A Non-Isothermal Model to Study the Influence of Blowing Agent Concentration on Polymer Viscosity and Gas Diffusivity in Thermoplastic Foam Extrusion

This fundamental study focuses on the influence of blowing agent on bubble growth during thermoplastic foam extrusion. The extruded molten mixture expands and cools simultaneously when exposed to ambient conditions. The bubble growth is influenced by the concentration-dependent blowing agent diffusion coefficient, transient cooling of the expanding foam, influence of blowing agent on polymer viscosity, and the escape of blowing agent from the surface of the foam. Previous models in the literature do not consider these significant influences. A model is presented accounting for those more subtle effects. In addition, a new experimental technique is described to collect experimental bubble growth data. Predictions of the new model reasonably agree with the experimental data.