A prepreg resin system formulation and preparation method suitable for T700 grade carbon fiber

Abstract

The application discloses a prepreg resin system formula suitable for T700-grade carbon fibers and a preparation method thereof, and mainly relates to the technical field of resin systems, and comprises liquid bisphenol A type epoxy resin, solid bisphenol A type epoxy resin, methyl phenol type phenolic epoxy resin, dicyandiamide curing agent and hyperbranched thermoplastic resin micro-nano filler. The preparation method comprises the following steps: mixing the liquid epoxy resin and the solid epoxy resin to obtain component A, mixing the liquid epoxy resin and the dicyandiamide curing agent to obtain component B, and mixing the component A and the component B to obtain the epoxy resin system. The application can improve the tensile and bending properties of the prepreg base composite material, and solve the problems of brittle fracture of the base body and interface debonding.

Description

Technical Field

[0001] This invention mainly relates to the field of resin system technology, specifically to a prepreg resin system formulation and preparation method suitable for T700 grade carbon fiber. Background Technology

[0002] As the core intermediate substrate of composite materials, prepreg directly determines the mechanical strength, environmental stability, and process adaptability of the final product. Therefore, it has wide applications in many high-end technology fields such as aerospace, high-end electronic equipment, rail transportation, new energy vehicles, and wind turbine blades. The preparation processes of prepreg are mainly divided into two types: hot-melt method and solvent method. The mainstream process of the hot-melt method is a two-step process, which involves first forming a resin film, and then compounding it with reinforcing materials. This method has advantages such as environmental friendliness, high efficiency, and controllable cost.

[0003] Epoxy resins possess excellent adhesive properties, mechanical properties, and chemical stability, making them the most widely used matrix material in prepreg manufacturing. The type and ratio of resin matrix, curing agent, and accelerator directly affect the storage stability, molding processability, and product performance of prepregs. Currently, the industry commonly uses bisphenol A type epoxy resin and bisphenol F type epoxy resin in combination with amine or acid anhydride curing agents. Bisphenol A type epoxy resin has many advantages, such as excellent mechanical properties, strong chemical corrosion resistance, wide process adaptability, and lower cost, and can show significant advantages in large-size, high-volume components.

[0004] As a typical representative of medium-to-high strength PAN-based carbon fiber, T700 grade carbon fiber has significantly improved core mechanical properties such as tensile strength and elastic modulus compared to T300 grade. At the same time, it has good process adaptability and cost performance, making it one of the fastest growing and most widely used reinforcing materials in the field of high-end composite materials. It has been widely used in the manufacturing of equipment such as aerospace main load-bearing structures, key components of rail transit vehicle bodies, and battery pack frames for new energy vehicles.

[0005] In resin systems that match epoxy resin with T700 grade carbon fiber, dicyandiamide is generally used as a latent curing agent. Therefore, their combination has the characteristics of no solvent evaporation, controllable curing temperature, and excellent thermal and chemical stability of the cured product. It can effectively meet the needs of environmentally friendly, efficient, and high-performance composite material preparation and is one of the most common systems in hot melt prepregs.

[0006] Several researchers have already conducted numerous improvements in the existing technology. For example, Wang Yang et al. studied the effect of hydroxylated carbon nanotubes on the mechanical properties of T700 carbon fiber composites. The results showed that the addition of 0.5 wt% hydroxylated carbon nanotubes could increase the flexural strength of the composite by 10% to 15%. However, the introduction of carbon nanotubes significantly increased the viscosity of the resin system, reduced the grinding efficiency of the three-roll mill, affected the uniformity and lay-up of the prepreg, and may also accelerate the viscosity increase during storage, shortening the pot life.

[0007] Another patent application (CN103087339A) proposes a preparation method for controlling the viscosity and flowability of epoxy resin system through chemical rheology. This invention uses a room temperature reactive curing agent and dicyandiamide in combination. Although the initial viscosity is low and the wettability is good, the crosslinking uniformity of the cured system decreases and the network stability is insufficient at high temperature. Micro-defects are easy to expand during compression and the interface is easy to debond under cyclic load.

[0008] In addition, Lei Pan et al. used a dicyandiamide curing system with a high proportion of phenolic epoxy resin. Dicyandiamide curing easily forms a rigid network with high cross-linking density, and the rigid benzene ring structure of phenolic epoxy resin further enhances the brittleness of the system. Furthermore, no toughening agent was added, resulting in insufficient elongation at break and toughness of the cured product.

