Abstract
Surface modification of nonwoven fabrics of polyolefin by graft polymerization of acrylic acid initiated by low temperature plasma was investigated to develop a new durable separator for secondary battery. The fabric, the thickness of which was 210 pm with 78 g/m2-fabric-density, was made of a two-component-fiber of 20 pm-diameter that consists of polyethylene surface on a core of polypropylene inside. The fabric was exposed to argon plasma under conditions of gaseous pressure of 13.3 Pa and 13.56MHz-RF-wattage of 10 W before introducing monomer vapor for graft polymerization at 299 K. Graft ing ratio (GR) estimated on weight basis of a piece of the fabric increased from 1.8% to 4.9% with graft polymerization time from 60 s to 10800s on 60s-plasma-exposure-time. However, GR was alomst constant of around 0.7% independent of plasma exposure time up to 300 s for 60 s-graft-polymerizationtime. By C1s (289 eV) and O1s, (535 eV) peaks of X-ray photoelectron spectroscopy (XPS), chemical bonding of acrylic polymer chains to fabric surface could be confirmed. It was also observed that the degree of electrolyte retention which is important as a battery separator increased up to 267% for a surface modified fabric of 0.4%-GR by only 30 s-graft-polymerization-time after 60s-plasma-exposuretime. This retention value is comparable with that of a conventional polyamide separator.
