prEN ISO 307

• Abstract:

  This document specifies a method for the determination of the viscosity number of dilute solutions of polyamides in certain specified solvents.; The method is applicable to the polyamides designated PA 46, PA 6, PA 66, PA 69, PA 610, PA 612, PA 11, PA 12, PA 6T/66, PA 6I/6T, PA 6T/6I/66, PA 6T/6I, PA 6I/6T/66 and PA MXD6 as defined in ISO 16396-1, as well as to copolyamides, compounds of polyamides and other polyamides that are soluble in one of the specified solvents under the specified conditions.; The method is not applicable to polyamides produced by anionic polymerization of lactams or produced with cross-linking agents; such polyamides are normally insoluble in the specified solvents.; The viscosity number is determined by the general procedure specified in ISO 1628‑1, observing the particular conditions specified in this document.

• Status: Not Published
• Publication Date: 29-Nov-2027
• ICS: 83.080.20 - Thermoplastic materials
• Technical Committee: CEN/TC 249 - Plastics
• Drafting Committee: CEN/TC 249 - Plastics
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Start Date: 04-Sep-2026
• Completion Date: 04-Sep-2026
• Ref Project: oSIST prEN ISO 307:2026 - Plastics - Polyamides - Determination of viscosity number (ISO/DIS 307:2026)

• Revises: EN ISO 307:2019 - Plastics - Polyamides - Determination of viscosity number (ISO 307:2019)
• Effective Date: 18-Dec-2024

prEN ISO 307 is a CEN adoption of ISO/DIS 307:2026 for plastics, focused on the determination of the viscosity number of polyamides in dilute solution. It specifies which polyamides and solvents the method applies to, and it is written for laboratories and users who need a comparable way to check material consistency by viscosity measurement.

The document is for testing polyamide materials by either an efflux time method or a differential pressure method, with the result reported as viscosity number.

What does prEN ISO 307 specify?

prEN ISO 307 specifies a method for measuring the viscosity number of dilute solutions of polyamides in selected solvents. It is intended for polyamides such as PA 46, PA 6, PA 66, PA 69, PA 610, PA 612, PA 11, PA 12, several PA 6T/66 and PA 6I/6T combinations, and PA MXD6, as well as compatible copolyamides and compounds.

The method is not intended for polyamides made by anionic polymerization of lactams or made with cross-linking agents, because those materials are normally insoluble in the specified solvents. The viscosity number is determined using the general procedure from ISO 1628-1, with the special conditions given in this document.

The document is organized into:

• Scope and normative references
• Terms and definitions
• Principle
• Reagents and materials
• Apparatus
• Sample preparation
• Test portion calculation
• Solvent selection
• Procedure
• Expression of results
• Repeatability and reproducibility
• Relationship to viscosity in other solvents
• Test report
• Informative annexes A to E

Annex	What it covers
A	Adjusting commercial sulphuric acid to 96 % by titration
B	Adjusting commercial sulphuric acid to 96 % by flow time measurement
C	Adjusting commercial formic acid to 90 % by titration
D	Adjusting commercial formic acid to 90 % by density measurement
E	Interconversion between viscosity numbers and related viscosity values

What are the key requirements of prEN ISO 307?

prEN ISO 307 centers on sample preparation, solvent choice, controlled dissolution, and a viscosity measurement at 25 °C. In practice, the result depends strongly on solvent concentration, temperature control, and whether the sample contains additives or insoluble reinforcement.

Sample preparation and test portion

The sample shall be soluble in the chosen solvent, apart from insoluble additives such as glass or carbon fibres. If the moisture content is above 0.28 %, the sample is dried, and the document notes vacuum drying at 70 °C for 4 h to 6 h as generally adequate.

For samples with less than 98 % polyamide, the content of additives, water, inorganic material, and other materials is taken into account when calculating the test portion. This matters because the actual mass of polyamide entering the solution must be known for the calculation to be meaningful.

Solvent selection matters

prEN ISO 307 links each polyamide family to one or more solvents. For example, PA 6, PA 46, PA 66, PA 69, PA 610, PA MXD6 and corresponding copolyamides use formic acid solution or sulphuric acid, while PA 11, PA 12 and PA 11/12 copolymers use m-cresol. For some polyamides, such as PA 6T/66 and related types, m-cresol, phenol/1,1,2,2-tetrachloroethane, or sulphuric acid may be used.

This matters because the viscosity number depends on the solvent used, so the solvent must be reported and chosen according to the material. For pure polyamides, the document also gives relationships for converting between some solvent systems.

Two measurement routes

prEN ISO 307 provides two measurement routes:

• the efflux time method
• the differential pressure method

In the efflux time method, solvent and solution flow times are measured in the same viscometer at 25 °C. In the differential pressure method, the pressure drop across two capillaries is measured for solvent and solution at 25 °C, using the procedure from ISO 1628-1.

