Fluorinated graphene oxide with tunable vertical graft density for the simultaneous enhancement of compressive and tensile properties in aramid fibers

Inferior compressive strength of organic fibers restricts their widespread application. Simultaneously improving the axial/transverse properties and tensile properties of organic fibers remains a significant challenge. To overcome this challenge, a modified fluorinated graphene oxide (GOP) with tunable vertical graft density was designed via C-F bond nucleophilic reactions to reinforce poly(p-phenylene-benzimidazole-terephthalamide) (PBIA) fibers. Direct fluorination technology successfully preserves the oxygen-containing groups when introducing C-F bonds into graphene oxide (GO), thus providing hydrogen bonding sites. Together with the π-π interactions generated by the grafted PBIA chains, this combination contributes to the superior dispersion stability of GOP compared to graphene and GO. Composite fibers co-mixed with GOP and PBIA prepared by solution spinning exhibited enhanced crystallinity. The vertically grafted chains formed a stable topological network, improving chain interactions within the composite fibers. Hence, by adjusting the PBIA chain grafting density, the composite fibers exhibited an 87.4% increase in axial compressive strength and a 37.2% increase in transverse compressive strength, along with improvements in tensile strength, modulus and interfacial shear strength. Moreover, molecular and finite element simulations confirmed that vertically grafted PBIA chains induce GOP layer deflection, optimizing axial stress transmission and distribution within the fiber, ultimately leading to a more significant improvement in axial compressive performance compared to transverse compressive performance.