Extreme Pressure Performance
The extreme pressure (EP) behaviour of the synthesized ILs was analyzed in two base oils and the results were shown in Fig. 8. It can be seen that the weld point of two base oils improved with addition of synthesized ILs. The base oils EKE and DOS exhibited weld points 160 and 120 kg respectively, further the addition of ILs showed significant enhancement in weld points due to the development of effective tribofilm on the rubbing surface. Fig. 8 compares the weld points of base oils with different IL concentration from 0.25 wt% to 1.5 wt%. While increasing the concentration from 0.25 to 1.25 wt% increase in weld point of the base oil was observed and further increasing the concentration to 1.5 wt% resulted in decrease of weld point, thus 1.25 wt% is taken as the optimized additive concentration. At this particular concentration all the synthesized additives were greatly effective in improving the weld point of the two base oils. The IL’s BHI-RA, TBA-RA, TPA-RA and CTB-RA enhanced the weld point by 43, 31, 25 and 25% respectively in base oil EKE. Exclusively, BHI-RA exhibited superior extreme pressure performance in both base oils. Yang et al. reported that the nitrogen containing heterocyclic compounds are capable to develop strong tribofilms under extreme pressure conditions (Yang et al., 2013). The weld points obtained with all the synthesized ILs were compared with commercially available additive dibenzyl disulfide (DBDS) and the results indicate that the synthesized ILs exhibited either comparable or better EP performance to DBDS.