Hydrophilization of microporous polypropylene Celgard® membranes by the chemical modification technique

Abstract

Microporous hydrophobic polypropylene (PP) membranes (Celgard® 2400 and 2500) were modified by the chemical modification technique to impart permanent hydrophilicity. The modification was carried out in two stages. In the first stage, the membranes were hydroxylated by treatment with aqueous potassium peroxydisulfate solution under a strong flow of nitrogen. In the second stage, the hydroxylated membranes were subjected to grafting of acrylamide using cerric ammonium nitrate as an initiator. Subsequently, acrylamide grafted PP membranes were partially hydrolyzed to have carboxvl functional groups at the membrane surfaces. Under given experimental conditions the grafting also took place within the pores of the microporous structure of hydrophobic PP Celgard® membranes. Modified membranes exhibited permanently wettable characteristics by aqueous solutions and appeared translucent when immersed in water. Contact angle measurements showed excellent wetting properties with water. In contrast to unmodified Celgard® membrane, the modified membranes exhibit water permeability even after repeated drying. Membranes were further characterized by FTIR and ESCA for the different types of functional groups. © 1996 John Wiley & Sons, Inc.