Hybrid Nano-Additive Systems for Improved Fire Resistance in NBR-Based Elastomers

Elastomers such as acrylonitrile–butadiene rubber (NBR) are widely used in high-performance applications, yet their intrinsic flammability poses serious safety challenges. This study introduces hybrid nano-additive systems designed to enhance the fire resistance of NBR-based elastomers through the synergistic action of organic, inorganic, and biopolymeric components. The developed formulations incorporate melamine (M), melamine polyphosphate (PM), casein (K), and keratin recovered from industrial waste (P), combined via conventional and hybrid compounding methods. Vulcanization was carried out at 160°C, with optimal curing determined rheometrically. The composites were extensively characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), microcalorimetry, Fourier-transform infrared spectroscopy (FTIR), optical microscopy, and mechanical testing (tensile strength, hardness, aging resistance). The results revealed that hybrid systems, particularly melamine polyphosphate or casein combined with keratin (PPM or PK), reduced heat release rate and combustion efficiency by more than 20% compared to single-component systems. The addition of nanoscale fillers further delayed thermal degradation and improved char stability. This work demonstrates a synergistic flame-retardant mechanism in NBR elastomers, integrating thermal shielding, char formation, and endothermic decomposition pathways. Moreover, the use of biodegradable waste-derived additives enhances the sustainability profile of the materials. The developed hybrid nano-additive systems offer a promising pathway toward eco-efficient, flame-retardant elastomers for applications in sectors with elevated fire hazard, such as automotive, aerospace, and electronics.