ISO 17744:2025

International
Standard
ISO 17744
Second edition
Plastics — Determination of specific
2025-05
volume as a function of temperature
and pressure, pvT diagram — Piston
apparatus method
Plastiques — Détermination du volume spécifique en fonction
de la température et de la pression, diagramme pvT — Méthode
utilisant un appareil à piston
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3  Terms and definitions . 1
4 Principle . 3
5 Apparatus . 4
5.1 General .4
5.2 Measurement cell .4
5.3 Piston .5
5.4 Temperature-regulating device .5
5.5 Test temperature measuring device .5
5.6 Device for measuring the distance travelled by the piston .5
5.7 Pressure-measuring device .6
5.8 Measurement system .6
5.9 Balance .6
6 Equipment calibration . 6
6.1 System .6
6.2 Measurement cell .6
6.3 Piston displacement measuring device .6
6.4 Test temperature .7
6.4.1 Location .7
6.4.2 Measurement of test temperature .7
6.4.3 Temperature calibration .7
7 Test sample . 7
7.1 Preparation .7
7.2 Conditioning.7
8 Procedure . 8
8.1 Preliminary phase .8
8.2 Measurements . .8
8.2.1 General .8
8.2.2 Isobaric measurements .8
8.2.3 Isothermal measurements .9
8.3 Final stage .9
8.4 Further measurements of density .9
9 Expression of results . 10
10 Precision . 10
11 Test report . 10
11.1 General and test conditions .10
11.2 Presentation of the results .11
Annex A (normative)  Sources of error when specific volume is measured as a function of
temperature and pressure .12
Annex B (informative) Examples of pvT diagrams . 14
Bibliography .18

iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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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 17744:2004), which has been technically
revised.
The main changes are as follows:
— procedure for measuring amourphous samples with a lower height of the sample once melted has
been added;
— a specification for the balance to determine specific volume or density has been added;
— a specification for temperature calibration and position of measurement has been added;
— a specification for further measurement of density in the melt has been added;
— the presentation of results has 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
Introduction
The characterization of changes in specific volume of plastics, as a function of temperature and pressure, is
necessary for the purpose of simulation studies and for optimizing polymer processing.
These thermophysical data can be used as they are or modelled in the form of suitable mathematical laws
(see References [7] to [12]).
In injection moulding, during the packing phase, most of the flow results from solidification. During
solidification, if the plastic is semi-crystalline, the shrinkage is primarily due to crystallization. For materials
with high shrinkage and fast cooling rates, material can lose wall contact especially at low holding pressures.
pvT data are used to model the volumetric shrinkage, which is translated into dimensional changes in the
moulding. Also, critical stress areas are detectable with a loss of wall contact.
All the techniques described hereafter are equivalent in their ability to characterize the melt state pvT
behaviour, the isobaric cooling measurement is the only one which allows characterization of both the
supercooling behaviour and the pressure dependency of the transition.

v
International Standard ISO 17744:2025(en)
Plastics — Determination of specific volume as a function
of temperature and pressure, pvT diagram — Piston
apparatus method
1 Scope
This document describes procedures for determining the specific volume of plastics as a function of
temperature and pressure in both the molten and solid states.
This document specifies the use of a piston-equipped apparatus in which the test sample, held in a
measurement cell, is pressurized by means of the piston. Measurements under conditions of constant
pressure or constant temperature can be made.
NOTE For the acquisition of data needed for processing design, the isobaric cooling method is found to be more
useful, see ISO 17282. The result of this measurement cannot be used directly for injection-moulding simulation.
This document is used to obtain:
— pvT diagrams that represent the relationship which exists between pressure, specific volume and
temperature for a given material;
— volumetric compressibility and volumetric thermal-expansion coefficients;
— information on first-order and glass transitions as a function of temperature and pressure.
2 Normative references
There are no normative references in this document.
3  Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
specific volume
v
volume per unit mass of a material at a given temperature, T, and pressure, p
Note 1 to entry: Specific volume is expressed in cm /g.
3.2
density
ρ
mass per unit volume of a material at a given temperature, T, and pressure, p
Note 1 to entry: Density is expressed in g/cm .

3.3
preheating time
interval between the end of the cylinder-filling operation at the test temperature and the beginning of the
measuring operation
3.4
pre-compression pressure
p
pressure applied during the pre-heating phase to achieve compaction of the sample
3.5
volumetric thermal-expansion coefficient
α
v
coefficient defined by the formula
α = (1/v × dv/dT)  (with p constant)
v p
where
dv/dT is the slope of the tangent to the v = f(T) curve taken at a point on the curve;
v is the specific volume;
p is the pressure;
T is the temperature
Note 1 to entry: The volumetric thermal-expansion coefficient can be a function of pressure and temperature.
-1
Note 2 to entry: The volumetric thermal-expansion coefficient is expressed in K .
3.6
volumetric compressibility coefficient
β
v
coefficient defined by the formula
β = − (1/v × dv/dp)  (with T constant)
v T
where
dv/dp is the slope of the tangent to the v = f(p) curve taken at a point on the curve;
v is the specific volume;
p is the pressure;
T is the temperature
Note 1 to entry: The volumetric compressibility coefficient can be a function of pressure and temperature.
-1
Note 2 to entry: The volumetric compressibility coefficient is expressed in Pa .
3.7
isobaric measurement
procedure in which the pressure is maintained constant during a test, the temperature being modified
continuously or stepwise by heating or cooling in a predefined manner
3.8
isothermal measurement
procedure in which the temperature is maintained constant during a test, the pressure being modified by
either increasing or decreasing its value in a predefined manner

