Viscosity studies of poly(DL-lactic acid) in supercritical CO2

The effect of supercritical CO2 on the viscosity and activation energy to viscous flow of PDLLA is investigated, using a high pressure parallel plate rheometer, over a range of temperatures (50140 degrees C) and pressures (512 MPa). The Cross model is fitted to the data to enable calculation of the zero shear viscosity and critical shear rate. A significant decrease in the viscosity is observed on increasing both variables; however, at high temperatures, the pressure effect becomes negligible. An increase in the critical shear rate is also observed on raising the pressure, indicative of a reduction in the relaxation time of the polymer. Manipulation of the Arrhenius equation shows a reduction in the activation energy to viscous flow as the pressure is increased. Together, these results show that the melt processing temperature of PDLLA can be reduced in the presence of supercritical and high pressure CO2. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012