A natural yellow colorant from Buddleja officinalis for dyeing hemp fabric

Natural dyes are more eco-friendly alternatives to synthetic dyes. This research focuses on natural dyes and improved dye craft using plants employed by various ethnic groups in Southwestern China. In this study, we assessed the suitability of dried extracts from Buddleja officinalis flowers for dyeing hemp fabric. and valuated indicators including color strength (K/S), color characteristics, and fastness properties in response to washing, rubbing, and perspiration using metallic and natural mordants under pre-, post-, and simultaneous mordanting conditions. Specifically, we investigated the pigment compound crocin by ultraviolet-visible spectroscopy and Fourier transform–infrared spectroscopy analysis before using it to dye hemp fabric. Optimum dyeing conditions including staining temperature, staining duration, and pH have been identified using an orthogonal array experimental design. Optimum results were achieved when dyeing at pH 5, and at 60 °C for 90 min. Hemp fabric dyed without mordant had a shade of yellowness, while fabric mordanted with gum rosin, plant ash, KAl(SO4)2, and Chaenomeles speciosa had a variety of pale to dark yellowness color shades. A darker yellow–green color shade was obtained with FeSO4 mordant. The color change of washing fastness was mostly very poor, while the color stain of washing and perspiration fastness were good to excellent, and rubbing fastness was also good to excellent. The color fastness was kept and improved by the three natural mordants, especially gum rosin and plant ash, but reduced by FeSO4. Those results show that the use of aqueous extract from B. officinalis flowers combined with natural mordants represents a promising approach for textile dyeing, revealing an alternative method that could improve and extend the dyeing properties of this indigenous dye plant. In addition, our findings lay the foundation for further basic studies and demonstrate the utility of preserving natural dye plants, along with the related traditional knowledge of indigenous groups in Yunnan, China.