关键词: 液体分散染料, 循环染色, 化学需氧量, 减排, 涤纶织物, 染色动力学, 残液

Abstract:

Objective In the field of textile printing and dyeing, the huge water consumption and pollution emission have become a problem restricting the sustainable development. Currently, polyester is the largest variety of chemical fiber, and it is reported that each ton of polyester fabric dyeing consumes about 60-80 tons of water and emits a large amount of wastewater. In response to the above issues, cyclic dyeing was implemented to reduce water consumption and wastewater emission so as to achieve low-carbon and environmental protection requirements.

Method The dyeing properties, dyeing kinetics, half dyeing time and diffusion coefficient of liquid C.I. Disperse Red 60 and powder C.I. Disperse Red 60 were studied. The cyclic dyeing of liquid dispersed dye dyeing wastewater was explored, and the economic analysis was also conducted.

Results The results shows that the uptake rate of C.I. Disperse Red 60 on polyester fibers is relatively fast in the initial stage. With the prolongation of dyeing time, the adsorption of the dye on the fibers gradually slows down until about 60 min later when the dyeing reaches equilibrium. Liquid C.I. Dispersed Red 60 has higher dyeing rate constants, greater diffusion coefficients and shorter half-dyeing times on polyester fabrics compared to powder C.I. Disperse Red 60 at a dyeing temperature of 130 ℃. In addition, as cyclic dyeing progresses, the color of the dyeing residue solution gradually deepens, and the chemical oxygen demand (COD) value of the dyeing solution also progressively increases. Compared with powder dispersed dyes, liquid dispersed dyes are more suitable for dyeing wastewater recycling dyeing by means of their dyeing residue showing lighter color and lower COD. Subsequently, the organic matter in the dyeing residue is decomposed using COD degrading agent to achieve rapid degradation of COD. When the amount of COD degrading agent is added up to 6.0 g/L, the COD value of dyeing residue decreases from 2 628 mg/L to 45 mg/L, and the COD removal rate in dyeing residue is above 98%. Afterwards, the dyeing residue treated with COD degrading agent is subjected to cyclic dyeing, and it is found that the liquid dispersed dyes still show good dyeing effect on polyester fabrics, as result that the cyclic dyeing of polyester fabrics using the treated wastewater is achievable. Liquid C.I. Disperse Red 60 dyeing wastewater was utilized to dye the polyester fabric using liquid C.I. Disperse Blue 291. The result indicated that the color light fastness of the dyed fabric is consistent with the dyed fabric using the fresh water as dyeing medium. However, when 10 cycles of dyed wastewater were used as dyeing medium, the color of dyed fabric became lighter, the green and blue light were weakened in comparation with the color parameter of the fabric dyed by fresh water.

Conclusion An effective method was developed for cyclic dyeing of polyester fabrics using liquid dispersed dye dyeing wastewater to reduce water consumption and wastewater emission. The results showed that the dyeing residue after 10 dyeing cycles could still be reused for dyeing after treatment with commercial COD degrading agent, and the water saving rate of 10 dyeing cycles reached 73% compared with the normal polyester dyeing process, which is in line with the requirement of low carbon and environmental protection.

Key words: liquid dispersed dye, cyclic dyeing, chemical oxygen demand, emission reduction, polyester fabric, dyeing kinetics, residual liquid