Study on the aging behavior and mechanism of nitrile rubber composites in combined radiation-thermal environments

This contribution investigates the aging property changes and mechanism of nitrile rubber (NBR) under the combined radiation-thermal environments in the N₂ atmosphere. Aging resulted in a decrease in elongation at break from 309.01 % to 64.74 %, an increase in modulus of elasticity from 3.84 MPa to 9.09 MPa, and a slight increase in thermal stability. The crosslink density increases and the mass loss of the sample is reduced, while the chemical structure of the sample surface is almost intact. By gas-phase infrared spectroscopy, the irradiation aging-induced gases from NBR were also analyzed, including CO₂, CO, and alkanes (CH₄, C₂H₆, C₃H₈). This indicates that chain scission and pendant group removal also take place, whereas chain breaking primarily occurs at the macromolecular chain end. The above degradation reactions and the decomposed additives account for the generated trace amount of small molecule gas products. These findings suggest that the primary aging mechanisms of NBR are the cross-linking of macromolecular chains and additive loss. Furthermore, radiation and thermal have a synergistic effect on NBR aging, and this effect has a threshold temperature that is clearly between 50 °C and 70 °C. The synergistic effect of additive cleavage is only apparent at temperatures above 65 °C under radiation-thermal conditions.