Tuning morphology and structure of non-woody nanocellulose: Ranging between nanofibers and nanocrystals

Abstract

Due to the increasing interest on lignocellulosic nanomaterials, alternative raw materials to wood sources have been explored. In this sense, annual plants can represent an important source of lignocellulose which may be used for cellulose nanofibers (CNFs) production. The present work aims at highlighting the virtues of three different non-woody resources (jute, sisal and hemp) as raw material for the production of TEMPO-mediated oxidized CNFs. The fibrillation stage was carried out by means of high-pressure homogenization (HPH), sequencing the process to obtain the initial, intermediate and final characteristics. Interestingly, it was found that while wood-based TEMPO-mediated oxidized CNFs lead highly fibrillated structures and thick gels, the obtained CNFs in this work exhibited a structure similar to cellulose nanocrystals (CNCs), particularly at high oxidation degrees, as rod-like morphologies were observed. Nonetheless, differences were observed between the selected raw materials, which was attributed to the differences on their relative recalcitrance. In addition, the rheological evaluation indicated that hemp CNFs tended to a Newtonian behavior, as flow behavior index tended to 1, leading to suspensions radically different to those obtained from wood sources. Further, the rheological behavior of the obtained nanocellulose suspensions has been found to correlate with the 2D fractal dimension of the nanostructured cellulose. Overall, the present work shows the feasibility of using non-woody plants as raw material for nanostructured cellulose production, with interesting characteristics unconceivable with wood resources.