Unconditioned Color Combination With Microencapsulated Disperse Dyes And Their Corresponding Mechanism

The traditional dyeing of hydrophobic fibers using commercial disperse dyes, such as PET, is the process of heavy pollution and energy consumption due to auxiliary solubilization. In addition, the discrepancies of dyeing compatibility among different dyes also cause the problems of color combination. While if disperse dyes are microencapsulated, their compatibility can be improved by the effective isolation and controlled-release behaviors of microcapsules. The values of COD, BOD and chromaticity of dyeing waste water can be reduced greatly through the dyeing of microencapsulated disperse dyes based on auxiliary-free solubilization.In order to promote the transformation of disperse dyes from conditioned color combination to unconditioned color combination, controlled dyeing of auxiliary-free solubilization disperse dyes were canied out in this paper by varying preparation conditions of microencapsulation. It aims at final realizing the comprehensive utilization of environment and resources of dyeing with microencapsulated disperse dyes. For the dyeing thermodynamics and kinetics, different dyeing mechanisms at high temperature pressure dyeing between auxiliary solubilization pure disperse dyes and auxiliary-free solubilization microencapsulated disperse dyes were also discussed and compared in this paper. The thermodynamics parameters （such as standard free energy△μ^o, standard staining heat△H^o, and standard staining entropy△S^o） and kinetics parameters (such as the values of equilibrium adsorption C_∞, rate constant k, half dyeing time t_1/2, and diffusion coefficient D etc.) were obtained respectively. The information related to dyeing theory of unconditioned color combination under the condition of auxiliary-free solubilization was also achieved.The main results are summarized as following:（1） The microencapsulated disperse dyes exhibit good compatibility and build-up, whereas the original pure disperse dyes show poor compatibility. The release rate of disperse dyes can be adjusted by varying wall materials and core-to-wall ratios during preparing the microcapsules. Unconditioned color combination of microencapsulated disperse dyes dyeing ultra-fine PET was performed basically based on auxiliary-free solubilization. The fastness to rubbing, fastness to soaping and levelness of ultra-fine PET dyed with microencapsulated disperse dyes without auxiliary solubilization are as good as those samples dyed with pure disperse dyes with auxiliary solubilization.（2） Both pure and microencapsulated disperse dyes of C.I. Disperse Red 73 and C.I. Disperse Blue 56, their adsorption isotherms reveal Nernst type. Distribution coefficient K increased gradually from 110℃to 130℃and the K value of the same dye increased after microencapsulating. The affinity of disperse dyes on fibers increased with the rise of temperature, and the affinity became larger after microencapsulating. Standard staining heat△H^o of auxiliary solubilization pure disperse dyes was higher than that of auxiliary-free solubilization microencapsulated disperse dyes. After dyeing, the ordered arrangement of disperse dyes on fibers exhibited an entropy reduction process. The standard staining entropy△S^o of auxiliary solubilization pure disperse dyes was higher than that of auxiliary-free solubilization microencapsulated disperse dyes.（3） Auxiliary solubilization pure disperse dyes possessed a higher dyeing rate and can reach equilibrium rapidly. While the dyeing rate of auxiliary-free solubilization microencapsulated disperse dyes was lower, and the dyeing equilibrium time were prolonged accordingly. Sustained-release effect of microcapsules reduced the initial dyeing rate and increased dye utilization rate. The dyeing rate constant k of microencapsulated disperse dyes was lower, and the half dyeing time t_1/2 was prolonged accordingly. Moreover, the diffusion coefficient D was increased. The relative standard deviation of coefficient D of microencapsulated C.I. Disperse Red 73 and microencapsulated C.I. Disperse Blue 56 reduced from 0.6456 to 0.2022, and the discrepancy of the dyeing rate decreased accordingly. Consequently, the synchronization and compatibility were improved during color combination with microencapsulated disperse dyes.This research show that pure disperse dyes, which have poor color combination under the condition of traditional auxiliary solubilization, can meet the requirement of color combination by microencapsulation based on the effective isolation and controlled-release behaviors. Excellent fastnesses can be obtained and the load of pollution can be reduced greatly by using microencapsulated disperse dyes. Dyeing PET with microencapsulated disperse dyes is of interest on both ecological and economic grounds.