Characterising exfoliated few-layer graphene interactions in co-processed nanofibrillated cellulose suspension via water retention and dispersion rheology

Highlights: • Sustainable process for few layer graphene production quality verified via rheological analysis. • Dispersing action of nanocellulose in few layer graphene production reflected in colloidal response to shear. • Combination of rheology with optical microscopy confirms graphite delamination efficiency. -- Abstract: Few-layer graphene has been produced by mechanical delamination of exfoliated and naturally obtained graphite in aqueous suspension using the dispersion and suspension properties of nanofibrillated cellulose (NFC). Various degrees of graphene platelet integrity were obtained depending upon the processing conditions and the optional adoption of surfactant to aid dispersion of the hydrophobic agglomerates of nanometre-thin carbon material. The presence of NFC in the suspension acts similarly to the presence of surfactant, increasing the hydrodynamic coupling between the particles and water as a function of processing time, regardless of the graphene-comprising source. By fitting the stress growth region in the stress-shear rate relation to a concatenated series of single exponential functions of shear rate, the power law exponent and suspension consistency parameters (n and k), within a shear rate-localised Herschel-Bulkley (HB) expression, provide a straightforward characteristic for monitoring the desired suspension coupling response, and hence a measure of product constancy.