Nanocellulose Production via One-Pot Formation of C2 and C3 Carboxylate Groups Using Highly Concentrated NaClO Aqueous Solution

Abstract

Nanocellulose was prepared from wood pulp via a one-pot oxidation reaction using only a highly concentrated solution of sodium hypochlorite pentahydrate (NaClO·5H2O) and subsequent mechanical treatment. The concentration of NaClO in the solution was 22%, and the oxidation reaction times were 0.5, 2, and 6 h. The carboxy group content in the pulp increased with reaction time and reached 0.87 mmol/g after oxidation for 6 h. The oxidized pulp fibers were successfully refined down to nanocellulose by gentle mechanical disintegration such as ultrasonic homogenizer treatment. The obtained nanocellulose showed good colloidal stability in water because of the introduced carboxy groups, and the dispersion showed high optical transparency. Scanning probe microscopy showed that the nanocelluloses had an average height and length of 2.7-3.2 and 173-398 nm, respectively. Nuclear magnetic resonance spectroscopy analysis of the oxidized pulp suggested that NaClO oxidized the C2 and C3 hydroxy groups of the glucose units.