Cellulose dissolution in aqueous NaOH–ZnO : cellulose reactivity and the role of ZnO

Abstract: Cellulose utilization at its full potential often requires its dissolution which is challenging. Aqueous NaOH is the solvent of choice due to the rapid, non-toxic, low cost and environmentally friendly dissolution process. However, there are several limitations, such as the required low temperature and cellulose´s moderately low degree of polymerization and concentration. Moreover, there is a tendency for gelation of semidilute solutions with time and temperature. The addition of ZnO aids cellulose dissolution and hinders self-aggregation in the NaOH solution; however, the exact role of ZnO has remained as an open question. In this work, we studied cellulose dissolution in the aqueous NaOH–ZnO system as well as the reactivity of the dissolved cellulose by oxidation with 4-AcNH-TEMPO⁺ (TEMPO⁺). Based on Raman spectroscopic studies and the TEMPO⁺-reactivities, we propose a new structure for cellulose dissolved in aqueous NaOH–ZnO. Graphic abstract: [Figure not available: see fulltext.]