Surface modification of PBO fibers by direct fluorination and corresponding chemical reaction mechanism

Due to their excellent mechanical properties and heat resistance, Poly(p-phenylene benzobisoxazole) (PBO) fibers are applied as one of most potential reinforcement in resin matrix composite. However, the poor adhesion with resin limits their application in advanced composite materials. In this study, PBO fibers were first modified by direct fluorination to improve the interface adhesion between fibers and resin. X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to characterize the change of chemical structure and surface topography of fluorinated fibers. The results show that polar groups of C-F and -COOH are produced and surface roughness is enhanced, which increases the interface bonding strength of PBO fibers/epoxy by 48%. The fluorination reaction mechanism of PBO fibers is investigated on the basis of chemical structure change. It's suggested that oxazole ring reacts with fluorine gas preferentially over benzene ring, and addition reaction dominates when fluorine reacts with benzene ring.