Development of new green lubricating grease formulations based on cellulosic derivatives and castor oil

Environmentally friendly lubricating greases may be produced by solely replacing the mineral base oil for vegetable oil. However, the substitution of traditional metallic soaps by biodegradable and renewable thickeners is, up to now, much less considered. This work is focused on the development of new oleogels, using castor oil and cellulose derivatives, which could be potentially used as biodegradable lubricating greases. Thermal and thermo-rheological behaviours of these materials were characterised by means of TGA analysis and SAOS measurements, in order to evaluate the evolution of oleogel microstructure with temperature. Moreover, both roll-stability and leakage tendency standard tests, usually performed in the grease industry, were used to evaluate the mechanical resistance of each sample. The evolution of biogrease linear viscoelasticity functions with frequency is quite similar to that found for traditional lithium lubricating greases. However, the influence of temperature on biogreases linear viscoelasticity functions is less important than that found for traditional greases. In general, the biogrease samples studied show both slightly lower mechanical stability and higher leakage tendency than traditional lubricating greases. The use of a blend of ethyl and methyl cellulose as thickener provides a mechanical stability comparable to that found for commercial greases.