On the morphology of cellulose nanofibrils obtained byTEMPO-mediated oxidation and mechanical treatment

Abstract

The morphological properties of cellulose nanofibrils obtained from eucalyptus pulp fibres wereassessed. Two samples were produced with the same chemical treatment (NaClO/NaBr/TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation), but distinct mechanical treatment intensities duringhomogenization. It was shown that the nanofibrils production yield increases with the mechanicalenergy. The effect of mechanical treatment on the yield was confirmed by laser profilometry of air-driednanocellulose films. However, no significant differences were detected regarding the nanofibrils widthas measured by atomic force microscopy (AFM) of air-dried films. On the other hand, differences in sizewere found either by laser diffraction spectroscopy or by dynamic light scattering (DLS) of the cellulosenanofibrils suspensions as a consequence of the differences in the length distribution of both samples.The nanofibrils length of the more nanofibrillated sample was calculated based on the width measured byAFM and the hydrodynamic diameter obtained by DLS. A length value of ca. 600 nm was estimated. TheDLS hydrodynamic diameter, as an equivalent spherical diameter, was used to estimate the nanofibrilslength assuming a cylinder with the same volume and with the diameter (width) assessed by AFM. Asimple method is thus proposed to evaluate the cellulose nanofibrils length combining microscopy andlight scattering methods.