Polypropylene/talc foams with high weight-reduction and improved surface quality fabricated by mold-opening microcellular injection molding

Microcellular injection-molded part can save materials usage and reduce energy con-sumption. However, the part molded by conventional microcellular injection molding often encounters problems of a limited weight-reduction and poor surface quality. Focusing on these problems, this paper adopted mold-opening microcellular injection molding and talc as nucleating agent to prepare foamed polypropylene (PP) part. Different PP/talc composites were obtained by twin-screw extruder compounding, and their crys-tallization and rheological behaviors were investigated. The results show that talc can significantly promote PP crystallization, and the crystallization temperature changes slightly with talc content. However, the viscoelasticity of PP melt cannot be enhanced by the added talc. Then, the effects of packing time, mold-opening distance and talc content on the foaming behavior of PP were studied. It is found that a high packing pressure for long time can effectively eliminate the cells generated in melt filling process, thus a transparent part is obtained. With increasing packing time, the unfoamed skin layer of the part increases and cell size decreases. With increasing mold-opening distance, cell density increases. At a same mold-opening distance, cell density remarkably increases because of the heterogeneous nucleation of talc, thus cell size decreases. When talc content is 10 wt.% and weight-reduction of the part is 62.1%, the average cell size is 56.5 mm and the cell density reaches 1.54 x 10(7) cells/cm(3). Because the high packing pressure is employed in the mold-opening microcellular injection molding, the surface quality of the part is improved. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

The study examined the preparation of foamed polypropylene parts using mold-opening microcellular injection molding with talc as a nucleating agent. Talc was found to promote PP crystallization but did not enhance its viscoelasticity. High packing pressure can eliminate cells, improving surface quality, while cell density and size are influenced by packing time and mold-opening distance.