Hollow Polystyrene Microspheres via Seeded Emulsion Polymerization for Thermal-Insulating Waterborne Polyurethane Coatings

Energy conservation in buildings has become a crucial approach to alleviating the energy crisis and reducing carbon emissions. Thermal insulation coatings are one of the effective methods for energy conservation in buildings. In this study, hollow polystyrene microspheres (HPMs) with varying particle sizes and enhanced thermal insulation performance were synthesized via seeded emulsion polymerization combined with alkali swelling. By adjusting the initiator content, core particle sizes were controlled between 142 and 354 nm, yielding HPMs with particle sizes ranging from 364 to 550 nm and cavity diameters from 127 to 370 nm. At a 40 wt% HPMs-0.775 loading, the composite coating exhibited enhanced solar reflectance (98.1% ± 0.7%) due to the synergistic effects of light reflection and thermal insulation from the hollow interiors. The coating's average transmittance was 6.5% ± 1.3%, and its average reflectance reached 43.1% ± 1.4%. The thermal conductivity of the coating (0.1098 ± 0.0056 W/m K) was found to be significantly lower than that of all other tested compositions.