Precise oxidation of the primary hydroxyls on the surface of cellulose microfibrils using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) has enabled an entire body of nanocellulose research. After oxidation, microfibrillated cellulose is readily produced using basic laboratory equipment such as a blender, stir plate, or an ultrasonication horn. Furthermore, a study by Okito, Saito, and Isogai (Biomacromolecules 11(6):1696-1670) showed that oxidation levels were connected to the size of the microfibril based on starting material; as a result, TEMPO mediated oxidation provided an indicator variable related to the accessible surface of cellulose for various plant materials. Interestingly for oxidized wood pulps, the sizes of the isolated microfibril dimensions changed as a function of mechanical energy input. Under intense ultrasonication treatment, nearly complete delamination of cellulose fibrils occurred breaking apart the TEMPO-oxidized cellulose (TOC) microfibrils into molecularly thin sheets consisting of cellulose chains latterly aggregated together. The sheets have a defined leveling off width of an average of 4nm, as determined with transmission electron microscopy (TEM) analysis. Atomic force microscopy (AFM) analysis of the sheets revealed the average thickness is below 1nm after the longest sonication times. Further evidence for changes in microfibril supramolecular structure after sonication was detected with <sup>13</sup>C cross-polarized magic angle spinning nuclear magnetic resonance spectroscopy. Shifts in the corresponding peaks for C1 and to a lesser extent, C4 indicated changes in the torsional angles of the glycosidic bond. The data from the spectroscopy and microscopy analysis of the deconstructed microfibrils were collectively used to understand the different possibilities of how cellulose assembles into supramolecular structures in the native state.

TEMPO mediated oxidation of cellulose: At the cross-section of experimental research on cellulose microfibrils

251st National Meeting (2016)

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