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

Abstract

Lyotropic colloidal aqueous suspensions of cellulose nanocrystals (CNCs) can, after solvent evaporation, retain their chiral nematic arrangement. As water is removed the pitch value of the suspension decreases and structural colour-generating films, which are mechanically brittle in nature, can be obtained. Increasing their flexibility while keeping the chiral nematic structure and biocompatible nature is a challenging task. However, if achievable, this will promote their use in new and interesting applications. In this study, we report on the addition of different amounts of hydroxypropyl cellulose (HPC) to CNCs suspension within the coexistence of the isotropic-anisotropic phases and infer the influence of this cellulosic derivative on the properties of the obtained solid films. It was possible to add 50 wt.% of HPC to a CNCs aqueous suspension (to obtain a 50/50 solids ratio) without disrupting the LC phase of CNCs and maintaining a left-handed helical structure in the obtained films. When 30 wt.% of HPC was added to the suspension of CNCs, a strong colouration in the film was still observed. This colour shifts to the near-infrared region as the HPC content in the colloidal suspension increases to 40 wt.% or 50 wt.% The all-cellulosic composite films present an increase in the maximum strain as the concentration of HPC increases, as shown by the bending experiments and an improvement in their thermal properties.

Genotoxicity of Three Micro/Nanocelluloses with Different Physicochemical Characteristics in MG-63 and V79 Cells

“…%, from 95–97%, Sigma-Aldrich, MO, USA, p.a.) and an acid solution/solid ratio of 8:1 from adaptations of the acid hydrolysis method described elsewhere [ 57 , 58 ]. The reactional process occurred at 55 °C, under mechanical stirring, and the mixture was quenched with ultrapure water after 75 min of reaction.…”

“…The droplets were allowed to dry at 60 °C until they were a constant weight and samples were kept in a desiccator until further use. Moreover, 4 × 4 µm 2 height images were used to measure the average length of individual nanoparticles, as described by Saraiva et al (2020) [ 58 ]. The width of each particle used in the length determination was returned from the height profile along its length, as described by Honoratos-Rios et al (2018) [ 61 ].…”

Current international research into cellulose as a functional nanomaterial for advanced applications

“…Recently, several strategies have been proposed to mitigate their intrinsically poor mechanical resistance. Such strategies usually involve the co-assembly with a plasticizer that does not compromise the self-assembly of the CNCs, such as surfactants [387], a neutral or anionic polymer [388][389][390], globular proteins [391], resins or sol-gel precursors [392,393]. Two recent examples from Walters et al [389] and from Saraiva et al [390] showed that a common cellulose derivative, hydroxypropyl cellulose (HPC), can be successfully used as a plasticizer for CNC photonic films, significantly preventing crack growth upon bending with respect to plain CNC films (Fig.…”

Mechanochromic, Structurally Colored, and Edible Hydrogels Prepared from Hydroxypropyl Cellulose and Gelatin

“…Despite its widespread use and seminal photonic studies in the 1970s and 1980s, the development of HPC‐based photonic applications has been slow. [ 7–13 ] Recently however, a growing interest in sustainable raw materials and their application has seen a shift in photonic HPC research toward practical applications [ 14–22 ] and large‐area processing. [ 17,18 ]…”