Rheological changes in Co₂ impregnated polystyrene reinforced with nanoclays

The addition of small quantities of plate-like nanoclay can substantially increase the polymer melt viscosity, while adding dissolved gases such as CO₂ can reduce the viscosity of a polymer melt. The combined effect of nanoclay and CO₂ on polymer melt rheology was investigated for an extrusion process. The shear viscosities of polystyrene/CO₂/nanoclay melts were measured using an extrusion slit die rheometer with a backpressure regulator. Our results show, without the presence of CO₂, that the viscosity of the nanocomposite increases with nanoclay loading. However, when the nanocomposite melt is swelled by CO₂, the nanoclay acts to reduce viscosity compared to the pure porystyrene/CO₂ system. A possible explanation is that a significant amount of CO₂ is adsorbed on the surface of the nanoclay to lubricate the flow due to the existence of surface modifier and a unique nanoclay particle layering structure.