Research On The Properties Of Carbon Fiber/Benzoxazine Composites

Benzoxazine is one kind of newly developed phenolic thermosetting resin. Besides with good mechanical integrity, thermal stability, and low water absorption, benzoxazine overcomes many deficiencies of traditional phenolic resins such as releasing condensation by-products and using strong catalysts. The curing characteristic, static and dynamic properties of benzoxazine composites reinforced by carbon fibers with different surface characteristics were measured, at the same time the interfacial morphologies of the composites were studied using SEM. The aim of this paper is to provide theoretic and experimental bases for the extensive applicant of benzoxazine resin in the field of high performance composites. Curing process of CF/benzoxazine composites with different surface characteristic carbon fibers as reinforcement were analyzed by nonisothermal differential scanning calimetry at different scanning rates. The apparent activation energies and reaction order of the resin and the composites were obtained by Kissinger equation. It was showed that thecure reaction of benzoxazine could be catalyzed by weakly acidic functional groups (-OH, -COOH) on the surface of carbon fibers. However, carbon fibers slowed down the cure reaction of benzoxazine. it also could be concluded that epoxy sizing materials had some effects on the reactive rate, the apparent activation energies as well as reaction order of curing reaction of benzoxazine.At the same time, the short-beam shear and flexural properties of the composites were measured. The effects of the sizing materials of the carbon fibers on the flexural fracture morphologies and dynamic mechanical properties of the composites were studied using SEM and DMTA. The results showed that the interlaminar shear strength (ILSS) and the flexural properties of the composites reinforced by carbon fibers sized by epoxy resin were maximum, reached 98Mpa and 2310Mpa respectively, and those of the other composites were not so good, which related with the interfacial adhesion of composites. It could be showed that the loss peak of the composites with the carbon fibers surface-coated with epoxy sizing materials was lowest in the dynamic mechanical properties. These facts also were proved by SEM.The properties of the benzoxazine composites with different kinds of carbon fibers (T300, T800, M40) as reinforcement were studied. The results showed that interfacial adhesion of the M40 carbon fibers/benzoxazine composites was weakest, and its mechanical properties...