| Autor: |
Tassieri, M., Embery, J., Klein, D. H., Hine, P. J. |
| Předmět: |
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| Zdroj: |
AIP Conference Proceedings; 7/7/2008, Vol. 1027 Issue 1, p48-50, 3p, 4 Graphs |
| Abstrakt: |
A rheo-optical study on both isothermal and non-isothermal die swell processes of pure and filled polystyrene (PS) melts is presented. The investigations, initially focussed on both nearly monodisperse (MW/MN = 1.04) and polydisperse (MW/MN = 2.74) linear polystyrenes, have been extended to filled systems comprising PS (matrix) and glass or highly cross-linked PS beads (fillers). Both the glass and PS beads had an average diameter of the order of 10 μm. Die swelling experiments were carried out over a wide range of temperatures (130–240 °C) and shear rates (0.1–200 s-1), and the extrudate shapes were captured in real time using a video camera and a DVD recorder. Post processing of the video images was carried out using a specially written Labview code, enabling the various profiles to be determined with great accuracy. The experimental results were compared with previously published theoretical models, which relate the die swell ratio (χ = d/D, where d is the steady diameter of the extrudate and D is the capillary diameter) to the first normal stress difference (N1). In the case of filled systems, particular attention was paid to understanding the origins of the cavitations, which were observed to occur at a particular shear rate. Image analysis, performed on non-isothermal post-processed samples using both optical microscopy and scanning electron microscopy (SEM), suggests that the ratio ωc/γw (where ωc. is the low-frequency crossover between the elastic and viscous moduli and γw is the wall shear rate) is the characteristic parameter determining the presence (ωc/γw<1) or the absence (ωc/γw>1) of cavitations. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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