Optimization of dark dyeing poly(lactic acid) yarn with indigo dyes applied to denim fabric

The application of new environment-friendly biological fiber materials in denim industry is becoming more and more popular, then the dyeing of the new biological fiber and yarn has become the focus of research. To better expand the use of the biological-based materials in denim industry and promote the dark color dyeing of poly(lactic acid)(PLA) yarn, the effects of dyeing temperature, dyeing pH, dyeing time and dyeing times on the dye depth (K/S) and mechanical properties (breaking strength) of PLA yarns are investigated. It is found that the dye depth of PLA yarn is the best when the dyeing temperature is 110 °C, pH of dyeing solution is 5, the dyeing time is 40 min and the dyeing times is 3 times, respectively, and the K/S value reaches 11.43, the color fastness of different types of dyed PLA yarns are all above grade 4. The orthogonal experiment shows that the optimum dyeing condition to dye 1 g PLA yarn with 23 Neβ is 10 g/L synthetic indigo, 10 g/L sodium hydrosulfite, 15 g/L sodium hydroxide, respectively.