Polyvinyl alcohol–sodium niobate–cellulose nanofiber composites: dielectric and electric study

Polyvinyl alcohol (PVA)–sodium niobate (NN)–cellulose nanofiber (CNF) composite films with different weight percentages of cellulose nanofibers (2%, 4%, 6%, 8% and 10% (all by weights)) were synthesized by a solution casting technique and their dielectric and electrical properties were studied. The structure and microstructure of these composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The surface morphology of the PVA–NN–CNF composite films shows the uniform dispersion of cellulose nanofiber and sodium niobate particles into the polyvinyl alcohol matrix. The incorporation of CNF into the PVA–NN composites improves their dielectric and electrical properties and is investigated in a wide range of frequencies from 10² to 10⁶ Hz. The percolation theory was used to explain the dielectric properties of PVA–NN–CNF composites and the percolation threshold value of f_CNF = 5.4%. These three-phase composites with 6% (by weight) of CNF exhibit the maximum dielectric constant (~ 102.14), minimizing dielectric loss (~ 1.2), and higher AC conductivity at 10² Hz. The AC conductivity of PVA–NN–CNF composites follows Jonscher’s power law, and their mechanical properties improve with an increase in CNF filler concentration. The PVA–NN–CNF composite films, due to their improved dielectric and mechanical properties, are highly promising for flexible energy storage applications.