A coupling agent is a molecule containing at least two functional groups with different properties. One functional group is an inorganic-philic group, generally a short alkoxy chain segment. One is an organophilic group, usually including ester acyl group, alkyl group, etc., which can react with groups existing on the surface of organic matter. At the interface, the coupling agent can chemically react with the active groups on the surface of reinforcing materials such as fiberglass , and can also undergo molecular chain interdiffusion with the polymer matrix to form physical entanglements, thereby serving as a "bond" between the fiber surface and the resin surface. The role of "bridge" can improve the surface wetting performance of inorganic substances and organic substrates, and the strong interface bonding performance can also reduce the water absorption of the material, thereby improving the comprehensive performance of the material. Currently commonly used coupling agents mainly include silane coupling agents, aluminate coupling agents and titanate coupling agents. Silane coupling agent is one of the most widely used, often expressed by the general formula YSiX3, where X is a hydrolyzable, inorganic group, mainly including methoxy, halogen and acetoxy, etc., hydrolyzed to form Si-OH;

Y is a non-hydrolyzing, organophilic group, such as vinyl, hydrocarbon and epoxy groups. Previous studies focused on the use of silane coupling agents to treat glass fiber reinforced polyvinyl chloride composites. Through the coupling agent treatment process, the difficulties brought about by the poor fluidity and heat resistance of polyvinyl chloride resins were overcome, and  fiberglass  reinforced polyvinyl chloride composites were made Vinyl chloride composite materials entered the market. Lee et al. used γ-[(-methacryloyloxy)propyltrimethyloxysilane] (MPS),

γ-Aminoxypropyltriethoxysilane (APS) and other silane coupling agents can be used for  fiberglass  modification by direct addition.

The fiberglass and unsaturated polyester (UPR) composite material was prepared, and the study showed that the interfacial bonding force between glass fiber and unsaturated polyester was significantly improved after the coupling agent treatment, so that the layer of fiberglass reinforced UPR resin composite material Intercut

The strength, flexural strength, and flexural modulus are higher than those of the composite without coupling agent treatment. Crespy et al treated the glass fiber surface with a mixture of n-propylene-trimethoxy and vinyl-triethoxy siloxanes containing double bonds and compatibilizing additives, and the impact and tensile properties of the prepared composite materials and bending strength are greatly improved. An aluminate coupling agent developed by Fujian Normal University has a structure similar to that of a titanate coupling agent, which can significantly improve the impact strength and heat distortion temperature of products, and the modification effect is not lower than that of titanate coupling agents. It is found that the surface treatment of glass fibers with aluminate coupling agent is better than that of silane coupling agent, and the flexural modulus, flexural and tensile strength of the composite material are higher than those of silane coupling agent. Effect. Macromolecular coupling agents are a new direction in the research and development of coupling agents in recent years. Compared with ordinary coupling agents, their molecular weight is relatively large, and they are usually polymer grafts. The use of macromolecular coupling agents can improve the compatibility and interfacial cohesion between the powder reinforcement and the matrix, so that the stress can be better transmitted to the filler particles. Studies have shown that in the preparation of many polymer-based reinforced composites , the use of macromolecular coupling agents is better than that of small molecular coupling agents. Shen Tao et al. used atom transfer radical polymerization (ATRP) to synthesize a two-block copolymer with controllable molecular chain structure and hydroxyl end-capping, which can be used as a macromolecular coupling agent to treat glass fibers, which can significantly reduce the hydrophilicity of the glass fiber surface. The interfacial shear strength of the glass fiber/polystyrene composite is about 117 times that of the untreated composite.