1. The sorption of binary solutions by vulcanizate of natural and sodium-butadiene rubber was studied over the entire composition range of the following binary systems: benzene-low weight alcohols, benzene-low weight acids, benzene-polar derivatives of benzene, toluene-low weight alcohols, carbon tetrachloride-low weight alcohols, p-dichlorobenzene-low weight alcohols, benzene-acetone, benzene-ethyl acetate, chloroform-acetone, chloroform-methyl ethyl ketone, benzene-ethyl iodide, benzene-propyl bromide, hexane-dioxane. With the help of these data, coefficients of distribution of components between phases and sorption potentials of the components were calculated. Effective sorption isotherms of solvent from all the systems were constructed. 2. There is a close connection between the value of the effective sorption of solvent from systems of the solvent-nonsolvent type and the nature of the binary solution. The effective sorption of solvent is greater the larger the positive quantity of excess free energy of formation of the binary solution. From systems characterized by a negative value of excess free energy the solvent is sorbed to a far smaller degree than from systems with a positive deviation from the laws of ideal solutions. Sorption from binary solutions by rubber produces all four types of effective sorption isotherms that are predicted from thermodynamic considerations. 3. Comparison of effective sorption isotherms from the same solvent-nonsolvent system by vulcanized rubber and by activated carbon shows that the maximum value of effective sorption of solvent is much greater for the rubber than for the carbon. The selective nature of the sorption is also more strongly evident with the rubber : the negative branch of the S-shaped sorption isotherm from binary solutions on carbon is practically missing when the sorption takes place from the same solution on vulcanized rubber. From this it follows that many binary liquid systems as well as mixtures of saturated vapors could be more effectively separated on rubber and its vulcanizates than on activated carbon. This conclusion could have practical value since the effective sorption by rubber changes little with temperature and the desorption process is easier to carry out with rubber than with carbon. 4. It was established that the shape of the equilibrium curve between polymer and binary solutions does not depend on the degree of vulcanization or the composition of the active fillers in the vulcanizate. From this it follows that the efficiency factor of the sorption process is determined only by the nature of the rubber and not by the composition of the vulcanizate. 5. From analysis of the experimental data it follows that sorption of solvent occurs largely as random mixing of its molecules with sections of the polymer chain. Sorption of nonsolvent takes place by more or less strong attachment of its molecules on sorption sites of the polymer.
1. The swelling in the gaseous phase at 20° C of a digested vulcanizate of natural rubber was studied through the entire range of compositions of the following binary systems: methyl alcohol-benzene, ethyl alcohol-benzene, n-propyl alcohol-benzene, n-butyl alcohol-benzene, and n-hexanol-benzene, and in a system of octadecanol-benzene at 60° V in the liquid phase. The swelling-composition curves show a maximum in the first three systems enumerated and a minimum in the latter system. 2. In the first five systems, the concentrations of the components of the equilibrium solution phase and the rubber phase were measured by means of an interferometer. 3. The coefficient of distribution of alcohol between the polymer and solution phases decreased from 1.6 in the methyl alcohol-benzene system to 0.3 in the n-hexanol-benzene system. The decrease of the coefficient of distribution of alcohol through the series of homologs is attributable to the dipolar character of the alcohol molecules. The coefficient of distribution of benzene between the two phases decreased from 16.6 in the methyl alcohol-benzene system to 6.3 in the n-hexanol-benzene system. This decrease of the coefficient of distribution of benzene is caused by the weakening of the quasi-crystalline structure in passing from methyl alcohol to the higher alcohols. 4. From an analysis of the distribution of alcohol between the solution and polymer, and also from a comparison of these curves with the curves of distribution of alcohol between the binary solution and its saturated vapor, it follows that rubber absorbs individual alcohol molecules, but not associates of them. 5. From a comparison of data on the distribution of the components of the binary solution between the polymer and equilibrium solution, and also from an analysis of the curves of partial free energy of the components of both phases, it follows that the general nature of the curves of isothermic equilibrium in the systems studied accords with the hypothesis of Konovalov; at the maximum points on the swelling curves, the composition of both phases is equal. The degree of swelling increases with increase of the concentration of the component in highest concentration in the polymer. 6. The existence of points of constant composition on the swelling curves is confirmed by measurements of the swelling by the volumetric method. Only for the compositions of solutions which correspond to the maximum points on the swelling curves, the volume in the condenser in whose vapors the specimen is suspended does not change with time. In more dilute solutions, the volume decreases ; in more concentrated solutions it increases, with time. 7. There is a close relation between the degree of swelling and the structure of a solution. The more pronounced the quasi-crystalline structure of the solution, the higher is the swelling-composition curve on the graph. The values of the degree of swelling and the Kirkwood-Anselm correlation parameter change in parallel for a given composition of the solution, in passing from one alcohol to another.
1. The swelling of vulcanizates of natural rubber and sodium-butadiene rubber in the saturated vapors of binary systems of benzene and low-molecular alcohols (from methyl to butyl) at 20° and 50° C was studied in the entire range of composition of binary solutions. 2. The general form of the curves of isothermic equilibrium between the swollen polymer and binary solution were found to conform to Konovalov's law. 3. The absorption of a binary solution by both polymers has a very pronounced selective character. The selectivity of absorption of the solution is more pronounced, the greater is the density of energy of cohesion of the alcohol. In natural rubber, the capacity of selective absorption is more pronounced than in sodium-butadiene rubber. This is probably due to the larger concentration of oxidized groups in natural rubber. 4. The changes of the free energy, the heat content, and entropy for the passage of one gram-mole of alcohol from an infinitely dilute solution into the polymer were calculated from the experimental data. These calculations indicate that the reaction of the alcohol molecules with the polar groups of the polymer is dipole-dipole. 5. The passage from pure benzene to a swollen polymer of any particular composition is characterized by a large increase of entropy in comparison with the passage to a binary solution of the same composition. The relation in alcohol is the reverse. The increase of the entropy of benzene can serve as a measure of the elasticity of the polymer chains. A decrease of the entropy of alcohols indicates the content of free polar groups in the polymer phase. 6. The values of the partial heat content of the low-molecular components are positive; consequently, the decrease of free energy during their sorption by the polymer is due exclusively to an increase of entropy.
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