A new method for determining solute diffusivity in polymers from data obtained by non-isothermal thermogravimetry

A numerical method for determining solute diffusivity in polymers over wide temperature ranges was developed based on non-isothermal thermogravimetry (TG). The method combines the Fickian equations with a heat transfer equati on in order to take into account temperature gradients within the polymer s ample during a heating scan. The requirement of thermal equilibrium in the specimen during the heating scan need not be fulfilled, and this permits th e study of desorption of solute from thick specimens at high heating rates. The numerical procedure is capable of considering concentration-dependent solute diffusivity and temperature-dependent thermal diffusivity. The metho d was tested on the desorption of n-hexane in polyethylene between 25 and 1 20 degrees C. The results obtained agreed with experimental data obtained a t heating rates from 10 to 40 degrees C/min up to 90 degrees C and yielded an activation energy of 46 kJ/mol, which is in agreement with earlier repor ted experimental data. (C) 2000 Elsevier Science B.V. All rights reserved.