Phenolic Grafting of Oxidized Cellulose Nanofibers Using Ferulic Acid: Structural and Antioxidant Analysis Toward Bioactive Nanomaterials.

Incorporating ferulic acid (FA) into a polymeric hydrogel impairs its bioactive properties. The synthesis used in this study involved radical-mediated surface grafting of nanocellulose for 24 h, using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) to oxidize cellulose nanofibers (oCNF) and phosphorylated cellulose nanofibers (pCNF), resulting in total polyphenol contents of 30.6 and 6.3 mg/g, respectively. Spectroscopic analyses of oCNF included solid-state high-power decoupling with magic-angle spinning nuclear magnetic resonance (13C HPDEC/MAS NMR), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS), confirming that FA was successfully grafted onto the backbone through ester linkages on the nanofibril surface. Rheology testing and morphological analysis via transmission electron microscopy (TEM) further supported these findings. TEM imaging revealed that the grafting process preserved the nanoscale morphology, yielding fibrils with an average diameter of approximately 28.2 ± 9.3 nm. Key aspects affecting FA grafting include the colloidal stability of the CNF suspension, evaluated by zeta potential, and surface activation via oxidation. In this study, FA was grafted onto oCNF through a radical-induced reaction to enhance their functional performance, enabling the development of functional and sustainable hydrogels with high antioxidant capacity (85.62% ± 1.65%).