Comparison of nanoclay and carbon nanofiber particles on rheology of molten polystyrene nanocomposites under supercritical carbon dioxide

The effects of nanoparticles and high‐pressure carbon dioxide (CO₂) on shear viscosity of polystyrene (PS) were studied. Master curves of PS, PS + 5 wt % carbon nanofibers (CNFs), and PS + 5 wt % nanoclay (Southern Clay 20A) without CO₂ were created based on parallel‐plate measurements. The results showed that addition of nanoparticles increased the viscosity of the neat polymer. Steady‐state shear viscosity of PS in the presence of CO₂ and nanoparticles was measured by a modified Couette rheometer. The effect of supercritical CO₂ on these systems was characterized by shift factors. It was found that under the same temperature and CO₂ pressure, CO₂ reduced the viscosity less for both PS‐20A and PS‐CNFs than neat PS. Between the two types of nanoparticles, CNFs showed a larger viscosity reduction than 20A, indicating a higher CO₂ affinity for CNFs than 20A. However, the advantage of CNFs over 20A for larger viscosity reduction decreased with higher temperature. A gravimetric method (magnetic suspension balance) was used to measure the excess adsorption of CO₂ onto CNFs and nanoclay, thus, CO₂ showed a higher affinity for CNFs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010