Effect of depletion forces on the morphological structure of carboxymethyl cellulose and micro/nano cellulose fiber suspensions

Abstract

Cellulose nanofibers (CNF) can present a high viscosity and thixotropic behavior when dispersed in water. In this work, CNF isolated from sugarcane bagasse and modified by N-oxyl-2,2,6,6-tetramethylpiperidine (TEMPO) oxidation was added to a solution of carboxymethyl cellulose (CMC). This process produced an unexpected viscosity due to a synergistic effect that was observed macroscopically through rheology analysis. The phenomenon known as depletion flocculation was observed, which was caused by the reduction of the excluded volume. The interactions of the system were studied by ultraviolet-visible spectroscopy (UV-Vis), optical microscopy, and cryogenic transmission electron microscopy (cryo-TEM), which demonstrated the presence of the particle/polymer repulsion and subsequent formation of domains composed of aligned micro and nanocellulose particles clusters and nanofibers distributed throughout the sample, forming a percolated 3D structure responsible for a strong gelling and colloidal stability.

Keywords: Cellulose nanofiber; Colloidal behavior; Depletion force; Viscosity enhancement.