High-binding-fastness dye from functional extracts of Keemun black tea waste for dyeing flax fabric

Black tea natural dye is usually recognised to contain functional colouring matters, which has long been used for the coloration of textile materials. However, due to poor binding and colour fastness, a large number of mordants have been used in the dyeing process, leading to serious environmental problems. To address these issues, we have developed a no-mordant pad-dry dyeing strategy for dyeing flax fabrics with functional components of Keemun black tea (KBT) waste. The dyed flax fabrics showed outstanding colour fastness to perspiration, rubbing, and washing. Moreover, increasing the KBT extract concentration, dyeing time, and temperature, and decreasing the pH level could significantly enhance the K/S values. Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) results revealed that theaflavin compounds dyed thoroughly the fibres successfully through hydrogen bonding force, and the theaflavin compounds could be bound to fibres stably through van der Waals and hydrogen bonding forces based on Independent Gradient Model (IGM) calculations. In addition, the dyed flax fabrics possessed good ultraviolet (UV) protection and antibacterial performance. This work proposes novel approaches for the reuse of KBT waste and the simultaneous coloration and functionalisation of flax fabric.