Migration of substances from unplasticized polyvinylchloride into drinking water. Estimation of conservative diffusion coefficients

Abstract

Migration modelling has become an increasingly accepted method to test the compliance of polymer articles with the existing national or European standards for drinking water contact. In the first part of this work, the diffusion/migration of six organic substances from height additivated unplasticized polyvinylchloride (PVC-U) samples was investigated to derive the diffusion coefficients of these substances in the polymers. In a first series of experiments, five types of samples were immersed in deionized water and the migration of four organic substances in this liquid was determined experimentally at 23 and 60 °C. In a second series of experiments, the diffusion of two well-known phenolic antioxidants from three other types of PVC-U samples into low density polyethylene (LDPE) films was investigated at 60 and 75 °C. In all these diffusion/migration experiments, time dependent diffusions/migrations were observed. The diffusion coefficients derived from the results were in good agreement with diffusion coefficient data for PVC-U published in the literature in the last five decades.In the second part of this work, the diffusion coefficients mentioned above as well as other ones in PVC-U compounds, compiled from literature, were used to develop a statistical approach to estimate without any further experimentation, conservative diffusion coefficients for any organic substance, with a molecular mass ranging from 50 to 1000 g/mol, diffusing in PVC-U at 23 and 60 °C. In the framework of the German Environmental Agency requirements, these are the temperatures for testing the compliance of polymer articles intended to be used in cold and warm drinking water, respectively. Pipes, fittings and other articles made of PVC-U are widely used in the production, transportation and storage of drinking water. Thus, the new approach to estimate conservative diffusion coefficients for organic substances present in PVC-U articles is a key achievement for an efficient and reliable use of migration modelling with this material.