XNBR

XNBR, short for extra nitrile rubber, is a class of nitrile rubber (NBR) grade with higher acrylonitrile content and a peroxide-crosslinked network. Increasing the ACN fraction enhances oil and heat resistance at the expense of flexibility, making XNBR stiffer than standard NBR grades. The term is used by several elastomer suppliers to designate high-ACN, peroxide-cured NBR; it is distinct from hydrogenated nitrile rubber (HNBR).

ACN content in XNBR typically ranges from 45 to 60 percent. The peroxide cure improves thermal aging, compression set, and mechanical strength, while hardness and modulus are higher than regular NBR. Elongation and low-temperature flexibility are reduced, and performance at very low temperatures is inferior to HNBR.

Processing involves conventional rubber methods (molding, extrusion, calendaring) followed by vulcanization at temperatures around 170 to 190 C. Peroxide systems may be used with coagents, such as trimethylolpropane trimethacrylate, to adjust crosslink density and aging resistance.

Applications include seals, gaskets, and O-rings for automotive, hydraulic, and industrial equipment that operate in petroleum-based fluids and high-temperature environments.

XNBR offers higher oil and heat resistance than standard NBR but is more costly and less flexible at low temperatures than HNBR; selection depends on service conditions such as temperature, fluids, and required mechanical performance.