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.