DSC STUDIES ON BOUND WATER IN POLYPROPYLENE FILMS PLASMA-GRAFTED WITH 2-HYDROXYETHYL ACRYLATE AND ACRYLIC-ACID OR METHACRYLIC-ACID

Water sorbed on porous polypropylene films, grafted to various extents by plasma-graft copolymerization of 2-hydroxyethyl acrylate with acrylic acid or methacrylic acid, was examined using differential scanning calorimetry. From the heat of crystallization or melting of water in the grafted membrane, the non-freezing water content (W(nf)) was calculated using the relationship W(c) = W(f) + W(fb) + W(nf), where W(t) is the total water content in the membrane and W(f) is the free water content with phase transition temperatures similar to those of ordinary water and W(fb) is freezing bound water. The W(nf) values became larger with increase in the number of hydrophilic groups (graft ratio) in the membrane. The separation factor of water-ethanol was correlated with W(nf) value. A simplified static heterogeneous model is suggested to explain the dynamic process of membrane separation for water and ethanol.