The role of the solvent nature in stretching polymer solutions (polyacrylonitrile spinning using different solvents)

We investigated how different solvents' affinity with polyacrylonitrile affects the formation of a jet that leads to stable fiber spinning. The study focused on two concentrations, one near and one above the crossover point where the topological entanglements are formed in the semi-dilute solutions. The role of the physical parameters of the solutions, including solvent-polymer affinity, viscosity, surface tension, and relaxation times, was analyzed. The experiment involved the uniaxial deformation of a solution drop under its weight, observed using a high-speed microscopic camera. The stability of the jet was associated with the relaxation time and solvent-polymer affinity. The continuous fiber spinning is mainly determined by the high enough polymer concentration in the solution, and the solvent nature, or by how the solution state is close to the theta conditions. Bicomponent mixed solvents offer two viable routes to achieve this – evaporating a more volatile component from the mixture to increase the polymer concentration, or modifying the solvent with a combination of solvents of different solvent quality. Both approaches have been experimentally validated, enabling the production of continuous stable fibers in the gel stretching regime. In this case, the jet stretching occurs under conditions Wi > 1. Thereby, the transition to the gel state promotes the necessary conditions for macromolecule orientation during fiber spinning.