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Impact modified polystyrene based nanocomposites

Yeniova, Canan Esma
Polystyrene, PS, is a preferable polymer in industry, but, its brittle characteristic restricts its utilization. The aim of this study is to improve the impact strength of PS by the help of elastomeric materials SEBS-g-MA and E-BA-GMA. In order to prevent the reduction in the tensile strength of the materials, three different types of organic montmorillonites, MMT, (Cloisite® 30B, 25A and 15A) were used as fillers. Nanocomposite preparation was performed in a co-rotating twin screw extruder. Initially elastomer and organoclay contents were kept at 5wt% and 1-2wt% respectively. Well dispersed silicate layers were obtained for the nanocomposite containing SEBS-g-MA and Cloisite® 25A owing to the high viscosity of SEBS-g-MA and the solubility of polystyrene end block of SEBS with PS matrix. Owing to higher hydrophobicity of Cloisite® 15A a better dispersion was expected compared to Cloisite® 25A, but, it was concluded that two long aliphatic tails of Cloisite® 15A limited the access of polymer chains to the clay surface. The desired impact strength values could not be achieved by using 5wt% elastomeric materials; therefore, it was decided to increase the SEBS-g-MA content up to 15, 20, 30 and 40wt%. With increasing elastomer content, increasing average elastomer domain size was obtained. Also, it was observed that with the addition of organoclay, the elastomeric domain size increases since the clay particles reside in the elastomer phase and at the interphase between elastomer and PS. The mechanical test results showed that the nanocomposites containing 15 and 20wt% SEBS-g-MA have the optimum average domain size that results in better impact strength values without deteriorating tensile properties.