Fabrication of microcellular epoxidized natural rubber foam with superior ductility by designable chemical and physical crosslinking networks

Abstract

Though the introduction of microcells improves the impact strength of polymer, it weakens the tensile properties since microcells act as defects, leading to stress concentration and crack initiation during stretching. Reducing the cell size to micro/nano-scale is a facile strategy to eliminate the stress concentration. Herein, we propose supercritical CO2 assisted post-vulcanization approach to fabricate microcellular epoxidized natural rubber-SiO2 foam (f-ENR-SiO2) with high ductility. The designable chemical and physical crosslinking networks facilitated by vulcanization and SiO2 increase the complex viscosity and storage modulus of ENR, while did not induce second nucleation. These effects reduced the cell size to 1 µm and endowed f-ENR-SiO2 with 600% elongation at break and high cell structure stability (the cell structure stays intact without deformation after 250 stretching cycles), far superior to those of the reported microcellular foams. Overall, this study adopted superimposed crosslinking networks to fabricate flexible microcellular rubber foam with excellent ductility.