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Deformation kinetics of polypropylene hollow fibers in a continuous drawing process

โœ Scribed by Moo Seok Lee; Tae Hwan Oh; Sang Yong Kim; Hyun Joo Shim


Publisher
John Wiley and Sons
Year
1999
Tongue
English
Weight
250 KB
Volume
74
Category
Article
ISSN
0021-8995

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โœฆ Synopsis


Effects of isothermal drawing conditions on the deformation kinetics and dimensional change of polypropylene (PP) hollow fibers in a continuous drawing process were investigated. The deformation behavior of solid PP polymers during stretching between two rolls in the isothermal bath was analyzed by a simple model describing the continuous drawing process with a constitutive relation that can express a true (stressstrain-strain rate) surface of solid semicrystalline polymers. Necking profiles during drawing can be calculated from this model without any special assumption for neck criterion, and the calculated results predict that the localization of deformation is promoted with the increase of applied draw ratios. It is also found that at 20ยฐC, the neck is observed apparently both from the calculated and experimental results, and the strain-rate sensitivity parameter is considered to be a critical factor that determines the intensity of the neck geometry. The calculated drawing forces are shown to increase with increasing the applied draw ratio and decreasing the drawing temperature, and these trends were verified by experimental results. The hollowness, defined as the ratio of inner to total cross-sectional area, increases as it is drawn at 30ยฐC, but decreases as drawn above this temperature compared with that of the undrawn fiber.


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