Investigation on thermal aging and scaling of NBR in alkaline solution

The thermal aging and scaling tests of Butadiene-acrylonitrile rubber (NBR) samples in alkaline solution were done, and after the tests the surface contact angle of samples was measured and the sample surface was analyzed by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and scanning electronic microscope (SEM). The test results shows that after the NBR samples were dipped in pH 11, 70 °C alkaline solution for 215 d, many microcracks were observed on the surface of NBR samples and a lot of small sized scales existed near the cracks; element constituents of scale adhering on the surface were: Ca, Fe and Al, of which Ca was from saturated CaCO3, Fe was from rust scale and Al was from Al2O3 ceramic existing also in the test environment; IR and XPS inspection indicate that there were outgrowths of carboxy group, acyloxy group, hydroxyl group, CaO and Ca3Si3O9, which showed that oxidation degradation and hydrolyzation happened on NBR and the scale appeared on the samples’ surfaces. Dissolution, aging or scale adhesion led to non-uniformity of contact angle and surface energy data.