L.P. Razumovskii

Sorption of water by aliphatic polyamides. Review

The published findings on the diffusion and solubility of water in aliphatic polyamides are systematized. Attention is focused on the influence of the chemical nature of the polyamide and its supramolecular structure on the sorption capacity and the diffusion and swelling coefficients. From perusal of the existing ways of predicting the values of solubility S and diffusion D coefficients in polyamides the authors propose a scheme for calculating S and D on the basis of only the structural formula of the polymer chain. The results may be used in study of the hydrolytic stability of the polyamides and prediction of their physiochemical properties on sorption of water.

Determining the crystallinity of polycaproamide by isotope H → D exchange☆

Using isotope H → D exchange coefficients of adsorption bands of ND groups were determined at 2480 cm−1 and of crystalline NH groups at 3300 cm−1. Extinction coefficients obtained enable the crystallinity of polycaproamide films to be calculated using both adsorption bands at the same time (for thin films up to 10 μm) or using only the adsorption band of ND groups (in the case of thicker films).

Solubility and diffusion coefficient of water in aliphatic polyamides

Abstract The diffusion of water at 25°C in the following unoriented polyamide films has been investigated: PA-11, PA-610, PA-69, an 80% PA-6+20% PA-12 copolymer and an 85% PA-6+15% PA-11 copolymer. The quantitative relationship between the chemical formula of the linear polyamides and their moisture adsorption at different vapour pressures has been established on the basis of the Flory-Huggins theory. Water exerts a plasticizing effect on all the aliphatic polyamides that is qualitatively the same. A method is proposed for the calculation of the diffusion coefficient of water in the polyamides.

Diffusion of alcohols into polyamides

A study was made of the diffusion of methyl and ethyl alcohols into PK-4 and PA-12 polyamide films. Diffusion coefficients were determined and their dependence on concentration established. The difference was examined in using the concepts “crystallinity” and “accessibility” when calculating solubilities. It was shown that the accessibility of PK-4 to water and ethanol molecules was 0·6 and 0·3, respectively. It was found that the solubility of the sorbate in polyamides increases in the order: H2OCH3OHC2H5OH and decreases on transition from PK-4 to PA-12.

The mutual influence of components of a medium on their sorption by polyamides

Abstract The mutual influence of components of a medium on their sorption by polymers has been investigated for the system polyamide-hydrogen chloride-water. It was found that the presence of previously adsorbed acid in polycaproamide makes for increased solubility and for a higher rate of diffusion of water in the matrix. An analysis of the experimental results shows that the observed phenomena are related to the plasticizing action of the acid and to the disintegration of clusters owing to the formation of hydrates of the type of (HCl) · (H 2 O) n between acid and water molecules.

Study of the solubility of water in polyamides based on the Flory-Huggins theory☆

Abstract The solubility of water has been investigated in relation to polyamide structure (with samples ranging from a polyamide based on α-pyrrolidone to PA-12). Analysis of experimental and published data was based on a method of group contributions, as well as on an empirical method, and on the Flory-Huggins theory. The results of the analysis show that on the basis of the Flory-Huggins theory it is possible with a good degree of accuracy to predict the absorption of water by unsubstituted polyamides with different values of p / p 0 . The suppsition that the same theory holds for substituted polyamides calls for additional substantiation. It is proposed that a cohesion energy of 90·7 kJ/mole for amide groups should be used in calculations of the solubility of water in polyamides (solubility parameter δ 2 ).

Use of accessibility as determined by H→D isotope exchange for the study of physico-chemical properties of aliphatic polyamides☆

H→D Isotope exchange was used to determine the extinction coefficient of the absorption band at 2470 cm−1, corresponding to bond-stretching vibrations of the ND bond. The dependence of accessibility on temperature was derived for two types of polyamide-12 films. Analysis of experimental results shows that on considering accessibility the rate of hydrolysis of amide bonds and the solubility of water in polyamide-12 are independent of the structure of the sample. It is considered that accessibility values determined by the H→ D isotope exchange method may be used successfully for investigating physico-chemical properties of aliphatic polyamides.

Degradation of polycaproamide in hydrochloric acid vapour

Degradation of polycaproamide films in hydrochloric acid vapour has been investigated at 96°. The methods used to determine the degree of hydrolysis of the polymer specimens were based on changes in MW and on HCl bonding by terminal amino-groups during the reaction. Either method may be used to calculate the effective rate of hydrolysis. An equation whereby keff may be calculated, taking polymer accessibility into account, has been proposed for analysis of the experimental results.

Sorption of water by segmented polyurethanes

Abstract The diffusion of water in a polyurethane of grade Vitur T-0533 has been investigated. It is shown that the solubility of water in segmented polyurethanes is a function of the urethane group concentration and of the accessibility of polymer macromolecules for H 2 O molecules. A method of evaluation of the degree of crystallinity of samples on the basis of H→D isotope exchange is proposed. An analysis of the data obtained is carried out using the method of group contributions, the theory of polymolecular adsorption and the Flory-Huggins theory.

Laws governing three-component sorption in the system water-hydrogen chloride-polyamide☆

The sorption of water and hydrogen chloride in polyamide-12 has been investigated. The diffusion coefficients have been determined and their temperature dependence has been established. Acid molecules, having been preliminarily sorbed by the polyamide, are (together with amide groups) the sites responsible for the sorption behaviour of water molecules. The amount of water additionally sorbed by the polymer is related not only to the acid concentration in the polymer but also to the vapour pressure. The results obtained are compared with data existing in the literature for the diffusion of H2O and HCl in polycaproamide.