Exploration on energy-saved dyeing method for polyimide fabrics with alkali treatment

The difficulty of dyeing is a disturbing problem for the various application of polyimide fabrics. Alkali treatment has been widely used as a preliminary step before dyeing, denoted as a two-bath method. With more attention being paid to energy resources, this work aims to explore more economical and environmentally friendly dyeing technology, combining the alkali treatment and the dyeing process together, named a one-bath method. Surprisingly, the K/S value of the one-bath dyed fabric is much higher than that of the two-bath sample, in which the red colour value is enhanced by 59.9% for the one-bath sample. As for the effect of dyeing on the physical properties, the two-step method has been demonstrated to exert more severe damage on the fibre, with lower crystallinity and tensile strength. To explain such results, it is deduced that when alkali is added together with dyes, it can play a bridge role between the dyes and the fibre, anchoring the dyes wherever the alkali can permeate. Furthermore, 17.25 J of the energy is calculated to be saved for the dyeing of 60 g of fabric, which is very inspiring for large-scale application.