Abstract:

Objective Fabrics made from blended fibers demonstrate their advantages and enrich textiles diversification, of which polyester/cotton blended fabrics are most widely used in the textile and fashion industry. In order to save energy and reduce emission, non-aqueous media dyeing technology has been applied to the dyeing of polyester/cotton blended fabrics, using non-aqueous media, such as decamethylcyclopentasiloxane (D5), paraffin liquid, cooking oil and so on. Nevertheless, the phenomenon of staining persists during the dyeing process of polyester/cotton blended fabrics, resulting in decreased production efficiency and heightened pollution. This paper aims to investigate the mechanism behind the staining of cotton components in polyester/cotton blended fabric by disperse dyes in non-aqueous dyeing systems, with the objective of mitigating the staining of dyes during the dyeing process.

Method Based on the determination of azo dyes which have high uptake rate and suitable for polyester dyeing in non-aqueous media, and anthraquinone and heterocyclic dyes commonly used in conventional water bath, this research focused the dyeing and staining of disperse dye for polyester/cotton blended fabric in non-aqueous medium dyeing system. The influence of disperse dye structure, dyeing temperature, accelerant, dyeing time and dispersant NNO on the disperse dye staining, and dyeing effect of polyester/cotton blended fabric in non-aqueous medium dyeing system were investigated. Owing to the structure of polyester/cotton blends, it was difficult to isolate cotton staining for independent study. Therefore, conducting experimental research using 1.3 g of polyester fabric and 0.7 g of cotton fabric to simulate 2 g of polyester/cotton(65/35) blended fabric was necessary to gain a better understanding of the degree of cotton staining, and to demonstrate it more intuitively. One-bath-two-steps method was used for dyeing. In order to investigate the influence of dyeing conditions on dyeing performance, C.I Disperse Red 177 was chosen as disperse dye in the subsequent experiments. The uptake rate and staining rate of disperse dyes were calculated by measuring the amount of dye in the dyeing residue and the stripping solution. The distribution of disperse dye on polyester/cotton fabric was characterized by the relative staining rate of disperse dye.

Results The uptake rate of anthraquinone disperse dyes on polyester in non-aqueous medium dyeing system was only 12.0%, which was too low for dyeing polyester/cotton blends ( Fig.2 and Fig.3). The uptake rate of azo and heterocyclic disperse dyes on polyester components was above 80%. The complexity of disperse dye structure, the number of molecular substituents, molecular planarity, and relative molecular weight showed great influence on the uptake and staining of disperse dye. C.I. Disperse Red 177 was chosen as a representative azo disperse dye, and the results of the uptake of dye and the color depth of the dyed fabric indicated that the Disperse Red 177 had a higher uptake rate and it was more efficient using in non-aqueous medium. The influence of temperature on dyeing performance of polyester/cotton blended fabrics was investigated in non-aqueous medium with different contents of accelerant X (Fig.4). No matter what content of accelerant, raising the dyeing temperature was found to improve obviously the dyeing performance of disperse dyes on polyester/cotton blended fabric. The accelerant affected the dyeing/staining of polyester and cotton simultaneously (Fig.5) because the swelling degree of polyester and cotton fiber were improved at the same time when a certain amount of dye accelerant was employed during dyeing, and because the resistance of disperse dyes to diffusion into inside of fiber was decreased. It revealed from the research that the swelling degree of polyester fiber was less than that of cotton fiber, and the relative staining rate of disperse dyes was increased with the increasing content of dye accelerant. Polyester/cotton blended fabric dyeing was carried out for different dyeing time periods to investigate the relationship between the dyeing time and the dyeing performance (Fig.6), suggesting that dyeing time had little influence on the staining of of disperse dye but it would increase the uptake of disperse dyes. The addition of dispersant NNO in the dyeing process would not improve the dyeing performance of disperse dyes (Tab.2), but it had an influence on the staining rate of disperse dyes.

Conclusion Based on the uptake/staining rate and the relative staining rate of disperse dyes, azo dyes are more suitable than anthraquinone and heterocyclic disperse dyes for dyeing polyester/cotton blended fabric in non-aqueous media dyeing system. Polyester/cotton blended fabric dyed with Disperse Red 177 was more effective and efficient in non-aqueous medium dyeing system. The optimum dyeing conditions for disperse dyes were found, which were 140 ℃ of dyeing temperature, 10% (o.w.f) of dyeing accelerant, and 60 min of dyeing time period. If the dye accelerant and dispersant NNO were used in the dyeing bath at the same time, the disperse dyes were easy to aggregate, and the staining of dye on the surface of the dyed fabric becomes seriously, resulting the level dyeing property was poor, indicating that the accelerant and dispersant NNO should not used in a same non-aqueous media dyeing system.

Key words: non-aqueous medium dyeing, polyester/cotton blended fabric, disperse dye, staining, accelerant, solubility