An investigation of process parameters on colour during the dyeing of polyester in supercritical carbon dioxide media

Abstract Innovative supercritical carbon dioxide (scCO₂) treatment conditions in fluidised media technology were examined for polyester dyeing. The different dyeing processes in scCO₂ media were carried out under a constant dyeing temperature of 120°C (at pressures ranging from 9 to 29 MPa), a constant pressure of 25 MPa (at dyeing temperatures ranging from 40 to 140°C) and a constant density range of 500‐550 kg/m³ (at combinations of dyeing temperatures ranging from 80 to 130°C and dyeing pressures ranging from 18 to 28 MPa). The constant dyeing temperature, constant dyeing pressure and constant density (120°C, 25 MPa, 500‐550 kg/m³, respectively) were selected according to the best results in the literature and recommendations from industrial applications for polyester dyeing in scCO₂ media. The different conditions of the studied parameters and their influence are discussed. Colour difference (ΔE) and colour strength (K/S), as well as washing fastness and bursting strength properties, were investigated and compared. Acceptable colour properties (similar to those for standard [control reference] fabric: dyed in scCO₂ media at 120°C, 25 MPa pressure and 506 kg/m³ density for 90 minutes) on polyester fabric, with commercially acceptable and quite high washing fastness levels and comparable bursting strength values (similar to those for standard fabric without significant or drastic strength loss), could be achieved with the following scCO₂ dyeing processes: at a lower dyeing pressure with the same dyeing temperature (in scCO₂ media at 120°C, 21 MPa pressure and 423 kg/m³ density for 90 minutes), at a lower dyeing temperature with the same dyeing pressure (in scCO₂ media at 100°C, 25 MPa pressure and 588 kg/m³ density for 90 minutes) and at both a lower dyeing pressure and a lower dyeing temperature with a constant density range of 500‐550 kg/m³ (in scCO₂ media at 110°C, 24 MPa pressure and 526 kg/m³ density for 90 minutes). Satisfactory and successful dyeing properties and performance similar to polyester fibre dyed under standard scCO₂ dyeing conditions with less energy consumption could be achieved with the correct scCO₂ dyeing process parameter optimisation. For instance, the dyeing process in the scCO₂ environment at the same dyeing temperature with the standard scCO₂ dyeing process (at 120°C), but with a lower dyeing pressure (at 21 vs 25 MPa), resulted in a 17 kWh decrease in energy consumption. In conclusion, it is very important to choose the correct dyeing pressure to obtain level dyeing in the polyester dyeing process carried out in a scCO₂ environment and to achieve a reduction in energy consumption during dyeing in a scCO₂ medium.