Industrial assessment of recycled steelmaking slag as a sustainable alternative to carbon black in NBR composites

This research assesses the industrial viability of black slag from electric arc furnace (EAF) as an eco-friendlier alternative to carbon black (CB) in nitrile butadiene rubber (NBR) formulations for technical components. Three compounds, at equal filler volume fraction, were prepared: a conventional CB-filled NBR, a fully slag-filled version, and a partial substitution (50 % slag and 50 % carbon black). Rheometric analysis showed that replacing CB with slag does not affect vulcanization kinetics, temperature dependence or activation energy; only the maximum torque (MH) and thus cured-rubber mechanical properties varied. Adding slag slightly lowers material viscosity (reduced minimum torque, ML). Injection molding of O-rings encountered filling problems: coarse slag particles (<= 100 mu m) blocked narrow mold gates (approximate to 50 mu m). By contrast, compression molding of flat plates encountered no processing issues. Mechanical tests revealed that tensile and tear strengths progressively decrease as slag content rises, driven by the slag angular shape and particle size. Tribological trials indicated that while friction coefficients drop with more slag, wear rates increase. ATR-FTIR spectra confirmed that slag does not alter the NBR's molecular structure, and thermal conductivity and glass transition temperature (approximate to-25.5 degrees C) remain unchanged. Notably, slag inclusion enhances thermal degradation resistance. Overall, the 50 % slag formulation strikes the best balance between environmental impact and performance, offering substantial eco-benefits with moderate loss of mechanical strength. Future work should target improved slag size and shape and/or alternative moulding techniques, such as injection-compression, to fully leverage EAF slag's potential as a sustainable, drop-in filler in high-performance elastomers.