Preparation and Characterization of Cellulose Nanocrystals from the Bio-ethanol Residuals

This study was to explore the conversion of low-cost bio-residuals into high value-added cellulose nanocrystals. Two enzymatic hydrolyzed residuals (i.e., HR_MMW and HR_SPW) were collected from two different bio-ethanol producing processes-hydrolyzing medium-milled wood (MMW) and hydrolyzing acid sulfite pretreated wood (SPW), respectively. The results showed that both residuals contained over 20 wt % glucan with a crystallinity of about 30%, confirming the existence of cellulose in a well-organized structure in two bio-residuals. The cellulose nanocrystals (CNCs) were successfully extracted by first bleaching the hydrolyzed residuals to remove lignin and then hydrolyzing them with sulfuric acid. The resulting CNCs displayed the flow birefringence under two crossed polarizers. Compared with CNCs from microfibrillated cellulose (CNC_MCC), HR_MMW and its resulted CNC present the smallest particle size and aspect ratio. CNC_MCC had the larger particle size, aspect ratio, and higher z-potential value, CNC_SPW presented a similar morphology to CNC_MCC, and had the largest aspect ratio. The CNC_MCC enhanced its high crystallinity to 85.5%. However, CNC_MMW and CNC_SPW had a better thermal stability and higher activation energy as well as onset temperature and maximum decomposition temperature. As a result, the CNCs from bio-ethanol residuals are valued and promising cellulose nanoparticle resources.