ISO 20965:2005

Plastics - Determination of the transient extensional viscosity of polymer melts

ISO 20965:2005 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 0,01 s-1 to 1 s-1, at Hencky strains up to approximately 4 and at temperatures up to approximately 250 °C. It is suitable for measuring transient extensional viscosity values typically in the range from approximately 104 Pa.s to 107 Pa.s.

Plastiques — Détermination de la viscosité élongationelle transitoire des polymères à l'état fondu

General Information

• Status: Withdrawn
• Publication Date: 28-Feb-2005
• Withdrawal Date: 28-Feb-2005
• ICS: 83.080.01 - Plastics in general
• Technical Committee: ISO/TC 61/SC 5 - Physical-chemical properties
• Drafting Committee: ISO/TC 61/SC 5/WG 9 - Rheology
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 07-Apr-2021
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO 9312:2013 - Resistance welding equipment - Insulated pins for use in electrode back-ups
• Effective Date: 06-Jun-2022
• Revised: ISO 20965:2021 - Plastics - Determination of the transient extensional viscosity of polymer melts
• Effective Date: 23-Apr-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20965
First edition
2005-02-15
Plastics — Determination of the transient
extensional viscosity of polymer melts
Plastiques — Détermination de la viscosité élongationelle transitoire
des polymères à l'état fondu
Reference number
©
ISO 2005
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ii © ISO 2005 – All rights reserved

Contents Page
Foreword. iv
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 General principles. 3
5 Apparatus. 3
6 Sampling and specimen preparation . 6
7 Procedure. 7
8 Analysis of extensional flow measurements .8
9 Precision. 11
10 Test report. 11
Annex A (informative) Checking for swelling of specimens due to immersion in silicone oil or
other fluids. 12
Annex B (informative) Uncertainties in transient extensional viscosity testing. 13
Bibliography . 18

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 20965 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
iv © ISO 2005 – All rights reserved

INTERNATIONAL STANDARD ISO 20965:2005(E)

Plastics — Determination of the transient extensional viscosity
of polymer melts
1 Scope
This International Standard 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
–1 –1
rates typically in the range 0,01 s to 1 s , at Hencky strains up to approximately 4 and at temperatures up
to approximately 250 °C (see Notes 1 and 2). It is suitable for measuring transient extensional viscosity values
4 7
typically in the range from approximately 10 Pa⋅s to 10 Pa⋅s (see Note 3).
NOTE 1 Hencky strains and strain rates are used (see Clause 3).
NOTE 2 Values of strain, strain rate and temperature outside these limiting values may be attained.
NOTE 3 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.
A list of documents related to this International Standard is given in the Bibliography.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 472, Plastics — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 472, together with the following,
apply.
[1]
Definitions 3.1 to 3.5 are given by Whorlow for strains and strain rates, and by the Nomenclature
Committee of the Society of Rheology for start-up flow in tensile uniaxial extension at constant Hencky strain
[2]
rate .
3.1
Hencky strain
ε
strain given by the natural logarithm of the elongation ratio
ε = ln(l/l ) (1)
where l is the specimen length and l is the original specimen length
NOTE 1 It is also referred to as the natural or true strain.
NOTE 2 It is dimensionless.
3.2
Hencky strain rate

ε
rate of change of Hencky strain with time, given by
ε=×1/ll∂ /∂t (2)
where t is time
NOTE 1 It is independent of the original specimen length l .
NOTE 2 It is expressed in reciprocal seconds.
3.3
net tensile stress
σ
E
for tensile uniaxial extension, stress given by
σ = σ – σ = σ – σ = σ – σ (3)
E 11 22 11 33 zz rr
where σ is a stress tensor in either rectangular or axisymmetric co-ordinates
ii
+ +
NOTE 1 The tensile stress growth function is indicated by σ where the indicates start-up of flow.
E
NOTE 2 Net tensile stress is expressed in pascals.
3.4
tensile stress growth coefficient
+
η
E
ratio of the net tensile stress to the Hencky strain rate
+

η (,tεσ) = /ε (4)
EE
+
for tensile uniaxial extension, where t is time and indicates start-up of flow
NOTE 1 It is also known for the purposes of this International Standard as “transient extensional viscosity”.
NOTE 2 It is a transient term.
NOTE 3 It is expressed in pascal seconds.
3.5
tensile viscosity
η
E
term given by
+

η (,ttεη) = lim[ (,ε)] (5)
EE
t→∞
NOTE 1 It is the limiting tensile stress growth coefficient value and represents an equilibrium extensional viscosity if a
steady value is achieved. However, for materials that do not exhibit a steady-state behaviour, the use of an “equilibrium
extensional viscosity” such as this is not appropriate.
NOTE 2 It is expressed in pascal seconds.
2 © ISO 2005 – All rights reserved

