ISO 6721-10:2015
(Main)Plastics — Determination of dynamic mechanical properties — Part 10: Complex shear viscosity using a parallel-plate oscillatory rheometer
Plastics — Determination of dynamic mechanical properties — Part 10: Complex shear viscosity using a parallel-plate oscillatory rheometer
ISO 6721-10:2015 specifies the general principles of a method for determining the dynamic rheological properties of polymer melts at angular frequencies typically in the range of 0,01 rad·s-1 to 100 rad·s-1 by means of an oscillatory rheometer with a parallel-plate geometry. Angular frequencies outside this range can also be used (see Note 1). The method is used to determine values of the following dynamic rheological properties: complex shear viscosity η*, dynamic shear viscosity η', the out-of-phase component of the complex shear viscosity η", complex shear modulus G*, shear loss modulus G", and shear storage modulus G'. It is suitable for measuring complex shear viscosity values typically up to ~10 MPa·s (see Note 2). NOTE 1 The angular-frequency measurement range is limited by the specification of the measuring instrument and also by the response of the specimen. When testing using angular frequencies lower than 0,1 rad·s?1, the test time can increase significantly as the time taken to obtain a single measurement is proportional to the reciprocal of the angular frequency. Consequently, when testing at low angular frequencies, degradation or polymerization of the specimen is more likely to occur and have an effect on the results. At high angular frequencies, the specimen can distort or fracture at the edge, consequently invalidating the test results. NOTE 2 The range of complex shear viscosity values that can be measured is dependent on the specimen dimensions and also the specification of the measuring instrument. For a specimen of given dimensions, the upper limit of the range is limited by the machine's torque capacity, angular-displacement resolution, and compliance. However, correction can be made for compliance effects.
Plastiques — Détermination des propriétés mécaniques dynamiques — Partie 10: Viscosité complexe en cisaillement à l'aide d'un rhéomètre à oscillations à plateaux parallèles
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 6721-10
Third edition
2015-09-15
Plastics — Determination of dynamic
mechanical properties —
Part 10:
Complex shear viscosity using a
parallel-plate oscillatory rheometer
Plastiques — Détermination des propriétés mécaniques dynamiques —
Partie 10: Viscosité complexe en cisaillement à l’aide d’un rhéomètre
à oscillations à plateaux parallèles
Reference number
ISO 6721-10:2015(E)
©
ISO 2015
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ISO 6721-10:2015(E)
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ISO 6721-10:2015(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
5.1 Measurement apparatus . 2
5.2 Temperature-controlled enclosure . 3
5.3 Temperature measurement and control . 3
5.4 Plate/specimen assembly . 4
5.5 Calibration . 4
6 Sampling . 4
7 Procedure. 5
7.1 Test temperature . 5
7.2 Zeroing the gap . 5
7.3 Introducing the test specimen . 5
7.4 Conditioning the test specimen . 5
7.5 Test mode (controlled stress or controlled strain) . 5
7.6 Determination of thermal stability of sample material . 6
7.7 Determination of region of linear-viscoelastic behaviour . 6
7.7.1 In the controlled-strain mode. 6
7.7.2 In the controlled-stress mode . 6
7.7.3 Confirmation of linear-viscoelastic behaviour . 7
7.8 Frequency sweep . 7
7.9 Temperature sweep . 7
7.10 Air entrapment. 7
8 Expression of results . 7
8.1 Symbols used . 7
8.2 Calculation of complex shear modulus and complex shear viscosity . 8
9 Precision .10
10 Test report .11
Annex A (informative) Uncertainty limits .12
Annex B (informative) Verification of rheometer performance .15
Bibliography .19
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ISO 6721-10:2015(E)
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 non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information.
The committee responsible for this document is ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
This third edition cancels and replaces the second edition (ISO 6721-10:1999), which has been technically
revised to include informative guidance on verification of the instruments performance (Annex B).
