Unveiling lightweight and high impact tough polypropylene foams through compatibilized in situ fibrillation integrated chemical foam injection molding

Lightweight and robust polypropylene foams are essential for resource efficiency; however, the poor foaming ability of polypropylene remains a significant challenge in developing high-performance foams. This study proposes a scalable and cost-effective strategy that integrates in situ fibrillation reinforcement with chemical foam injection molding. Nanofibrillar polypropylene/polyamide 6 composites were fabricated via twin-screw compounding and melt spinning. For the first time, polyamide 6 nanofibrils were observed to exhibit selective dispersion with distinct morphologies in the skin and core layers of in situ fibrillation injection-molded samples. The incorporation of maleic anhydride-grafted polypropylene induced a 70% reduction in polyamide 6 nanofibril diameter. Rheological and crystallization analyses demonstrated that polyamide 6 fibrils significantly enhance polypropylene viscoelasticity and crystal nucleation rate, thereby improving foamability. Compared to polypropylene foam, in situ fibrillation composite foam exhibited a refined and homogeneous cellular structure, with a cell size of 61 µm and a cell density of 5.8 × 10⁵ cells·cm⁻³ in the core layer, alongside elongated cells in the skin layer. The synergistic effects of polyamide 6 nanofibrils and maleic anhydride-grafted polypropylene resulted in a 15.4% weight reduction and 100% enhancement in impact strength compared to polypropylene foam. This work provides new insights into developing lightweight, highperformance industrial porous materials.