[0009] Therefore, although existing technologies have formed relatively mature process routes for the preparation of T300 grade carbon fiber prepregs, the following technical bottlenecks still exist when adapting them to high-performance T700 carbon fibers: (1) Insufficient mechanical properties: The tensile and bending properties of composite materials are low, and the structure is prone to deformation or fracture. It is urgent to toughen and modify the resin system. (2) Poor wettability: The resin viscosity is too high, which leads to poor wetting effect on the fiber and defects are easy to occur during the molding process; (3) Insufficient thermal stability: The glass transition temperature is low, and the performance degrades significantly under high temperature conditions, which restricts its application under high temperature conditions.

[0010] An epoxy resin system with excellent wettability, high glass transition temperature and good toughness is proposed, which is of great significance for improving the overall performance of T700 grade carbon fiber prepreg and expanding its application in high-end equipment. Summary of the Invention

[0011] (a) Technical problems to be solved In view of the above-mentioned problems, the present invention provides a prepreg resin system formulation and preparation method suitable for T700 grade carbon fiber. The present invention introduces hyperbranched thermoplastic resin micro-nano fillers, and constructs an interpenetrating polymer network structure by utilizing its molecular-level toughening mechanism and interface compatibility modification technology. At the same time, the steric hindrance effect of the fillers is used to optimize the interfacial bonding state of the resin system, improve the load transfer efficiency between the resin matrix and the reinforcing phase, and thus improve the tensile and bending properties of the prepreg matrix composite material, solving the problems of matrix brittle fracture and interfacial debonding that are prone to occur during its application. Meanwhile, the uniformly dispersed thermoplastic fillers combined with the ratio control of liquid and solid bisphenol A epoxy resin achieve precise control of the system viscosity. Methylphenol type phenolic epoxy resin is selected to construct a dense three-dimensional network cross-linked network, thereby increasing the glass transition temperature of the prepreg resin system.

[0012] (II) Technical Solution To address the aforementioned technical problems, this invention provides a prepreg resin system formulation suitable for T700 grade carbon fiber, wherein the raw materials and proportions are as follows: 52 parts of liquid bisphenol A type epoxy resin, 20 parts of solid bisphenol A type epoxy resin, 20 parts of methylphenol type phenolic epoxy resin, 8 parts of dicyandiamide curing agent, and 5 parts of hyperbranched thermoplastic resin micro-nano filler.

[0013] Furthermore, the 52 parts of liquid bisphenol A type epoxy resin are composed of 30 parts of liquid bisphenol A type epoxy resin one and 22 parts of liquid bisphenol A type epoxy resin two.

[0014] Furthermore, the ends of the hyperbranched thermoplastic resin micro-nano fillers have active groups, which can serve as crosslinking sites to promote the reaction process between dicyandiamide and epoxy groups, accelerate the molecular chain crosslinking reaction, speed up the formation of three-dimensional networks, and shorten the gelation time.

[0015] Furthermore, the hyperbranched molecules of the hyperbranched thermoplastic resin micro-nano filler have a dendritic structure, and the micro-nano size of the particles can fill the gaps between resin molecules, reducing intermolecular friction. At the same time, the filler can disperse dicyandiamide agglomerates to avoid viscosity increase caused by particle agglomeration, ultimately achieving a reduction in system viscosity.

[0016] A method for preparing a prepreg resin system suitable for T700 grade carbon fiber includes the following steps: S1. First, add 20 parts of liquid bisphenol A type epoxy resin I and 22 parts of liquid bisphenol A type epoxy resin II to a planetary mixer; after preheating to 150°C, add 20 parts of solid bisphenol A type epoxy resin, 20 parts of methylphenol type phenolic epoxy resin and 5 parts of hyperbranched thermoplastic resin micro-nano filler; after the two solid resins are fully melted, mechanically stir for 30 minutes to prepare component A; S2. Add 8 parts of dicyandiamide curing agent to 10 parts of liquid bisphenol A type epoxy resin, stir mechanically for 20 minutes, and then grind with a three-roll mill until the powder particle size is less than 5μm to prepare component B. S3. Adjust the temperature of the prepared component A to 70℃, add component B, stir with a planetary mixer for 30 minutes and perform vacuum degassing to obtain the target resin system.

