High Performance Fiber——Study On Structure Control And Drawing Mechanics Of PVA Fiber

Processing conditions, structure and properties of polyvinyl alcohol fiber, especially the partially Saponificated PVA fiber have been studied. Actually, effects of degree of saponification, conditions of spinning and drawing both with and without solvent and the like on high performance of PVA fiber have been investigated in detail. The results showed that the effects of the methods described above were remarked and further confirmed that inter-and intra-molecular hydrogen bonds prevented the fiber from ultra-high drawing, which induced the decree the decrease of the fiber strength. And these were proposed new approaches for manufacturing high strength and high modulus PVA fiber. This paper was divided into three chapters as follows:The first chapter reviewed the progress in the research on high strength and high modulus PVA fiber, based on polymerization degree, spinning, drawing, solvent, coagulating conditions and extraction etc. The two key factors that affect high performance of PVA fiber were as follows : one was structural factor of polymerization degree and tacticities; the other was ultra-high drawing. Consequently, in order to get high performance PVA fibe, we brought forward a different method by gel-spinning of partially saponified PVA, pre-drawing of as-spun fiber containing solvent and hot-drawing without solvent.The second chapter discussed both gel-spinning conditions and pre-drawing processes containing solvent. The effects of coagulating temperature, storage conditions on the maximum drawing ratios and of the pre-drawing ratios, total drawing ratios on fiber properties were studied in this chapter. The differential scanning calorimetry was used for the analyzing of fiber micro-structure. The results indicated that at lower coagulating and storage temperature, with storage time of 20~24 hours caused optimized mechanical properties, also, the melting temperature of the PVA fiber and the total drawing ratios increased with the increase of the pre-drawing ratios. As a result, it is important to obtain high strength PVA fiber by using pre-drawing and proper drawing ratios.The third chapter discussed the effect of saponification on structure and properties of a series of PVA fiber. The FT-IR, 1H-NMR, DSC and XRD were used to analyze the problem. The results can be divided into three parts. Firstly, partially saponificated PVA was in favor of drawability and reduction of hydrogen bonds in the course of drawing. Secondly, thermal properties of those fiber had some relations with hydrogen bonds, which further explained the effect of degree of saponifacation on hydrogen bonds. Lastly, degrees of crystallinity calculated by computer separating peak of all PVA fiber whichwere drawn to some extent decreased as drawing proceeded, which indicated some changes in the crystalline phase. And the size of the face of crystalline (100) decreased with drawing ratios increasing, which caused increase of the fiber mechanical properties.