A cleaner and eco-benign process for wool dyeing with madder, Rubia tinctorum L., root natural dye

In this study, an alternative cleaner process over traditional metallic mordanting process for wool dyeing with madder, Rubia tinctorum L., root natural dye was presented. Wool surface was modified with novel eco-friendly and biocompatible cationizing agent having numerous free amine groups, namely chitosan–polypropylene imine dendrimer hybrid (CS-PPI). Modified wool demonstrated remarkable increase in dye uptake as compared to raw wool. Optimal dyeing results were obtained when CS-PPI 7 %, madder dye 20 % and dyeing pH 7 were employed. Dyeing results such as percent dye exhaustion and color depth emphasized auxiliary agents, i.e., metallic mordant and acid could be eliminated from wool dyeing process with madder dye. Saturation point shifted to lower dye concentrations in the treated wool suggested the same color depth could be obtained using lower amount of crude dye material. Wool modification with CS-PPI demonstrated no adverse impact on other properties such as colorfastness and color shade characteristics. In addition, treated wool exhibited excellent antimicrobial activity (nearly 100 % microbial reduction) against two common pathogenic microorganisms, Escherichia coli and Staphylococcus aureus which were almost durable after dyeing and subsequent repeated washes. In general, the results of this investigation showed that CS-PPI can be employed as an alternative eco-friendly “bio-mordant” as well as effective antimicrobial finishing material in wool dyeing with madder dye.