Oil structuring properties of electrospun Kraft lignin/cellulose acetate nanofibers for lubricating applications: influence of lignin source and lignin/cellulose acetate ratio

Abstract

In the present work, electrospun Kraft lignin/cellulose acetate nanostructures were produced, assessed and proposed as structuring or thickening agents of castor oil for lubricating applications. Solutions of Kraft lignins (KL) derived from different sources (eucalyptus, poplar and olive tree pruning) and cellulose acetate (CA) were prepared and used as feed for electrospinning. The rheological properties (shear and extensional viscosity), electrical conductivity and surface tension of KL/CA solutions influence the morphology of the electrospun nanofibers, which in turn is affected by the chemical structure and composition of the Kraft lignins. Electrospun KL/CA nanostructures consisting of filament-interconnected nanoparticles, beaded nanofibers or uniform nanofiber mats were able to form gel-like homogeneous fine dispersions by simply mechanically dispersing them into castor oil. The swelling of KL/CA nanofibers in the percolation network was demonstrated. The rheological, tribological and microstructural properties of these oleogels are essentially governed by the morphological characteristics of the electrospun nanostructures, i.e. fiber diameter, number of beads and porosity. Rheological properties of the resulting oleogels may be tailored by modifying the lignin source and KL:CA weight ratio. According to their rheological and tribological properties, KL/CA electrospun nanostructures-based oleogels can be proposed as a sustainable alternative to conventional lubricating greases.

Oleo‐Dispersions of Electrospun Cellulose Acetate Butyrate Nanostructures: Toward Renewable Semisolid Lubricants

“…Similar evolution of the conductivity with polymer concentration have been reported previously for other biopolymers. [20,22] Figure 1a displays the log-log plot of the viscosity versus shear rate for CAb solutions at concentrations ranging from 1.5% to 20 wt.%. All the solutions showed a Newtonian behavior for concentrations lower than 7.5 wt.%, with viscosity values ranging between 0.009 and 0.169 Pa s. However, at higher polymer concentrations the flow behavior turned to shear thinning above a critical shear rate (see Figure 1a).…”

Assessment of the Tribological Performance of Electrospun Lignin Nanofibrous Web-Thickened Bio-Based Greases in a Nanotribometer

“…High porosity is one of the most striking characteristics of the electrospun lignin networks used as thickener agents, which roughly ranges from 50 to 70%, as well as their ability to adsorb or entrap vegetable oils in the voids (see for instance refs. [35,36]). As can be seen in Figure 9, the friction coefficient and the wear scar volume increase with the porosity of the electrospun lignin network.…”

“…Nevertheless, these chemical modifications usually require chemicals, solvents and/or catalysts that make the synthesis of biopolymeric thickeners and the subsequent oil structuring process relatively complex and not entirely environmentally friendly, despite the fact the final product is. Very recently, we demonstrated that nanostructures generated with electrospinning from non-modified biopolymers can be proposed as effective oil structuring agents [35,36]. The high porosity, small size and high surface/volume ratio of nanofibrous webs are able to induce the formation of three-dimensional networks with a superior capacity to promote physical interactions between the oil and the nanofibers stabilizing the colloidal system through the formation of a percolation network.…”

“…However, producing lignin nanofibers using electrospinning is particularly challenging as a consequence of its chemical structure and relatively low molecular weight [38], and often requires the use of a co-spinning polymer [35,39]. However, non-uniform nanostructures typically obtained with lignins, consisting of particles or globules distributed along the filaments, which have come to be called BOAS (beads-on-a-string) [40,41] or weakly mixed particle-fiber nanostructures might also be appropriate for lubricating purposes, in terms of an easy oil release, i.e., oil bleeding [36]. The aim of this work is to investigate the tribological performance of novel bio-based lubricating greases, thickened with different electrospun lignin nanostructures, in a ball-on-disc nanotribometer by addressing the impact of the electrospun network morphology on friction and wear.…”

Prediction of Lubrication Performances of Vegetable Oils by Genetic Functional Approximation Algorithm

“…Vegetable-based oil, derived from renewable resources, is environmentally friendly with high biodegradability, providing excellent lubrication and extending the lifespan of machinery and equipment. Therefore, vegetable-based oil holds a distinct advantage in the lubricant field and deserves further research and development [6][7][8][9].…”