Polypropylene natural aging studied by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been used to investigate the effect of natural aging on polypropylene (PP). The analysis showed a marked degradation of the surface, which is mainly caused by the contamination of the superficial structure by oxygen. This study was conducted with the aid of three samples of PP: the first was new, the second was aged under ambient atmosphere and protected from ambient light, and the third was exposed to both ambient atmosphere and ambient light. Spectral analysis shows that oxygen is the predominant element of contamination. The aging process induces a chemical modification of the surface, creating double bonds and bonding to more than one atom causing the polymer chain to break. The presence of ambient light through time seems to favour double bonding. According to the spectra obtained at different analysis angles, this type of bonding spreads and remains homogeneous to a depth of a few monolayers (8 nm). The comparison of this study with that of the literature has allowed us to propose a reaction mechanism for the polymer oxidation. (C) 2000 Elsevier Science B.V. All rights reserved.