Recycled Ferromagnetic Fillers Endow Excellent Magnetic Field Tunable Viscosity and Electromagnetic Radiation Shielding within Elastomer Composites

We report the integration of an unconventional filler ferrosilicon nitride (FSN), within two elastomers, to develop composites having concurrent magnetic field-tunable viscosity and electromagnetic radiation shielding capabilities. FSN is a refractory ceramic which possesses a soft ferromagnetic nature and low electrical conductivity at room temperature. Moreover, a porous microstructure and light weight nature enables FSN to disperse uniformly within elastomers, making it an attractive magnetically active filler, a domain that remains unexplored. Recycled FSN, possessing an irregular morphology was integrated at varying parts per hundred rubber within hydrogenated nitrile butadiene rubber (HNBR), and liquid silicone rubber (SR), possessing different values of stiffness. FSN displays good dispersion within the HNBR matrix leading to improved mechanical properties; however, minor agglomeration occurs within the softer SR. The fillers align well with an external magnetic field sweep of 0 <-> 1 T, effectively altering the viscosity values by 42% in the HNBR and 59.3% in the SR. Furthermore, the composites demonstrate excellent electromagnetic radiation shielding across the X and Ku bands. The primary mode of shielding was absorption through resonance in the magnetic particles, with a subdued reflection component. Thus, recycled FSN can be capitalized where functionality should complement sustainability and 3R targets.