Abstract
Water vapor permeability of composite membrane has been studied referring to each permeability of the component membranes. As the components, the hydrophilic cellophane and the hydrophobic polyethylene film have been used. Experiments have been performed first on the water vapor permeability of each single membrane and secondly on that of the cellophane-polyethylene composite membrane, examining the direction of permeation also.
Both the permeability coefficient P and the diffusion coefficient D of water vapor in the cellophane single membrane increase with the water vapor pressure in the ingoing side. This result is explained by the combinated effects of increasing free volume of the system and clustering of water molecules. The P and D of polyethylene single membrane change slightly with the water vapor pressure.
As for the composite membrane, when the water vapor permeates along the direction from the cellophane to the polyethylene, the permeability of the composite membrane increases compared with that of the polyethylene single membrane in the relative pressure range less than 0.6. The phenomenon is explained by the application of the partition law to the partition of water on the boundary surface between cellophane and polyethylene. On the other hand, when the water vapor permates along the direction from the polyethylene to cellophane, the permeability of the composite membrane decreases extremely comparing with the case of the opposite direction, and the attainment of the stationary permeation state delays. Thus, the direction of permeation has significant influence on the permeability of composite membrane.
