Thermodynamic study of non-solvent/dimethyl sulfoxide/polyacrylonitrile ternary systems: effects of the non-solvent species

In order to investigate the effects of the non-solvent species on the formation mechanism of polyacrylonitrile (PAN) fiber in wet spinning, theoretical ternary phase diagrams of water/DMSO/PAN and ethanol/DMSO/PAN systems were constructed based on the extended Flory–Huggins theory. The cloud-points of dilute PAN solutions of the two systems were determined by titration method and those of concentrated PAN solutions from Boom’s linearized cloud-point correlation. Binary interaction parameters were calculated and optimized to construct the theoretical phase diagram. The obtained diagrams were used to investigate the effects of the non-solvent species on the formation of PAN fibers. If the non-solvent water is replaced with ethanol, the meta-stable two-phase region in the ternary phase diagram increases. This favors the de-mixing of the filament via nucleation and growth mechanism during the coagulation process, resulting in homogenous dense PAN fibers with low porosity.