Effect of the degree of esterification of disperse dyes on the dyeing properties of polyethylene terephthalate in supercritical carbon dioxide.

• Changes of absorbances and melting points were not related to color differences. • Changes in solubilities and affinities were fundamental reason for color differences. • Degree of esterification had greatest effect on disperse red 167:1′s color difference. [Display omitted] The reason of color differences caused by different degree of esterification disperse dyes were investigated by disperse orange 30, disperse red 167:1, disperse blue 79:1 with different degree of esterification. The results showed that the changes of light absorbance abilities and melting points caused by ester groups had no obvious correlation with the color differences caused by ester groups. The changes in the solubilities and affinities caused by the ester groups were the fundamental reason for the changes in the dyeing properties of disperse orange 30, disperse red 167:1 and disperse blue 79:1. As a joint result of the decrease in solubilities and affinities, the dye sorption in polyethylene terephthalate of unesterified disperse orange 30, unesterified disperse red 167:1 and unesterified disperse blue 79:1 were reduced by 37.7%, 83.6% and 54.6%, respectively, compared with those of the corresponding completely esterified dyes. [ABSTRACT FROM AUTHOR]