Millefeuille-inspired biomass alternate multilayer composite, for excellent absorption-dominated, broadband EMI shielding and joule heating

The development of biomass electromagnetic interference (EMI) shielding materials with low cost, low reflection(R-value), and high shielding efficiency is promising but also challenging. Inspired by the alternate structure of a millefeuille, we propose an alternating assembly approach for conductive and magnetic layers. Employing sustainable bamboo fibers (BF) and biodegradable polylactic acid (PLA) as raw matrix, the magnetic and conductive layers were fabricated by compositing copper-plated BF (Cu@BF) and iron-plated BF (Fe@BF) with PLA, respectively. By alternately stacking magnetic and conductive layers and followed by hot pressing, the high EMI SE and low R-value biomass multilayer composite with "multi-(absorption-reflection-reabsorption)" structures were obtained. The performance of different alternating layers (3/5/7/9 layers) was studied, and a linear correlation between layer number, SE, and R-value was established. The results demonstrate that increasing the alternate layer number could readily tune the SE in the X-band from 45.02 dB (3-layer) to 80.2 dB (9-layer) and reduce Rmin from 0.40 to 0.25. Furthermore, the 9-layer composite exhibits approximately 75 dB SE in 1–18 GHz, simultaneously realizing high efficiency, low reflectivity, and broadband shielding. Notably, its excellent conductivity also provides reliable Joule heating performance. The shielding and thermal features of the composite highlight its potential in construction and smart housing heating applications.