Micro- and nano-fibrillated celluloses are roughly categorized to microfibrillated cellulose (MFCs), cellulose nanonetworks (CNNeWs), cellulose nanofibers (CNFs), and nanocrystals (CNCs) based on their morphologies. These four different micro- and nano-celluloses can be prepared from the same starting wood cellulose fibers by the following two different procedures: 1) controlling TEMPO-mediated oxidation conditions to introduce different amounts of C6-carboxylate groups (0.01-1.7 mmol/g) to wood cellulose fibers and successive mechanical disintegration of the oxidized cellulose fibers in water under the same conditions, and 2) controlling mechanical disintegration conditions of TEMPO-oxidized cellulose fibers with, e.g., ~1.5 mmol/g, in water under different conditions, e.g., sonication for 0-120 min. Especially, the original fibrous morphology of wood cellulose fibers can be maintained after TEMPO-mediated oxidation, fibrous TEMPO-oxidized celluloses, TEMPO-MFCs, TEMPO-CNNeWs, TEMPO-CNFs, and TEMPO-CNCs can be prepared from the same fibrous TEMPO-oxidized wood cellulose fibers with carboxylate contents of 1-1.7 mmol/g by controlling sonication time in water. The gelation points of TEMPO-CNCs in water increased by four folds from those of TEMPO-CNFs because of clear decreases in their lengths, roughly maintaining the widths of ~3 nm as those of TEMPO-CNFs prepared from wood cellulose fibers. Changes of width, length, and molar mass of TEMPO-CNCs prepared from the same TEMPO-CNF under different sonication times in water were carefully analyzed by AFM height images, turbidities of dilute dispersions irradiated with visible light at various wavelengths, and viscosities/SEC-MALLS. The results showed that the lengths of TEMPO-CNFs efficiently decrease with sonication time, eventually forming needle-like TEMPO-CNCs, which corresponded to the decreases in molar masses. Moreover, the widths of TEMPO-CNFs gradually and slightly decreased with increasing sonication time. These results indicates that even transparent TEMPO-CNF/water dispersions, indicating complete nanofibrillation, contained some aggregated fibrils, although the aggregation points and the aggregation levels are quite low. These TEMPO-CNFs containing small amounts of aggregates turns to completely individual TEMPO-CNCs with sonication time in water in association with obvious decreases in their lengths.

Preparation and characterization of TEMPO-oxidized cellulose nanonetworks, nanofibers, and nanocrystals

2019 Spring National Meeting

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