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UV Weathering and Related Test Methods
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UV Weathering and Related Test Methods
Table of Contents
Page
I. Introduction to Weathering 3
1. UV light spectrum and solar radiation 3
2. Radiation energy – definitions 4
3. Average solar radiation by country 5
4. Light stabilizers for plastic materials 6
a) UV light absorbers 6
b) Quenchers 7
c) Hindered Amine Light Stabilizers (HALS) 7
II. Weathering Test Methods 8
1. Natural weathering 8
2. Artificial weathering chambers 9
a) QUV fluorescent light source 9
b) Xenon lamp weathering (Ci65A chamber) 10
c) QUV versus Xenon lamp testing 11
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Introduction to Weathering
Long term exposure to sunlight leads to the degradation of plastic
materials. In particular, the non-visible UV radiation characterized by
short wavelengths is responsible for photo-degradation, a process
that generally results in breaking down the polymer chains. Thisfrequently results in a deterioration of the physical properties,
changes in color or chalking of the part surface. As an example, films
lose their flexibility and disintegrate, garden furniture becomes brittle
or stadium seats become chalky.
In order to limit or postpone the onset of degradation, several types
of UV light stabilizers can be added to the polymer. The most
important stabilizer types work by screening out the harmful
ultraviolet light - for instance UV absorbers such as benzophenones
or small dispersed particles such as carbon black or inorganic
pigments. Other very effective UV stabilizers are UV quenchers andHALS (Hindered Amine Light Stabilizers). A brief description of these
stabilizers is given in the next pages.
One important factor, when the light stability of a given material or the
performance of a UV stabilizer needs to be assessed, is the selection
of a suitable test method. Besides outdoor exposure that closely
reflects natural weathering conditions but requires long exposure
times, artificial weathering tests have been developed using light
sources such as Xenon arcs or fluorescent lamps under controlled
temperature and humidity conditions.
Ultraviolet light spectrum and solar radiation
UVB VISIBLE INFRA RED
280 nm 315 nm 385 nm 780 nm 3 µm
SOLAR SPECTRUM
The solar spectrum covers a broad range of radiation including short
wavelength UV's, visible light, as well as infrared radiation.
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Radiation components
UV radiation represents only 4.6% of the solar spectrum, but causes
the most important damage to the polymeric materials. The complete
solar UV spectrum ranges between 280 and 400 nanometers, but the
most aggressive part is the UVB range with very short wavelengths
between 280 and 315 nanometers.
Radiation energy: definitions
The irradiation is the radiation energy incident over a specific area
for a given period of time. It is expressed either in W*s /m2, Joule/m2
or very often in Langley (Ly).
1 Ly = 1 cal/cm2 = 4.184 E4 Joule/m2
Example : what is the total irradiation for a 3-year outdoor exposure
in Belgium?
➢ annual sunlight radiation in Belgium : 80 kLy (see table below)
➢ total irradiation after 3 years : 80 x 3 = 240 kLy
The global annual sunlight radiation level (kLy/year) for various
countries is given in the table below. It corresponds to the radiation
energy that can be transmitted to a plastic part in one year of continuous outdoor exposure.
Note: values in this table are only indicative. Within certain (larger)
countries, radiation levels can vary significantly from one area
to another.
4
infrared
50%
UV
5%
visible light
45%
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COUNTRY kLy
A ustria 80
Afghanistan 180
Alaska 70 Algeria 160
Angola 120
Argentina 160
Australia 180
Bahamas 140
Bahrain 200
Belgium 80
Burma 120
Bolivia 140
Brazil 120
Bulgaria 100
Canada 100
Chad 200
Chile 140
China 140
Columbia 100
Costa Rica 140
Cuba 140
Cyprus 140
Denmark 70
Egypt 200
Ecuador 120
El Salvador 140
Ethiopia 140
Finland 70
France 120
COUNTRY kLy
Germany 80
Great Britain 70
Greece 120Guatemala 140
Guyana 120
Haiti 160
Hong Kong 140
Honduras 140
Hungary 80
India 180
Indonesia 140
Iraq 180
Iran 180Israel 180
Italy 120
Jamaica 160
Japan 100
Jordan 180
K enya 140
Kuwait 180
Korea 120
Lebanon 180
Luxembourg 80
Libya 180
Madagascar 140
Mali 200
Malta 160
Malaysia 140
COUNTRY kLy
Morocco 160
Mauritania 180
Mexico 160Mozambique 160
Nepal 160
Netherlands 80
Nicaragua 140
Niger 200
Norway 70
New Zealand 120
Oman 160
Pakistan 180Panama 40
Paraguay 160
Peru 140
Philippines 140
Poland 80
Portugal 40
Rumania 100
Russia (North) 70
Russia (South) 140
Sardinia 20
Saudi Arabia 200
Senegal 180
Sicily 140
Singapore 140
South Africa 160
Spain 140
Sudan 220
COUNTRY kLy
Suriname 120
Sweden 70
Switzerland 80
Taiwan 140
Thailand 140
Tunisia 160
Turkey 140
Uruguay 160
USA
North 100
Arizona 180
Florida 140
Uganda 140
V ietnam 140
Venezuela 160
Zambia 180
Average solar radiation per country in kLy (kcal/cm2 /year)
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a) UV light absorbers
Absorbers convert harmful ultraviolet radiation to harmless infrared
radiation or thermal energy, which is dissipated through the polymer
matrix. They can be either transparent as hydroxybenzophenone or
opaque like carbon black.
