Preparation and characterization of nanocellulose obtained by TEMPO-mediated oxidation of organosolv pulp from reed stalks

Abstract

Renewable plant materials are of interest for the development of new biodegradable materials. The study describes the preparation process of nanocellulose from organosolv reed pulp (ORP). ORP was obtained from reed stalks in two stages: by extraction of the raw material with NaOH solution and cooking using a mixture of acetic acid and hydrogen peroxide. Nanocellulose was extracted from ORP using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in a TEMPO/NaBr/NaClO system followed by ultrasonic treatment to obtain a stable nanocellulose gel. It was found that an increase in the TEMPO consumption and oxidation time increases the density and tensile strength, the content of carboxyl groups, and the transparency of the nanocellulose films, but decreases the yield and crystallinity of the nanocellulose. Structural and chemical changes and the crystallinity index of reed stalks, ORP, and nanocellulose were studied using SEM, FTIR, and XRD methods. Nanocellulose films had a density of up to 1.51 g/cm3, a transparency of up to 82.4%, a carboxyl group content of up to 1.18 mmol/g, and a tensile strength of up to 69.7 MPa. The crystallinity index of nanocellulose decreases from 78.8 to 64.9% with an increase in the oxidation time. TEM and AFM methods have shown that the width of nanocellulose particles is from 3 to 20 nm. TGA confirmed a decrease in the crystallinity index of nanocellulose as a result of its prolonged oxidation. The properties of the obtained nanocellulose from ORP demonstrate the great potential of its application for the preparation of new nanocomposite materials.