Investigation on the blooming behavior of additives in nitrile butadiene rubber at elevated temperature

The degradation of rubber performance in service environments is closely associated with the blooming behavior of additives in the rubber. This study investigates surface precipitates and changes in tensile properties of nitrile butadiene rubber (NBR) after storage at 85 degrees C in air. The morphology, elemental composition, phase composition, and functional groups of the precipitates were analyzed by scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, and fourier transform infrared spectroscopy. Based on the morphology of internal rubber particles and precipitates and variations in the Zn/C mass ratio (ERZn), the reaction between zinc oxide and stearic acid in rubber under long-term thermal environment was determined. Four stages of blooming for the mixture of zinc oxide and zinc stearate were inferred, and the impact of the blooming on the degradation of tensile properties of NBR was established. A dramatic decrease in the elongation at break (delta k) of NBR was correlated with the blooming of zinc stearate and its correspondingly weakened plasticizing effect.Highlights The core-shell structured mixture of ZnO and Zn(St)2 bloomed onto the surface of nitrile butadiene rubber. The ratio of mass percentages of Zn to C evaluated the blooming process of additives. The migration and blooming process of precipitates were divided into four stages. The decrease in elongation of the rubber was attributed to the blooming of Zn(St)2. The core-shell structured mixture of zinc oxide and zinc stearate bloomed onto the surface of nitrile butadiene rubber after thermal aging 85 degrees C for 130 days. The blooming process of mixtures was driven by the thermal stress generated in the reaction between zinc oxide and stearic acid. The decrease in elongation of the rubber was attributed to the blooming of Zn(St)2. image