[0017] Furthermore, the resin system is cured according to the following procedure: (1) Preheat at 100℃ and keep warm for 2 hours; (2) Heat from 100℃ to 120℃ at a rate of 2℃ / min and hold for 1 hour; (3) Continue heating from 120℃ to 130℃ at a rate of 2℃ / min and hold for 1 hour; (4) Then heat from 130°C to 145°C at a rate of 2°C / min and hold for 1 hour; (5) Heat from 145°C to 155°C at a rate of 2°C / min and hold for 1 hour; (6) Heat from 155℃ to 170℃ at a rate of 2℃ / min and hold for 1 hour; (7) Finally, cool naturally in an oven from 170°C to room temperature.

[0018] Furthermore, the gel time of the obtained resin system at 120°C was 674 s.

[0019] Furthermore, the glass transition temperature of the resulting resin system is 144.6℃.

[0020] Furthermore, the resulting resin system has an elongation at break of 2.0%, a flexural strength of 80.9 MPa, and a flexural modulus of 2.8 GPa.

[0021] The beneficial effects of this invention compared with the prior art are as follows: 1. It achieves enhanced toughness of prepreg products. This invention introduces hyperbranched thermoplastic resin micro-nano fillers, constructs an interpenetrating polymer network structure with molecular-level toughening, and optimizes the interfacial bonding state of the resin system using the steric hindrance effect of the fillers, thereby improving the load transfer efficiency between the resin matrix and the reinforcing phase. Compared with the comparative example, the tensile and bending properties of the composite material made from the prepreg are significantly improved, solving problems such as matrix brittle fracture and interfacial debonding that are prone to occur during use; 2. It optimizes the resin processing performance. By dispersing thermoplastic fillers and adjusting the ratio of liquid-solid bisphenol A epoxy resin, the viscosity of the resin system is precisely controlled. Compared with the comparative example, the viscosity of the resin system is reduced, improving the wettability of the resin to carbon fibers, effectively reducing defects in the molding process, and improving the product molding qualification rate; 3. It increases the glass transition temperature of the resin system. A three-dimensional network cross-linked network is constructed using methylphenol-type phenolic epoxy resin, which increases the glass transition temperature of the resin system compared with the comparative example. Attached Figure Description

[0022] Figure 1 This is a comparison of the viscosity-temperature curves of the resin systems in Example 1 and Comparative Example 1.

[0023] Figure 2 This is a temperature-enthalpy curve of the resin system in Example 1.

[0024] Figure 3 The temperature-enthalpy curve of the resin system in Comparative Example 1 is shown.

[0025] Figure 4 This is a graph showing the glass transition temperature of the resin system in Example 1.

[0026] Figure 5 This is a graph showing the glass transition temperature of the resin system in Comparative Example 1. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments. The invention is explained through illustrative embodiments and descriptions, but is not intended to limit the invention.

[0028] Example: Figures 1-5 The above describes a prepreg resin system formulation suitable for T700 grade carbon fiber, in which the raw materials and proportions are as follows: 52 parts of liquid bisphenol A type epoxy resin, 20 parts of solid bisphenol A type epoxy resin, 20 parts of methylphenol type phenolic epoxy resin, 8 parts of dicyandiamide curing agent, and 5 parts of hyperbranched thermoplastic resin micro-nano filler.

[0029] The 52 parts of liquid bisphenol A type epoxy resin consist of 30 parts of liquid bisphenol A type epoxy resin one and 22 parts of liquid bisphenol A type epoxy resin two.

[0030] Liquid bisphenol A type epoxy resin I (epoxy equivalent 184-190 g / eq, viscosity 12000-15000 cps at 25℃), liquid bisphenol A type epoxy resin II (epoxy equivalent 190-200 g / eq, viscosity 15000-20000 cps at 25℃), solid bisphenol A type epoxy resin (epoxy equivalent 450-500 g / eq, softening point 64-74℃), and methylphenol type phenolic epoxy resin (epoxy equivalent 200-220 g / eq, softening point 85-95℃).

[0031] Hyperbranched thermoplastic resin micro / nano fillers have active groups at their ends. These active groups can serve as crosslinking sites, promoting the reaction between dicyandiamide and epoxy groups, accelerating the crosslinking reaction of molecular chains, speeding up the formation of three-dimensional networks, and shortening the gelation time.