The practical point is that laboratories can use either manual or automated equipment, but they must keep the sample concentration, temperature, and measurement conditions under control.

Dissolution and measurement conditions

The solution concentration is based on a target of 0.005 g/ml in the efflux time method, and 0.50 g per 100 ml of solution in the exact polymer-content variants. Dissolution time can range from about half an hour to several hours depending on the material and particle size, and the document limits the temperature used during dissolution depending on the solvent.

For the efflux time method, the solution is filtered or centrifuged before measurement if needed, and the viscometer must be cleaned at defined intervals and after discordant readings. For routine quality control, a single determination may be acceptable if the laboratory has validated the precision and process limits.

Result expression and reporting

The viscosity number is calculated from the measured flow times or from the differential pressure result together with the polymer concentration. The report shall identify the material, the solvent, the method used, any additive-determination method, any deviations, and the test date.

That reporting is important because the same polyamide can give different values in different solvents, and additives can affect the result in different ways.

What terms does prEN ISO 307 define?

Viscosity number - The reported result of the test, expressed in millilitres per gram, derived from the behavior of a dilute polymer solution relative to the solvent.

Efflux time method - The method that compares the flow time of the polymer solution with the flow time of the solvent in the same viscometer.

Differential pressure method - The method that compares the pressure behavior of solvent and solution flowing through two capillaries.

Hagenbach correction - A correction applied to flow time measurements when kinetic-energy effects need to be taken into account.

Polyamide - The material family covered by the document, including the listed PA designations, copolyamides, and compatible compounds.

Solvent - The specified liquid used to dissolve the polyamide for the test; the choice of solvent is part of the method and affects the result.

Repeatability - The closeness of agreement between results under the same test conditions, used here as part of the acceptance of repeated determinations.

Reproducibility - The closeness of agreement between results from different conditions or laboratories, discussed in the document’s precision information.

Who uses prEN ISO 307?

prEN ISO 307 is used by polymer laboratories, production-control teams, and quality managers working with polyamides. It is also relevant to buyers and specifiers who need a documented viscosity number to compare lots, grades, or suppliers.

The document is especially useful in:

• production control for polyamide materials
• intra-product comparison when additives may interfere
• laboratory testing of incoming or outgoing material
• process monitoring where consistent viscosity is used as a material indicator
• reporting and documentation of polyamide quality data

What changed in prEN ISO 307 from the previous edition?

prEN ISO 307 states that the seventh edition cancels and replaces ISO 307:2007 and that it has been technically revised. The main change named in the document is the addition of an alternative procedure: the differential pressure method, aligned with the corresponding change in ISO 1628-1:2024.

Which standards are used with prEN ISO 307?

prEN ISO 307 refers to several standards that supply general principles, related methods, or supporting measurements.

• ISO 1628-1:2024 - provides the general principles for viscosity measurement in dilute solution and the basis for the differential pressure method
• ISO 25337:2010 - provides a statistical method for using single measurements in production quality control
• ISO 16396-1 - defines the PA designations used to identify the polyamides covered
• ISO 15512 - is used to determine sample water content
• ISO 3451-4 - is used to determine ash content
• ISO 1042 - is referenced for volumetric flask requirements
• ISO 3105 - is used for viscometer types and dimensions
• ASTM D789 and JIS K 6920-2:2009 - are used in Annex E for related viscosity interconversion guidance

What does the prEN ISO 307 document contain?

The document contains two complete measurement routes, practical guidance for solvent preparation, and detailed sample-preparation rules for dry materials and materials with additives. It also includes instructions for cleaning the viscometer, setting the bath temperature, filtering or centrifuging the solution, and repeating measurements until the acceptance criteria are met.

Annexes A to D give procedures for adjusting sulphuric acid and formic acid to the required concentrations, using either titration, flow time, or density. Annex E provides interconversion graphs and tables for comparing viscosity numbers measured in different solvents, together with precision information and the basis for some of the relationships.

