Modeling of polymer drying and devolatilization processes

This work presents models for drying solvent coated polymer films and for supercritical devolatilization of polymers. The drying model development has progressed from the consideration of a binary polymer solvent system to a multicomponent solvent-solvent polymer systems. Furthermore, the model has been extended to the case of two layers of two different polymers with a common solvent. The results of the binary and multicomponent drying model were compared to drying data and excellent agreements were found between the experimental data and the predictions. The predictions from the models provide detailed information about the relative importance of internal and external resistances to drying, and effect of operating conditions and therefore they establish frameworks for the design and optimization of drying conditions. The model developed for supercritical devolatilization of polymers incorporates swelling of the polymer film and convection induced by diffusion that arises because of nonideal volumetric behavior. In conventional supercritical extraction, high solubility of impurities in the supercritical fluid can enhance the thermodynamic driving force for extraction. In addition, high solubility of supercritical fluid in the polymer can increase the mobility of the volatile impurity. This study suggests that in addition to these two effects, there are two other phenomena that can be important in this process. The nonideal volumetric behavior can cause diffusion induced convection which can influence the transport of impurities out of the polymer. Also, coupling between mass transfer and relaxation can be important. The most significant conclusion resulting from this analysis is that the mass transferred during the very short depressurization step may be the dominant mechanism for removal of impurities in supercritical devolatilization of polymers.