Abstract
Rheological data, at elevated temperature and pressure, for pure polystyrene, pure acrylic and polystyrene / acrylic blends containing R134a are contrasted with similar data for polymers containing R22 and R142b blowing agents. The variation of polymer melt viscosity with blowing agent concentration (R22, R142b and R134a) is interpreted in terms of equilibrium blowing agent solubility and molecular plasticization effects. Equilibrium solubility data for all blowing agents are presented.
Information on the variation of extruded foam density with blowing agent content for pure polystyrene, pure acrylic and polystyrene / acrylic polymer blends is described. Inclusion of modest quantities (∼10% w/w) of acrylic into the polystyrene is shown to allow the manufacture of reduced density foams using R134a blowing agent. Inclusion of the acrylic also stabilizes extruder pressure profiles and facilitates easier plant operation.
The observed reduced foam density, both with polymer composition and blowing agent content, and easier extruder operation are explained in terms of blowing agent solubility and secondary relaxation processes associated with the acrylic component.
