Rheological behavior of mixtures of polystyrene with HCFC 142b and HFC 134a

The processes for the production of thermoplastic foams, often in the shape of extruded sheets or boards, are largely dictated by the rheology of the mixture of a polymeric matrix with a blowing agent. This paper focuses on the rheological behavior of mixtures of polystyrene (PS) and physical blowing agents (HCFC 142b and HFC 134a), examined using a commercial on-line rheometer mounted on an intermeshing co-rotating twin-screw extruder. The PS resin was extruded while the blowing agent was injected at high pressure and various compositions. The extent of plasticization was found to be dependent on the blowing agent concentration and its type. The effects of type of blowing agent, composition, pressure, shear rate and temperature on the rheological response were measured. These variables were incorporated into a generalized mathematical model, which described the viscosity of the PS/blowing agent mixture over the studied range.