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.
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