Microcellular injection molding of polymers: a review of process know-how, emerging technologies, and future directions

Microcellular injection molding (MIM) is a fast-growing technology with high potential to become an innovative and green manufacturing platform for fabrication of porous, polymer-based products. In this review article, the process know-how of MIM in terms of blowing agent and cell structures is discussed first. Then, some emerging and complementary processing technologies that incorporate MIM are introduced. The technologies presented here include core-back foaming, supercritical fluid-laden pellet injection molding foaming technology (SIFT), subcritical gas assisted processing (SGAP), and the in-situ fibrillation process. By employing a special mold design and novel processing steps, gas-laden pellet extrusion, alternate and cost-effective gas sources, and/or in-situ fibrillation, these technologies aim to improve the performances and quality of the resulting foamed parts. Finally, the current challenges along with future directions of MIM, such as surface quality improvement, nano-cellular structures, and accurate simulations, are presented.