Biomimicking properties of cellulose nanofiber under ethanol/water mixture.

The two types of cellulose nanofiber (CNF) surface characteristics were evaluated by oil contact angle under ethanol-water solution at several concentrations as well as in air. Wood pulp-based 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-oxidized cellulose nanofiber (TOCNF) sheets and bamboo-derived mechanical counter collision cellulose nanofiber (ACC-CNF) sheets were fabricated by casting followed by drying. The CNF shows underwater superoleophobic mimicking fish skin properties and slippery surface mimicking Nepenthes pitcher. The underwater superoleophobic properties of CNF was evaluated theoretically and experimentally. The theoretical calculation and experimental results of contact angle showed a large deviation. The roughness, zeta potential, and water absorption at different concentrations were key factors that determine the deviation. Antifouling investigation revealed that CNF was a good candidate for antifouling material.

Cellulose Nanocrystal Isolation from Hardwood Pulp using Various Hydrolysis Conditions.

To expand the application field of the pulping industry, this study conducted a series of sample preparations for processing cellulose nanocrystals (CNCs) from a dry hardwood pulp to achieve optimal sulfuric acid hydrolysis. The properties of laboratory-prepared pulp CNCs (P-CNCs) were investigated with different preparation conditions including sulfuric acid concentrations, hydrolysis temperatures, and hydrolysis durations. Results showed a gradient of color changes observed with the increase of hydrolysis duration and temperature. Under certain conditions, the derived P-CNCs exhibited nanoscale dimensions, detected by transmission electron microscopy, and a crystallinity index similar to commercial products. In addition, the surface sulfate groups were assumed to be contributed by sulfuric acid hydrolysis. However, a high acid concentration and long hydrolysis processing duration introduced more sulfate groups on the derived P-CNCs, which may have acted as flame retardants and, thus, increased the amount of char residue.

An analysis on the electrophoretic mobility of cellulose nanocrystals as thin cylinders: relaxation and end effect.

Cellulose nanocrystals (CNCs) are extracted from cellulosic fibers via sulfuric acid hydrolysis and found to exhibit unique properties due to their nanoscale, ordered structure, and surface morphology. The dispersion stability of a CNC suspension is a significant factor when CNCs are applied for reinforcement of a composite or ink jet printing. Since sulfuric acid hydrolysis introduces sulfate groups on CNC surfaces, we considered that charging conditions needed to be characterized, typically based on electrophoretic mobility. After the electrophoretic mobility was measured, several theoretical equations were applied to fit those values to assume the proper CNC particle shape. While Smoluchowski's equation is often used for this purpose, its applicability to CNCs should be reconsidered due to the thin, rod-like shape of CNCs with a finite length and high charge density. In this sense, we measured the surface charge and electrophoretic mobility of well-characterized CNCs. The obtained experimental data have been analyzed by using various electrokinetic equations. Our analytical results suggested that Smoluchowski's equation and the Ohshima-Henry equation overestimated the magnitude of the mobility of CNCs because it ignores the double layer relaxation and end effect. They also suggested that neither the Ohshima-Overbeek averaged equation nor the Ohshima-Overbeek perpendicular equation described the mobility of CNCs appropriately because those equations consider the double layer relaxation and end effect of a cylinder in a limited manner. Instead, the modified Ohshima-Overbeek equation was presented to be preferred for such a charged cylinder with a small aspect ratio.