Comparison of sulfate and other anionic functional groups in cellulose pulp sheet functionality

Sulfated cellulose pulp (SCP), phosphorylated cellulose pulp, and 2,2,6,6-tetramethylpiperidine 1-oxyl radical-oxidized cellulose pulp are cellulose derivatives with distinct functional groups introduced through controlled chemical modifications. SCP has been reported to be synthesized in the cellulose pulp/sulfamic acid/urea system. The molar ratio of sulfamic acid to urea affects the fiber morphology and pulp water retention properties of SCP; however, its dry-state functionality of SCP remains uncharacterized. Therefore, in this study, we investigated the specific functionalities of SCP sheets by comparing them to other cellulose pulp sheets with anionic functional groups. A functional sheet was prepared from SCP using a hand-made method, and its water solubility, oil resistance, antibacterial properties, and flame retardancy were characterized. The functionality of the sheets was assessed by comparing the three anionic functional groups: sulfate, phosphate, and carboxyl groups, obtained through the oxidation of the primary hydroxy groups of cellulose. The high water retention of SCP was decreased by removing fine fibers with lengths of ≤ 0.2 mm, facilitating the preparation of SCP sheets using a hand-made method. SCP sheets prepared from SCP containing with a sulfate group of approximately 1.5 mmol/g of sulfate groups exhibited outstanding water solubility, oil resistance, antibacterial properties, and fire-retardant properties, owing to the introduction of monovalent strongly acidic functional groups. In conclusion, sulfate groups confer SCP sheets with various functionalities, suggesting their potential use as sustainable sheet materials.