ISO 6721 consists of the following parts, under the general title Plastics — Determination of dynamic
mechanical properties:
— Part 1: General principles
— Part 2: Torsion-pendulum method
— Part 3: Flexural vibration — Resonance-curve method
— Part 4: Tensile vibration — Non-resonance method
— Part 5: Flexural vibration — Non-resonance method
— Part 6: Shear vibration — Non-resonance method
— Part 7: Torsional vibration — Non-resonance method
— Part 8: Longitudinal and shear vibration — Wave-propagation method
— Part 9: Tensile vibration — Sonic-pulse propagation method
— Part 10: Complex shear viscosity using a parallel-plate oscillatory rheometer
— Part 11: Glass transition temperature
— Part 12: Compressive vibration — Non-resonance method
Annex A and Annex B of this part of ISO 6721 is for information only.
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INTERNATIONAL STANDARD ISO 6721-10:2015(E)
Plastics — Determination of dynamic mechanical
properties —
Part 10:
Complex shear viscosity using a parallel-plate oscillatory
rheometer
1 Scope
This part of ISO 6721 specifies the general principles of a method for determining the dynamic
-1
rheological properties of polymer melts at angular frequencies typically in the range of 0,01 rad·s to
-1
100 rad·s by means of an oscillatory rheometer with a parallel-plate geometry. Angular frequencies
outside this range can also be used (see Note 1). The method is used to determine values of the following
dynamic rheological properties: complex shear viscosity η*, dynamic shear viscosity η’, the out-of-phase
component of the complex shear viscosity η”, complex shear modulus G*, shear loss modulus G”, and
shear storage modulus G’. It is suitable for measuring complex shear viscosity values typically up to
~10 MPa·s (see Note 2).
NOTE 1 The angular-frequency measurement range is limited by the specification of the measuring instrument
–1
and also by the response of the specimen. When testing using angular frequencies lower than 0,1 rad·s , the test
time can increase significantly as the time taken to obtain a single measurement is proportional to the reciprocal
of the angular frequency. Consequently, when testing at low angular frequencies, degradation or polymerization
of the specimen is more likely to occur and have an effect on the results. At high angular frequencies, the specimen
can distort or fracture at the edge, consequently invalidating the test results.
NOTE 2 The range of complex shear viscosity values that can be measured is dependent on the specimen
dimensions and also the specification of the measuring instrument. For a specimen of given dimensions, the
upper limit of the range is limited by the machine’s torque capacity, angular-displacement resolution, and
compliance. However, correction can be made for compliance effects.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 6721-1, Plastics — Determination of dynamic mechanical properties — Part 1: General principles
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6721-1, ISO 5725-1, ISO 472,
and the following apply.
3.1
controlled-strain mode
testing by applying a sinusoidal angular displacement of constant amplitude
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ISO 6721-10:2015(E)
3.2
controlled-stress mode
testing by applying a sinusoidal torque of constant amplitude
3.3
complex shear viscosity
η*
ratio of dynamic stress, given by σ(t) = σ exp iωt, and dynamic rate of strain where the shear strain
0
γ t is given by γ(t) = γ exp i(ωt - δ), of a viscoelastic material that is subjected to a sinusoidal vibration,
() 0
where σ and γ are the amplitudes of the stress and strain cycles, ω is the angular frequency, δ is the
0 0
phase angle between the stress and strain, and t is time
Note 1 to entry: It is expressed in pascal seconds.
3.4
dynamic shear viscosity
η’
real part of the complex shear viscosity
Note 1 to entry: It is expressed in pascal seconds.
3.5
out-of-phase component of the complex shear viscosity
η”
imaginary part of the complex shear viscosity
Note 1 to entry: It is expressed in pascal seconds.
4 Principle
The specimen is held between two concentric, circular parallel plates (see Figure 1). The thickness of
the specimen is small compared with the diameter of the plates.
