Advanced Multifunctional Oil Structurants for Sustainable Lubricants Engineered by Electrospinning Lignin/Cellulose Acetate Butyrate Nanofibers and TiO2 Atomic Layer Deposition

Abstract

This work investigates the potential of electrospun nanofibers derived from alkaline kraft lignin (AKL) and cellulose acetate butyrate (CAB) as renewable structuring agents for vegetable oils and their modification with TiO2 by means of atomic layer deposition (ALD). These nanofibers are targeted to replace the traditional components of lubricating greases with more ecofriendly multifunctional ingredients derived from renewable resources. The electrospinnability of AKL/CAB solutions improves with concentration, with a critical entanglement concentration (Ce ≈ 7.2 wt%) that needs to be exceeded to obtain fiber-dominated nanostructures. Above Ce, increasing solution concentration yields larger fiber diameters (from 0.63 to 2.69 μm) and higher structural homogeneity. Higher CAB contents favor the formation of uniform nanofiber networks with improved elongational properties. Dispersions of AKL/CAB nanofiber mats in castor oil produce stable gel-like systems, with tunable rheological properties depending on nanofiber content and AKL:CAB ratio. Oleo-dispersions of AKL-rich nanofibers provide lower friction coefficients (≈0.11) and reduced wear (365 μm average scar diameter) in a tribological contact. ALD of TiO2 on AKL/CAB nanofibers remarkably improves the tribological properties of these oleo-dispersions, significantly reducing friction (by 41%) and totally preventing wear, which is reported as a noticeable advance in the customization of renewable semisolid lubricants.