SLOVENSKI STANDARD
01-september-2026
Polimerni materiali - Poliamidi - Ugotavljanje števila viskoznosti (ISO/DIS 307:2026)
Plastics - Polyamides - Determination of viscosity number (ISO/DIS 307:2026)
Kunststoffe - Polyamide - Bestimmung der Viskositätszahl (ISO/DIS 307:2026)
Plastiques - Polyamides - Détermination de l'indice de viscosité (ISO/DIS 307:2026)
Ta slovenski standard je istoveten z: prEN ISO 307
ICS:
83.080.20 Plastomeri Thermoplastic materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 307
ISO/TC 61/SC 9
Plastics — Polyamides —
Secretariat: KATS
Determination of viscosity number
Voting begins on:
Plastiques — Polyamides — Détermination de l'indice de viscosité
2026-06-12
Voting terminates on:
ICS: 83.080.20
2026-09-04
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
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Reference number
ISO/DIS 307:2026(en)
DRAFT
ISO/DIS 307:2026(en)
International
Standard
ISO/DIS 307
ISO/TC 61/SC 9
Plastics — Polyamides —
Secretariat: KATS
Determination of viscosity number
Voting begins on:
Plastiques — Polyamides — Détermination de l'indice de viscosité
2026-06-12
ICS: 83.080.20 Voting terminates on:
2026-09-04
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland Reference number
ISO/DIS 307:2026(en)
ii
ISO/DIS 307:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
4.1 Efflux time method .1
4.2 Differential pressure method .1
5 Reagents and materials . 2
5.1 Solvents and reagents .2
5.1.1 General .2
5.2 Cleaning liquids .3
6 Apparatus . 3
6.1 Efflux time method .3
6.2 Differential pressure method .4
7 Preparation of test samples . 5
7.1 General .5
7.2 Samples containing less than 98 % (by mass) polyamide .5
8 Calculation of test portion . 5
9 Selection of solvent . 6
10 Procedure . 6
10.1 Efflux time method .6
10.1.1 Cleaning of the viscometer .6
10.1.2 Preparation of test solution .6
10.1.3 Measurement of flow times .8
10.2 Differential pressure method .9
10.2.1 Preparation of test solution .9
10.2.2 Determination of viscosity ratio increment .9
11 Expression of results . 9
12 Repeatability and reproducibility .10
13 Relationship between the viscosity number determined in 96 % (by mass) sulphuric
acid solution and the viscosity determined in various solvents.10
14 Test report .11
Annex A (informative) Determination of the concentration of commercial sulphuric acid (95 %
to 98 %) and adjustment to 96 % by titration .12
Annex B (informative) Determination of the concentration of sulphuric acid (95 % to 98 %) and
adjustment to 96 % by flow time measurement in a small capillary viscometer .15
Annex C (informative) Determination of the concentration of commercial formic acid and
adjustment to 90 % by titration . 17
Annex D (informative) Determination of the concentration of commercial formic acid and
adjustment to 90 % by density measurement . 19
Annex E (informative) Relationship between the viscosity number determined in 96 % (by
mass) sulphuric acid solution and the viscosity determined in various solvents .22
Bibliography .33

iii
ISO/DIS 307:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the 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 the following URL:
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 9, Thermoplastic
materials.
This seventh edition cancels and replaces the sixth edition (ISO 307:2007), which has been technically
revised.
The main change is the incorporation of an alternative procedure, the differential pressure method
(following same change in ISO 1628-1:2024), based on comparing the differential pressure in capillary
tubing due to the flow of polymer solution and neat solvent simultaneously.
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/DIS 307:2026(en)
Introduction
This document specifies a method for the determination of the viscosity number of dilute solutions of
polyamides in certain specified solvents. The determination of the viscosity number of a polyamide provides
a value that depends on the molecular mass of the polymer, but does not strictly correlate with the molecular
mass.
Additives such as flame-retardants and modifiers often interfere with the viscosity measurement and may
have an increasing effect on the viscosity number in one solvent and a decreasing effect in another solvent.
The extent of the effect depends among others on the additive, the quantity of the additive, the presence of
other additives and reactions.
The viscosity number of a polyamide sample containing additives that interfere with the viscosity
measurement, measured in a specific solvent, represents a specific viscosity number for the polyamide
under investigation and the actual measurement conditions. The measured viscosity number cannot, in
principle, be converted from one solvent to another and is only suitable for intra-product comparison.
The viscosity number of pure polyamides or polyamides containing additives that do not interfere with the
viscosity measurement can be converted from one solvent to another by a general relationship for that type
of polyamide.
Polyamide test samples for the determination of the viscosity number are intended to be completely soluble
in the solvents mentioned. Additives contained in them, like glass and carbon fibres, are to be separated
from the solution.
As it is not possible to distinguish between extractables such as caprolactam, its oligomers and other
extractable additives, these are considered as an essential part of the sample and therefore included in the
sample mass.
The test method is applicable for production control and intra-product comparison even if the polyamide
contains additives that do interfere with the viscosity measurement. However, it should be realised that
deviations of the viscosity number can be caused by either the polyamide itself, effects caused by the
additives present, or a combination of these.
The interference of additives with the viscosity determination can be checked by comparing the viscosity
results of dry blend mixtures and regular production samples at several concentrations of the additive
under investigation and in the solvents concerned. It should be noted that the other additives present also
could influence the viscosity result.
The repeatability and reproducibility of the test method are strongly influenced by the correctness of the
solvent concentration, the use of the Hagenbach correction if applicable and the temperature of the solvent
on diluting the sample solution.
In this document, two specific glass capillary viscometers are recommended. Furthermore, other types of
viscometers listed in ISO 3105 may also be used, provided that the results are demonstrated to be equivalent
to those measured with the recommended viscometers. It is to be expected that in the next revision the use
of the other types of viscometers will be excluded.
The differential pressure method general principles are described in ISO 1628-1:2024 and can be used as an
alternative to the efflux time method with equivalent results.

