Rheological and mechanical properties of oleogels based on castor oil and cellulosic derivatives potentially applicable as bio-lubricating greases: Influence of cellulosic derivatives concentration ratio

Nowadays the lubricating market is demanding new biodegradable or more environmentally acceptable products based on renewable resources as a consequence of progressively more strict environmental regulations. In this framework, this study deals with the design of gel-like dispersions potentially applicable as environmentally friendly lubricating greases. These dispersions were formulated using castor oil and ethyl cellulose/α-cellulose or ethyl cellulose/methyl cellulose blends. In particular, the influence of cellulosic derivatives concentration ratio on the linear viscoelasticity and mechanical stability of the resulting oleogel formulations was studied. The modification of ethyl cellulose/α-cellulose or ethyl cellulose/methyl cellulose weight ratios allows obtaining some formulations with suitable rheological characteristics and mechanical stability for potential lubricating applications. An important decrease in the values of the linear viscoelasticity functions down to a minimum value was found by increasing ethyl cellulose/α-cellulose or ethyl cellulose/methyl cellulose weight ratios (W) up to a critical value, which depends on both nature of the cellulosic derivatives employed and temperature. Above this critical value, the linear viscoelastic functions increase with W, at temperatures in the range 0–75 °C, and continuously decrease at higher temperatures, i.e. 125 °C. Thermal susceptibility is significantly dampened by reducing ethyl cellulose concentration. Gel-like dispersions formulated with ethyl cellulose/methyl cellulose blends showed appropriate mechanical stabilities to be used as bio-lubricating greases.