Time domain NMR evaluation of thermal and thermochemical aging of nitrile rubber on crosslinking and mechanical properties

Abstract

This study investigates the impact of aging on nitrile rubber (NBR) compositions under thermal and thermochemical aging conditions. The effects of aging were assessed using the 1H Double Quantum Time Domain NMR (DQ-NMR) technique, providing molecular-scale insights into average cross-link density, spatial heterogeneity, and network inelastic defects. The aging's influence on the macroscopic mechanical properties of NBR, including hardness, elongation, and stress at break, known to be closely related to cross-linking, was examined. It was observed that temperature-induced aging affected NBR differently based on the acrylonitrile content and solvent absorption capacity. 1H Double Quantum Time Domain NMR provided evidence of increasing heterogeneous cross-linking, which created a denser network structure. The changes in mechanical properties during aging were consistent with the NMR analyses, providing valuable insights for understanding, customizing, and predicting the service life of a specific O-Ring based NBR formulation.