Boosting the interlaminar toughening capacity of PBO microfiber for carbon fiber laminates through the interface regulation of interleaving layer

Abstract

Poor interfacial properties limit the toughening effect of the high-performance poly(p-phenylene benzobisoxazole) (PBO) microfiber for the carbon fiber laminate. Herein, a rigid-flexible transition interface was developed on the PBO fiber surface to enhance its interfacial adhesion and improve the interlaminar toughening effect for carbon fiber laminates. The rigid-flexible structure also provides a smooth modulus gradient for the interfacial load transfer to effectively utilize the excellent mechanical properties of the PBO fiber and dissipate more fracture energy. This allows the Mode I failure mode to change from stick-slip failure to stable crack propagation by triggering the toughening mechanism of fiber debonding and bridging, crack deflection, and sub-crack evolution. The $G_{I-C}^{prop}$ value increases from 238.3 to 496.5 J m⁻². In addition, the Mode II interlaminar fracture changes from interfacial failure to cohesive failure, dissipating additional energy through fracture behavior such as buffer layer damage, crack deflection, and sub-crack development. Accordingly, the $G_{II-C}$ value increases from 1509.7 to 3336.2 J m⁻². The interfacial regulation strategy developed for the PBO fiber opens a new avenue for the interlaminar toughening of the carbon fiber laminate using smooth and inert organic fibers.