Lightweight, strong, flame-retardant PVDF/PMMA microcellular foams for thermal insulation fabricated by supercritical CO2 foaming

An innovative method of improving PVDF foaming behavior and foam performance by blending with polymethyl methacrylate (PMMA) was devised, and lightweight, strong, flame-retardant foams with wider foaming window and excellent thermal insulation performance were successfully achieved. PMMA not only improves CO2 uptake and melt viscoelasticity, but also decreases PVDF crystallinity and increases melting range of PVDF crystals. Compared to PVDF foams, expansion ratio of the blend foams increased from 21.9 to 31.2, and effective foaming window was expanded from 3.6 °C to 17.4 °C. Thanks to the blend foams' high expansion and PMMA's strong infrared absorption ability and high rigidity, thermal conductivity and compression modulus of the foams are 33.85 mW m−1 K−1 and 3.51 MPa, respectively. Moreover, the blend foams also show a lower heat release rate and favorable flame retardancy.