Sorption-desorption isotherms for fibres with high hygroscopicity

Abstract

The hygiene and comfort of clothing are determined to a significant degree by the hygroscopicity of the fibres from which they are made. Natural fibres such as wool and cotton have elevated hygroscopicity and are in high commercial demand. Viscose fibres and the new fibre Togilen [1][2][3], created at the Khimvolokno LenSRI also have good water absorption. The mechanical characteristics of the articles are also a function of the hygroscopicity of the fibres and threads.Finishing processes are also a function of the hygroscopicity of the materials to a significant degree. Knowledge of the equilibrium moisture content of materials at different temperatures and relative humidities is required, for example, in calculating the drying parameters of these materials.In studying the sorption properties of fibres, thread, and textiles [I], their sorption characteristics are determined in standard conditions (relative humidity ~, of 65 + 5 %, temperature of 20 + 2"C). The standard indexes of the moisture content W and hygroscopicity of textiles are determined for ~, = 65 and 98 % [1].The sorption-desorption isotherms plotted for the complete range of variation of ~o most completely characterize the hygroscopicity of materials. There is still no rigorous theoretical description of the sorption-desorption isotherms. A semiempirical theoretical probability equation of equilibrium sorption [1, 4], used for ,t, of up to 95 % (i.e., to the beginning of capillary condensation), is recommended in [1] for calculation of equilibrium sorption-desorption. However, it contains a number of difficult to determine parameters which are calculated by computer software in [1]. In routine practice, it is frequently more convenient to use simpler empirical dependences which do not require complex calculations.Some investigators have noted the virtual absence of any effect of the temperature in the interval they investigated [5, 6]. At the same time, the sorption statics are determined by steady-state diffusion and as we know, the molecular diffusion coefficient is a function of the temperature to a degree of 3/2. Then there are the empirical and semi-empirical equations of Langnuir, Freundlieh, and the Russian investigators A. A. Rode, Ya. M. Miniovich, A. V. Lykov, and B. A. Posnov [5, 6], used for special cases.We proposed an empirical dependence of the following type for fibre materials with high hygroscopicityThis dependence can be used for describing both desorption and sorption isotherms. However, the latter, especially for materials with significant hysteresis of the sorption characteristics and high hygroscopicity, are better described by a dependence of the typeWe will demonstrate the possibility of using the proposed curves on the example of the isotherms of the four types of fibres listed above; these convex-concave shapes of the isotherms are characteristic of textile materials. The experimental points from [2] and paired isotherms for cotton (lower) and viscose fibre (upper) are shown in Fig. la, and

Analysis of the parameters of sorption-desorption isotherms for highly hygroscopic fibres

“…(5)- (7) are reported in [4]. The desorption isotherm, which determines the equilibrium moisture content of the material during drying, is most important for drying processes.…”

“…Their calculated values for the fibres examined are reported in Table 1. In all calculations, in contrast to [4], the quantities w and q) are expressed in fractions.…”

“…Chemical fibres, Capron, nylon, etc., for example, are less hygroscopic. However, in this group of materials as well, there are fibres with high hygroscopicity, for example, the Togilen fibre created at Khimvolokno Leningrad Scientific-Research Institute [1][2][3][4][5][6].The kinetics of finishing of fibres and textile materials also determines their hygroscopicity to a significant degree. Data on the equilibrium moisture content at different temperatures and relative humidity are necessary, for example, in calculating the drying parameters of textile materials and fibres [6][7][8][9][10].…”

“…In a previous publication [10], a new equation Was reported for the drying rate gradient. In consideration of this equation, we proposed in [4] a relation of the following type for the water vapor sorption---desorption isotherms of fibre materials q~ = 1 -exp(-w 'z / A)…”

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“…Lim et al [11] studied sorption of water vapour in Nylon 6 films by controlling the atmosphere of the sealed glass chamber enclosing a Cahn 2000 recording microbalance and by using saturated salt solutions. Sorption isotherms for fibres with high hygroscopicity [12] and hydrophilic polymers [13] and for peptides, proteins and their formulations [14] were studied in recent years using automatic gravimetric systems.…”