Biocompatible reduced graphene oxide sheets with superior water dispersibility stabilized by cellulose nanocrystals and their polyethylene oxide composites

Organic molecular and polymeric stabilizers are useful for preparing individually dispersed graphene sheets, thus offering new possibilities for the production of nanomaterials. Although exfoliated graphene flakes with good dispersibility can be produced, their use in polymer composites remains limited due to their low stability and mechanical strength. In this work, stable high concentration aqueous dispersions (>10 mg mL^-1) of reduced graphene oxide (RGO) sheets were prepared by exfoliation/in situ reduction of graphene oxide (GO) in the presence of cellulose nanocrystals (CNC). The sandwich-like structure formed with the hydrophilic outer surface of CNC forms CNC decorated RGO (CNC-RGO) which is easily dispersed in water with a high thermal stability (>320 °C) comparable to pristine CNC and other common stabilizers. Polyethylene oxide (PEO) based nanocomposites, using fully exfoliated CNC-RGO hybrids, were prepared with a simple procedure. The PEO/CNC-RGO composite films show superior mechanical properties compared to PEO composite films enhanced by other small molecules, polymer dispersants, stabilized RGO or pristine CNC. Not only are the elastic modulus and tensile strength of the composites significantly improved, but their thermal stability is also retained. The hydrothermal dehydration of GO to RGO, using biodegradable and renewable materials such as CNC, offers a "green approach" to large-scale preparation of highly biocompatible and easily dispersed RGO for a range of applications.