 with the fiber fabric to form a toughened prepreg tape; Step 4: After laying up the toughened prepreg tape, cure it to obtain the toughened composite material.

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