Self-assembled optically transparent cellulose nanofibril films: effect of nanofibril morphology and drying procedure

Abstract

Cellulose nanofibril (CNF) films currently provide great opportunity in many applications with advantages of excellent mechanical strength, high light transmittance, and good barrier properties. However, processes for preparing CNFs are typically tedious and vary, along with their properties. Here, five preparation methods using various combinations of filtration, freeze-drying, and casting are applied to produce CNF films, and their major properties are compared. Three different types of CNFs having a range of fiber diameter and aspect ratio were examined using each of these five preparation methods. Because of limited hydrogen bonds and nanofibril arrangement, the freeze-dried CNF films displayed reduced mechanical strength and light transmittance compared to the other methods, although freeze-drying was relatively fast. Some effects of film production methods on measured crystallinity were also observed with freezedried samples having lower crystallinity than films similarly produced by filtration and drying. Freestanding CNF films produced by casting at room temperature required long times and mold growth was sometimes observed, but cast films made from 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized CNFs had the highest light transmittance of any samples. Filtration of CNF suspensions followed by air-or oven-drying produced films with minimal defects, high mechanical strength, and good light transmittance with relatively little effort. Therefore, this filtration procedure is recommended for producing CNF films.

Nanofibrillated Cellulose from Appalachian Hardwoods Logging Residues as Template for Antimicrobial Copper

“…The wet films (hydrogels) were peeled from the membrane, processed, stacked, and placed between an assembly of waxy coated papers, absorbent blotter paper, and two metal caul plates. The assembly was air-dried at room temperature for 24 h and then oven-dried at 60 ∘ C for 8 h under a load of approximately 250 N. The blotter and filter papers were replaced several times over the first 24 h to minimize wrinkling of the films [22].…”

Preparation of highly charged cellulose nanofibrils using high-pressure homogenization coupled with strong acid hydrolysis pretreatments

“…Even small amounts of sulfate groups on CNCs surfaces will cause electrostatic repulsion among CNCs, resulting the excellent dispersion and stability of the aqueous suspension (Yu et al, 2013). The presence of these negative charges are crucial factors for the self-assembling (Habibi, Lucia, & Rojas, 2010;Han, Zhou, Wu, Liu, & Wu, 2013;Qing, Sabo, Wu, Zhu, & Cai, 2015), rheological properties (Boluk, Lahiji, Zhao, & McDermott, 2011) and thermal stability (Araki, Wada, Kuga, & Okano, 1998) of the resultant cellulose nanocrystals (CNCs). Therefore, surface charges play important roles for obtaining excellent surface functionality, which determines the manner of interactions of nanocelluloses with other nanocellulose molecules and with other kinds of polymers (Kalia, Boufi, Celli, & Kango, 2014;Moon, Martini, Nairn, Simonsen, & Youngblood, 2011).…”

Hierarchical porous structures in cellulose: NMR relaxometry approach

“…Traditional methods for characterizing the porous structure and inner surface of materials, such as nitrogen adsorption method and SEM, require dried samples. The porous structure of cellulose material changes dramatically during the drying process [20][21][22][23], so the porous structure of cellulose materials in dried state characterized by traditional methods cannot represent the real porous structure of cellulose in the soaking state. Thus, the understanding of the change of the porous structure during the activation and in soaking states is still limited.…”