Thermal and mechanical characterization of cellulosic derivatives-based oleogels potentially applicable as bio-lubricating greases: Influence of ethyl cellulose molecular weight

This work deals with the design of new gel-like formulations based on blends of cellulosic derivatives and castor oil, which could be potentially applicable as environmentally-friendly lubricating greases. In particular, the influence of ethyl cellulose molecular weight, blended with α-cellulose or methylcellulose, on the thermal and rheological properties of the resulting gel-like dispersions was explored. Thermal and rheological behaviours were characterized by means of TGA tests and linear viscoelasticity (SAOS) measurements. Moreover, some standard mechanical tests, usually performed on commercial lubricating greases, were carried out in order to evaluate the suitability of these oleogels for lubricant applications. From the experimental results obtained, it can be deduced that SAOS functions of gel-like dispersions are not significantly influenced by ethyl cellulose molecular weight below a critical threshold value (Mw < 70,000 g/mol). On the contrary, a significant increase in both SAOS functions is noticed when using ethyl cellulose with Mw values higher than the critical one. Moreover, temperature does not have a large influence on oleogels SAOS functions, which is opposite to the behaviour found with standard lubricating greases. Formulations containing methylcellulose/ethyl cellulose blends show excellent mechanical stability parameters, enhanced by increasing ethyl cellulose molecular weight. On the other hand, all the oleogel formulations studied display much higher decomposition temperatures than standard lubricating greases, independently of ethyl cellulose molecular weight.