Non-ionic assembly of nanofibrillated cellulose and polyethylene glycol grafted carboxymethyl cellulose and the effect of aqueous lubrication in nanocomposite formation

Abstract

A facile route to significantly lower the frictional forces between cellulose nanofibrils (NFC) has been presented. The concept is based on the surface modification of NFC by adsorption of polyethylene glycol grafted carboxymethyl cellulose (CMC-g-PEG) via non-ionic interactions. The adsorption was studied using quartz crystal microbalance with dissipation (QCM-D). The changes in viscoelastic properties of the adsorbed layers, upon changes in pH were evaluated and attributed to the conformation of CMC. Surface forces and frictional properties of NFC films were examined using the AFM colloidal probe technique and were shown to be highly pH dependent. A significant difference in behaviour was observed upon the surface modification of NFC. After adsorption of CMC-g-PEG, repulsive forces were acting over a much longer distance than predicted by DLVO theory. This was ascribed to the CMC-g-PEG chain extension, the effect of which was even more pronounced at higher pH due to the deprotonation of carboxyl groups on CMC. A higher anionic charge resulted in increased water content and swelling of the layer. Additionally, the adsorption of CMC-g-PEG onto NFC films markedly increased the lubrication by the reduction of the friction coefficient by 65% and 88% at pH 4.5 and pH 7.3, respectively.