BS ISO 20965:2021

This document specifies the general principles of a method for determining the transient extensional viscosity of polymer melts. The procedure details the measurement of polymer melt specimens stretched uniaxially under conditions of constant strain rate and constant temperature.The method is capable of measuring the transient extensional viscosity of polymer melts at Hencky strain rates typically in the range 0,01s–1 to 1s–1, at Hencky strains up to approximately 4 and at temperatures up to approximately 250°C (see NOTEs1 and2). It is suitable for measuring transient extensional viscosity values typically in the range from approximately 104Pa?s to 107Pa?s (see NOTE3). NOTE1 Hencky strains and strain rates are used (see Clause3). NOTE2 Values of strain, strain rate and temperature outside these limiting values can be attained. NOTE3 The operating limit of an instrument, in terms of the lowest transient extensional viscosity values that can be measured, is due to a combination of factors, including the ability of the specimen to maintain its shape during testing and the resolution of the instrument.