Expanding the Color Range of Natural Dyes on Cotton through Sequential Dyeing of Brazilein and Curcumin

Abstract

Natural dyes are increasingly recognized as a sustainable and environmentally benign alternative to synthetic dyes in the textile industry. However, the practical application of natural dyes is severely limited by their narrow color range and relatively low color fastness. This study investigated the effects of chemical environment and dye application sequence on the color development of cotton fabrics dyed with brazilein and curcumin. Cotton samples were dyed using three methods: single-dye dyeing, blended dyeing, and sequential dyeing. All samples were tested under neutral, acidic, alkaline, and three metal mordant conditions including Al³⁺, Cu²⁺, Fe²⁺. Color parameters were quantified using CIELAB coordinates and color difference values (ΔE), and UV‑Vis absorption spectroscopy was used to characterize changes in dye molecular structures. The results revealed that brazilein, the oxidized chromophore of brazilin, was highly sensitive to metal ions, especially Fe²⁺, which induced the most significant color change relative to the neutral control. Curcumin exhibited strong pH‑dependent behavior, with the most dramatic color shift observed under alkaline conditions. Compared with blended dyeing, sequential dyeing produced a significantly wider and more diverse color palette. In particular, the sequence of brazilin followed by curcumin generated the most distinct and varied color outcomes across all chemical conditions. These findings confirm that sequential dyeing is an effective and sustainable strategy to expand the color range of natural dyes using only two plant‑based colorants. This approach provides a simple, low‑cost, and eco‑friendly method to enhance the practicality of natural dyes for green textile manufacturing.