Microwave-assisted dichromate oxidation of cellulose: structural evolution

Abstract

Oxidized nanocellulose is a promising material for advanced polymer systems, where performance depends on both chemical functionalization and supramolecular structure. In this study, oxidized nanocellulose was prepared from cotton-derived microcrystalline cellulose using microwave-assisted potassium dichromate oxidation under acidic conditions. The structural evolution of cellulose during oxidation was systematically analyzed using X-ray diffraction, infrared spectroscopy, and theoretical calculations. The results show that oxidation does not simply degrade the structure but leads to a non-monotonic change in crystallinity while preserving the cellulose I polymorph. This behavior arises from the competition between the removal of amorphous regions and the reorganization of crystalline domains. Infrared analysis confirms the formation of carboxyl groups and reveals significant redistribution of hydrogen bonding, including a decrease in intramolecular interactions and strengthening of intermolecular associations. Theoretical calculations support these findings, indicating increased molecular polarity and reduced interchain interaction energy after oxidation. Overall, this study provides new insight into the multiscale structural transformation of cellulose under microwave-assisted oxidation and demonstrates the potential of this approach for designing functional nanocellulose-based polymer materials.