Crosslink density–property relationship in NBR rubber vulcanizates: Influence of cure system and accelerator type on RGD resistance with RSM-based formulation optimization

Nitrile butadiene rubber (NBR) is widely used in high-pressure sealing applications, where rapid gas decompression (RGD) failure remains a critical challenge. This study investigates the effects of curing system type (SEV, EV) and secondary accelerator (TMTD, ZDEC, ZDBC) on the mechanical properties and RGD resistance of NBR. The RGD testing was caried out in nitrogen gas environment at 80°C and 80 bar. This procedure was executed over 8 cycles for a duration of 7 days. The mechanical properties including hardness, tensile strength and elongation at break were performed for all samples. The SEM-EDS analyses were evaluated for selected NBR vulcanizates. In addition, response surface methodology (RSM) was employed to identify the optimal range of sulfur and TMTD content required to simultaneously achieve desirable RGD resistance, tensile strength, and elongation at break. The optimized formulation was experimentally validated, with the measured mechanical properties including tensile strength and elongation of NBR vulcanizates. Among the secondary accelerators, the ZDBC showed the best RGD resistance, followed by ZDEC and TMTD. Beyond a certain density, the vulcanized network became stiffer and RGD resistance decreased as hardness increased from 74 to 83 Shore A. The vulcanizates with lower hardness and higher elongation resist the better RGD testing, because the rubbery network could realigned around blisters and slow the micro-crack growth. The RSM approach effectively reduced the number of required experiments. These findings provide practical guidance for selecting the appropriate secondary accelerator and optimizing NBR formulations for high-pressure sealing applications.