Characterization of cellulose fibril aggregates isolated by the combination of ultrasonication and homogenizer

Cellulose fibril aggregates (CFAs) in micro/nano scales are made by the process of delaminating cellulosic fibers in high-pressure homogenizers. However, blockage of the slot during processing by cellulose fibers or particles is possible and so high-intensity ultrasonication was probed as a pretreatment method. This study was unique because of the combination of ultrasonication and homogenizer to produce high quality cellulose fibrils while preventing blockage that typically occurs using conventional homogenizer methods. The CFAs were characterized by the water-retention value (WRV), dynamic light scattering, scanning electron microscopy, atomic force microscopy, and two-dimensional (2-D) correlation spectroscopy. It was found that the ultrasonic treatment was helpful for CFA isolation before homogenizer processing. Less than 10 minutes of ultrasonic processing eliminated most of the blockage at the beginning of the homogenizer process. The results indicate that increasing the ultrasonic treatment time or homogenizer pressure significantly increased the WRVs of the treated cellulose while the CFAs were a mixture of different sized particles in the range of micro to nano scales. 2-D correlation spectroscopy between the near- and mid-infrared region helped to further explain the mechanism of size reduction which was attributable to the breakage of β-1,4-glucosidic bonds along the molecule axis due to shear forces.