Microstructure and rheologic development of polypropylene/nano‐CaCO3 composites along twin‐screw extruder

Abstract

AbstractPolypropylene/nano‐calcium carbonate (PP/nano‐CaCO3) composites were prepared by using an intermeshing, co‐rotating twin‐screw extruder. Two different screw configurations, denoted by screws A and B, respectively, were employed. The former provided high dispersive mixing and the later provided high dispersive and distributive mixing. Effect of mixing type on microstructure and rheologic development of nanocomposites was investigated by taking samples from four locations along screws A and B. Transmission electron microscopy results show that in the sample at the exit of extruder, the percentage of nano‐CaCO3 particles with the equivalent diameter lower than 100 nm along screws A and B is 66.5 and 79.0%. respectively. Moreover, for screw B, the number‐averaged diameter at four sampling locations is smaller than that for screw A. This means that the distributive mixing, provided by screw B, favors the size decrease of nano‐CaCO3 in the PP matrix. In addition, rheologic results show that the decrease of complex viscosity for the nanocomposites is deeply related to turbine mixing elements, which provides distributive mixing. The online melt shear viscosity of the nanocomposite at the exit of extruder prepared by screw B is lower than that of pure PP. This is related to the dispersion of nano‐CaCO3 in PP matrix. Finally, the relationship between rheologic properties and microstructure was analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009