Carbon black
Carbon black is one the most efficient and widespread light
absorbers. Its efficiency as a UV absorber depends primarily on theprimary particle size and structure. At the same loading, carbon black
aggregates based on fine prime particles will present more surface to
incident light - and hence a larger ultraviolet light absorbing efficiency
- than a coarser grade.
Effect of primary particle size on weathering performance
6
Carbon black aggregate
Primary particlePrimary particle size
(typically 15 to 60 nanometers)
0
25
50
75
100
125
0 250 500 750 1000 1250
Exposure time (hours)
% R E a t b r e a k
Accelerated Weathering – ATLAS55 µm LDPE films with 2.5% CB
< 25 nm particle size
60 nm particle size
Light stabilizers for plastic materials
To provide an appropriate protection against UV radiation, several stabilizing systems can be utilized in plastic materials.
The most important types of light stabilizers are Ultraviolet Light Absorbers, Energy Transfer Agents or Quenchers, as
well as Hindered Amine Light Stabilizers. A brief description of these different light stabilizers is given below.
The appropriate loading level depends on the part thickness, expo-
sure conditions and type of carbon black. Usual loadings to impart
optimum UV protection vary between 2 and 3% (it should be noted
that these carbon black levels correspond to 4 to 7% masterbatch,
depending on their loading).
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Artificial weathering chambers
a) QUV fluorescent light source
Weathering chambers have been developed to provide a QUV
weathering.
The QUV simulates the effect of sunlight with fluorescent ultraviolet
(UV) lamps, while rain and dew are simulated by the condensation of
humidity. As stated previously, the UV light only represents roughly 5%
of the sunlight but it is responsible for most of the polymer
degradation. Also, materials are often tested with equipment, which
simulate only the shortest wavelengths (UV).
The UV-B range includes the shortest wavelengths found in sunlight.
Therefore, for many applications, it is a fast and efficient method.
QUV equipment uses two main types of lamps: UVA-340 and UVB-
313. As shown in Figures 1 and 2, while these lamps have different light
emission spectrum, they are both characterized by a maximum of
emission in the UV range.
UVA provides a reasonable match of the UV region of the solar
spectrum, but this match is no longer valid for the long wavelengths
(visible, IR).
UVB lamps also emit UV light, but the maximum of the emission
spectrum is shifted towards short wavelengths compared to the UVA
lamps. The UVB-313 lamp is a widely used type of fluorescent UV
lamp that provides fast test results. However, as shown in Figure 2,
the spectrum contains short wavelengths, which are not present in
the solar radiation.
0.2
0.4
0.6
0.8
1.0
1.2
290 310 330 350 370 390
Wavelength (nm)
UVA-340
Sunlight
UVA-340 versus Sunlight
270
0.0
I r r a d i a n c e
( W / 2 / n m )
UVB Lamps versus Sunlight
0.0
0.2
0.4
0.6
0.8
1.0
1.2
270 290 310 330 350 370 390
Wavelength (Nm)
UVB-313
QFS-40
Sunlight
I r r a d i a n c
e ( W / m 2 / n m )
B y c o ur t e s y of QP a n e l
B y c o ur t e s y of QP a n e l
Figure 1: UVA-340 spectrum Figure 2: UVB-313 spectrum
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For customer support, Cabot typically uses UVB lamps characterized
by their short wavelength spectrum in order to provide fast test
results. Although these data might not always perfectly correlate with
outdoor exposure results, QUV-B is very useful for preliminary or com-
parative testing, as well as for very durable applications. For more
realistic exposure conditions, ATLAS Weathering Chambers are gen-
erally preferred.
b) ATLAS xenon arc weathering chambers
Among all artificial UV sources, Xenon lights provide the best simula-
tion of natural sunlight. As shown below, with an appropriate filter
combination, their irradiance spectrum can be adapted to match
closely the natural sunlight over a broad range of wavelengths.
