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 (eta(ap)) of PVA aqueous solutions arising from the variables of T-op (up to 160 degrees C), C-PVA (high as 28%) and PD (largest at 3000). Applying Andrade's equation, the activation free energy of viscous flow (E-eta) is deduced from ln lap proportional to 1/T-op. It shows that all the values of E-eta 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 lap. Meanwhile, the contour plots of lap in C-PVA-T-op 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 C-PVA-T-op- PD on eta(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.

Automated summary

Understanding the viscous behavior of concentrated PVA solutions is important for PVA solution fabrication. However, previous studies have paid less attention to the fluidity of PVA solutions under severe conditions. In this study, we used a hydrothermal kettle with an online viscometer to track the changes in apparent viscosity of PVA solutions under high temperature, high concentration, and large polymerization degree. The activation free energy of viscous flow was deduced, and it was found that it remained constant regardless of changes in concentration and polymerization degree. Additionally, contour plots were used to illustrate the development trend of fluidity under different external conditions. Clarifying the effect of concentration, temperature, polymerization degree, and viscosity on PVA solution flow may guide the preparation of PVA films. The results of this study are helpful for PVA fabrications that require precise control of solution flowability.