The Structures And Thermal Properties Of Cashmere Fiber

Both the quality and quantity of Chinese cashmere are on the top in the world. Nowadays, it's important and necessary to improve the finishing technologies on cashmere textiles in our country. The available literatures on the fundamental studies of cashmere fiber mostly aim to identify cashmere and fine wool. In this dissertation, the structures and thermal properties of cashmere fiber are primarily studied in comparison with fine wool.Many new techniques are used in this dissertation. The contents of disulfide bonds and the secondary structures of cashmere and fine wool fiber are analyzed using Confocal Laser Raman Microscopy for the first time, concluding that the disulfide content of cashmere fiber is 60% of that of fine wool and its content of the ordered α-helix chains is more than that of fine wool. Wide Angle X-ray Diffraction (WAXD) and Differential Scanning Calorimeter (DSC) show that the cry stallinity of cashmere fiber is higher than that of wool, especially that α- crystallinity of cashmere fiber are higher than that of wool. The crystallinity and α- crystallinity of fine wool are respectively 81% and 76% of that of cashmere fiber.The thermal properties of cashmere and wool fiber are investigated by DSC technique. Both these two kinds of fiber show bi-modal melting peaks and similar melting temperature, and the shapes of their melting peaks have small differences. The glass temperature of cashmere fiber is 5℃ higher and its temperature range of glass transition is 5℃ broader than that of wool. The TMA mode of Dynamic Thermal Mechanical Analyzer shows that cashmere yarn contracts at 219℃ and abruptly extends at 230℃. In this dissertation, it is pointed out for the first time that the melting mechanism is different between dry cashmere fiber and cashmere fiber in excess water. During the melting of dry cashmere, its double-stranded α-helix proto-filament may be separated, which results in the slippage between the molecularchains and the abrupt extension of the yarn. However, during the melting of cashmere in excess water, a-helix chains in crystalline region are transformed to random coils, which results in the supercontraction of the yarn.The effects of heat treatments on the structures of cashmere fiber and the properties of cashmere yarn and fiber are uniquely investigated by High Temperature Laboratory Dyeing Machine and the heat case. The higher the moisture contents in cashmere yarn, the more severe the damages the yarn suffers during heat treatment. The cashmere yarn in stretched state suffers more damages than that in relaxed state during steaming treatment. The crystalline regions of cashmere fiber melt and the yarn supercontracts after the cashmere yarn is crabbed above 130 in relaxed state. After the cashmere yarn is treated in steam of 120 for 5 minutes in stretched state, the extension in "yield region" and the extension at rupture of the treated cashmere fiber are obviously lower, and its strength and initial modular are mildly lower than that of original cashmere fiber. The conformation of disulfide bonds, secondary structures, crystallinity and a-crystallinity of the cashmere fiber are changed after the cashmere yarn is steamed above 120 in relaxed and stretched state or crabbed at 98 130 for different time, which is firstly found out. These structure changes of the treated cashmere fiber are related to temperature, time, and moisture content and tensile during heat treatment.Using a torque testing apparatus, developed by Wu Xiongying, andthe tensile stress relaxation mode of Dynamic Thermal Mechanical Analyzer, the properties of torsional setting and tensile setting of cashmere yarn are studied. The torque relaxation rate and tensile stress relaxation rate of cashmere yarn are lower than that of wool yarn, i.e, the torsional setting and tensile setting properties of cashmere yarn are weaker than that of wool yarn. This conclusion is also first reported.By fiber tensile tester and DCS-500 strength machine, the tensile properties of ca...