Study On Kevlar Fibers/bismaleimide Resin Composites

Advanced polymeric composites (APCs) have been one kind of high-tech materials owing to their light weight, large specific strength and modulus, outstanding thermal resistance, and high designability. Kevlar fiber is an organic fiber with high performance, bismaleimide (BMI) resin is an excellent high-temperature thermosetting resin, so composites based on Kevlar fibers and BMI resin are expected to have more desirable performance. However, the surface of Kevlar fibers has low chemical activity, few polar functional groups, high crystallinity and smooth morphology, resulting in the poor interface bonding with the resin matrix, so it can't be used to prepare advanced polymer composites. The aim of this thesis is to overcome above mentioned problem associated with Kevlar fiber-reinforced composites.First, three different methods, such as phosphorous acid (PA) solutions, oxygen-plasma treatment, coupling agent combined with plasma treatment, were used to modify the surface of Kevlar fiber. The changes in the chemical structure, element composition, surface morphology and surface roughness of fiber surface were characterized to investigate the effects of different treatment methods on the surface of Kevlar fibers; meanwhile, the aging behavior after oxygen-plasma treatment of fiber surface was studied. Results show that oxygen plasma can introduce a lot of oxygen-containing functional groups onto the surface of fiber, and the surface of fiber is etched obviously. In addition, the aging behavior of the fiber surface after oxygen plasma treatment can be detected obviously in chemical composition after storing in air, which may be related to the rearrangement or reversal of polar functional groups on the surface of fiber.Second, the reinforced BMI composites based on original or treated Kevlar fiber were prepared through solution impregnating process and high temperature molding technique. The interfacial adhesion of composites were evaluated by interlaminar shear strength (ILSS), the water absorption and the composite fracture mechanism. Results show that compared with the composites based on original Kevlar fiber, the composites based on treated Kevlar fiber have increased ILSS and significantly decreased water absorption, in addition, the primary failure mode varies from the interface failure to the matrix or fiber failure.Finally, the dielectric properties of different composites and their relationship with the interface nature were studied. Results show that these composites exhibit different interfacial polarization in the applied electric field, and thus have significantly different dielectric properties. In addition, the dielectric properties are also affected by the temperature through the variety of the polarization and thermal movement of molecular chains.