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 (HSO 3 Cl) followed by blending. The direct sulfation of cellulose with chlorosulfonic acid (HSO 3 Cl) was optimized at acid ratios of 1–1.5 HSO 3 Cl 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.