Modified ammonium persulfate oxidations for efficient preparation of carboxylated cellulose nanocrystals

Ammonium persulfate (APS) was able to produce carboxylated cellulose nanocrystals (CNCs-COOH) directly from the raw materials of cellulose. However, the industrial production of CNCs-COOH by this method is obstructed by the lower preparation efficiency. Herein, by the activation via N,N,N',N'-tetramethylethylenediamine (TMEDA) and ultrasonic assisted disintegration, modified APS method to extract CNCs-COOH from pulp was presented. A high yield (up to 62.5 %), low usage of APS (8.5 g APS per gram pulp) and less reaction time (6 h) was achieved. The as-prepared CNCs-COOH exhibited high carboxyl group content (1.45 mmol/g) and high crystallinity index of 93 %. The reaction mechanism has been studied, and the results show that with the addition of TMEDA, S₂O₈^2-can be converted to free radicals and hydrogen peroxide more quickly. Our studies suggested that modified APS method may be a suitable and economic alternative for the preparation of CNCs-COOH.