ISO 16790:2021
(Main)Plastics — Determination of drawing characteristics of thermoplastics in the molten state
Plastics — Determination of drawing characteristics of thermoplastics in the molten state
This document specifies a method for determining the drawing and break characteristics of molten plastics. The method involves the measurement of the force generated in deforming a molten filament under defined extrusion temperature and drawing conditions. Data is generated under non-isothermal and non-homogeneous deformation conditions. However, it is useful for the interpretation of polymer behaviour in extensional flow. The method is suitable for thermoplastics moulding and extrusion materials that can be extruded using a capillary extrusion rheometer, or an extruder with capillary rod die or other extrusion devices and have sufficient melt strength to be handled without difficulty. The method is applicable to chemically stable materials that produce a uniform extrudate free from heterogeneities, bubbles, unmelted impurities, etc. This method can provide information on — processability for all extrusion techniques, — the effect of mechanical and thermal history, and — the effect of chemical structure, such as branching, entanglements and molecular mass. This technique is one of a number of techniques that can be used to measure the extensional flow behaviour of a material. This method of measurement does not necessarily reproduce the drawing conditions to which thermoplastics are subjected to during their processing.
Plastiques — Détermination des caractéristiques d'étirage des thermoplastiques à l'état fondu
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INTERNATIONAL ISO
STANDARD 16790
Second edition
2021-02
Plastics — Determination of drawing
characteristics of thermoplastics in
the molten state
Plastiques — Détermination des caractéristiques d'étirage des
thermoplastiques à l'état fondu
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 3
5.1 Apparatus for heating the polymer and forming the extrudate . 3
5.1.1 General. 3
5.1.2 Capillary extrusion rheometer. 3
5.1.3 Extruder . 4
5.2 Apparatus for drawing the polymer extrudate . 5
5.2.1 Drawing unit . 5
5.2.2 Drawing unit design . 5
5.3 Data-acquisition system . 7
6 Calibration . 7
6.1 General . 7
6.2 Test temperature . 7
6.3 Capillary or rod die . 7
6.4 Drawing-force transducer . 7
6.5 Drawing velocity and drawing acceleration . 7
6.6 Drawing length . 7
7 Sampling . 8
8 Procedure. 8
8.1 Cleaning the apparatus . 8
8.2 Rheometer or extruder preparation . 8
8.3 Loading the capillary rheometer barrel . 9
8.4 Preheating . 9
8.5 Running the extruder .10
8.6 Preliminary checks of the extrudates .10
8.6.1 Absence of defects .10
8.6.2 Check on drawing down under gravity .10
8.7 Determination of the extrudate behaviour .12
8.7.1 Determination of the mean velocity .12
8.7.2 Determination of the drawing force as a function of the drawing velocity .12
8.7.3 Measurement of melt strength .13
9 Calculation and expression of results .14
9.1 Initial cross-sectional area of the extrudate .14
9.2 Initial velocity .14
9.3 Drawing velocities .14
9.4 Drawing forces .15
9.5 Draw ratio.15
10 Precision .15
11 Test report .15
Bibliography .17
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).
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constitute an endorsement.
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 5, Physical-
chemical properties.
This second edition cancels and replaces the first edition (ISO 16790:2005), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the normative references have been updated;
— the figure keys have been completed;
— the test procedure and parameters have been revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
INTERNATIONAL STANDARD ISO 16790:2021(E)
Plastics — Determination of drawing characteristics of
thermoplastics in the molten state
1 Scope
This document specifies a method for determining the drawing and break characteristics of molten
plastics. The method involves the measurement of the force generated in deforming a molten filament
under defined extrusion temperature and drawing conditions.
Data is generated under non-isothermal and non-homogeneous deformation conditions. However, it is
useful for the interpretation of polymer behaviour in extensional flow.
The method is suitable for thermoplastics moulding and extrusion materials that can be extruded using
a capillary extrusion rheometer, or an extruder with capillary rod die or other extrusion devices and
have sufficient melt strength to be handled without difficulty.
The method is applicable to chemically stable materials that produce a uniform extrudate free from
heterogeneities, bubbles, unmelted impurities, etc.
