Lubrication properties of separated Ov estolides and synthetic castor estolides. Capped (red), uncapped (gray), and mixed (green) Ov TAG estolides showed different CoF at 25 °C (a) and 100 °C (b). Coefficient of friction results for castor oil with estolides (blue) and unmodified castor oil (black) at 25 °C (c) and 100 °C (d). (e) MALDI-MS/MS confirmed the structure of synthetic castor estolides with esterified 16:0. (f) ESI-MS of synthetic castor estolides showed fragmentation of the esterified 16:0 unlike the fragmentation of hydroxy TAG of unmodified castor oil, as seen in Fig. 4b.