The structure of solutions and films of cellulose acetate

Abstract

The optical rotatory dispersion of solutions of cellulose acetates with different degrees of acetylation in a series of solvents is studied. Increasing the degree of esterification of the cellulose acetate results in a shift of the optical rotation to more negative values. These changes have been explained on the assumption of various contributions to the optical rotation from hydroxyl and acetate groups. The cellulose acetate solutions studied fall into two groups. Solutions in acetic acid, dimethylformamide, nitromethane, and acetone give anomalous curves, whereas in methylene chloride, chloroform, tetrachlorethane, and dioxane normal curves of rotatory dispersion are produced. Attempts to fit the results by calculations based on a one‐term Drude equation proved all the curves to be more complex. The influence of solute is probably due to specific interaction with hydroxyl and acetate groups and fixing of rotatory isomers of the side groups. A complex pattern of the rotatory dispersion curves is dictated by the contributions from asymmetric carbon atoms associated with hydroxyl and acetate groups having a different rotatory dispersion. Polymer‐solvent interaction affects the film structure. Crystalline films are obtained from cellulose acetate solutions (AcOH = 60.3%) with anomalous dispersion while solutions with a normal dispersion give amorphous firms.

Modification of the structure of cellulose triacetate films in the course of solvent vapor sorption

“…Changes in the IR spectra of CTA fi lms in the region of C=O stretching vibrations in acetate groups of the polymer, observed upon solvent sorption, relative to the initial fi lm and dilute solutions of the polymer indicate that the interchain polymer-polymer interaction via C=O groups is broken under the action of solvents, which is consistent with the data of [17,18]. Some of the С=О groups become free, and other groups interact with solvent molecules probably by the dipoledipole mechanism, because the low-frequency shifts of the ν С=О band relative to the free С=О group, observed in the presence of DMSO, NM, and TCE (Δν С=О ), are the larger, the higher is the dipole moment of the solvent.…”

Liquid-crystal state in the system polysaccharide-mesophasogenic solvent

“…The arrows mark the process of sorption corresponding to the spontaneous "shrinkage" of the elongated fiber. Probably, precisely because nitromethane is a specific solvent of cellulose acetates [22,23], the behavior of fibers in its vapors is unusual. The anomalous character of the swelling curves, i.e., the extreme sorption kinetics, the squeezing out of the solvent reflected by the "dropping" sections of the curves C s = f(t), as well as the sharp increase in the rate of absorption of the solvent vapors at the final stage, point to a structural transformation in the polymer matrix in the diffusion process [19,25].…”

“…As a sorbate, we used analytically pure nitromethane, d = 1.14 g/cm 3 , T boil = 101.2 o C. We used nitromethane an -electron-donor, dipolar, aprotic solvent [21], in which cellulose acetates form a lyotropic LC phase [4,8,10]. Moreover, nitromethane specifically interacts with the functional groups of cellulose ester, solvating mainly hydroxyl groups [22,23].…”

“…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].…”

“…At the initial instant of time, while the polymer system is vitrified and the macromolecular mobility is limited, it is in the nonequilibrium conformation state (even despite some preliminary orientation acquired in the process of fiber formation). Since nitromethane belongs to selective solvents interacting mainly with OH-groups of DAC [19,22,23], upon absorption by the fiber of the first small portions of specific solvent vapors, disruption of the intermolecular hydrogen bonds occurs, whereas the intermolecular bonds (or at least some of them) remain intact, which preserves natural rigidity of the ester cellulose chains [5]. Upon removal of kinetic disturbances, macromolecules, by virtue of their natural rigidity and acquired mobility, to attain an equilibrium, more straightened conformation, elongate, unfold (which is evidenced by the inversion of the sign of [α]), and self-orientate themselves.…”