Upcycling steel industry waste into waste-derived barium hexaferrite for flexible magnetic natural rubber composites

Barium hexaferrite (BaFe 12 O 19 or BaF) is a hard ferrite with high coercivity and strong magnetization. In this work, flexible magnetic rubber composites were developed by incorporating waste-derived BaFe 12 O 19 (W-BaF) filler, synthesized from steel industry waste, into natural rubber (NR) at loadings of 0–60 phr. The vulcanization characteristics, mechanical behaviors, and magnetic properties of the NR composites were evaluated and compared with those of NR composites containing commercial BaFe 12 O 19 (C-BaF) filler. It was found that both W-BaF and C-BaF powders showed a plate-like hexagonal morphology. However, differences in particle size and morphology between W-BaF and C-BaF powders resulted in distinct dispersion behaviors of the fillers within the NR matrix. Consequently, the NR/BaF composites containing W-BaF filler exhibited differences in vulcanization characteristics, mechanical behavior, and magnetic properties compared with those containing C-BaF filler. Although the addition of W-BaF filler enhanced the magnetic properties of NR, its effect was less pronounced than that of the C-BaF filler. This finding suggests that a higher loading of W-BaF filler may be necessary to achieve the desired magnetic performance in flexible magnetic rubber composites for practical applications. Notably, this work found that the NR composites containing W-BaF exhibited better retention of tensile properties during thermal aging than those containing C-BaF. These findings demonstrate the feasibility of upcycling locally available steel industry waste into BaFe 12 O 19 filler through local synthesis and processing, providing a waste valorization strategy for developing magnetic NR composites with potential applications as bonded permanent magnets in refrigerator gaskets and small motors.