Achieving low-thermal conductivity and high beta phase in PVDF/PMMA blend foams via low-pressure microcellular foaming

Polyvinylidene fluoride (PVDF) foam exhibits wider applications than traditional foams such as polyethylene and polystyrene foams due to its good corrosion resistance, flame retardant and wide operating temperature range. However, PVDF is difficult to foam and rigorous operating conditions including high pressure and high temperature were unavoidably adopted to prepare PVDF foams. Herein, microcellular PVDF foam was successfully fabricated with the combination of adding polymethylmethacrylate (PMMA) and batch foaming at mild processing condition. Compared to the pure PVDF foam with a low-expansion-ratio of 1.1 times, the PVDF/PMMA (70/30) blend foam showed an expansion ratio as high as 20 times together with a small cell size of approximately 5 mu m. Additionally, the prepared PVDF/PMMA blend foam exhibited a low-thermal conductivity (0.039 w m(-1) k(-1)) and high content of beta-phase crystal (95%), which shows promising application in areas like electronic devices, thermal insulation and packaging materials.