Chemically-induced ultra-weak photon emission (UPE) — Measurement as an analysis method of degradation of polymeric material

This document provides a method for assessing the very early oxidative degradation state of polymers during outdoor weathering and indoor accelerated weathering tests and the influence of various additives can also be evaluated. This method is based on an analytical method in which the degree of progress of the oxidative degradation reaction of a polymer is sensitively detected by measurement of chemically induced ultra-weak photon emission (UPE).

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ISO 4765:2022 - Chemically-induced ultra-weak photon emission (UPE) — Measurement as an analysis method of degradation of polymeric material Released:4/1/2022
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INTERNATIONAL ISO
STANDARD 4765
First edition
2022-04
Chemically-induced ultra-
weak photon emission (UPE) —
Measurement as an analysis method of
degradation of polymeric material
Reference number
ISO 4765:2022(E)
© ISO 2022
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ISO 4765:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
© ISO 2022 – All rights reserved
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ISO 4765:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Measurement principle and its limitations ............................................................................................................................. 2

5 Sample ............................................................................................................................................................................................................................. 2

6 UPE measuring apparatus ......................................................................................................................................................................... 3

6.1 Composition of UPE apparatus body................................................................................................................................... 3

6.2 Composition of sample chamber............................................................................................................................................. 3

6.3 Installation environment for UPE apparatus .............................................................................................................. 4

6.4 Sensitivity check ................................................................................................................................................................................... 4

7 Measurement method .................................................................................................................................................................................... 5

7.1 UPE apparatus preparation......................................................................................................................................................... 5

7.2 Confirmation of normal operation of UPE apparatus .......................................................................................... 5

7.3 Measurement procedure ............................................................................................................................................................... 5

7.3.1 Setting of measurement condition ..................................................................................................................... 5

7.3.2 Measurement of background ................................... ................................................................................................ 6

7.3.3 Sample measurement ..................................................................................................................................................... 6

8 Display of measurement results ......................................................................................................................................................... 7

8.1 General ........................................................................................................................................................................................................... 7

8.2 Measurement in inert gas atmosphere ............................................................................................................................. 7

8.3 Measurement in oxidation accelerating atmosphere ........................................................................................... 8

9 Test report ...............................................................................................................................................................................................................10

Annex A (informative) Detection of oxidation deterioration by UPE measurement .....................................11

Annex B (informative) Examples of time courses of UPE of thermally oxidized polypropylene

(PP) for isothermal and non-isothermal measurement .........................................................................................16

Annex C (informative) Example of measurements of oxidation deterioration degree of

thermally oxidized polyethylene (PE) .......................................................................................................................................18

Annex D (informative) Example evaluation of oxidation induction time (OIT) .................................................20

Annex E (informative) Example of UPE of PP oxidized by accelerated weathering test ............................22

Bibliography .............................................................................................................................................................................................................................26

iii
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ISO 4765:2022(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.

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

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 61, Plastics, Subcommittee SC 6, Ageing,

chemical and environmental resistance.

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.
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INTERNATIONAL STANDARD ISO 4765:2022(E)
Chemically-induced ultra-weak photon emission (UPE) —
Measurement as an analysis method of degradation of
polymeric material
1 Scope

This document provides a method for assessing the very early oxidative degradation state of polymers

during outdoor weathering and indoor accelerated weathering tests and the influence of various

additives can also be evaluated.

This method is based on an analytical method in which the degree of progress of the oxidative

degradation reaction of a polymer is sensitively detected by measurement of chemically induced ultra-

weak photon emission (UPE).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purpose of this document, the following terms and definitions 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
ultra-weak photon emission
UPE

phenomenon of light emission observed when electrons are excited to at least one-level higher energy

level due to the energy produced by chemical reaction and then are deactivated from the higher energy

levels to the ground state

Note 1 to entry: UPE is often used synonymously with “chemiluminescence”. “Chemiluminescence” means

luminescence accompanied with a chemical reaction.
3.2
dark current value

numeric data measured in a state where the detection element is not irradiated with light

