Lead‒acid battery separators have traditionally been manufactured from the extrusion, calendering, and extraction of ultrahigh molecular weight polyethylene (PE) / silica/ oil mixtures to form microporous ribbed sheets that are processed into ‘envelopes. Separator manufacturers utilize trichloroethylene or hexane for removing most of the process oil during the extraction step. After evaporation in the drying oven, these solvents are then recovered through low temperature condensation or adsorption/desorption onto activated carbon. As environmental regulations and emission standards become more stringent, there is a need to investigate alternative approaches to the manufacture of lead‒acid battery separators.

This presentation discusses a novel approach in which isotactic polypropylene (i-PP) is combined with lesser amounts of silica, naphthenic process oil, surfactant, and a nucleating agent at elevated temperature in a twin screw extruder. The extrudate is cast onto a heated roll to form a non-porous flat sheet that is then biaxially oriented. Microporosity is created as the i-PP undergoes a beta to alpha crystal transformation in combination with the extension of polypropylene chains in both the machine-direction (MD) and transverse-direction (TD). Because of the high degree of orientation, the MD and TD elongations-at-break are typically less than 50%, and the puncture resistance is ~ 2.5 times higher than traditional PE/SiO₂ separators of an equivalent thickness (150-200 um). Good wettability and porosities as high as 70% have been achieved.

A report will be given on ENTEK separator characterization results and the performance of the i-PP separators in 2V cells using commercial lead‒acid battery electrodes.