Enhanced Cashmere Quality Through Sustainable Betalain Dyeing

Driven by demand for sustainable textiles, this study evaluates red beetroot (Beta vulgaris L.) betalains as a natural dye for cashmere. We compared two dyeing approaches: conventional dyeing at pH 3.5 (acetate buffer), 85°C for 55 min (yielding yellow tones), and pre-functionalization with ethanol in acidic conditions at 25°C for 30 min followed by low-temperature dyeing (yielding red – violet tones). Optimization identified preferred conditions of 50°C, 5 wt.% initial dye concentration, pH 3.0, and 60 min. Betalains were extracted with 6% yield, and characterized by adsorption peaks at 530 nm and 480 nm, indicating betacyanins and betaxanthins. Adsorption followed pseudo-first-order kinetics and fit the Freundlich isotherm, implying heterogeneous, multi-stage adsorption with spontaneous tendencies (Freundlich n > 1). The process was endothermic, with adsorption capacity increasing with temperature, and the activation energy was 29.8 kJ mol−1, consistent with electrostatic and van der Waals interactions. Dyed cashmere retained the natural cuticle morphology, required no metallic mordants, and showed improved mechanical properties (breaking strength +3.8%, elongation +22.5%) and color fastness scores of 4–5. Results sipport betalains as an eco-friendly dye for high-quality cashmere.