High Melt Strength Polypropylene with Wide Molecular Weight Distribution Used as Basic Resin for Expanded Polypropylene Beads

The high melt strength polypropylene (HMSPP) is fabricated by direct polymerization through controlling the species and ratios of the external electron donors in the ZieglerNatta catalyst system at different reaction stages. The polypropylene exhibits wide molecular weight distribution and higher melt strength. The expanded polypropylene (EPP) beads are prepared by the above HMSPP through an autoclave-based batch process. The effects of melt strength on the cellular morphology of EPP are investigated by scanning electron microscope and melt strength meter, respectively. Results indicate higher melt strength facilitates the control of the foaming process and the cellular structure compared with a commercial propylene homopolymer such as T03. The bimodal cell structure is obtained with the single foaming agent CO2 in both of the EPP beads from HMSPP and commercial polypropylene.