Chemical Modification of Beef Tallow for Lubricant Application

The possible application of beef tallow as a biolubricant by improving its physicochemical properties through chemical modification has been explored. The unsaturated fatty acid chain of the regular beef tallow (RBT) was alkylated with isopropyl groups in the presence of ethylaluminum sesquichloride. The alkyl-branched beef tallow (BBT) was characterized using a combination of various analytical techniques, including gas chromatography–mass spectroscopy (GC–MS), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy, and gel permeation chromatography (GPC). GC–MS and NMR results indicate complete saturation (>95%) of the RBT double bonds with the attachment of isopropyl groups. GPC indicates the presence of oligomers in BBT. The physicochemical and tribological properties of the RBT and BBT as well as their blends with polyalphaolefin (PAO-6) or high-oleic sunflower oil (HOSuO) were evaluated. BBT has better oxidative stability than RBT, due to the elimination of the unsaturation. The introduction of alkyl groups into beef tallow led to improved low-temperature properties compared to RBT, both as neat materials and as blends in HOSuO or PAO-6. The BBT also displayed higher density (0.9030 vs 0.8969 g/mL) and kinematic viscosity (112.7 vs 44.2 mm2/s) than the RBT, possibly due to the presence of oligomers. The introduction of branching was also accompanied by higher solubility in HOSuO and POA-6, but a lower viscosity index (186 vs 149). Both RBT and BBT displayed good lubricity as HOSuO and were effective at improving PAO-6 lubricity at low concentrations (5 wt %). This study indicates that introducing branching into RBT produces new biobased materials, which can be blended into lubricants with improved properties.