Lightweight and High Mechanical Properties of In Situ Poly(ethylene terephthalate) Reinforced Polypropylene Composite Foams by Chemical Foam Injection Molding

The issue of saving energy and reducing environmental pollution has attracted enormous interest in developing lightweight plastic materials. As a cost-effective technology for manufacturing porous plastic products, chemical foam injection molding (CFIM) has become one of the most widely used processes in industry fields, especially for automotive. However, it is still challenging to fabricate high-performance plastic cellular products for structural application. Herein, a facile, efficient, and easy-to-scale-up strategy was reported to produce lightweight and strong foamed polypropylene (PP) composites by combining in situ polyethylene terephthalate (PET) fibrillation (INF) and CFIM technologies. First, the INF composite was prepared using a co-rotating twin-screw compounding and melt spinning. SEM micrographs showed nanoscale reticular PET fibrils with φ231 nm were achieved and distributed uniformly in the PP matrix due to the particle-induced PET domain elaboration. Rheological analysis and DSC combined with online optical microscopy observation revealed that PET fibrils pronouncedly improved viscoelasticity and crystallization rate, respectively. Compared with PP foam, the INF foam showed a uniform and refined cell structure with 69 μm cell size and 7.3 × 10⁵ cells/cm³, respectively. Moreover, more than 12% of the average weight loss rate was achieved for the INF foamed sample. Due to the refined cellular morphology, as well as the synergistic effect of PET fibrils in the skin layer and Talc particles distributed in the cell wall, the yield strength and impact strength of INF foam were 38 and 112% higher than that of PP foam. Thus, the results gathered in this study demonstrated a promising future in offering lightweight porous components with improved mechanical strength.