Biocomposites with increased dielectric constant based on chitosan and nitrile-modified cellulose nanocrystals.

The motivation of the present work was the preparation of bio-based thin film nanocomposites with improved dielectric properties using modified nanocellulose and chitosan, both materials known to derive from industrial waste. Cyanoethylation of cellulose nanocrystals (CNC) was achieved through a "green" method for the first time. Then, modified CNCs were incorporated into a chitosan (Chi) matrix, obtaining a homogeneous and flexible material with higher dielectric constant due to the high dipole moment of the nitrile functional group. The value of dielectric constant rises with the content of modified CNCs, from a value of 5.5 for pure chitosan at 25 °C and 1 kHz up to a value of 8.5 for the nanocomposite with 50 wt% at the same conditions. These bio-based nanocomposites show an improvement in their dielectric properties compared to pure chitosan and chitosan/unmodified CNC nanocomposites (for which dielectric constant decreases up to 4.5 at 25 °C and 1 kHz) and can be considered for high-temperature applications. Characterization of cyanoethylated cellulose nanocrystals (CN-CNC) and nanocomposites was carried out by infrared spectroscopy (FT-IR), attenuated total reflectance spectroscopy (ATR), atomic force microscopy (AFM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and solid-state NMR and broad band dielectric spectroscopy (BDS). Tensile tests were developed for mechanical characterization.