Microcellular foams simultaneous reinforcing and toughening strategy of combining nano-fibrillation network and supercritical solid-state foaming

Foams with excellent mechanical performance are extremely valuable, as playing a key role in structural materials. However, it is still a significant challenge to simultaneously strengthen and toughen foam materials. In this work, a novel strategy combining nano-fibrillation network and supercritical carbon dioxide (scCO2) solidstate foaming was proposed as follows: 1) In designing micro-scale cellular structure, chain extension and fibrillation technologies were synergistically adopted to improve the matrix viscoelasticity for cell stability, scCO2 solid-sate foaming was then adopted to improve cell nucleation and cell growth. The combination of the above technologies helps to obtain a microcellular foam with large expansion ratio and small cell size; 2) In designing nano-scale hierarchical structure of crystalline and multiphase, flexible fibrils were dispersed in cell walls to compensate for matrix's brittleness and hence increased the foam impact strength, the crystals in cell walls improved the bending strength of cell walls and hence increased the foam compression strength. Herein, the obtained microcellular foam has simultaneous improvements in compression strength from 1.7 MPa to 2.7 MPa and impact toughness from 0.26 kJ/m2 to 0.46 kJ/m2 while maintaining a low foam density of 0.13 g/cm3.