Enhancing Compression Set Resistance of Nitrile Rubber Composites Through a Hybrid Mixture of Sustainable Filler Lignin and Carbon Black

Minimizing compression set in industrial rubber products such as O-rings, seals, and gaskets is one of the most desirable features. Nitrile rubber (NBR) is an oil-resistant polar rubber which is intentionally selected as the matrix to mix with polar lignin to reduce the time for preparation. In this study, a hybrid mixture of carbon black and lignin is incorporated as filler in the rubber matrix. The NBR–lignin–carbon black composite is prepared by dry rubber compounding in a laboratory internal mixer. The maximum filler loading is limited to 30 parts per hundred rubber (phr), and the composite is tested for various mechanical properties by varying the amount of lignin and carbon black. The curing time obtained for lignin-filled samples is within the acceptable limits of the rubber industry. The minimum value of the compression set is obtained at a loading of 25 phr of lignin in the hybrid mixture. Furthermore, the inclusion of lignin did not reduce the mechanical properties such as hardness and tensile strength considerably. Morphological study shows good dispersion of lignin in the rubber matrix up to 25 phr of loading. Replacement of carbon black with lignin through industrially viable dry rubber compounding is a significant observation that points out to scalability and sustainability.