[0032] The hyperbranched thermoplastic resin micro-nano filler has a dendritic structure in its hyperbranched molecules, and its micro-nano size can fill the gaps between resin molecules, reducing intermolecular friction. At the same time, the filler can disperse dicyandiamide agglomerates to avoid viscosity increase caused by particle agglomeration, ultimately achieving a reduction in system viscosity.

[0033] Example 1: A method for preparing a prepreg resin system suitable for T700 grade carbon fiber, comprising the following steps: S1. First, add 20 parts of liquid bisphenol A type epoxy resin I and 22 parts of liquid bisphenol A type epoxy resin II to a planetary mixer; after preheating to 150°C, add 20 parts of solid bisphenol A type epoxy resin, 20 parts of methylphenol type phenolic epoxy resin and 5 parts of hyperbranched thermoplastic resin micro-nano filler; after the two solid resins are fully melted, mechanically stir for 30 minutes to prepare component A; S2. Add 8 parts of dicyandiamide curing agent to 10 parts of liquid bisphenol A type epoxy resin, stir mechanically for 20 minutes, and then grind with a three-roll mill until the powder particle size is less than 5μm to prepare component B. S3. Adjust the temperature of the prepared component A to 70℃, add component B, stir with a planetary mixer for 30 minutes and perform vacuum degassing to obtain the target resin system.

[0034] In S1 above, the selected hyperbranched thermoplastic resin has good storage stability at 150°C and will not undergo premature cross-linking; in S2 above, 10 parts of liquid bisphenol A type epoxy resin and 20 parts of liquid bisphenol A type epoxy resin in S1 total 30 parts.

[0035] Based on the characteristics of the enthalpy-temperature curve, this step-curing regime was developed to ensure full cross-linking of the resin and avoid concentrated exothermic reactions. The resin system was cured according to the following regime: (1) Preheat at 100℃ and keep warm for 2 hours; (2) Heat from 100℃ to 120℃ at a rate of 2℃ / min and hold for 1 hour; (3) Continue heating from 120℃ to 130℃ at a rate of 2℃ / min and hold for 1 hour; (4) Then heat from 130°C to 145°C at a rate of 2°C / min and hold for 1 hour; (5) Heat from 145°C to 155°C at a rate of 2°C / min and hold for 1 hour; (6) Heat from 155℃ to 170℃ at a rate of 2℃ / min and hold for 1 hour; (7) Finally, cool naturally in an oven from 170°C to room temperature.

[0036] The resin casting preparation method is as follows: prepare the resin system according to the above resin system preparation method; clean the mold, apply a release agent and preheat it in an environment of 120℃ for 30 minutes; slowly inject the prepared resin system into the mold cavity, complete the resin crosslinking reaction according to the preset curing regime, and ensure that the casting is fully cured; after curing, demold and polish the sample to meet the dimensional accuracy, the specific dimensions refer to GB / T2567-2021.

[0037] The specific method for preparing the composite material sample of the present invention is as follows: 1. Prepreg layup: Cut the prepreg to 300mm×300mm size according to the preset layup direction, and then strictly follow the layup design to complete the layup layer by layer. When designing the layup, pay attention to controlling the thickness of the formed board within (2±0.2)mm.

[0038] 2. Place the laid prepreg blank in an autoclave, and the curing process is as follows: a) The vacuum bag is evacuated, and the vacuum pressure inside the vacuum bag is not less than 0.092 MPa; b) Pressurize the autoclave to 0.5 MPa; c) Heat from room temperature to (80±5)℃ at a heating rate of 3℃ / min, and hold at that temperature for (30±5) minutes; d) Heat to (125±5)℃ at a heating rate of 3℃ / min and hold for more than 90min; e) Cool to below 60°C at a cooling rate of 3°C / min (maintain pressure until cooling is complete), then open the autoclave and remove the part.

[0039] 3. Reinforcing sheet bonding: Based on the force direction of the tensile and bending tests, structural adhesive is used to bond reinforcing sheets to the clamping area of ​​the laminate. The tensile test reinforcing sheet width × thickness is 50mm × 2mm, and the compression test reinforcing sheet width × thickness is 63.5mm × 2mm.

[0040] 4. Sample finishing: After the structural adhesive has fully cured, use a grinding machine to process the laminate to the sample size specified in the national standard. The standard for tensile test specimen preparation is GB / T 3354-2014, the standard for bending test specimen preparation is GB / T 3356-2014, the standard for compression test specimen preparation is ASTM D 6641-16, and the standard for interlaminar shear test specimen preparation is JC / T 773-2010.

