Synthesis of Guar Gum Acyl Esters and Their Application as Additive in Lubricant

Development of novel eco-friendly lubricant additives from sustainable reserouces is a matter of great concern due to the environmental issues raised by using the conventional toxic additives like ZDDPs (zinc dialkyldithiophosphates). This study investigated the potential of guar gum (GG) fatty esters as lubricant bio-additives. Five GG fatty esters denoted as GGLY, GGMY, GGPY, GGSY and GGOY were prepared using the reaction between guar gum and lauroyl chloride, myristoyl chloride, palmitoyl chloride, stearoyl chloride and oleoyl chloride respectively. Molecular characterization using FT-IR, ¹H-NMR and ¹³C-NMR confirm the successful synthesis of all five guar gum fatty esters. Solubility study showed that GGPY, GGSY and GGOY have good solubility in MAK-150, a mineral reference base oil. The tribological and rheological studies were perfomed with these three esters after blending in base oil in different concentrations. In tribological study, GGOY showed a reduction of 36.17% in COF (coefficient of friction) and a reduction of 61.93% in AWSD (average wear scar diameter) at 4000 ppm concentration in comparison to the reference base oil. It was also concluded that GGOY enhances the rheological properties at 40 and 100 °C and GGOY was found to show Newtonian behaviour at 40 °C under the influence of shear stress and shear rate. At high temperature beyond the shear rate of 100 s^− 1, GGOY showed better rheological behavior too.