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

机译：羊毛水混合物冻结和解冻中的水焓

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摘要

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.
机译：通过DSC评估羊毛-水混合物中水的冻结和解冻焓。两种不同的样品是用丙酮萃取的干净羊毛和用氯仿，乙醇和水的体积比为19：8：1的混合溶剂萃取制备的脱脂羊毛。在两个样品均以5 K / min的冷却曲线上，在228、240和255K处存在三个主要的结晶峰。根据热量和水含量之间的线性关系的斜率确定与每个峰对应的水的焓。从三个放热值估算出的丙酮提取羊毛的焓分别为17、181和287 J / g水，脱脂羊毛的值为17 J，85和281 J / g。在加热曲线上，有两个峰-从温度T_d开始的宽的吸热，随温度的变化而变化，而在273K时由于冰的融化而出现了一个尖峰。丙酮萃取的羊毛的焓分别为222和330 J / g，脱脂羊毛的焓为110和326 J / g。对于样品在冷冻和解冻时的焓的显着差异，提出了一种可能的解释。去除未结合的内部脂质增加了对纤维内水传输的扩散阻力。还讨论了T_d与水含量的关系。

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