Structural Modification of Polyester Fibers in Supercritical Carbon Dioxide Fluid

Abstract

Several types of polyester fibers, i.e. high speed spun (HSS) fibers, partially oriented yarns (POY), and fully oriented yarns (FOY), were subjected to the supercritical CO 2 fluid treatment (SFT) at 120℃, 20MPa for 1 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 CO 2 fluid dyeing is producible by controlling the fibrous structure and designing the amorphous regions using the high speed spinning process.

Oligomer Deposition on the Surface of PET Fiber in Supercritical Carbon Dioxide Fluid

“…However, the peak intensity of E ″ was a little weakened and the position was shifted to the higher temperature side. In the previous paper,5 it has been reported that such viscoelastic changes are due to binding of amorphous chains by the imperfect small crystallites generated in amorphous regions.…”

“…The oligomer deposition was obvious for SDY. However, the oligomer deposition was not so serious as compared with FOY5 or shin‐gosen12 produced from virgin PET pellets.…”

“…E ′ at glass state was a little elevated by SFT. This peculiar change in storage modulus for HSS fibers are closely related to the well‐developed fibrillar structure 5. Yoshioka et al reported that each of the recognized stacked‐lamellar structures in uniaxially oriented thin films of poly(butylene terephthalate) is assigned to a shish‐kebab structure or a part of it on the basis of crystallographic consideration 11.…”

“…When birefringences are compared between SDY and HSS fibers in Table 1, the value for SDY is larger although crystallinity is smaller than HSS fibers. In such somewhat disordered amorphous regions, the generation of imperfect crystallites will tend to construct network structure which will work as a barrier to oligomer migration 5. Morphological study using AFM was previously made on the HSS poly(ethylene 2,6‐naphthalene dicarboxylate) fibers and it was postulated that several crystalline lamellae are closely stacked in each of the constituents which form the fine network structure 10…”

“…As compared with a conventional dyeing process, oligomer trouble is becoming more serious in developing new dyeing process, i.e., supercritical fluid dyeing (SFD) since the swelling of fiber to s‐CO 2 fluid promotes oligomer migration to the surface as well as relaxation shrinkage of fiber. In order to overcome such oligomer troubles, the authors pointed out that PET fibers with well‐developed fibrillar structure produced via high‐speed spinning is suitable 5,6…”