Fabrication of High Expansion Microcellular Injection-Molded Polypropylene Foams by Adding Long-Chain Branches

Herein, 10-fold expansion ratio foams were successfully fabricated for the first time by a core-back foam injection molding (FIM) technique using a newly developed long-chain branching polypropylene (LCBPP). Different rheological curves were investigated to distinguish the strain hardening behavior and melt strength of the LCBPP from isotactic polypropylene (iPP). Fast scanning chip calorimetry (FSC) results revealed that the long-chain branches could increase the crystallization temperature even at fast cooling rates. The FIM of LCBPP could notably not only reduce the cell sizes but also increase the cell densities through the capability of LCBPP to stabilize cells and prevent cells from coalescence. Furthermore, the foam processing window of manufacturing 10-fold expansion foams was significantly broadened for LCBPP foams. This study revealed that the introduction of long chain branches is a good approach to fabricate high expansion microcellular foams for different potential applications such as construction and transportation.