Multiscale hollow MnO2 for high-performance thermal insulating polyurethane foams

Polyurethane (PU) foams are widely used as lightweight thermal insulators; however, their broader application is limited by the inherent trade-off between thermal insulation performance and foam-induced mechanical deterioration. Although various fillers have been introduced to regulate cellular structure and thermal transport, conventional solid fillers often form continuous heat-transfer pathways or increase foam density, resulting in limited improvement in thermal insulation while further compromising mechanical integrity. In this study, hollow MnO 2 -based fillers were incorporated into PU composite foams to simultaneously enhance thermal insulation and mechanical performance through structural and interfacial engineering. The hollow MnO 2 particles improved filler dispersion and acted as heterogeneous nucleation sites during foaming, leading to reduced cell size and a more densely distributed cellular structure. As a result of the hollow structure, refined cellular morphology, and enhanced interfacial interaction, the surface-modified MnO 2 /polyurethane (SMO/PU) composite foam achieved a low thermal conductivity of 0.018 W m -1 K -1 . In addition, the composite foam exhibited a tensile strength of 1.18 MPa, indicating that MnO 2 incorporation effectively mitigates the mechanical weakening typically associated with foamed structures. Thermogravimetric analysis further showed that MnO 2 incorporation did not significantly alter the thermal degradation behavior of the PU matrix while maintaining sufficient thermal stability. These findings demonstrate that hollow inorganic fillers can effectively regulate cellular structure and heat-transfer pathways, providing a viable strategy for designing lightweight polymer foams with improved thermal insulation and mechanical reliability.