An eco-friendly dyeing method: bromophenol blue (BPB) applied for dyeing cotton fabrics coated with cationic finishing agents

Poly(hexamethylene biguanide) (PHMB) is a commercially available cationic bactericide which can form stable and water-insoluble blue complex salt with bromophenol blue (BPB) at room temperature. Herein, we reported the feasibility and applicability of BPB for dyeing PHMB-coated fabrics. The colour yield, levelling property, dye uptake, fastness behavior and antimicrobial efficacy of PHMB-coated fabrics were fully investigated by a variety of analytical methods. The controllable blue colour shade depth depended on the concentration of BPB dyebath and the quantities of PHMB coated on the fabrics, and the colour levelness showed good and above rating. The dye uptake was positively proportional to the quantities of PHMB coated on the fabric, but showed negatively correlation to BPB concentration. The colour fastness to rubbing and washing were excellent, excluding anionic detergents washing. Continuous dyeing was found to be feasible at room temperature without any additives simply via replenishing BPB dyebath, hence avoiding dye wastewater discharge, which may provide an eco-friendly and sustainable dyeing method to reduce generation and emission of wastewater in textile industry. Meanwhile, the antibacterial efficacy of PHMB-coated fabrics was slightly compromised after BPB dyeing, but was still satisfactory, particularly against the gram-positive S. aureus.