The Effect of Surface Conditions on Diffusion and Permeability of Acetone through uPVC

Understanding diffusion and permeability processes in organic materials is important for applications to structural components, protective coatings or packaging. In this work some basic behaviour of solvent diffusion into and through a polymer are studied using acetone and un-plasticized polyvinyl chloride at room temperature as model materials. Special cell for gravimetric measurements is used to provide data on diffusion and permeability rates through samples of different thicknesses. It is shown that the rates of mass transport are slowing down with thickness for diffusion and also for permeability, as expected. However permeability mass transport is slower than mass delivered to the outer surface by diffusion. This is explained and experimentally verified by insufficient saturation of the surface layer, as the solvent evaporates before a full saturation is reached. When the outer surface layer is pre-saturated with solvent, permeability will increase several times. When evaporation is restricted (e.g. closed cavity) the liquid solvent will accumulate, filling up the cavity. Concentration profiles, measured by infrared microscopy, confirm this observation. It is suggested that the experimental data can be explained by using chemical potential and chemical reaction kinetics.