To study the film thickness, 22.000 g of the cooled casting solution was poured into polystyrene petri dishes with internal diameter of 6.1 cm. The thickness of each film was measured at fifteen different locations with a hand-held micrometer (Mitutoyo, Japan). Average of each five random points was considered as one datum. It is worth mentioning each sample was prepared three times and their average results were reported. After 36 h, films were carefully separated and stored in poly ethylene bags. All films were prepared in triplicates. The prepared samples were designated with label such as G30C2.5, where G and C referred to glycerol and clay, respectively and the number 30 indicated 30% glycerol and 2.5 referred to 2.5% Na–MMT.