4 Principle
The pvT behaviour of a plastic material describes the specific volume as a function of temperature and
pressure. The method specified here consists of measuring, under given temperature and pressure
conditions, the specific volume of a test sample, the mass of which is known and constant. The test sample
is placed in a cylindrical measurement cell which is closed at one end by a moveable piston and sealed at
the other end. The test sample is heated or cooled down in the cell and pressure is applied via the piston.
Changes in the specific volume are determined from the movement of the piston.
There are two measurement procedures:
— at a constant pressure (isobaric measurement);
— at a constant temperature (isothermal measurement).
Both measurement procedures are generally plotted in isobaric curves but the choice between an increasing
or a decreasing temperature profile for isobaric testing or increasing or decreasing pressure for isothermal
measurement can have a significant effect on the results. It is important to specify the appropriate increasing
or decreasing profile as well as the rate of change of the parameter.
When the temperature, the pressure or applied force, the mass of the test sample, the cross-sectional area
of the cell and the length of the test sample derived from the piston position are known, the pvT data can be
obtained in absolute terms.
Figure 1 shows schematic curves of a semi crystalline and amorphous polymer. Mainly the transition zone is
influenced by the choice of temperature profile and pressure order during measurement. The association of
several such curves obtained at different pressures gives the pvT diagram.
Key
X temperature (°C) 2 semi-crystalline polymer
Y specific volume (cm /g) 3 amorphous polymer
1 melting or crystallization zone 4 glass transition temperature
Figure 1 — Specific volume of semi-crystalline and amorphous polymers at a given pressure
in isobaric mode
5 Apparatus
5.1 General
The apparatus (see Figure 2) includes a cylinder (called a measurement cell), the bottom of which is closed,
and a temperature-regulating device. Pressure is exerted on the test sample contained in the cylinder by
means of a piston. A suitable seal will minimize the likelihood of leaks during the test.
Key
1 sample
2 measurement cell of a known diameter
3 heating
4 cooling
5 die plug (necessary for air free filling of granules) which closes the die
6 force transducer
7 test piston
8 seals
9 piston displacement
10 die
Figure 2 — Schematic diagram of typical apparatus
5.2 Measurement cell
The cylindrical measurement cell shall be as smooth as possible on the inside surface, i.e. free of any visible
scratches or defects. It shall have an inside diameter constant to within ±0,01 mm along its whole length to
produce a homogeneous sample. It shall be made of a material which is resistant to wear and corrosion up
to the maximum temperature produced by the heating device. It may include an opening at the side or in the
base into which a pressure sensor can be inserted. It shall be manufactured using a method that produces an
[3] [2]
inside surface with a Vickers hardness of at least 800 HV 30 and a roughness R of less than 0,25 µm. A
a
die plug should preferably be used, to avoid gas enclosures during the filling period with granules.

5.3 Piston
The piston shall be fitted with a seal made of a material which is inert to the test sample and suitable for use
at the test temperature. A suitable seal will minimize the likelihood of leaks during the test.
The hardness of the piston shall be less than that of the cylinder, without, however, being less than 375 HV 30.
[3]
The piston shall be designed so that there is minimum friction between it and the cylinder wall.
The maximum tolerance between the outer diameter of the piston without sealing and the inner diameter of
the barrel shall not exceed 0,3 mm at ambient conditions. Piston and cell diameter shall not exceed 30 mm at
ambient conditions.
NOTE Examples of suitable seal materials are polytetrafluoroethylene up to 280 °C and polyimide for higher
temperatures.
5.4 Temperature-regulating device
The temperature-regulating device shall be designed so that:
— for isothermal measurements, the temperature shall be controlled so that the maximum allowable
temperature differences given in Table 1 are not exceeded during the test;
— for isobaric measurements, the heating or cooling rate can be controlled at a value between 1 K/min and
40 K/min as described in 8.2.2.1.
In the cooling mode, it is necessary to check that the pre-set minimum temperature is compatible with the
cooling rate used, taking into account the available cooling power of the cooling device used.
5.5 Test temperature measuring device
The test temperature is measured with a platinum resistance thermometer or thermocouple, the end of
which shall be in contact either with the molten material or, should that not be possible, with the metal inner
wall of the cell at a point adjacent to the test sample, preferably mid-way along its length. A heat-conducting
fluid can be used in the thermometer well to improve conduction.
For all temperatures that can be set, the temperature control shall be designed so that, over the whole
region occupied by the test sample, the temperature difference measured at the wall during the test does
not exceed the relevant value given in Table 1.
Table 1 — Maximum allowable temperature differences as functions of distance and time
Test temperature,T Temperature difference
°C °C
as a function as a function
of distance of time
≤200 ±1,0 ±0,5
200 < T ≤ 300 ±1,5 ±1,0
> 300 ±2,0 ±1,5
The temperature-measuring device used for the test shall have a resolution of 0,1 °C and be calibrated by
means of a device with error limits of ±0,1 °C. The calibrating device shall have a heat sink effect on the
instrument that is similar to that of the piston when in its working position.
5.6 Device for measuring the distance travelled by the piston
This device shall be capable of determining the position of the piston with an accuracy of ±5 µm.

5.7 Pressure-measuring device
The pressure can be measured by:
— a pressure sensor in the hydraulic circuit;
— a pressure sensor in the measurement cell;
— a load cell firmly attached to the piston.
The device shall only be used within a range of 10 % to 90 % of its nominal rating.
An external hydraulic bench can be used to cali
...