National Physical Laboratory

Extensional flow properties of polymers using stretching flow methods.


Rides, M, Allen, C R G

Measurement Good Practice Guide No. 63, December 2002
NPL Doc. Ref:
PDB: 3432
Document Type:

Note: An asterisk after an author's name indicates a non-NPL author.


In many forming processes the polymer melt undergoes predominantly extensional deformation, for example in blow moulding and film blowing. Furthermore, the extensional flow behaviour of melts differ significantly from their shear flow behaviour. Thus extensional flow measurement methods are necessary to appropriately characterise the melt behaviour. Such data can be used for the development and selection of materials, and for improving processing. This Guide discusses various issues related to the need for, and measurement of the extensional flow properties of polymer melts using stretching methods. It describes practical considerations for measuring extensional flow behaviour, including measurements at very high and low strain rates, and includes details on the analysis of the raw data and assessment of the effect of uncertainties on the measured values. To illustrate the measurement technique, typical data obtained using the NPL extensional rheometer are presented along with results obtained from an international intercomparison. This Guide is aimed at those carrying out, or intending to carry out, such testing or are building/modifying test equipment.

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