4 General principles
In contrast to shear flow where reference is normally made only to steady shear flow behaviour, extensional
flow behaviour is best described as being transient. In describing the transient behaviour of materials in
extension at constant strain rate, they may exhibit either an unbounded stress growth behaviour in which the
stress continually increases with increasing strain until the material fails, or the stress reaches a steady value
with increasing strain thus yielding a tensile or equilibrium extensional viscosity. The latter occurs typically at
large strains. An equilibrium extensional viscosity is thus dependent on strain rate but not on strain or time.
Normally, the extensional viscosity will vary as a function of both strain and strain rate as well as temperature.
In describing and modelling plastics processing, the use of Hencky strain is preferred. The rate of Hencky
strain of an element of fluid within a flow is independent of its original length and is determined only from the
velocity field of that element. It is thus a more suitable characteristic of the flow. Strain and strain rate are
taken by default herein to be Hencky values.
Stretching flow methods can be used to generate quantitatively accurate data on the extensional
viscoelasticity of polymer melts. In carrying out extensional flow measurements, there are four types of
measurement that are normally made: constant strain rate, constant stress, constant force and constant
speed. This International Standard describes the first of these: constant strain rate. In this method, the strain
rate is uniform throughout the specimen and is held constant with time.
The basic principle behind stretching flow measurements is to subject a specimen to a tensile stretching
deformation. By measurement of the force and deformation of the specimen, the stresses and strains and
hence strain rate can be determined.
5 Apparatus
5.1 General description
The measuring apparatus shall consist of one of the following types, shown in Figures 1 to 4. These types
define the various instrument configurations. The notation used in these figures is defined in 8.1.
Type A: Two rotating clamps. Each clamp shall consist of either a single rotating element or a pair of rotating
elements — only the pair arrangement is shown. The force exerted on the specimen can be measured at the
fixed or rotating end.
NOTE It is likely that the force will be easier to measure, and will be measured with greater accuracy, on a fixed
clamp rather than on a moving clamp as there will be fewer complications due, for example, to vibration and the inertia of
the clamp which may introduce noise and errors into the force signal.

Figure 1 — Schematic diagram of type A test instrument
Type B: A single rotating clamp and a fixed clamp. The rotating clamp shall consist of either a single rotating
element or a pair of rotating elements. The force exerted on the specimen is normally measured at the fixed
end.
Figure 2 — Schematic diagram of type B test instrument
Type C: Two translating (non-rotating) clamps.

Figure 3 — Schematic diagram of type C test instrument
Type D: Single translating (non-rotating) clamp.

Figure 4 — Schematic diagram of type D test instrument
In each of these configurations, the specimen is mounted between the clamps and is stretched uniaxially. The
requirements for the apparatus are that it shall permit the measurement or determination of the force acting on
the specimen, and the strain and strain rate of the specimen subjected to a constant strain rate under
isothermal conditions. The strain and strain rate of the specimen shall either be derived from the
displacements and/or speeds of the clamp or clamps, or be measured directly from the dimensions and/or
local velocities of the specimen.
5.2 Silicon bath/temperature-controlled chamber
Heating may be provided by placing the specimen in a silicone oil bath or in a temperature-controlled chamber
with a forced gas flow through it.
NOTE 1 When heating using forced gas, a gas may be used in the chamber surrounding the test specimen to provide
the required test environment, for example nitrogen to provide an inert atmosphere.
NOTE 2 The use of a silicone oil bath may permit more rapid heating of the specimen.
4 © ISO 2005 – All rights reserved

