Single-step bleaching versus organosolv-bleaching of sugarcane bagasse: tuning TEMPO-oxidized nanocellulose morphology via delignification strategy

TEMPO-mediated oxidation is an effective and widely used method for producing carboxylated cellulose nanofibrils (CNFs) from lignocellulosic substrates. However, the morphology of the resulting nanocelluloses can vary significantly when TEMPO oxidation is applied to sugarcane bagasse (SCB) substrates with minimal lignin content, depending on the amount of oxidizing agent used. This work elucidates strategies for tailoring nanocellulose morphology from SCB by TEMPO oxidation and reveals the effect of a delignification step prior to bleaching on nanocellulose properties. To this end, two delignified substrates with minimum lignin content, obtained via sequential organosolv-bleaching or single-step bleaching, were subjected to TEMPO oxidation and ultrasonication. Although both substrates exhibited similar lignin contents, the use of a pre-delignification step was crucial for producing short particles characterized as cellulose nanocrystals (CNCs), whereas single-step bleaching produced CNFs. These findings highlight that morphological changes induced by the two-step delignification process, rather than lignin content alone, play a key role in determining the final nanocellulose morphology. Therefore, the most appropriate nanocellulose production route can be selected based on the target application, whether CNFs or CNCs are preferred.