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

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 (T op), high concentration (C PVA) 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 (η ap) of PVA aqueous solutions arising from the variables of T op (up to 160 °C), C PVA (high as 28%) and PD (largest at 3000). Applying Andrade's equation, the activation free energy of viscous flow (E η) is deduced from ln η ap ∝ 1/ T op. It shows that all the values of E η approximate to 37 (±3) kJ·mol−1 although both C PVA and PD increased progressively, indicating that these two factors will not affect the T op sensitivity of η ap. Meanwhile, the contour plots of η ap in C PVA - T op space are established for various PVAs with different PD s, to manifest the development trend of fluidity upon multiple external-fields coupling. Clarifying the synergic effect of C PVA - T op - PD on η ap 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. [Display omitted] • On-line viscometer is a powerful tool to monitor the viscosity change of polymer solution. • The dissolution temperature will significantly affect the transparency of solution. • T op , C PVA and PD independently affect the η ap of PVA solutions in this study. • The contour plots of η ap are constructed to provide indicative information. [ABSTRACT FROM AUTHOR]