Evaluation of X‐ray‐excited Valence Band Measurements for the Determination of the Surface Composition of Model Thermoplastic Olefins

In this study we evaluate the utility of using x-ray-excited valence band measurements for the determination of the surface composition of simple model thermoplastic olefin systems composed of binary blends of semicrystalline polypropylene (PP) and an amorphous ethylene-propylene copolymer (E-co-P). Blend compositions included combinations of high- and low-molecular-weight (MW) PP and E-co-P composed of 60 wt.% PP/40 wt.% E-co-P and 80 wt.% PP/20 wt.% E-co-P blends. Results demonstrate that experimental valence band spectra for the polyolefin blends can be approximated by a linear combination of the pure-component valence band spectra. Bulk compositions determined from spectra recorded from cryomicrotomed cross-sections were found to be consistent with the bulk component wt.%. The surface compositions of the binary blends were all found to be enriched in PP. Measurements taken from the 60/40 wt.% blends were 10-20% higher in PP concentration than the bulk compositions, and were found to vary depending on the MW combination of the components. No MW dependence was observed for the 80/20 wt.% blends, apparently due to a near saturation of the surface with PP. The development of methods for assessing the surface composition of these types of materials may prove useful in monitoring changes in composition with material formulation and process conditions. Information of this nature could be helpful in permitting an evaluation of potential influences of composition on adhesion.