Analysis of the Humidity-Time Superposition for Wool Fibers

Abstract

Data on the linear viscoelastic relaxation of wool fibers for a range of relative hu midities below the gas transition ( Tg) are systematized by a humidity-time superposition method. The differences in the relaxation behavior in water where the fiber is above its Tg are pointed out. The analysis relates to the properties of the water sensitive, viscoelastic component of the wool fiber and consists of superimposing the relaxation curves for different humidities onto the curve for the dry state by multiplicative scaling and shifting on the logarithmic scale of the reduced time variable λ, that corrects for the influence of ageing. The change of the scaling and shift factor with the absorption mechanism of the water is discussed.

The viscoelastic properties of wool and the influence of some specific plasticizers

“…Table 1 shows that the initial modulus increases from water to alcohol and with the aliphatic chainlength of the alcohols. Referring to the relaxation behaviour of wool fibers at different relative humidities [14][15][16] and to the similarity of the relaxation of a variety of materials in general [16,17] the whole relaxation curve is anticipated to be sigmoid and symmetrical in shape covering approximately nine decades of time, equivalent to 21 units of ln-rime.…”

“…Various investigations have shown the applicability of the log-normal distribution in its integral form [2,15,16,19] to describe the relaxation function under various environmental and experimental conditions, yielding for the ln-time scale:…”

“…Danilatos observed that even at high frequencies, equivalent to short relaxation times, no upper plateau value for the modulus is reached and that the part of the relaxation curve experimentally accessible spans considerably more than the expected nine decades of time. This can be related to the appearance of highly mobile water in the structure of the fiber [15,21] when the glass transition temperature drops below 20 ~ at a water content around 20 0/0 [22]. Consequently the relaxation behaviour of the wool fibers in water was not included in the present analysis, but is in detail discussed elsewhere [15].…”

“…This can be related to the appearance of highly mobile water in the structure of the fiber [15,21] when the glass transition temperature drops below 20 ~ at a water content around 20 0/0 [22]. Consequently the relaxation behaviour of the wool fibers in water was not included in the present analysis, but is in detail discussed elsewhere [15].…”

“…The small variation of the value of /~ implies that the form of the relaxation function and hence the form of the rdated spectrum of rdaxation times is largdy medium invariant and very similar to the relaxation function of the wool fiber at various rdative humidities [15] and for a variety of materials in general [16]. Changes in the rdaxafion behaviour with plasticizer occur in the moduli of morphological components and in the position of the relaxation function on the In-time scale.…”