THE EFFECT OF TALC ON CELL NUCLEATION IN EXTRUSION FOAM PROCESSING OFPOLYPROPYLENE WITH CO2 AND ISOPENTANE

The effect of talc on cell nucleation of polypropylene (PP) foam was i nvestigated. 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 conce ntration, and the isopentane content did not affect the cell density v ery much. By contrast, when CO2 was used as a blowing agent, both talc and CO2 concentrations determined the cell-population density. Howeve r, the effect of talc on nucleation was significant only when the CO2 content was low. In addition, the maximum achievable cell density was not improved by talc when CO2 was used whereas the maximum cell densit y was dramatically improved by talc when isopentane was used. The expe rimental results indicate that the heterogeneous bubble nucleation mec hanisms in plastic foam processing with CO2 are fundamentally differen t from those in the processing with a long-chain blowing agent such as isopentane.