First step toward recycling end-of-life permanent magnets: α-Fe micrometer-sized particles mixed with polypropylene as a model for NdFeB plastic composites

The market for rare-earth (RE)-based permanent magnets (PMs), especially NdFeB, is growing rapidly. However, the criticality of their raw materials poses supply risks, prompting industries to seek alternatives. One promising solution is the recycling of end-of-life (EOL) RE-based PMs as urban mines. This study presents a simple method to produce thermoplastic-based magnetic composites (TPMCs) by melt-mixing micrometer-sized, crushed EOL RE-based PMs, with a printable polymer. These TPMCs are intended as precursors for plastic magnet additive manufacturing. As a model system, micrometer-sized iron (Fe) particles—as Fe is the most abundant element in NdFeB—were combined with polypropylene (PP) to form nearly homogeneous 1x1x1 cm3 cubes. These served as substrates to study the effect of filler content on mechanical and magnetic properties. The work analyses TPMCs with various Fe content, examining how Fe impacts PP crystallization—critical for printability—and how PP affects magnetic behavior. Results show that Fe particles act as nucleating agents, modestly accelerating primary nucleation and overall crystallization. TPMCs display magnetic properties consistent with the soft ferromagnetic nature of Fe, with a linear increase in both saturation magnetization and initial susceptibility as Fe loading increases, reflecting the additive contribution of the micro-ferromagnets to the composite’s magnetic response.