Morphology and chemical properties of polypropylene pellets degraded in simulated terrestrial and marine environments

Polypropylene (PP) pellets exposed to solar radiation, ultraviolet B (UVB) radiation and heat in four stimulated treatments: dry-air, seawater-air, seawater-darkness, and dry-darkness for 0.5-1.5 years to investigate morphology and chemical change under various environmental conditions. Scanning electron microscopy and infrared spectroscopy were employed to characterize the virgin and degraded pellets. The degraded PP pellets under solar and UVB irradiation revealed 35% and 12% cracks, respectively. Moreover, carbonyl and hydroxyl groups formed on the surface gradually extended to the interior. However, under photo-irradiation, PP pellets floating in seawater showed less degradation than those in a dry environment. The formation of biofilm may retard the photo-degradation of PP pellets in the seawater when biocides are absent. Results also indicated that the photo oxidation dominated over thermal oxidation during the degradation process in the terrestrial and marine environments.