This method can provide information on
— processability for all extrusion techniques,
— the effect of mechanical and thermal history, and
— the effect of chemical structure, such as branching, entanglements and molecular mass.
This technique is one of a number of techniques that can be used to measure the extensional flow
behaviour of a material. This method of measurement does not necessarily reproduce the drawing
conditions to which thermoplastics are subjected to during their processing.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 291, Plastics — Standard atmospheres for conditioning and testing
ISO 11443, Plastics — Determination of the fluidity of plastics using capillary and slit-die rheometers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
drawing
process of stretching a filament of polymer melt that is being continuously formed by a capillary
extrusion rheometer or extruder or other extrusion device
3.2
melt strength
F
b
value of the melt tension at break of the extrudate
Note 1 to entry: Also known as the force to break.
Note 2 to entry: It is expressed in newtons.
3.3
draw ratio at break
DR
ratio of the drawing velocity (3.7) of the material at break to the mean velocity (3.4) of the material
flowing from the die
3.4
mean velocity
v
m
average velocity of the extrudate at the die exit, determined as the ratio of volume flow rate to die
cross-sectional area
Note 1 to entry: It is expressed in metres per second.
3.5
initial diameter
D
i
maximum diameter the extrudate attains after swelling on exiting from the die, the extrudate not yet
having been subjected to significant drawing
Note 1 to entry: Initial diameter is expressed in metres.
Note 2 to entry: If no swelling of the extrudate occurs after exiting the die, the initial diameter is taken as the
diameter of the die.
Note 3 to entry: This method can be unsuitable for testing materials that do not exhibit swelling of the extrudate
after exiting the die as such materials will be difficult to handle in drawing off and will exhibit small drawing
forces (3.8).
3.6
initial velocity
v
i
velocity of the extrudate near the die exit after swelling, the extrudate not yet having been subjected to
significant drawing (3.1)
Note 1 to entry: It is determined at the position of the initial diameter of the extrudate.
Note 2 to entry: It is expressed in metres per second.
3.7
drawing velocity
v
t
velocity imposed on the lower end of the extrudate by the drawing unit
Note 1 to entry: It is expressed in metres per second.
3.8
drawing force
F
t
force exerted on the extrudate by the drawing unit
Note 1 to entry: It is expressed in newtons.
2 © ISO 2021 – All rights reserved
3.9
drawing length
l
e
distance between the die exit and the point where the extrudate first contacts the drawing unit’s
rotating wheels
Note 1 to entry: It is expressed in metres.
3.10
drawing acceleration
a
rate of increase in the drawing velocity (3.7)
Note 1 to entry: It is expressed in metres per square second.
3.11
drawing velocity at break
v
b
velocity recorded at break when a constant drawing acceleration (3.10) is used
Note 1 to entry: It is expressed in metres per second.
4 Principle
Molten polymer is extruded from a capillary rheometer, extruder or other extrusion device at a specified
temperature. The extrudate is drawn from the die by take-off wheels. Two techniques are used.
a) A series of take-off wheel velocities is used to determine the drawing force as a function of the
drawing velocity.
b) A constant rate of acceleration of the take-off wheels is used to determine the melt strength (force
to break) of the extrudate.
5 Apparatus
5.1 Apparatus for heating the polymer and forming the extrudate
5.1.1 General
The device to supply the molten polymer at a controlled temperature and flow rate shall consist of a
heatable barrel [either a capillary extrusion rheometer (5.1.2) or an extruder (5.1.3)], the bore of
which is closed at the bottom end by a die (see Figure 1). The test pressure shall be exerted on the melt
contained in the barrel by a piston, a screw or pressurized gas.
5.1.2 Capillary extrusion rheometer
If a capillary extrusion rheometer is used, it shall have capillary dies, a piston, a temperature-measuring
device and a pressure-measuring device meeting the requirements of ISO 11443.
