Natural dye extracted from Pterocarpus santalinus wood waste for green dyeing and its binding mechanism with yak wool fabrics

Pterocarpus santalinus is a precious wood, which produces a large scale of wood waste during the furniture production. These wood wastes are commonly treated with low value include incineration and landfill. Pterocarpus santalinus wood waste is an excellent source of natural dyes. However, the colored components and the binding mechanism between Pterocarpus santalinus natural dye (PSND) and animal fibers are still unclear during dyeing. Herein, santalin A, santalin B and santarubin B were proved to be the colored components of PSND. PSND was combined with yak wool fibers by in -situ polymerization and covalent binding, which was proved from two scales including macroscopic (micro -nano) scale and microscopic (molecule) scale. At the macroscopic scale, PSND was absorbed to the yak wool fiber by van der Waals forces and fixed on the fibers by covalent bonds. At the microscopic scale, the santalin compounds and the amino group of yak wool fiber were combined by C -N covalent bond. The dyeing process of yak wool with PSND was optimized by single factor experiment and orthogonal experiment. The optimum dyeing condition was obtained: ethanol concentration of dye solution was 10%, temperature was 90 celcius, pH value was 5 and dyeing time was 60 min. Importantly, the light fastness was grade 3, which meant that PSND had satisfied the requirements of textiles. These results clearly explain the binding mechanism between PSND and yak wool fibers, and have far-reaching significance for the green dyeing of Pterocarpus santalinus.