ISO 22768:2020

Raw rubber and rubber latex - Determination of the glass transition temperature by differential scanning calorimetry (DSC)

This document specifies a method using a differential scanning calorimeter to determine the glass transition temperature of raw rubber and rubber latex.

Caoutchouc et latex de caoutchouc brut — Détermination de la température de transition vitreuse par analyse calorimétrique différentielle (DSC)

General Information

• Status: Published
• Publication Date: 07-Jul-2020
• ICS: 83.040.10 - Latex and raw rubber
• ICS: 83.060 - Rubber
• Technical Committee: ISO/TC 45/SC 3 - Raw materials (including latex) for use in the rubber industry
• Drafting Committee: ISO/TC 45/SC 3/WG 5 - Synthetic and reclaimed rubber
• Current Stage: 9092 - International Standard to be revised
• Start Date: 22-Dec-2025
• Completion Date: 27-Dec-2025

Relations

• Revises: ISO 22768:2017 - Rubber, raw - Determination of the glass transition temperature by differential scanning calorimetry (DSC)
• Effective Date: 23-Apr-2020

Overview

ISO 22768:2020 - "Raw rubber and rubber latex - Determination of the glass transition temperature by differential scanning calorimetry (DSC)" specifies a standardized DSC method to measure the glass transition temperature (Tg) of raw rubber and rubber latex. The document defines the test principle, sample preparation, instrument calibration, thermal cycle, result expression (inflection point at a 20 °C/min heating rate) and reporting requirements. It also includes precision data (Annex A for raw rubber and Annex B for rubber latex).

Key topics and technical requirements

• Test principle: Measure the change in specific heat capacity vs temperature using a differential scanning calorimeter (DSC) and determine Tg as the inflection point of the transition curve.
• Sample preparation:
  • Raw rubber: representative specimen; ISO cites specimen mass around 0.01–0.02 g.
  • Rubber latex: dry films (105 °C ±5 °C) and cut into ~2 mm × 2 mm pieces (see ISO 124:2014).
• Specimen mass and loading: DSC determinations typically use 5–20 mg; ensure good thermal contact and sealed pans; avoid handling with bare hands.
• Thermal cycle:
  • Cooling to a stable baseline (e.g., ~−140 °C for very low-Tg rubbers) at 10 or 20 °C/min.
  • Heating at 20 °C/min until ~30 °C above the upper limit of the glass transition range.
  • Tg is defined as the midpoint/inflection point of the DSC curve (software or first-derivative DDSC may be used).
• Instrumentation & calibration:
  • Use a DSC compliant with ISO 11357-1.
  • Inert gas (nitrogen or helium) with flow rates typically 10–100 ml/min (±10%).
  • Calibrants recommended: n‑octane, n‑heptane, cyclohexane, and indium for higher temperatures.
• Reporting: Must reference ISO 22768:2020 and include sample ID, specimen mass, instrument type, gas and flow rate, calibrants, thermal cycle, Tg (°C) with DSC curve, and test date.
• Precision: Interlaboratory precision data are provided; consult Annexes A and B before applying precision limits to acceptance criteria.

Applications and users

ISO 22768:2020 is intended for:

• Quality control and acceptance testing in rubber manufacturing
• R&D and formulation development to characterize polymer behavior and Tg
• Material selection, processing temperature selection and performance assessment for elastomers
• Independent test laboratories performing standardized DSC rubber testing

Typical uses include monitoring batch-to-batch consistency, evaluating the effect of additives or extraction residuals, and comparing natural vs synthetic rubbers or latex-derived materials.

Related standards

• ISO 11357-1:2016 - Plastics - Differential scanning calorimetry (DSC) - General principles
• ISO 124:2014 - Latex, rubber - Determination of total solids content
• ISO 1407 - Rubber - Determination of solvent extract
• ISO 23529 - Conditioning procedures for rubber test pieces

