Multicomponent drying of semicrystalline polymers

The focus of this research is to gain a better understanding of multicomponent drying behavior of semicrystalline polymers. A combination of experimental and theoretical approaches was used in this work. A mathematical model involving free-volume theory and solvent-induced crystallization kinetics as the backbone was developed to examine the complex relationship between polymers and solvents during drying. External conditions such as temperature, external mass transfer rate and film shrinkage were considered. A poly(vinyl alcohol)/water/methanol test system was chosen. The parametric studies of the model show that it can be adapted for wide range of initial and operating conditions, and the interactions of the two solvents with each and with the polymer were found to have a significant effect on residual solvent content. A gravimetric method was used to validate the model's predictions. The model was extended for glassy polymer systems. The effects of glassy skin formation on drying characteristics were investigated. The solvent diffusion behavior differed significantly from rubbery phase to glassy phase and affected the overall solvent removal rate. Experimental techniques were used to examine the predictions of the model and were found to be in good agreement. The crystallinity of poly(vinyl alcohol) during drying was examined using infrared spectroscopy and the development of crystals during drying was monitored and rate of crystallization determined. These insights into the drying process led to the development of multi-zone drying scheme aimed at lowering the final solvent content within the polymer. Drying temperature and partial pressure of each solvent within each zone were manipulated to optimize drying behavior and minimize residual solvent content. We found that the multi-zone was superior in removing more solvents from the film than the single zone method, as predicted by our models. Drying processes in polymers are important in determining final properties of the polymer. This research helps us understand the drying behavior of semicrystalline polymers and can be used to develop new strategies based on these insights, to improve drying processes.