The specimen is subjected to either a sinusoidal torque or a sinusoidal angular displacement of
constant angular frequency. These are referred to as “controlled-stress” or “controlled-strain” test
modes, respectively. When using the controlled-stress mode, the resultant displacement and the phase
shift between the torque and displacement are measured. When using the controlled-strain mode, the
resultant torque and the phase shift between the displacement and torque are measured.
The complex shear modulus G*, shear storage modulus G’, shear loss modulus G”, phase angle δ, and
corresponding shear viscosity terms (see Clause 3) are determined from the measured torque and
displacement and the specimen dimensions. In deriving these values, it is assumed that the specimen
exhibits a linear-viscoelastic response.
The mode of oscillation used is designated as oscillatory mode I (see ISO 6721-1, Clause 4).
5 Apparatus
5.1 Measurement apparatus
The measurement apparatus shall consist of two concentric, rigid, circular parallel plates between
which the specimen is placed (see Figure 1). One of these plates shall be made to oscillate at a constant
angular frequency while the other remains at rest.
The requirements on the apparatus are that it shall permit measurement of the amplitudes of the
torque and the angular displacement and the phase difference between them for a specimen subjected
to either a sinusoidal torque or a sinusoidal displacement of constant angular frequency.
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ISO 6721-10:2015(E)
A torque-measuring device shall be connected to one of the plates, thus permitting measurement of the
torque required to overcome the viscoelastic resistance of the specimen.
An angular-displacement measuring device shall be fitted to the moving plate, thus permitting
determination of its angular displacement and angular frequency.
The apparatus shall be capable of measuring the torque to within ±2 % of the minimum torque
amplitude used to determine the dynamic properties.
−6
The apparatus shall be capable of measuring the angular displacement to within ±20 × 10 rad.
The apparatus shall be capable of measuring the angular frequency to within ±2 % of the absolute value.
Key
1 test specimen
ω angular frequency
d specimen thickness
D diameter of plate
Figure 1 — Parallel-plate rheometer geometry
5.2 Temperature-controlled enclosure
Heating may be provided by the use of forced convection, radio-frequency heating, or other suitable
means.
An environmental chamber surrounding the plate/specimen assembly can be used to provide specific
test environments, for example a nitrogen atmosphere.
Check that the chamber is not in contact with the plate/specimen assembly.
5.3 Temperature measurement and control
The test temperature shall preferably be measured using a device that is either in contact with or
embedded in the fixed plate.
The test temperature shall be accurate to within ±0,5 °C of the set temperature for set temperatures
up to 200 °C, within ±1,0 °C for temperatures in the range 200 °C to 300 °C, and within ±1,5 °C for
temperatures above 300 °C.
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.
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ISO 6721-10:2015(E)
5.4 Plate/specimen assembly
The plate/specimen assembly comprises two concentric, circular parallel plates with the specimen
held between them. The plates shall have a surface finish corresponding to a maximum roughness of
Ra = 0,25 µm and shall have no visible imperfections.
The results may be dependent on the type of material that is used to form the surfaces of the plates.
This can be identified by testing using plates with different surface materials.
The plate diameter, D, is typically in the range of 20 mm to 50 mm. It shall be measured to within ±0,01 mm.
The specimen thickness, d, is defined by the plate separation and shall be determined to within
±0,01 mm. It is recommended that the specimen thickness lie in the range of 0,5 mm to 3 mm and that
the ratio of the plate diameter to the specimen thickness lie in the range of 10 to 50 in order to minimize
errors in the determination of properties. For low-viscosity polymeric liquids, it may be necessary to
employ dimensions outside these recommended ranges. The total variation in the plate separation due
to non-parallelism of the plates shall be less than ±0,01 mm. Variation in the plate separation during
testing shall be less than ±0,01 mm.
The plates shall be sufficiently flat to enable the requirement on the total variation in the plate
separation due to non-parallelism of the plates be less than ±0,01 mm.
