Effect of processing conditions on the properties of high molecular weight conductive polyaniline fiber

Abstract

Polyaniline-emeraldine base (EB) fiber with excellent mechanical and electrical properties have been spun from highly concentrated (20% w/w), EB/N-methyl-2-pyrrolidinone (NMP)/2-methylaziridine (2 MA) solution. These solutions had gelation times, which varied from hours to days depending on the molar ratio of 2 MA to EB tetramer repeating unit in the N-methyl-2-pyrrolidinone (NMP) solvent. To better compare the mechanical and electrical properties, dense films were also prepared by thermal evaporation of less concentrated solution (1% w/w). Both fibers and films were amenable to thermal stretching with maximum draw ratios of 4:1 and these stretched samples exhibited the greatest tensile strength overall. Wide-angle X-ray diffraction (WAXD) of as-spun and 4-times stretched fiber showed a completely amorphous structure. Fiber subjected to heat treatment at 250 °C under N2 flux for 2 h displayed further improvements in mechanical properties because of crosslinking between the polymer chains. Fibers and films were later doped by immersion in a variety of aqueous acid solutions. Room temperature DC conductivities for the doped samples ranged from 6×10-4 to 45 S/cm depending on the specific choice of acid. Scanning electron microscopy of fiber samples shows the presence of macrovoid formation during fiber spinning. Continued refinement of the processing parameters and fiber post-treatment, to enhance chain alignment and increase fiber density, will likely lead to additional improvements in the fiber mechanical and electrical properties. Characterization of emeraldine base (EB) powder, solution, films, and fibers by UV-Vis, DSC, TGA, and WAXD were also performed.