Degradation of polyethylene terephthalate bottles after long sunlight exposure

Abstract

Effects of sunlight on PET bottles degradation and liquid filled inside the bottles were studied. Three types of soft drinks filled in Polyethylene terephthalate (PET) bottles; drinking water in clear bottle, carbonated water in green, and pink bottles was left on the rooftop of building for 8 months. After long exposure to sunlight, the bottles’ shapes were not changed, but the tensile strength of plastics decreased. Moreover, the enthalpy of fusion which corresponds to molecular rearrangement of plastics increased. The results from FTIR showed slightly increased of peak hydroxyl group at 3,400 cm-1 on outer surface of PET bottle. Sunlight slowly degraded the chemical structure on outer surface of PET bottle by photo-hydrolysis reaction. The pH of water for all samples changed from acid to base. By using Tollen’s reagent, aldehyde was found clearly in drinking water after sunlight exposure, but was not observed in green and pink water.