Development and Characterization of Polyurethane foam Reinforced with Hollow Silica Nanospheres

Rigid polyurethane foam (PUF) composites reinforced with hollow silica nanospheres (HSNSs) are fabricated, and their insulation performance and mechanical strength are investigated. It is observed that HSNSs are successfully embedded into the nano-thickness cell wall of the PUF to interrupt the heat transfer path inside the wall structure. With the addition of catalysts and ethylene glycol of optimal concentrations, cell walls of submicron thickness can be fabricated, despite the increased resin viscosity and hindered curing reaction caused by HSNSs. Although the cell walls are thicker and more irregular compared to pure PUF, the thermal conductivity coefficient (TCC) of the PUF nanocomposite matches that of pure PUF at 0.020 W/m·K, indicating that the HSNS-embedded cell wall material has a lower TCC value. Long-term TCC increases over 5, 14, and 45 days are reduced by 26%, 19%, and 13%, respectively. The compressive strength of the PUF composites is 17% higher than that of pure PUF by reinforcing the effect of the HSNSs inside polymeric matrices of cell walls. This study underlines the potential of super-insulation performance of PUF composites including HSNSs, achieved through Knudsen diffusion in the nanopores and enhanced phonon scattering at the nano-shells.