Sandwich-Structured Polypropylene/Polyurethane Composite Foam with High Thermal Insulation for Infrared Radiation Absorption

With the increasing demand for green buildings and energy conservation, high-performance insulation foam materials with comprehensive properties will become the focus of research and development while also facing certain challenges. This study developed a Polypropylene/Polyurethane/Polypropylene (PP/PU/PP) sandwich foam via chemical foaming and nonsolvent-induced phase separation, with PP foam as outer layers and PU foam as the core. This unique structure enhances insulation performance by reducing the solid content to decrease phonon conduction, increasing gas conduction, minimizing the size of foam units to suppress convection, and reducing radiative heat transfer. Under the condition of an expansion ratio of only 3.71, its thermal conductivity drops significantly to 51.27 mW/(m·K). The PP outer layers effectively shielded the PU core from moisture and air, significantly improving the moisture resistance. Incorporating PTFE nanoparticles optimized the PP foam's microporous structure and boosted mechanical strength, increasing the tensile modulus to 321 MPa. This scalable approach offers a strategy for the preparation of low foaming ratio and high thermal insulation performance foam.