In-process measurement of polymer melt flow in extrusion process
การวัดสมบัติทางกระแสวิทยาของพอลิเมอร์หลอมโดยตรงในกระบวนการอัดรีด
Charoen Nakason, Asst. Prof., D. of Rubber Tech. and Polymer Sci., F. of Sci. and Tech., PSU.
Sarote Changchum, M.Sc. Student in Polymer Tech., PSU.
Manus Saedan, Asst. Prof., D. of Sci., F. of Sci. and Tech., PSU.
Corresponding e-mail : ncharoen@bunga.pn.psu.ac.th
Grant : The National Metal and Materials Technology Center (MTEC)
Published : Songklanakarin J Sci Technol 2000, 22(3) : 347-356
Key words : in-process, rheometry, shear flow, extensional flow, Cogswell, extrusion die
Extrusion-based in-process rheometry was carried using a specially designed capillary extru-sion die, fitted to a single screw extruder with a screw of 25 : 1 L/D ratio. A pressure transducer and a thermocouple were attached to the extrusion die. Processing parameters in terms of pressure drop across capillary channel and melt temperature were captured by means of a data acquisition system. Shear properties were quantified using rheometric equations. Baglay corrections were made for all
sets of data. Cogswell's free convergence model for capillary flow was used to access extensional properties. Comparison of shear flow results from off-line Rosand single bore capillary rheometer and in-process measurement are in good agreement. It is therefore concluded that shear flow for polymer melt in both techniques did not depend on processing history and characteristics of the techniques. Extensional flow results for a linear polymer, HDPE, showed good agreement between the two techniques. However, comparison for flow of branched polymers, LDPE and LLDPE, showed poor agreement. This is attributed to the difference in flow nature between the two techniques. Also degree of chain branching (DCB) plays a significant role on flow behaviour of polymer. Branched materials, such as LDPE and LLDPE, exhibit strain hardening or extensional stress growth behaviour, while
linear polymer displays less stress growth during flow.
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