Polypropylene/waste ground rubber tire powder foams: A study of the relationship between processing and structure using supercritical carbon dioxide

In this study, processing-structure relationships in polypropylene (PP)/waste ground rubber tire powder (WGRT) foams made using supercritical carbon dioxide as a physical blowing agent were investigated. In order to investigate the relationship between structure and properties of PP/WGRT foams, it was necessary to make samples with a wide range of controlled structures. For this reason, a systematic investigation of the relationship between processing conditions and structure was performed based on a statistical experimental design. Regression analysis was conducted on the data and expressions were developed to quantify the relationships between structural parameters and processing conditions. The samples were saturated with carbon dioxide at high temperature and high pressure and the saturated specimens were expanded during the pressure-quench process. The importance of the individual processing parameters was determined. Statistical analysis of data showed that saturation temperature was the most important factor determining cell size, cell density and relative density. By controlling the foaming conditions, PP/WGRT samples having the same foam density and different cell size or having the same cell size and different foam density were produced.