On the Electro-Active Control of Nanocellulose-Based Functional Biolubricants.

Abstract

This research work aims to explore the development of functional nanocellulose-based biolubricants which allow for an electro-active control of the friction behavior. With this purpose, the influence of both nanocellulose concentration and electric field strength on the lubricant's electro-rheological behavior was analyzed. Electric fields strengths up to 4 kV/mm were imposed and two different kinds of nanocellulose were studied as polarizable particulate phase: nanofibers (CNF) and nanocrystals (CNC). Nanocellulose particles were added to castor oil at weight fractions ranging 0-6 wt.%. All dispersions exhibited a noticeable variation in dielectric constant, but not in conductivity, within a wide frequency range between 100 Hz to 200 kHz, and their dielectric behavior was significantly affected by the particle weight fraction. Noteworthy, it was found a critical value of nanocellulose concentration, 4 wt.%, upon which the electro-viscous effect displayed by these dispersions was constrained, yielding a limiting electrorheological (ER) behavior. In addition, the dynamic yield stress dependence on the electric field strength showed a critical value within the interval 0.8-1.2 kV/mm, suggesting a nonlinear conduction model for these nanocellulose-based ER dispersions. Finally, it was found a maximum leak current intensity for 1 wt.% CNF or CNC dispersions, and an asymptotic decay at higher concentrations. We conclude that both CNC and CNF nanoparticles have demonstrated to endow castor oil with significant ER properties, which remarkably reduced the friction coefficient within the boundary and mixed lubrication regions at electric field strengths lower than 40 V.

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Identifiers

DOI

10.1021/acsami.0c12244

Journal

ACS Applied Materials & Interfaces

Year

2020