Recent progress in indigo dyeing of cotton denim yarn

30-34During the past several years, significant progress has been made in understanding the important parameters that influence the sorption of indigo dye by cotton denim yarn. It has been observed that dye uptake by cotton fiber and the extent of penetration of indigo dye into the denim yarn crosssection are influenced strongly by the pH-controlled ionic species of both dye and cotton in the dyebath. High dyebath pH results in a high level of ionization of both indigo dye and cotton cellulose, resulting in decreased substantivity and increased penetration of the yarn fiber bundle by the dye, with associated lower color yield. On the other hand, moderate dyebath pH promotes lower ionization of dye and fiber, resulting in increased ring-dyed yarn, greater color yield, and a denim garment that washes down quickly and consistently to produce the current appearance demanded by fashion