Lightweight polypropylene/BaTiO3 composite foams with tunable dielectric constant

Abstract

Lightweight dielectric foam materials with tunable dielectric constant of 2–1 have broad application prospects in the field of Luneburg lens. Expandable polystyrene (EPS) foam is commonly used for fabricating discrete dielectric layers of Luneburg lens, while its temperature resistance and mechanical properties are poor. EPS foam with dielectric constant of >1.5 is also difficult to prepare because of its low expansion ratio. In this work, choosing polypropylene (PP) with better temperature resistance and mechanical properties as polymer matrix, PP/BaTiO3 composite foams are fabricated by subcritical CO2 batch foaming and steam-chest molding. Through the dual regulation of expansion ratio and mold-opening distance, the dielectric constant of PP/BaTiO3 foams can be tunable from ∼1.19 to ∼1.91, with the density increasing from ∼0.14 to ∼0.59 g/cm3. Compared with EPS foams, PP/BaTiO3 foams have lower density under the similar dielectric constant, indicating the weight reduction of polymer dielectric foam materials by introducing high dielectric fillers.