Amino Acids as Sustainable Alternatives to Allergenic Sulfur Vulcanization Accelerators for Carbon Black-Filled Nitrile Rubber

Acrylonitrile–butadiene rubber (NBR) is one of the most widely used elastomers in healthcare products owing to its excellent mechanical performance, chemical resistance, and durability. However, conventional sulfur vulcanization systems rely on accelerators such as tetramethylthiuram disulfide (TMTD), 2-mercaptobenzothiazole (MBT), and 1,3-diphenylguanidine (DPG), which are associated with allergenic reactions and potential toxicological concerns. The replacement of these substances with naturally derived compounds represents an attractive strategy for developing safer and more sustainable elastomeric materials. In this work, three naturally occurring amino acids, L-cystine, L-cysteine, and creatine, were investigated as alternative health-friendly sulfur vulcanization accelerators in NBR compounds filled with carbon black. Their influence on curing characteristics, crosslink density, morphology, mechanical performance, viscoelastic behavior, thermal stability, and thermo-oxidative aging resistance of NBR composites was systematically evaluated and compared with that of conventional accelerator systems. The amino acids effectively promoted sulfur crosslinking, although their activity depended strongly on molecular structure. Cystine and creatine exhibited the most promising performance, providing cure characteristics and mechanical properties comparable to those achieved with commercial accelerators while maintaining satisfactory thermal stability and aging resistance of carbon black-filled rubber composites. These findings demonstrate that naturally occurring amino acids constitute promising bio-derived and non-allergenic alternatives to conventional sulfur vulcanization accelerators and may contribute to the development of safer elastomeric materials with reduced reliance on potentially hazardous or allergenic substances.