CO2-Induced Mechanical Reinforcement of Polyolefin-Based Nanocellular Foams

The effect of CO2‐induced crystallization on the mechanical properties, in particular the yield and the ultimate stresses, of polyolefins is studied. PP and SEBS copolymer blends are used as examples and foamed after sorption of CO2 at temperatures below Tm. CO2 sorption thickens the crystalline lamellae and consequently increases Tm from 160 to 178 °C for both pure PP and PP/SEBS blend systems. Foams with an average cell size smaller than 250 nm retain the ultimate stress at the level of the polymer before foaming, even without the effect of CO2‐induced crystallization. Including CO2‐induced crystallization, the yield and the ultimate stresses of the foam can be improved by 30 and 50% over solid PP and by 22 and 40%, for solid PP/SEBS blends, respectively. The CO2‐induced improvement of the mechanical properties of polyolefin‐based nanocellular foams is studied. Reducing the cell size of foamed plastics to nanoscale allows retention of the ultimate stress at the level of the polymer before foaming. By including CO2‐induced crystallization, the yield and the ultimate stresses of the foam can be significantly improved.