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Synergistic Effects of Modification with Nanoclay and Polystyrene on the Foaming Behavior of a Random Copolymerized Polypropylene

Microcellular polypropylene/polystyrene/nanoclay (PP/PS/nanoclay) composites were processed in a continuous extrusion foaming system using supercritical CO2 as the foaming agent. Neat PP foam showed quite a broad distribution of cell sizes and thick cell walls. Under the same foaming conditions, nanoclay and PS were introduced in the foaming process of PP. Consequently, foams with uniform cell size distribution, reduced cell size of 10~30 μm and enhanced cell-population density of 2.16×108 cells/cm3 were obtained. The heterogeneous nucleation of PS and nanoclay dramatically increased the nucleation rate, decreased the nucleation time interval, and hence facilitated an almost instantaneous growth of cell size. This method also provided new insight into the mechanism of improving the foaming performance of PP.