Sustainable Water-Efficient Dyeing of Wool Fibers: Enhancing Fiber Protection and Maximizing Dye Fixation Rates

In accordance with environmentally friendly dyeing standards and the trend toward low carbon emissions, sustainable nonaqueous dyeing is a promising technology for reducing the water and energy consumed in dyeing wool fibers. Under optimized conditions—a cylinder density of 240 g/m² and 150% (o.w.f.) water—the process achieved a dye fixation rate of 98.35%, exceeding that of conventional methods, while reducing water consumption by more than 60%, with the D5 medium being recyclable for at least 50 cycles. To further clarify the advantages of this approach, the dyeing mechanism and fiber structure were investigated. The results showed that the extraction capacity of the medium and the swelling action of water increased the number of dye channels, enabling smaller dye particles to penetrate the cortical layer and yield uniformly colored fibers. Compared with conventional dyeing, the nonaqueous method preserved the F layer and cuticle, provided more stable cross-linking, and increased the fiber strength, resulting in reduced damage (weight loss of 1.27% vs. 6.08%). Moreover, the excellent reusability of the medium enabled the dyeing of 300 g of fibers with comparable colorfastness, as the rubbing and soaping fastness reached ≥ Grade 4–5, indicating that this technique is approaching industrial application. Overall, less water use, a recyclable medium, reduced chemical demand, and lower energy consumption demonstrate that the nonaqueous dyeing system offers a promising pathway toward the sustainable and greener coloration of wool fibers.