Rubber seed oil-based biolubricant base stocks: A potential source for hydraulic oils

Rubber seed oil (Hevea Brasiliensis) a non-edible oil, widely grown in India with fatty acid composition, palmitic, 9.3%; stearic, 8.4%; oleic, 25.4%; linoleic, 41.1% and linolenic, 15.3% acids, was exploited for the preparation of lubricant base stocks. The oil was hydrolyzed to obtain fatty acids and these fatty acids were reacted with branched chain alcohol, 2-ethyl-1-hexanol (2-EtH) and polyols namely neopentyl glycol (NPG), trimethylolpropane (TMP), pentaerythritol (PE) at 135-140 °C in the presence of para toluene sulfonic acid (p-TSA) as catalyst in xylene medium. The branched and polyol esters were obtained in the range of 91-96.5% yields. These esters were characterized using IR, 1H NMR, 13C NMR and mass spectral techniques. The esters were evaluated for lubricant properties namely kinematic viscosity, viscosity index, copper corrosion, oxidative stability (RBOT), weld load, wear, pour and flash points using standard ASTM methods. Among the base stocks prepared, polyol esters were found to possess good viscosity indices (205-222) compared to branched esters (187). Good weld load behavior was observed in the case of PE (170 kg) and TMP (160 kg) esters compared to NPG (130 kg) and 2-ethyl-1-hexanol (120 kg) esters. All the esters exhibited good copper corrosion values of 1a. The study revealed that all the esters can be well exploited for a number of hydraulic fluid formulations.