Dyeing Properties Of Poly(Lactic Acid) Fiber And Changes In Its Structures During Dyeing Process

Being a most popular hydro and biodegradable material, poly(lactic acid) fiber draws much attention for its excellent properties. The research on its dyeing properties and structures is of much importance for the development of PLA fiber. In this paper, the dyeing properties of PLA fiber and the changes in its structures during the dyeing process were investigated. The research results obtained are as follows.The structure character of PLA fiber that we used in this thesis had an obvious distinction compared with the PTT and PET fibers which also belong to the family of polyester fiber. This maybe due to the fact that there are no benzene rings in PLA molecules while there are in other two fibers. And the similar molecule structures of the PTT and PET fibers lead to the similarities in various analysis. Therefore, it is easy to distinguish PLA fiber among these three fibers.Many basic experiments on the dyeing performance of PLA fiber were carried out. The effect of dyeing temperature on the uptake rate and visual color depth value was carried out. Though the rate and color depth increased with temperature, it is appropriate to treat under 110℃considering the extension strength and degradation of the fiber. The azobenzene disperse dyes showed a better building-up property on PLA fiber compared with anthraquinone dyes. In terms of the color shades on PLA PTT and PET fibers, the disperse dyes exhibited a difference and the maximum absorption wavelength shifting to a shorter range on the PLA fiber. More than ten popular disperse dyes with different energy levels and chemical constitutions were used to compare their exhaustion, color yield on PLA fiber. The dyeing rates of azobenzene disperse dyes were faster than those of anthraquinone dyes. The color yields were inclined to increase with the decreasing I/O values of the disperse dyes. The dyes with similar I/O values to that of the PLA fiber appeared better building-up properties. A group of tricolor namely O 30, Red 54/Red 74 and Blue 148 was also recommended. The effect of dyeing temperature and time on fiber structure were investigated by DSC and WAXD analysis and strength test. It was observed that the melting enthalpy increased with the increase in dyeing temperature within 90-130℃, indicating that the degree of crystallinity increased with temperature. Meanwhile, the maximum degradation temperature decreased at first, and then went up when the dyeing temperature was higher. This may have something to do with both the reduced molecular weight and the increased crystallinity. The melting enhalpy increased and The onset melting temperature, maximum melting temperature decreased with dyeing time. The time had a more obvious influence on the changes in fiber structure than the temperature did. WAXD analysis indicated that the degree of crystallinity increased with the increase in dyeing temperature and the time.