5.5 Calibration
The rheometer and test geometries shall be calibrated periodically by measuring the torque, angular-
displacement, angular-frequency and temperature response of the machine and the relevant dimensions
of the geometries, or checked by using reference liquids of known viscosity or complex viscosity, in
accordance with the instrument manufacturer’s instructions. It is preferable that the viscosities of the
reference liquids used for checking the calibration span the range in viscosity values of the specimens
that are to be measured.
It is preferable that calibration be carried out at the test temperature.
NOTE Guidance on verification of the performance of the instrument is given in Annex B.
6 Sampling
The sampling procedure, including any special methods of specimen preparation and introduction into
the rheometer, shall be as specified in the relevant materials standard or as otherwise agreed.
As the test specimens are typically small, being of the order of 3 g to 5 g, it is essential that they are
representative of the material being sampled.
If samples or specimens are hygroscopic or contain volatile ingredients, then they shall be stored to
prevent or minimize any changes in viscosity. Drying of samples may be required prior to preparing
test specimens.
The test specimens shall be in the form of a disc when produced by injection or compression moulding or
by cutting from sheet. Alternatively, they may be formed by placing pellets or liquid or molten polymer
between the plates. The specimen may be introduced in the molten state only if it is not sensitive to
oxidation or loss of volatile matter.
The specimen shall not contain any visible impurities or air bubbles. The specimen shall not show any
obvious discolouration prior to or after testing.
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ISO 6721-10:2015(E)
7 Procedure
7.1 Test temperature
Generally, because of the temperature dependence of viscosity, measurements for comparison purposes
shall be carried out at the same temperature. Details shall be as specified in the relevant materials
standard or as otherwise agreed.
7.2 Zeroing the gap
Allow the apparatus to come to thermal equilibrium at the desired test temperature. The suggested
equilibrium time is 15 min to 30 min. Bring the plates into contact with each other. Set the gap
indicator to zero.
7.3 Introducing the test specimen
The specimen shall be loaded into the instrument in either the solid or the molten state as specified
in Clause 6. It shall completely fill the gap between the two plates. Any excess material round the
edges of the plates shall be removed before testing is started. The specimen may need to be slightly
squeezed after trimming to promote good contact, but precautions shall then be taken to ensure that
the specimen does not extend beyond the edges of the plates.
The specimen and plates shall then be allowed to reach thermal equilibrium at the test temperature.
This period of time is referred to as the preheat time. For any particular instrument, plate/specimen
assembly geometry, polymer type, sample thickness, loading procedure, and test temperature, the
preheat time shall be determined by repeating the measurement but using a preheat time that is 10 %
greater (see note). If there is no change in the measured values of the complex shear modulus G*,
shear storage modulus G’, and shear loss modulus G”, then the preheat time is sufficient for thermal
equilibrium to have been established.
NOTE This check can be incorporated into the time-sweep test for thermal stability of the sample (see 7.6).
When the instrument and specimen have reached the test temperature, measure the specimen
thickness, d, which is equivalent to the plate separation (see 5.4). This value of the specimen thickness
shall be used in all calculations.
7.4 Conditioning the test specimen
The test specimen may be conditioned before testing by holding it at zero shear at the test temperature
for a specified period of time and/or by pre-shearing.
7.5 Test mode (controlled stress or controlled strain)
Measurements are made using instruments either in a controlled-strain mode or in a controlled-stress
mode.
In the controlled-strain mode, a sinusoidal displacement is produced at constant angular frequency, and
the resultant sinusoidal torque and the phase shift between the torque and displacement are measured.
In the controlled-stress mode, a sinusoidal torque is applied at constant angular frequency, and the
resultant sinusoidal displacement and the phase shift between the torque and displacement are measured.
Measurement of the dynamic rheological properties of specimens in accordance with this part of ISO 6721
is restricted to the linear-viscoelastic region of behaviour. Linear-viscoelastic behaviour is defined, for
the purposes of this part of ISO 6721, as behaviour in which the viscosity or modulus is independent of
the applied stress or strain. This assumption is necessary for the analysis of the test data. It is therefore
necessary for the amplitude of oscillation in the controlled-stress or controlled-strain modes to be set
such that the deformation of the specimen occurs within the linear-viscoelastic region.
