Multiwalled carbon nanotube (MWCNT)-doped polyamide 12 (PA12) films with various nanofiller loadings were prepared via a solution casting method to simultaneously improve the electrical conductivity and fracture toughness of carbon fiber/epoxy (CF/EP) composites. The films were interleaved between CF/EP prepreg layers and melted to bond with the matrix during the curing process. To improve the interfacial compatibility and adhesion between the conductive thermoplastic films (CTFs) and the epoxy matrix, the CTFs were perforated and then subjected to a low temperature oxygen plasma treatment before interleaving. Fourier transform infrared (FTIR) spectra results confirm that oxygen-containing functional groups were introduced on the surface of the CTFs, and experimental results demonstrate that the electrical conductivity of the laminates was significantly improved. There was a 2-fold increase in the transverse direction electrical conductivity of the laminate with 0.7 wt% MWCNT loading and a 21-fold increase in the through-thickness direction. Double cantilever beam (DCB) tests demonstrated that the Mode-I fracture toughness (G_IC) and resistance (G_IR) of the same laminates significantly increased by 59% and 113%, respectively. Enhancements of both interlaminar fracture toughness and electrical conductivity are mainly attributed to the strong interfacial adhesion achieved after plasma treatment and to the bridging effect of the carbon nanotubes.

Sulfonated poly(etheretherketone)/polybenzoxazine (SPEEK/PBa) crosslinked blends were prepared as a proton exchange membrane (PEM) for direct methanol fuel cell (DMFCs) application. SPEEK catalyzed the ring-opening polymerization of benzoxazine (Ba) monomers and then reacted with PBa to form a crosslinked membrane with greatly improved mechanical integrity. Extraction testing, Fourier-transform infrared, and X-ray photoelectron spectroscopy results indicate that the crosslinking reaction took place at 150 °C between the SPEEK and PBa. The crosslinked SPEEK/PBa structure gives a better dimensional stability, thermal stability, and mechanical integrity than the SPEEK membrane alone. The proton conductivity of the SPEEK/PBa-15% membrane is 4.25 × 10⁻³ S cm⁻¹ at 30 °C, and reaches 2.46 × 10⁻² S cm⁻¹ at 80 °C. The methanol diffusion coefficient of the SPEEK/PBa-15% is reduced by 93% when compared to a Nafion-117 membrane under the same testing conditions. The maximum selectivity at 80 °C is 4.45 × 10³ S s cm⁻³ for SPEEK/PBa-15%, which is nearly 1.3 times higher than that of a Nafion-117 membrane. The observed excellent properties of SPEEK/PBa membranes are attributed to the uniformly crosslinked structure of SPEEK/PBa and the rigid backbone of PBa.