Stress measurements for contraction flows of viscoelastic polymer melts
การวัดความเค้นของพอลิเมอร์หลอมในดายเอกซ์ทรูดที่มีการเปลี่ยนขนาดอย่างทันทีทันใด

Martyn, M. T., D. of Mechanical and Medical Eng., IRC in Polymer Sci. and Tech., U. of Bradford, England
Charoen Nakason, Asst. Prof., D. of Rubber Tech. and Polymer Sci., F. of Sci. and Tech., PSU.
Coates, P. D., D. of Mechanical and Medical Eng., IRC in Polymer Sci. and Tech., U. of Bradford, England
Corresponding e-mail : ncharoen@bunga.pn.psu.ac.th

Grant : Government Budget, PSU., ESRC Council and University of Bradford
Published : J of Non-Newtonian Fluid Mechanics 2000, 91 : 123-142
Key words : contraction flow, stress measurement, polyolefin melt

This work presented in the second of a series of three papers providing a comprehensive in-process study of polyolefin melt flows through the convergent section of the slit die. Here we focus on stress fields developed in several liner and branched polyolefin melts. Accurate measurement of stress optical coefficients derived from flow induced birefringence has enables determination of shear and first normal stress difference fields in these polymers in an abrupt entry convergent flow geometry. The progression of stress growth with increase in melt flow rate is also described. The dimensionless stress ratio (centre line tensile stress to slit wall shear rate) has been identified as a quantify which correlates with the relative vortex size in the linear and branched polyolefins. Fully developed entry flows on melt passage into the slit section are also studied and reflect relaxation characteristics of each polymer.

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