Bio-Based Antiwear/Extreme Pressure Additive Synthesized from Natural Renewable Cardanol

Cardanol, agro-waste generated from the cashew nut processing industry, has captured great attention of researchers in recent years in view of its renewable, low cost, and abundant availability. Herein, we utilized a simple and efficient method to obtain a novel and high-valued extreme pressure and antiwear (EP/AW) additive CPS, derived from agricultural waste cardanol, a primary constituent of CNSL. Tribological properties of CPS used in base oil were evaluated by a high-frequency reciprocating rig (HFRR) and SRV-IV oscillating reciprocating friction and wear tester. The HFRR results indicate that CPS could effectively reduce the friction coefficient and wear scar diameter (WSD) of sliding pairs, and its WSD was reduced by nearly 65% with 1.0 wt% CPS compared to that of pure base oil. Moreover, SRV test results show that CPS exhibits better tribological properties at 100 and 200 N than that of pure base oil and commercial products triphenyl thiophosphate (TPPT) which is derived from petroleum. All of the results demonstrate that the addition of CPS could significantly improve the tribological properties of base oil and could be used as an optimized primary EP/AW additive in lubricants. The worn steel surface evaluated by XPS revealed that metal phosphides, metal sulfide, organic phosphines, and sulfide compounds were formed, which resulted in excellent friction reduction and AW performance. CPS, which exhibited superior properties to commercial petroleum-derived TPPT, has great potential application as a bio-based EP/AW additive used in the lubricating oil industry.