Aqueous exfoliation and dispersion of monolayer and bilayer graphene from graphite using sulfated cellulose nanofibrils.

Amphiphilic sulfated cellulose nanofibrils were synthesized with yields in excess of 99% by sulfation of dissolving pulp cellulose using chlorosulfonic acid in anhydrous N,N-dimethyl formamide followed by high-speed blending. The sulfation level was stoichiometrically tunable to between 1.48 and 2.23 mmol g-1. The optimized SCNF demonstrated the ability to act as an effective dispersant for graphene produced via exfoliation in aqueous media, allowing for the production of aqueous stabilized graphene with 3.9 ± 0.3 wt% graphite to graphene conversion and suspended solids comprised of 19.5 ± 1.5 wt% graphene. Graphene exfoliated with SCNF was observed to consist exclusively of mono- and bilayers, with 42% of sheets being monolayer. Furthermore, it was demonstrated that SCNF defibrillation and graphene exfoliation could be combined into a single one-pot process.

Sulfated Cellulose Nanofibrils from Chlorosulfonic Acid Treatment and Their Wet Spinning into High-Strength Fibers.

This paper presents the proof of concept for a facile sulfation-disintegration approach toward generating sulfated cellulose nanofibrils (SCNF) via direct sulfation of rice straw cellulose with chlorosulfonic acid (HSO3Cl) followed by blending. The direct sulfation of cellulose with chlorosulfonic acid (HSO3Cl) was optimized at acid ratios of 1-1.5 HSO3Cl per anhydroglucose unit (AGU) and short reaction times (30-60 min) at ambient temperature to produce SCNF with tunable charges of 1.0-2.2 mmol/g, all in impressively high yields of 94-97%. SCNF were characterized via AFM, TEM, FTIR, and XRD. SCNF lengths (L: 0.75-1.24 µm) and widths (W: 3.9-5.9 nm) decreased with harsher sulfation, while heights (H: 1.23-1.32 nm) remained relatively static. The SCNF had uniquely anisotropic cross sections (W/H: 3.0-4.7) and high aspect ratios (L/H: 568-984) while also exhibiting amphiphilicity, thixotropy, and shear thinning behaviors that closely followed a power law model. Aqueous SCNF dispersions could be wet spun into organic and mixed organic/ionic coagulants, producing continuous fibers possessing an impressively high tensile strength and Young's modulus of up to 675 ± 120 MPa and 26 ± 5 GPa, respectively.