Viscoelastic properties of polycarbonate-graphene nanoplatelets nanocomposite foams

The viscoelastic properties of polycarbonate (PC) nanocomposite foams containing graphene nano platelets (GnP), prepared by one and two-step supercritical CO2 dissolution, were characterized by dynamic-mechanical-thermal analysis. Three factors were detected to influence the mechanical performance of foams: relative density, the eventual presence of a PC crystalline phase and GnP's amount. Relative density was found to be the most important one, with the storage modulus following a power law behavior with increasing relative density. Foams prepared in one-step presented higher storage moduli than two-step foams even having bigger cells, explained by their higher relative density. The eventual presence of PC crystals in one-step foams, induced by the combination of high CO2 dissolution temperatures and GnP's presence during foaming, was found to be the cause of their higher storage moduli when compared to two-step foams at similar relative density. A slight effect of GnP could only be observed in two-step foams with 5% GnP, as these foams displayed storage moduli as high as one-step foams having lower relative densities. Regarding the viscous contribution, PC's glass transition temperature resulted higher in one-step foams, related to a restriction in the molecular mobility of PC induced by the presence of a PC crystalline fraction and GnP. (C) 2016 Elsevier Ltd. All rights reserved.