Keywords: ISO 22768:2020, glass transition temperature, Tg, differential scanning calorimetry, DSC, raw rubber, rubber latex, rubber testing, ISO standard.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 22768
Third edition
2020-07
Raw rubber and rubber latex —
Determination of the glass transition
temperature by differential scanning
calorimetry (DSC)
Caoutchouc et latex de caoutchouc brut — Détermination de la
température de transition vitreuse par analyse calorimétrique
différentielle (DSC)
Reference number
©
ISO 2020
© 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
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Phone: [phone]
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Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus and materials. 2
6 Preparation of the test sample . 2
6.1 Raw rubber . 2
6.2 Rubber latex . 2
7 Conditioning . 2
8 Calibration . 2
9 Procedure. 3
9.1 Gas flow rate . 3
9.2 Loading the test specimen . 3
9.3 Temperature scan . 3
10 Expression of results . 3
11 Test report . 4
12 Precision . 5
Annex A (informative) Precision on raw rubber . 6
Annex B (informative) Precision on rubber latex . 9
Bibliography .11
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
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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
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 45, Rubber and rubber products,
Subcommittee SC 3, Raw materials (including latex) for use in the rubber industry.
This third edition cancels and replaces the second edition (ISO 22768:2017), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— rubber latex has been added to the scope and to Clause 6 as 6.2;
— a new Annex B on the precision of rubber latex has been added.
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 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 22768:2020(E)
Raw rubber and rubber latex — Determination of the
glass transition temperature by differential scanning
calorimetry (DSC)
WARNING — Persons using this document should be familiar with normal laboratory practice.
This document does not purport to address all of the safety problems, if any, associated with its
use. It is the responsibility of the user to establish appropriate safety and health practices.
1 Scope
This document specifies a method using a differential scanning calorimeter to determine the glass
transition temperature of raw rubber and rubber latex.
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 124:2014, Latex, rubber — Determination of total solids content
ISO 1407, Rubber — Determination of solvent extract
ISO 11357-1:2016, Plastics — Differential scanning calorimetry (DSC) — Part 1: General principles
ISO 23529, Rubber — General procedures for preparing and conditioning test pieces for physical test methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11357-1 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/
3.1
glass transition
reversible change in an amorphous polymer, or in amorphous regions of a partially crystalline polymer,
from (or to) a rubbery or viscous condition to (or from) a glassy or hard condition
3.2
glass transition temperature
T
g
approximate midpoint of the temperature range over which glass transition (3.1) takes place
Note 1 to entry: For the purposes of this document, the glass transition temperature is defined as the point of
inflection of the DSC curve which has been obtained at a heating rate of 20 °C/min (see A.3).
4 Principle
The change in specific heat capacity of the test sample as a function of temperature under a specified
inert atmosphere is measured using a differential scanning calorimeter (DSC). The glass transition
temperature is determined from the curve thus produced.
5 Apparatus and materials
5.1 Differential scanning calorimeter, in accordance with ISO 11357-1:2016, 5.1.
The calorimeter should be operated in a room held at standard laboratory temperature. It should be
protected from draughts, direct sunlight and sudden temperature changes.
5.2 Specimen pans (crucibles), in accordance with ISO 11357-1:2016, 5.2.
5.3 Gas supply, analytical grade, usually nitrogen or helium.
5.4 Balance, capable of measuring the specimen mass to an accuracy of ±0,1 mg.
5.5 Oven, capable of being maintained at 105 °C ± 5 °C.
6 Preparation of the test sample
6.1 Raw rubber
The test specimen shall be as representative as possible of the sample being examined and shall have a
mass between 0,01 g and 0,02 g.
To determine T of polymers, extract raw rubber in accordance with ISO 1407.
g
6.2 Rubber latex
Dry rubber latex samples at 105 °C± 5 °C in accordance with ISO 124:2014, 6.2. Remove the rubber latex
film and cut into pieces about 2 mm × 2 mm.
7 Conditioning
Condition the sample to be examined and the test specimen in accordance with ISO 23529.
8 Calibration
Calibrate the calorimeter according to the manufacturer's instructions.
The use of suitable analytical grade substances is recommended to check the accuracy of the
temperature scale. Ideally, substances whose melting points bracket the temperature range of interest
should be chosen. n-Octane, n-heptane and cyclohexane have been found to be useful. Indium should be
used if a higher temperature calibrant is required.
2 © ISO 2020 – All rights reserved

9 Procedure
9.1 Gas flow rate
The same inert gas flow rate with a tolerance of ±10 %, shall be used throughout the procedure. Flow
rates between 10 ml/min and 100 ml/min have been found to be suitable.
9.2 Loading the test specimen
Determine the mass of the test specimen to an accuracy of ±0,1 mg. Unless otherwise specified in the
materials standard, use a mass between 5 mg and 20 mg. The same nominal mass shall be used for all
determinations. If possible, the specimen shall have a flat surface so as to give good thermal contact
with the bottom of the pan.
NOTE 1 Intimate thermal contact between the test specimen and the bottom of the pan is essential for good
repeatability.
Place the specimen in the pan, using tweezers and seal with a lid. Place the sealed pan in the calorimeter
using tweezers.
Do not handle the test specimen or the pan with bare hands.
NOTE 2 Placing an empty pan with a lid as a reference helps to obtain stable DSC thermograms.
9.3 Temperature scan
9.3.1 Cool the test specimen to a temperature of approximately −140 °C at a rate of 10 °C/min or 20 °C/
min and hold at this temperature for 1 min to 10 min until the baseline becomes stable.
A starting temperature of −140 °C is required for the determination of rubbers and rubber latices with
very low glass transition temperatures, e.g. high-cis polybutadiene. For rubbers and rubber latices with
higher glass transitions, this temperature is not necessary.
A starting temperature should be chosen so that a stable base line is achieved b
...