Comparative evaluation of reactive dye structures on colour strength enhancement in caustic‐treated regenerated bamboo fabrics

Abstract

Regenerated bamboo fibres offer a sustainable alternative to conventional cellulosic materials; however, achieving high and reproducible colour strength with reactive dyes may depend on both fibre accessibility and dye molecular architecture. This study comparatively evaluated the influence of reactive dye structure on the coloration performance of caustic‐treated regenerated bamboo fabrics. Eight commercial reactive dyes representing different chromophore classes and reactive‐group chemistries were investigated using a three‐stage experimental design to (i) select an appropriate sodium hydroxide concentration, (ii) evaluate bath configuration and (iii) compare dye‐dependent colorimetric responses under the selected conditions. An sodium hydroxide concentration of 8°Bé provided the most favourable balance between whiteness, colour‐strength enhancement and bursting‐strength retention. Depending on the dye, caustic treatment increased K / S by approximately 6%–50%. The magnitude of improvement varied with chromophore architecture, approximate molecular bulk, reactive‐group functionality, substantivity and dye‐specific application conditions. Scanning electron microscopy (SEM), X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) results were consistent with alkali‐induced surface modification, hydrogen‐bond rearrangement, structural relaxation and reduced apparent crystalline order without evidence of cellulose derivatisation or a major polymorphic transformation. Relative unlevelness index measurements showed that the caustic‐treated fabrics exhibited excellent within‐specimen colour uniformity. Fastness results indicated that the increased colour strength was durably retained under the applied wash, rubbing, perspiration, water and light‐fastness tests. The findings demonstrate that the effectiveness of caustic‐assisted dyeing of regenerated bamboo fabrics is dye‐specific and governed by the combined influence of substrate modification, dye molecular architecture and processing conditions.