Cellulosic liquid crystals for films and fibers

ABSTRACT

Cellulose, the most abundant natural polymer on earth, is used in numerous applications in our day-to-day life. However, the discovery that cellulose-based systems could lead to the formation of liquid crystalline phases only dates to the 1970s. Compared with all known applications of cellulose, the liquid crystalline behavior has been less considered. Associated with this are the low solubility of cellulose and the existence of a chiral nematic precursor solution and its processing under the action of a shear field, which is used to produce fibers and films. In this review, we first conduct a short review of the main features of cellulosic liquid crystalline phases including the main textures observed by polarizing optical microscopy and the cholesteric phase characteristics of thermotropic and lyotropic systems observed for cellulose and cellulose derivatives. Then, we focus on the rheological properties of liquid crystalline solutions and special attention is given to the formation of striations developed during shear and the formation of the band texture, which appears during the relaxation process. Among the different techniques used, special emphasis is given to the results obtained by coupling rheology with optical microscopy (Rheo-optics) and nuclear magnetic resonance (Rheo-NMR) techniques. Some examples described in the literature, related to the use of cellulose and cellulose derivatives liquid crystals to the production of structural color scaffolds, stimuli-responsive films and fibers, are addressed. In these systems, the initial cholesteric phase determines the unique properties exhibited by the films and the fibers produced from cellulosic liquid crystalline systems.

KEYWORDS:

• Liquid crystals
• cellulose derivatives
• cholesteric liquid crystals
• lyotropic and thermotropic cellulosic systems
• films and fibers

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was funded by FEDER funds through the COMPETE 2020 Programme and National Funds through FCT – Portuguese Foundation for Science and Technology – Portuguese Foundation for Science and Technology under the project number POCI-01-0145-FEDER-007688, Reference UID/CTM/50025 and the project PTDC/CTM-BIO/6178/2014. S.N. Fernandes acknowledges the Minister of Science, Technology and Higher Education for National Funds, European Social Funds and FCT for fellowship number SFRH/BDP/78430/2011. C. Echeverria and J.P. Canejo acknowledge funding from the Portuguese Science and Technology Foundation through grants SFRH/BPD/88779/2012 and SFRH/BPD/101041/2014.