States of Water Sorbed on Wool as Studied by Differential Scanning Calorimetry

Abstract

The states of water sorbed on Merino wool fibers, their histological components, and chemically modified wool fibers were investigated by differential scanning calorimetry (DSC) in order to elucidate the amount of bound water on wool fibers, the differences between the histological components of wool fibers, and the effect of polar groups on the states of water sorbed on wool fibers. For the sake of comparison, the states of water sorbed on cotton and silk were also examined. There may exist three different kinds of water sorbed on wool fibers, i.e., free water, freezing bound water, and nonfreezing bound water. The amount of bound water on wool fibers is larger than that on cotton yam and silk. The amount of bound water on cortical cells is about two times higher than that on cuticular cells. The amount of bound water on nonkeratinous cell components is about three times higher than that on keratinous cell components. The cell membrane complex plays an important role in water penetrating to wool fibers, but its contribution to the amount of bound water is negligible. The contribution of polar groups in wool fibers to the amount of bound water is not specific at high water contents, indicating that the peptide groups of the main chain play a significant role as water binding sites at high water contents.Many of excellent properties of wool as a textile fiber are more or less associated with the specific interactions of wool proteins with water. The ability to bind and absorb large amounts of water is one of the characteristics of wool fibers [ 13]. A relatively large number of .papers have examined the interaction of wool fibers with water using water vapor sorption isotherms [5, 14, 30, 32, 331 and basic calorimetric techniques [4, 20, 26]. Workers have established that part of the water sorbed on natural polymers such as keratin proteins and cellulose and silk fibroin has properties that are markedly different from free water. Many different works have substantiated this consideration [8, 10, 18; 19, 21, 22, 24, 34].On the other hand, wool consists of several histological components that are very different in chemical and physical properties [2,13,36]. It is important to elucidate the differences between these histological components and the functions of individual cell components. Numerous efforts have been devoted to this problem [2,11,12,36]. The accessibility of water molecules to individual histological components of wool has also been studied extensively from various points of view [6,7,23,27,28,29,36], but no study has reported so far on the states of water sorbed on the individual histological components of wool fibers.Recently, Nakamura et al. [22] pointed out that there are three different kinds of sorbed water on polymer: free water, freezing bound water, and nonfreezing bound water, based on the studies using differential scanning calorimetry (DSC). Recent developments in microcalorimetry by DSC enable us to evaluate the contents of free and bound water on polymers [22]. It is of interest to exam...

Enthalpies of Water in Freezing and Thawing of Wool-Water Mixtures

“…new sharp exothermic peak 3C2 appears at about 256K. The top temperature of the 3c~ peak is in accord with that of bulk water reported by Sakabe et al [21 ]. With increasing water content over the saturated water retention value of 48.0% ( W, = 0.480), shown by curve 6 ( W~.…”

Investigation of the moisture adsorptivity of polar and hydrophilic groups in wool keratin by its chemical modifications.

“…22) have investigated the state of water sorbed on a Merino wool by differential scanning calorimetry not only from histological view points, but also on molecular basis of constitutive amino acid residues. They modified the wool by deamination, acetylation, and esterfication, and concluded that the peptide groups, in the main chains played a significant role as water binding sites at high water contents.…”

Effect of microwave irradiation on the physical properties and structures of wool fabric

“…An amount of bound water on wool is about 33.5%. Free water adsorbs on wool until the water content exceeds 30% by weight 15, 16. An amount of water on wool in nature humid state is about 12%.…”