Empirical and Theoretical Indigo Dye Models Derived from Observational Studies of Production Scale Chain Rope Indigo Dye Ranges

An observational study of production scale chain rope indigo dye ranges was conducted using 100% cotton open end spun yarns to confirm previously published dye trends, investigate the effects of dye range speed, and develop dye prediction models. To achieve these objectives, several milestones were identified and systematically addressed. A comprehensive laboratory preparation method was developed to ensure consistent yarn preparation. Equilibrium sorption experiments were conducted to determine the functional relationship between dye bath concentration and pH to indigo dye uptake in the cotton yarn. Additionally, the resulting shade from equilibrium sorption data was expanded to create an innovative method of quantitatively characterizing indigo penetration level of non-uniformly dyed yarns.;The following dye range set-up conditions were recorded for each observational point: yarn count, number of dips, dye range speed, dwell length, nip pressure, dye bath indigo concentration, dye bath pH, dye bath reduction potential, and oxidation time. All observations were conducted after the dye range had been running for several hours and no feed rate adjustments were required. Later the following measurements were taken to determine each response variable state: total percent chemical on weight of yarn, percent of fixed indigo on weight of yarn, and Integ shade value.;Analysis of data from the observational study confirmed most previously published dye trends relating to dye uptake, shade, and penetration level. Notably, the percent indigo on weight of yarn as a function of dye bath pH was not confirmed. Although it was noted this relationship may be dependent on the pH range evaluated during the observational study and not the broader general trend. All other general trends were confirmed. Additionally several new dye range set-up conditions were determined to significantly affect dye uptake, shade, and/or penetration level. Yarn count, speed, and dwell time were deemed significant in affecting dye uptake behavior. Increasing yarn count to finer yarns resulted in greater percent indigo on weight of yarn, Integ, and penetration level. Increasing dye range speed resulted in less percent indigo on weight of yarn, lighter Integ shade, and lower penetration level or more ring dyeing. And, increasing dwell time resulted in lighter Integ shade.;Using the dye range set-up conditions and measured response variables from the observational study data, empirical and dye theory models were constructed to predict percent indigo on weight of yarn, Integ shade, and the resulting penetration level. An independent production scale indigo dye range, which was not included in dye model creation, was used to validate of each model for accurate prediction of percent indigo on weight of yarn, Integ shade, and corresponding penetration level. The dye model predictions were compared to actual production scale indigo dyed cotton yarns. By making adjustments in yarn porosity values the dye theory model outperformed the empirical model in predicting final Integ shade although both models accurately predicted the total percent indigo on weight of yarn.