Introduction to polymer weathering.

1. KEJ4604 POLYMER AND
ENVIRONMENT
SEM II 2015/2016
Group 1
Ooi Chi Kuan
(UK30787)
Wong Yee Mun
(UK29652)
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2. INTRODUCTION
 The aging of natural and artificial polymeric materials is
a natural phenomenon in polymer products.
 Main environmental parameters influencing the
degradation of polymeric materials:
1. Solar Radiation
2. Temperature
3. Moisture
4. Oxygen.
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3. SOLAR RADIATION
 Physical changes resulting from exposure to the
environment are initiated by chemical bond breaking
reactions caused by the absorbed light.
 The ultraviolet portion of solar energy, with the shortest
wavelengths often having the greatest effect.
 Solar absorptivity is closely related to color, thus
samples of different colors will reach different on-
exposure temperatures.
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4. SOLAR RADIATION
 Short wavelength UV radiation causes yellowing; long
wavelength UV is primarily responsible for degradation
of physical properties, such as tensile strength and
impact strength.
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5. SOLAR RADIATION
 This is because short wavelengths are more strongly
absorbed by most materials, have a greater effect on the
layers close to the surface and cannot penetrate as far
into the material as the longer wavelengths.
 Longer wavelengths penetrate more deeply into
materials, where the physical property changes occur.
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6. TEMPERATURE
 At high temperatures molecules have greater mobility.
 The rate of oxygen diffusion increases and free radical
fragments formed in primary photochemical processes
are more readily separated.
 The chance of recombination is reduced and secondary
reactions are promoted.
Drops in temperature can cause water to condense on
the material as dew, a rise in temperature causes
evaporation, and sudden rainfall can cause thermal
stress.
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7. MAIN DEGRADATION MECHANISMS OF EVA (CO-POLYMER OF
ETHYLENE & VINYL ACETATE) INDUCED BY UV &
TEMPERATURE
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8. MOISTURE
 Moisture, in combination with solar radiation,
contributes significantly to the weathering of many
materials
Moisture participates both physically and chemically in
degradation.
 Mechanical stresses imposed when moisture is
absorbed or desorbed and to the chemical participation
of moisture in the chemical evolution cause weathering
 The span of time over which the precipitation occurs
and the frequency of wetness are important in the
weathering of materials20/3/2016

9. MOISTURE
 Water absorption in the surface layers produces a
volume expansion which places mechanical stress on the
dry subsurface layers.
 Drying out of the surface layers would lead to a volume
contraction.
 The hydrated inner layers resist this contraction, leading
to surface stress cracking.
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10. ATMOSPHERIC OXYGEN
 Photooxidation occurs when solar radiation combines
with oxygen.
 Free radicals, formed as a result of the cleavage of
chemical bonds by solar radiation, react with oxygen to
form peroxy radicals that initiate a series of radical chain
reactions.
The extent of photochemical reactions involving oxygen
differ in the inner and outer layers of both aromatic and
aliphatic polymers due to their dependence on the
diffusion of oxygen through the polymer.
Photooxidation is significantly reduced at depths beyond20/3/2016

11. 20/3/2016
Mechanisms of photooxidation:

12. SECONDARY FACTORS OF
WEATHERING
 Ozonolysis typically results in stiffening and cracking,
particularly under mechanical stress.
Atmospheric pollutants such as sulphur dioxides + solar
radiation + oxygen = crosslinking of polyethylene and
polypropylene & rapid loss of color in pigmented
coatings
Moisture + temperature = microbial growth, may cause
material degradation.
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13. WEATHERING TESTING OF
POLYMERS
 The controlled polymer degradation and polymer
coating degradation under lab or natural condition.
Weathering
Test
Natural
Laboratory-
Accelerated
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14. NATURAL WEATHERING
 The result of exposure of a material in its actual indeed
location and orientation.
 On fixed angle racks in locations and orientations that
maximize the effect of weathering.
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15. Natural
Exposure
“Static”
Exposure
“Dynamic”
Exposure
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16. “STATIC” EXPOSURE TEST
 Fixed position
 Variables:
 Tilt angle
 Unbacked or backed exposure with various type of backing materials
 Under glass exposure
 Additional wetting
 45° angle facing toward the equator is the most widely
used.
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17. “DYNAMIC” EXPOSURE TEST
 Sample orientations are changed during the test
 Sun is tracked
 To further optimize the annual radiant exposure,
temperature, and moisture delivery to specimen.
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18. ACCELERATED NATURAL
WEATHERING
 To speed up the weathering process while still using
natural weather condition.
 Techniques that further increase:
Temperature
Solar irradiance
Moisture
Some combination of these features
 Repeated testing during different seasons and over a
period of at least 2 years is recommended.
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19. ACCELERATED NATURAL
WEATHERING
Black-Box Exposure:
To simulate the air heatsink characteristics of an automotive body.
Black-Box under-Glass Exposure:
To simulate and accelerate the effect of interior automotive
condition.
Fresnel Reflector Solar Concentrator:
Maximum acceleration of aging processes in outdoor weathering, by
exposure on a Fresnel-reflector panel rack that provides high
intensity solar radiation.
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20. LABORATORY-ACCELERATED
WEATHERING/ARTIFICIAL WEATHERING
Accelerated through the use of specially designed
weathering chamber.
To determine in a short time the effects of natural
exposures over prolonged period.
Under controlled and consistent test conditions.
Useful in research and development of new polymeric
formulations and also used for quality control and
specification testing.
20/3/2016 UV Accelerated Weathering Tester

21. LABORATORY-ACCELERATED
WEATHERING
Fluorescent Ultraviolet Devices
Predicts the relative durability of materials exposed to
outdoor environments.
Developed with spectral distributions in the UV region.
Deficient in long wavelength UV radiation, but higher
energy
Not suitable for testing materials that are sensitive to these
spectral regions.
Often caused reversals in stability rankings of polymers and
error in the performance of stabilizers compared with
outdoor test.
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UVTest® Fluorescent / UV Instrument

22. LABORATORY-ACCELERATED
WEATHERING
Xenon Arc Devices
 Properly filtered xenon arc is more closely simulates
terrestrial solar radiation in both the UV and visible
regions than any other artificial test source.
 Two systems: air cooled & water cooled.
 Includes temperature control & moisture provided.
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Rotating rackFlat bed

23. LABORATORY-ACCELERATED
WEATHERING
Metal Halide Lamps
A relatively good simulation of terrestrial solar radiation
in the UV region above 300nm.
High efficiency and low infared output, eliminates the
need for water cooling.
Ideally suited for use in large-scale multiple source
arrays and are effective in thermal loading studies.
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24. REFERENCES
1. Griffini, G. and Turri, S. (2016), Polymeric materials
for long-term durability of photovoltaic systems. J.
Appl. Polym. Sci., 133, 43080, doi:
10.1002/app.43080
2. http://www.q-lab.com/applications/paints-coatings/
3. http://atlas-mts.com/products/product-
detail/pid/238/
4. Searle, N. D., McGreer, M. and Zielnik, A. 2010.
Weathering of Polymeric Materials. Encyclopedia of
Polymer Science and Technology.
5. Wikipedia-Factors of polymer weathering. Retrieved
from
https://en.wikipedia.org/wiki/Factors_of_polymer_we
athering (18 March 2016)
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