Evaluation of PET degradation under accelerated weathering

S-S. Jhang, R. Cook, S. Rostampour, B.H. Liu,, L-P. Sung
National Institute of Standards and Technology,
United States

Keywords: Plastic waste, PET, photodegradation, accelerated UV


Plastic materials are widely used in daily life due to their high environmental resistance, low fabrication cost, and easily shapeable properties. Polyethylene terephthalate (PET) is a common plastic used in beverage and food packaging. However, degraded plastic waste can pose various unknown effects on the ecosystem. The purpose of this study is to evaluate the environmental impact of PET water bottles using laboratory accelerated weathering tests. In the research, degraded PET water bottles are first generated via ultraviolet (UV) exposure in the NIST Simulated Photodegradation via High Energy Radiant Exposure (SPHERE) device. Degradation is performed using a customized sample holder to simulate different outdoor weather or oceanic conditions. There are 4 sample compartments in the sample holder in which different conditions can be applied individually under the same temperature. The used conditions are as follows: dry (i.e., ≅ 5% RH), humid (i.e., ≥ 95% RH), immersed in simulated “fresh” water, immersed in simulated ocean water. Additionally, the effect of temperature on the degradation process is investigated by employing temperatures from 30°C to 50°C. For toxicity and characterization method development study, there are two approaches to generate microplastic or nanoplastic (1) degrade PET first, then cryo-mill the degraded samples; (2) cryo-mill the PET water bottle first, then degrade PET micro-nano- particles at different weathering stages. Physical and chemical changes following weathering are characterized using microscopy, spectroscopy, and differential scanning calorimetry (DSC). Optical and laser scanning confocal microscopies are used to identify surface changes of PET and to identify the formation of micro-/nano- plastics following weathering. Fourier-transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) is further used to characterize the oxidation or hydrolysis reaction of water bottles that occurs during the weathering process. For characterization of the thermal properties of PET, DSC is used to identify the changes in crystallinity, melting temperature (Tm), and glass transition temperature (Tg). Comparing the obtained laboratory accelerated weathering results with natural weathering results will allow prediction of the degradation process of PET