A visualization study of poly(ethylene terephthalate) flow using potential chain‐ordering die geometries

Abstract

Streak‐photographic and stress birefringence techniques were used to analyze the flow of poly(ethylene terephthalate) through potential chain‐ordering die geometries. The streak photographs were used to determine velocity distributions and streamlines in various convergent dies. The different contours were seen to have a significant effect on the polymer streamlines and velocity distributions. The measured velocities were used to develop empirical equations, specific for each geometry, which relate velocity to position within the die and to throughput rate. Flow birefringence was used to determine the extent of molecular ordering. The optimum chain‐ordering die geometry was determined to be one which included a rapid initial decrease in cross‐sectional area. Birefringence was also used to monitor polymer flow instability. An unusual mechanism for instability was observed at intermediate throughput rates.

Simulation of Flow in the Silk Gland

“…From the extension rate profile (Figure ), it is immediately obvious that neither silk gland is shaped as a constant extension rate funnel, as has been previously suggested for the spider MA gland. , Constant extension rate funnels have been under investigation in the fiber spinning community because they are believed to minimize the pressure drop required for flow as well as induce and maintain the highest degree of molecular alignment in a solution. − The spider MA gland actually acts as an increasing extension rate funnel, perhaps in order to maintain extension despite the strain hardening character of highly strained silk dope …”

“…1,9 Constant extension rate funnels have been under investigation in the fiber spinning community because they are believed to minimize the pressure drop required for flow as well as induce and maintain the highest degree of molecular alignment in a solution. [38][39][40] The spider MA gland actually acts as an increasing extension rate funnel, perhaps in order to maintain extension despite the strain hardening character of highly strained silk dope. 16 The maximum extension rate in the spider silk MA gland rises to an order of magnitude higher than that in the silkworm gland.…”

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.…”

Reinforcement of mechanical properties of a poly(ethylene terephthalate) and polycarbonate blend by the addition of thermotropic liquid crystalline polymer

“…Fibers were prepared by using an Instron Capillary Rheometer (Model 321 1) equipped with a conical die with 90" entry angle and 1.27 mm diameter ( L / D = 40) under environmental air at 20°C. The conical die was chosen because it generated an elongational flow in the converging section and had greater potential for ordering chains than conventional cylindrical dies (23). In order to investigate the effect of draw ratio on the morphology and mechanical properties, the extrudate in the molten state was elongated by a takeup apparatus located 60 cm below the capillary die.…”