The preparation of resin-based high-performance composite materials as a reinforcement is one of the most important application fields of aramid fiber. At this stage, aramid-reinforced resin-based composite materials have a wide range of applications, and play an important role in aerospace, military anti-ballistic, sports equipment, automobiles and construction. In the 1960s, the United States first used the winding molding method to prepare aramid-reinforced solid rocket motor shells, which opened the application of aramid fibers in the aerospace field. At this stage, aramid composite materials also have many applications in aircraft weight reduction, noise reduction, safety, etc. For example, the proportion of aramid composite materials in the outer skin of the S-76 commercial helicopter developed by Sikorsky Corporation The ratio has reached 50%. In construction, aramids are increasingly replacing asbestos to reinforce cement, providing lighter, higher-strength structural parts and preventing cement products from cracking. Aramid composite materials can also be used to manufacture yachts, golf clubs, tennis rackets, skis, snowmobiles, fishing rods, bows, javelins and other civilian products. Therefore, aramid composite materials have broader application prospects.

However, as a reinforcement of composite materials, aramid fiber has not fully exerted its excellent performance. This is because the overall performance of composite materials not only depends on the properties of resin matrix and fibers, but also is closely related to the interface properties of composite materials. During the molding process of composite materials, various physical and chemical interactions and interpenetration occur between fibers and resins. These interaction areas are generally between fibers and resins, called interfaces, and their thickness can reach tens of Nano, as shown in Figure 3-27. As an important part of the composite material, the interface is very important to the overall performance of the composite material. For example, when the aramid fiber reinforced epoxy resin composite material is stretched by external force, the interface layer acts as a stress transfer medium to transfer the stress from the resin The effect transmitted to the fiber reinforcement. Good interfacial adhesion can effectively disperse the load borne by the composite material, so that the mechanical properties of the fiber can be fully exerted, and the overall performance of the composite material can be improved. The interfacial bonding of composite materials is realized by various interactions between fibers and resins, which mainly include the following forms of action.

Figure 3-27 Macroscopic morphology of fiber/resin interface layer

(1) Mechanical lock between resin and fiber. Since the surface of the fiber may have uneven morphology, the resin matrix will infiltrate and fill it, so after curing, the resin and the fiber will be meshed and fixed; the rougher the fiber surface, the more meshing points, which is more conducive to the reinforcement of the composite material. interface bonding.

(2) Van der Waals force between resin and fiber. This interaction comes from various electrostatic mutual attraction and hydrogen bond interactions between the resin matrix and fiber macromolecular chains, and these interactions affect the wettability of the resin to the fiber surface and the bondability of the interface.

(3) Diffusion entanglement of resin and fiber macromolecular chains. As polymers, fibers and resins have relatively high molecular weights. On the surface of fibers and resins, there may be entanglements between macromolecular side chains or end groups.

(4) Chemical bonding between resin and fiber. The fiber surface groups can chemically react with the resin surface groups to form chemical bonds between the interfaces. Due to the high energy of chemical bonds, a large amount of energy is required to break them, so the formation of chemical bonds can greatly improve the interfacial bonding performance of composite materials. Therefore, in order to achieve good interfacial bonding of composite materials and prepare high-performance aramid composite materials, it is necessary to modify the surface of aramid fibers.