Wavelength Sensitivity in Polypropylene/Clay Composite Photo-Oxidation
The photo-oxidation behaviour of polypropylene/maleic anhydride-grafted polypropylene/organic modified montmorillonite (PP/PPgMA/OMMT) composites with short wavelength (UVC) and long wavelength (UVA) ultraviolet radiation was examined. The samples were prepared in a co-rotating twin-screw extruder and compatibilizers with different degrees of maleation were used. The photo-oxidative stability was studied using FTIR spectroscopy and microscopy. During UVA exposure, the rate of photo-oxidation of PP/PPgMA/OMMT increased with the amount of maleic anhydride from 0.1 to 0.5 wt.% in PPgMA. However, even after 2500 h of exposure to the radiation, the FTIR spectrum of pristine PP did not show significant changes. For UVC radiation, the rate of photo-oxidation of PP/PPgMA/OMMT composites was the same as that of pristine PP. On the other hand, there was a difference between PP and PP/PPgMA/OMMT composites in the formation of a crack on the back surfaces of the sheets facing the UVC sources. The difference was due to the presence of Fe3+ in clay layers that had the effect of UV-protection and blocking in the UVC region.