Dewatering Cellulose Nanomaterial Suspensions and Preparing Concentrated Polymer Composite Gels via Reverse Dialysis

Cellulose nanomaterials (CNMs) are typically produced in aqueous suspensions at low concentrations, which require subsequent dewatering to reduce transportation cost or as a preprocessing step for applications that require higher CNM loadings such as rheological modifiers and composites. Reverse dialysis is an effective method that avoids common dewatering issues like irreversible aggregation and sample heterogeneity. In this study, samples for dewatering were placed inside a dialysis bag and immersed in poly(ethylene glycol) (PEG) solution. The water removal process is driven by the osmotic pressure difference. Dewatered TEMPO-cellulose nanofibril (TEMPO-CNF) was redispersible after allowing for time to rehydrate; the original viscosity was recovered after a dewatering-redilution cycle. The generalizability of reverse dialysis was demonstrated by also dewatering suspensions of cellulose nanocrystal and chitin nanofiber. Furthermore, concentrated and well-dispersed poly(vinyl alcohol) (PVA)/TEMPO-CNF composite gels were obtained via reverse dialysis at loadings that were difficult to achieve by other methods. Reverse dialysis thus increases the processing range for these sustainable nanomaterials while preserving their beneficial morphological properties. Reverse dialysis can be added to manufacturing processes; recycling of the PEG solutions via ultrafiltration can be used to create an energy-efficient, sustainable, closed-loop dewatering process for cellulose nanomaterials that are hard to redisperse.