Enhanced both in-plane and through-thickness thermal conductivity of carbon fiber/epoxy composites by fabricating high thermal conductive coaxial PAN/PBO carbon fibers

PAN-based carbon fibers (PAN-CFs) have been widely used as structural reinforcements of various advanced composites due to their excellent mechanical properties. However, PAN-CFs have no obvious superiority in terms of the heat dissipation ability compared to mesophase pitch-based CFs and vapor grown CFs. In the present work, Poly-p-phenylene benzobisoxazole (PBO) macromolecules, which could contribute to the development of highly ordered graphite from conjugated aromatic backbone, were introduced onto PAN-CF surfaces to prepare coaxial PAN/PBO carbon fibers (PAN/PBO-CFs). Results showed that functional graphene oxide (GO) could result in uniform grafting of PBO macromolecules onto fiber surfaces owing to 7C-7C conjugations between GO and benzoxazole backbone. The coaxial PAN/PBO-CFs were subsequently obtained through high-temperature graphitization and the rigid state could be also retained. Results by XRD and TEM demonstrated that PAN/PBO-CFs had smaller interlayer spacing and higher crystallinity compared to PAN-CF, and PBO derived graphite crystals could also be perpendicular to fiber surfaces. As for the thermal conductivity of composites, the in-plane thermal conductivity of PAN/PBO-CF reinforced epoxy composite was as high as 82.86 W/(m.K) which was almost 1.5 times of PAN-CF/epoxy composites, and the through-thickness thermal conductivity with the value of 2.54 W/ (m.K) also increased by 65%. The introduction of PBO macromolecules could contribute new conductive paths and alleviate the problem of interfacial temperature gradients between CF and resin matrix. As a result, thermal conductivity properties of coaxial PAN/PBO-CF reinforced composites significantly improved.