Sulfated cellulose pulp with high water retention and a swollen fiber structure for the preparation of completely dispersed cellulose nanofibers.

In this study, sulfated cellulose pulps (SCPs), synthesized via environmentally friendly methods by supporting sulfamic acid and urea on wood-derived cellulose pulps (CPs), were used to prepare completely dispersed cellulose nanofibers (CNs). CP is a sustainable natural polymer that is biodegradable, nontoxic, and relatively inexpensive. Additionally, cellulose nanofibers prepared from CPs have attracted attention as promising natural nanofibers with various useful properties. Therefore, sulfation of CP with sulfamic acid and urea was investigated as a method for preparing completely dispersed CNs. The SCPs were synthesized in high yields through the sulfamic acid ≥ urea (molar ratio) reaction system at 393 K for 30 min. The SCPs contained sulfate groups with 0.79–1.33 mmol g⁻¹ at hydroxy groups of C6, and C2 and/or C3 positions of cellulose, maintained long fibers and exhibited a 429–880 degree of polymerization (DP), retaining 60% more DP than the original CP. Some SCPs attained a maximum water retention value of approximately 3000%, suggesting a swollen fiber structure. Completely dispersed sulfated CNs with a fiber diameter of approximately 3–4 nm could be prepared by defibrating these SCPs. The swollen fiber structure observed in the SCPs reduced the defibrated energy and time required to achieve complete dispersion. [ABSTRACT FROM AUTHOR]