Binary Cellulose Nanocrystal Blends for Bioinspired Damage Tolerant Photonic Films

Abstract

Most attempts to emulate the mechanical properties of strong and tough natural composites using helicoidal films of wood-derived cellulose nanocrystals (w-CNCs) fall short in mechanical performance due to the limited shear transfer ability between the w-CNCs. This shortcoming is ascribed to the small w-CNC-w-CNC overlap lengths that lower the shear transfer efficiency. Herein, we present a simple strategy to fabricate superior helicoidal CNC films with mechanical properties that rival those of the best natural materials and are some of the best reported for photonic CNC materials thus far. Assembling the short w-CNCs with a minority fraction of high aspect ratio CNCs derived from tunicates (t-CNCs), we report remarkable simultaneous enhancement of all in-plane mechanical properties and out-of-plane flexibility. The important role of t-CNCs is revealed by coarse grained molecular dynamics simulations where the property enhancement are due to increased interaction lengths and the activation of additional toughening mechanisms. At t-CNC contents greater than 5% by mass the mixed films also display UV reflecting behaviour. These damage tolerant optically active materials hold great promise for application as protective coatings. More broadly, we expect the strategy of using length-bidispersity to be adaptable to mechanically enhancing other matrix-free nanoparticle ensembles.

Flexible and Structural Coloured Composite Films from Cellulose Nanocrystals/Hydroxypropyl Cellulose Lyotropic Suspensions

“…Crystals 2019, 9, From an LC colloidal aqueous suspension with a concentration of CNCs of 3.3 wt.%, different mixtures of CNC/HPC with ratios of 10,20,30,40 and 50 were prepared. In the range of concentrations of HPC used in this study we did not observe the gelation as detected by Hu et al when adding small amounts of other polysaccharides (e.g., hydroxyethyl cellulose or hydroxypropyl guar) to a diluted suspension of CNCs [30].…”

“…More recently, Qu et al were able to show that the D-glucose also acts as a plasticiser and enables active tuning of the left-handed helical organisation while under mechanical deformation [19]. The use of 30 wt.% of long CNCs, extract from tunicates, in a lyotropic suspension of short CNCs, derived from wood, gave rise to a composite system that presents improved mechanical properties (Young's modulus, tensile strength and strain to failure) and when bent they do not break [20]. This example is, to the best of our knowledge, the first where the LC phase of the CNCs is retained in an all-cellulosic based composite film, so keeping in mind the high number of cellulose derivatives, and especially the water-soluble ones, an array of different all-cellulosic composites systems can be examined.…”

Impact resistance of nanocellulose films with bioinspired Bouligand microstructures

“…This was done to illustrate the relationship between two key designing factors, g and D 0 , and the impact resistance of Bouligand thin lms at the microscale. Moreover, berreinforced composites in experiments more oen incorporate short bers to construct helicoidal structures 66 and use midplane symmetry 14,15 to exclude any potential extensionbending coupling behavior. Additionally, the effect of polymer matrices on the ballistic impact response is neglected here.…”

Microstructure and Size Effects on the Mechanics of Two Dimensional, High Aspect Ratio Nanoparticle Assemblies

“…One such example of this type of material is cellulose nanopaper. Cellulose nanopapers, derived from cellulose nanocrystals (CNCs), have emerged as a promising candidate for applying the outstanding properties of CNCs at the macroscale (Henriksson et al, 2008;Eichhorn, 2011;Dumanli et al, 2014;Natarajan et al, 2018). CNCs are an abundant and renewable material that can be extracted from many biological sources, including plants, bacteria, and tunicates (Moon et al, 2011;Sinko et al, 2015), as well as the by-products of the timber, paper, and pulp industries (Fratzl and Weinkamer, 2007).…”

“…Between atomistic MD and continuum models lie mesoscopic, or coarse-gained (CG), MD models. These models have been highly successful at describing the mechanical properties of all CNC materials, both during quasi-static (Qin et al, 2017;Natarajan et al, 2018) and dynamic (Qin et al, 2019) deformation processes. Furthermore, MD simulations do not require explicit failure criteria and can capture discrete and non-affine deformation events, like bond breakage and molecular sliding.…”