v
DRAFT International Standard ISO/DIS 307:2026(en)
Plastics — Polyamides — Determination of viscosity number
1 Scope
This document specifies a method for the determination of the viscosity number of dilute solutions of
polyamides in certain specified solvents.
The method is applicable to the polyamides designated PA 46, PA 6, PA 66, PA 69, PA 610, PA 612, PA 11, PA 12,
PA 6T/66, PA 6I/6T, PA 6T/6I/66, PA 6T/6I, PA 6I/6T/66 and PA MXD6 as defined in ISO 16396-1, as well as
to co-polyamides, compounds of polyamides and other polyamides that are soluble in one of the specified
solvents under the specified conditions.
The method is not applicable to polyamides produced by anionic polymerization of lactams or produced
with cross-linking agents; such polyamides are normally insoluble in the specified solvents.
The viscosity number is determined by the general procedure specified in ISO 1628-1:2024, observing the
particular conditions specified in this document.
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 1628-1:2024, Plastics — Determination of the viscosity of polymers in dilute solution using capillary
viscometers — Part 1: General principles
ISO 25337:2010, Plastics — Production quality control — Statistical method for using single measurements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1628-1:2024 and the following
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/
4 Principle
4.1 Efflux time method
The times of flow of a solvent and a solution of the polyamide at a concentration of 0,005 g/ml in the solvent
are measured at 25 °C, the same viscometer being used for both measurements. The viscosity number is
calculated from these measurements and from the known concentration of the solution.
4.2 Differential pressure method
The differential pressure across each of the 2 capillaries connected in series, one of them receiving the solvent
having the differential pressure ∆p , the other receiving the solution of the polyamide at a concentration of
ISO/DIS 307:2026(en)
0,005 g/ml in the solvent having the differential pressure ∆p, are measured at 25°C. The viscosity number is
calculated from these measurements and from the known concentration of the solution.
5 Reagents and materials
5.1 Solvents and reagents
5.1.1 General
Only reagents of recognised analytical grade and only distilled water or water of equivalent purity shall be
used.
When using an automated instrument to apply the differential pressure method, use only solvents compatible
with the specific instrument used. In particular, some components of the equipment are not compatible with
acids.[AC1] Furthermore, any solvent used in the equipment shall be filtered through a 0.45 µm membrane
to prevent clogging of the tubing.
WARNING — Persons using this document should be familiar with laboratory practice. This document
does not purport to address all of the safety concerns associated with its use. Some chemicals, for
example 1,1,2,2-tetrachloroethane, are prohibited in some countries. It is the responsibility of
the user to establish appropriate safety and health practices and to ensure compliance with any
regulatory requirements.
WARNING — WARNING — Avoid contact with the skin and inhalation of any vapours of the solvents
and cleaning liquids.
5.1.2 Sulphuric acid, 96,00 % ± 0,20 % (by mass) solution.
For the determination of the concentration of commercial sulphuric acid (95 % to 98 %) and adjustment to
96,00 %, is referred to Annex A and Annex B.
5.1.3 Formic acid, 90,00 % ± 0,15 % (by mass) solution.
The solvent shall be stored in a brown glass bottle. Its concentration shall be checked at least every 2 weeks.
It shall not contain more than 0,2 % acetic acid or methyl formate.
For the determination of the concentration of commercial formic acid (90 %) and adjustment to
90,00 % ± 0,15 %, is referred to Annex A and Annex B.
5.1.4 m-Cresol, meeting the following specifications:
— appearance: clear and colourless;
— m-cresol content: 99 % (by mass) min.;
— o-cresol content: 0,3 % (by mass) max.;
— water content: 0,13 % (by mass) max.
m-Cresol of the required purity may be obtained by distillation of chemically pure m-cresol, preferably
in vacuum. If distillation is used, nitrogen shall be used for pressure compensation to avoid oxidation. Its
purity may be checked by gas chromatography. The solvent shall be stored in a brown glass bottle.
5.1.5 Phenol, 99 % (by mass) min.
5.1.6 1,1,2,2-tetrachloroethane, 99,5 % (by mass) min.

