DRYING AT ROOM-TEMPERATURE OF PLASTICIZED PVC PREVIOUSLY IMMERSED IN LIQUIDS - MODELING AND EXPERIMENTS

For preparation of plasticized PVC sheets with low matter transfer when contacted with liquids, the process of drying of plasticized PVC previously immersed in the liquid is of interest. The complex process of drying for plasticized PVC has been elucidated with the help of experiments and a mathematical model. The model, based on a numerical method with finite differences, takes into account the diffusion of the liquid with a diffusivity depending on the concentrations of liquid and plasticizer, as well as the evaporation rate on the surface. At the end of the immersion of PVC in the liquid, two profiles of concentration are developed through the polymer for the liquid and for the plasticizer, with a high concentration of liquid and a low concentration of plasticizer on the PVC surface. Because of the evaporation of the liquid, another lower value of concentration is obtained for the liquid on the PVC surface. For these reasons, the liquid which has entered the PVC is trapped in the polymer; it can be evaporated only at high temperature. © 1990.