Graphene oxide/waterborne polyurethane nanocoatings: Effects of graphene oxide content on performance properties
David G. Goodwin, Coralie Bernard, Xiaohong Gu, Mat Celina, Marc R. Nyden, Deborah S. Jacobs, Li Piin Sung, Tinh Nguyen
Graphene oxide (GO) is a good nanofiller candidate for waterborne coatings because of its outstanding physical and mechanical properties, good dispersibility in water, and low cost. Here, we report on the performance of a one-part, water-borne polyurethane (WPU) nanocoating formulated with four different GO loadings (0.4 % - 2.0 % by mass). The results show that GO sheets were well-dispersed in, and have a good adhesion with WPU. At 2 % mass loading, GO increased the modulus and yield strength of WPU by 300 % and 200 %, respectively, increased the thermal conductivity by 38 %, and reduced the burning heat release rate (flammability) by 43 %. At 1.2 % mass loading, GO reduced the oxygen permeability 7-fold with only a slightly smaller oxygen permeability reduction at 2 % mass fraction. The presence of GO, however, increased water vapor uptake at high humidity; the moisture content of 2 % mass loading GO/WPU nanocoatings at 90 % RH was almost twice that of the moisture content for unfilled WPU (6.9 % ± 0.17 % vs 3.50 % ± 0.11 %). In summary, with the exception of water uptake at very high humidity (>70% RH), GO/WPU nanocoatings have superior performance properties relative to neat WPU in terms of mechanical strength, barrier properties, flammability, weathering resistance, thermal conductivity, and thermal stability. The observed improvements in performance properties combined with the ease of processing and low manufacturing cost suggest that GO is an economically viable nanofiller for WPU coatings.