Distribution of disperse dyes between supercritical CO2 and polyester fibers: A combined molecular dynamics simulation and experimental study

Molecular dynamics simulations were used to predict the partitioning behavior of disperse dyes between supercritical CO2 fluid (ScCO2) and polyester fibers under varying temperature and pressure conditions. Based on these results, the ScCO2 dyeing equipment was enhanced with a stepwise pressure-reduction unit. A modified process, involving heat retention and gradual pressure reduction at the end of the dyeing process, was proposed to improve dye uptake. Experimental validation showed a 6%–7.5% increase in dye uptake compared to conventional methods, while maintaining good colorfastness. Further dyeing experiments and analysis of dye dissolution and phase distribution revealed that the timing and extent of pressure reduction should differ for various dyes. For dyes with lower solubility, the heat retention and pressure reduction process should begin only after most of the dye has been absorbed, and the pressure reduction should not be too large. Although pressure reduction decreases solubility, the phase distribution of the dyes shifts more toward the fibers, leading to an increase in the final dye-uptake rate.