The objective of this work was to find a rapid, high-yield process to obtain an aqueous stable colloid suspension of cellulose nanocrystals/whiskers. Large quantities are required since these whiskers are designed to be extruded into polymers in the production of nano-biocomposites. Microcrystalline cellulose (MCC), derived from Norway spruce (Picea abies), was used as the starting material. The processing parameters have been optimized by using response surface methodology. The factors that varied during the process were the concentration of MCC and sulfuric acid, the hydrolysis time and temperature, and the ultrasonic treatment time. Responses measured were the median size of the cellulose particles/whiskers and yield. The surface charge as calculated from conductometric titration, microscopic examinations (optical and transmission electron microscopy), and observation of birefringence were also investigated in order to determine the outcome (efficiency) of the process. With a sulfuric acid concentration of 63.5% (w/w), it was possible to obtain cellulose nanocrystals/whiskers with a length between 200 and 400 nm and a width less than 10 nm in approximately 2 h with a yield of 30% (of initial weight).
We thank the Research Council of Norway for financial support and Borregaard ChemCell in Sarpsborg, Norway, for providing us with MCC. We also thank Kristin Brevik Antonsen and Dr. Simon Ballance at the Department of Biotechnology at the Norwegian University of Science and Technology for providing us with the necessary equipment used in this research, Associate Prof. John Tyssedal at the Department of Mathematical Sciences at the Norwegian University of Science and Technology for discussions regarding statistics, Christer Albano at Umetrics for discussions concerning model design, Dr. Bjørn Steinar Tanem for TEM images, and PhD-student Ingvild Kvien for TEM images and WAXD analysis.
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