DERIVATIZATION OF CELLULOSE AND ITS CHARACTERIZATION BY SOLID-STATE 13C NMR

This research is focus on the derivatization of cellulose through different kind of chemical reactions aiming to obtain oxidized cellulose, Carboxymethylcellulose (CMC), and oxidized CMC. First of all, commercial cellulose was used for further functionalization in order to obtain CMC via alkali process as well as oxidized cellulose through an oxidation process using sodium metaperiodate. Owing to the difficulties of solubilizing pristine cellulose in aqueous medium, all cellulose-based materials were characterized by solid-state 13C NMR.
As shown in Figure 1A, carachteristics cellulose peaks around 50-110 ppm were observed, especially those peaks at 59-68 ppm and 72 ppm were assigned to C6 and C5-C3-C2, respectively. Likewise, the peak in the range of 80.4 – 92.8 ppm was associated with C4, whereas C1 was assigned to glycosidic linkage of cellulose. Additionally, in Figure 1B and Figure 1C as well as Figure 2B was expected a peak around 200-180 ppm due to the presence of aldehyde groups. Instead of this, oxidation process occurs at C3 and C4 carbons because of a selective oxidation attack. Due to this, an increase in the peaks around 90 – 100 ppm is clearly evidenced by the imminent formation of hemiacetal groups due to the linkage of neighboring hydroxyl groups and aldehyde groups [1]. Finally, it was identified a peak at 105 ppm observed in cellulose, whereas this peak decreases in CMC probably by the oxidation process [2], being able to identify the influence of the oxidation degree and the effect on depolymerization as a consequence of breaking of the glycosidic linkage (β - (1-4) glycosidic bonds) in cellulose and CMC.