Multifunctional nanocomposite foams based on polypropylene with carbon nanofillers

This work considers the preparation and characterization of polypropylene foams with variable concentrations of graphene and carbon nanofibres, focussing on the influence of the foaming process and the nanofillers on the microstructural and dynamic-mechanical-thermal properties of the foams. Great differences were found in terms of foam morphology depending on the type of foaming process, with foams prepared by physical foaming showing a vertically deformed cell structure, while chemical foams presented an isotropic-like cellular structure. The addition of graphene resulted in foams with higher cell densities and more uniform cellular structures when compared to the ones with nanofibres. Direct result of the combination of their particular cellular structure and higher expansion, polypropylene foams obtained by physical foaming presented a higher orientation of the alpha-monoclinic polypropylene crystal perpendicular to the foam's surface and higher exfoliation of the nanofillers, resulting in foams with improved mechanical properties. All these considerations are of extreme importance, as some of the most promising applications of these polymer foams require a good electromagnetic interference shielding efficiency, which greatly depends on the developed foam morphology.