Temperature dependence of the water-sorption isotherms of wool

Against the background of various other theories, the well-established D'Ar cy/Watt model is applied to sorption data of wool between 20 and 100 degree sC to determine its suitability to describe the isotherms and to systematiz e their temperature dependence. The model contains three components that re present two types of primary adsorption processes (Langmuir- and Henry-type adsorption) and a third one, describing multilayer formation of water mole cules. Sorption isotherm data, as taken from the literature, could, in all cases, be fitted extremely well by the model. The temperature dependence of the five parameters of the model, related to the continuous decrease of wa ter regain with increasing temperature for all humidities, reveals a number of inconsistencies. Probably the most important of these is that the Langm uir capacity constant apparently becomes zero at the glass transition tempe rature of dry wool. This is at variance with the idea of specific molecular sites of water sorption, which is inherent to the model. Other inconsisten cies relate to the small van't Hoff enthalpies and possible compensation ef fects for various parameters. These observations indicate that the D'Arcy/W att theory, despite its physicochemical plausibility and empirical success, overinterprets the complexity of the mechanisms underlying the sorption be havior of wool and other cu-keratin fibers. (C) 2000 John Wiley & Sons, Inc .