3.3
background

numeric data measured in a state where samples are not placed in a sample container

3.4
oxidation induction time
OIT

time when the emission intensity rapidly increases due to the disturbance of the equilibrium between

the generation rate and the disappearance rate of the peroxide produced in plastics

Note 1 to entry: The oxidation induction time varies according to the type of antioxidant, additive concentration,

measurement temperature, ageing status, etc.
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ISO 4765:2022(E)
3.5
gate time
duration over which the incoming photon flux of UPE is accumulated
Note 1 to entry: Typically values between 0,1 s and 10 s are chosen.
4 Measurement principle and its limitations

Ultra-weak photon emission (UPE), generated when peroxide formed in an oxidation reaction is

decomposed by heat or other stimulators, is measured with an apparatus using highly sensitive

photodetection elements (e.g. photomultiplier tube or CCD camera). The time course of UPE intensity is

indicated by a measurement of peak height, inclination, time, peak area, light emission image, etc. While

the UPE is proportional to the reaction rate of the chemiluminescent oxidation reaction (i.e. the kinetics

of the reaction), its time-integrated curve is proportional to the amount of oxidation products formed.

The details of the measurement of UPE of substances and the view of oxidation deterioration are given

in Annex A. Values given in Table 1 are reported as the emission wavelength range of emitting species

in general chemical reactions.
Table 1 — Emission wavelength range and peak wavelength of emitting species
[1]
(chemical material species) in general chemical reactions (example)
Emitting species Emission wavelength
3-aminophthalic acid 350 to 550 (425)
N-methyl acridone 400 to 600 (470)
Dibenzoylbenzoamide 520 to 590 (530)
O 420 to 720 (478, 634)
Excitation carbonyl 420 to 450 (530)
HCHO 300 to 600 (435)
NO 540 to 3 000 (1 200)
SO 250 to 400 (312)
The numerical values in parentheses indicate peak wavelength
(maximum wavelength).

The method is very useful to follow the ageing process of a polymer with the photon emission being

measured as a relative value of the oxidation products. However, the photon emission of the considered

material depends on a lot of effects, which can change during ageing and differ for various materials,

such as surface of the material and its absorption, or the depth from which photons reach the surface.

NOTE The method can be used to probe the residual stabilization or oxidation state of the material,

subsequent to a stepwise weathering exposure.

The method is a relative comparison method and cannot give an absolute measure of a materials ageing

status.
5 Sample

Weigh out 10 mg to 20 g of the sample with a weighing apparatus capable of measuring 1 mg at least.

Among samples all made of the same composition of plastics, choose samples that differ in either one

of the conditions (e.g. degree of deterioration, additive agent type or additive amount), and weigh out

the same mass of each sample. For a solid sample, the sample area shall also be the same. The shape,

dimension and mass of the sample shall be as agreed between the customer and the manufacturer.

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ISO 4765:2022(E)

Handle the sample with gloves, not with bare hands. Remove any soil on the sample entirely before

measurement.

NOTE Since UPE intensity is theoretically proportional to the surface area of a sample, the absolute value

of samples in the same shape can be compared among samples, but the absolute value of UPE for samples in

different shapes cannot be compared.
6 UPE measuring apparatus
6.1 Composition of UPE apparatus body

The body of the UPE measuring apparatus (hereafter referred to as UPE apparatus) shall be capable of

controlling the addition of heat to the sample and of selecting the atmosphere. For the temperature, the

UPE apparatus shall have the structure that allows to perform isothermal measurement and/or non-

isothermal measurement. For the light receiving section which detects UPE from the sample, highly

sensitive detection elements (e.g. photomultiplier and highly sensitive CCD camera) shall be used. The

detection element shall be capable of detecting the light emission of the peroxide under measurement.

