Microcellular Foaming-derived Superlight Ultra-high Molecular Weight Poly(vinylidene fluoride) Foams for Outstanding Thermal Insulation Applications

Poly(vinylidene fluoride) (PVDF) foam has received widespread attention due to its high strength, and excellent combination of flame-retardancy, antibacterial performance, and chemical stability. However, the foaming ability of conventional PVDF is severely limited by its rapid crystallization kinetics and poor melt strength. Although ultra-high molecular weight PVDF (H-PVDF) theoretically offers prolonged melt elasticity favorable for foaming, the extremely high melt viscosity poses substantial processing challenges, and its foaming behavior has remained largely unexplored. To address these issues, this study proposes a novel fabrication strategy combining solvent casting with microcellular foaming to prepare H-PVDF foams. Dynamic mechanical analysis and differential scanning calorimetry reveal that extensive chain entanglements in H-PVDF impose constraints on crystallization and significantly enhance melt strength. By tuning the processing parameters, the distinctive foaming behavior of H-PVDF under various conditions is systematically elucidated. Remarkably, a record-high expansion ratio of 55.6-fold is achieved, accompanied by a highly uniform and fine cellular structure. The resulting H-PVDF foams exhibit a low thermal conductivity of 31.8 mW·m^–1·K^–1, while retaining excellent compressive strength, flame-retardancy, and hydrophobicity. These outstanding properties highlight the great potential of H-PVDF foams as the thermal insulation materials for applications in aerospace, energy infrastructure, and other extreme environments.