Rides, M; Allen, C R G; Chakravorty, S (1999) Intercomparison of extensional flow characterization techniques for polymer melts: tensile stretching and converging flow methods. NPL Report. CMMT(A)171

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Abstract

Although extensional flow properties of polymer melts play an important role in their behaviour in processing, these properties are rarely characterised compared with that of their shear flow properties. Furthermore, the measurement of extensional flow behaviour is more complex than that of shear flow behaviour, and the variation in data that is likely to be obtained when using different instruments and techniques is not established. An intercomparison of extensional flow characterization techniques for polymer melts was organised to assess the variation in data obtained when using different instruments and methods. The results of this intercomparison are reported.
The methods used in the intercomparison were principally tensile stretching and converging flow methods, although fibre spinning and a flow visualisation method were also included. A high density polyethylene that was stable at 190 °C for in excess of two hours was used as the intercomparison material. Measurements were made at 150 °C and 190 °C.
For tensile stretching methods the variation in extensional stress growth coefficient values was estimated to be up to ± 60%. The variation in peak extensional stress growth coefficient values was up to ± 100%. For converging flow methods using the Cogswell model the variation in extensional viscosity values was estimated to be up to ± 230%. In comparing peak transient extensional viscosity values obtained from stretching methods with “equilibrium” values obtained by the other methods, the level of agreement was considered to be good with significant overlap of data from the different methods being obtained. This finding supports the use of converging flow methods for determining extensional viscosity values, albeit “equilibrium” values.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	CMMT(A)171
Subjects:	Advanced Materials Advanced Materials > Polymer Rheology
Last Modified:	02 Feb 2018 13:18
URI:	http://eprintspublications.npl.co.uk/id/eprint/1137

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