Supercritical fluid dyeing of polycarbonate in carbon dioxide

•An environmentally benign process for polycarbonate dyeing is proposed.•Waterless dyeing in one single step without the use of any organic solvent.•Entirely, equally deep-dyed polymer pellets with excellent dyeing fixation.•New solubility data and equilibrium constants are reported.

In this work, the applicability of the supercritical CO2 dyeing process on polycarbonate pellets was investigated by the use of two azo-disperse dyes; disperse red 1 (DR1) and disperse red 13 (DR13). Experiments were performed in the range of 100–300 bar and 40 °C–60 °C with 3–24 h of impregnation time. Dyeing took place in a high pressure vessel and kinetics was studied and explained. Impregnation efficiency on the polymer pellets was measured by UV–vis spectroscopy. The process was successfully applied and resulted in an entirely, equally deep-dyed polymer with excellent dyeing fixation. Arising from the different solubility and chemical structure of the dyes, their sorption kinetics was found to be different. Maximal dye uptake obtained with DR1 and DR13 were 0.010 wt% and 0.055 wt% respectively, with respect to the mass of the polymer. New solubility data for DR13 in supercritical CO2 has also been measured and partition coefficients (Kc) for the dyes between the fluid and the polymer phase were calculated.

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