Tailoring the graphene oxide chemical structure and morphology as a key to polypropylene nanocomposite performance

In this work, we designed and studied two synthetic routes, based on modified Hummers method, to obtain graphene oxide (GO), and investigated their influence on the performance of polypropylene (PP)/GO nanocomposites. The two synthetic routes differed in the application condition of the oxidizing agent, potassium permanganate (KMnO4), which was added either as a powder (GO-P) or as a water solution (GO-S). This apparently subtle synthetic change yielded GOs with different degrees of oxidation and particle sizes, where GO-P presented a higher oxidation degree and smaller particles. The different GOs were then melt-blended with PP and the correlation between their different chemical/morphological structures and the nanocomposites' thermomechanical/rheological properties were evaluated. The milder oxidation process suffered by GO-S, and consequent less hydrophilic character, yielded a PP/GO-S nanocomposite with improved performance as the consequence of a better matrix/filler chemical affinity, mainly in compositions with lower GO-S contents. The thermal stability was increased by more than 10°C when 0.1 wt% GO-S was inserted into PP. When compared to the composition with 0.1 wt% GO-P, the increase was 13°C. Reinforcing effects were also observed in that sample (with 0.1 wt% GO-S), which exhibited the highest storage modulus and complex viscosity. These results suggest that tailoring the GO's oxidation degree and morphology is a key point to obtain an ideal interfacial interaction between phases