Fickian diffusion of erucamide (13-cis-docosenamide) in poly(laurolactam) (Nylon 12) (PA-12)

Abstract

Diffusion of erucamide (13-cis-docosenamide) [H3C— (—CH2—)11—HC=CH—(—CH2—)7—CO— NH2] (eru) in poly(laurolactam) (Nylon 12) (PA-12) has been studied in a temperature range from 343 to 353 K. In previous investigations on the diffusion of eru in isotactic poly(propylene) (i-PP) it was found that the diffusion took place by a non-Fickian mechanism. This feature was explained by taking into account the microstructure of i-PP films and the incompatibility of eru and i-PP. The same experimental method to determine the concentration profiles was previously employed in this system. The experimental profiles have been compared with theoretical curves based on solutions of Fick's diffusion equation for the best fitting, with the appropriate boundary conditions. The measured concentration profiles show a good agreement with the Fickian law. Values of the diffusion coefficient D in the range from 10–10 to 10–11 cm2·s–1 have been obtained. The activation energy for diffusion (Ed) has been calculated from the D values in the temperature range investigated assuming an Arrhenius-type behaviour. The activation energy has been calculated as Ed = 156 kJ·mol–1. The values of diffusion coefficients and activation energy are in the range found for some other additives. By using Fujita's equation a good correlation between diffusion coefficient and free volume fraction estimated by means of the Williams-Landel-Ferry equation have been found.