Polypropylene natural aging studied by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been used to investigate the eff ect of natural aging on polypropylene (PP). The analysis showed a marked de gradation of the surface, which is mainly caused by the contamination of th e 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 b oth ambient atmosphere and ambient light. Spectral analysis shows that oxyg en 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 amb ient light through time seems to favour double bonding. According to the sp ectra obtained at different analysis angles, this type of bonding spreads a nd remains homogeneous to a depth of a few monolayers (8 nm). The compariso n of this study with that of the literature has allowed us to propose a rea ction mechanism for the polymer oxidation. (C) 2000 Elsevier Science B.V. A ll rights reserved.