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 16790:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 16790:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 16790:2021(E)
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

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 16790:2021(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 of the voluntary nature of standards, the meaning of ISO specific terms and

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
---------------------- Page: 4 ----------------------
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
© ISO 2021 – All rights reserved 1
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ISO 16790:2021(E)
3.2
melt strength
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

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

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

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

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
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
force exerted on the extrudate by the drawing unit
Note 1 to entry: It is expressed in newtons.
2 © ISO 2021 – All rights reserved
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ISO 16790:2021(E)
3.9
drawing length

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
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
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.
© ISO 2021 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO 16790:2021(E)
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 )
D initial diameter
l drawing length
v initial velocity
v drawing velocity (= 2πrn)
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
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ISO 16790:2021(E)
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,

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.

© ISO 2021 – All rights reserved 5
---------------------- Page: 9 ----------------------
ISO 16790:2021(E)
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 )
D initial diameter
l drawing length
v initial velocity
v drawing velocity (= 2πrn)
Figure 2 — Drawing unit — Typical “take-off after return pulley” design
6 © ISO 2021 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 16790:2021(E)
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

capillary inlet. This also pertains to the rod die of the extruder. When the barrel wall temperature is

measured, thermally conductive fluids may be used in the thermometer well to improve conduction.

The temperature-measuring device used during the test shall have a resolution of 0,1 °C and be

calibrated to an accuracy of ±0,5 °C by a method traceable to certified reference standard(s).

No liquids that can contaminate the die and barrel and influence the ensuing measurements (e.g. silicone

oil) shall be used as heat-transfer media during calibration. Woods metal has been found to be a suitable

thermal conductor.
6.3 Capillary or rod die

The dimensions of the die shall be measured to an accuracy of ±0,007 mm for the diameter, D,

and ±0,025 mm for the length, l.

For comparisons between laboratories, a die having an l to D ratio of 16 to 1 and with a 180° inlet angle

shall be used.
6.4 Drawing-force transducer

Calibration of the drawing-force transducer shall be carried out in accordance with the manufacturer’s

recommendations. The accuracy of the force measurement system shall have a maximum permissible

error of ±1 % of full scale.
6.5 Drawing velocity and drawing acceleration

The drawing velocity and drawing acceleration shall both have a maximum permissible error of ±1 % of

full scale. The apparatus may be calibrated with respect to these parameters by measuring the time for

a known length of (non-stretchable) material, e.g. paper, to traverse the drawing rollers with and

without acceleration, or from measurement of the rotational speed of the drawing rollers.

6.6 Drawing length

This is measured using a device such as a ruler or tape measure. The distance shall be measured to an

accuracy of within ±5 %.

For comparisons between laboratories, the drawing length shall be 100 mm ± 10 mm.

NOTE This short drawing length minimizes the cooling of the extrudate and thus maintains a more uniform

temperature range over the entire length of the extrudate.
© ISO 2021 – All rights reserved 7
---------------------- Page: 11 ----------------------
ISO 16790:2021(E)
7 Sampling

A representative sample shall be taken from the product for use as the test sample. Any conditioning

of the sample shall be as described in the material specification standard, if available, or by agreement

between the interested parties, or in accordance with ISO 291.
8 Procedure
8.1 Cleaning the apparatus

Before each measurement, ensure that the barrel, pressure transducer bores (where applicable), piston

and capillary die are free of foreign matter. Make a visual examination to check for cleanliness.

If solvents are used for cleaning, ensure that no contamination of the barrel, piston or capillary die has

occurred that might influence the test results.

NOTE 1 For the purpose of cleaning, circular brushes made of copper/zinc alloy (brass) and linen cloths have

proven satisfactory. However, the use of copper-containing materials can accelerate degradation of the polymer

when testing polyethylene and polypropylene. Cleaning can also be performed by cautious burning out.

NOTE 2 Using graphite on threads facilitates their unlocking after testing.

WARNING — The operating conditions chosen can entail partial decomposition of the material

under test and any materials used for cleaning purposes, or cause them to release dangerous

volatile substances. Also, both the instrument and extrudate are likely to be very hot and

present the risk of contact burns. The user of this document is therefore responsible for keeping

him- or herself informed of possible risks of accident and for providing the appropriate means of

protection.
8.2 Rheometer or extruder preparation

Assemble the capillary rheometer or the extruder with the appropriate capillary or rod die. Allow the

assembled apparatus to reach thermal equilibrium at the test temperature before applying the final

torque on the die (where applicable).

It is recommended that a 2 mm diameter die be used for high-viscosity materials and a 1 mm diameter

die for low-viscosity materials, although selection of the die diameter should depend on the extrudability

of the material.

