Impact of cellulose supramolecular structure on its carboxymethylation reaction activity

The reaction activity of cellulose samples is determined according to their supramolecular structure, especially the degree of crystallinity and degree of polymerization. The carboxymethylation reaction kinetics of cotton cellulose (CC), microcrystalline cellulose (MCC), and powder cellulose (PC), with different degrees of crystallinity and degree of polymerization, were studied by the solid-phase method and in an ethanol-water solution medium. In the row of CC, MCC, and PC with different supramolecular structures, it was found that with decreasing crystallinity degree of the raw materials, during carboxymethylation by the solid-phase method and in an ethanol-water solution medium, the degree of substitution (DS) of sodium-carboxymethylcellulose (Na-CMC) increased. In this row, the activation energy values of the carboxymethylation reaction of CC, MCC, and PC were 27.79, 18.30, and 10.74 kJ/mol, respectively, by the solid-phase method. Furthermore, the activation energies of the carboxymethylation reaction of CC, MCC, and PC were 59.26, 25.20, and 17.59 kJ/mol, respectively, in an ethanol-water solution medium. Decreasing activation energies led to an increase in the reaction activity, which, after CC, MCC, and PC carboxymethylation, the DS of Na-CMC reached 0.63, 0.86, and 0.97, respectively, using the solid-phase method. In an ethanol solution medium, the DS values of Na-CMC reached 0.89, 1.10, and 1.31 after carboxymethylation of the CC, MCC, and PC, respectively.