Strong PP/CaCO ₃ nanocomposite foams with refined cellular morphology and enhanced surface appearance achieved by mold-opening microcellular injection molding

Polypropylene (PP) is one of the most commonly used thermoplastics in automotive field owing to its low cost and excellent properties. Microcellular injection molding was an environmental-friendly foaming technique which can fabricate large geometrically complex microcellular structured components. PP foams fabricated by conventional microcellular injection molding (MIM) suffers from poor mechanical properties and surface quality. In this study, we prepared high strength and excellent surface quality PP based foams by adding nano-CaCO 3 fillers and using mold-opening microcellular injection molding process. Firstly, PP and nano-CaCO 3 were melt blended using twin screw extruder to prepare PP/CaCO 3 nanocomposites. The crystallization, as well as viscoelastic properties of nanocomposites were analyzed according to DSC and rheological experiments. Afterwards, MIM and MOMIM were conducted to fabricate PP/CaCO 3 nanocomposite foams and then the mechanical performance of MIM and MOMIM foams were compared. Furthermore, optical microscope and white light interferometer were utilized to analyze the surface roughness of foams under various foaming processes. The results showed that nano-CaCO 3 fillers greatly refine the cellular morphology by improving PP’s viscoelasticity and crystallization. In addition, MOMIM process shows outstanding advantages in optimizing cellular structure, improving mechanical properties and surface quality of PP based foams.