Interface properties of composites from PBO fibers modified by polyurethane sizing agent

To improve the interfacial properties of poly-p-phenylenebenzobisoxazole(PBO) fiber/epoxy resin (EP)composites, the surfaces of acidified PBO fibers were coated with the sizing agents of waterborne polyurethane modified using γ-aminopropyltriethoxysilane(KH550). The surface chemical composition of PBO fibers was characterized by X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). Scanning electron microscopy (SEM)was employed to characterize the surface morphology of PBO fibers and the tear surface morphology of PBO/EP composites. Furthermore, the mechanical properties of single PBO fibers and PBO/EP composites were analyzed. The results show that the active groups on the surfaces of PBO fibers increase significantly with the values of O/C(atomic ratio)from 0.16 to 0.25 after being coated with the sizing agents, and the defects on the surfaces of PBO fibers can be repaired effectively. By adjusting the contents and structure of the sizing agents on the fibers, the interlaminar shear strength and tensile strength of PBO/EP unidirectional composites reach 41.3 MPa and 1.70 GPa, respectively. In contrast to the untreated ones, the interlaminar shear strength and tensile strength of modified composites increase by 44.9% and 15.6%, respectively.