Sorption of water vapors by high-strength para-aramid fibres

Abstract

677.494.675.66.081 and N. P. LebedevaThe water vapor sorption isotherms were measured for different types of high-strength fibres based on carbocyclic and heterocyclic para-aramids: Rusar (copolymers of amidobenzimidazole and p-phenylene terephthalamide), Twaron and Kevlar (poly-p-phenylene terephthalamide), and for comparison, capron (polycaproamide). The parameters of the thermal sorption equation and the thermodynamic characteristics of sorption of water vapor were calculated with previously obtained sorption data with the previously developed theoretical-probability model of sorption. A correlation was found between the integral heat of sorption in amorphous regions of para-aramid fibres and the specific cohesive energy.The para-aramid fibres and filaments created at the end of the last century have been widely used for fabricating highload, low-deformation textile articles, high-strength composite materials, and rescue and occupational safety equipment whose performance and storage frequently involve moisture. Sorption of moisture by fibres affects the physicomechanical and performance properties of fibres and materials made from them [1-3]. As a result of sorption of water vapors, plasticization, changes in the structure and properties of the fibres which are a function of the molecular structure, number of polar and functional groups, and the accessibility in amorphous regions of the structure, as well as the effect of the external conditions (temperature, partial water vapor pressure, exposure time), take place.However, an analysis of the literature showed that the sorption properties of high-strength para-aramid fibres have been insufficiently investigated and the available data are somewhat contradictory [4][5][6][7]. There has been no generalization and analysis of the sorption data using existing mathematical models for these fibres [8][9][10].We investigated the sorption properties of the basic types of high-strength para-aramid fibres as a function of the relative humidity. The experimental data were processed with a theoretical-probability model of sorption of vapors of lowmolecular-weight substances by polymer materials [11,12] and the heat effects and change in the thermodynamic functions in sorption of water vapor by para-aramid fibres were also calculated.Sample of domestic and foreign para-aramid fibres provided by the manufacturers were investigated. The characteristics of the objects investigated are reported in Table 1.Before measuring the sorption, the fibre samples were extracted with carbon tetrachloride to remove the oiling agent and dried to a constant weight at a temperature of 108±2°C. Equilibrium sorption of water vapor was measured by the isopiestic method and relative humidity was measured in the desiccators was created above saturated solutions of salts [13]. The desiccators were thermostated at 298 K. Equilibrium sorption values were established for 5-6 weeks.The water vapor sorption isotherms obtained in the study were S-shaped (Fig. 1), characteristic of amorphous and amorp...

High-strength, high-modulus fibres made from linear polymers: principles of fabrication, structure, properties, and use

“…The presence of polar functional groups in the molecular structure of para-aramids causes marked sorption of water vapors and swelling in water [1, 4, [78][79][80][81][82][83]. The presence of tertiary carbon atoms and the amorphous structure of PABI and cpPABI fi bres causes higher sorption of water from the vapor and liquid phase.…”

Study of acid generation from copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole

“…Differences in the sorption properties of these materials are attributed to the lower crystallinity of SVM and Rusar as compared with PPTA. As previously discussed, the benzimidazole linkages in these polymers do not crystallize as readily as do the more linear polyamide linkages [11,12].…”

Molecular mobility in the superstrong para-aramid fibre—water system

“…We used these two methods to study a number of highstrength para-aramid fibres: Rusar (copolymer of amidobenzimidazole with p-phenylene terephthalamide manufactured by Kamenskvolokno Co.), Kevlar (poly-p-phenylene terephthalamide manufactured by DuPont de Nemours, USA), Technora (copolymer of copoly(paraphenylene/3,4′-oxydiphenylene terephthalamide) from Teijin, Japan), Capron (aliphatic polyamide manufactured by Grodnokhimvolokno Co., Belarus). All objects investigated are amorphous-crystalline polymers with a 65-68% degree of crystallinity [4]. With respect to Rusar fibre, it has been assumed that its degree of crystallinity is much lower, but this is a polymer with highly oriented chains, i.e., with a relatively large number of physical bonds between the macromolecules.…”

“…With respect to Rusar fibre, it has been assumed that its degree of crystallinity is much lower, but this is a polymer with highly oriented chains, i.e., with a relatively large number of physical bonds between the macromolecules. In contrast to crystallites, these bonds can be broken by a highly polar sorbate.The water-vapor sorption isotherms are given in [4]. They have the σ-shape characteristic of glassy amorphous-crystalline polymers.…”

“…The water-vapor sorption isotherms are given in [4]. They have the σ-shape characteristic of glassy amorphous-crystalline polymers.…”