Premium
Unstable flow of amorphous polymers through capillaries I. Velocity profiles of polymer having discontinuous flow curve
Author(s) -
Bartǒs Otakar,
Holomek Josef
Publication year - 1971
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760110410
Subject(s) - materials science , capillary action , die swell , mechanics , laminar flow , turbulence , flow (mathematics) , composite material , physics , extrusion
Ciné film was employed for recording the movement of tracer particles, thus directly determining the velocity profile in the capillary flow of model materials of polybutadiene over a range of shear stresses relating to (1.) flow conditions in which there is no distortion of the regular stream of melt emerging from a capillary, (2.) severe surface fracture, (3.) elastic turbulence, (4.) oscillatory flow of melts with discontinuous flow curves. No qualitative difference was found between the velocity profiles in conditions (1) and (2); surface fracture is not related to laminar flow disturbances and originates at the capillary exit. Surface fracture must be distinguished from elastic turbulence. The streamline velocities undergo both local and time variations within the capillary under conditions of developed elastic turbulence; the wall velocity is non‐zero. A periodic pulsation of velocities occurs in the flow curve discontinuity region; it takes place throughout the capillary and is caused by stick‐slipping of polymer on the capillary wall. The frequency of velocity pulsations coincides with the frequency of extrudate variations.