Coloration in Flow: The Potential of In Situ Coloration of Casein Fibers to Mitigate Environmental Impact of Traditional Dyeing Methods

The environmental impact of the textiles and food industries can no longer be ignored, and while combining natural protein-based fibers with natural colorants, each derived from food waste, has the potential to offer increased sustainability based on a circular economy, it fails to address other environmentally detrimental textile production steps, such as coloration. This work explores the potential of a new, novel method for in situ coloration of regenerated protein fibers using an anthocyanin-based natural dye, used within the wet-spinning process, to reduce the environmental impact of the dyeing process. It is observed that similar or improved dye sorption and much improved 3D sustainability metrics (energy and material intensity) can be achieved through dyeing of casein fibers in flow, with higher color strength (K/Sλmax = 2.5) observed under milder conditions (room temperature, 10 s) compared to conventional dyeing (K/Sλmax = 1.0 at 40 °C, 30 min; K/Sλmax = 2.7 at 80 °C, 30 min). Energy intensity calculations show conventional dyeing requires 1.7–5.0 MJ kg–1 fiber, depending on the dyeing temperature for experiments performed in this paper and up to 13.4 MJ kg–1 fiber for examples in the literature. Using coloration in flow, energy intensity is negligible showcasing a vast improvement in energy-based metrics. The in situ experimental method showed a material intensity of 10.2 compared to 21.2 of the conventional method explored and up to 40.2 for examples in the literature, making the process in flow far less material intensive than conventional coloration methods, with additional potential for further material savings due to the recycling potential of the dyebath, which does not require auxiliary dyeing chemicals. Space time yield calculations showed that the productivity of the proposed method in flow is much higher (182.4 g L–1 h–1) compared to the conventional batch process (33.3–60.0 g L–1 h–1).