A comparison of theoretically determined and experimentally measured velocity distributions of poly(ethylene terephthalate) flow in a capillary

Abstract

A streak photographic technique was used to determine the velocity distribution in a capillary produced by the flow of poly(ethylene terephthalate) (PET). This uniquely designed quartz die assembly, which was fitted onto a melt extruder, permitted visualization of polymer flow behavior during melt spinning. Aluminum tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system that illuminated the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. A pressure‐drop analysis was also performed on PET, under the same experimental conditions, to determine rheological properties of the polymer. By using these rheological properties theoretical velocity distributions were calculated for PET and then compared with the profiles obtained by the streak photographic technique.