Influence Of Co-Rotating Twin Screw Configurations On Polypropylene Foaming

Because of the excellent properties, widespread sources, low costs, Polypropylene became more and more popular in the foam industry. The granules were made by co-rotating twin screw extruder, and were foamed in the batch foaming process with supercritical carbon dioxide. The influences of nucleating agent and screw configurations on the polypropylene foaming were studied in this paper.The experiment of nucleating agent on foaming effect was carried out under different type, granularity and using dosage of nucleating agent. The result showed that:when calcium carbonate was used as the nucleating agent, high integrity of the cell structure, uniform distribution of the cell size were achieved. The foaming effect was better than that of montmorillonite and talc. While the mesh number of the nucleating agent was between 1250 and 10000, the smaller particle size of the nucleating agent, the larger expansion ratio and cell density was obtained. When the mesh number of the nucleating agent is 10000, the expansion ratio was 32.8, the cell density was 3.94×106 cell·cm-3. As the addition amount of nucleating agent was 3 phr, the expansion ratio and cell density was higher than that of 1phr and 5phr.The effect of screw configuration in the melt conveying section on the nucleating agent dispersion and foaming effect was studied in the screw configuration experiment. The result showed that large size particles and poor cell size uniformity was appeared when the TME element and the S element was used, and the expansion ratio of these two elements was 15.16 and 12.46 separately. In the flow field of the three kneading block elements, particle experienced higher shear and were broken intensely. The particle size uniformity was better than that of the three other elements, and perfect cell morphology with uniform cell size and no collapse was obtained. The expansion ratio and cell density of reverse kneading block element was 32.86 and 6.94×106 cell cm-3.