**2.1. Lubricant preparation**

The crude vegetable oils were modified to enhance certain limitations such as low thermal and oxidative stability due to unsaturation in oil molecule. There are various methods of modification that have been identified by Shashidhara and Jayaram [41] which included reformulation of additives, chemical modification, and genetic modification of oilseed. Prior to this experiment, fatty acid methyl esters (FAMEs) from Jatropha oil and RBD palm olein were chemically modified through transesterification process to develop modified Jatropha oil (MJO) and modified RBD palm olein (MRPO) [18, 31]. They are the product of the transesterification process (ester) between FAMEs from the vegetable oils with a polyol of trimethylolpropane (TMP) and better known as the TMP triester. After the transesterification process, the absence of hydrogen atom at carbon-β in the structure of the ester oil has enhanced the thermal and oxidative stability [42]. Both MJO and MRPO were mixed with two different types of additives; hexagonal boron nitride (hBN) and phosphonium-based ionic liquid (PIL). A small amount of 0.05 wt. % of hBN particles were blended in the base oils using a magnetic follower at a temperature of 60°C for 30 min. Meanwhile, 1 wt. % of PIL was heated at 70°C to reduce its viscosity prior to the mixing procedure with the base oils. Next, the preheated PIL was poured into the base oil and heated at 60°C and stirred rigorously by using the magnetic follower for 30 min. The modified oils were compared with a commercial synthetic ester (SE, Unicut Jinen MQL) as a reference oil.
