Extensibility-Enriched Spinnability and Enhanced Sorption and Strength of Centrifugally Spun Polystyrene Fiber Mats

Abstract

We show that incorporating ultrahigh molecular weight (UHMw) polymer fractions into spinning dopes improves their spinnability and facilitates the centrifugal force spinning (CFS) of polystyrene (PS) fiber mats with enhanced mechanical and sorption properties. For matched polymer concentration, c, and solvent type, the UHMw additive at a low weight fraction (<0.1) only weakly influences shear viscosity. We attribute the enhanced spinnability and fiber properties to change in extensibility (stretched to equilibrium coil size ratio), quantified using the extensibilityaveraged molecular weight, M-L, that accounts for the role of stretched chain hydrodynamics and extensional rheology response. Although many studies argue that spinnable solutions lie above the entanglement concentration on the c-M-w plots, we show that the UHMw additives facilitate fiber formation below the computed entanglement concentration for extensibility-enriched (EE) polymer solutions. We highlight the role of extensibility and dispersity by locating the minimum spinnable concentration, c(spin), and the concentration, c(BC), for the transition from beaded to continuous fiber formation on a c-M-L plot. We show that extensibility-enriched solutions display c(spin) proportional to M-L(-b) with b = 1 + nu and c(BC) proportional to M-L(-b) with b = 3 nu - 1 due to significant strain hardening and large Trouton ratios that delay pinch-off. Additionally, we posit that in low-extensibility solutions, including low M-w or lower flexibility polymers, spinnability benefits from the steep viscosity increase on the solvent loss for volatile entangled (VE) polymer solutions, requiring c(spin) proportional to c(e) proportional to M-W(-b) with b = 1 + nu, explaining why entanglements promote fiber formation.