As wireless devices and high-frequency electronics become more widespread, materials that prevent electromagnetic interference are increasingly important. Many conductive shields work primarily by reflecting incoming waves, which can create unwanted secondary radiation. Polymer composites offer a lightweight and versatile alternative, and biochar provides a renewable source of conductive carbon. Yet untreated biochar has limited conductivity and can bond poorly with polymers. Adding more filler may improve shielding but can also weaken a composite through aggregation. Researchers therefore need ways to help a material absorb electromagnetic waves while preserving the strength and toughness required for use.
A study (DOI: 10.48130/scm-0026-0026) published in Sustainable Carbon Materials on 28 August 2026 by Deli Zhang's & Qingfa Zhang's team, Anhui Agricultural University, reports that a layered polymer structure incorporating treated bamboo biochar improved both absorption-dominant shielding and mechanical performance.
The team first converted bamboo powder into biochar through heating under nitrogen, then applied a brief pulse of flash Joule heating to restructure its carbon framework. They treated the resulting particles with a silane compound, APTES, to improve their interaction with the polymers. Next, they coated biochar onto films of poly(butylene adipate-co-terephthalate) and assembled those films with polylactic acid in alternating layers, concentrating the filler near the interfaces. To identify the contribution of each step, they compared composites containing untreated biochar, flash-heated biochar and flash-heated, surface-modified biochar. They also tested a nonlayered blend with the same filler loading.
Mechanical tests showed that the layered composite containing modified biochar had a tensile strength of 25.5 megapascals, 81% higher than the unfilled polymer blend. Its toughness rose by 173% to 2.68 megajoules per cubic meter, while its elongation at break increased from 11.5% to 24.7%. Microscopy of fractured samples showed rougher surfaces, consistent with a more winding crack path and improved stress distribution. Electrical measurements found a conductivity of 12.8 siemens per centimeter in the optimized composite, compared with 1.7 siemens per centimeter for the layered version containing untreated biochar. The researchers then measured shielding across the X-band frequency range of 8.2 to 12.4 gigahertz. The optimized material averaged 36.7 decibels of shielding effectiveness; the nonlayered comparison with the same filler loading averaged 7.5 decibels. Analysis of shielding components attributed 30.8 decibels to absorption and 5.9 decibels to reflection. The team linked these results to conductive pathways formed by the treated biochar and to layered interfaces that lengthened the paths of electromagnetic waves through the material.
Together, the findings show how filler treatment and layer arrangement can address two common obstacles in biochar-based shielding materials: weak polymer interfaces and a loss of mechanical performance as conductivity increases. The results come from laboratory-made composites tested under specified conditions, so performance in finished products remains to be established. Even so, the study offers a design route for materials that combine effective electromagnetic shielding with the strength and toughness needed in practical components.