Valorization of ripe banana peels and cocoa pod husk hydrochars as green sustainable “low loss” dielectric materials

Abstract

The banana and cocoa crops are relevant worldwide and tons of their residues do not enter the industrial value chain. With this in mind, it is imperative to find alternative uses for these residues that could lead to novel and sustainable applications in diverse fields, such as consumer electronics. Lignocellulosic residues can be hydrothermally carbonized to produce a solid fraction called hydrochar. In this work, the dielectric characteristics of ripe banana peels and cocoa pod husks hydrochars are explored. Hydrothermal carbonization (HTC) treatments were carried out at two temperatures (150 °C and 210 °C) and three HTC times (2 h, 4 h, and 6 h). The materials were characterized electrically using a Semiconductor Analyzer under frequency swepts of 1 KHz to 1 MHz. Cocoa pod husk hydrochars (CHH) showed less variability in relative permittivity values compared to ripe banana peel hydrochars (BPH). The relative permittivity values of CHH ranged between 9.83 and 10.29 (150 °C) and 8.25–9.39 (210 °C), while for BPH, these values ranged between 6.89 and 14.14 (150 °C) and 6.39–8.77 (210 °C). In addition, the loss tangent values of CHH varied from 0.034 to 0.041 (150 °C) and from 0.036 to 0.038 (210 °C), while in BPH, these values varied from 0.056 to 0.091 (150 °C) and from 0.046 to 0.051 (210 °C). In both cases, HTC produced highly stable materials with low loss tangent values, making them good candidates for insulation and possessing good dielectric properties that can be further processed for downstream applications in the electronics industry.