New Poly(phenylene oxide)/Polystyrene Blend Nanocomposites with Clay: Intercalation, Thermal and Mechanical Properties Rajkiran R. Tiwari, 1 Kartic C. Khilar, 2 Upendra Natarajan 1 1 Polymer Science and Engineering Division, National Chemical Laboratory, Pune 411008, India 2 Department of Chemical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, India Received 8 June 2007; accepted 6 November 2007 DOI 10.1002/app.27743 Published online 29 January 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: We present the first study and results on the preparation and characterization of montmorillonite clay filler based polymer blend nanocomposites of the mis- cible poly(phenylene oxide)/polystyrene blend. Interca- lated nanocomposites, prepared by a melt-processing method with 2–6 wt % commercially available organically modified sodium montmorillonite, have been characterized with wide-angle X-ray diffraction, transmission electron microscopy analysis, thermal analysis (thermogravimetric analysis and differential scanning calorimetry), and me- chanical tensile tests. We show that nanocomposites can be successfully prepared in a batch mixer at temperatures much below the conditions conventionally used for this blend without organic degradation. Thermal stability is enhanced by nanoscale hybrid formation. The level of intercalation (change in the d-spacing) does not change with the clay loading. Better dispersion of clay in the blend matrix has been observed at a low level of clay con- tent. The nanocomposites show improved tensile modulus (by 31%) in comparison to the blend, whereas the tensile strength (stress at break) and elongation decrease in the presence of the filler with an increase in the clay loading. The Halpin–Tsai model is able to predict the modulus of the nanocomposites in very good agreement with the experimental data. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 1818–1828, 2008 Key words: mechanical properties; nanocomposites; orga- noclay; poly(phenylene oxide); polystyrene; thermal prop- erties INTRODUCTION Research in the field of polymer-layered silicate nanocomposites has gained tremendous importance in recent years as a result of enhancements in ther- mal stability and mechanical properties for such advanced materials. 1–4 The pioneering work of researchers at Toyota led to the discovery of nano- scale polymer–clay nanocomposites as candidates for light-weight-material applications. 5,6 Most commonly known thermoplastic polymers have been investi- gated either in an exploratory manner or in depth for their structure and morphology, thermal behav- ior, mechanical properties, dynamic behavior, and so forth. At this time, very few publications in the literature have reported nanocomposites of polymer blends and clay. Li and Shimizu 7 looked at poly(phenylene oxide) (PPO)/polyamide 6 (PA6) blend nanocompo- sites by melt mixing. They obtained a significant decrease in the domain size of the dispersed PPO phase in the presence of organoclays. However, an increase in the organoclay loading (>5 wt %) led to the formation of a cocontinuous morphology. 7 Gelfer et al. 8 prepared nanocomposites of the immiscible polystyrene (PS)/poly(methyl methacrylate (PMMA) blend by a melt-mixing process, using commercially available dimethyl dioctadecyl ammonium modified montmorillonite. The presence of the organoclay par- tially compatibilizes the immiscible PS/PMMA blend by reducing the average microdomain size (from 1–1.5 lm to ca. 300–500 nm). 8 The area of polymer blend–clay nanocomposites is open to considerable research with the possibility of providing very inter- esting fundamental and practical progress. The structure–property relationships in the case of advanced materials formed by polymer blends and clays can be even more challenging with respect to property variations, control, and tailoring with molecular parameters and design. Tensile strength, thermal stability, and flame retardancy are desirable properties for machine and appliance housings. PPO and PS are amorphous and Correspondence to: U. Natarajan (u.natarajan@ncl.res.in or upen.natarajan@gmail.com). Contract grant sponsor: Council of Scientific and Indus- trial Research of India (through a graduate senior research fellowship to R.R.T.). Journal of Applied Polymer Science, Vol. 108, 1818–1828 (2008) V VC 2008 Wiley Periodicals, Inc.