Since the cooling of a detection element increases the sensitivity, the detection element should be cooled

down and kept lower than 0 °C. The sample chamber shall be located directly under the detection

element, and UPE shall be generated by decomposing the peroxide in the sample by heating. An example

of the composition of an UPE apparatus body is shown in Figure 1. The data processing device should be

capable of measuring light emission amount as a numerical value (e.g. light emission count value) and

of displaying the time-course of light intensity temporal change on a monitor display. Furthermore, for

a certain level of strong light incident on a detection element, the UPE apparatus shall have a function

of suspending the measurement by, for example, closing a shutter automatically for the protection of

the detection element. The measurement (upper) limit value of the detection element shall be set by the

detection element manufacturer or the UPE apparatus manufacturer.
6.2 Composition of sample chamber

The sample chamber shall consist of a gas inlet and outlet and a heating section, and the inside of the

sample chamber shall be sealed with an inner lid with an aperture plate. The aperture plate shall be

made of quartz glass normally, that does not inhibit light emission and have high permeability. The

sample container shall have a flat bottom and fixed open area. The sample container shall be made of a

material that has high thermal conductivity and very low level of light emission, such as stainless steel

and aluminium. The anticorrosion container such as a glass container and ceramic container may be

used depending on the measurement purpose. The sample chamber shall have a function of introducing

and discharging inert gas such as nitrogen and/or oxidation accelerating gas such as oxygen.

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ISO 4765:2022(E)
Key
1 photomultiplier tube (PMT) 7 inner lid with aperture plate
2 electron cooling 8 heating section
3 cooling water 9 gas introduction tube
4 sample chamber 10 gas exhaust tube
5 sample container 11 data processing
6 sample 12 shutter
Figure 1 — Composition of an UPE apparatus body (example)
6.3 Installation environment for UPE apparatus

The installation environment for an UPE apparatus shall have the following characteristics:

a) a place not exposed to direct sunlight (photo darkroom is recommended);

b) a place not exposed to strong ultraviolet radiation, electromagnetic waves or vibration;

c) a place where an UPE apparatus is not affected by dust, soot, etc. containing chemical agents;

d) a place where indoor temperature can be kept constant (about 20 °C to 25 °C is recommended);

e) a place where indoor humidity can be maintained constant (the humidity of about 45 % to 65 % is

recommended);

f) a place where the UPE apparatus can be installed far away from the air outlet of an air conditioner;

g) a place where a general precision analytical instrument is installed.
6.4 Sensitivity check
Regularly, there are two ways to check the sensitivity.
a) Sensitivity check of detection elements (e.g. PMT or CCD camera)

1) Prepare the calibrated source which should be as constant in its emission as possible over time

or its time dependence should be extremely well repeatable and reproducible and documented.

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ISO 4765:2022(E)

2) The calibrated source can be a material which shows UPE, or a ready assembled unit such as

LED elements with diffusion plate on top. Ideally, the calibration source should be in the range

of about the emission level(s) to be detected in the following measurements.
b) Sensitivity check for the UPE system [see 7.3.2 f)]

Measure UPE with an empty sample container and compare with the normal background level. The

check process should ideally start any new measurement series as for instance condensation products

from samples measured earlier can contaminate the optics and reduce the emission detected.

NOTE This sensitivity check, at least, allows making a semiquantitative comparison of measurements in

terms of relative amount of products formed (relative emission axis) within one sequence of sensitivity check

and subsequent measurement cycle.
7 Measurement method
7.1 UPE apparatus preparation

a) Start the cooling function of the UPE apparatus, if it is installed, and check that the circulation of

cooling water is working properly.
b) Start the UPE apparatus and wait until the detection element is stabilized.
7.2 Confirmation of normal operation of UPE apparatus

Measure the dark current value and confirm that the value is within the normal range specified by the

manufacturer.
7.3 Measurement procedure
7.3.1 Setting of measurement condition

Determine atmosphere, temperature, gate time and measurement time which are optimal for

measurement as follows.

a) Measurement atmosphere: Select the atmosphere of inert gas or oxidation accelerating gas.

