The colloidal stability of CNF (Cellulose NanoFibrils) has a profound effect of basically all practical applications including CNF. When included in nanocomposites, in aerogels and foams these interactions will be decisive for how efficiently the excellent properties of the fibrils can be utilised in macroscopic materials and devices. This means that new procedures and a fundamental characterization of the colloidal state of the CNF are necessary to advance the application of CNF in materials and devices.In order to establish the colloidal behaviour of the CNF it is first of all necessary to find ways for preparing dispersions that can be repeated and reproduced without suffering from large variations. It is then necessary to identify methods that can be used to clarify the stability of the CNF dispersion and how it changes with time or with a change in dispersion conditions. In the present work a mechanical homogenization was combined with an ultrasonic treatment of the homogenized sample followed by a centrifugation to make sure that the CNF dispersion was homogeneous and that the dispersion as such was stable over an extended period of time to allow for accurate comparisons between different treatments. Dynamic light scattering (DLS), rheology and simple tube inversion tests were then used to study the colloidal properties of the CNF dispersions. The results show that the CNF dispersions can reach an arrested state at very low concentrations (&lt; 1.5 g/l) despite from being far from the instability regions described by the classical DLVO-theory. Simple calculations and experimental estimates of the distance between the contact points between the fibrils in dispersion, at 1.5 g/l, show that the arrested state can be reached when the fibrils are around 200 nm and even longer apart. By comparing CNFs and CNCs (cellulose nanocrystals) with different aspect ratios and different charges it was possible to identify different factors of vital importance for the creation of an arrested state of the fibrils in dispersion. The results also showed that a dilution of the samples in an arrested state was enough to bring them back to a dispersed state showing that the arrested state is a type of secondary minimum.<br/>It was also realised that the surface charge density of the most highly charged fibrils is so large that the standard Poisson-Boltzmann can not be used to estimate to double layer forces between the fibrils and the effect of this will be discussed.

Colloidal properties of cellulose nanofibrils

251st National Meeting (2016)

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