Nanohydroxyapatite embedded blends of ethylene-co-vinyl acetate and millable polyurethane as piezoelectric materials: dielectric, viscoelastic and mechanical features

We report the piezoelectric, dielectric and dynamic mechanical features of nanohydroxyapatite (nHA) embedded ethylene-co-vinyl acetate (EVA)/millable polyurethane (MPU) elastomer blends. The EVA/MPU/nHA systems were prepared by two-roll milling followed by compression moulding. The piezoelectric features were probed by dynamic contact electrostatic force microscopy (EFM).The neat EVA/MPU blend was not found to exhibit ferroelectric properties. However, upon incorporation of nHA, butterfly loops of EFM amplitude signals as well as complementary hysteresis curves were obtained, confirming the introduction of ferro-piezoelectric properties. The ferro-piezoelectric features were found to be improved with an increase in nHA loading which recorded highest signals for 8 parts per hundred parts of rubber (phr) loaded composites. The fabricated devices generated a peak voltage of 4.02 V and 4.89 V respectively with 6 phr and 8 phr nHA loaded composites. Electrical properties such as dielectric constant, volume resistivity and loss factor as well as dynamic mechanical properties were examined. The viscoelastic features of the systems support the reinforcing feature with filler loading. TEM analysis of the composites indicated a uniform distribution of filler particles in the blend matrix, complementing the observed ferro-piezoelectric, dielectric and dynamic mechanical properties. The simultaneous modulation of piezoelectric and viscoelastic properties is a preferred feature for fast-responsive dielectric elastomers for their applications in various piezoelectric devices. (c) 2020 Society of Chemical Industry