Biodegradable multiphase poly(lactic acid)/biochar/graphite composites for electromagnetic interference shielding

High performance electromagnetic interference (EMI) shielding materials that are of lightweight, thin, and easy to -design are extremely important for future portable and wearable electronic and telecommunication devices. Achieving such functionalities using environmentally friendly and biodegradable materials is becoming increasingly important and adds on even more value. Herein, we demonstrate two- and three-phase composites of poly(lactic acid), graphite and biochar that can be produced in large quantities and practically in any shape or form by applying facile twin-screw extrusion and subsequent hot-pressing methods. The developed conducting polymer composites with a wide range of filler loading level enable excellent shielding with an effectiveness beyond 30 dB at K-band frequency range (18-26.5 GHz) using very thin films (0.25 mm). The corresponding specific shielding effectiveness 890 dB cm(2) g(-1) is particularly high among biodegradable shielding materials. The outstanding performance is due to scattering and thus increased propagation distance of electromagnetic waves in the multiphase composite medium. The presented novel environmentally friendly and biodegradable materials are not only promising for wearables and portable devices but also for other applications, where size and weight matters such as in aeronautics, astronautics and robotics.