Effects of the Tropical Climate of Vietnam on the Properties of Synthetic Greases with Urea Thickeners

This study investigated, for the first time, the effects of the tropical climate of Vietnam on the properties of synthetic greases with urea thickeners. The greases were exposed to seven-month field tests at climatic test stations of the Joint Russian–Vietnamese Tropical Research and Technological Center in three regions of Vietnam. This short-term exposure decreased the ultimate strength and affected the colloidal stability of the samples (in the colloidal stability measurements, the amount of separated oil was reduced). At the same time, the chemical composition of the greases remained essentially unchanged, as confirmed by IR spectroscopy. It would be reasonable to assume that the degradation of polyurea greases in tropical climates is primarily associated with their colloidal structural changes. This assumption, however, requires confirmation in further research that should involve longer exposure and a larger number of grease samples prepared from different base oils. It was additionally found that introducing a heterogeneous modifier into polyurea greases impairs their stability in tropical climate.