Tribological Properties of Two Cellulose Nanofibers as Water-Based Lubricant Additives

In order to explore the tribological properties of cellulose nanofibers obtained by different preparation methods and their potential as water-based lubrication additives, a thorough analysis was conducted. This study focused on two types of cellulose nanofibers (CNF) variants: TO-CNF and C-CNF obtained by TEMPO (2, 2, 6, 6-tetramethylpiperidine-1-oxyl radical) oxidation and mechanical methods respectively. To gain insights into the morphology and structural characteristics of these CNFs, several analytical techniques were employed. Optical microscopy (POM) allowed for the initial visualization of the surface properties of these cellulose nanofibers, offering a macroscopic perspective. Subsequently, scanning electron microscopy (SEM) was harnessed, capitalizing on its capacity for high-resolution imaging. SEM unearthed the minute intricacies of these nanofibers, unveiling their structural intricacies. In addition to visual inspection, the structural constituents of these cellulose nanofibers were probed using Fourier-transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD). FT-IR was instrumental in detecting specific functional groups within the nanofibers, with particular emphasis on the presence of carboxyl groups. XRD findings unveiled vital insights into the crystalline arrangement of both TO-CNF and C-CNF. It was discerned that both variants featured rod-shaped structures and were classified under the cellulose I category. Notably, TO-CNF obtained through oxidation exhibited a perceptible quantity of carboxyl functional groups. Beyond structural characterization, the thermal stability of these CNFs was meticulously scrutinized, given its paramount significance in potential applications as lubrication additives within high-temperature environments. The outcomes of our investigation unveiled that C-CNF showcased marginally superior thermal stability compared to TO-CNF, a noteworthy attribute that could augment their performance in demanding conditions. Frictional properties of both types of CNF as water-based lubricant additives were studied by reciprocating friction tests using the UMT tribometer. The results proved highly promising. Both TO-CNF and C-CNF exhibited exceptional anti-friction properties when introduced at concentrations not exceeding w=1%. In fact, they demonstrated remarkable anti-friction capabilities across a spectrum of concentrations. It was noteworthy that TO-CNF showcased slightly superior anti-friction performance in comparison to C-CNF. For instance, the inclusion of w=1% TO-CNF led to a remarkable 51% reduction in the friction coefficient when juxtaposed with the base liquid. These findings underscore the substantial potential of CNF in augmenting the lubrication performance of water-based systems, rendering them an enticing prospect for a gamut of industrial applications. The lubrication mechanism of CNF was analyzed by investigating surface contact angles and post-wear surface analysis of steel plates. It was speculated that the polar functional groups in the CNF structure, such as hydroxyl or carboxyl groups, could adsorb to the surface of the friction pair in different degrees as additives, forming a lubricating protective film to prevent direct contact of sliding surface asperities and improve frictional properties. To sum up, the continued research endeavors and optimization of CNF as lubrication additives might potentially lead to more efficient and eco-friendly industrial applications, thereby addressing the critical requisites across diverse industries.