Structure Formation and Optical Activity of Cellulose Acetate Modified by the Vapors of Mesophasogenic Solvents

Timofeeva

2006

Fibre Chem

Self Cite

Mesophasogenic solvents in the vapor state actively affect the structure of cellulose acetates of different morphological forms (fibre, film, bulk polymer). On the supramolecular level, this is manifested by initiation of orientation processes and on the conformational level by a change in the optical density, up to a change in the direction of rotation of the cholesteric helix to the opposite direction. The approach found creates conditions for formation of a given structure and three-dimensional organization of the polymer matrix for manufacture of materials with improved properties and new qualities.Of the large number of polysaccharides, cellulose and cellulose derivatives are the most important in the total production volume of polymeric materials for industrial and domestic applications. This class of macromolecular compounds has been actively studied up to now both to obtain fundamental knowledge and for their practical use.Domestic scientists specializing in polymer science have made an enormous contribution to the study of the structure, composition, and properties of cellulose and its ethers. They include the internationally known scientists

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confidence: 77%

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confidence: 99%

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The liquid-crystalline state of cellulose acetates: From past to present. Experience of the Saratov school

Timofeeva

2006

Fibre Chem

Self Cite

“…This, in turn, made it possible to discover new phenomena and mechanisms that have not been reported in the literature before [11,19,20]. In this paper, we present the results of the investigation of the influence of vapors of the mesophasogenic solvent nitromethane, forming with a polymer a lyotropic LC phase, on the structure of acetate fibers widely manufactured by modern industry.…”

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confidence: 93%

“…The fiber elongated under the action of vapors is able to preserve for a long time this dimension with a slight time shrinkage in the absence of vapors (i.e., when removed from the vapor medium). The reason for the double influence of nitromethane on the polymer is likely the specificity of the polymer-solvent interaction [19,22,23]. Nothing of the kind has been revealed for acetate fibers swelling directly in liquid media [13][14][15][16][17][18].…”

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confidence: 99%

Liquid-crystal state in the system polysaccharide-mesophasogenic solvent

Timofeev

2006

J Eng Phys Thermophys

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Data on the influence of vapors of nitromethane -a mesophasogenic solvent, i.e., a solvent forming with a polymer a lyotropic liquid-crystal phase -on the structure of acetate fibers are presented. It has been established that nitromethane in the vaporous state initiates in the polymer matrix orientation processes: induced anisotropy, spontaneous elongation of the fiber (which, in terms of Flory, is considered to be the transition to the nematic phase), as well as the process inverse to the self-elongation discovered for the first time, etc. It has been shown that the realization of both the direct and inverse processes of spontaneous deformation of cellulose acetate in mesophasogenic solvent vapors is associated with the optical asymmetry, i.e., the optical activity of the polysaccharide.Intensive experimental and theoretical studies of liquid-crystal (LC) polymer systems of synthetic origin, whose macromolecules are characterized by a high rigidity of the chain, date back to the 1950s [1, 2]. Later, the LC state was also revealed for natural polymers, e.g., such as cellulose and its derivatives [3,4], the conformation of whose macromolecules is far from a rigid rod and is closer to the conformation of a semirigid chain.Because the melting temperatures are much higher than the temperatures of intensive thermal decomposition, most cellulose derivatives cannot go to the LC state in melts and create only lyotropic LC systems. The formation of mesomorphous solutions of this class of substances is complicated because of the necessity to use high polymer concentrations (over 25 mass %) and in a rather limited range of solvents, in which the LC phase is formed [3][4][5]. The best studied in this respect are systems based on cellulose ethers: oxypropyl-, oxymethyl-, ethylcellulose, and ethers in such solvents as water, dimethylacetamide, dimethylsulfoxide, acetic, dichloracetic, and formic acids [3,5]. The series of polymer LC systems based on natural polysaccharides that have received fairly complete and detailed studies includes cellulose esters, in particular, cellulose acetates [4, 6, 7] having in the composition of the macromolecular chain (depending on the degree of etherification of the samples) a different ratio between acetate and hydroxyl groups. It has been established that in the presence of a solvent specifically interacting with the functional groups of the polymer acetic-acid cellulose esters can form systems with phenomena and signs characteristic of the LC state [6][7][8][9][10][11]. Among such criteria are, for example, the distinguishing features of the rheological behavior of mesomorphous solutions [6][7][8][9]. For the solid-like state these are induction of time-independent optical anisotropy in acetate films [7,10], the phenomenon of spontaneous elongation of fibers of the same nature [11], which according to Flory, directly confirms the transition of the polymer-solvent system to the nematic phase [1, 12], etc.The effect of spontaneous elongation of fibers and films based on cellulose acetates at...

Optical activity of the anisotropic phases of cellulose acetates

J Polym Sci B Polym Phys

Shmakov

Kazmicheva

et al. 2009

In this study, the optical activity of cellulose di and triacetate films with a highly oriented vitrified structure was studied. The systems possess high values of specific optical rotation [a], which is in favor of the formation of a cholesteric mesophase.[a] depends on the sample orientation angle relative to the light polarization vector in the plane perpendicular to the light ray (optical activity anisotropy). This dependence (indicatrix) is irregular and is described by a distorted sinusoid in the Cartesian coordinates. The results of indicatrix decomposition into harmonic components are discussed, with the contributions of the isotropic and anisotropic components (each with the corresponding structural element of a certain symmetry type) being separated.