On-line ascertain the processing fluidity of concentrated poly(vinyl alcohol) aqueous solutions

Abstract

Understanding the viscous fluid behavior of concentrated aqueous solution of poly (vinyl alcohol) (PVA), wherein macromolecular coils severely overlap and/or entangle each other, is of significance to the process design of PVA solution fabrication. However, exploiting the fluidity of PVA solutions under severe conditions of simultaneously high operational temperature (Top), high concentration (CPVA) and large polymerization degree (PD) has been less involved in the past studies irrespective of practical importance. Herein, we utilize a self-made hydrothermal kettle with a built-in online viscometer to systematically trace the changes of apparent viscosity (ηap) of PVA aqueous solutions arising from the variables of Top (up to 160 °C), CPVA (high as 28%) and PD (largest at 3000). Applying Andrade's equation, the activation free energy of viscous flow (Eη) is deduced from ln ηap ∝ 1/Top. It shows that all the values of Eη approximate to 37 (±3) kJ·mol−1 although both CPVA and PD increased progressively, indicating that these two factors will not affect the Top sensitivity of ηap. Meanwhile, the contour plots of ηap in CPVA-Top space are established for various PVAs with different PDs, to manifest the development trend of fluidity upon multiple external-fields coupling. Clarifying the synergic effect of CPVA-Top-PD on ηap may offer guidance for the preparation of PVA films by determing appropriate solution processing variables. The results of our study are of help to the PVA fabrications such as spinning fiber and casting film, in which precise control of flowability of concentrated solution is crucial.