New Generation Layered Nanocomposites Derived from Ethylene-co-Vinyl Acetate and Naturally Occurring Graphite Jinu Jacob George, 1 Abhijit Bandyopadhyay, 2 Anil K. Bhowmick 1 1 Rubber Technology Centre, Indian Institute of Technology, Kharagpur 721302, India 2 Department of Polymer Science and Technology, University of Calcutta, Kolkata 700009, India Received 4 May 2006; accepted 3 July 2006 DOI 10.1002/app.25067 Published online 28 January 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: New ethylene-co-vinyl acetate (EVA, with 60% vinyl acetate content) based nanocomposites were prepared with graphites modified by various techniques and a commercially available expanded graphite (EG). The infrared spectra and the surface energy measurements indicated better oxidation and higher surface energy of the graphite modified by mixed acids followed by high tem- perature treatment (GO). Interlayer space and surface area were increased as a result. EG possessed higher surface area. GO was found to distribute in finer tactoids of aver- age thickness of 25 nm in the matrix, as compared with the unmodified graphite (UG), having average tactoid thickness more than 40 nm along with aggregation. EG also showed finer dispersion in the EVA matrix with some network formation. The dynamic mechanical and the me- chanical properties were superior at the 2 wt % concentra- tion of the GO, beyond which the improvement was less, possibly because of aggregation of GO. Greater EVA-GO interaction at 2 wt % concentration was also supported from the swelling analysis, thermal conductivity, and the thermo- oxidative degradation data of the hybrid composites. The melt viscosity was lower at 2 wt % GO concentration. EG based nanocomposites registered similar properties. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 1603–1616, 2008 Key words: graphite; nanocomposite; reinforcement INTRODUCTION Since the introduction of polyamide 6/clay hybrid nanocomposites via intercalation polymerization, the research and application on this area has made a striking progress till date. The ever-increasing inter- est in nanoscience and technology using fillers of nano dimensions in polymer matrices are principally due to some exceptional properties that are derived from the resultant materials. 1–4 These nano fillers could be spherical metal oxides, 5–7 nanotubes, 8,9 or layered clays. 10–13 Till date, numerous literatures have been pub- lished from various laboratories including ours, exploring the different aspects of clay 14–19 and silica 20–24 based polymer nanocomposites. Clay is the first generation layered, one-dimensional nanofiller, whereas silica is the spherical, zero-dimensional nano filler among the metal oxide family. In the last five years, layered graphite has appeared in the arena as new generation one-dimensional nano filler for the polymeric systems with a lot of promise. Graphite is an allotrope of carbon, the structure of which consists of graphene layers stacked along the c-axis in a staggered array. 25 It has been known since long back that certain atoms and molecules swell graphite and increase its weight. In the modern terminology, this phenom- enon has been elucidated as the intercalation of guest chemical moieties within the graphene layers of the host graphite lattice. 26 High crystallinity of graphite is disadvantageous in forming the nanocomposites with polymers, as the giant polymer molecules do not find spaces within the graphene sheets. This has been overtaken by modifying the graphite flakes with several oxidiz- ing agents. 27 This treatment introduces some polar groups on to graphite, which helps in widening the interlayer spacing in the material so that giant poly- mer molecules get access into it. The modified gra- phite, quite often, has been termed as graphite oxide and designated as GO. 28 The chemical modification turns graphite slightly hydrophilic and therefore bet- ter dispersion could be anticipated within polar polymer matrices. Till date, some literatures are available on nonpolar thermoplastics like polysty- rene by using in situ intercalative polymerization technique 29 along with few polar polymers like poly- amide 30 and poly(methyl methacrylate). 26 But the authors are not aware of any reference on graphite Correspondence to: A. K. Bhowmick (anilkb@rtc.iitkgp. ernet.in). Contract grant sponsor: DRDO, New Delhi, India. Journal of Applied Polymer Science, Vol. 108, 1603–1616 (2008) V V C 2008 Wiley Periodicals, Inc.