The Impact and Fate of Graphene Oxide in Graphene Oxide/Polymer Nanocomposites Exposed to Ultraviolet Irradiation
David G. Goodwin, Trinny Lai, Yadong Lyu, Chen Yuan Lu, Alejandro Campos, Vytautas Reipa, Tinh Nguyen, Li Piin Sung
Ultraviolet (UV) radiation, heat and moisture can lead to polymer degradation outdoors but the effect of graphene oxide (GO) nanofiller incorporation on this process is unknown. Since GO can improve the mechanical, barrier, and thermal properties of a polymer in GO/polymer nanocomposites (GO/PNCs), this study sought to evaluate the effect of GO on polymer degradation, the exposure of GO at the polymer surface, and the release of GO from degraded nanocomposites. In this study, different mass loadings of GO were incorporated into waterborne polyurethane (WBPU), a commonly used exterior coating, and GO/WBPU nanocomposites were exposed to different weathering conditions using the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure), an accelerated weathering device that uniformly irradiates samples with high intensity UV light under controlled temperature and humidity conditions. The transformations of GO/WBPU nanocomposites relative to neat WBPU controls were measured using thickness loss and infrared spectroscopy (IR). GO exposure was assessed using Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) modulus measurements. GO release was measured after UV degradation using a simulated rain spray followed by collection of the rain run-off for analysis. Overall, this study improves identification of potential environmental, health, and safety issues of degraded GO/PNCs and evaluation of GO/PNC service life outdoors.