Modifying Mechanical, Optical Properties and Thermal Processability of Iridescent Cellulose Nanocrystal Films Using Ionic Liquid

Biomimetic Optical Cellulose Nanocrystal Films with Controllable Iridescent Color and Environmental Stimuli-Responsive Chromism

As a wise and profound teacher, nature provides numerous creatures with rich colors to us. To biomimic structural colors in nature as well as color changes responsive to environmental stimuli, there is a long way to go for the development of free-standing photonic films from natural polymers. Herein, a highly flexible, controllably iridescent, and multistimuli-responsive cellulose nanocrystal (CNC) film is prepared by simply introducing a small molecule as both plasticizer and hygroscopic agent. The presence of the additive does not block the self-assembly of CNC in aqueous solution but results in the enhancement of its mechanical toughness, making it possible to obtain free-standing iridescent CNC films with tunable structural colors. In response to environmental humidity and mechanical compression, such films can change structural colors smoothly by modulating their chiral nematic structures. Notably, the chromism is reversible by alternately changing relative humidity between 16 and 98%, mimicking the longhorn beetle Tmesisternus isabellae. This chromic effect enables various applications of the biofilms in colorimetric sensors, anticounterfeiting technology, and decorative coatings.

Bioinspired Bouligand cellulose nanocrystal composites: a review of mechanical properties

The twisted plywood, or Bouligand, structure is the most commonly observed microstructural motif in natural materials that possess high mechanical strength and toughness, such as that found in bone and the mantis shrimp dactyl club. These materials are isotropically toughened by a low volume fraction of soft, energy-dissipating polymer and by the Bouligand structure itself, through shear wave filtering and crack twisting, deflection and arrest. Cellulose nanocrystals (CNCs) are excellent candidates for the bottom-up fabrication of these structures, as they naturally self-assemble into 'chiral nematic' films when cast from solutions and possess outstanding mechanical properties. In this article, we present a review of the fabrication techniques and the corresponding mechanical properties of Bouligand biomimetic CNC nanocomposites, while drawing comparison to the performance standards set by tough natural composite materials.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

The Effect of Reactive Ionic Liquid or Plasticizer Incorporation on the Physicochemical and Transport Properties of Cellulose Acetate Propionate-Based Membranes

Pervaporation is a membrane-separation technique which uses polymeric and/or ceramic membranes. In the case of pervaporation processes applied to dehydration, the membrane should transport water molecules preferentially. Reactive ionic liquid (RIL) (3-(1,3-diethoxy-1,3-dioxopropan-2-yl)-1-methyl-1H-imidazol-3-ium) was used to prepare novel dense cellulose acetate propionate (CAP) based membranes, applying the phase-inversion method. The designed polymer-ionic liquid system contained ionic liquid partially linked to the polymeric structure via the transesterification reaction. The various physicochemical, mechanical, equilibrium and transport properties of CAP-RIL membranes were determined and compared with the properties of CAP membranes modified with plasticizers, i.e., tributyl citrate (TBC) and acetyl tributyl citrate (ATBC). Thermogravimetric analysis (TGA) testified that CAP-RIL membranes as well as CAP membranes modified with TBC and ATBC are thermally stable up to at least 120 °C. Tensile tests of the membranes revealed improved mechanical properties reflected by reduced brittleness and increased elongation at break achieved for CAP-RIL membranes in contrast to pristine CAP membranes. RIL plasticizes the CAP matrix, and CAP-RIL membranes possess preferable mechanical properties in comparison to membranes with other plasticizers investigated. The incorporation of RIL into CAP membranes tuned the surface properties of the membranes, enhancing their hydrophilic character. Moreover, the addition of RIL into CAP resulted in an excellent improvement of the separation factor, in comparison to pristine CAP membranes, in pervaporation dehydration of propan-2-ol. The separation factor β increased from ca. 10 for pristine CAP membrane to ca. 380 for CAP-16.7-RIL membranes contacting an azeotropic composition of water-propan-2-ol mixture (i.e., 12 wt % water).