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Weathered Thermoplastic PolyolefinRoofing: Characterization, SurfaceAnalysis and Best Practices forCoating
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Coating
Joe Rokowski,RCMA Symposium 7,17,2012
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Agenda
• TPO Basics
• Surface Analysis
• Coatings Formulation Influences
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• Surface Cleaning
• Summary
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TPO Basics
•Single ply waterproof membrane
•Thermoplastic
•Scrim Reinforced
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•White = Energy star Compliant
•Heat weldable = installation ease
•Economical
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TPO Roofing History
• TPO membranes for roofing began in Europe inlate 1980’s targeting plasticizer & halogen freeproducts
• US introduction in 1992
• Significant US market penetration 2000
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• Significant US market penetration 2000
• 2005/2006 US growth rates 25-35% !!
•TPO = 40-50% less expensive than conventionalroofing membranes.
• And its White !!
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Composition of TPO Polymer
• Polypropylene (Tough/Hard, no functionality)
+
• EPR= Ethylene/propylene rubber
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Or
EPDM Rubber
(Both are flexibilizing agents with somefunctional groups)
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Formulation TPO Roof Membrane:
•Pigments (TiO2, CaCo3)
• Fire retardant: Mg(OH)2 , brominated organics,Aluminum TriHydrate
• Crosslinker: peroxides, etc.
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• Crosslinker: peroxides, etc.
• Antioxidant: phenols, amines, phosphites
• Lubricant/Processing aids
• UV absorbers
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TPO Failure Mechanism
• Over time, on a roof: UV, H20, Thermalcycling, soil, etc.
- Slow surface erosion occurs, eventuallyrevealing reinforcing scrim
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revealing reinforcing scrim
- Micro cracks develop
- Dirt decreases reflectance, increasestemperature
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Early TPO Issues
Early Failures due toformulation ingredients (e.g.halogenated fire retardants)and compounding issueshave largely been corrected.
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have largely been corrected.
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DOW’s Role in Low Slope Roof Coatings
• Emulsions Polymers into Pigmented Coatings
• High exterior durability – roof life extension
• White for Energy Savings
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• Must have excellent wet adhesion
• We understand how roof substrates fail
• Goal: Improve adhesion of coatings toweathered TPO Roofs.
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Why Coat TPO Membranes ?
-All exterior roofs and coatings eventuallydegrade and have a finite service life
- Provide an alternative to tear-offs
- A retrofit/maintenance solution
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- A retrofit/maintenance solution
- TPO is waterproof
- Coatings do not replace waterproofing-
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Conventional commercial elastomeric roofcoatings in their recommended pigmentedformulations generally don’t adhere well to
Typical Elastomeric Roof Coating
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formulations generally don’t adhere well toNew or Weathered TPO.
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Current Products: Adhesion to Weathered TPO
Dry Adhesion
Adhesive Failure
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Wet AdhesionAdhesive Failure
Poor Adhesion
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Difficulty of Coating TPO Roofing
• Lack of functional groups
• Low surface energy
• Poor wettability
• Difference in the type of TPO on the
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• Difference in the type of TPO on thesurface whether semi-crystallineamorphous
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Contact Angle Measurements
TPO:
AverageContactAngle
Percent Differencevs. Unweathered
TPO Membrane #1 New 48 ---
TPO Membrane #1 5 Year Weathered 71 + 36 %
TPO Membrane #2 New 32 ---
TPO Membrane #2 1 Year Weathered 66 + 106 %
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TPO Membrane #2 1 Year Weathered 66 + 106 %
TPO Membrane #3 New 44 ---
TPO Membrane #3 6 months WOM* 68 + 55 %
Elastomeric Coatings:Standard ERC #1 67 ---Hydrophobic ERC #2 44 ---New Coating w/ Weathered TPOAdhesion 65 ---
* Atlas Weather-O-Meter
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Surface Characterization
Contact Angle:
New = 32-48o
Weathered = 66-71o !!!!!!
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Weathered = 66-71 !!!!!!
