One-step bleaching method for animal fiber by persulphate/hydrogen peroxide

Animal fibres are coloured using dyes to satisfy the individual needs; thus, dark animal fibres must be bleached. Compared with frequently used Fe 2+ -catalysed H 2 O 2 (Fe 2+ /H 2 O 2 ) bleaching, persulphate (PDS)/H 2 O 2 bleaching is advantageous owing to its high efficiency, low damage of fibre and environmental friendliness. Herein, different free radical species were precisely controlled by changing the pH of the PDS/H 2 O 2 solution and regulating the existence of NH 4 + . When NH 4 + was absent, sulphate radicals (·SO 4 − ) and hydroxyl radicals (·HO) could be produced at pH = 8–9 and superoxide anions (·O 2 − ) could be produced at pH = 10. In the presence of NH 4 + , ·SO 4 − and ·HO could be produced at pH = 8, and ·O 2 − was dominant in the solution when pH = 9–10. Black yak wool was used as the research object to demonstrate that the bleaching ability of the generated ·O 2 − was stronger than those of the generated ·SO 4 − and ·HO. Compared with that of the commercial product (prepared using Fe 2+ /H 2 O 2 bleaching), the bleaching time of the decolourised yak wool was reduced by 83.33% (from 24 to 4 h) without the catalysis by heavy metal ions . Meanwhile, the whiteness of the decolourised yak wool (72.31%) was close to that of the commercial product (78.79%). Furthermore, the damage to the cuticle layer and cortex of yak wool was low after bleaching. The breaking strength of the decolourised yak wool was 1.79 cN·dtex −1 , which only decreased by 17.13% compared with that of raw yak wool. These results hold great potential in developing environmental-friendly bleaching methods for dark animal fibres with high efficiency and low damage.