MODEL STUDY FOR RELEASE OF PLASTICIZERS FROM POLYMER FILMS THROUGH VAPOR PHASE

A model has been applied to release of plasticizers from polymer films through vapor phase, for which the overall rate of release may be generally determined by evaporation of the plasticizer from the surface of the film, and/or by migration to the surface at below saturation in the polymer. The experimental system employed made use of n-butyl formate, diethylphthalate, di-n-butylphathalate, and N,n-butylbenzenesulfonamide in polycaprolactam films. Experimental measurements were made (at 298-333 K) by investigating in a suitable cell the permeation of plasticizers both at concentrations below and above the saturation limit. Rate of evaporation of plasticizers from the membrane surface above the saturation limit, measured in this cell, were found to coincide satisfactorily with those calculated by application of the mass transfer theory to evaporation from a stationary liquid into a stirred gas, at a known velocity of gas flowing past the surface. In the light of the theoretical model a correlation was found between activation energies of H and evaporation enthalpies of the model molecules.