Carbon as a solution for nanocellular foam superinsulation

Abstract

This work demonstrates the substantially improved thermal radiation blocking capability of polymer foams with the utilization of carbonaceous nanoparticles to overcome the limitation of the nanocellular foam's thermal insulation capability to achieve superinsulation. Without carbon, the radiation heat transfer becomes extremely high through thin and transparent cell walls and struts of the low-density nanocellular foams. However, this high radiative heat transfer can be successfully reduced by incorporating multi-walled carbon nanotubes (MWCNTs). The effect of carbon on heat transfer in foams was mathematically modelled and experimentally verified. The model includes contributions of thermal transport through conduction and radiation, while convection is negligible. The effects of MWCNTs on thermal conductivity, refractive index, absorption index, dielectric permittivity and dielectric loss of the solid were studied using two examples of polystyrene/MWCNT and PMMA/MWCNT nanocomposite foams. It was found that, with carbon, the radiation blocking capability is significantly improved and nanocellular foams could achieve superinsulation level through the Knudsen effect. The optimal cellular structure at which heat transfer is minimized was investigated with the aim of manufacturing superinsulation. The foam's total heat transfer decreased while the optimal expansion ratio increased with the filler content, which is preferable for manufacturing high performance insulation with less polymer.