Improved order parameter (alignment) determination in cellulose nanocrystal (CNC) films by a simple optical birefringence method

Chowdhury, Raqib; Peng, Shane X.; Youngblood, Jeffrey P.

doi:10.1007/s10570-017-1250-9

Cited by 73 publications

(93 citation statements)

References 54 publications

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“…This in turn will increase the visible light transmittance by lowering the dispersive losses in the film. 45 The increased CNC particle size at higher NaOH concentrations caused more scattering of incident light reducing the transparency of resulting films. After 4 wt %, the film transmittance was reduced ( Figure 6 b) in accordance with the increased CNC particle size ( Figure 6 a) resulting in hazy films ( Figure 7 g–i).…”

Section: Resultsmentioning

confidence: 99%

Transparent and Homogenous Cellulose Nanocrystal/Lignin UV-Protection Films

et al. 2018

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In the context of valorization of lignin produced from the pulp and paper industries, biodegradable UV-protection films were prepared using lignin and cellulose nanocrystals (CNCs). Initially, CNC films were optimized for improving their transparency by studying the effect of various sodium hydroxide (NaOH) concentrations. Maximum (%) transmittance of CNC film was obtained for NaOH addition between 3 and 4 wt %. The optimized CNC suspensions were used for incorporating alkaline lignin (AL) and softwood kraft lignin (SKL) in various concentrations (1–10 wt %). Morphological characterization showed homogeneity of the lignin distribution in CNC/lignin films. Complete UV blocking was achieved at 10 wt % lignin (AL or SKL) in CNC films. Cross-polarized optical microscopy and scanning electron microscopic images of films showed some degrees of global alignment of CNC rods upon addition of NaOH, which remained unaffected by lignin addition. Lignin modification through acetylation reduced the lignin color and improved visible light transmission of films without significantly affecting the UV-absorption properties. Presence of lignin also enhanced the thermal and contact angle stability of the films. This work shows for the first time that CNC aqueous suspensions with and without containing lignin could be tuned through the addition of NaOH to produce transparent and homogenous films, providing a simple and green approach in engineering CNC/lignin UV-protection films.

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Section: Resultsmentioning

confidence: 99%

Transparent and Homogenous Cellulose Nanocrystal/Lignin UV-Protection Films

et al. 2018

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“…Alignment can be induced by applying hydrodynamic shear to a CNC suspension (Figure c) . In the isotropic phase, the average orientation of nanorods under low shear (0.5 s −1 ) is normal to the shear plane, while at high shear (500 s −1 ) it is parallel to the shear direction .…”

Section: Controlling the Alignmentmentioning

confidence: 99%

“…In the cholesteric phase, high shear disrupts the helicoidal order and leads to parallel alignment . Solid birefringent materials with nematic order can thus be produced by applying shear continuously during the evaporation process, or during fast deposition by either spin‐coating or blade‐coating . More importantly, applying moderate hydrodynamic shear to a drying suspension can lead to helicoidal nanostructures with uniform vertical alignment of the helical axis, as observed near the center of a suspension dried on a circularly oscillating plate …”

Section: Controlling the Alignmentmentioning

confidence: 99%

The Self‐Assembly of Cellulose Nanocrystals: Hierarchical Design of Visual Appearance

et al. 2017

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By controlling the interaction of biological building blocks at the nanoscale, natural photonic nanostructures have been optimized to produce intense coloration. Inspired by such biological nanostructures, the possibility to design the visual appearance of a material by guiding the hierarchical self‐assembly of its constituent components, ideally using natural materials, is an attractive route for rationally designed, sustainable manufacturing. Within the large variety of biological building blocks, cellulose nanocrystals are one of the most promising biosourced materials, primarily for their abundance, biocompatibility, and ability to readily organize into photonic structures. Here, the mechanisms underlying the formation of iridescent, vividly colored materials from colloidal liquid crystal suspensions of cellulose nanocrystals are reviewed and recent advances in structural control over the hierarchical assembly process are reported as a toolbox for the design of sophisticated optical materials.

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“…The uniaxial deformation experienced by the fibers during melt-spinning in both the molten and in the solid state affords nanocomposite fibers in which the polymer chains and CNCs adopt a preferred orientation along the fiber direction. Unidirectional molecular and CNC orientation are well-known to lead to an increase in the tenacity and the toughness along the direction of orientation compared to isotropic nanocomposites [28,29,31,32,57]. To examine the effect of molecular orientation on the mechanical properties of nanocomposites, PU/P-tCNC melt-spun fibers, and solvent-cast PU/P-tCNC nanocomposite films were compared.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Melt-Spun Nanocomposite Fibers Reinforced with Aligned Tunicate Nanocrystals

et al. 2019

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The fabrication of nanocomposite films and fibers based on cellulose nanocrystals (P-tCNCs) and a thermoplastic polyurethane (PU) elastomer is reported. High-aspect-ratio P-tCNCs were isolated from tunicates using phosphoric acid hydrolysis, which is a process that affords nanocrystals displaying high thermal stability. Nanocomposites were produced by solvent casting (films) or melt-mixing in a twin-screw extruder and subsequent melt-spinning (fibers). The processing protocols were found to affect the orientation of both PU hard segments and the P-tCNCs within the PU matrix and therefore the mechanical properties. While the films were isotropic, both the polymer matrix and the P-tCNCs proved to be aligned along the fiber direction in the fibers, as shown using SAXS/WAXS, angle-dependent Raman spectroscopy, and birefringence analysis. Tensile tests reveal that fibers and films, at similar P-tCNC contents, display Young’s moduli and strain-at-break that are within the same order of magnitude, but the stress-at-break was found to be ten-times higher for fibers, conferring them a superior toughness over films.

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Improved order parameter (alignment) determination in cellulose nanocrystal (CNC) films by a simple optical birefringence method

Cited by 73 publications

References 54 publications

Transparent and Homogenous Cellulose Nanocrystal/Lignin UV-Protection Films

Transparent and Homogenous Cellulose Nanocrystal/Lignin UV-Protection Films

The Self‐Assembly of Cellulose Nanocrystals: Hierarchical Design of Visual Appearance

Melt-Spun Nanocomposite Fibers Reinforced with Aligned Tunicate Nanocrystals

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