Flow‐induced crystallization of polymer melts in convergent flow regimes and imposed temperature gradient to form ultra‐oriented fiber structures

Abstract

Flow crystallization experiments which utilized the Instron rheometer in conjunction with convergent dies were conducted for the purpose of producing high-modulus poly-(ethylene terephthalate) filaments directly. from the melt. A temperature gradient was imposed on the lower extremity of the dies in an attempt to control the site of the fluid-solid phase transformation, and "freeze in" any orientation derived from the elongational flow regime. Com arative studies were made sion temperatures ranging from 255 to 270°C. Die angle influenced the pressure at which maximum die swell and the onset of extrudate distortion occurred; however, barrel temperature showed little effect on this pressure. The minimum temperature produced by the temperature gradient was the over-riding factor involved with cessation of flow. In each experiment, the fluid-solid phase transformation produced by the temperature was always accompanied by extrudate distortion. Thus, only minimal comparative studies of the extrudates could be performed. In view of the above, it appears that utilizing a temperature gradient, by itself, to "freeze in" preferred orientation within the confines of the die presents difficulties. A modification which combines a temperature gradient with external tension and a rapid after-quench outside the die, now holds appeal for continuing studies.using dies with included angles o P 20,30, and 40", and extru-324

Rheological Features and Flow‐Induced Crystallization of Branched Poly[ethylene‐co‐(1,4‐cyclohexanedimethylene terephthalate)] Copolyesters

“…The pioneering work about induced crystallinity in polyethylene in a extrusion capillary rheometer, published by Southern and Porter almost 40 years ago,52 was developed and extended to the case of PET by Cuculo and coworkers53–56 in the late 1970s and early 1980s. These authors focused on the role played by converging flows at the entrance of the capillary die, concluding that the formation of crystals should be attributed to elongational rate in the converging stream.…”