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Textile industry is one of the most polluting industries due to the large quantities of dyeing wastewater it generates and discharges. Herein, we report an eco-friendly and sustainable circular coloration technology based on cationic polyelectrolyte complex to realise salt-free, zero-e uent-discharge circular dyeing for cotton fabrics with a recyclable dyebath by using a typical cationic polyelectrolyte polyhexamethylene biguanide (PHMB) bonded with anionic dyes. The cotton fabrics were rst treated with PHMB and then dyed with three commercial acid dyes. Colour measurements show that the colour strength is controllable by adjustment of concentrations of both PHMB and the dyebath. The dyed fabric samples were found to have good/excellent colour levelness (< 0.49), and the colour fastness (Grade 3 ~ 5) was basically satisfactory and acceptable. The dyebath was proved to be recyclable for circular dyeing occurring at room temperature, which greatly reduces consumption of both water and heat energy for textile dyeing. Meanwhile, the dyed fabrics showed antimicrobial activity, particularly for the grampositive S. aureus, which may help reduce the healthcare-associated infections that transmit through textiles. These results suggest that cationic polyelectrolyte-based circular dyeing could provide a promising and practicable strategy to address the pollution issue caused by wastewater generated in dyeing process in the textile industry.

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It is a challenge to determine the quantity of cationic finishing agents on the surface of cellulosic fabrics. Herein, we report a direct and feasible method by Kubelka-Munk equation to quantify the cationic poly (hexamethylene biguanide) hydrochloride (PHMB) adsorbed onto cotton fabrics based on the principle of formation of a stable blue dye between PHMB and bromophenol blue sodium (BPB). The adsorption of PHMB onto cotton fabrics was first investigated and the maximum adsorption of PHMB was found to be around 8 mg per gram of cotton fabric. After being dyed with BPB, colour strength shows a positive correlation with PHMB at low concentrations (< 2400 mg/L). A linear relationship with a high correlation (C(PHMB) = (K/S—0.7411)/3.4517, R2 = 0.9983) was thus established between colour strength and PHMB concentration. However, this equation should fulfill four requirements for quantifying PHMB: (1) the distribution of PHMB on the surface of cellulosic fabric should be in the form of a monolayer with the content less than 5.3 mg/g; (2) an excess of BPB dyebath should be applied; (3) the dyeing should come to equilibrium; and (4) the fabrics should be evenly dyed. Moreover, MTT assay results indicate that excess PHMB coated on cotton fabrics can cause cytotoxicity and the quantity of PHMB should not exceed 4.62 mg per gram of cotton fabrics for the purpose of biosafety. The sample can be considered non-cytotoxic if the K/S value is lower than 13.2 after dyeing with BPB.

Textile industry is one of the most polluting industries due to the large quantities of dyeing wastewater it generates and discharges. Herein, we report an eco-friendly and sustainable circular coloration technology based on cationic polyelectrolyte complex to realise salt-free, zero-effluent-discharge circular dyeing for cotton fabrics with a recyclable dyebath by using a typical cationic polyelectrolyte polyhexamethylene biguanide (PHMB) bonded with anionic dyes. The cotton fabrics were first treated with PHMB and then dyed with three commercial acid dyes. Colour measurements show that the colour strength is controllable by adjustment of concentrations of both PHMB and the dyebath. The dyed fabric samples were found to have good/excellent colour levelness (< 0.49), and the colour fastness (Grade 3 ~ 5) was basically satisfactory and acceptable. The dyebath was proved to be recyclable for circular dyeing occurring at room temperature, which greatly reduces consumption of both water and heat energy for textile dyeing. Meanwhile, the dyed fabrics showed antimicrobial activity, particularly for the gram-positive S. aureus, which may help reduce the healthcare-associated infections that transmit through textiles. These results suggest that cationic polyelectrolyte-based circular dyeing could provide a promising and practicable strategy to address the pollution issue caused by wastewater generated in dyeing process in the textile industry.