Modification of the fine structure of heat‐set polyester on dyeing at high temperature

Polyester woven fabrics for upholstery comprising multilobal filament yarn warp and textured yarn weft have been heat‐set at different temperatures and then dyed at high temperature (130 °C) using dyes of small and large molecular size, in order to study the influence of dyeing on the fine structure of the fibre. The heat‐set substrates have also been blind dyed under the same conditions for comparison. The modification of the fine structure and the influence of the dye and its molecular size have been evaluated by density/crystallinity, differential solubility and iodine sorption measurement. The results show that the thermal treatment associated with dyeing at 130 °C decreases the differential solubility and the iodine sorption of heat‐set polyester. This is the result of a more compact fine structure and in consequence a degree of supplementary setting in the fabric. This effect is more pronounced in fabrics heat‐set at relatively low temperatures.