2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibrils (TOCNF) possess many attractive functional properties and exhibit remarkable application values. However, recycling of TEMPO is highly desirable because of the ecological and economic demands. In this study, a new strategy integrating direct reuse and extraction recovery of TEMPO was developed. 50% of filtrates after TEMPO oxidation were directly reused for next cycle and half of the fresh TEMPO was added to maintain a constant dosage. The obtained TOCNF within two cycles showed similar carboxylate content (~1.3 mmol g<sup>–1</sup>), crystallinity (~70%), and homogeneous width (~4 nm) compared to the original one. Furthermore, the TEMPO in the another 50% of filtrates was extracted by ethyl acetate followed by distillation. The TOCNF produced with the extracted TEMPO had almost the same properties compared to those of original one, suggesting a negligible loss of activity of the recovered catalyst. Compared to the traditional route without TEMPO recycling, the combined strategy for TEMPO recycling exhibited a 31.3% reduction in production cost. This new route enables clean and cost-effective production of TOCNF and shows a promising industrial feasibility.

Integrating direct reuse and extraction recovery of TEMPO for production of cellulose nanofibrils

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