Publish Time: 2025-01-07 Origin: 中国复合材料工业协会
The main requirements for reinforcing materials in prepregs are:
Good resin wetting properties.
Excellent drapability to meet the forming requirements of complex-shaped products.
Ability to meet the primary performance requirements of the product.
Reinforcing fibers include glass fibers, carbon fibers, and aramid fibers. Common reinforcement forms include unidirectional fibers, plain weave fabrics, twill weave fabrics, and multiaxial fabrics.
The primary functions of the matrix resin are:
To orient, position, and bond the fibers into a unified structure.
To transmit stress during the product's load-bearing process.
The matrix resin imparts excellent mechanical properties, thermal performance, chemical corrosion resistance, and ease of processing to the composite material. The reinforcing fibers primarily determine the mechanical performance of the composite. Most thermoplastic resins can serve as the matrix for continuous fiber-reinforced thermoplastic polymer composites, ranging from general-purpose resins like polypropylene (PP) and polyethylene (PE) to specialized engineering resins like polyphenylene sulfide (PPS) and polyether ether ketone (PEEK). A comparison of the basic properties of different resin matrices is shown in Table 2.
Typically, a single resin struggles to meet process performance requirements. Multiple resin combinations are often used to enhance processability, such as blending different epoxy resins to optimize viscosity under normal or low temperatures. For instance, phenolic epoxy resins can enhance reactivity and heat resistance, while bisphenol A epoxy resins can adjust viscosity.
Research shows that resin systems suitable for prepregs often combine liquid bisphenol A epoxy resin, solid bisphenol A epoxy resin, and phenolic epoxy resin. The choice of matrix materials should balance the performance requirements of the composite material and processing demands. For example, medium-temperature hot-melt epoxy resin prepregs are required not to feel sticky in summer or brittle in winter. This necessitates adjusting the ratio of components to ensure the resin system softens at 36–37°C in summer and 30–32°C in winter, while limiting the curing temperature of the epoxy resin. The optimal curing temperature is generally 120–130°C, with a curing time not exceeding 90 minutes.
The curing system includes curing agents, accelerators, catalysts, and diluents. To ensure prepregs have a certain shelf life at room temperature, latent curing agents are typically used. These agents do not react with the resin at normal temperature and pressure but promote resin cross-linking and curing under specific temperature and pressure conditions.
Latent curing agents are usually in a dispersed solid state at room temperature, insoluble in epoxy resin, but become miscible with it when heated near their melting point, initiating rapid curing. Accelerators promote the dissolution of curing agents in the resin matrix and increase the curing reaction rate. Toughening agents reduce the brittleness of the thermoset resin matrix, enhancing its impact resistance. Diluents lower the resin viscosity to improve processability. Catalysts accelerate the curing reaction during molding but remain in a "latent" state at normal temperature and pressure, which is advantageous for prepreg manufacturing.