Disperse dyeing of nylon 6 fiber using gemini surfactants containing ammonium cations as auxiliaries

The dyeing behavior of the disperse dye, 1,4-diaminoanthraquinone (1,4-DAA) , on nylon 6 fiber in the presence of the cationic gemini surfactants, prop anediyl-alpha,omega -bis(dimethyldodecylammonium bromide) (DC3-12) and hexa nediyl-alpha,omega -bis(dimethyldodecylammonium bromide) (DC6-12) as auxili aries, was investigated, and compared with that obtained in the presence of the corresponding conventional surfactant, dodecyltrimethylammonium bromid e (C12C1NBr). The dyeing rate increased in the order of C12C1NBr < DC3-12 < DC6-12, reflecting a difference in surfactant property. The extent of dye uptake altered slightly below the critical micelle concentration (CMC), but dye uptake decreased hyperbolically with an increase in surfactant concent ration above the CMC. The decrease in the extent of dye uptake above the CM C is concerned with the solubilization capacity of 1,4-DAA into the micelle s: the greater solubilization capacity reduced dye uptake. This result show s that the dye which is solubilized in the surfactant micelles rarely takes part in dyeing the fiber and the surfactant micelles act as a reservoir fo r the dye. A linear relationship was obtained between the amount of dye in the fiber and that in the dyebath, leading to the calculation of the appare nt partition coefficients, K. The K values in the presence of the surfactan ts whose concentration was above the CMC increased in the order of C12C1NBr < DC6-12 < DC3-12 ii water, indicating that they were also related to solu bilization capacity. On the other hand, the K values increased in the order of water < C12C1NBr < DC6-12 < DC3-12 for the dyebath which contained a 1: 1 molar ratio of dye:surfactant in which the surfactant concentrations were below the CMC. This result suggests that K is dependent not only on the so lubilization capacity but also on the dispersing ability of the surfactant. The maximum extent of dye uptake on to nylon 6 fiber in the presence of su rfactants whose concentration was above the CMC was 3.0x10(-5), 4.0 x 10(-5 ), and 3.3x10(-5) mol g(-1) for DC3-12, DC6-12, and C12C1NBr, respectively, at 100 <degrees>C, whereas those obtained in a dyebath containing a 1:1 mo lar ratio of dye:surfactant were 4.0x10(-5), 4.2x10(-5), and 3.3x10(-5) mol g(-1) for DC3-12, DC6-12, and C12C1NBr, respectively, at 100 degreesC. Thi s suggests that an improvement in dye uptake occurred in the presence of th e gemini surfactants. Thus, it is concluded that gemini surfactants can be used to control dyeing kinetics or to improve dye uptake in the disperse dy eing of nylon. (C) 2001 Elsevier Science Ltd. All rights reserved.