Influence of the relaxation behaviour of polyester molecular chains in supercritical carbon dioxide fluid on dyeing performance

Abstract This study investigated the mechanism of dye uptake in supercritical carbon dioxide fluid (ScCO 2 ) by examining fibre swelling and molecular chain relaxation. The swelling rate of 30 D/3 Fila polyester fibres was tested under varying temperatures and pressures using a high‐temperature and high‐pressure in situ imaging platform. The swelling rate increased with temperature and pressure, but the rate of increase slowed above 100°C. The Williams–Landel–Ferry equation was used to analyse the relationship between the thermal relaxation of polyester macromolecular chains and dye uptake at high pressure (27 MPa) during ScCO 2 dyeing. For dyes with poor solubility, dyeing behaviour above 100°C aligns closely with the free volume diffusion model. Conversely, for dyes with good solubility, dyeing behaviour follows the free volume diffusion model within the 50‐100°C range and reaches equilibrium above 100°C.