Participation of sodium sulfamate as hydrogen bond-donating and hydrogen bond-accepting additive in the dissolution of cellulose in NaOH aqueous solution

A NaOH/urea (or thiourea) solvent system capable of dissolving cellulose at lower temperatures is a breakthrough in cellulose chemistry, but dissolution of cellulose with a degree of polymerization (DP) greater than 740 in NaOH/urea (or thiourea) at low temperature will be inadequate due to its limited dissolving capacity. It is known that the addition of additives to a precooled NaOH system enables the dissolution of more cellulose with a higher DP. Therefore, the development of new aqueous NaOH/additive solutions is of interest to the scientific community. Considering that sodium sulfamate has two hydrogen bond donors and four hydrogen bond acceptors, which is similar to urea (or thiourea) with its four hydrogen bond donors and three acceptors, in the present work a different source of commercial dissolving pulps with DP higher than 740 was selected as cellulose raw material, and the dissolving capacities of mixed aqueous solutions of 7 wt% NaOH and 0.05–0.6 wt% sodium sulfamate were examined. Dissolution of cellulose in dissolving pulps using a 7% NaOH/0.1% sodium sulfamate aqueous solution improved upon the addition of sodium sulfamate, and when the addition of sodium sulfamate was optimal, the amount of dissolved cellulose in three dissolving pulps was increased by 25.6, 28.7 and 17.9%, respectively. This effect is likely due to the participation of sodium sulfamate as a hydrogen bond-donating and hydrogen bond-accepting additive that promotes dissolution of cellulose in NaOH aqueous solution.