MODELING THE PROCESS OF DRYING OF PLASTICIZED PVC PREVIOUSLY IMMERSED IN NORMAL-HEXANE

When plasticized PVC is immersed in a liquid such as n-hexane, two mass transfers take place simultaneously: the liquid enters the PVC and the plasticizer leaves the polymer. Both these transfers are controlled by transient diffusion. The problem to be considered is the desorption of the liquid which has previously entered the PVC. It has been shown that temperatures as high as 120° are necessary for complete drying of the polymer under atmospheric pressure. A first attempt has been made to build models able to describe the process of drying. These models are based on numerical methods with finite differences and take into account the following facts: the profile of concentrations of the liquid throughout the PVC at the end of immersion in the liquid; the diffusion of the liquid within the PVC with a constant diffusivity obtained experimentally; the evaporation rate of the liquid on the surface of PVC, determined either from experiments done with PVC or from experiments made with pure-n-hexane.