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 gamma -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.