In Process Monitoring Of The Flow Properties Of Polymer Melts Using On Line And In Line Methods PDF Download

A flow visualisation cell was used together with image capture and image processing systems to observe the convergent flows of polymer melts in steady state single screw extrusion through a slit die. This technique provided useful information for assessment of any vortex and entry flow patterns for different flow conditions and various polymer types. Entry flow patterns are characterised in terms of natural entry profile, vortex boundary profile, location of vortex centre and detachment length. Stress birefringence provides principal stress difference measurements, which can be obtained from the digital image analysis of isochromatic fringes. The assessment of stress distribution in terms of centre line principal stress difference (PSD) or the extensional stress along the centre line of a slit, shear stress and first normal stress difference are obtained from the digitised isochromatic and isoclinic fringes together with stress optical coefficients via the stress optical law. Stress distributions can be combined with flow velocity measurements for the full entry flow. Average strain rate fields for the polymer melts flow at various flow conditions and different polymer types are therefore obtained. This technique also provides the assessment of apparent extensional viscosity from the ratio of extensional stress (...) and extensional strain rate (...). Two different approaches of the extensional viscosity assessments: particle tracking and digitised entry profile methods are established. Fully developed flow regions in terms of entrance and exit length for polymer melt flows of various flow conditions are determined using gradients of centre line extensional stress (or PSD) and the parallel patterns of isochromatic fringes in a downstrewn slit.