Highly filled biochar/ultra-high molecular weight polyethylene/linear low density polyethylene composites for high-performance electromagnetic interference shielding

Highly filled (up to 80 wt%) biochar/ultra-high molecular weight polyethylene (UHMWPE)/linear low density polyethylene (LLDPE) composites with excellent electromagnetic interference (EMI) shielding performance were successfully prepared using mass-producing extrusion and hot-compression methods. Carbonizing bamboo charcoal (BC1100) at 1100 °C resulted in a graphite-like structure leading to good electrical conductivity and a high specific surface area. The surface morphology and crystalline structure, as well as the thermal, mechanical, electrical, and EMI shielding properties of the composites, were characterized. The addition of BC1100 enhanced the Young's modulus, tensile strength, and hardness of the composites, but reduced the ductility. Most importantly, the BC1100 biochar remarkably improved the electrical conductivity and EMI shielding effectiveness (SE) of the composites. In particular, the composite with 80 wt% BC1100 exhibited a conductivity of 107.6 S/m, one of the highest values among reported conductive polymer composites fabricated by melt processing, and a very high EMI SE of 48.7 dB (99.998% attenuation) at 1500 MHz. The specific EMI SE of the 80 wt% BC1100 composite was 39.0 dB cm³/g, nearly four times higher than that of copper (10 dB cm³/g). These results suggest a new, scalable way of effectively utilizing renewable biochar in conductive polymer composites, especially for EMI shielding applications.