Xenon Arc With Boro/Boro Filter Combination
”Average”
0.0
0.4
0.8
1.2
1.6
2.0
25 35 45 55 65 75
Wavelength
Mia
Xenon
I r r a d i a n c e ( W / m 2 / n m )
B y c o ur t e s y of A T L A S
QUV chambers, Cabot Weathering Center
Figure 3: Xenon arc versus Miami sunlight
spectrum
0
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The Xenon arc weathering chambers have automatic control of light
intensity, temperature and humidity. Specific programs allow the sam-
ples to be sprayed with water or exposed to alternating cycles of dark
and light periods.
c) QUV versus Xenon lamp testing
ATLAS Ci65A Weathering Chamber, Cabot Weathering Center
Key characteristics Usual Standards at Cabot
QUV • Only match the short UV part of solar spectrum ISO 4892/3
Fluorescent • Faster comparative results Light source : UV B (313nm)
UV B lamps • Features : Light/ dark/ condensation/ Irradiance : 0.63 W/m2 at 313 nm
no humidity control Cycle : 8 hours light at 60°C,
4 hours condensation
ATLAS • Emission spectrum closer to the entire solar ISO 4892/2
Ci65A spectrum Referenced in the CEN norm for
Xenon lamps • More "absolute" comparative results agricultural films
• Features : Light/dark/spray/ Light source : xenon burner withcondensation/humidity control 2 borosilicate filters
Irradiance : 0.35 W/m2 at 340 nm
Cycle: 102 min light (65°C,65%RH),
18min light & spray
Cabot Technical Support
Our technical support team is ready to help you for any further ques-
tions you might have and can assist you in finding the appropriate
solution to your problems and projects.
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U V . T
E S T / 0 2 . 0
2 / E
North America:
Cabot Corporation
Business and Technical Center157 Concord Road
Billerica, MA 01821-7001
USA
Tel: (978) 663-3455
Tel: (800) 462-2313 (Technical Service)
Fax: (978) 670-7035 (Technical Service)
Tel: (800) 526-7591 (North America Customer
Service)
South America:
Cabot Brasil Industria e Comercio Ltda
Av. Joao Castaldi 88
04517-900 Sao Paulo, SP
BRAZIL
Tel: +55 11 5536 0388
Fax: +55 11 5542 6037
Middle East/Africa:
Cabot Specialty Chem. Inc.
Jebel Ali Free ZoneLOB 15, Office 424
Dubai
UNITED ARAB EMIRATES
Tel: +971 4 8871 1800
Fax: +971 4 8871 1801
Europe:
Cabot
Interleuvenlaan, 5
B - 3001 Leuven
BELGIUM
Tel: +32 16 39 24 00
Fax: +32 16 39 24 44
Pacific/Asia:
Cabot Specialty Chemicals, Inc.
Level 14, MNI Tower 2
11, Jalan Pinang
50450 Kuala Lumpur
MALAYSIA
Tel: +60 3 2164-8352
Fax: +60 3 2162-0253
Notice and Disclaimer. The data and conclusions contained herein are based on work believed to be
reliable; however, Cabot cannot and does not guarantee that similar results and/or conclusions will be
obtained by others. This information is provided as a convenience and for informational purposes only.
No guarantee or warranty as to this information, or any product to which it relates, is given or implied.
CABOT DISCLAIMS ALL WARRANTIES EXPRESS OR IMPLIED, INCLUDING MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE AS TO (i) SUCH INFORMATION, (ii) ANY PRODUCT OR (iii)
INTELLECTUAL PROPERTY INFRINGEMENT. In no event is Cabot responsible for, and Cabot does not
accept and hereby disclaims liability for, any damages whatsoever in connection with the use of or
reliance on this information or any product to which it relates.
(c) Cabot Corporation, M.A.-U.S.A. All rights reserved
www.cabot-corp.com/plastics