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ABSTRACT A sulfur cured nitrile rubber compound was subjected to high heat conditions from 175°C to 350°C for a duration of less than 2 h. The heat aged samples were thereafter characterized by hardness, tensile properties, volatile content, chemical crosslink density by Double Quantum Nuclear Magnetic Resonance (DQ‐NMR) and equilibrium solvent swell testing in toluene, Fourier Transform Infrared Spectroscopy (FT‐IR), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Thermal aging at temperatures above 175°C caused a rapid increase in compound stiffness (hardness and 10% tensile stress) with a corresponding loss in tensile ultimate properties due primarily to the rise in the crosslink density and accompanying loss of plasticizer. The 350°C heat aged samples showed surface bubbling and physical distortion, and were not used for quantitative analysis. High heat application significantly alters the surface chemistry of the compound, causing the chemical loss of the cyano (CN) and unsaturation contents. The high heat aging process promoted primarily thermal aging with no detectable signs of oxidation. The glass transition temperature measured by DSC proved to be sensitive to the degradative changes given the increase in its magnitude in the heat aged nitrile rubber. Activation energies are slightly lower than expectations for hardness, mechanical properties and chemical crosslink density. Activation energies measured by FTIR and DSC were more in agreement in comparison to those measured using lower temperature aging. The data generated in this investigation on exposing a sulfur cured nitrile rubber to high temperatures for short durations can be applied to help determine exposure times and/or temperatures near the heat generating source.
Porter et al. (Mon,) studied this question.