Impact of the Mechanical Processing of Nanocellulose on the Characteristics of Nanocellulose Derived Solids*

Nanocellulose fibers were formed by ultrasonic mechanical processing of a mixture of powdered microcrystalline cellulose and distilled water which results in a water-based suspension. We found that the feature sizes of the resultant nanocellulose particles depended strongly on processing parameters like ultrasonic power, processing time, and the concentration of cellulose in the suspension. We found a dimensional crossover in the nanocellulose features with highly viscous suspensions forming 2D sheets rather than 1D fibers. We also found there were significant differences between batch and flow-through processing, with flow-through resulting in a higher percentage of the microcrystalline cellulose broken down into nanocellulose. Suspensions were air-dried to form hardened solids and freeze dried to form aerogels. We found that the void concentration in the aerogels closely aligned with the water concentration in the original suspension. Aerogels composed of 1D fibers were significantly stronger than those formed of 2D sheets. Larger air-dried solids were able to be formed with smaller nanocellulose particles without cracking. These results enable us to determine optimal processing parameters to create nanocellulose with desired feature size in the most efficient manner possible.