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SPECTROSCOPIC ANALYSIS OF ARCHITECTURAL COATINGS FOR IMPROVED WEATHERING
Karl Booth
Western Coatings Show
October 23, 2019
Exterior Product Development Pain Points
Formulation & Stability
3 months
QUV evaluation/ qualifications
3+ months
Exterior exposure & Validation
24+ months
Exterior Exposure
• Gold standard for product validation
• Dirt pickup• Grain crack• Adhesion• Gloss retention• Mildew
• Disadvantages• Multi-year investment• Variability within and
between studies
EPS Exposure Progam
Los Angeles, CA Marengo, IL Ft Myers, FL
Climate: Dry-Subtropical• Dirt Pickup Resistance• Gloss Retention
Climate: Continental• Grain-Crack Resistance• Chalk Adhesion• Alkaline Substrates
Climate: Subtropical Savanna• Gloss Retention• Mildew Resistance
Exposure Study for Gloss Retention
Main objectives:1. Identify the conditions that are most
challenging to gloss retention performance.
2. Identify conditions that are most stable, consistent and reproducible.
Polymer Substrate Location Color
1 Primed Aluminum California White
2 Primed Cedar Florida Yellow Oxide
3 Galvanized Illinois Lamp Black
4 Primed Hardie
5 Bare Aluminum
6 SYP
7
Paints were all <50 g/L and adjusted to pass LTC 972 individual panels 3,400 readings taken over 6 months
Exposure Study for Gloss Retention
Location Selection• Florida shows the largest
variation, highest mean• California shows lowest gloss
• Gloss evaluated both washed & unwashed
• Dirt pickup responsible for gloss reduction
Sample Mean Std. Dev Grouping
California 17.2 3.7 A
Florida 36.7 7.3 B
Marengo 30.0 6.1 C
60o
Glo
ss -
6 M
onth
s
Florida ILCalifornia
Location
Exposure Study for Gloss Retention
• Substrate Selection• Dimensionally stable types
showed lowest Std. Dev• Primed aluminum & cement
board were most consistent
60o
Glo
ss -
6 M
onth
s St
d D
ev
Primed Aluminum
Primed Cedar
Primed Galv.
Primed Hardie.
SYP
Substrate
Sample n Mean Std. Dev Grouping
SYP 162 3.1 2.0 A
PrimedCedar 143 2.0 1.4 B
PrimedHardie 107 1.8 1.1 B C
Primed Galvanized 108 1.6 1.6 B C
PrimedAluminum 108 1.4 1.1 C
Primed Aluminum, Florida Selected
Std. Dev. 60o Gloss at 6 Months Exterior Exposure
Accelerated Approaches
• QUV-A (340nm)• Industry Standard for coatings• 8hr UV, 4 condensation; 60/50oC• Mimics higher energy portion of solar
radiation, 340nm
• Xenon Arc (290-800)• Stronger match for full range solar
radiation• Less common than QUVA
• QUV-B (313nm)• Highest energy wavelength, 313nm• Typically only used for extremely
durable materials
Onset of Gloss Loss in Cyclic Testing
• High performance architectural coatings tend to maintain constant gloss over a period of time
• After a exposure, sufficient UV induced degradation has occurred that film erosion and roughness is detectable by gloss measurement
• It is important to validate QUVA with true exterior weathering 0
10
20
30
40
50
60
70
80
90
0 500 1000 1500 2000 2500
60 G
loss
Uni
ts
Hours
QUVA
Relating QUV to Exterior Exposure
0
10
20
30
40
50
60
0 1000 2000 3000 4000 5000
60 G
loss
Hours
Cyclic QUVA
White
Black
Yellow Oxide
0
10
20
30
40
50
60
0 2 4 6 8 10 12 14 16 18 20
60 G
loss
Months
Florida Exposure – Primed Aluminum
Modes of UV-Degradation
γ-Lactone - 1780cm-1
Ketone - 1710cm-1
Carboxy Acid - 1705cm-1
Ester - 1735cm-1
-CH3OH
-β Scission
