Dielectric Properties of Sustainable Nanocomposites Based on Zein Protein and Lignin for Biodegradable Insulators

Two types of lignin, alkali lignin and lignosulfonic acid sodium salt, are blended into thermoplastic zein through melt mixing in order to develop biodegradable insulator materials for multifunctional applications in electronics. The effects of lignin type and content on the dielectric properties of the resulting bio-nanocomposites are investigated. The results indicate that, by modifying the structural arrangement of the zein with the use of lignin, it is possible to obtain bio-nanocomposites characterized by tunable dielectric properties. The bio-nanocomposites containing low amounts of lignin derivatives exhibit extensive protein structural changes together with a modification of the dielectric properties compared to the pristine thermoplastic zein. Changes in the dielectric properties of these systems are also observed to change over time, indicating a loss of plasticizer, as is evident by a decrease in the glass-transition temperature. At high frequencies, the resulting values of the dielectric permittivity and of the loss tangent demonstrate that the bio-nanocomposite can be used as biodegradable dielectric material for transient (temporary) electronics.