[0041] Example 2: Prepreg was prepared by hot melt method. The prepreg was cut, laid up and cured in a hot autoclave. The cut size was 300mm×300mm. Seven sheets of prepreg were laid up in the same direction to prepare a 2mm thick laminate.

[0042] The autoclave curing process is as follows: a) The vacuum bag is evacuated, and the vacuum pressure inside the vacuum bag is not less than 0.092 MPa; b) Pressurize the autoclave to 0.5 MPa; c) Heat from room temperature to (80±5)℃ at a heating rate of 3℃ / min, and hold at that temperature for (30±5) minutes; d) Heat to (125±5)℃ at a heating rate of 3℃ / min and hold for more than 90min; e) Cool to below 60°C at a cooling rate of 3°C / min (maintain pressure until cooling is complete), open the autoclave to remove the part, and obtain the required laminate.

[0043] Based on the force direction of the tensile and bending tests, reinforcing sheets are bonded to the clamping area of ​​the laminate using structural adhesive. The tensile test reinforcing sheet has a width × thickness of 50 mm × 2 mm, and the compression test reinforcing sheet has a width × thickness of 63.5 mm × 2 mm. After the structural adhesive has fully cured, the laminate is machined to the test specimen dimensions specified in the national standard using a grinding machine. The tensile test specimen preparation standard refers to GB / T 3354-2014, the bending test specimen preparation standard refers to GB / T 3356-2014, the compression test specimen preparation standard refers to ASTM D6641-16, and the interlaminar shear test specimen preparation standard refers to JC / T 773-2010.

[0044] Comparative Example 1: A commercially available resin system for a similar purpose was preheated at 70°C for later use. The mold was cleaned, coated with a release agent, and preheated at 120°C for 30 minutes. The prepared resin system was slowly injected into the mold cavity, and the resin crosslinking reaction was completed according to the preset curing regime to ensure that the casting was fully cured. After curing, the mold was demolded, and the sample was polished to meet the dimensional accuracy. The specific dimensions refer to GB / T2567-2021.

[0045] The pre-defined fixed system is as follows: 1. Preheat at 100℃ and keep warm for 2 hours; 2. Heat from 100℃ to 120℃ at a rate of 2℃ / min and hold at that temperature for 1 hour; 3. Heat from 120℃ to 130℃ at a rate of 2℃ / min and hold at that temperature for 1 hour; 4. Heat from 130℃ to 145℃ at a rate of 2℃ / min and hold at that temperature for 1 hour; 5. Heat from 145℃ to 155℃ at a rate of 2℃ / min and hold at that temperature for 1 hour; 6. Heat from 155℃ to 170℃ at a rate of 2℃ / min and hold at that temperature for 1 hour; 7. Allow to cool naturally from 170°C to room temperature in an oven.

[0046] Comparative Example 2: Prepreg was prepared by hot melt method. The prepreg was cut, laid up and cured in a hot autoclave. The cut size was 300mm×300mm. Seven sheets of prepreg were laid up in the same direction to prepare a 2mm thick laminate.

[0047] The autoclave curing process is as follows: a) The vacuum bag is evacuated, and the vacuum pressure inside the vacuum bag is not less than 0.092 MPa; b) Pressurize the autoclave to 0.5 MPa; c) Heat from room temperature to (80±5)℃ at a heating rate of 3℃ / min, and hold at that temperature for (30±5) minutes; d) Heat to (125±5)℃ at a heating rate of 3℃ / min and hold for more than 90min; e) Cool to below 60°C at a cooling rate of 3°C / min (maintain pressure until cooling is complete), open the autoclave to remove the part, and obtain the required laminate.

[0048] Based on the force direction of the tensile and bending tests, structural adhesive is used to attach reinforcing sheets to the clamping area of ​​the laminate. The tensile test sheet has a width × thickness of 50 mm × 2 mm, and the compression test sheet has a width × thickness of 63.5 mm × 2 mm.

[0049] After the structural adhesive has fully cured, the laminate is machined to the specimen size specified in the national standard using a grinding machine. The tensile specimen preparation standard refers to GB / T 3354-2014, the bending specimen preparation standard refers to GB / T 3356-2014, the compression specimen preparation standard refers to ASTM D 6641-16, and the interlaminar shear specimen preparation standard refers to JC / T 773-2010.

