Green oleogels based on elm pulp cellulose nanofibers: effect of the nanofibrillation pre-treatment on their thermo-rheological behavior

Sustainable lubricating oleogels were obtained based on elm ( Ulmus minor Mill.) pulp cellulose nanofibers in castor oil. Before their nanofibrillation, two samples of the same bleached pulp were subjected to two different pre-treatments, either mechanical PFI (Paper and Fibre Research Institute) refining or chemical TEMPO-mediated oxidation. Their effect on the oleogels’ viscous flow and oscillatory shear behaviors was determined at different temperatures. Very pronounced differences were observed between these oleogels. The oleogel from the chemically-pretreated nanofibers showed evidences of being much more sensitive to both temperature and large shear deformations. Hence, its shear modulus underwent a very remarkable decay of 95.8% when subjected to a non-linear stress value of 100 Pa for 30 min. In turn, under the same conditions, a decay of only 41.4% was observed for the oleogel based on the nanofiber from the mechanically-pretreated nanofibers. Graphical abstract