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Understanding the effect of skin formation on the removal of solvents from semicrystalline polymers
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The effect of glassy skin formation on the drying of semicrystalline polymers was investigated with a comprehensive mathematical model developed for multicomponent systems. Polymers with high glass-transition temperatures can become rubbery at room temperature under the influence of solvents. As the solvents are removed from the polymer, a glassy skin can form and continue to develop. The model takes into account the effects of diffusion-induced polymer crystallization as well as glassy-rubbery transitions on the overall solvent content and polymer crystallinity. A Vrentas-Duda free-volume-based diffusion scheme and crystallization kinetics were used in our model. The polymer-solvent system chosen was a poly(vinyl alcohol) (PVA)-water-methanol system. The drying kinetics of PVA films were obtained by gravimetric methods with swollen films with known water/methanol concentrations. The overall drying behaviors of the polymer system determined by our model and experimental methods were compared and found to match well.