Graphene-like nanocarbon: An effective nanofiller for improving the mechanical and thermal properties of polymer at low weight fractions

Epoxy composites were prepared with graphene-like nanocarbon sheets (GNCs) at weight fractions between 0.005 and 2 wt%. At these weight fractions, the composites showed substantial improvements in the mechanical, physical and thermal properties. However, above 0.01 wt%, GNCs formed micron-size aggregates in the matrix as revealed by optical microscopy likely due their high aspect ratio and the density of aggregates increased with weight fraction and followed a power law curve. For 0.01 wt% composite, the mechanical properties, notably fracture toughness (K-IC) and critical strain energy release rate (G(IC)) are found to increase by similar to 51% and similar to 140%; while flexural strength and modulus increased by 22% and 23%, respectively as compared to pristine epoxy. The unprecedented enhancements in the mechanical properties at such a low weight content of GNCs (0.01 wt%) is attributed to the excellent dispersion of these high aspect ratio functional fillers in the matrix as revealed by spectral Raman mapping. Further the nanocomposites showed improved thermal degradation and, asymmetric and broad loss tangent peaks as against symmetric narrow peak for neat epoxy, obtained from dynamic mechanical analysis. These curves suggest significant alteration of glass transition temperature upon GNC incorporation. Fracture mechanisms in the nanocomposites were predominantly governed by formation of a large number of micro-cracks and their path deflection and higher extent of plastic deformation at the notch tip. The mutual effects of these phenomena resulted in higher fracture toughness of composites as compared to that of pure epoxy. On account of their ability to enhance various key mechanical properties, GNC may also be used as an effective reinforcing agent in other polymer matrices. (C) 2016 Elsevier Ltd. All rights reserved.