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TPO Membrane Differences
• Recent research by the National Roofing Contractors
Association (NRCA) found that there are significantdifferences between TPO membranes currently beingsold in the U.S. The effects of some of these differencesare still unknown at this time. NRCA believes otherdifferences will have notable effects on the usability and
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differences will have notable effects on the usability andlong-term field performance of TPO membranes. Sincethese types of roofs have either had a history ofproblems or not enough of a track record, we are closelywatching the performance of these products before weinstall them.
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Surface Analysis
• XPS = X-Ray Photoelectron Spectroscopy
• It measures atomic elements on the surface of amaterial
• How far down? About 10 nanometers or 1/100th
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• How far down? About 10 nanometers or 1/100of a micron
• Light elements like Hydrogen and Helium areexcluded.
• C = polymer
• O, Al, Si = metal oxides and pigment (Ti)
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TPO Surface Analysis
TPO #1 Al C Ca Cl O S Si P N
New 1.1 90.2 0.3 0.2 3.9 0.1 2.7 0.2 1.3
6 MonthWeathered 2.8 76.2 0.4 0.2 13.3 0.4 4.7 0.2 1.7
1Yr Weathered 3.7 69.1 0.5 0.4 17.1 0.3 6.8 0.3 0.2
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TPO #2 Al C Ca Cl O S Si P N
New 0.9 90.3 0.2 0.3 6.0 0.2 1.8 0.3
6 MonthWeathered 1.9 72.8 0.4 0.4 14.7 0.4 7.3 0.3 1.8
1 Yr Weathered 2.0 57.7 0.2 0.3 19.2 0.2 20.1 0.3
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TPO #3 Al C Ca Cl O S Si P N
New 0.8 87.1 0.2 0.2 6.5 0.4 1.2 0.2 3.2
6 Month ExteriorWeathered 2.6 72.4 0.4 0.4 15.2 0.3 6.8 0.3 1.5
1Yr ExteriorWeathered 4.0 64.1 0.5 0.5 20.2 0.3 7.9 0.3 1.8
TPO Surface Analysis
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Weathered 4.0 64.1 0.5 0.5 20.2 0.3 7.9 0.3 1.8
TPO #4 Al C Ca Cl O S Si P N
New 0.9 80.2 0.4 0.4 10.0 0.2 5.4 0.3 2.0
7Yr ExteriorWeathered 4.9 54.3 1.0 0.3 26.2 0.2 10.9 0.6 0.8
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Surface Characterization
Assumption:
New TPO = smooth, polymer rich,hydrophobic
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Weathered TPO = rough, pigment rich, andrelatively hydrophilic
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Formulation
• Typical Elastomeric Roof Coating
• 40% PVC/50% VS
• No zinc oxide
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• Slightly higher TiO2 than normal
• 1 gal/square as basecoat plus 1gal/square as topcoat
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INGREDIENTS: POUNDS:
GRIND Water 145.00TAMOL™ 851 5.70Aqueous Ammonia(28%) 3.00BYK 012 2.00Omyacarb 12 392.50TiPure R-960 62.50
:LETDOWN BYK 012 3.00
RHOPLEX EC-3100 (55%) 490.10
Formulation
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RHOPLEX EC-3100 (55%) 490.10Water 13.90UCAR™ Filmer IBT 6.00SKANE™ M-8 3.00Propylene Glycol* 10.00Dow hydroxyethyl cellulose 4.00
1141.70
PVC= 40% % Volume solids =50%% Weight Solids = 64.2%
pH = 10.0
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ERC with Adhesion to Weathered TPO
• DOW Commercial name =
Rhoplex™ EC-3100
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Pigment Dispersant
• Dry Pigments are supplied in an agglomeratedpowdered form
• Mechanical shearing in water physically separatesthe clumps
• Water soluble dispersants adsorb onto and coat
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• Water soluble dispersants adsorb onto and coatpigments to keep them separate to maintain smallincrease act efficiently
• Use levels are 0.3 to 1.0% on pigment
• Impact performance
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Dispersant Description Neutralizer MW HanschValue
A Poly - Acid Sodium(Hydrophilic)
High -2.2
B Acid/Copolymer Sodium(Hydrophobic)
High +0.3
Pigment Dispersant Description
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(Hydrophobic)
C Poly Acid Ammonia(Hydrophilic)
Low -2.2
D Acid/Copolymer Ammonia(Hydrophobic)
High + 0.3
E Poly Acid Sodium(Hydrophilic)
Low -2.2
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Adhesion vs. Formulation Components
• Very small particle size pigments have highersurface area than large particle size pigments
•High oil absorption pigments need more polymer tobind to than low oil absorption pigments
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bind to than low oil absorption pigments
• This reduces the amount of “free polymer” availablein the formulation
•Does this impact adhesion of a coating?
