Barrier Properties of Polymer/Clay Nanocomposites

In this chapter we review the current literature associated with the barrier properties of polymer/layer silicate nanocomposites, with a special focus on the use of clay nanoparticles to affect permeability to gases and vapours. The majority of papers on nanocomposites have been focused on the use of smectite type clays as nanoparticles. They are a group of swelling clay minerals including montmorillonite, nontronite, saponite, sauconite, and hectorite. Mostly smectite clays have been studied because they are naturally occurring minerals that are commercially available and exhibit platy morphology with high aspect ratio and substantial cation exchange capacities. The platelet structure of these aluminosilicate materials has proven its ability to improve the barrier properties of polymeric materials, according to a tortuous path model in which a small amount of platelet particles significantly reduces the diffusivity of gases through the nanocomposite. The key for nanocomposite technology is exfoliation of the clay into its individual platelets, thereby achieving the greatest barrier improvement as well as the lowest haze. The advantage of this approach is based on the use of conventional cheap polymers with barrier improvement arising from dispersion of low levels of inexpensive clay minerals. Several models for barrier properties have been proposed for predicting the behaviour of polymer nanocomposites. This chapter examines in some detail the existing literature on barrier properties of polymer nanocomposites, comparing the results and trying to correlate the different experimental results, where possible.