Crystallization of poly(vinyl alcohol) during solvent removal: Infrared characterization and mathematical modeling

Abstract

Crystallization of semicrystalline polymer films during drying has a significant effect on the rate of solvent removal. Understanding and controlling the crystallization kinetics is important in controlling residual solvent levels and drying kinetics. The degree of crystallinity of the poly(vinyl alcohol) films during multicomponent drying was investigated using Fourier transform infrared spectroscopy (FTIR). The 1141 cm À1 band is sensitive to the degree of crystallinity of the polymer and the growth of intensity of this band was monitored as drying progressed. The results from the FTIR studies were comparable to the results obtained from differential scanning calorimetry. Studies were conducted to test the effect of initial solvent composition (water-methanol mixture), drying temperature, and polymer molecular weight on the rate of crystallization and the final crystallinity of the films. An increase in initial methanol composition increased the crystallization rate but did not affect the final degree of crystallinity. An increase in drying temperature and decrease in polymer molecular weight increased the rate of crystallization as well as the final degree of crystallinity. Based on the experimental data, rate constants for crystallization kinetics were extracted from our previously developed model based on free volume theory. The experimental data and the simulation results showed good agreement. The ability of the free volume theory to illustrate the crystallization behavior validated the model and improved its capability.

Influence of kaolin addition on the dynamics of oxygen mass transport in polyvinyl alcohol dispersion coatings

“…The location of the crystalline regions could not be determined in this study. However, since the crystallinity decreases as the kaolin content decreases, the starting point for crystalline ordering of the polymer might not be at the surfaces of the clay particles, but rather related to the consolidation and drying process (Wong et al 2007).…”

Dehydration of water‐plasticized poly(vinyl alcohol) systems: particular behavior of isothermal mass transfer

“…Dehydration of PVA/water (P/W) systems has attracted much attention in recent years, and many studies have aimed to understand the dehydration mechanism of this semicrystalline polymer by considering the crystallization kinetics during dehydration, from where mathematical models have been developed to describe the dehydration process 13–17. The dehydration of aqueous PVA is accompanied by an increase in its crystallinity, which in turn affects the dehydration rate, showing that there are apparent relations between crystallization and dehydration of aqueous PVA 13.…”

“…The dehydration of aqueous PVA is accompanied by an increase in its crystallinity, which in turn affects the dehydration rate, showing that there are apparent relations between crystallization and dehydration of aqueous PVA 13. An increase in dehydration temperature and decrease in molecular weight increase the rate of crystallization as well as the final crystallinity 14. From the theory of crystallization kinetics developed by Lauritzen and Hoffmann,18 a chain folding rate was introduced, and the model considered the crystallization kinetics and the changes of crystallinity during solvent removal 13, 15.…”

Experimental Studies and Modeling of the Drying Kinetics of Multicomponent Polymer Films

“…These studies show that increasing the drying temperature and decreasing the molecular weight of the polymer can increase the rate of crystallization and the final crystallinity of the polymer. Lauritzen et al have introduced a crystallization kinetics model (18) explaining the chain-folding rate and the crystallinity of the polymer during solvent movement (13)(14)(15). The crystallization rate was inversely related to the molecular weight, which is explained by the inability of long polymer chains to fold themselves into crystals.…”

“…The drying mechanisms of semicrystalline polymers like PVA have been mathematically modeled in a few studies (13)(14)(15)(16)(17). These studies show that increasing the drying temperature and decreasing the molecular weight of the polymer can increase the rate of crystallization and the final crystallinity of the polymer.…”