Morphology, thermal stability and visco-elastic properties of polystyreneepoly(vinyl chloride) blends Z. Ahmad * , N.A. Al-Awadi, F. Al-Sagheer Department of Chemistry, Kuwait University, Faculty of Science, P.O. Box 5969, Safat 13060, Kuwait Received 22 January 2007; received in revised form 18 February 2007; accepted 20 February 2007 Available online 28 February 2007 Abstract The morphology, thermal and mechanical properties of polystyrene (PS) blends with 2.5e20 wt% of poly(vinyl chloride) (PVC) have been studied. The measurement of the glass transition temperature (T g ) from the maxima of tan d data using dynamic mechanical thermal analysis showed that the blends were incompatible and homogenously distributed only within a limited range of PVC contents in PS. The value of the storage modulus was found to increase initially but then decreased with further addition of PVC in the matrix. Distribution of the phases in the virgin and degraded blends was also studied through scanning electron microscopy. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800  C at different heating rates varying from 2.5 to 20  C/min. The thermal decomposition tem- peratures of blends were found higher than that of pure PS which indicated the stabilizing effects of PVC on PS. The effect varies with the heating rates and the composition of the blends and the phenomenon has been explained due to changing morphology of the blends with com- position and the degradation time which affect the interfacial interaction between the degrading products from the polymer components. The kinetic parameters of the degradation process calculated from a method described by Ozawa have been reported for these blends. Ó 2007 Published by Elsevier Ltd. Keywords: PSePVC blends; Morphology; TGA; DMTA 1. Introduction Polystyrene (PS) is considered as an excellent polymer suit- able for various commercial and domestic applications. In recent times the blending of polymers has gained considerable importance as a cost-effective method [1,2] to improve the physical properties of polymers. Although PS is widely used as a component of blends and in copolymers, not much work is available on its degradation in the presence of other poly- mers. The possibility of interactions between PS or its degrada- tion products and a second polymer in the same environment in the case of polymer blends or graft copolymers, has been exam- ined in few degradation studies in blends. Whereas in some pairs e.g., PS with poly(methyl methacrylate) (PMMA) there is no evidence of interaction during the degradation of blend [3], in other cases, it has been found that the products of deg- radation of one polymer can influence the degradation behavior of the other [4e7]. In some recent studies degradation in PSePVC blends and copolymers has been studied using different techniques [8e 12]. McNeill et al. [8] have studied the degradation in PS/ PVC graft copolymers. They suggested that chlorine radicals from degrading PVC can abstract hydrogen atoms from PS producing polystyryl radicals which undergo further scission and transfer reactions. The styrene production was found to be delayed at higher temperatures, which was ascribed to some modification in the PS structure during degradation. The TGA results indicated a retardation of dehydrochlorina- tion in PVC film containing 50 wt% of PS as compared to that from pure PVC. The degradation results, however, were not related with the resulting morphology of the blends and its effect on the mutual interaction between the phases. * Corresponding author. Tel.: þ965 4985326; fax: þ965 4816482. E-mail address: zahmad@kuc01.kuniv.edu.kw (Z. Ahmad). 0141-3910/$ - see front matter Ó 2007 Published by Elsevier Ltd. doi:10.1016/j.polymdegradstab.2007.02.016 Polymer Degradation and Stability 92 (2007) 1025e1033 www.elsevier.com/locate/polydegstab