Carboxylated nanocrystalline cellulose from Salix psammophila prepared by sulfuric acid hydrolysis combined with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidation

Abstract

Salix psammophila (SP) is an important sand plant, and could be utilized to develop high-value products. In this work, SP was used as raw material and cellulose nanocrystals (CNC) were prepared by hydrolysis in 64 wt% sulfuric acid (H2SO4) solution, and then, TEMPO/NaBr/NaClO system was used to oxidize CNC to obtain TEMPO-oxidation-cellulose nanocrystals (TOCNC). Fourier transform infrared analysis (FTIR) revealed that after oxidation, there were obvious carboxyl functional groups. Scanning electron microscopy (SEM) showed that both CNC and TOCNC were agglomerated. Under atomic force microscope (AFM) and transmission electron microscopy (TEM), CNC and TOCNC presented short rod fibers, average diameters of 23 nm and 21 nm and average lengths of 213 nm and 165 nm, respectively. X-ray photoelectron spectroscopy analysis (XPS) showed that TOCNC generated a new energy spectrum peak at 289.06 eV, which was the peak of C=O in the carboxyl group. The crystallinity of the CNC and TOCNC were 70.8% and 26.9%, respectively.