Graphene-like nanocarbon: An effective nanofiller for improving the mechanical and thermal properties of polymer at low weight fractions Arvind Kumar a , Devesh Kumar Chouhan b , Prashant S. Alegaonkar a, ** , T. Umasankar Patro b, * a Department of Applied Physics, Defence Institute of Advanced Technology, Pune, India b Department of Materials Engineering, Defence Institute of Advanced Technology, Pune, India article info Article history: Received 20 November 2015 Received in revised form 15 February 2016 Accepted 19 February 2016 Available online 23 February 2016 Keywords: Graphene-like nanocarbon Nanocomposites Dispersion Raman mapping Mechanical properties Structural reinforcement abstract 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 ~51% and ~140%; while flexural strength and modulus increased by 22% and 23%, respectively as compared to pristine epoxy. The unprecedented enhancements in the me- chanical 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 for- mation of a large number of micro-cracks and their path deflection and higher extent of plastic defor- mation 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 me- chanical properties, GNC may also be used as an effective reinforcing agent in other polymer matrices. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Graphene is two-dimensional single-atom-thick sheet like ma- terial with exceptionally high in-plane elastic modulus (~1 TPa), high strength (~130 GPa) [1] and high specific surface area (>2000 m 2 /g) [2]. Graphene also possesses excellent thermal con- ductivity (~5000 W/mK) [3], thermal stability [4] and high electron mobility at room temperature (~210 5 cm 2 /Vs) [5]. These extraor- dinary properties make it an ideal filler material for developing polymer composites [6,7]. These composite materials find appli- cations in conducting composites [6], transparent electrodes [8], high strength composites [7,9], electromagnetic interference shielding [10], etc. Graphene based nanofillers; such as expanded graphite [11], graphite nanoplatelets [12,13], graphene oxide (GO) [14,15] and graphene nanoribbons (GNR) [16] have been exten- sively used as reinforcing agents in various polymer matrices with weight fractions up to 5 wt%. However, formation of agglomeration as a result of poor dispersion of nanofillers in polymer matrix limits transfer of its properties to polymer matrix [17]. Agglomeration of graphene platelets is attributed to strong interlayer van der Waals forces between graphene sheets and its poor interfacial bonding with matrix polymer. Hence, chemical functionalization of gra- phene has been carried out to address these issues [9,18]. Investigation of mechanical properties is probably one of the most studied phenomena in epoxy composites due to their wide range of applications from aerospace to wind-mill. In this context, there are consistent efforts to reduce the amount of filler content in * Corresponding author. ** Corresponding author. E-mail addresses: prashantalegaonkar@diat.ac.in (P.S. Alegaonkar), umasankarp@diat.ac.in (T.U. Patro). Contents lists available at ScienceDirect Composites Science and Technology journal homepage: http://www.elsevier.com/locate/compscitech http://dx.doi.org/10.1016/j.compscitech.2016.02.028 0266-3538/© 2016 Elsevier Ltd. All rights reserved. Composites Science and Technology 127 (2016) 79e87