NOTE 1 Typical inert gas is nitrogen or argon. The sample is not oxidized during the measurement in an

inert gas; therefore, the state of oxidation can be detected.

NOTE 2 Examples of oxidation accelerating gas are oxygen, air and ozone. In the oxidation accelerating

gas, the sample is oxidized during the measurement, then, the resistance to oxidation of the sample can be

evaluated.

The atmosphere may be changed during measurement according to the purpose. Certain type of

atmosphere gas can affect the heating control of the sample chamber.

b) Measurement temperature: Set the optimal temperature according to the measurement purpose

in consideration of the physical information (glass transition, melting, and decomposition

temperature) of a sample. The temperature shall be controlled by the following two methods,

which can be applied in combination.
1) Isothermal measurement: Maintain the temperature of the sample chamber at the

predetermined temperature beforehand and perform the measurement at the predetermined

temperature from the start until the end of the measurement.

2) Non-isothermal measurement: Perform the measurement while raising the temperature from

low temperature (around room temperature) to the predetermined temperature at a constant

rate (approximately 1 °C/min to 150 °C/min).
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ISO 4765:2022(E)

Measurement temperature should be as low as possible compared to the application conditions

of the sample material or correlation is lost. Especially, phase transitions and glass temperature

should not occur in the comparison of experiment’s temperature range and application temperature

range. On the other hand, this temperature level should be high enough to achieve a suitable signal

to noise ration of UPE.

c) Gate time: In general, it is set within 0,1 s to 10 s. When the emission intensity is low, it is better to

set longer, such as within 1 min to 5 min.

d) Measurement time: Set the time from the start of measurement of UPE until the end.

NOTE 3 When the measurement is performed in an inert gas atmosphere, light emission often reaches its

peak approximately in 5 min to 1 h.

NOTE 4 When the measurement is performed in an oxidation accelerating atmosphere, light emission

often reaches its peak in, approximately, several hours to several days.
7.3.2 Measurement of background
The measurement of a background shall be as follows.

a) When gas is used as measurement atmosphere, fill the sample chamber with the gas beforehand.

Change the gas flow rate according to the capacity of the sample chamber. The flow rate should

be measured and controlled, for example, 50 ml/min to 150 ml/min, for an about 40 ml sample

chamber.

b) For the isothermal measurement, set the temperature of the sample chamber to measurement

temperature, and wait until the temperature is stabilized at the preset temperature. For the non-

isothermal measurement, set the measurement start temperature, temperature rise rate and target

temperature, and wait until the temperature is stabilized at the measurement start temperature.

c) Set the gate time and measurement time. The measurement time should be the same as the time for

actual sample measurement.

d) When the temperature is stabilized, put an empty sample container into the sample chamber, and

close the inner lid with an aperture plate to seal the inside. When gas is used as measurement

atmosphere, a gas discharge monitor should be connected to the piping connected to the gas outlet.

e) Start the measurement.

f) When an abnormally high light emission is observed compared with the light emission amount

before measurement, the sample container or other parts could be soiled; therefore, clean the

surrounding of the sample chamber and exchange the sample container.
7.3.3 Sample measurement

a) Set the same measurement condition as the condition for background measurement.

b) Put the sample into the sample container, install the sample container in the sample chamber, and

attach the inner lid with an aperture plate.

c) When gas is used as measurement atmosphere, confirm that gas is surely charged into and

discharged from the sample container.
d) Start the measurement.

e) After the measurement, open the inner lid with an aperture plate using heat resistant gloves, and

take out the sample. Wash the inside of the sample chamber and the inner lid with an aperture

plate, if being soiled.

f) Check the measurement data (e.g. light emission count value, peak value, integrated value and light

emission after a lapse of a fixed time) of each sample.
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ISO 4765:2022(E)

g) When the measurement results indicate that the degree of oxidation deterioration has not been

evaluated as intended, re-examine the temperature condition and atmosphere condition, and

repeat the measurement from the beginning.