ISO/DIS 307:2026(en)
5.1.7 Phenol/1,1,2,2-tetrachloroethane.
6 parts by mass of phenol (5.1.5) shall be weighed and dissolved in 4 parts by mass of 1,1,2,2-tetrachloroethane
(5.1.6). Work to an accuracy of 1 % or better in the weighing. The mixture shall be stirred in its original
container at 23 °C to prevent crystallization.
5.1.8 Ortho-phosphoric acid, 85 % (by mass), density 1,71 g/ml.
5.1.9 m-Cresol/phosphoric acid.
50 ml of m-cresol (5.1.4) shall be transferred into a weighing flask (6.1.4) and added with a glass pipette
(6.1.5) 0,14 ml of Ortho-phosphoric acid (5.1.8). The flask shall be closed and stirred with a magnetic stirrer
for 30 min at 100 °C. The solution shall be added to approximately 800 ml of m-cresol in a volumetric flask
while continuously stirring. The weighing flask shall be rinsed several times with m-cresol adding this to
the m-cresol solution. Remove the magnetic stirrer and dilute to the mark. Stir the solution for 30 min.
5.2 Cleaning liquids
5.2.1 Chromic acid solution, prepared by mixing equal volumes of sulphuric acid (96 %, ρ = 1,84 g/ml,
industrial quality) and a saturated solution of potassium dichromate (99,5 %, industrial quality). If required,
the chromic acid solution may be replaced by other equally effective cleaning liquids.
5.2.2 Acetone (99,5 %, industrial quality), or any water-soluble low-boiling-point solvent (industrial
quality).
6 Apparatus
6.1 Efflux time method
6.1.1 Vacuum drying cabinet, with pressure less than 100 k Pa.
6.1.2 Balance, accurate to 0,1 mg.
6.1.3 Volumetric flask, of capacity 50 ml or 100 ml, complying with the requirements of ISO 1042, fitted
with a ground-glass stopper.
6.1.4 Weighing flask, 100 ml, fitted with a ground-glass stopper.
6.1.5 Pipette, 0,2 ml, readable to 0,01 ml.
6.1.6 Shaking apparatus or magnetic stirrer.
6.1.7 Sintered-glass filter, with a pore size between 40 μm and 100 μm (grade P 100), or stainless-steel
sieve, with apertures of about 0,075 mm .
6.1.8 Viscometer, of the suspended-level Ubbelohde type, complying with the requirements of ISO 3105.
The essential dimensions of the viscometer are shown in Figure 1. For use with the formic acid solution
(5.1.3), the inside diameter of the capillary shall be 0,58 mm ± 2 % (complying with the requirements of size
No. 1 of ISO 3105). For use with the sulphuric acid solution (5.1.2) or m-cresol (5.1.4), the inside diameter of
the capillary shall be 1,03 mm ± 2 % (complying with the requirements of size No. 2 of ISO 3105).
Other types of viscometer listed in ISO 3105 may be used, provided that the results are demonstrated to
be equivalent to those of the Ubbelohde viscometers specified above. In cases of dispute, the recommended
viscometer shall be used.
ISO/DIS 307:2026(en)
ISO 1628-1:2024 shall be followed on selecting other type(s) of viscometer.
In this document, the No. 1 and No. 2 Ubbelohde viscometers according to ISO 3105 are recommended.
NOTE It is to be expected that at the next 5 year revision only these two viscometers will be allowed.
Dimensions in millimetres
Key
1 graduation marks for a volume of 4 ml ± 0,2 ml
2 capillary tube of diameter 0,58 mm ± 2 % for formic acid; 1,03 mm ± 2 % for sulphuric acid and m-cresol
3 filling marks
Figure 1 — Ubbelohde viscometer
6.1.9 Thermometer, a liquid-in-glass, “total immersion” thermometer, reading to 0,05 °C in the range to be
used and in a known state of calibration, is suitable. Other thermometric devices of at least equal precision
may be used.
6.1.10 Thermostatic bath, capable of being maintained and controlled at 25,00 °C ± 0,05 °C.
6.1.11 Time device, for example a stop-watch, accurate to 0,1 s.
6.1.12 Centrifuge.
6.2 Differential pressure method
6.2.1 Analytical balance, accurate to 0,1 mg.
6.2.2 A schematic diagram of a relative viscometer used in this method is depicted in ISO 1628-1:2024.
The reference/solvent capillary and the measurement/polymer solution capillary shall be kept at the same
temperature of 25 °C, enclosed in a proper temperature-controlled device with variations from the specified