When using an extruder, adjust the temperature of the equipment and the rotational speed of the

extruder to obtain the desired melt temperature and material flow rate from the die.

Conditions for the test should be set based on the ability to handle the extrudate during take-off.

Typical test temperature ranges for several materials are given in Table 1 (see Note). Table 1 also

includes a temperature that should be used to allow comparisons between laboratories as a quality

control check.

NOTE The most useful data are generally obtained at temperatures, shear stresses and shear rates used in

processing of the material.
8 © ISO 2021 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 16790:2021(E)
Table 1 — Typical test temperatures
Material Temperature range Temperature for comparison
°C °C
Polyacetal 190 to 220 190
Polyacrylate 140 to 300 230
Acrylonitrile/butadiene/styrene (ABS) 200 to 280 220
Cellulose esters 190 to 210 190
Polyamide 190 to 300 235
Polybutylene 160 to 250 190
Poly(chlorotrifluoroethylene) 185 to 310 265
Polyethylene and ethylene copolymers and
150 to 250 190
terpolymers
Polycarbonate 260 to 300 300
Polypropylene 180 to 270 230
Polystyrene and styrene copolymers 180 to 280 200
Poly(vinyl chloride) 170 to 210 175
Poly(butylene terephthalate) 245 to 270 250
Poly(ethylene terephthalate) 275 to 300 285
PMMA and copolymers 180 to 300 230
Poly(vinylidene fluoride) 195 to 240 230
Poly(vinylidene chloride) 150 to 170 150
Ethylene/vinyl alcohol copolymer 190 to 230 190
Polyetheretherketone 340 to 380 372
Polyethersulfone 330 to 380 372
8.3 Loading the capillary rheometer barrel

To avoid air inclusions in the capillary rheometer, introduce the sample into the barrel in separate

small quantities, performing intermediate compactions by means of a piston. Fill the barrel to within

approximately 12,5 mm of the top. Accomplish charging in a maximum of 2 min.
8.4 Preheating

For the capillary rheometer, immediately after charging the barrel, start the preheat timer. Extrude a

small portion of the charge out of the barrel. Stop the extrusion and wait until a preheat time of at least

5 min is completed, unless otherwise specified by the referring standard.

Check that the preheat time used is sufficient to obtain thermal equilibrium of the test sample

throughout the volume of the barrel for each mate
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 16790
ISO/TC 61/SC 5
Plastics — Determination of drawing
Secretariat: DIN
characteristics of thermoplastics in
Voting begins on:
2020­11­24 the molten state
Voting terminates on:
Plastiques — Détermination des caractéristiques d'étirage des
2021­01­19
thermoplastiques à l'état fondu
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 16790:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 16790:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 16790:2020(E)
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 Drawing­force 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

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 16790:2020(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 of the voluntary nature of standards, the meaning of ISO specific terms and

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.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 16790:2020(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 non­isothermal and non­homogeneous 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
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ISO/FDIS 16790:2020(E)
3.2
melt strength
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

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

average velocity of the extrudate at the die exit, determined as the ratio of volume flow rate to die

cross­sectional area
Note 1 to entry: It is expressed in metres per second.
3.5
initial diameter

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

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
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
force exerted on the extrudate by the drawing unit
Note 1 to entry: It is expressed in newtons.
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ISO/FDIS 16790:2020(E)
3.9
drawing length

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
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
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.
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ISO/FDIS 16790:2020(E)
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 )
D initial diameter
l drawing length
v initial velocity
v drawing velocity (= 2πrn)
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.
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ISO/FDIS 16790:2020(E)
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,

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.

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ISO/FDIS 16790:2020(E)
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 )
D initial diameter
l drawing length
v initial velocity
v drawing velocity (= 2πrn)
Figure 2 — Drawing unit — Typical “take-off after return pulley” design
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ISO/FDIS 16790:2020(E)
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

capillary inlet. This also pertains to the rod die of the extruder. When the barrel wall temperature is

measured, thermally conductive fluids may be used in the thermometer well to improve conduction.

The temperature­measuring device used during the test shall have a resolution of 0,1 °C and be

calibrated to an accuracy of ±0,5 °C by a method traceable to certified reference standard(s).

No liquids that can contaminate the die and barrel and influence the ensuing measurements (e.g. silicone

oil) shall be used as heat­transfer media during calibration. Woods metal has been found to be a suitable

thermal conductor.
6.3 Capillary or rod die

The dimensions of the die shall be measured to an accuracy of ±0,007 mm for the diameter, D,

and ±0,025 mm for the length, l.

