Graphite nanoplatelet/pyromellitic dianhydride melt modified PPC composites: Preparation and characterization

The properties of composites prepared by melt compounding from graphite nanoplatelets (GNP) and pyromellitic anhydride modified poly(propylene carbonate) (PPC) were investigated. GNPs of different morphologies and acid residue levels were selected. Acid residues in GNP grades were detrimental for PPC in terms of thermal stability, stiffness and conservation of the molecular weight. The exfoliation of graphite nanoparticles was challenging, and morphologies of combined tactoids with thicknesses both on the micro and nano scales were observed. The filler contributed to the thermal stability, and the mechanical reinforcement was observed from approximately 6 wt% GNP and accompanied by an increase in the glass transition temperature. For a specific GNP grade, at a 15 wt% filler content, the glass transition temperature increased by 10 °C and the storage modulus measured at 20 and 30 °C increased correspondingly by a factor of ca. 3 and 30, respectively. Solid state NMR spin-spin relaxation time T2 measurements (Carr-Purcell-Meiboom-Gill pulse sequence) revealed three significantly different components. Using PLS, empirical models were established which enable the prediction of some viscoelastic parameters as a function of filler parameters and the average T2.