Differential Thermal Analysis of Wool—The Phase-Transition Endotherm Under Various Conditions1

Abstract

Wool samples in vacuo, as well as samples sealed with various amounts of water, were studied by differential thermal analysis (DTA). In all cases, a phase-transition endotherm, often a doublet, was observed. The temperature of the first peak T _m depends on the amount of water present, heating rate, level of disulfide reduction, and type of keratin fiber. Parallel x-ray studies showed that the conformation of the polypeptide chains in samples at room temperature, after heating to the completion of the endotherm, depended on the first three of these parameters. T_m was 142°C for a Merino wool heated at 3.8°C/min in a sealed tube with an amount of water greater than 80% of the dry weight of the wool and, after fusion, the sample showed no x-ray reflections other than a diffuse ring at 9.8A and the usual halo at 4.15Å. Cystine-reduced samples similarly treated and unreduced samples sealed with 7-10% of water subsequently gave a sharp arc at 4.65A, indicating the presence of partially disoriented β-crystallites. Relative entropies of transition were computed from the DTA curves and showed a correlation with the x-ray results. For instance, when the relative entropy was low the x-ray patterns showed loss of the α-form and appearance of the β-form, but when the relative entropy of transition was high, the α-pattern was replaced by one showing no specific ordered form.