VALENCE-BAND REGION XPS, AFM AND NEXAFS SURFACE-ANALYSIS OF LOW-PRESSURE DC OXYGEN PLASMA-TREATED POLYPROPYLENE

Biaxially stretched polypropylene (PP) foils treated with oxygen plasma at low pressure were analysed by core level and valence band region X-ray photoelectron spectroscopy (XPS), atomic force microscopy and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Applying short treatment times the XPS O C atomic ratios are less than or equal to 0.1. Valence band electron spectroscopy for chemical analysis (ESCA) and NEXAFS spectroscopy reveal that a certain number of C-O and a smaller amount of C=O functionalities together with C=C bonds exist at a short-time treated PP surface. These species were not observed or resolved by a standard core level XPS analysis of the same surface. The surface is smoothed by the plasma treatment and the C-O and C=O bonds are slightly non-statistically oriented (parallel to the surface plane). Considering the results obtained after prolonged plasma treatment, NEXAFS spectroscopy provides a direct indication for the formation of conjugated carbon double bonds in the surface region of the PP samples.