Structural transitions in commercial cellulose systems

Abstract

The problems of phase transitions in commercial cellulose systems during processing are considered. The formation of structures in regenerated cellulose from viscose solutions during precipitation in different regenerated baths and in highly concentrated solutions of cellulose in N-methylmorpholin-N-oxide at different temperatures and shear deformations has been selected for this review. The difficulties in defining the type of structural ordering in these systems are demonstrated. Fractal analysis is used to study the structures. A close relationship between the characteristics of the structures and the fractal dimensions is elucidated. The prospects for the different methods of regulating structures in cellulose systems are discussed.

Colloidal Particle-Induced Microstructural Transition in Cellulose/Ionic Liquid/Water Mixtures

“…As χ increases above 0.08, with a decrease in solvent quality and due to the consequent increase in polymer–polymer interaction, the biphasic domain, that is, the region in which a concentrated anisotropic phase coexists with a dilute isotropic phase broadens, and the formation of anisotropic phase commences at a much lower polymer concentration. This has been experimentally verified for solutions of several polymers, including cellulose. ,,− Moreover, the generation of an anisotropic phase by this route, in principle, is not solvent specific. The poor solvent quality can be achieved by manipulating temperature or using a suitable antisolvent. , Recently, we have shown the formation of anisotropic gels in cellulose/IL mixtures with the addition of water .…”

“…In the recent years, owing to increased awareness on environmental issues created due to the use of synthetic polymers, there has been a lot of interest in the development of biopolymer-based liquid crystalline (LC) materials without compromising much on their mechanical and chemical properties. At sufficiently high concentration, semiflexible polymers, such as cellulose, DNA, and chitin, dissolved in good solvents and are known to exhibit LC behavior due to high probability of overlap of polymer chains and their rearrangement. − Because the critical concentration required for the generation of anisotropic phase is inversely proportional to the persistence length of the polymer molecule, cellulose with comparatively low persistence length needs to be dissolved in large quantity (high concentration) which in turn results in highly viscous solutions where the processability and the dissolution themselves become difficult. ,,, Even though the advent of cellulose dissolving ionic liquids (ILs) has helped to overcome the dissolution issues, high viscosity of cellulose/IL solutions at high cellulose concentration and extreme hygroscopicity of ILs make the realization of the LC phase from cellulose solutions still challenging. ,− The high viscosity of a polymer solution at concentrations sufficiently high for the formation of an LC phase may cause forced orientation of the polymer chains rather than the formation of thermodynamically stable mesophase, as pointed out earlier by several authors. , …”

“…2,11−13 The high viscosity of a polymer solution at concentrations sufficiently high for the formation of an LC phase may cause forced orientation of the polymer chains rather than the formation of thermodynamically stable mesophase, as pointed out earlier by several authors. 12,13 According to Flory's prediction, 14 a semirigid polymer in a good solvent (negative χ parameter) undergoes a transition from the isotropic phase, wherein the polymer chains are randomly distributed to an oriented mesophase through a narrow biphasic domain, as the polymer concentration increases. As χ increases above 0.08, with a decrease in solvent quality and due to the consequent increase in polymer− polymer interaction, the biphasic domain, that is, the region in which a concentrated anisotropic phase coexists with a dilute isotropic phase broadens, and the formation of anisotropic phase commences at a much lower polymer concentration.…”

The formation of dissipative structures in polymers as a model of synergy

“…The formation of such structures from chaotic state described by a decrease in entropy due to the exchange with the external environment. An example of such is the appearance of dissipative structures in the process of coagulation of supramolecular structures of various types, which ultimately determine the physical and mechanical properties of the finished product [4].…”