A Green and Iridescent Composite of Cellulose Nanocrystals with Wide Solvent Resistance and Strong Mechanical Properties

Abstract

Cellulose is the most abundant plant-based natural material. As a green and multifunctional material, the chiral nematic films from self-assembled cellulose nanocrystals (CNCs) have drawn considerable attention in recent years. Although the swellability in water and other solvents has been used to develop CNCs-based moisture sensors, CNCs films with a wide range of solvent resistance will greatly expand their practical applications. In this study, we demonstrated that the iridescent and hydrophilic CNCs films have been changed to films with excellent water resistance, even the strongly acidic or basic aqueous solutions, and various organic solvents via co-assembly with oxidized starch (OS) and tannic acid (TA). The composite films retain their structural integrity and preserve their vivid structural color after being immersed in water for 24 h. Moreover, the CNCs/OS/TA composite film with the weight ratio of CNCs and OS of 85:15 and the weight percentage of TA 8 wt % shows a tensile strength of up to 70.89 ± 3.21 MPa and the maximum Young's modulus to 18.67 ± 1.25 GPa, while, in the wet state, those values are still as high as 58.60 MPa and 13.60 GPa, respectively. The hydrogen-bond-based cross-linking via tannic acid endows CNCs films with an extraordinary solvents resistance and a significant increase in mechanical properties, which opens up a wide range of applications for CNCs-based iridescent films in harsh conditions.

Cellulose Nanocrystal Chiral Nematic Composites with Wet Mechanical Adaptability

“…Meanwhile, wet composites with higher ER content showed higher mechanical strength, agreeing with previous studies on improving the wet strength of cellulose materials by introducing a hydrophobic component. 42,61 This is probably associated with the partial preservation of interrod interactions in the presence of high ER content. In addition, all of the wet composites exhibited increased elongation (Figure 4e) and toughness.…”

“…38−41 Additives like oxidized starch and tannic acid have also been shown to improve the solvent resistance of CNC films. 42 Recently, our group functionalized CNC-(hydroxypropyl cellulose) chiral nematic composite films with methacrylate groups to improve their stability in water. 43 Despite this, the mechanical performance of most water-stable CNC chiral nematic films is still unsatisfactory; investigations on the wet mechanical properties of chiral nematic CNC composites are also limited.…”

Optimizing the performance of the near-infrared (NIR) photothermal conversion via modulating the domain size of the chiral nematic phase in co-assembled cellulose nanocrystal composite films

“…CNCs suspensions were prepared through the sulfuric acidmediated hydrolysis of Whatman ashless filter paper according to our previous work. 32,33 Briefly, 5 g filter paper was cut into small pieces and hydrolyzed in 50 mL of 64 wt% sulfuric acid at 45 1C under vigorous stirring for 45 min. Then the resulting faint yellow slurry was added into cold deionized water (10-fold of the acid solution) to stop the hydrolysis.…”

“…28,29 On the other hand, the liquid crystalline tactoids of CNCs varied in their size, from several tens of micrometers (440 mm) 30,31 to several micrometers (B2 mm). 32 However, there is a lack of knowledge regarding the influence of the domain size of CNCs' chiral nematic structure on their photothermal properties.…”

Chiral Cellulose Nanocrystal Humidity-Responsive Iridescent Films with Glucan for Tuned Iridescence and Reinforced Mechanics

“…Generally, CNC-based photonic structures can generate bright colors, but films made with only CNCs are too brittle. To address this issue, polymers are commonly added as reinforcement/plasticizing agents to enhance the toughness. ,, Some natural polymers have been applied to meet the mechanical demand of CNC composites. − For example, polysaccharides (xylan, dextran, and pullulan) with similar molecular weights and chemical compositions have been used to prepare CNC chiral composite films . As the polysaccharide content increases, the CNC film shows a redshift.…”