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
SynopsisThe viscous and elastic properties of linear high density polyethylene (HDPE), poly(buty1ene terephthalate) (PBT), and poly(ethy1ene terephthalate) (PET) are investigated using an Instron capillary rheometer and the Philippoff-Gaskins-Bagley analysis. The viscous properties studied are the shear viscosity and the constant shear rate activation energy and the elastic properties studied are the entrance pressure drop and the end correction. The variables are shear rate and temperature.The order of decreasing viscosity is HDPE > PET > PBT; the order of decreasing activation energy is PB > PET > HDPE the order of decreasing entrance pressure drop is HDPE > PET > PBT; and the order of decreasing end correction is PBT > PET > HDPE. As temperature increases, both viscosity and entrance pressure drop decrease. The observed behavior is discussed in terms of the difference in number of terephthalic acid moities in the polymer chains and in terms of oligomer plasticization.
SynopsisThe flow behavior of four cellulose acetate-acetone solutions varying from 20.00% to 28.18% solids concentration was observed using flow visualization techniques a t 24°C with an industrial-type dry spinning system. Fibrous particulate matter entraimd in the solutions and crossed polars revealed the streamlines and the birefringence due to flow in glass spinnerets. The streamlines of the four solutions were radially convergent at all obtainable throughputs. The crossed polars revealed a cone of birefringence with the order of the interference colors decreasing upstream of the capillary inlet. The intensity and extent of birefringence varied somewhat with concentration and throughput. Except for kneeing, the emerging extrudates were undeformed. The kneeing was not a result of flow instability a t the capillary inlet but was due to another, undetermined instability. A separate study of the kneeing revealed both a concentration dependence and hysteresis. The birefringence of the emerging extrudates was a function of both concentration and throughput, and it yielded some information about the structure of the solutions.
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