Sorption of water vapor by water‐soluble polymers: Kinetic, equilibrium, and glass temperature data

Abstract

AbstractEquilibrium and kinetic studies of the sorption and desorption of water vapor by poly(acrylic acid), poly(sodium acrylate), sodium carboxy methyl cellulose, methyl cellulose, and a series of poly(methyl acrylate) hydrolyzates in acid and sodium salt forms were made at 30°C. It was found, as expected, that equilibrium sorption increased and was greater for polymers containing strong‐electrolyte type substituents than for those containing an equivalent number of weakly ionizable units. In general, the diffusion is somewhat slower than in the case of water‐insoluble polymers. It was also found that water solubility of a polymer does not per se result in anomalous water sorption. In Methocel, for example, water diffusion is both Fickian and concentration‐independent. All of the results, particularly those on the poly(methyl acrylate) hydrolyzates which ranged from completely water‐soluble to insoluble systems, support the following conclusion: For water‐soluble polymers both anomalous diffusion and relatively high glass temperatures are associated with high concentrations along polymer chains of very polar or ionic groups, such as OH, COOH, and CO2−Na+. Presumably both the anomalies and high transition temperatures are associated with restricted segmental mobility resulting from strong chain‐chain interactions which originate in the highly polar and ionic, water‐solubilizing chain substituents.