Journal of Membrane Science 318 (2008) 129–136 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Barrier properties of model epoxy nanocomposites Luyi Sun a,b , W.-J. Boo a , A. Clearfield b , H.-J. Sue a,∗ , H.Q. Pham c a Polymer Technology Center, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, USA b Department of Chemistry, Texas A&M University, College Station, TX 77842, USA c Epoxy R&D, The Dow Chemical Company, Freeport, TX 77541, USA article info Article history: Received 1 November 2007 Received in revised form 5 February 2008 Accepted 14 February 2008 Available online 4 March 2008 Keywords: Barrier properties Epoxy nanocomposite -Zirconium phosphate Degree of exfoliation Aspect ratio abstract The barrier properties of two sets of model epoxy nanocomposites with variations in nanoplatelet exfo- liation level and aspect ratio have been investigated. The results show that both the exfoliation level and aspect ratio of nanoplatelets have a significant effect on the nanocomposite barrier properties. The results have also been correlated with a number of semi-empirical and physical models. It is found that both Gusev–Lusti’s 3D model and Nielsen’s 2D model give good correlation with experimental find- ings. Implication of the present study for barrier properties improvement of polymer nanocomposites is discussed. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Polymeric materials have long been utilized for packaging applications. However, overwhelming demands in the market- place have put significant pressure for material developers to pursue novel routes to manufacture low cost packaging films with greatly improved barrier properties. Typical approaches to lower permeability of polymeric materials are to apply barrier coating on the film surface, such as aluminum metallization on polymer surfaces [1], and to laminate expensive high barrier material, such as ethylene vinyl alcohol [2] and polyvinyl alcohol (PVA) [3], between less expensive, but stronger films. However, such approaches are usually too expensive and cannot achieve desired long-term barrier properties needs [2]. The emergence of polymer nanocomposites introduces a new opportunity to improve barrier properties of polymers. When the nanoplatelets are well exfoliated, in addition to the improved barrier property, polymer nanocomposites usually exhibit enhanced mechanical properties and better thermal sta- bility [4–6], which adds extra values for polymer nanocomposites using as packaging materials. Initial commercial target of polymer nanocomposites is for high barrier packaging applications, such as food packaging [7]. As a result, the barrier properties of poly- mer nanocomposites have been extensively investigated based ∗ Corresponding author. Tel.: +1 979 845 5024; fax: +1 979 862 3989. E-mail address: hjsue@tamu.edu (H.-J. Sue). on a wide range of polymer matrices, including polyethylene terephthalate (PET) [8,9], polyethylene (PE) [10,11], poly(methyl methacrylate) (PMMA) [12], polyamide [13], polyimide [14], polyurethane [15], poly(-caprolactone) [16,17], polylactide [18], epoxy [19,20], natural rubber [21], styrene–butadiene rubber [22], acrylonitrile–butadiene rubber [23], and Nafion ® [24], for different targeted applications. In addition to the study on permeability of oxygen [11,13,18,25–29], moisture [11,27,28,30], carbon dioxide [11,31], nitrogen [11,21,31], and liquid water [32,33], for regular food packing [7] and coating applications [33], permeability studies on special gases and liquids, such as hydrogen [13], helium [13,19], methanol [24,34], ethanol [35], toluene [35], and acetone [36], have also been performed for hydrogen storage [19] and fuel cell [24] applications. These promising applications in turn fuel intensive researches on polymer nanocomposites for barrier properties improvement. Significant improvement on barrier properties by up to two to three orders of magnitude has been reported [29,37]. Most studies on polymer nanocomposite barrier properties are based on the tortuous pathway concept [38], where the nanofiller phase is assumed to be impermeable for gas and liquid molecules. Quite a few models have been developed based on this concept and will be discussed in more detail later. It has also been noticed that the interaction between certain polymer matrices and nanoplatelets can affect crystallinity, molecular orientation, and packing of the molecules near the nanoplatelets [39]. The alteration of the molecular packing around the nanoplatelets may further enhance the barrier properties of polymer nanocomposites. Wang et al. [22] reported that the layered rectorite has a strong effect on 0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2008.02.041