ISO/DIS 21870:2026(en)

ISO/TC 45/SC 3

Secretariat: AFNOR

Date: 2025-12-04

Rubber compounding ingredients — Carbon black — Determination of high-temperature loss on heating by thermogravimetry

Ingrédients de mélange du caoutchouc — Noir de carbone — Détermination de la perte à la chaleur à haute température par thermogravimétrie

© ISO 2026

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Contents

Foreword iv

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Principle 1

5 Apparatus 1

6 Materials 2

7 Procedure 2

8 Expression of results 2

9 Precision 3

10 Test report 3

Annex A (informative) Precision 4

Bibliography 6

Foreword

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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 21870:2005), which has been technically revised.

The main changes are as follows:

— inclusion of precision statement in Annex A.

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.

Rubber compounding ingredients — Carbon black — Determination of high-temperature loss on heating by thermogravimetry

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.

This document describes a method for the quantitative determination of the loss on heating (pyrolysis) of carbon black due to the elimination of volatile materials other than those liberated when heating to 125 °C. The method is applicable to carbon black for the rubber industry.

It serves to assess the decomposition of functional groups and adsorbed substances (e.g. hydrocarbons) present on the surface of the carbon black.

There are no normative references in this document.

No terms and definitions are listed in this document.

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/

A known mass of carbon black is placed in the cradle of a thermobalance and heated according to a predetermined temperature programme in a controlled, oxygen-free atmosphere. The mass variation recorded provides a thermogram which can be used for quantitative evaluation.

The usual laboratory apparatus and, in particular, the following shall be used.

5.1 Thermobalance, with a sensitivity of 1 μg and equipped with an appropriate cradle made of a non-oxidizing material.

5.2 Furnace, allowing temperature regulation from the ambient temperature up to approximately 1 000 °C.

NOTE There are several thermogravimetric measurement instruments available commercially.

5.3 Temperature programmer, allowing a heating rate of up to 50 °C/min.

5.4 Nitrogen gas distributor, associated with flow-control equipment allowing measurements in a range from 10 cm³/min to 250 cm³/min.

5.5 Data acquisition and processing system.

6.1 Cylinder of compressed nitrogen containing less than 10 ppm of oxygen.

7.1 Power up the various elements of the analyser and preheat the furnace to 40 °C in accordance with the instructions of the instrument manufacturer.

7.2 Close the furnace of the thermobalance, purge with a constant, predefined flow of nitrogen (usually 100 cm³/min) in accordance with instructions of the instrument manufacturer and maintain a constant flow for the duration of the test.

7.3 Wait for the thermobalance to stabilize.

7.4 Place the test sample in the cradle and weigh it to the nearest 0,01 mg. The sample mass should not be less than 5 mg.

7.5 Start the test.

7.6 Heat the furnace to 125 °C at a rate of 20 °C/min.

7.7 Maintain the temperature at 125 °C for 15 min and record the mass.

7.8 Heat the furnace from 125 °C to 950 °C at a rate of 20 °C/min. Due to instrumental limitations, the user can be obliged to run the test at a lower maximum temperature, e.g. at 800 °C. These conditions can lead to slightly lower test results for the loss on pyrolysis and shall therefore be mentioned in the test report.

7.9 Maintain the furnace at a temperature of 950 °C until the mass remains constant. A mass loss lower than 0,05 %, relative to the initial mass, during 15 min is considered as the constant mass.

The volatile matter at 125 °C in nitrogen, V, and the loss on pyrolysis at 950 °C in nitrogen, P, are calculated using Formulas (1) and (2).

(1)

(2)

where

V is the volatile matter at 125 °C in nitrogen, in per cent of the initial mass;

P is the loss on pyrolysis at 950 °C in nitrogen, in per cent of the initial mass;

m₄₀ is the initial mass at 40 °C, in gram;

m₁₂₅ is the mass at 125 °C, in gram;

m₉₅₀ is the mass at 950 °C, in gram.

See Annex A.

The test report shall contain the following information:

a) all information necessary for the identification of the sample tested;

b) a reference to this document, i.e. ISO 21870;

c) the type of apparatus used;

d) the loss on heating to 125 °C (volatile matter), to the nearest 0,1 %;

e) the loss on further pyrolysis (125 °C to 950 °C), to the nearest 0,1 %;

f) any deviations from the procedure specified, e.g. a maximum temperature lower than 950 °C;

g) any unusual features (anomalies) observed during the test;

h) the date of the test.

1. 
   (informative)
   
   Precision

A.1 The precision of this test method was determined in accordance with ISO/TR 9272:2005^[1]. Refer to this document for terminology and other statistical details.

A.2 The precision results give an estimate of the precision to be expected. The precision parameters shall not be used for acceptance/rejection testing of any group of materials without documentation that they are applicable to those particular materials and the specific testing protocols that include this test method.

A.3 A type 1 precision interlaboratory-trial programme was conducted. Both the repeatability and the reproducibility determined represent short-term testing conditions. Eight laboratories tested two different carbon blacks on two different days in duplicate.

A.4 The results of the precision calculations are given in Table A.1 and Table A.2.

Table A.1 — Volatile matter

Table A.2 — Loss on pyrolysis

Bibliography

[1] ISO 1126, Rubber compounding ingredients — Carbon black — Determination of loss on heating

[2] ISO/TR 9272:2005, Rubber and rubber products — Determination of precision for test method standards

1. Replaced by ISO 19983:2017. ↑