Effect of processing temperature and mixing time on the properties of PP/GnP nanocomposites

During processing of molten polymers the thermal and mechanical stress acting on the melt in presence of oxygen can induce degradation with a modification of the chemical structure of the polymers. This picture can become even more relevant if the melt is a multiphasic polymer system. In this last case, the effects of the degradation depend also on the presence of a second phase and on the interactions between the two phases. In this work, the effect of the processing conditions, temperature and time, have been considered in order to investigate the thermo-mechanical and thermo-oxidative degradation of nanocomposites made by polypropylene and different contents of graphene nanoplatelets. Graphene nanoplatelets improve the stability of the polymer matrix and the sample with the lower content of nanofiller shows a lower level of degradation. The better resistance of the filled samples has been interpreted with a barrier effect to the oxygen of the nanofiller that hinders the transport of oxygen necessary for the oxidation of the polypropylene. The unexpected effect of the concentration of graphene nanoplatelets has been correlated with the agglomeration of the nanoplatelets that reduces the surface area of the filler and then the barrier effect to the oxygen.