For comparisons between laboratories, a die having an l to D ratio of 16 to 1 and with a 180° inlet angle

shall be used.
6.4 Drawing-force transducer

Calibration of the drawing­force transducer shall be carried out in accordance with the manufacturer’s

recommendations. The accuracy of the force measurement system shall have a maximum permissible

error of ±1 % of full scale.
6.5 Drawing velocity and drawing acceleration

The drawing velocity and drawing acceleration shall both have a maximum permissible error of ± 1 %

of full scale. The apparatus may be calibrated with respect to these parameters by measuring the time

for a known length of (non-stretchable) material, e.g. paper, to traverse the drawing rollers with and

without acceleration, or from measurement of the rotational speed of the drawing rollers.

6.6 Drawing length

This is measured using a device such as a ruler or tape measure. The distance shall be measured to an

accuracy of within ±5 %.

For comparisons between laboratories, the drawing length shall be 100 mm ± 10 mm.

NOTE This short drawing length minimizes the cooling of the extrudate and thus maintains a more uniform

temperature range over the entire length of the extrudate.
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ISO/FDIS 16790:2020(E)
7 Sampling

A representative sample shall be taken from the product for use as the test sample. Any conditioning

of the sample shall be as described in the material specification standard, if available, or by agreement

between the interested parties, or in accordance with ISO 291.
8 Procedure
8.1 Cleaning the apparatus

Before each measurement, ensure that the barrel, pressure transducer bores (where applicable), piston

and capillary die are free of foreign matter. Make a visual examination to check for cleanliness.

If solvents are used for cleaning, ensure that no contamination of the barrel, piston or capillary die has

occurred that might influence the test results.

NOTE 1 For the purpose of cleaning, circular brushes made of copper/zinc alloy (brass) and linen cloths have

proven satisfactory. However, the use of copper-containing materials can accelerate degradation of the polymer

when testing polyethylene and polypropylene. Cleaning can also be performed by cautious burning out.

NOTE 2 Using graphite on threads facilitates their unlocking after testing.

WARNING — The operating conditions chosen can entail partial decomposition of the material

under test and any materials used for cleaning purposes, or cause them to release dangerous

volatile substances. Also, both the instrument and extrudate are likely to be very hot and

present the risk of contact burns. The user of this document is therefore responsible for keeping

him- or herself informed of possible risks of accident and for providing the appropriate means of

protection.
8.2 Rheometer or extruder preparation

Assemble the capillary rheometer or the extruder with the appropriate capillary or rod die. Allow the

assembled apparatus to reach thermal equilibrium at the test temperature before applying the final

torque on the die (where applicable).

It is recommended that a 2 mm diameter die be used for high-viscosity materials and a 1 mm diameter

die for low-viscosity materials, although selection of the die diameter should depend on the extrudability

of the material.

When using an extruder, adjust the temperature of the equipment and the rotational speed of the

extruder to obtain the desired melt temperature and material flow rate from the die.

Conditions for the test should be set based on the ability to handle the extrudate during take-off.

Typical test temperature ranges for several materials are given in Table 1 (see Note). Table 1 also

includes a temperature that should be used to allow comparisons between laboratories as a quality

control check.

NOTE The most useful data are generally obtained at temperatures, shear stresses and shear rates used in

processing of the material.
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ISO/FDIS 16790:2020(E)
Table 1 — Typical test temperatures
Material Temperature range Temperature for comparison
°C °C
Polyacetal 190 to 220 190
Polyacrylate 140 to 300 230
Acrylonitrile/butadiene/styrene (ABS) 200 to 280 220
Cellulose esters 190 to 210 190
Polyamide 190 to 300 235
Polybutylene 160 to 250 190
Poly(chlorotrifluoroethylene) 185 to 310 265
Polyethylene and ethylene copolymers and
150 to 250 190
terpolymers
Polycarbonate 260 to 300 300
Polypropylene 180 to 270 230
Polystyrene and styrene copolymers 180 to 280 200
Poly(vinyl chloride) 170 to 210 175
Poly(butylene terephthalate) 245 to 270 250
Poly(ethylene terephthalate) 275 to 300 285
PMMA and copolymers 180 to 300 230
Poly(vinylidene fluoride) 195 to 240 230
Poly(vinylidene chloride) 150 to 170 150
Ethylene/vinyl alcohol copolymer 190 to 230 190
Polyetheretherketone 340 to 380 372
Polyethersulfone 330 to 380 372
8.3 Loading the capillary rheometer barrel

To avoid air inclusions in the capillary rheometer, introduce the sample into the

...

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