The effect of micro‐fibrillated cellulose upon the dielectric relaxations and DC conductivity in thermoplastic starch bio‐composites

Abstract

AbstractThermoplastic starch (TPS) bio‐composites were prepared with natural rubber latex (NR) and/or cellulose microfibers of variable size, as reinforcements. The relaxation processes are investigated via broadband dielectric spectroscopy in a broad temperature and frequency range. By means of the electric modulus formalism, the dynamic glass‐to‐rubber transition process of the starch‐rich regions in TPS (α‐relaxation), and the presence of water molecules at the interfaces between the TPS matrix and the fillers (MWR‐IP), is observed and discussed. The dielectric behavior and energy storage were found to be affected by the presence of the aforementioned water molecules, hindering the polarizability of the samples due to hydrogen bonding with the hydrophilic constituents. Following the temperature dynamics of the α‐relaxation, good adhesion between the TPS matrix and the cellulose microfibers was revealed, although the addition of natural rubber latex microparticles has the opposite effect attributed to their hydrophobic character. Finally, the dc conductivity was estimated from the ac dielectric spectra with a new mathematical formulation that is introduced here, and showed nonlinear temperature dependence for all the samples under study. The purpose of this study is to investigate the use of biodegradable eco‐friendly thermoplastic starch bio‐composites as dielectric materials for capacitor applications. Microfibrillated cellulose and/or natural rubber latex are employed as reinforcements and insight upon their dielectric relaxation behavior is provided by broadband dielectric spectroscopy in a broad temperature and frequency range.