Modelling migration of substances from polymers into drinking water. Part 1 - Diffusion coefficient estimations

Abstract

In a first part of this work the permeation through and diffusion/migration from high density polyethylene, polybutylene, polypropylene and cross linked polyethylene films was investigated experimentally with three different methods to determine diffusion coefficients in these polyolefins for a series of additives, their degradation products and other organic substances in the 20–60 °C temperature range. The experimental methods used were dynamic permeation through additive free the polymer films, kinetic desorption from additivated films into water and kinetic migration from additivated into additive free polymer films. It was found that in general the temperature dependence of the obtained diffusion coefficients was well represented by the Arrhenius law. Some of these results also suggested that the contact of the polyolefins with water had an influence on the magnitude of the diffusion coefficients and on their apparent activation energy of diffusion.In the second part of this work the obtained pools of diffusion coefficients for each of the investigated polymers were used to develop an approach to estimate theoretically and without any further experimentation “conservative” diffusion coefficients for any organic substance, with molecular mass ranging from 50 to 1250 g/mol, diffusing in these polymers at temperatures between 15 and 85 °C. The possibility to estimate such conservative diffusion coefficients is very important when it comes to use efficiently migration modelling as an alternative method to test the compliance of polymeric articles with the existing national and/or European standards for drinking water. The use of polymer specific diffusion coefficients in migration modelling is required in the framework of the “Migration modelling guideline” recommendation of the German Environment Agency.