ISO 12492:2012
(Main)Rubber, raw — Determination of water content by Karl Fischer method
Rubber, raw — Determination of water content by Karl Fischer method
ISO 12492:2012 specifies a test method for the determination of water content of raw rubber and compounded rubber using a coulometric Karl Fischer titration method. It applies to the range for the water content between 0,01 % and 1 %. As this is a very sensitive method, contact of sample with any moisture, even from the surrounding environment, must be eliminated as much as possible.
Caoutchouc brut — Détermination de la teneur en eau par la méthode de Karl Fischer
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 12492
First edition
2012-10-01
Rubber, raw — Determination of water
content by Karl Fischer method
Caoutchouc brut — Détermination de la teneur en eau par la
méthode de Karl Fischer
Reference number
ISO 12492:2012(E)
©
ISO 2012
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ISO 12492:2012(E)
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ii © ISO 2012 – All rights reserved
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ISO 12492:2012(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 2
5 Apparatus . 2
6 Calibration . 3
7 Sampling and preparation of test piece . 3
8 Procedure. 3
8.1 Power on . 3
8.2 Selection of the generator electrode . 4
8.3 Filling the electrolysis cell . 4
8.4 Equipment check . 4
8.5 Analysis. 5
9 Precision . 6
10 Test report . 6
Annex A (normative) Calibration schedule . 7
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ISO 12492:2012(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
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.
ISO 12492 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee
SC 2, Testing and analysis.
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ISO 12492:2012(E)
Introduction
The water content of raw rubber is one of the important characteristics to be determined as a quality
control test. Different synthetic rubbers contain varying amounts of water. Water can affect product
quality, texture, shelf life, chemical stability and reactivity. A high amount of water can cause processing
difficulties.
Water contamination is a cause for major concern in a large number of applications. In the rubber
industry, water is one of the major damaging contaminants and is often overlooked as a primary cause
of component failure. For certain applications in the rubber industry, even a small amount of water may
have damaging effects on production.
Several methods are available for the determination of water content. A Karl Fischer (KF) coulometric
titrator is one of the most accurate methods. Unlike other techniques, it can trace low levels of free,
emulsified and dissolved water (which cannot be detected with normal gravimetric methods). The test
is capable of measuring water levels as low as 0,01 %.
Unlike gravimetric measurements, which are indirect methods that assume, all volatiles removed are
water, Karl Fischer titration is a direct method that is almost specific for water. The method is especially
useful for low moisture levels (<1 %).
The new test method will help to determine the water content of the raw rubber and rubber compounds
in shortest possible time and will be helpful for quality control at the laboratories. Coulometric
determination of water is an absolute method.
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INTERNATIONAL STANDARD ISO 12492:2012(E)
Rubber, raw — Determination of water content by Karl
Fischer method
WARNING — Persons using this International Standard should be familiar with normal laboratory
practice. This International Standard 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 and to ensure compliance with any national regulatory conditions.
CAUTION — Certain procedures specified in this International Standard may involve the
use or generation of substances, or the generation of waste, that could constitute a local
environmental hazard. Reference should be made to appropriate documentation on safe
handling and disposal after use.
1 Scope
This International Standard specifies a test method for the determination of water content of raw
rubber and compounded rubber using a coulometric Karl Fischer titration method. It applies to the
water content range between 0,01 % and 1 %. As this is a very sensitive method, contact of sample with
any moisture, even from the surrounding environment, must be eliminated as much as possible.
2 Normative references
The following referenced documents are indispensable for the application 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 760, Determination of water ― Karl Fischer method (General method)
ISO 1795, Rubber, raw natural and raw synthetic ― Sampling and further preparative procedure
ISO 18899:2004, Rubber ― Guide to the calibration of test equipment
3 Principle
The water determination test (Karl Fischer method) is designed to determine the water content in
substances, utilizing the quantitative reaction of water with iodine and sulfur dioxide in the presence of
a lower alcohol such as methanol and an organic base, as shown in the following formulae:
-
H O + I + SO + 3 RN → 2(RN+H)I + RN·SO
2 2 2 3
RN·SO + CH OH → (RN+H)O-SO ·OCH .
3 3 2 3
There are two determination methods which differ in the way the iodine is provided: the volumetric
titration method and the coulometric titration method.
In the volumetric titration method, iodine required for reaction with water is previously dissolved and
the water content is determined by measuring the amount of iodine consumed as a result of reaction
with water present in a sample.
In the coulometric titration method, first, iodine is produced by electrolysis of the reagent containing
iodide ion, then the water content in a sample is determined by measuring the quantity of electricity
which is required for the electrolysis, i.e. for the production of iodine, based on the quantitative reaction
of the generated iodine with water.
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ISO 12492:2012(E)
–
In coulometric Karl Fischer titration, iodine (I ) is generated electrochemically from iodide (I ). When
2
iodine (I ) comes in contact with the water in the sample, water is titrated according to the above
2
mentioned reaction scheme. Once all of the water available has reacted, the reaction is complete. The
amount of water in the sample is calculated by measuring the current needed for the electrochemical
–
generation of iodine (I ) from iodide (I ) according to the following reaction:
2
−−
22II→+ e
2
According to Faraday’s Law, the quantity of the iodine produced is proportional to the current genera
...
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