New Method of Dyeing Keratin Fibers Using Poly(Ethylene Imine) and Its Coloring Mechanism

The study developed a novel method for dyeing keratin fibers, specifically human hair, using poly(ethylene imine) (PEI) as a counterion reagent to improve colorability at lower temperatures. The hair was pre-treated with a PEI solution before being colored with an acid dye, resulting in enhanced coloring and color fastness to shampooing compared to traditional methods. Optical microscopy revealed that the penetration of PEI and the dye Orange II into bleached hair increased with longer PEI treatment times and lower PEI molecular weights. The findings demonstrated that PEI penetrated the cortex region of the hair, facilitating the counterionization and increased penetration of Orange II.