Rheological characteristics of coconut grease with graphene nanoplatelets

The depletion of crude oil stock and the worldwide concern in safeguarding the environment from pollution have revived interest in formulating environmentally friendly lubricants derived from vegetable oils. The current paper investigates the effect of different concentrations of thickener (lithium stearate) and graphene nanoplatelets on the rheological properties of coconut oil-based grease. The thickener is added in a concentration of 6 wt.%, 12 wt.%, and 18 wt.%. The graphene nanoplatelets are added in a concentration of 0.5 wt.%, 1 wt.%, and 2 wt.%. The rheological properties studied are viscosity, shear rate, storage modulus, loss modulus, yield stress, and dropping point. The rheological tests of the grease are performed on Anton Paar rheometer (MCR-102) with parallel plate geometry of diameter 25 mm. The tests are performed at varying shear rates (0.1 s(-1) to 8.3 s(-1)) and at different temperatures (45 degrees C and 75 degrees C). The experimental results show that the rheological properties of the coconut grease increase with the increase in lithium stearate and nanoparticle concentration. It is observed that viscosity and shear stress of the grease increase by 25% and 33%, respectively, at 2 wt.% GNP concentration. Further, the effect of GNP concentration on the dropping point of the grease is also studied. It is observed that the dropping point of the coconut grease increases by 13.19% at 2 wt.% GNP concentration. It is deduced that coconut oil-based grease with 2 wt.% GNP can be a good lubricant replacement for industries with regard to environmental concern.