NOTE 1 The measured UPE intensity includes the background. Therefore, the UPE intensity from the sample is

the intensity obtained by subtracting the background from the measured value of UPE intensity.

NOTE 2 When a sample absorbs light, the result with an unoxidized sample can be used as background data.

8 Display of measurement results
8.1 General

The measurement temperature condition (isothermal measurement or non-isothermal measurement)

and the atmosphere condition (inert gas atmosphere or oxidation accelerating atmosphere) inside

the sample chamber are set, and the emission intensity is measured. Then, the measurement results

are displayed. The time-course of emission intensity is illustrated in 8.2 and 8.3. Examples of UPE

measurement of polypropylene (PP) and polyethylene (PE) materials are given in Annex B and Annex C.

Examples of measurement of OIT of PP materials with different antioxidant concentration are given in

Annex D. Examples of UPE measurement of PP oxidized by an accelerated weathering test are given in

Annex E.
8.2 Measurement in inert gas atmosphere

a) Non-isothermal measurement: The emission intensity generally changes with passage of time as

shown in Figure 2. Light is emitted when the temperature reaches the point where peroxides or

other components in a sample react.
Key
X time
Y1 emission intensity
Y2 temperature
1 emission intensity curve
2 sample chamber temperature
Figure 2 — Time course of emission intensity for non-isothermal measurement
in inert gas atmosphere (example)

NOTE 1 The peak can appear more than once due to two or more components contained in a sample

which react at different temperatures. Phase change such as crystallization, melting and phase separation of

the sample, viscosity change, are the other causes of multiple peaks in the non-isothermal measurement.

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ISO 4765:2022(E)

b) Isothermal measurement: The emission intensity generally changes with passage of time as shown

in Figure 3. The light emission is derived from the peroxide which exists in a sample, and the

light emission amount is equivalent to the degree of oxidation deterioration at the time of start

of measurement. After the light emission amount reaches its peak, it decreases. For a sample of a

thin film which conducts heat quickly, the light emission peak may appear before measurement.

In this case, the measurement temperature is required to be re-examined, such as lowering the

measurement temperature, for example.
Key
X time
Y1 emission intensity
Y2 temperature
1 emission intensity curve
2 sample chamber temperature
Figure 3 — Time course of emission intensity for isothermal measurement
in inert gas atmosphere (example)

NOTE 2 From the peak(s) in non-isothermal measurements, the information of the temperature range at which

the chemical reactions related with UPE becomes dominant can be obtained. Referring to this peak temperature

in non-isothermal measurement, it is possible to determine the temperature of isothermal measurement.

8.3 Measurement in oxidation accelerating atmosphere

a) Non-isothermal measurement: With this measurement, the information of the temperature of the

oxidation initiation is obtained. A typical emission intensity change with passage of time is shown

in Figure 4.

NOTE 1 The peak can appear more than once due to the multiple components contained in a sample

which react at different temperatures. Phase change such as crystallization, melting and phase separation of

the sample, and viscosity change with temperature rising can be also the cause of multiple peaks.

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ISO 4765:2022(E)
Key
X time
Y1 emission intensity
Y2 temperature
1 emission intensity curve
2 sample chamber temperature
Figure 4 — Time course of emission intensity for non-isothermal measurement
in oxidation accelerating atmosphere (example)

b) Isothermal measurement: The emission intensity generally changes with passage of time as

shown in Figure 5. The first light emission peak is achieved by the same factors as in the case of

the measurement in inert gas atmosphere. After the generation rate and disappearance rate of the

peroxide produced in the sample are kept in equilibrium for some period of time, the equilibrium

is broken, and the emission intensity increases rapidly. The emission intensity in equilibrium

indicates the stability of materials and the effectiveness of the stabilizer added.

For some cases, a rapid increase of emission is observed before a distinct equilibrium. In that case

the measurement conditions should be re-examined to catch OIT clearly.

NOTE 2 OIT indicates the ease of oxidation and the effectiveness of a stabilizer and is used as an index for

predicting the end of life cause
...

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