[0050] The gelation time at 120°C of the resin systems in Example 1 and Comparative Example 1 was tested using a gelation time meter, and the specific method is as follows: 1. Adjust the temperature to 120℃ and stabilize it at this temperature; 2. Gently rub the hot plate with release wax, then wipe the hot plate clean with clean paper towels; 3. Use a small spoon to take 200mg±20mg of resin sample, pour it into the resin pool in the hot plate, and start timing immediately; 4. Use a toothpick to slide the resin in the hot plate in a circular motion to make the resin move evenly in the resin pool of the hot plate. 5. During the stirring process, you will feel the resin in the hot pan becoming thicker and thicker. At this point, you can slide the resin while using a toothpick to pick up and pull out the strands. 6. When the picked resin filament breaks, stop timing immediately. The time recorded at this moment is the resin gelation time.

[0051] The gel times at 120°C for the resin systems in Example 1 and Comparative Example 1 were 674 s and 708 s, respectively. The terminal active groups of the hyperbranched resin can serve as crosslinking sites, promoting the reaction between dicyandiamide and epoxy groups. On the one hand, the active groups reduce the activation energy of the curing reaction and accelerate the crosslinking of molecular chains. On the other hand, the interfacial effect of the micro-nano fillers enriches the surrounding resin and curing agent molecules, forming a local high-concentration reaction region, accelerating the formation of the three-dimensional network, thereby shortening the gel time.

[0052] The viscosity-temperature profiles of the resin systems in Example 1 and Comparative Example 1 were tested using a rotational viscometer. A No. 29 rotor was used, with a rotational speed of 30 r / min and a heating rate of 1 °C / min. The test results are as follows: Figure 1 As shown.

[0053] After adding hyperbranched thermoplastic resin micro-nano fillers, the viscosity of Example 1 decreased compared to Comparative Example 1. This is because the hyperbranched molecules have a dendritic structure without long chain entanglement, and the micro-nano size can fill the gaps between resin molecules, reducing intermolecular friction. At the same time, the large number of active groups at the ends have good compatibility with epoxy resins and phenolic resins, which can disperse dicyandiamide agglomerates and avoid viscosity increase caused by particle agglomeration, ultimately achieving a reduction in system viscosity.

[0054] The temperature-enthalpy curves of the resin systems in Example 1 and Comparative Example 1 were tested using a differential scanning calorimeter. The heating rate was 10 °C / min, and the nitrogen flow rate was 60 mL / min. The test results are as follows: Figure 2 and Figure 3 As shown.

[0055] A reasonable curing process was developed based on the temperatures at the start, peak, and end points.

[0056] The glass transition temperatures of the resin systems in Example 1 and Comparative Example 1 were tested using a differential scanning calorimeter. The heating rate was 10 °C / min, and the nitrogen gas flow rate was 60 mL / min. The test results are as follows: Figure 4 and Figure 5 As shown.

[0057] The glass transition temperature of Example 1, 144.6℃, is higher than that of Comparative Example 1, 126.0℃. This result confirms that the hyperbranched thermoplastic resin filler and the resin matrix form stronger intermolecular interactions, which restricts the mobility of resin molecular chains and thus increases the glass transition temperature of the resin system.

[0058] The tensile and flexural properties of the resin castings in Example 1 and Comparative Example 1 were tested according to GB / T 2567-2021, and the results are shown in Table 1.

[0059] In the resin casting, the elongation at break of Example 1 (2.0%) was nearly doubled compared to that of Comparative Example 1 (1.1%), and the toughness was improved. The flexural strength and flexural modulus increased from 32.6 MPa and 1.8 GPa to 80.9 MPa and 2.8 GPa, respectively, achieving a modification of the resin matrix that combines strength and toughness.

[0060]

[0061] Mechanical properties were tested on the composite material specimens in Example 2 and Comparative Example 2. Tensile properties were tested according to GB / T3354-2014, flexural properties were tested according to GB / T 3356-2014, compressive properties were tested according to ASTM D 6641-16, and interlaminar shear properties were tested according to JC / T 773-2010. The results are shown in Table 2.

