Suitability of ethyl cellulose as multifunctional additive for blends of vegetable oil-based lubricants

Abstract

In a previous study, ethyl cellulose was successfully blended with castor oil and the results demonstrated its suitability to be used as additive to expand the range of operating conditions under which fluid film lubrication is sustained, mainly at high temperature. However, apparent solubility problems were detected when mixed with other vegetable oils with lower polarity than castor oil. In this work, a suitable combination of ethyl cellulose (EC) with both high oleic sunflower (HOSO) and castor (CO) oils was found able to reach stable and non gel-like blends with viscosities at 40 °C ranging between 62 and 493 cSt, and viscosity indexes fitting into group III (VI ≥ 120) of API classification of base fluids. The ternary HOSO/CO/EC blend showed an important reduction in friction coefficient at low entrainment speed, and generated a stable EHD-film at 100 °C of around 20 nm, which suggests better boundary properties than HOSO/EC or CO/EC blends. On the other hand, ethyl cellulose hindered wax crystallization process of these vegetable oil-based lubricants at 5 °C, yielding comparable results to those obtained with standard polymethacrylate backbone additives. Therefore, the suitable combination of both castor and HOSO with EC as multifunctional additive allow a set of eco-friendly base fluids to be formulated with a wide kinematic viscosity range, better viscosity-temperature dependence than many mineral or synthetic oils lubricants and excellent boundary lubrication properties, making them suitable for many lubricant applications.