Effects of mixing and processing on the viscosity of polycarbonate blends with low molar mass liquid crystal

Abstract

This research was to investigate the effects of mixing and processing on the viscosity of Polycarbonate blends with low molar mass thermotropic liquid crystals, Cyclohexylbiphenyl- cyclohexane (CBC33). Two different molecular weights of Polycarbonate used in this work had melt flow indecies of 19.9 and 23.1 g/10min (300 ํC / 2.16kg.), denoted as PC-2600 and PC-2405, respectively. Stirring melt mix was utilized in the first step blending of Polycarbonates and CBC33 with content at 0.1, 0.2, 0.4, 0.8 and 1 percent by weight. Viscosity of the resulting blends were investigated and compared with the base Polycarbonate. The results showed that 0.2 percent by weight of CBC33 is the suitable concentration because at higher concentration the effects of CBC33 on the viscosity were less significant.To further study the effects of mixing methods on the viscosity, mixing by stirring melt mix at 0.2 percent by weight of CBC33 were selected. By comparing stir meltmixing with mixing by single screw extruder and mixing by twin screw extruder at the same percent composition of CBC33, the results showed that the viscosity of the PC-2600 and PC-2405 blends prepared by single screw extruder had the lowest viscosity values. In addition, in most cases viscosities of Polycarbonate blends were lower than that for pure Polycarbonate.This work also included preliminary study of the possibility of recycling Polycarbonate blends with CBC33. Viscosities of the runner from injection molded product were studied. The results revealed that CBC33 had slight effects on viscosities of PC-2600 and PC-2405 products at low shear rate levels. It should be interesting to further measure the viscosity of the blends by capillary rheometer at higher shear rates.