The effect of talc on cell nucleation in extrusion foam processing of polypropylene with CO2 and isopentane

The effect of talc on cellnucleation of polypropylene (PP) foam was investigated. Branched high-melt strength PP was used to reduce bubble coalescence during extrusion foam processing. When isopentane was used as a blowing agent, bubble nucleation was dominated by the talc concentration, and the isopentane content (lid not affect the cell density very much. By contrast, when CO 2 was used as a blowing agent, both talc and CO 2 concentrations determined the cell-population density. However, the effect of talc on nucleation was significant only when the CO 2 content was low. In addition, the maximum achievable cell density was not improved by talc when CO 2 was used whereas the maximum cell density was dramatically improved by talc when isopentane was used. The experimental results indicate that the heterogeneous bubble nucleation mechanisms in plastic foam processing with CO 2 are fundamentally different from those in the processing with a long-chain blowing agent such as isopentane.