Cold-Flow Properties of Estolides: The Older (D97 and D2500) versus the Mini-(D5773 and D5949) Methods

Abstract

There is growing research on developing new and sustainable lubricants. Sustainable lubricants with adequate cold-flow properties are of particular interest for many applications. One limitation of the established methods for measuring cold flow properties is the large volume needed to test samples. This makes initial screening of many hard-to-synthesize samples difficult. In the current study, we compared the results of the older, widely accepted ASTM methods D97 (pour point, PP) and D2500 (cloud point, CP) to the newer, smaller-volume, and easier-to-perform methods D5949 and D5773 for bio-based base oils (estolides and iso-estolides). The CP results were in good agreement for less colored samples, but D5773 gave lower values for some darker (Gardner color >8) samples, especially esters. The D5949 showed a tendency to report slightly higher PP, especially for the lower values. Viscosities and densities in a wide temperature range (15 to 120 °C) were also measured. The surface tensions were estimated by a literature group method. Viscosity and density effects can only partially explain the differences in the PP values from the two methods. In conclusion, the newer mini-methods are an acceptable substitution when larger volumes are not accessible, unless the sample is too dark.