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IS0
I N T ER N AT1 O N A L O RG A N I Z AT 1 ON FOR STAN DARD I Z AT I ON
IS0 RECOMMENDATION
R 305
PLASTICS
DETERMINATION OF THE THERMAL STABILITY
OF POLYVINYL CHLORIDE AND RELATED COPOLYMERS
AND THEIR COMPOUNDS
BY THE DISCOLORATION METHOD
1st EDITION
May 1963
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The copyright of IS0 Recommendations and IS0 Standards
IS0 Member Bodies. Reproduction of these
belongs to
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 305, Determination of the Thermal Stability of Polyvinyl
Chloride and Related Copolymers and their Compounds by the Discoloration Method, was
drawn up by Technical Committee ISO/TC 61, Plastics, the Secretariat of which is held
by the American Standards Association Inc. (ASA).
Work on this question by the Technical Committee began in 1955 and led, in 1957,
'd
to the adoption of a Draft IS0 Recommendation.
This first Draft IS0 Recommendation (No. 217) was circulated to all the IS0 Member
Bodies for enquiry in May 1959. As the results of this consultation were not considered
satisfactory, the Technical Committee presented a second Draft IS0 Recommendation,
which was circulated to all the Member Bodies in October 1960, and which was approved,
subject to a few modifications of an editorial nature, by the following Member Bodies:
Argentina Hungary Romania
Australia India Spain
Austria Israel Sweden
Belgium Japan Turkey
Netherlands United Kingdom
Chile
Czechoslovakia New Zealand U.S.A.
U.S.S.R.
Five Member Bodies opposed the approval of the Draft:
France, Germany, Italy, Poland, Switzerland.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in May 1963, to accept it as an IS0 RECOMMENDATION.
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IS0 / R 305 - 1963 (E)
IS0 Recommendation R 305 May 1963
PLASTICS
DETERMINATION OF THE THERMAL STABILITY
OF POLYVINYL CHLORIDE AND RELATED COPOLYMERS
AND THEIR COMPOUNDS
BY THE DISCOLORATION METHOD
1. SCOPE
This method of test is designed to determine the thermal stability of polyvinyl chloride and of
chlorinated polymers and copolymers and their compounds by the extent of the discoloration
that occurs when, in the form of sheet or film, they are exposed to elevated temperatures.
2. SIGNIFICANCE OF TEST
2.1 The polymers and copolymers of vinyl chloride or related monomers and their compounds
tend to decompose at elevated temperature. The rate of decomposition is rather high at
the processing temperature range (from 120 to 200 OC) but, in practice, can be prevented
or at least reduced by the inclusion of suitable stabilizers.
The decomposition of the polymers causes a change in colour. The stabilizers may act as
acceptors of hydrochloric acid or as inhibitors of the subsequent discoloration.
2.2 The thermal decomposition of polyvinyl chloride is influenced by oxygen.
2.3 This method is suitable for evaluating the resistance of polyvinyl chloride compounds to
degradation by heat, as assessed by the change in colour after specified times of heating
under standardized conditions.
2.4 The results obtained are comparative only. For possible correlation of values, the tem-
perature selected for testing should be near to that of the specific processing conditions.
A quantitative evaluation may if needed be obtained by comparison with a colour scale or
by a photometric method.
3. TEST SPECIMENS
3.1 The test specimens consist of disks with a diameter of 14 mm and a thickness of about 1 mm.
They are punched
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