Water Vapor Permeability of Plastics Used for Electrolyte Immobilized Lead-Acid Battery Containers.

The Water Vapor Permeability (WVP) properties of three polymer resins used for battery container materials were investigated. The resins were, Acrylonitrile-Butadiene-Styrene (ABS), Poly (vinyl chloride) (PVC) and Polypropylene (PP). The water vapor transmission rate through each plastic was determined according to ASTM E96-80, "Water Vapor Transmission of Materials". Experiments were performed at 2% Relative Humidity and within a temperature range of 21-50C. The conclusions of this study are: 1) At all temperatures PP had the lowest water vapor transmission rate followed by PVC and, finally, ABS. 2) The WVP of ABS and PVC were independent of temperature while by contrast, that of PP demonstrated a temperature dependency. 3) The apparent Activation Energy (E sub (AC)), determined from the rate measurements, for ABS and PVC indicated that the process of water vapor transmission was diffusion controlled. 4) The process of water vapor transmission for PP, determined from the value of the apparent E sub Ac, was not diffusion but, possibly controlled by water chemically reacting at the plastic surface. This work emphasizes the importance of including water vapor permeability properties in the process of selecting a plastic material to contain the Electrolyte Immobilized Lead-Acid Battery.