ISO/DIS 307:2026(en)
temperature lower than ± 0,2 K. The nominal inside diameter of the capillaries shall be 0,5 mm, or 0,75 mm,
and length 80 mm to 600 mm.
7 Preparation of test samples
7.1 General
Polyamide test samples for the determination of the viscosity number shall be soluble in the solvents
mentioned, except for additives present, such as reinforcement or fillers.
The sample shall contain less than 0,28 % moisture. If it contains more than 0,28 % moisture the sample
shall be dried. Generally, drying at 70 °C in a vacuum for 4 h to 6 h is adequate.
It is possible that the dissolution time of some samples is too long for adequate production control. In these
cases, the material may be ground in order to shorten the dissolution time, provided that the results are
demonstrated to be equivalent.
7.2 Samples containing less than 98 % (by mass) polyamide
For samples containing more than 2 % additives, the amount of additives shall be either determined by a
specifically developed method or taken from the recipe. The method of determination shall be mentioned in
the report.
The water content of the sample shall be determined according to ISO 15512. The ash content shall be
determined according to ISO 3451-4.
The correct amount of polyamide sample to be weighed out shall be calculated using Formula (1).
Some additives, such as antimony trioxide and zinc sulphide, are completely volatilized during the calcination
according to ISO 3451-4. Materials reinforced with glass fibre contain flame-retardant antimony trioxide
and/or other volatilizable additives. If the total content of additives is more than 2 %, these shall be brought
into account by the formulation of the sample for calculating the exact test portion.
It is possible that for production quality control purposes, the laboratory response time for determination
of the additives is too long for adequate production control. In these cases, the additive(s) content in the
production recipe may be used for calculating the amount of sample, if the total variation of the polymer
content is less than 4 % (by mass), e.g. 65 % PA would range from 63 % to 67 %.
8 Calculation of test portion
Calculate the mass m , in milligrams, of the test portion according to Formula (1):
c
(1)
where
250 required weight in mg to achieve the target concentration of 0.005 g/ml when using 50 ml of
solvent;
w is the water content of the sample, expressed as a percentage by mass, determined in accordance
with ISO 15512;
w is the content of inorganic materials (for example fillers or glass fibres) in the sample, expressed
as a percentage by mass, determined in accordance with ISO 3451-4;
w is the content of other materials (for example other polymers, such as polyolefin, or additives,
such as flame-retardants), expressed as a percentage by mass, determined by appropriate
methods.
For the content of the additive(s) which cannot be determined, the content according to the product recipe
shall be used.
ISO/DIS 307:2026(en)
9 Selection of solvent
The value of the viscosity number of a polyamide depends on the solvent used.
The solvent or solvents to be used for a particular polyamide are specified below.
a) For PA 6, PA 46, PA 66, PA 69, PA 610, PA MXD6 and corresponding co-polyamides, formic acid solution
or sulphuric acid shall be used as solvent. For polyamides containing additives that liberate gases in
acidic solvents, m-cresol shall be used as the solvent. In cases of dispute, formic acid shall be used as a
solvent.
b) For PA 612, the sulphuric acid solution or m-cresol shall be used as solvent. In cases of dispute, m-cresol
shall be used.
c) For PA 11, PA 12, PA 11/12 copolymers, m-cresol shall be used as a solvent. In cases of dispute about
ammonium carboxylate influencing viscosity through the formation of end-group associations,
additional measurements shall be made using m-cresol/phosphoric acid solution as a solvent (5.1.9).
d) For PA 6T/66, PA 6I/66, PA 6I/6T, PA 6T/6I/66, PA 6T/6I, PA 6I/6T/66, m-cresol, phenol/1,1,2,2-
tetrachloroethane or sulphuric acid shall be used as solvent. In cases of dispute, m-cresol shall be used.
e) For other polyamides, any of the mentioned solvents may be used.
NOTE Viscosity numbers of polyamides not containing additives that interfere with the viscosity measurement
can be converted from one solvent to another by a general interconversion formula. Graphs for interconversion are
mentioned in Clause 13 and presented in Annex E. The reliability of the conversions is discussed in Annex E.
10 Procedure
10.1 Efflux time method
10.1.1 Cleaning of the viscometer
The viscometer (6.1.8) shall be cleaned prior to the first use, again after discordant readings (for example,
when two successive determinations of the efflux time of the solvent differ by more than 0,4 s) and, further,
at intervals during regular use. For this purpose, it shall be allowed to stand for at least 12 h filled with a
cleaning agent (5.2), for example chromic acid solution (5.2.1). The cleaning agent shall be removed, the
viscometer shall be rinsed with water then with acetone (5.2.2) and dried, for example by a slow stream of
filtered air or in the vacuum drying cabinet (6.1.1).
After each determination, the viscometer shall be drained, rinsed with the solvent, then with water, followed
by, for example, acetone (5.2.2) and dried as described above.
However, if the next solution to be measured is of a polyamide of the same type and of a similar viscosity,
it is permissible to drain the viscometer, wash it with the solution to be measured, and then fill it with this
solution.
NOTE In the case of, for example, production control and automated flow time measurement the viscometer may
be filled with the solvent in anticipation of the next sample.
10.1.2 Preparation of test solution
10.1.2.1 General
Three different methods for preparing the test solution are described in this document. The first volumetric
method (see 10.1.2.2), without correction for the volume of insoluble additives in the test portion, is equal
to the method described in the previous version of this document (ISO 307:2007). For practical reasons,
test portion masses of (m ± 5) mg are allowed. For pure polyamide, this results in a concentration range of
c
0,004 9 g/ml to 0,005 1 g/ml. The actual polymer concentration is taken into account in the calculation of

