Synergistic improvement of piezoelectric properties of PVDF/ CaCO3/montmorillonite hybrid nanocomposites

Poly (vinylidene fluoride), PVDF, based hybrid nanocomposites (micro-CaCO3 + Montmorillonite (Mt)) containing varying amounts of CaCO3 (30-40 parts (wt.)) were developed via co-rotating twin-screw extrusion and were subjected to uniaxial stretching. A systematic study was performed to investigate the effect of micro-CaCO3 content of the hybrid filler and subsequent uniaxial stretching at various draw ratios, R (4-5), on the mechanical, dielectric, electrical and piezoelectric properties of hybrid nanocomposites. For the as-extruded hybrid nanocomposites (without post-extrusion stretching), both dielectric properties and DC volume resistivity improved significantly, probably due to the enhanced charge trapping capability of Mt. in the presence of CaCO3 micro-filler. Similarly, hybrid nanocomposite containing 40 parts of CaCO3 and 3 parts (wt.) of Mt. presented the maximum piezoelectric coefficient, d33 of 7.4 pC/N. For stretched nanocomposites, the volume resistivity and dielectric properties of hybrid nanocomposite containing 40 parts of CaCO3 and 3 parts of Mt. decreased gradually with R presumably due to its porous structure, as observed in SEM. However, stretched hybrid nanocomposites consistently exhibited enhanced piezoelectricity where the highest d33 value of 30.6 pC/N at R of 5 was obtained, which is attributed to the almost 100% β phase content and dipolar orientation induced by stretching and subsequent poling.