Water absorption by acrylic-based latex blend films and its effect on their properties

The absorption of moisture, from liquid as well as gaseous states of water, is known to strongly influence the properties of many polymeric materials. In this article, we examine the unusually high affinity for water of acryl ic-based latex blend films, which lose their transparency and turn white up on water absorption. Composed of rubbery and glassy phases at room temperat ure, these blends absorb significant amounts of water, which results in onl y a minor plasticization of the glassy component. When redried at elevated temperatures, the blend films return to their original transparent state bu t remain white and opaque when freeze-dried at -70 degrees C. Scanning elec tron micrographs of the freeze-fractured surfaces of wet samples exhibit mi cron-sized holes that suggest clusters of water inside the bulk of the film s. A qualitative model associates these water clusters to residual surfacta nt inside the samples that is left behind after the drying of original lati ces. (C) 1999 John Wiley & Sons, Inc.