Moisturized Polyacrylonitrile Copolymer for Stronger Precursor Fibers

Polyacrylonitrile-methyl acrylate (PAN-MA) copolymers have been used as precursor materials for carbon fibers due to their excellent properties for developing carbonaceous microstructures during thermal treatment. High electron density in the acrylate part of the MA polymer is mainly responsible for the hygroscopicity of the copolymer. Adsorbed water can affect microstructures and material properties of precursor fibers. This study investigated the role of adsorbed water in precursor fibers prepared by conventional and electrochemical wet-spinning processes. Although the molecular structures and rheological properties of the spinning dope were hardly changed, voids, which are one of the most critical fracture-inducing defects, were minimized by improved electrostatic interactions due to absorbed water. Consequently, the strength of the precursor fibers was the greatest at an adsorbed water content of 0.5 wt % in conventionally wet-spun fibers and 1.0 wt % in the electrochemically wet-spun fibers. The adsorbed water improved the electron distribution of the raw and demethylated MA and improved the intermolecular interactions between the electron-poor hydrocarbon side and the electron-rich electronegative side. Thus, it is clear that the optimum amount of adsorbed water plays a beneficial role to improve limitedly the mechanical performance of precursor fibers.