The effects of physical aging on the quasi-static and dynamic viscoelastic properties of Nitrile Butadiene Rubber

The effect of physical natural aging of nitrile butadiene rubber (NBR) on the degradation of its viscoelastic properties was investigated in both time and frequency domains. Quasi-static and dynamic mechanical tests were conducted on virgin and naturally aged NBR specimens to analyse their structural integrity for damping applications. The generalized Maxwell model was used to fit the Dynamic Mechanical Analysis (DMA) experimental data to determine the deterioration of the constitutive viscoelastic parameters with age. Fourier transform infrared spectroscopy (FTIR) was used to investigate the aging of functional groups in NBR. Thermogravimetric Analysis (TGA) was performed to estimate the changes in the activation energy and frequency factor with age to estimate the shelf life of the NBR. The structural damping characteristics of the NBR were analyzed using an unconstrained sandwich beam with NBR and aluminum as the base material. According to experimental results, the mechanical properties deteriorated by approximately 43%. With age, constitutive viscoelastic properties, such as the storage modulus (52%), loss modulus (66%), loss factor (31%), and damping coefficient (31.25%) deteriorated. The relaxation strength and modulus decreased by 41.2% and 43.9%, respectively. The activation energy at higher conversion rates decreased from 529.77 kJ mol−1 to 280.15 kJ mol−1 for aged NBR. After two years, the damping ability of the aged NBR sandwich beam decreased by 8, 34, and 22% at the first three natural frequencies compared to virgin NBR sandwich beam.