Microcellular Structure of PP/Waste Rubber Powder Blends with Supercritical CO2 by Foam Extrusion Process

A new approach towards the recycling of waste ground rubber tire (WGRT) powder was demonstrated in this study by introducing the polypropylene/ waste ground rubber tire (PP/WGRT) foaming method by using CO2 as the foaming agent in an extrusion foaming process. The regression models were constructed to study the relationships between the foam structure (i.e., void fraction, average cell size, and cell density) of foamed PP/WGRT blends, the processing parameters (extruder’s die temperature and CO2 concentration), and WGRT content by applying a three-factor central composite design (CCD) statistical approach. The response surface plots generated using the regression models allow the rapid selection of the proper process parameters to obtain microcellular PP/WGRT blends with the desired density and morphology.