Colloidal Chemical Properties of Cellulose NanoFibrils (CNFs) - Accepted Knowledge, New Boundary Conditions and Challenges, 2017 NANO

ABSTRACT ONLY

In order to liberate cellulose nanofibrils (CNF) from the fibre wall it is necessary to add considerable mechanical or chemical energy to overcome the restraining energies of the fibre wall. Once liberated, the fibrils will stay separated provided the repulsive forces are larger than the attractive forces and the nanocellulose dispersion will hence be in a meta-stable state. In many of the recent developments considerable amounts of anionic charges are added to ease the liberation of the nanocelluloses and to keep them well dispersed. When reaching charges in the range of 800 to 1000 µeq./g these charges and their counterions will dominate the properties of the CNF, for 4x4 nm wide CNFs. This also means that the use of the classical DLVO theory to describe the properties of the nanocellulose dispersions is no longer appropriate since polarization interactions will start to have a dominating effect, especially in the presence of multivalent counterions.

It has recently been shown that different types of highly charged nanocelluloses have a remarkable stabilizing effect of non-modified nano-carbon materials. By using highly charged CNFs and CNCs, in the present work, it has been possible to prepare stable dispersions of single wall carbon nanotubes (SWCNT) and reduced graphene oxide (RGO). By using differently charged CNFs it has also been possible to show that the higher the charge the higher the stabilizing ability of the nanocellulose. Model experiments using colloidal probe AFM measurements also show that the adhesive interaction energy between the CNFs and graphene model surfaces increases with the charge of the CNF. The colloidal probe measurements also show that the interaction is sensitive to the added electrolyte. All this indeed indicate that polarization interactions between the counterions to the nanocellulose and the nanocarbon are responsible for the interaction between the CNF and the SWCNT/RGO.

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