Nanocelluloses are colloidal structures including cellulose nanofibers (CNFs) and nanocrystals (CNCs) that can be isolated from cellulose pulps, i.e., lignocellulosic biomasses after lignin removal. CNFs are longer and prone to entangle and are isolated from delignified lignocellulosic pulps by mechanical disintegration, a process that can be facilitated by a previous step of TEMPO-mediated oxidation. CNCs in turn are short and rigid rod-like particles, commonly obtained by acid hydrolysis of the cellulose pulps. In this work, we evaluated two different strategies for lignin removal to obtain both CNFs or CNCs from sugarcane bagasse (SCB) cellulose pulps depending on the chosen route. In the first strategy, organosolv treatments were carried out in raw SCB to obtain a delignified pulp that presented ca. 14% of remaining lignin. The second strategy consisted of a sequential bleaching step applied in the previous organosolv-treated substrates, which resulted in a cellulose pulp with lignin quantities lower than 5%. Then, both organosolv and organosolv-bleached substrates were TEMPO-oxidized under the same conditions using 25 mmol of oxidizing agent and sonicated for 30 min. After sonication, the dried aqueous suspension obtained from the organosolv-treated substrate was analyzed by Atomic Force Microscopy (AFM), indicating the presence of CNFs with an average length and diameter of 650 nm and 2 nm, respectively. On the other hand, the sonication of organosolv-bleached substrates resulted in shorter particles (230 nm long) with an average diameter of 4 nm, as typically reported for CNCs. Both nanoparticles presented high colloidal stability (zeta potential of ca. -50 mV in pH 7) due to the presence of deprotonated carboxyl groups onto their surface. Therefore, this methodology is a versatile alternative to obtain CNFs and CNFs functionalized with carboxyl groups, which enables the application of these renewable nanoparticles in hydrogels, aerogels, foams, and nanocomposites.

Cellulose nanofiber or nanocrystal? Choosing the type of nanocellulose by changing the method of lignin removal from plant biomass

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