Sulfated cellulose pulp with ultra-high water retention characteristics

A sulfated cellulose pulp (SCP) exhibiting ultra-high water retention properties has been developed, and its water retention mechanisms have been analyzed based on molecular structures determined by solid-state ¹³C nuclear magnetic resonance (NMR). Cellulose pulp (CP) from wood is sulfated using a sulfamic acid and urea reaction system with varying concentrations of sulfamic acid. SCP has 1.04–1.93 mmol/g of sulfate groups and exhibits a high water retention value (WRV) of 16,000%, which is approximately 100 times greater than that of CP. After the sulfate reaction, new peaks at 69 ppm are observed in the ¹H–¹³C cross-polarization/magic angle spinning and dipolar decoupling/MAS (DDMAS) ¹³C NMR spectra, which are assigned to the sulfated C6. Quantitative evaluation of area ratios of the corresponding peaks in the ¹³C DDMAS NMR spectra indicates that approximately 18% of C6 in CP is maximally converted to sulfated C6 when R = 4.19. The present work demonstrates that the WRV is related to the amount of sulfated C6, which guides the design of future absorbent materials based on CP.