Green Chemistry in Hemp Dyeing

Hemp plants are precious resources for the textile industry, being considered a sustainable and more economical alternative to cotton. Sustainable dyeing processes should minimize the consumption of water, energy, and chemicals while ensuring high color intensity and reducing the pollution load of residual baths. Black carrot (Daucus carota L. ssp. sativus) is a valuable source of dyes for dyeing hemp materials because it is rich in anthocyanins and anthocyanidins, which generate colors ranging from red-orange and muted magenta to blue, depending on the pH. In this article, the dye extraction process was colorimetrically monitored for 26 days to determine the optimal fermentation/storage period that generates the most intense color during the dyeing process. The dyeing parameters tested were temperature (40–100 °C), pH (4.33–9.15), duration (1–24 h), concentration (2.5–10%), and the presence of organic acids (ascorbic and citric acids). Virgin baths and the first three residual baths were used in the dyeing process. While the results of FTIR, SEM, and EDX analyses confirmed the dyeing process, the CIEL*a*b* measurements quantified the characteristics of the colors obtained using virgin and residual baths. The 12 principles of green chemistry were also discussed, together with their implementation in hemp dyeing.