Microcellular nanocomposites based on millable polyurethane and nano-silica by two-step curing and solid-state supercritical CO2 foaming: Preparation, high-pressure viscoelasticity and mechanical properties

Abstract

The cell structure of microcellular millable polyurethane/nano-silica composites prepared by combining the solid-state supercritical CO2 foaming with the two-step curing were investigated in detail according to the high-pressure viscoelasticity of pre-cured polyurethane. The complex viscosity and storage modulus of pre-cured polyurethane saturated under supercritical CO2 increased with improving the crosslinking network induced by either pre-curing or nano-silica. Moreover, the raised crosslinking density could depress the CO2 diffusion and thus the reduction of the viscosity and modulus. It was shown that the matrix viscoelasticity impacted the cell morphology in different ways as the cell diameter was varied significantly. The compressive hysteresis results showed that the energy absorption of millable polyurethane elastomer was enhanced after the introduction of microcells. The tensile strength of millable polyurethane nanocomposite foam decreased with increasing the cell diameter, and displayed a linear relationship with cell diameter on a double logarithmic scale.