Submitted to: Lubrication Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2011
Publication Date: 7/28/2011
Citation: Bantchev, G.B., Biresaw, G. 2011. Film-forming properties of castor oil polyol ester blends in elastohydrodynamic conditions. Lubrication Science. 23(5):203-219.
Interpretive Summary: There is a need for more environmentally-friendly and renewable lubricants. This need can be met by formulating lubricants with bio-based components. However, for such an approach to be successful, it will require a thorough understanding of the lubricating properties of lubricant blends with bio-based components. One of the most important properties of lubricants is its ability to form films between moving parts, such as those encountered in gears and bearings. The thickness of the lubricating film must be optimized to lower friction and reduce the wear of the moving parts. In the current work, the film-forming properties of blends of bio-based oils with synthetic esters were investigated as a function of blend physical/chemical properties and lubricating conditions. The results were then compared to the predictions of existing theoretical models. The film thickness of the blends displayed complex dependence on the composition of the blends and could not be fully described with existing simple models. The results showed that strict control of blend composition must be maintained in order to have the desired lubricating performance. These findings will be useful to researchers and developers of bio-based lubricating fluids.
Technical Abstract: The viscosities and elastohydrodynamic (EHD) film thickness properties of binary blends of castor oil with polyol esters were determined experimentally. Predicted blend viscosity was calculated from the viscosity of the pure blend components. Measured viscosity values were closer to the values predicted using the Lederer’s model than the Arrhenius’ model. EHD Ffilm thickness data were mostly in agreement with the predictions of the Hamrock-Dowson model. Observed deviations of EHD film thickness were attributed to boundary film formation and thermal effects. Calculated pressure-viscosity coefficients, a, displayed a complex relationship with blend viscosity. At 40°C, the addition of 10% polyol esters resulted in a 12-17% drop in a of castor oil. Higher concentrations of polyol esters resulted in an increase of a. At 70°C and 100°C, a displayed an almost linear dependence on blend composition.