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-butadine-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 a temperature range of 21-50°C. At all temperatures PP had the lowest water vapor transmission rate, followed by PVC and finally ABS. The WVP of ABS and PVC were independent of temperature while that of PP demonstrated a temperature dependence. The activation energy determined from the rate measurements for ABS and PVC indicated that the process of water vapor transmission was diffusion-controlled. For PP, the activation energy indicated that the process of water vapor transmission was not diffusion controlled but was possibly controlled by water chemically reacting at the plastic surface. The importance of including WVP properties in the process of selecting a plastic material to contain the electrolyte-immobilized lead-acid battery is emphasized