Towards designing strong porous carbon fibers through gel spinning of polymer blends

Blends of polyacrylonitrile (PAN) with three different sacrificial polymers: poly (acrylic acid) (PAA), poly (methyl methacrylate) (PMMA), and poly (styrene-co-acrylonitrile) (SAN), were gel spun, oriented through the drawing process, stabilized and carbonized to obtain porous carbon fibers. Carbon fibers with an average pore diameter of 15 nm, 31 nm, 37 nm and 115 nm have been obtained from PAN-PAA (90/10), PAN-PMMA (90/10), PAN-SAN (90/10) and PAN-SAN (80/20) precursor fibers, respectively. The variation in pore size caused by the differences in compatibility between PAN and the sacrificial polymer was evaluated experimentally through blend rheology and theoretically using interaction parameter values. Despite their porosity, carbon fibers from PAN-PAA (90/10) and PAN-PMMA (90/10) exhibited tensile strength (∼1.6 GPa) comparable to that of the non-porous PAN based carbon fibers, processed under similar conditions. Specific tensile modulus of the porous carbon fibers was 15–40% higher than that for the PAN based carbon fibers, and the electrical conductivity was as high as 74 kS/m due to high graphitic ordering. Porous channels presented in this study were obtained by combining phase separation in the nano/micro scale range, with pore orientation and elongation achieved through gel spinning.