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

TEMPO-oxidized cellulose nanofibrils (CNFs) possess lots of attractive properties. However, recycling of TEMPO is desirable because of ecological and economic demands. In this study, a novel strategy integrating direct reuse and extraction recovery of TEMPO was developed. 50 % of filtrates after TEMPO oxidation were directly reused and half of the fresh TEMPO was added to maintain a constant dosage, the obtained CNFs within 2 cycles shared similar carboxylate contents, crystallinity, and homogeneous width compared to the original ones. Furthermore, TEMPO in another 50 % of filtrates was extracted by ethyl acetate followed by distillation. The CNFs produced using the extracted TEMPO had almost the same properties compared to those of original ones, suggesting a negligible loss of activity of the recovered catalyst. Compared to the traditional route, the combined strategy exhibited a 31.3 % reduction in production costs, which enables clean and cost-effective production of CNFs and shows a promising industrial feasibility.