HYDROPHOBIC FILMS AND THEIR EFFICIENCY AGAINST MOISTURE TRANSFER .2. INFLUENCE OF THE PHYSICAL STATE

Moisture transfer has been studied in a system composed of a support (cellophane) and a coating material containing different proportions of a solid phase (paraffin wax or n-octacosane) mixed with a liquid one (paraffin oil or n-hexadecane). In the test conditions (25-degrees-C, 22-84% RH, and 45 +/- 6 g of hydrocarbon/m2) a significant increase in permeability of the coated film was obtained for mixtures containing less than 25% solid. Different structural features were established which explain the difference in permeability: orientation, length, and size and shape of the aliphatic chains. The actual proportions of n-alkanes and the presence of the two phases were verified. Results suggest that liquid lipids up to 75% may be used to improve coating performance of solids without diminishing their moisture barrier properties.