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

Abstract

In this work, the electrospinnability of cellulose acetate butyrate (CAb) solutions, and the ability of the resulting micro‐ and nano‐architectures to structure castor oil are studied aiming to develop eco‐friendly lubricating greases. Particles, beaded‐fibers, defect‐free fibers, and porous nanostructures are successfully prepared by dissolving CAb in N,N‐dimethylacetamide/acetone (DMAc:Ac, 1:2 w/w) and methylene chloride/acetone (DM:Ac, 1:1 w/w) solvent mixtures at different concentrations (2.5–15 wt.%). The formation of bead‐free nanofibers is favored at concentration above 10 wt.%, when solutions achieve relaxation times of ≈50 ms and shear‐thinning in extensional and shear flow tests, respectively. Non‐porous and porous CAb nanostructures are successfully used as castor oil thickeners at concentrations of 3–5 wt.%, leading a wide variety of rheological responses which mimic those of traditional semisolid lubricants. The surface properties of the nanofibers have a significant impact on the wear and friction performance in metal–metal contact, which has been associated with the oil release ability of the generated 3D network. Oleo‐dispersions prepared with smooth fibers show tribological performance comparable to, or even better than, commercial lithium greases. Overall, this study reveals the potential of CAb electrospun nanostructures for the development of next‐generation renewable semisolid lubricant formulations.

Exploring Cellulose Triacetate Nanofibers as Sustainable Structuring Agent for Castor Oil: Formulation Design and Rheological Insights

“…The surface tension values decreased with increasing CTA concentration, ranging from 29.01 to 19.77 mN/m. This decrease is consistent with other studies and supports the formation of uniform electrospun nanofibers [22,23,25]. This is due to several factors.…”

“…Nevertheless, as the CTA concentrations increased, the viscous flow behavior transitioned to shear thinning above a critical shear rate. This flow behavior can be observed to be characterized by three distinct regions: (i) a Newtonian region at low shear rates (η 0 ); (ii) a subsequent shear thinning region at intermediate shear rates; and (iii) a tendency to stabilize at a constant high shear rate, limiting the viscosity (η ∞ ) [23]. The viscosity's dependence on the shear rate aligns quite well with the Carreau model [30].…”

“…Different concentration regimes have been identified, including dilute, semi-dilute unentangled, semi-dilute entangled, and concentrated regimes. Several boundaries between concentration regimes have been identified: (i) the chain overlap concentration, C*, is the point where the dilute and semi-dilute unentangled regimes intersect; (ii) the entanglement concentration, Ce, is the point where the semi-dilute unentangled and semi-dilute entangled regimes intersect [23]. At this point, the macromolecular chain motion is constrained by a significant overlap of the polymer chains topologically.…”

“…Therefore, innovative approaches for incorporating thickeners into an oil phase that enables true control of the three-dimensional network of gel-like dispersions would be highly beneficial for many applications. In this sense, recent works have described a new method of structuring vegetable oils using electrospun nanostructures as an alternative approach [22][23][24]. This method offers a novel way to structure vegetable oils, which could have significant implications in fields such as pharmaceuticals, cosmetics, food technology, and lubricants.…”