THE USE OF ONLINE RHEOMETRY TO CHARACTERIZE POLYMER MELTS CONTAINING PHYSICAL BLOWING AGENTS

The application of on-line rheometry is considered with particular ref erence to polymer melts plasticized by physical blowing agents. Experi mental investigations were performed on polystyrene containing 0-15 wt % of HCFC-142b or HFC-134a or 0-5 wt% of carbon dioxide at various tem peratures and shear rates. It was shown that results could be used to indicate the solubility limit and related to the glass transition temp erature. Rheological modelling and data fits were compared indicating that a time/temperature-composition (i.e. relative concentrations of p olymers/blowing agent mixtures) superposition principle was valid. The model was extended to consider effects using a semi-crystalline polym er (polypropylene). It was concluded that an on-line return-to-stream process control rheometer could satisfactorily measure and monitor mix tures of polymers and physical blowing agents used in thermoplastic fo am extrusion. Appropriate viscosity measurements could be directly lin ked to a number of critical variables.