Investigation of Oxygen Barrier Properties of Organoclay/HDPE/EVA Nanocomposite Films Prepared Using a Two-Step Solution Method S.M. Reza Dadfar, S.A. Ahmad Ramazani, S.M. Ali Dadfar Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran In this article, oxygen barrier properties of nanocompo- site films composed of organoclay (OC), high-density polyethylene (HDPE), and ethylene vinyl acetate (EVA) copolymer have been investigated. The nanocomposite films whose EVA forms a dominant fraction were pre- pared using the solution method. The dispersion of the OC in the HDPE/EVA blend was improved through tak- ing two-step procedure in the preparation of nanocom- posite. First, the OC and EVA were dissolved in chloro- form. Then, the resulting product, after evaporating most of the solvent, along with HDPE was dissolved in xylene. The obtained nanocomposite films underwent a number of tests in order to examine their barrier prop- erties including X-ray diffraction (XRD) and transmis- sion electron microscopy (TEM). The results showed that OC/HDPE/EVA nanocomposites are intercalated and partially exfoliated. Furthermore, from the TEM micrographs, the organoclay experimental aspect ratio was found. Also, the O 2 permeability through the films was evaluated, which showed that adding both OC and HDPE to EVA leads to a remarkable increase in the barrier properties of EVA films. Finally, by using the gas permeation results and existing permeation theo- ries, the organoclay theoretical aspect ratio was pre- dicted. POLYM. COMPOS., 30:812–819, 2009. ª 2008 Society of Plastics Engineers INTRODUCTION Polymer nanocomposites are mixtures of polymers with nanoscale fillers with at least one dimension of which is in the nanometer range. In recent years, these materials have attracted substantial attention from both academic and industrial researchers. This is because of their superior physical and mechanical properties com- pared to the unfilled polymers or conventional micro and macrocomposites. These advantages can include increased modulus and strength, high dimensional stability and heat resistance, and decreased gas permeability. It is worth mentioning that all these improvements are obtained at very low filler contents [1–8]. Presently, polymer nanocomposites reported in the lit- erature are typically based on impermeable lamellar fillers such as nanoclay. Montmorillonite (MMT) is one of the most commonly used nanoclays for the preparation of nanocomposites. MMT is a naturally laminated silicate with layer thickness of about 1 nm. Natural MMT is hydrophilic and not compatible with polymers. The most common way to remove this difficulty is to replace sodium cations in the interlayer space of MMT with long- chain organic cations to yield organically modified mont- morillonite [1–4, 9, 10]. Depending on the strength of interactions between the polymer matrix and layered silicate, two different struc- tures of polymer/clay nanocomposites are achievable: intercalated and exfoliated nanocomposites. In an interca- lated nanocomposite, the spacing between layers increases due to the intercalation of polymer chains between the sili- cate layers. In this state, the layers remain parallel to each other. However, when the individual silicate layers are sep- arated from the intercalated tactoids and dispersed in the polymer matrix, an exfoliated nanocomposite is produced. Usually, the percentage of intercalation and exfoliation would be expected in real nanocomposites [1–3]. Nanoclays are then distributed into a polymer matrix cre- ating multiple parallel layers, which force gases to flow through the polymer in a ‘‘torturous path’’ forming complex barriers to gases and water vapor. In particular, polymer/clay nanocomposite films show great promise in providing excel- lent barrier properties. It has been reported that gas perme- ability can be reduced considerably using adding only 3 wt% of nanoclay into polymer. Therefore, polymer/clay nanocom- posite films have gained many applications for producing ox- ygen barrier film for food packaging [10–22]. Generally, two strategies are considered to prepare polymer/clay nanocomposites: insertion of suitable mono- mers in the interlayer space of clay and subsequent poly- merization, which is called in-situ polymerization [10]; and direct insertion of polymer chains in the interlayer space of clay from either the solution or the melt state. Correspondence to: A. Ramazani S.A.; e-mail: ramazani@sharif.edu DOI 10.1002/pc.20711 Published online in Wiley InterScience (www.interscience.wiley.com). V V C 2008 Society of Plastics Engineers POLYMERCOMPOSITES—-2009