26 / 2021-05-26 11:50:08

APPLICATION AND PREPARATION OF CELLULOSE NANOFIBRILS BY MODIFIED FENTON OXIDATION PRETREATMENT

Cellulose nanofibrils; Modified Fenton oxidation; High shear mixing process; Composite materials

A more efficient method combining high shear mixing process (HSM) with follow-up Fenton (Fe²⁺/H₂O₂) oxidation to pretreat cellulose fibers for the preparation of cellulose nanofibrils (CNF) was developed. The hydroxyl radical (HO·), which could introduce aldehyde and carboxyl groups to cellulose backbone during the oxidation process, was produced by the one-electron transfer of hydrogen peroxide in the Fenton oxidation system at pH 3-5. However, it had been reported that excess hydrogen peroxide in the bulk solution would lead to a secondary reaction, resulting in inefficient decomposition of hydrogen peroxide and lower oxidation efficiency. In this work, ferrous ions were preloaded into softwood bleached kraft pulp (SWBK) fibers in high consistency by high shear refining method to realize the in-situ oxidation of cellulose chains, which in turn facilitated nano-fibrillation of fibers in subsequent homogenizer treatment. The adsorption and diffusion of Ferrous ions initiated the catalytic oxidation of cellulose simultaneously inside the fiber cell wall structure when hydrogen peroxide was introduced. Observed by energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM)，the HSM process had a higher ferrous ions preloaded efficiency inside the fibers compared to that in the conventional mixing (CM) process. The injection of ferrous iron into the fibers during the HSM process significantly reduced the consumption of ferrous ions, the dosage of H₂O₂, and increased the Fenton oxidation efficiency. When the dosage of hydrogen peroxide was 0.08 g/g, the carbonyl content of the fibers in the HSM process increased significantly from 42.39 to 149.79