Chiantore, O., L. Trossarelli, and M. Lazzari. “Photooxidative Degradation of Acrylic and Methacrylic Polymers.” Polymer 41, no. 5 (March 2000): 1657
O2H2O
Functional Group Analysis
• ATR-FTIR allows semi-quantitative analysis of film degradation
• Relating C-H to C=O demonstrates trends in degradation
• ∫ 1600−1800𝑐𝑐𝑐𝑐−1
∫ 2800−3050𝑐𝑐𝑐𝑐−1=
• Comparing changes in index between samples predicts relative degradation rates
C-H= Carbonyl
Index
C-H
- The change in index predicts the relative rate of oxidative polymer degradation
QUVA and Carbonyl Index
0
1
2
3
4
5
6
Polymer 1 Polymer 2 Polymer 3 Polymer 4
1w C
arbo
nyl I
ndex
Del
ta
0102030405060708090
100
0 500 1000 1500 2000 2500 3000
60 G
loss
Hours
Polymer 1
Polymer 2
Polymer 3
Polymer 4
- Carbonyl index run on a polymer series at 0 and 7 days cyclic exposure
Delta Carbonyl Index by Polymer
Cyclic QUVA Gloss
QUVA and Carbonyl Index
0
1
2
3
4
5
6
Polymer 1 Polymer 2 Polymer 3 Polymer 4
1w C
arbo
nyl I
ndex
Del
ta
y = 5.3024e-0.002x
R² = 0.9977
0.1
1
10
0 200 400 600 800 1000 1200 1400 1600 1800 2000
1 w
eek
Carb
onyl
Inde
x
Critical Failure Hour
0102030405060708090
100
0 500 1000 1500 2000 2500 3000
60 G
loss
Hours
Polymer 1
Polymer 2
Polymer 3
Polymer 4
Delta Carbonyl Index by Polymer
Cyclic QUVA Gloss
Accelerating Development
Experiment• Replace primary monomer in polymer 1
with 3 alternatives, maintain Tg
• Expose to standard QUVA testing
• Evaluate carbonyl index at regular intervals0
0.05
0.1
0.15
0.2
0.25
0.3
Monomer 1 Monomer 2 Monomer 3 Monomer 4
24h
Carb
onyl
Inde
x De
lta
Carbonyl Index of Monomer Replacements
0
20
40
60
80
100
120
140
0 500 1000 1500 2000 2500 300060
Glo
ssHours
Gloss Retention of Monomer Replacements
Monomer 1
Monomer 2
Monomer 3
Monomer 4
Results• Carbonyl Index provides early indication of
polymer performance
• Tight formulation control allows for strongest predictive power
Cyclic QUVA vs. Alternative Exposures
• UV-only highlights the positive side of UV exposure, crosslinking, which can increase gloss
• Cyclic QUVA involves both a UV step and a humidity step, so it is valuable to determine their individual impacts
• The combination of UV and condensation provides a severe change in gloss behavior
• Humidity exposure (Cleveland) can also severely impact gloss, but carbonyl indexing is insensitive to this mode of failure
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Paint 1 Paint 2 Paint 3 Paint 4 Paint 5 Paint 6 Paint 7 Paint 8 Paint 9 Paint10
Paint11
Paint12
Delta
Car
bony
l Ind
ex
Delta Carbonyl Index by Method @1000hrs
Cyclic2/3 UV-Only1/3 Humidity Only
0
20
40
60
80
100
120
140
160
0 1000 2000 3000 4000 5000
20 G
loss
Per
cent
age
Hours
CyclicUVHumidity
Paint 1: Gloss vs Time
Summary
• Understanding the fundamentals of weathering is pivotal to developing innovative and differentiated technology
• ATR-FTIR allows for the characterization of UV degradation at a molecular level, and gives early predictions of polymer performance where carbonyl functionality is changing
• The study of separate UV or humidity cycles demonstrates that the presence of water has both a physical and chemical impact
Specials thanks to: Matt Andersson, Paige Booth, Chuck Myers, Jacob Bolton, Mike Wildman, Robert Sandoval, Gunnar Duner, Heidi Docktor
Thermo Fischer Nicolet iS10 with Smart iTR fixture
THANK YOU QUESTIONS?