Key
1 rheometer or extruder
2 melt (temperature, T)
3 capillary (diameter, D; length, l)
4 axis
5 extrudate/roller contact
6 drawing bench
7 drive rollers (radius, r; rotational speed, n)
8 data acquisition (drawing force, F )
t
D initial diameter
i
l drawing length
e
v initial velocity
i
v drawing velocity (= 2πrn)
t
Figure 1 — Drawing unit — Direct drawing by two take-off rollers
5.1.3 Extruder
5.1.3.1 General
If an extruder is used, it shall be a small extruder with a screw diameter of 25 mm or less. This unit
shall be equipped with a rod die and temperature-measuring device.
4 © ISO 2021 – All rights reserved
5.1.3.2 Melt pump
If available, a melt pump may be used to provide a uniform flow of material from the extruder to the die.
If a melt pump is used, an extruder with a screw diameter larger than 25 mm may be used.
5.1.3.3 Dies
The die, of known dimensions, shall be angled vertically downwards to allow gravity to act on the
extrudate.
For determining the apparent shear rate γ and the apparent shear stress, τ with one capillary die,
ap
ap
in accordance with ISO 11443, the ratio l/D of the length, l, to the diameter, D, of the die shall be at least
16:1 and its inlet angle shall be 180°.
5.1.3.4 Temperature-measuring device
To measure the temperature of the molten polymer (see 6.2), thermocouples or platinum resistance
sensors are preferred, but thermometers may be used.
5.2 Apparatus for drawing the polymer extrudate
5.2.1 Drawing unit
5.2.1.1 The drawing unit shall draw the extrudate over a specified length (the drawing length) at a
controlled drawing velocity and measure the resulting drawing force.
5.2.1.2 The drawing unit shall have take-off wheels to draw the extrudate.
5.2.1.3 The drawing unit shall have controllers for the speed and acceleration of the take-off wheels.
5.2.1.4 The drawing unit shall have a force sensor to measure the drawing force exerted on the
extrudate.
5.2.2 Drawing unit design
Drawing may be carried out directly under the die using two rollers to take off the extrudate without
excessive slippage or pinching (see Figure 1). Alternatively, it may be carried out, after the extrudate
passes around the groove of one or more free-return pulley(s), by a set of two rollers that pinch and
take off the extrudate without excessive slippage (Figure 2 shows a possible design: other designs are
applicable). Drawing can also be done by winding up the extrudate onto a single wheel. In all cases, the
axis of the extrudate in contact with the rollers (see Figure 1), the first return pulley (see Figure 2) or
the take-off wheel shall coincide with the capillary die axis.
Where the extrudate passes over a return roller, drawing is considered to occur only in the section
between the die exit and the initial point of contact between the extrudate and the pulley groove. In
this case, the speed and drawing force of the first return pulley should preferably be measured.
The return pulley may be cooled in order to prevent any sticking of the molten polymer. The same
precaution may be taken for the drawing rollers. In both cases, it is important to ensure that these
devices do not have a significant influence on the measurement of the drawing force due to frictional or
inertial effects or on the drawing velocity and drawing acceleration due to slippage and pinching.
Key
1 rheometer or extruder
2 melt (temperature, T)
3 capillary (diameter, D; length, l)
4 axis
5 driven, pinched extrudate
6 drive rollers (radius, r; rotational speed, n)
7 return pulleys (free axis of rotation)
8 extrudate contact
9 data acquisition
10 force transducer (drawing force, F )
t
D initial diameter
i
l drawing length
e
v initial velocity
i
v drawing velocity (= 2πrn)
t
Figure 2 — Drawing unit — Typical “take-off after return pulley” design
6 © ISO 2021 – All rights reserved
5.3 Data-acquisition system
The data-acquisition system shall be capable of continuously monitoring the drawing force, the drawing
velocity, the temperature of the molten material, and the pressure of the melt at the entrance to the die
throughout the test.
6 Calibration
6.1 General
The extruder or the rheometer shall be calibrated with respect to the measured variables and
parameters, such as temperature, pressure, volume flow rates and capillary dimensions, in accordance
with the procedures described in ISO 11443.
6.2 Test temperature
When capillary dies are used, the test temperature shall be either the temperature of the melt in the
barrel near the capillary inlet or, if this is not possible, the temperature of the barrel wall near the
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