[0062] In the composite material samples, the tensile strength of Example 2 increased from 761.0 MPa to 1007.1 MPa compared to Comparative Example 2, and the flexural strength increased from 817.3 MPa to 848.5 MPa. This improvement in core flexural toughness, combined with the simultaneous increase in tensile and compressive modulus and strength, proves that the filler has achieved toughening of the resin-based material by optimizing the molecular chain interaction of the resin matrix and strengthening the interlayer interface bonding of the composite material, fully demonstrating its excellent toughening modification effect. The interlayer shear strength remained basically stable (54.9 MPa vs 56.6 MPa), indicating that the toughening modification did not have a significant negative impact on the interfacial bonding performance, and the overall performance was optimized.

[0063]

[0064] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A prepreg resin system formulation suitable for T700 grade carbon fiber, characterized in that, The raw materials and proportions are as follows: 52 parts of liquid bisphenol A epoxy resin, 20 parts of solid bisphenol A epoxy resin, 20 parts of methylphenol type phenolic epoxy resin, 8 parts of dicyandiamide curing agent, and 5 parts of hyperbranched thermoplastic resin micro-nano filler.

2. The prepreg resin system formulation suitable for T700 grade carbon fiber according to claim 1, characterized in that, The 52 parts of liquid bisphenol A epoxy resin are composed of 30 parts of liquid bisphenol A epoxy resin one and 22 parts of liquid bisphenol A epoxy resin two.

3. The prepreg resin system formulation suitable for T700 grade carbon fiber according to claim 1, characterized in that, The hyperbranched thermoplastic resin micro / nano filler has active groups at its ends. These active groups can serve as crosslinking sites, promoting the reaction process between dicyandiamide and epoxy groups, accelerating the molecular chain crosslinking reaction, speeding up the formation of three-dimensional networks, and shortening the gelation time.

4. The prepreg resin system formulation suitable for T700 grade carbon fiber according to claim 1, characterized in that, The hyperbranched thermoplastic resin micro-nano filler has a dendritic structure in its hyperbranched molecules, and its micro-nano size can fill the gaps between resin molecules, reducing intermolecular friction. At the same time, the filler can disperse dicyandiamide agglomerates to avoid viscosity increase caused by particle agglomeration, ultimately achieving a reduction in system viscosity.

5. A method for preparing a prepreg resin system suitable for T700 grade carbon fiber, characterized in that, Includes the following steps: S1. First, add 20 parts of liquid bisphenol A type epoxy resin I and 22 parts of liquid bisphenol A type epoxy resin II to a planetary mixer; after preheating to 150°C, add 20 parts of solid bisphenol A type epoxy resin, 20 parts of methylphenol type phenolic epoxy resin and 5 parts of hyperbranched thermoplastic resin micro-nano filler; after the two solid resins are fully melted, mechanically stir for 30 minutes to prepare component A; S2. Add 8 parts of dicyandiamide curing agent to 10 parts of liquid bisphenol A type epoxy resin, stir mechanically for 20 minutes, and then grind with a three-roll mill until the powder particle size is less than 5μm to prepare component B. S3. Adjust the temperature of the prepared component A to 70℃, add component B, stir with a planetary mixer for 30 minutes and perform vacuum degassing to obtain the target resin system.

6. The method for preparing a prepreg resin system suitable for T700 grade carbon fiber according to claim 5, characterized in that, The resin system is cured according to the following procedure: (1) Preheat at 100℃ and keep warm for 2 hours; (2) Heat from 100℃ to 120℃ at a rate of 2℃ / min and hold for 1 hour; (3) Continue heating from 120℃ to 130℃ at a rate of 2℃ / min and hold for 1 hour; (4) Then heat from 130°C to 145°C at a rate of 2°C / min and hold for 1 hour; (5) Heat from 145°C to 155°C at a rate of 2°C / min and hold for 1 hour; (6) Heat from 155℃ to 170℃ at a rate of 2℃ / min and hold for 1 hour; (7) Finally, cool naturally in an oven from 170°C to room temperature.

7. The method for preparing a prepreg resin system suitable for T700 grade carbon fiber according to claim 5, characterized in that, The gel time of the obtained resin system at 120°C was 674 s.

8. The method for preparing a prepreg resin system suitable for T700 grade carbon fiber according to claim 5, characterized in that, The glass transition temperature of the resulting resin system was 144.6℃.

9. A method for preparing a prepreg resin system suitable for T700 grade carbon fiber according to claim 5, characterized in that, The resulting resin system had an elongation at break of 2.0%, a flexural strength of 80.9 MPa, and a flexural modulus of 2.8 GPa.

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