Cost-effective preparation of highly amorphous cellulose nanofibrils with TEMPO oxidation promoted by mild molten salt hydrate pretreatment

Abstract

2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/NaBr/NaClO catalytic oxidation system is a commonly used method to prepare carboxylated cellulose nanofibrils (TOCNF), but the traditional reaction system is relatively time consuming with high production cost. Herein, a facile and clean process of lithium bromide trihydrate (LBTH) pretreatment of hardwood dissolving pulp (HDP) was conducted, which promoted the reaction and reduced the use of chemicals for TEMPO oxidation. Characterizations verified that the LBTH pretreatment could significantly improve the efficiency of the subsequent TEMPO oxidation of HDP. Particularly, the obtained TEMPO-oxidized cellulose nanofibrils (TOCNF) had highly amorphous structure, the carboxyl content (1.06 mmol/g) of the obtained TOCNF with LBTH pretreatment for 5 min could increase by 58%, and the corresponding oxidation time was shortened by 57%, compared to the unpretreated HDP. Moreover, the fabricated TOCNF with increased carboxyl content exhibited strong ability to stabilize high internal phase Pickering emulsions (HIPPEs) with analogous average particle sizes. Additionally, LBTH solvent could be easily recovered, and the recycling does not affect the effectiveness of LBTH pretreatment. Compared to the unpretreated HDP, the operation cost of TEMPO-mediated oxidation could be reduced by 31% with the LBTH pretreatment. This work has potential to boost the commercial production and application of TOCNF and nanocellulose-based materials.