A semi-empirical model for density gradient in microcellular thermoplastic foams

In microcellular plastics, produced by the solid-state batch method, an integral solid skin and a core with graded porosity can be created by allowing absorbed gas to diffuse from the surface of a saturated specimen prior to foaming. In this article a semi-empirical model is proposed to predict the local density of microcellular foam as a function of dissolved gas concentration. To this end, Henry's law is applied on available experimental data for polystyrene-nitrogen system. The resultant spatial variation of mass density would be interesting for analyzing engineering structures made of microcellular plastics.