Preparation of cationic viscose and its salt‐free dyeing using reactive dye

Abstract The traditional dyeing process of reactive dyes requires a large amount of inorganic salts to accelerate the combination of dyes and textiles, which leads to substantially more water pollution. In this work, we used a quaternary ammonium‐type cationic modifier, 3‐chloro‐2‐hydroxypropyl trimethylammonium chloride (CHPTAC), to modify the viscose acetal fibre before the dyeing process. After the modification, reactive dyes were dyed without any inorganic salt. Then the fabric was finished with a commercial wet rubbing fastness enhancer, FM‐8, to improve the colour fastness. The modified viscose acetal fibre was characterised by Fourier Transform–infrared spectroscopy and scanning electron microscopy. The results showed that viscose acetal fibre was modified successfully by CHPTAC and that the physical structure did not noticeably change following the modification. The optimum process was determined by establishing the ideal amount of modifier and the modification temperature, as well as the concentrations of sodium hydroxide and soda ash. The results show that the most suitable parameters were 80 g/L for the modifier dosage, a modification temperature of 70°C, 20 g/L of sodium hydroxide and 10 g/L of soda ash. The wet rubbing fastness was grade 4‐5 after finishing and dyeing. The exhaustion percentage was significantly higher than that for traditional dyeing, and the K / S and dyeing uniformity were both higher than traditional salt dyeing.