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

Abstract

Innovative supercritical carbon dioxide (scCO(2)) treatment conditions in fluidised media technology were examined for polyester dyeing. The different dyeing processes in scCO(2) media were carried out under a constant dyeing temperature of 120 degrees C (at pressures ranging from 9 to 29 MPa), a constant pressure of 25 MPa (at dyeing temperatures ranging from 40 to 140 degrees C) and a constant density range of 500-550 kg/m(3) (at combinations of dyeing temperatures ranging from 80 to 130 degrees C and dyeing pressures ranging from 18 to 28 MPa). The constant dyeing temperature, constant dyeing pressure and constant density (120 degrees C, 25 MPa, 500-550 kg/m(3), respectively) were selected according to the best results in the literature and recommendations from industrial applications for polyester dyeing in scCO(2) media. The different conditions of the studied parameters and their influence are discussed. Colour difference (Delta E) 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 scCO(2) media at 120 degrees C, 25 MPa pressure and 506 kg/m(3) 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 scCO(2) dyeing processes: at a lower dyeing pressure with the same dyeing temperature (in scCO(2) media at 120 degrees C, 21 MPa pressure and 423 kg/m(3) density for 90 minutes), at a lower dyeing temperature with the same dyeing pressure (in scCO(2) media at 100 degrees C, 25 MPa pressure and 588 kg/m(3) 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/m(3) (in scCO(2) media at 110 degrees C, 24 MPa pressure and 526 kg/m(3) density for 90 minutes). Satisfactory and successful dyeing properties and performance similar to polyester fibre dyed under standard scCO(2) dyeing conditions with less energy consumption could be achieved with the correct scCO(2) dyeing process parameter optimisation. For instance, the dyeing process in the scCO(2) environment at the same dyeing temperature with the standard scCO(2) dyeing process (at 120 degrees 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 scCO(2) environment and to achieve a reduction in energy consumption during dyeing in a scCO(2) medium.