A More Efficient Fenton Oxidation Method with High Shear Mixing for the Preparation of Cellulose Nanofibers

A more efficient Fenton oxidation method with high shear mixing for the preparation of cellulose nanofiber (CNF) is investigated. The Fenton reaction is the reaction between Fe²⁺ and H₂O₂ to produce a series of free radicals that leads to oxidation of the cellulose. With the new technology, the Fe²⁺ is preloaded into the kraft pulp by a high shear refining method to realize in situ oxidation of cellulose fibers. It is found that the carbonyl content in the fibers using high shear mixing process is 149.79 μmol g⁻¹ when the dosage of hydrogen peroxide is 0.08 g/g (weight of dry fibers), compared to the 126.40 μmol g⁻¹ of fiber without high shearing when the dosage of hydrogen peroxide is 0.15 g/g, which indicates that the new Fe²⁺ pre-loading process has higher oxidation efficiency with lower H₂O₂ consumption compared with traditional Fe²⁺ preloading process. The ¹³C NMR results show that the C₂, C_3, and C₆ hydroxyl groups are oxidized to aldehyde and carboxyl groups, which is beneficial to increase the electrostatic repulsion between fibers and facilitate the subsequent homogenization treatment. The obtained CNF is uniform in size and slightly lower in thermal stability.