Quantitative analysis of surface ethylene concentrations in ethylene-propylene polymers using XPS valence bands

Abstract

Polyolefin surfaces and interfaces can have a substantial effect on polyolefin processing and properties. Despite the importance of these surfaces and interfaces, there have been few good ways of determining the type of polyolefin on a surface. In this work, a quantitative XPS method for the determination of surface ethylene concentrations in ethylene–propylene polymers is presented. Calibration lines are created using differences in the valence band spectra of various polyethylene (PE), polypropylene (PP) and ethylene–propylene polymer (EP) standards. These lines are then used to determine surface ethylene concentrations on propylene–ethylene polymers. This procedure yields accurate ethylene determinations (±5 wt.% ethylene) when surface contamination (such as additives) is low. At higher surface contamination levels, the accuracy of the method degrades unless valence band contributions from the contamination (or additives) are accounted for. When surface additive levels are high, valence band analyses are shown to be useful in determining the nature of the additives present. Valence band spectra obtained from other polyolefins (polyisobutylene, poly-1-butene, poly-1-hexene and poly-1-octene) are also presented. The spectra for polyisobutylene and poly-1-butene are distinctly different from that obtained from PE (also PP). The spectra obtained from poly-1-hexene and poly-1-octene are similar to that obtained from PE, but are distinctly different from those obtained from polyisobutylene, poly-1-butene and PP. This valence band approach for determining surface compositions should be applicable to other mixed polyolefins that have significantly different valence bands. Case studies involving haze on injection-molded plaques and PE cling-films are presented. © 1998 John Wiley & Sons, Ltd.