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?