T 5 dupont ( mr. shirish)
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Assessing Coatings Durability Assessing Coatings Durability via COvia CO22 Generation RatesGeneration RatesAn Alternative Rapid Test of Paint Durability
DuPont Titanium TechnologiesS.Daptardar, Michael P. Diebold30 January, 2011
DUPONT CONFIDENTIAL
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AbstractAbstract
�Coating durability is of high importance in most outdoor applications.
�Durability must, therefore, be assessed and accurately characterized
�Existing Test Methods are either time consuming or having poor correlation to actual
outdoor results.
�A new accelerated test that relies on UV exposure conditions typical of exterior
exposures.
�With a focus on the effect of TiO2 pigment grade on paint durability.
�With better correlation to exterior results than longer term accelerated tests.
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Agenda
• Effect of TiO2 on paint durability• Paint durability test strategies• Using [CO2] to monitor paint degradation
– Development of the technique
– Effect of exposure conditions
• Conclusions
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Binder Degradation MechanismsPhotocatalytic:
TiO2 + UV light mostly heat, some radicals
radicals + binder degradation products
Direct:
UV light + binder degradation products
Thermal degradation also occurs
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The TiO2 Durability Balance
Protection fromDirect Degradation
Destruction fromPhotocatalytic Degradation
The balance depends on the grade of TiO2 and the resin chemistry
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Existing Test Methodologies
Conditions
Real
Artificial
Actual Degradation
Secondary Reaction
Response
Outdoor Exposures
Accelerated Exposures
Lab Tests
AppearanceChange
SecondaryEffect
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Outdoor ExposureDescription:
– Expose paints under natural conditions
Advantages:
– Measures the changes of interest (appearance) under the conditions of interest (ambient)
Disadvantages:
– Very slow (years to decades)
– Slowest for paints of the most interest (superdurable)
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Accelerated ExposureDescription:
– Expose paints under high UV light conditions
Advantages:– Measures the changes of interest (appearance)
– Quicker than traditional exterior exposure
Disadvantages:– Relatively slow (weeks to months)
– Does not measure reaction under conditions of interest
• Degradation occurs via complex reaction chains, and increased light intensity affects each reaction rate differently
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Lab TestsDescription:
– Measure non-appearance (physiochemical) changes to paint on exposure
– Often under intense (accelerated) conditions
Advantages:– Fast (hours to days)
Disadvantages:– High intensity (accelerated) conditions
– Measures a property that is of no interest to the paint consumer
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Existing Test Methodologies
Conditions
Real
Artificial
Actual Degradation
Secondary Reaction
Response
Outdoor Exposures
Accelerated Exposures
Lab Tests
New Approach
AppearanceChange
SecondaryEffect
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Monitor the Formation of Carbon Dioxide
– Flexibility – CO2 is the eventual degradation product for all organic resins
– Unambiguous - Does not further react• High concentrations can only mean fast degradation
– Manifests quickly (hours to days)• Even under ambient conditions – no need for high
intensities• Therefore maintains proper balance of different
degradation reactions.
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Experimental Set-up - Lab
“Full Spectrum” fluorescent lighting
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Effect of Liquid Water
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
1 2 3 4 5
ml water added
CO
2 A
mo
un
t (A
rbit
rary
Un
its)
0.25 0.5 0.75 1.00.0
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Effect of Pigment Durability
R2 = 0.9288
4000
4500
5000
5500
6000
6500
7000
7500
8000
0 5 10 15 20 25 30 35 40
Chalk/Fade Value
[CO
2] p
pm
One week exposure to Summer Sunlight
Approximately 1.5x rate seen in lightbox
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7 Day Comparison of 3 Paints
0
50000
100000
150000
200000
250000
A B C A B C A B C
Co
un
ts
Paint A Paint B Paint CPigment
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Effect of Light Intensity
0
500
1000
1500
2000
2500
3000
3500
4000
0 1 2 3 4 5 6 7 8
Day
[CO
2] (
ppm
)low durability pigment 0.5 intensity
low durability pigment 1.0 intensity
low durability pigment 2.0 intensity
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Conclusions• CO2 evolution rate from paint film
degradation, under ambient conditions, is a simple, useful predictor of TiO2 grade durability performance.– Method appears general since most paints
ultimately degrade to CO2 and H2O– A number of options for exposure and CO2
detection
• This technique can also be used to probe the degradation mechanism
DUPONT CONFIDENTIAL
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Thank You