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The foaming behavior of high‐melt strength polypropylene (HMS‐PP) and HMS‐PP/Cloisite 20A nanocomposites (PPNC) was studied in a batch process. PPNCs with 2, 4, 8, and 10 wt% clay were prepared in a twin screw extruder. The morphology of the nanocomposites was studied using XRD and TEM. Subsequently, foaming experiments were conducted using supercritical CO2 as the blowing agent in a batch process, and foams with cell sizes varying from the sub micrometer to the micro meter range were prepared. The effect of variation in saturation pressure and temperature, foaming temperature, foaming time, and quench temperature was determined experimentally. Dynamic rheological measurements were conducted to relate the influence of nanocomposites morphology with foam cell growth and nucleation. Extensional rheological measurements were also conducted to detect the presence of strain hardening effect at the foaming temperatures used in the experiment. It was found that the nucleation efficiency of clay reduces with increase in clay loading. Also, the optimum amount of filler for generation of fine celled foams was found to be around the percolation threshold of the polymer. The extended strain hardening effect shown by the polymer in presence of clay plays an important role in stabilizing foam cell sizes. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

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Born more out of necessity, the "awareness-attitude" of our society has caused the channeling of technological developments toward immediate economic and ecological benefits. The polymer industry has a newfound interest in fillers from industrial by-products and other waste materials having potential "recyclability." This new class of fillers includes fillers from natural sources (e.g., natural fibers), industrial by-products (e.g., saw dust, rice husks), and a recent entry in the form of rice husk ash-an industrial waste material-obtained by burning rice husks. Their recyclability and utilization has become a major driving factor in their acceptance and employability, as well as low cost and abundant availability. However, their performance in composites and processing requirements has hindered their applicability within the current economic framework. The present article reviews the performance of rice husk ash, or silica ash, in polymeric composites. Silica ash, composed mainly of silica, is obtained after burning rice husks and is a major industrial waste material in rice growing countries. Optimism surrounds the application of silica ash as a potential filler in a variety of polymeric composites, however, its performance has been limited by its inherent characteristics. This paper emphasizes the need for better characterization of silica ash to obtain an in-depth understanding of its behaviour with the view to identifying suitable modifications to improve its performance as a filler. It is emphasized that poor understanding of silica ash as a