USE OF DSC TO STUDY THE FLOW PROPERTIES OF HYDROCRACKED BASE STOCKS AND LUBRICATING OILS

The differential scanning calorimetry (DSC) technique was found useful in assessing the effect of different processing conditions on the wax content and the wax-type of hydrocracked base stocks. The DSC thermograms showed a wide crystallization peak, in the range from −40 to −20°C, indicating the presence of paraffinic wax molecules. The second, narrow crystallization peak at about −75°C, indicated the presence of lower melting isoparaffinic or branched-type wax molecules. The DSC technique was used to study the onset wax crystallization temperature and the wax formation in hydrocracked base stocks containing different chemistry pour point depressants. The fumarate-vinylacetate (FVA) pour point depressant was not as effective as polymethacrylate (PMA) type chemistry. A decrease in depressed pour points of hydrocracked base stocks was found to follow a decrease in the onset wax crystallization temperature. In engine oil formulations containing hydrocracked base stocks, a decrease in depressed pour point was also found to follow a decrease in the onset wax crystallization temperature. For pour point depressants used in lubricating oils, the mechanism of decreasing the onset wax crystallization was found to be more important than the mechanism of suppressing the wax formation.