WoodBark-Based Films as Electrical Insulators withUltralow Dielectric Constant and Loss Factor

Dielectric polymers, particularly thermally stable synthetic types, play a crucial role in capacitors, circuit boards, insulators, and high-frequency devices. However, they also contribute significantly to electronic waste, making up approximately 20% of the 74.7 million metric tons of e-waste generated each year. Unfortunately, less than 18% of this waste is properly recycled, posing serious risks to human health and the environment. To address these challenges, we present a circular approach to fabricating biobased dielectric structures with ultralow dielectric constant and dielectric loss factor. Our method utilizes forestry residues derived from birch bark, after the extraction of high-value bioactive compounds. Specifically, we process the thermally stable, lignin-rich fibers in the residual bark through partial dissolution and cross-linking to produce “birch dielectric (BD)” films. These films exhibit exceptional dielectric properties, with dielectric constant (D<i>k</i>) and loss factor (D<i>f</i>) values as low as ∼1.8 and ∼0.002, respectively, outperforming or matching the requirements of modern electrical insulators, including advanced polymer blends based on polyimides. In addition to their functional performance, BD films demonstrate remarkable mechanical and thermal stability, photothermal conversion capabilities, strength retention after cycling, and biodegradability. These findings, supported by experimental data and simulation studies of intermolecular interactions, highlight the potential of BD films as a sustainable and efficient alternative to conventional dielectric materials.