Ultrastructural Characterization of the Core–Shell Structure of a Wide Range of Periodate-Oxidized Cellulose from Different Native Sources by Solid-State 13C CP-MAS NMR

The periodate oxidation of cellulose, which leads to the opening of the glucosyl rings to yield two aldehyde groups in the so-called dialdehyde cellulose, stands as one of the major and promising pathways for the derivatization of cellulose for the design of new biosourced materials. Despite the wide use of this method and the simplicity of its chemistry, the measurement of the degree of oxidation (DO) of the periodate-oxidized cellulose is not straightforward due to the concomitant side reactions and heterogeneity of the oxidized products. Here, we present a new simple method based on solid-state 13C CP-MAS NMR spectroscopy relying on the quantification of the intricate signals of the washed oxidized sample, using the sharp C1 signal of intact cellulose as an internal standard, allowing the determination of degrees of substitution from 0 to 2. This new NMR method, applied first to microfibrillated cellulose, is compared to the current conventional methods, namely, the UV absorbance monitoring of the peri...