Boron Functionalized Cellulose-Nanocrystals Via Green Esterification Method as Lubricant Additive for Friction and Wear Reduction

Abstract

Boron Functionalized Cellulose-nanocrystal (BFC) was prepared by a facile and green esterification route. BFC had a high crystallinity of more than 80% and a needle-like morphology with a length of hundreds nm and a diameter of 10~20 nm, very similar to those of cellulose nanocrystal. The largest degree of substitution of hydroxyl by borate ester group was obtained for BFC under the optimum conditions of reaction time and temperature (5 h, 80 °C). When used as a lubricant additive in castor oil, BFC-5-80 achieved a stable, homogeneous and monodisperse state and the tribological performances were evaluated by a reciprocating ball-on-plate tribometer. The friction coefficient and wear volume of castor oil with 2wt.% BFC-5-80 are 0.058 and 0.281×10-3 mm3 under certain conditions of load, frequency and testing time (6 N, 8 Hz, 2 hours), 23.7% and 59.2% lower than those of pure castor oil as well as 8.0% and 33.9% than those of castor oil with CNC. Based on the analysis results of worn surfaces and wear residues, the outstanding friction-reduction and anti-wear performances of BFC-5-80 can be explained by two facts that a complete film consisting of BFC-5-80 network and adsorbed castor oil molecules forms between the mating surface and a chemical transfer film composed of ferrum boride and iron oxides is also generated on the steel interface.

Keywords: Cellulose nanocrystal, surface modification, Lubricant additive, Friction-reduction and anti-wear, Lubrication mechanism