Migration of 4-substituted 2-hydroxy benzophenones in low density polyethylene: Part I—Diffusion characteristics

Abstract

Intrinsic diffusion coefficients and equilibrium solubilities of a series of 4-substituted 2-hydroxy benzophenone (HBP) compounds were determined in low density polyethylene over a wide temperature range (5–100°C) using a polymer stack technique (diffusion coefficients of stabilisers have been determined in the literature but in general only over a limited temperature range). The experimental values are in good agreement with the literature values for analogous compounds when compared at the same temperature of measurements but these are very different if compared with extrapolated values from the literature. The dependence of diffusion coefficient on temperature followed an Arrhenious-type relationship only over a narrow temperature range and extrapolation from high temperatures to ambient is seen to be invalid. The effect of varying the chemical structure of the substituents on the 4-position of the HBP stabilisers on diffusion characteristics has also been investigated. It is shown that diffusion coefficients in a homologous series depends primarily on the chemical structure and shape of the diffusant rather than on molar mass.