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2
2.5
3
A
D
H
E
S
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Peel Adhesion vs. Formulation Ingredients
Adhesion vs. Formulation Components
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0
0.5
1
1.5
W/ ZN OX NO ZN OX CACO3 UF CACO3 3µ CACO3 5µ
I
O
N
P
L
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Formulation Difference
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Swell the amorphous boundary layer, allowpenetration, bonding and adhesion ?
1) IPA / VM&P Naptha 50/50
Solvent Cleaning of TPO
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2) Jeffsol / Propylene Carbonate = VOCExempt
Flammability, Odor ?
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Solvent Cleaning: Current Products &Formulas: Adhesion to New TPOMixed Results: Some Adhesive Failure, Some Delamination Failure
Dry Adhesion
Wet Adhesion
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Wet Adhesion
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Solvent Cleaning Current Products & Formulas:Adhesion to Weathered TPOMore Mixed Results
Dry Adhesion
Wet Adhesion
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Description Chemistry Adhesion PLI /
Failure
No cleaning --- 0.3 / Adhesive
Water powerwashing --- 0.6 / Adhesive
Cleaner 1 + Phosphate and 1.6 / Cohesive
Adhesion Method vs. Surface Treatment
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Cleaner 1 +
powerwashing with
water
Phosphate and
nonionic surfactant
1.6 / Cohesive
Solvent wipe 1 Isopropanol &
VM&P Naptha
50/50
2.2 / Cohesive
Solvent wipe 2 Jeffsol/ PM 50/50 2.0/ Cohesive
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Al C Ca Cl O S Si P NTPO 1 New 1.1 90.2 0.3 0.2 3.9 0.1 2.7 0.2 1.3TPO 1 YrWeathered 3.7 69.1 0.5 0.4 17.1 0.3 6.8 0.3 0.2TPO 1 , 1 YrWeatheredCleaner 1 1.0 83.2 0.4 0.3 10.5 0.3 1.6 0.2 2.3
Surface Analysis Before and After Cleaning
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Cleaner 1 1.0 83.2 0.4 0.3 10.5 0.3 1.6 0.2 2.3
Al C Ca Cl O S Si P NTPO 2 new 0.9 90.3 0.2 0.3 6.0 0.2 1.8 0.3 ---TPO 2 1yrweathered 2.0 57.7 0.2 0.3 19.2 0.2 20.1 0.3 --TPO 2, 1 YrWeathered,Cleaner 1 0.8 86.5 0.3 0.3 5.7 0.1 3.0 0.2 3.1
®Adhesion to New and Weathered TPO:New Emulsion Polymer
New TPO WeatheredTPO
Dry Adhesion
Wet AdhesionAdhesive
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Wet AdhesionAdhesive
Delamination
®Mechanism of Adhesion
• Coating hydrophobicity must match thehydrophobicity of the weathered TPOsurface i.e. allows coating to effectivelywet the TPO surface
• Adhesion chemistry must be present in
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• Adhesion chemistry must be present inthe polymer to adhere to sites madeavailable by weathering
• Formulation ingredients and surfacepreparation must be selected to optimizeadhesion
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TPO• Contact angle starts low but increases substantially as TPO weathers.• New TPO membranes vary in surface composition primarily in polymeric topigment ratio.• Exterior weathering of TPO via XPS/atomic analysis decreases surfacepolymer and increases surface pigment at the surface.
Conclusions
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Coatings:• Match the contact angle of the coating and the substrate• Hydrophilic dispersants better than hydrophobic dispersants to improveadhesion• Large particle size, low oil absorption extenders help to maximize adhesion .• Adhesion can be increased by cleaning weathered TPO with commercialcleaners and powerwashing with sufficiently high pressure (i.e. ≥3000 psi).