Investigation into the aqueous and supercritical carbon dioxide dyeing of polyester and cellulose acetate: The influence of temperature and carriers on fabric coloration and dye levelling

This paper investigated the effect of temperature and time on the dyeing of polyester and cellulose diacetate and demonstrated the benefits of supercritical carbon dioxide (SC-CO2) dyeing. It was evident that the SC-CO2 medium enabled effective coloration of polyester at lower temperatures, ca. 100°C, and lower dyeing times in comparison with aqueous dyeing, and also reduced the necessity for water. By contrast, the comparable aqueous disperse dyeing of polyester needed to be at 120°C to achieve full coloration. Energy costs are important in textile dyeing and lowering the dyeing temperature is one approach to minimising energy consumption. In this study, we demonstrated for the first time the beneficial effect of a range of dyebath carriers/accelerants in lowering the SC-CO2 dyeing time and temperature for polyester, while still achieving effective coloration. The beneficial effect of salicylic acid carrier was similarly observed in the SC-CO2 dyeing of cellulose acetate, where the dyeing temperature could be reduced from 85 to 60°C and dyeing time similarly reduced. The recycling of textiles is an ongoing challenge for the textile industry. In this study, we have further explored the use of the SC-CO2 fluid as a medium for reprocessing of discarded dyed polyester and the potential reuse of the “locked-in” colourant. It was evident that the p-Vanillin accelerated the SC-CO2 colour mixing of the blue and yellow dyed polyester fabrics and could assist in producing new colours in “first life and second life” polyester at lower processing temperatures.