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.
Highlights
Much interest has been given by the scientific community to cellulose nanocrystals (CNCs)-based materials, since these nanoparticles present a set of advantages that built on the ones derived from their precursor, the biopolymer cellulose
In the range of concentrations of hydroxypropyl cellulose (HPC) used in this study we did not observe the gelation as detected by Hu et al when adding small amounts of other polysaccharides to a diluted suspension of CNCs [30]
In the LC-CNCs suspension seems not to influence the liquid crystalline phase, if one compares the birefringence obtained in the CNCs/HPC/H2 O mixtures and the CNCs/H2 O suspension
Summary
Much interest has been given by the scientific community to cellulose nanocrystals (CNCs)-based materials, since these nanoparticles present a set of advantages that built on the ones derived from their precursor, the biopolymer cellulose. CNCs are lightweight, present a high Young’s modulus, a high surface area and superficial hydrophilicity [1]. If. CNCs are extracted by sulphuric acid hydrolysis from a cellulosic biomass, such as cotton or wood pulp, and when suspended in water above a critical concentration (C*), they can self-assemble into a lyotropic chiral nematic liquid crystalline (LC) phase [2]. CNCs are extracted by sulphuric acid hydrolysis from a cellulosic biomass, such as cotton or wood pulp, and when suspended in water above a critical concentration (C*), they can self-assemble into a lyotropic chiral nematic liquid crystalline (LC) phase [2] In this LC phase, the local orientation of *. The stabilisation of this colloidal suspension and its self-assembly into a lyotropic phase are Crystals 2020, 10, 122; doi:10.3390/cryst10020122 www.mdpi.com/journal/crystals
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