Evaporation behaviour of water and its plasticizing effect in modified poly(vinyl alcohol) systems

Several modified poly(vinyl alcohol) (PVA) systems with various plasticizers were prepared and their melt-processing was successfully realized. This paper focuses on the study of the evaporation behaviour of water in these modified PVA systems, exploring its plasticizing mechanism by using differential scanning calorimetry. The evaporation characteristics of bulk water, water in aqueous solutions of the plasticizers, and the thermal properties of PVA were also studied. The experimental results show that water in aqueous solutions of glycerol and/or caprolactam evaporates at a lower temperature than bulk water, but water in the PVA/water system evaporates at a higher temperature, with a wider DSC peak due to the interaction between water and PVA. Incorporation of glycerol, caprolactam or their mixtures further strengthens the interactions between water and the other components, retarding water evaporation. During the processing, the less closely associated water has the plasticizing effect through molecule movement, while the strongly bound water, which breaks the intermolecular hydrogen bonding of PVA and decreases its intermolecular interaction, is more beneficial to the melt-processing of PVA. (C) 2003 Society of Chemical Industry.