Study of natural ageing of polypropylene by X-ray photoelectron spectroscopy

The natural ageing of polypropylene (PP) in a non-controlled environment has been studied by X-ray photoelectron spectroscopy (XPS). Two PP samples were exposed outside for one year and another one was kept as the reference sample (inside at constant temperature). The analysis shows that oxygen is bounded to the polymeric chain and the light seems to act as a catalyst for the oxidation of the material. The main initiator mechanism of oxidation is the scission of the bond between the second carbon atom of the monomer and the associated hydrogen [J. Appl. Polym. Sci. 64 (1997) 2497]. The C 1s and O 1s spectra show that the most significant bonds between oxygen and PP are C-OH, C-O and O-O. According to the intensities of the XPS peaks, the C-OH bonds are the predominant ones in the oxidation process