Studies on the permeation of inorganic salts through plastic films.

Permeation tests were carried out under several conditions for various metal ions, anions, temperatures and solvents. The study was designed as lag-time experiments where the amount of metal penetrating through the polymer was plotted against time. Diffusion and permeability coefficients were measured using the time-lag technique and by calculating the permeation rate. Graphite furnace atomic absorption spectroscopy was used to quantify the amounts of metal ions. Permeation of inorganic salts through low density polyethylene (LDPE) showed a strong dependency on the solvent used. With water as solvent, no permeation was measurable even at 60 degrees C, while ethanol, 1-propanol and 2-propanol gave increasing permeation. Small amounts of water in pure ethanol diminished the permeation rate considerably. Chloride salts led to the fastest diffusion, whereas bromide salts gave the highest permeation rate. Acetates and nitrates show virtually no permeation. In ethanol, copper chloride permeated faster than iron, zinc, cobalt, nickel or lithium chloride, and only tin chloride diffused faster than copper chloride. Reasons for the observed permeation behaviour are assumed to be the molecular size of an undissociated molecule, the degree of dissociation and the solvation in a solvent.