Effect of Environmental Conditions and Polymer Ratio on Water Vapor Transmission through Free Plasticized Cellulose Films

Abstract

Experiments were conducted to evaluate the effects of changes in the polymer ratio and environmental conditions on the water vapor transmission properties of plasticized films containing combinations of hydroxypropyl methylcellulose and ethyl-cellulose. Rates of water vapor transmission were calculated from a formula based on Fick's first law of diffusion. Inverse relationships were observed between the rate of water vapor transmission and film thickness for all films studied. In these plasticized systems, the polymer ratio of hydroxypropyl methylcellulose to ethylcellulose produced essentially no difference in the water vapor transmission properties from one film composition to another. Films subjected to a water vapor environment at both film surfaces were more permeable to water vapor than films subjected to a water vapor environment at only one surface. In the thickness range studied, films subjected to 40 and 50° conditions had lower rates of water vapor transmission than those studied at 30°. The findings of this study demonstrated the presence of another mechanism of vapor transmission, in addition to diffusion, that is apparently related to the hydrophilic character of the film.