G. N. Timofeeva

Phase processes and energetics of spontaneous change in the dimensions of acetate fibers in nitromethane vapors

The phenomenon of cyclic change (elongation and contraction) in the dimensions of acetate filaments and monofibers in the vapors of nitromethane as a specific solvent is quantitatively described. An algorithm for calculating the energy characteristics of the deformation, including the specific work, is developed. The longitudinal viscosity is estimated according to the deflection of a horizontally stretched sample. It is shown that the stereomeric structure of the polysaccharide is altered in the process of cyclic change in the filament dimensions, as is confirmed by reversal of the sign of specific optical rotation. The resultant data are interpreted in terms of phase (amorphous vitreous versus liquid-crystal states) and conformational transitions.

Effect of molecular mass on the optical activity of chitosan

The optical activity of chitosan has been examined by the optical rotary dispersion method in a wide molecular mass range, beginning from low-molecular analogs of the monomer unit and oligomers. In the spectral range from 300 to 710 nm, all samples demonstrate smooth curves of the optical rotary dispersion. For the polymers and oligomers, these curves lie in the region of negative values of specific optical rotation [α], while for monosaccharides, these curves are in the positive region. High-molecular-mass samples are characterized by maximal −[α] values that are practically independent of molecular mass. For partially depolymerized samples with M < 2 × 105 and for oligomers, the smaller the molecular mass of the sample, the greater the decrease in the modulus of −[α]. The passage to D-glucosamine chlorohydrate and to N-acetyl-D-glucosamine is characterized by inversion of the sign of rotation and achievement of high +[α] values.

New information concerning spontaneous elongation of acetate fibers

The ability of acetate fibers to experience spontaneous changes in their linear dimensions under the action of vapors of aprotic, amphiprotic, and protic solvents, which are widely used in scientific studies and engineering practice, has been investigated. In the vapor phase of solvents that are able to produce the lyotropic LC phase in cellulose derivatives, the phenomenon of spontaneous elongation of fibers has been discovered. This phenomenon has been observed for both cellulose diacetate and triacetate yarns, and their elongation can achieve ∼ 120–180%. In some systems, one can observe the reverse process that represents a spontaneous contraction of the sample after its self-elongation in solvent vapor. To study the above phenomena, a well-known system based on cellulose acetate and nitromethane is considered to be a reference system. The phenomenon of spontaneous elongation is proposed for use as a test for estimating the ability of the (cellulose ether)-solvent system to experience LC ordering.

Orientation processes in cellulose acetate under the action of dimethyl sulfoxide vapor

Spontaneous variation of the linear size (elongation-contraction) of acetate fibers in a vapor of dimethyl sulfoxide, which is a mesophasogenic solvent, i.e., a solvent forming a liquid crystal phase with the polymer, is described. A mechanism of the interaction of the polymer with the solvent vapor is suggested.

Orientational processes in the yarns of high-molecular-mass cellulose acetate in vapors of nitromethane and its mixture with water

The phenomenon of spontaneous changes in the linear dimensions (elongation-contraction) is described for commercial and laboratory samples of acetate yarns processed by wet spinning from high- molecular -mass cellulose diacetate in vapors of a mesophas ogenic solvent (which is able to form a lyotropic LC phase with the polymer), nitromethane, and its mixtures with water. The thermodeformational, elastic- plastic, physicomechanical, and surface characteristics of the yarns at different stages of their spontaneous deformation are analyzed. When samples are treated with probe vapors, orientational processes in the polymer matrix are activated, and this observation makes it possible to prepare yarns with improved physicomechanical characteristics and with low linear density. A new phenomenon (to our knowledge) of cyclic three- stage deformation of acetate monofilaments in nitromethane vapors is discovered. This evidence is interpreted from the standpoint of phase (amorphous glassy-liquid crystalline state) and conformational transitions as well as by the mechanism of interaction between polymers and solvent vapors and related development of the LC phase.

Effect of Ethyl Alcohol Vapors on the Structure of Polycaproamide Fibre

It was found that ethyl alcohol vapors induce a spontaneous elongation effect in PCA fibres. Modification of PCA fibres with ethyl alcohol vapors makes the structure pass from the unstable β-modification to the stable α-modification, eliminating the process of repeated orientational drawing.

Physicomechanical properties of acetate fibres modified with nitromethane vapors

The physicomechanical characteristics of acetate fibres were investigated in different stages of their spontaneous elongation in nitromethane vapors. It was shown that acetate fibres are strengthened and the coefficients of variation for the breaking strength and elongation at break decrease at the beginning of treatment with vapors of a specific solvent. A hypothesis was advanced concerning the possible mechanism of the reaction of the polymer with the solvent vapors in which it forms a mesophase.

Orientation processes in acetate yarns under the influence of certain solvent vapors

ConclusionsTreatment of acetate yarns with vapors from solvents which form a liquid-crystal phase with the polymer leads to initiation of orientation processes which are accompanied by spontaneous yarn elongation. This makes it possible to prepare yarns of low linear density and with improved physicomechanical properties.It has been found that the action of vapor from nitromethane, which forms a lyotropic, liquid-crystal phase in cellulose acetates, takes place in several stages.A mechanism has been proposed for the interaction of the polymer with vapor from a solvent which forms a liquid-crystal phase with it.