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ISO 6721-10:2015(E)
For methods of determining the limits of the linear-viscoelastic behaviour region, see 7.7.
7.6 Determination of thermal stability of sample material
Before testing a particular material, carry out a timed run at the test temperature to determine the
thermal stability of the material. The run shall be made using the same plate/specimen assembly
geometry, and angular frequencies and torque or angular displacement similar to those to be used in
subsequent testing. It may be necessary to carry out runs at more than one frequency of oscillation (see
Note 1). The thermal-stability time is defined as the time taken from the start of the run to the point in
time at which any of the measured values of G*, G’, and G” have changed by 5 % from their initial value
(see Note 2). It shall be expressed as a time at a given temperature and angular frequency, for example
500 s at 250 °C and 1 rad/s. Subsequent measurements on new specimens from the same sample at that
temperature shall be completed in a time shorter than the thermal-stability time.
NOTE 1 Specimen-degradation effects on rheological properties are normally most easily identifiable when
testing at low frequencies of oscillation.
NOTE 2 It might be necessary to discard initial spurious results when determining the initial modulus values.
For some materials, it might not be possible to obtain the desired results within the thermal-stability
time due to rapid degradation or crosslinking of the material. In such cases, the test report shall state
the percentage change in modulus occurring over the duration of the test, this value having been
determined from timed runs.
7.7 Determination of region of linear-viscoelastic behaviour
7.7.1 In the controlled-strain mode
When working in the controlled-strain mode, determine the maximum permissible amplitude of
oscillation by performing a strain sweep. The strain sweep shall be made using the same plate/specimen
assembly geometry, and angular frequency and temperature similar to those to be used in subsequent
testing. It may be necessary to carry out strain measurements at more than one oscillation frequency to
check for any dependence of the limit of linear-viscoelastic behaviour on the angular frequency. Test the
specimen by increasing the amplitude of oscillation over a range of values, preferably commencing with
a strain, measured at the edge of the plate, of not more than 1 %.
Measure the complex shear modulus G*, shear storage modulus G’, and shear loss modulus G” as
functions of the amplitude of oscillation to determine the maximum permissible amplitude of oscillation
for measurements within the linear-viscoelastic region.
The maximum value of the strain to be used in actual testing shall be less than the lowest value of
the strain at which a difference of 5 % occurred in the values of any of the parameters G*, G’, or G”
compared with their values in the linear-viscoelastic region. If it is not possible to determine properties
within the linear-viscoelastic region, this shall be stated in the test report.
NOTE For some materials, the linear-viscoelastic region is confined to very small strains. The associated
measurement errors prevent properties being determined reliably in this region.
7.7.2 In the controlled-stress mode
When working in the controlled-stress mode, determine the range of linear-viscoelastic behaviour by
performing a stress sweep. The stress sweep shall be made using the same plate/specimen assembly
geometry, and angular frequency and temperature similar those to be used in subsequent testing. It may
be necessary to carry out measurements at more than one frequency to check for any dependence of
the limit of linear-viscoelastic behaviour on the angular frequency. Test the specimen by increasing the
torque over a range of values, preferably commencing with a torque that results in a strain, measured at
the edge of the plate, of not more than 1 %.
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ISO 6721-10:2015(E)
Measure the complex shear modulus G*, shear storage modulus G’, and shear loss modulus G” as
functions of the torque to determine the maximum permissible torque for measurements within the
linear-viscoelastic region.
The maximum value of the applied torque to be used in actual testing shall be less than the lowest value
of the torque at which a deviation of 5 % occurred in the values of any of the parameters G*, G’, or G”
compared with their values in the linear-viscoelastic region. If it is not possible to determine properties
within the linear-viscoelastic region, this shall be stated in the test report (see Note to 7.7.1).
7.7.3 C
...
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