Particulate reinforced PC/PBT composites. I. Effect of particle size (nanotalc versus fine talc particles) on dimensional stability and properties

Abstract The effect of particle size (nanotalc versus fine talc) on the dimensional stability, mechanical properties, and morphology of composites consisting of polycarbonate (PC), poly(butylene terephthalate) (PBT), and talc was investigated at various talc loadings. It was found that, by using nanotalc as opposed to fine talc particles, the level of talc reinforcement could be reduced from 6 to 1 wt% without sacrificing the dimensional stability, i.e. coefficient of linear thermal expansion and shrinkage of injection‐molded plaques, or flexural modulus of the PC/PBT/talc composites at a PC‐to‐PBT blend ratio of 60/40 by weight or greater. Further benefits included a 14% increase in flexural strength, 120% increase in the tensile toughness and 3% reduction in the density of the PC/PBT/talc composites. The improved stiffness is attributed to the higher aspect ratio (diameter/thickness of the platelets) of nanotalc (20–25) relative to that of the fine talc (5–10). An increase in the flexural modulus of the PC/PBT/talc composites with an increase in nanotalc loading was observed even though there was evidence of significant degradation in the molecular weight of the PC/PBT matrix. Possible degradation in the molecular weight of the PC/PBT matrix was supported by a significant reduction in the storage modulus and complex viscosity, at high frequencies of the composites generated with the nanotalc relative to that of the unfilled matrix. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.