uv weathering

8/12/2019 Uv Weathering

http://slidepdf.com/reader/full/uv-weathering 1/12

UV Weathering and Related Test Methods



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

2



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.



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%



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)



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).



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

9



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



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.

11



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

uv weathering

Documents