For low-viscosity materials, it is essential to support the specimen during heat-up and testing (to avoid it
sagging under the influence of gravity).
NOTE 3 The use of a silicone oil bath results in the specimen being supported by the silicone oil due to its buoyancy,
particularly if the densities of the silicone oil and specimen are matched at the test temperature. If a forced-gas oven is
used, then support of the specimen can be obtained by the cushioning effect provided by the gas.
Silicone oil may be absorbed by some polymers. A check should preferably be made to see if the immersion
time affects the measured properties of the polymer by varying the length of the immersion time (see Annex A
and also Note 1 in 7.1). When quantitative results are required, then this check shall be made.
NOTE 4 Even if the silicone oil does not affect the shape of the tensile stress growth coefficient versus strain (or time)
plot, it may affect the point of failure of the specimen. Thus assessment of the effect of the silicone oil on the measured
properties should consider both of these aspects.
NOTE 5 Alternative methods for checking the effect of immersion in silicone oil on the specimen may also be used.
Such methods include the measurement of the mass or dimensions of the specimen before and after immersing in silicone
oil and identifying whether a change has occurred due to that immersion — see Annex A.
5.3 Temperature measurement and control
The test temperature should preferably be measured using a device that is mounted close to the specimen.
Contact of the device with the specimen is not permitted. It is essential to mount temperature sensors in at
least two positions to monitor temperature uniformity along the length of the specimen.
NOTE The uniformity of the temperature along the specimen length is critical to the measurement of the transient
extensional flow properties of polymer melts. Localized hot spots will result in excessive strain in those regions. This may
lead to premature failure, particularly for materials that do not exhibit a high degree of strain hardening.
The spatial temperature variation shall be within ± 0,75 °C.
The temporal temperature variation shall be within ± 1,0 °C of the set temperature.
The temperature-measuring device shall have a resolution of 0,1 °C and shall be calibrated using a device
accurate to within ± 0,1 °C.
5.4 Strain and strain rate measurement
The strain and strain rate of the specimen shall be determined either from measurement of the displacements
and/or speeds of the clamp or clamps, or measured directly from the dimensions and/or local velocities of the
specimen.
NOTE The diameter of the specimen may be measured during the test by use of optical or cutting methods to derive
strains and strain rates and to assess the uniformity of deformation. The cutting method results in the test being
terminated once the cuts have been made and thus prevents data to failure from being obtained. Local velocities may be
measured using optical methods.
Corrections for slippage of the specimen at the clamp or clamps may be applied, obtained through
independent measurement of the strain of the specimen during testing through measurement of its diameter
or local velocities by other methods.
The apparatus shall have an accuracy of strain determination or measurement to within ± 3 % of the absolute
value.
The apparatus shall have an accuracy of strain rate determination or measurement to within ± 3 % of the
absolute value.
5.5 Force measurement
The force on the specimen shall be measured during the test by an appropriate means, for example a leaf
spring arrangement (see Note 1).
The resolution of the force-measuring device should preferably be no greater than 0,1 % of the full-scale value.
The apparatus shall have an accuracy of force measurement to within ± 2 % of the full-scale value (see
Note 2).
NOTE 1 Typical peak forces measured in testing of polyethylenes are estimated to be up to ≈ 1 N for specimens
approximately 3 mm in diameter.
NOTE 2 It is desirable, in particular for accurate measurements at low forces, that the accuracy of the force
measurement device be within ± 2 % of absolute, but this may be difficult to achieve in the lower part of the force
transducer’s range.
5.6 Calibration
The force, displacement, rate of displacement and temperature functions of the rheometer shall be calibrated
periodically.
It is preferable that calibration be carried out at the test temperature as measurement of these functions, in
particular that of force, may be temperature sensitive.
NOTE No traceable standard reference materials are known to exist for checking the calibration of such instruments.
Where a reference material is used for checking the instrument, it is preferable that the transient extensional viscosity of
the reference material, and the dimensions of the specimen produced using it, have values that are similar to those
encountered or used during normal operation of the instrument.
6 Sampling and specimen preparation
6.1 Sampling
The sampling method, including any special methods of specimen preparation and introduction into the
rheometer, shall be as specified in the relevant materials standard or otherwise by agreement.
If samples or specimens are hygroscopic or contain volatile ingredients, then they shall be stored to prevent or
minimize any effects on the measurements. Drying of samples may be required prior to preparing test
specimens.
As the test specimens are typically small, being of the order of a few grams, it is essential that they be
representative of the material being sampled. Repeat testing may be used to identify batch-to-batch or within-
batch variation.
6.2 Specimen preparation
The specimen shall be either cylindrical or rectangular in cross-section.
Test specimens in the form of a cylinder may be produced by extrusion or by injection, transfer or
compression moulding.
Test specimens in the form of a strip may be produced by extrusion or by injection or compression moulding
or by cutting from sheet.
The length-to-diameter ratio of cylindrical specimens should preferably be at least 10.
6 © ISO 2005 – All rights reserved

NOTE A length-to-diameter ratio of at least 10 is required to minimize end-effects. However, a longer specimen will
result in a reduction in the maximum strain rate that can be achieved. The magnitude of the end-errors can be assessed
by using specimens of different length or diameter to produce different length-to-diameter aspect ratios. The effect on
measured values can then be determined.
The specimen shall not contain any visible impurities, voids or air bubbles. The specimen shall not show any
obvious discoloration prior to or after testing.
For cylindrical specimens, measure the diameter D of the specimen at at least three positions along its length.
Repeat these measurements after rotating the specimen by 90°. Calculate an average value for the diameter
from these measurements.
For rectangular specimens, measure the width and thickness at at least three positions along its length.
Calculate average values for the width b and thickness h from these measurements.
Calculate the cross-sectional area of the specimen from the measurements.
The diameter, or width and thickness, of the specimen, as appropriate, shall be determined to and be uniform
to within ± 2 % of their average value.
6.3 Specimen mounting
Specimens may be either gripped by the clamps or attached using adhesive to studs that are then clamped
into the instrument.
Attachment by a suitable high-temperature epoxy adhesive has been found suitable. Treat the ends of the
specimen by passing them through a butane flame and then dipping them into concentrated sulfuric acid for
30 s. Prevent any other part of the specimen, except that to be bonded, from being exposed to either the
flame or the acid. Dip the ends of the specimen into the adhesive and then attach them to the studs. Place the
specimen with its studs into an oven and cure the adhesive using a suitable time-temperature cycle (100 °C
for 1 h has been found suitable). Allow the specimen to cool before handling.
7 Procedure
7.1 Specimen loading
Mount a specimen in place in the rheometer.
Measure the length of the specimen between the clamps to within 1 % of its absolute value.
After mounting the specimen in the instrument, immerse it in the silicone oil bath or place it in the temperature-
controlled chamber (see 5.2). Where possible, bring the bath or chamber to the test temperature before
inserting the specimen to reduce
...