Tribological performance of prepared polymerized jojoba grades including jojoba oil and their optimization
The scope of this study is investigating the tribological characteristics of prepared bio-based thread grease from renewable sources with polymerization products from jojoba oil as additives. Accordingly, the first part in this study aims to prepare three molecular weights grades from polymerization of jojoba oil using microwave technique. The physicochemical and tribological properties of obtained polymerized jojoba including jojoba oil were determined; their tribological behavior studied in term of coefficient of friction and wear scar diameter using four ball machine. The results revealed that the polymerized jojoba with low molecular weight shows the lowest friction coefficient and wear scar diameter compared with high molecular weight polymerized jojoba grades and jojoba oil before polymerization. This has been discussed based on the unique properties of the chemical structure of jojoba. Two correlations are introduced using regression analysis to relate the coefficient of friction (FCO) and wear scar diameter (WSD) to the affecting variables. The studied affecting variables are the load, the velocity (revolution per minute, RPM) and the polymerization time. Optimization of these variables showed that minimum FCO and WSD could be achieved after polymerization time of 1.2 hr, under load of 196 N with a speed of 600 rpm. It was concluded that the polymerized jojoba grade with low molecular weight has superior tribological performance and could be used as a significant potential additive for bio-based thread grease in the next part of this study.