Lignin addition to polyacrylonitrile copolymer solution and its effect on the properties of carbon fiber precursor

Polyacrylonitrile copolymer (PAN) fiber and PAN/lignin (PL) fiber were wet spun from the PAN copolymer solution and PAN/Lignin blend solution using dimethyl sulphoxide (DMSO) solvent. A blend of 90% by weight (wt %) PAN terpolymer and 10wt% lignin dissolved in DMSO was used in wet spinning of PL fiber. Viscoelastic properties of PAN solution and PAN/lignin solution in DMSO were determined by rheometer. The properties of precursor fiber with and without lignin were evaluated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and mechanical testing. The diffusion of lignin out of coagulated filament was observed during wet spinning of PL solution and was quantitatively estimated by UV–Vis studies. DSC results showed that blending lignin with PAN copolymers can improve the thermal oxidation performance of the precursor fiber and accelerate the thermal stabilization process. A schematic illustration has been deduced for the decrease in tensile strength of PL fiber compared to that of PAN fiber.