ISO 23706:2020

INTERNATIONAL ISO
STANDARD 23706
First edition
2020-08
Plastics — Determination of apparent
activation energies of property changes
in standard weathering test methods
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Abbreviated terms . 2
4 Principle . 2
5 Apparatus . 3
5.1 General . 3
5.2 Surface temperature measurement . 3
6 Test specimens. 3
7 Test method . 3
7.1 Test conditions . 3
7.2 Test duration . 4
7.3 Increased/decreased temperatures . 4
7.4 Calculation of activation energy, E .
a 4
7.4.1 Exposures at two different temperatures . 4
7.4.2 Exposures at two or more different temperatures . 5
8 Exposure conditions . 5
9 Procedure. 5
9.1 General . 5
9.2 Mounting the test specimens . 5
9.3 Exposure . 5
9.4 Measurement of radiant exposure . 5
9.5 Determination of changes in properties after exposure . 6
10 Test report . 6
Annex A (normative) Arrhenius concept . 7
Annex B (informative) Examples .10
Annex C (informative) Effective temperature calculation .14
Annex D (informative) Potential contributions to the uncertainty budget .15
Bibliography .17
Foreword
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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 6, Ageing,
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iv © ISO 2020 – All rights reserved

Introduction
Temperature is an important influencing factor on correlation and acceleration in lightfastness and
weathering testing. This is acknowledged in international general weathering standards like ISO 4892-1
or ISO 16474-1.
The Arrhenius concept describes the influence of temperature on the reaction rate of chemical reaction.
This model is also used (with limitations) to describe the reaction rate of photochemical/weathering
reactions. Several assumptions and limitations should be taken into account; the Arrhenius concept
might not be sufficient to describe complex degradation behaviours. However, this basic approach
might help to better understand the influence of temperature on weathering degradation of polymeric
materials.
An important material specific property to describe the temperature influence on degradation reactions
is the activation energy E , which describes the required energy barrier for a chemical reaction to
a
occur. E is only valid for a specific material and a specific degradation pathway. In weathering, this
a
degradation pathway is usually attributed to a specific property change.
The Arrhenius principle is applied to determine the temperature dependency of the thermal
degradation of polymers. The thermal activation energy can be calculated based on ISO 11358-2. There
is no such standard to determine the activation barrier for weathering or photo-chemical degradation
of polymers.
Limited information is available on the activation energies of photochemical degradation/weathering
reactions. To determine activation energies, weathering experiments at least at two different
temperatures are required. Due to this high effort, available activation energies are often calculated
based on unsuitable weathering experiments (for example based on outdoor weathering and accelerated
weathering).
There are some basic test requirements which help to increase the significance of the Arrhenius
concept and the determination of the activation energy in accelerated weathering. These requirements
are described in this document.
NOTE 1 Different property changes, for example yellowing and surface cracking of one material can have
different activation energies.
NOTE 2 In this approach, the activation energy is considered as temperature independent for the selected
temperature range.
The determination of activation energies of photo-chemical degradation processes allows including the
temperature into the evaluation and correlation of different weathering experiments as quantitative
factor. Knowing the activation energy improves the reliability and predictive value of artificial
weathering.
NOTE 3 The use of the Arrhenius concept in artificial weathering simplifies complex chemical degradation
processes and is therefore, in this context, a limited model to estimate the temperature dependency in
weathering. However, by following some basic experimental preconditions, the relevance of the estimates can be
increased.
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patent rights other than those in the patent database. ISO shall not be held responsible for identifying
any or all such patent rights.
vi © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 23706:2020(E)
Plastics — Determination of apparent activation energies
of property changes in standard weathering test methods
1 Scope
This document describes a test method to determine the activation energy (E ) of photochemical
a
degradation reactions in accelerated weathering tests according to the Arrhenius model in the most
comprehensive manner.
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 4582, Plastics — Determination of changes in colour and variations in properties after exposure to
glass-filtered solar radiation, natural weathering or laboratory radiation sources
ISO 4892-1, Plastics — Methods of exposure to laboratory light sources — Part 1: General guidance
ISO 4892-2, Plastics
...