Janus Nanosheet–Assisted CO 2 Foaming of Polypropylene

Polypropylene (PP) foaming using CO 2 as a physical blowing agent is challenged by the limited CO 2 solubility in PP, inefficient heterogeneous nucleation, poor additive dispersion, and insufficient melt strength. Herein, we report a Janus nanosheet (JNS)‐assisted foaming strategy based on interfacial engineering. JNS feature an octadecyl‐functionalized face designed to improve filler‐matrix compatibility and an amine‐functionalized face designed to promote CO 2 uptake. These nanosheets are generated in situ by fragmentation of Janus hollow microspheres during screw extrusion with PP. The dispersion state, crystallization and melting behavior, CO 2 uptake, and rheological properties of the composites were systematically investigated. A JNS loading of 0.6 wt% provides the most favorable balance between bubble nucleation and cell growth, yielding a relatively uniform cellular structure (50 ± 10 µm) and a high cell density (6 × 10 8 cells/cm 3 ). Comparative experiments using JNS containing a higher amine content, JNS with reduced PP compatibility, and hydrophobic silica without amine groups indicate the combined effects of surface chemistry, CO 2 uptake, and PP–filler interactions on foaming. The composite expanded beads were molded into foams with enhanced mechanical properties and further fabricated into full‐size foldable stools, demonstrating the product‐scale processability of the JNS‐based formulation.