Extrusion of polypropylene foams with hydrocerol and isopentane

An experimental investigation was conducted to research the cell nucleation behavior in the extrusion foam processing of polypropylene (PP) using hydrocerol and isopentane. While the hydrocerol and isopentane are considered to function as the nucleating agent which determines the cell-population density and as the blowing agent to control the volume expansion ratio respectively, both agents affected the cell-population density. In addition, synergistic effects of these agents on the cell density were observed. In foam processing with hydrocerol, a higher cell-population density was noted at lower processing pressures and at higher polymer flow rates. This phenomenon is of interest since the cell density, in general, increases as the processing pressure increases when only a physical blowing agent is used in the foam processing. The experimental results indicate that the nucleation in the foam processing with hydrocerol is governed by a heterogeneous nucleation mechanism; also, the quality of the mixing of the polymer and the agents, as well as the amount of gas lost during the plastication of the pellets in the barrel, exerts a strong influence on the resulting cell density.