A Small Angle Scattering Study of Water-resistant All-Cellulose Nanocomposites

Cellulose nanofibers (CNF) are the basic structural elements of cellulosic materials; they show excellent mechanical properties due to their high crystallinity. Molecular cellulose solutions (MCS) with no apparent aggregation can be made using an ionic liquid and dimethyl sulfoxide (DMSO) binary solvent mixture. Solutions containing a minimum amount of ionic liquid can be made by maintaining a 3:1 molar ratio of ionic liquid to cellulose sugar units, with the remainder of the solvent mixture being DMSO. In this study, all-cellulose nanocomposites of CNF and regenerated cellulose from MSC have been fabricated by co-precipitation. CNF with average diameters of 2.5+/-0.5 nm and lengths of 300+/-100 nm were first dispersed in water, then transferred to DMSO by solvent exchange and subsequently mixed with MSC. Nanocomposites show higher water resistance compared to neat CNF films, similar to cellulose films regenerated from MSC. Atomic force microscopy shows even dispersion of CNF within the regenerated cellulose. Small angle neutron and x-ray scattering of these films show a prominent shoulder corresponding to a real-space size of 25 nm in the nanocomposites that is not present in films from neat CNF or MC. Mechanical properties of the nanocomposites will also be discussed.