Thermogravimetric analysis to establish thermal characteristics of disposed ophthalmic lenses: an interdisciplinary study

Spectacle and contact lenses comprise various polymers and additives, and are typically discarded after a period of use. Uncertainty regarding the thermal stability, decomposition characteristics, and consequent environmental impact of these lenses upon landfill disposal prompted this interdisciplinary study. The study aimed to determine the onset of decomposition temperature and subsequent thermal behaviour of these lenses to predict the environmental consequences of their disposal. This information can guide eyecare practitioners regarding sustainable waste management practices. Simultaneous thermogravimetric analysis and differential scanning calorimetry were conducted on a sample of commonly used spectacle and contact lenses. The lowest extrapolated onset of decomposition temperature of the study lenses was ∼249°C. Exothermic heat flow behaviour was evident and some samples exhibited the release of indeterminate content, potentially attributable to moisture loss or volatile compounds. Ophthalmic lenses can be considered thermally stable as they are unlikely to encounter temperatures above 249°C upon disposal under natural landfill conditions. Therefore, they are predicted to remain as solid waste. Increasing volumes of landfilled plastics, however, pose an environmental threat due to persistence and associated methane emissions. This study highlights the value of interdisciplinary research and the need to integrate sustainable waste management into health professions curricula and continuing education programmes.