ISO/DIS 307:2026(en)
the viscosity number . For samples containing insoluble additives, a test portion of exactly the calculated
mass will give a solution that is almost equal to 0,005 g/ml.
The second volumetric method (see 10.1.2.3) and the gravimetric method (see 10.1.2.4) take into account
the insoluble additives and the polyamide volume. The latter two methods are often used in combination
with (semi-)automatic viscosity measurement equipment.
NOTE For polyamide samples containing only insoluble additives, the concentration of the solution prepared
according to the volumetric or gravimetric method will be exactly 5 mg/ml.
10.1.2.2 Volumetric method
A test portion of mass m mg shall be weighed to the nearest 0,2 mg, where m lies in the range (m ± 5) mg
t t c
where m is the mass calculated in accordance with Formula (1), working rapidly to minimize moisture
c
pick-up by the polymer. If the weighing takes more than 2 min, the material shall be rejected to begin another
weighing.
The test portion shall be transferred to the 50 ml volumetric flask (6.1.3) and about 40 ml of the solvent (see
Clause 9) shall be added. The flask shall be closed and the contents shaken, or stirred with the magnetic
stirrer (6.1.6), until the polymer has dissolved. This may take from approximately 0,5 h to several hours,
depending on the type of polyamide and the particle size of the test portion. When sulphuric acid or formic
acid solution is used as the solvent, the temperature shall not exceed 30 °C. When m-cresol or phenol/1,1,2,2-
tetrachloroethane is used as the solvent, the temperature may be raised to 95 °C to 100 °C. If, in the latter
case, dissolution takes more than 2 h, this shall be reported. For PA 6T/66, suitable conditions have been
found to be 2 h at 90 °C.
When dissolution is complete, the solution shall be cooled to 25 °C ± 2 °C, diluted to the mark with the solvent
and mixed well. If the magnetic stirrer (6.1.6) is used, it shall be removed from the solution before dilution
and rinsed with the solvent, adding the rinsing to the flask before further dilution.
10.1.2.3 Volumetric method, in exact relation to the polymer content
A test portion of mass m mg shall be weighed to the nearest 0,2 mg, where m lies in the range (m ± 10 %) mg,
t t c
where m is the mass calculated in accordance with Formula (1), working rapidly to minimize moisture
c
pick-up by the polymer. If the weighing takes more than 2 min, the material shall be rejected and to begin
another weighing.
The test portion shall be transferred to the 100 ml volumetric flask (6.1.3) or weighing bottle (6.1.4) and the
volume of the solvent (see Clause 9) required to prepare a concentration of 0,50 g of sample per 100 ml of
solution shall be added. The volume of solvent to be added shall be corrected for the volume of the soluble
mass of the sample. The solvent shall be added by means of a suitable dosing device (e.g. a burette accurate to
0,01 ml). The flask shall be closed and the contents shaken, or stirred with the magnetic stirrer (6.1.6), until
the polymer has dissolved. This may take from approximately 0,5 h to several hours, depending on the type
of polyamide and the particle size of the test portion. When sulphuric acid or formic acid solution is used as
the solvent, the temperature shall not exceed 30 °C. When m-cresol or phenol/1,1,2,2-tetrachloroethane is
used as the solvent, the temperature may be raised to 95 °C to 100 °C. If, in the latter case, dissolution takes
more than 2 h, this shall be reported. For PA 6T/66, suitable conditions have been found to be 2 h at 90 °C.
When dissolution is complete, the solution shall be cooled to 25 °C ± 2 °C.
EXAMPLE
Mass of polyamide in the sample 275 mg
Polyamide density 1,130 0 kg/dm
Volume of the polyamide mass 0,275 g/1,130 0 g/ml = 0,243 4 ml
Volume of solvent to be added (275/250) × 50 − 0,243 4 = 54,76 ml

