Interfacial stabilizing and reinforcing effects of silsesquioxane-based hybrid Janus molecules in extrusion supercritical CO2 foaming of polypropylene

High-melt-strength (HMS) polypropylene (PP) has enabled easy supercritical-CO2 (scCO2) foaming of PP. However, producing microcellular PP foams via simple scCO2 extrusion still remains challenging, whereas macrocellular with high expansion ratios (ER) generally exhibit poor mechanical strengths. In this study, to simultaneously enhance both ER and compressive strengths foams, a type low-cost Janus molecules, heptaisobutyl open-cage silsesquioxane (HOS), is incorporated into HMS-PP. Since HOS PP-philic groups partially condensed cage that relatively CO2-philic, it could diffuse like surfactant the PP-CO2 interface during stabilise cells in their growth stage reinforce cell surface upon solidification. The effect validated X-ray Photoelectron Spectroscopy. Moreover, 1 wt% HOS, PP/HOS foam offer 38 % improvement, 23 density reduction, 20 strength increase over neat foam. also slightly improve extensional viscosity melt at ≤1 loadings reduce shear by acting as lubricant. This approach provides economically viable materials design guideline for alleviating ER-compression trade-offs polymer foams.