Structural modification of polyester fibers in supercritical carbon dioxide fluid

Several types of polyester fibers, i.e. high speed spun (HSS) fibers, partially oriented yams (POY), and fully oriented yams (FOY), were subjected to the supercritical CO2 fluid treatment (SFT) at 120degreesC, 20MPa for I h and structural modifications were investigated. Large shrinkage and not a small amount of oligomer deposition on the fiber surface were observed for POY and FOY. On the contrary, as for HSS fibers produced at a spinning speed of 6 km/min the shrinkage was suppressed within 2 % as compared with an initial fiber length and the oligomer deposition could hardly be observed. The shrinkproof property for HSS fibers seems to be closely related to the well developed fibrous structure. Such structure can be easily confirmed via the alkaline etching. The oligomer migration can be lowered by accelerating the orientation-induced crystallization rate on the high speed spinning line and disordering the molecular orientation in amorphous regions. In addition ultra-crystallites formed in amorphous regions during SFT will also be effective for the suppression to the oligomer migration. The disordered macromolecules and the ultra-crystallites formed in amorphous regions will develop a network-like structure that suppresses the oligomer migration. Therefore, a novel polyester fiber suitable for the supercritical CO2 fluid dyeing is producible by controlling the fibrous structure and designing the amorphous regions using the high speed spinning process.