Studies on effect of different parameters on dyeing of eco-friendly polyester fibres

Abstract

In this study, two eco-friendly polyester fibres, viz. Poly-trimethylene terephthalate (PTT) and Poly-lactic acid (PLA), were dyed with different dyes and the effect of various parameters observed vis-à-vis Poly-ethylene terephthalate (PET), the traditional commercial polyester fibre. The effect of dyeing temperature, time, material to liquor ratio, initial pH of dye bath and rate of heating was observed when three different disperse dyes (Disperse Yellow 56, Disperse Blue 79 and Disperse Red 167) were applied. The effects were observed on the color strength (K/S value), wash fastness (dE value), tenacity (grams per denier) and elongation (%) of the fibres after dyeing. Temperature, time and initial pH of the dye bath were found to have statistically more significant effects than the other parameters after dyeing. Optimization was carried out using Response Surface Methodology (RSM) based on 23-Factorial Central Composite Design (23-FCCD) was carried out with these three parameters. The optimal values were found to be temperature of 120 OC, initial pH of 5.6 and time of 58-59 min, in case of PTT. For PLA, the optimal values observed were temperature of 124 OC, initial pH of the dye bath of 5.8 and time of 55 min with Disperse Yellow 56. For Disperse Blue 79 and Disperse Red 167, the optimal values were temperature of 120 OC, initial pH of dye bath of 5.6 and time of 43 min. The three fibres were also dyed with three different natural dyes, viz. Lac, catechu and Myrobalan. The fastness to washing, perspiration, acids, alkalis and hydrogen peroxide was observed for PTT and PLA fibres after dyeing with the natural dyes, both without and with biomordants. It was found that with meta-mordanting, the color strength as well as fastness properties were superior than the other mordanting techniques. The color strength was found to decrease in the order of alum> ferrous sulfate> stannous chloride for inorganic mordants and Catechu> Myrobalan> Pomegranate in case of biomordants. Although the color strength for alum and ferrous sulfate was higher than that obtained with biomordants, the results obtained with Catechu were in close proximity, and sometimes higher, than that with stannous chloride. It indicated that Catechu, a biomordant, can replace some inorganic mordants in dyeing of PTT and PLA with natural dyes. The optimal values for PTT were observed at temperature of 113-114OC, initial pH of dye bath of 6.2-6.4, and time of 50-51 min. For PLA, they were temperature of 113-114OC, initial pH of dye bath of 6.2-6.4, and time of 33-36 min. In both cases, the K/S value obtained with the Lac-Catechu combination was the highest. The FT-IR spectra of the fibres before and after dyeing did not indicate any chemical bonding between the natural dyes and the fibres (PTT and PLA). The optimal values for temperature, initial pH of the dye bath as well as dyeing time were all lower for PTT and PLA, both with disperse and natural dyes, than those in case of PET. It suggested that PTT and PLA could be satisfactorily dyed at conditions which were less harsh than those used to dye PET.