ISO/DIS 307:2026(en)
10.1.2.4 Gravimetric method, in exact relation to the polymer content
A test portion of mass m mg shall be weighed to the nearest 0,2 mg, where m lies in the range (m ± 10 %) mg,
t t c
where m is the mass calculated in accordance with Formula (1), working rapidly to minimize moisture
c
pick-up by the polymer. If the weighing takes more than 2 min, the material shall be rejected to begin another
weighing.
The test portion shall be transferred to a 100 ml volumetric flask (6.1.3) or weighing bottle (6.1.4) and the
mass of solvent (see Clause 9) required to prepare a concentration of 0,50 g of sample per 100 ml of solution
shall be added. The mass of solvent to be added shall be corrected for the volume of the soluble mass of the
sample. The flask shall be closed and the contents shaken, or stirred with the magnetic stirrer (6.1.6), until
the polymer has dissolved. This may take from approximately 0,5 h to several hours, depending on the type
of polyamide and the particle size of the test portion. When sulphuric acid or formic acid solution is used as
the solvent, the temperature shall not exceed 30 °C. When m-cresol or phenol/1,1,2,2-tetrachloroethane is
used as the solvent, the temperature may be raised to 95 °C to 100 °C. If, in the latter case, dissolution takes
more than 2 h, this shall be reported. For PA 6T/66, suitable conditions have been found to be 2 h at 90 °C.
When dissolution is complete, the solution shall be cooled to 25 °C ± 2 °C.
EXAMPLE
Mass of polyamide in the sample 275 mg
Density of polyamide 1,130 0 kg/dm
Density of solvent 1,204 4 kg/dm
Volume of the polyamide mass 0,275 g/1,130 0 g/ml = 0,243 4 ml
Volume of solvent to be added (275/250) × 50 − 0,243 4 = 54,76 ml
Mass of solvent to be added 54,76 ml × 1,204 4 = 65,95 g
NOTE 1 An automated weighing system for preparing the sample solution is often used in production control.
NOTE 2 In the case of polyamides with extremely high relative molecular masses, solutions free from the so called
streaking phenomenon cannot always be obtained, in spite of prolonged periods of shaking or stirring. Such test
solutions can only be used for mutual comparison with similar products.
10.1.3 Measurement of flow times
The mean flow time of the solvent shall be determined in the same viscometer and in the same manner
as that of the solution. The flow times of the solvents shall be determined at least once each day that they
are used, or at a different frequency if statistically validated by the laboratory. If the flow time of a solvent
differs by more than 0,5 % from the initial value at the time of preparation, the solvent shall be discarded
and fresh solvent prepared.
The solution shall be filtered through the sintered glass filter (6.1.7) or the metal sieve into tube L of the
viscometer (see Figure 1). Alternatively, the solution shall be centrifuged at a rotational frequency of
−1
approximately 50 s and the clear supernatant liquid poured into the viscometer (6.1.8). The volume of
liquid shall be such that, after draining, the level lies between the filling marks. For hand-filled viscometers,
the filling should preferably be done with the viscometer out of the thermostatic bath (6.1.10) to avoid
contamination of the bath in case of accidental spills.
The viscometer shall be mounted in the thermostatic bath maintained at 25,00 °C ± 0,05 °C ensuring that
tube N is vertical and that the upper graduation mark E is at least 30 mm below the surface of the liquid in
the bath. At least 15 min shall be allowed for the charged viscometer to attain the temperature of the bath.
Tube M shall be closed and and the liquid shall be blown or drawn into the upper bulb of tube N using a
rubber bulb or similar equipment. Tube N shall be closed. Tube M shall be opened so that the liquid drops
away from the lower end of the capillary tube. Tube N shall be open and the flow time shall be measured
to the nearest 0,2 s, as the time taken for the bottom of the meniscus to pass from mark E to mark F. With
cloudy solutions, view the top of the meniscus. The measurement of the flow time shall be repeated until two

ISO/DIS 307:2026(en)
successive values agree within 0,25 %. The mean of these two values shall be taken as the flow time of the
solution.
With each polyamide sample, at least two determinations of the viscosity number shall be carried out, using
a fresh solution each time, until two successive values meet the repeatability requirement corresponding to
the solvent used (see Clause 12). The mean of these two values shall be reported, rounded off to the nearest
whole number, as the viscosity number of the sample. If two successive determinations of the solution mean
flow time differ by more than 0,5 %, the viscometer shall be cleaned (see 10.1.1).
When necessary, the solution of the sample shall be filtered through a filter (6.1.7) before making the
measurement. Any glass fibres contained in the sample will sediment completely after 3 h to 4 h. In such
cases, the test solution can be decanted for the measurement and thus shall not be filtered.
For automated solution-viscosity-measurement equipment, the procedure may differ from the described
method. However, the requirements concerning the measurement solution, the equipment, bath temperature
and the flow times shall be maintained in all respects.
For production quality control purposes, a single viscosity number determination is, in principle, permitted
on condition that the precision of the test method is known and permits the process variation to be identified
(precision <30 % of the process variation, preferably <10 %), and the process control limits and the process
warning limits are determined, based on a known precision interval, and statistically validated. It is strongly
recommended that the statistical model is incorporated in the quality manual, including written procedures
on how to handle the product and the actions that should be taken if the result of the single de
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