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

Abstract

Enthalpies of freezing and thawing of water in wool-water mixtures are evaluated by DSC. The two different samples are clean wool extracted with acetone and delipided wool prepared by extraction with a mixed solvent composed of chloroform, ethanol, and water in volume ratios of 19:8:1. On cooling curves at 5 K/min for both samples, there are three main peaks for crystallization at about 228, 240, and 255K. The enthalpy of water corresponding to each peak is determined from the slope of the linear relationship between heat and water content. The enthalpies estimated from the three exotherms are 17, 181, and 287 J/g of water, respectively, for the acetone extracted wool, and the values for the delipided wool are 17, 85, and 281 J/g. On the heating curves, there are two peaks—a broad endotherm beginning at a temperature of T _d, which varies with the water content, and a sharp peak due to melting of ice for bulk water at 273K. The respective enthalpies are 222 and 330 J/g for the acetone-extracted wool and 110 and 326 J/g for the delipided wool. A possible explanation is proposed for the marked difference in enthalpy between the samples upon freezing and thawing. Removing the unbound internal lipids increases diffusion resistance to water transport within the fibers. The relationship of T_d to water content is also discussed.

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