Lightweight and strong glass fiber reinforced polypropylene composite foams achieved by mold-opening microcellular injection molding

Abstract Microcellular injection molding (MIM) is a flexible, efficient, and environmentally friendly foaming technology to prepare plastic foams with complex shapes. However, MIM product suffers from deteriorated mechanical properties, limited weight reduction, and poor surface appearance. In this study, mold-opening microcellular injection molding (MOMIM) was used to prepare high-performance polypropylene/glass fiber (PP/GF) composite foams. GF was used to improve the foaming behavior of PP and to enhance the mechanical properties of foamed samples. Firstly, the crystallization and rheological behavior of PP and PP/GF were analyzed. Afterwards, the foaming behavior of PP and PP/GF in microcellular injection molding process were investigated. Finally, the mechanical properties of PP and PP/GF foams were measured and discussed. It was found that PP/GF composite foams show a rather uniform cellular structure than the pure PP foams. Moreover, PP/GF composite foams exhibit much higher strength and stiffness than the pure PP foams. Furthermore, MOMIM can significantly enhance the flexural modulus of the molded samples. For the foams with an expansion ratio of 1.5-fold, by adding 20 wt% GF, the tensile strength and modulus can be increased by 60% and 50%, respectively. For the PP/GF composite with 20 wt% GF, the foamed sample prepared by MOMIM can have a flexural modulus nearly 200% higher than that of the unfoamed sample. Thus, MOMIM PP/GF composites show a promising perspective in providing lightweight and strong plastic products that can be widely used in automotive, electronics, and appliances.