Production of TEMPO-oxidized cellulose nanofibers: Tuning the physio-chemical properties by controlling the process

TEMPO-oxidized cellulose nanofibers (TOCNFs) are very popular among cellulose nanomaterials (CNMs). However, the impact of production strategies (combination of chemical and mechanical treatments) on their physio-chemical properties has not been systematically clarified yet. In this work, TOCNFs were extracted from virgin pulp following three pathways, varying the duration of the chemical pre-treatment (quenched, S, versus non-quenched, L) and the mechanical fibrillation method (high-pressure homogenization, HPH, or ultrasonication, US). TOCNFs were characterized through morphological, rheological, and structural analyses, including carboxyl content (CC = 0.7-0.8 mmol/g), scanning-transmission electron microscopy, viscosity assessment and cryogel compression. An S-type reaction yields shear-thinning suspensions, with such behavior more pronounced for S-HPH (hysteresis loop area A = 227.18 Pa·s^-1) then for S-US (A = 2.57 Pa·s^-1), and with markedly different viscosity curves (K = 23,148 versus 91.45). Moreover, US gave longer fibrils while HPH promoted stable gel formation. In turn, prolonged TEMPO-oxidation paired with HPH yielded a non-shear-thinning, but stable suspension (A < 0 and K = 89.07). Overall, this systematic evaluation allowed us to establish clear process-properties-application relationships and highlight how TOCNFs properties can be fine-tuned through the accurate choice of production processes, enabling the selection of parameters according to the desired target application requirements.