Facile preparation of high dielectric flexible films based on titanium dioxide and cellulose nanofibrils

A series of high dielectric composite films based on low-cost and eco-friendly titanium dioxide (TiO2) and cellulose nanofibril (CNF) was prepared under a facile condition. The relative dielectric constants (er) and dielectric loss ( $$ \tan\updelta $$ ) were studied as the function of frequency and filler content. The er of CNF/TiO2 composite film was 19.51 (at 1 kHz) with a relatively low dielectric loss. Compared with pure CNF films (er = 6.92 at 1 kHz), the er of the composite film was improved about three times with the dielectric loss increased slightly. The effects of TiO2 addition and hot-press treatment on microstructure, thermal stability, and dynamic mechanical properties of the composite films were also analyzed. It was found that the addition of TiO2 particles reduces the cellulose–cellulose bonding so generates more pores in the films, which has significant impacts on both dielectric and physical strength properties.