Degradation of food-contact plastics in use: Effect of temperature and chemical composition

Microplastics (MPs) have gained global attention due to their pervasive presence and potential risks to human health. Plastic food containers have been found to release MPs into food or liquids during everyday use, serving as a direct source of human exposure. Understanding the mechanisms and influencing factors of MPs release from plastic containers is therefore of vital importance. In the present work, four types of commonly used plastics, namely polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), and polycarbonate (PC) were collected from commercial cups and subjected to conditions mimicking daily use. The surface zeta potential, crystallinity, and functional groups of the plastic sheets were analyzed to investigate the surface degradation of these plastics. Results indicate that elevated temperatures promote the oxidation and hydrolysis of these plastics, leading to a significant increase in surface positive charges and crystallinity. Both acidic and alkaline pH levels of the contacting solution were found to enhance the surface degradation of these plastics, potentially exacerbating the release of MPs. The addition of salt in an alkaline solution notably increases the negative charges on the PP surface. Glucose was observed to accelerate the accumulation of negative charges on PP surfaces across all studied pH conditions.