TPO Weathering By: Zebonie Sukle OVERVIEW OF PRESENTATION
TPO Weathering By: Zebonie Sukle OVERVIEW OF PRESENTATION Introduction on Product Standards Single Ply Product Standards Overview Focus on Accelerated Aging Predicting What is Next Case Study Taking TPO to 275oF Risks and Benefits Summary 2
INTRODUCTION Importance of Product Standards Establish Baseline Requirements for durability/ performance Provides Assurance Minimizes material failures Examples of Product Standards Miami Dade 3 INTRODUCTION Risk of Product Standards Do not represent field related issues Developing products that meet the test requirements Unintended Consequences 4
PRODUCT STANDARDS FOR MEMBRANES Membrane durability Typically quantified by physical property test methods Accelerated physical property testing Moisture Temperature UV Atmospheric Pollutants Test of Time Historical performance Impractical for the rapid growth of new technologies 5
8.12 references ASTM D570 (water absorption) 8.6 references ASTM D3045 (heat aging) 7 HOW ROOFING DOES ACCERATED HEAT Heat aging for roofing membranes typically uses laboratory ovens. -Critical Requirements: - Oven size - Oven controls requirements - Air flow requirements 8 HOW ROOFING DOES ACCELERATED UV Sunlight or UV aging in the roofing industry is typically done with either a QUV or a Xenon Arc Weatherometer. Critical Requirements UV Spectrum Moisture Cycle
Etc. 9 TEST OF TIME 10 FOCUS IS ON ACCELERATED AGING Definition: Accelerated aging is testing that uses aggravated conditions of heat, oxygen, sunlight, vibration, etc. to speed up the normal aging processes of items. It is used to help determine the long-term effects of expected levels of stress within a shorter time, usually in a laboratory by controlled standard test methods. 11 KEY REQUIREMENT
the aging conditions are chosen in order to reduce the time required to achieve a desired material end-state, but without changing the damage mechanisms identified for the operational environment. (Italics added.) (Gates & Grayson, 1999.) 12 HISTORY ON ACCELERATED AGING METHODS 1960 1980 EPDM roofing membranes were commercialized in the US. In the 1970, PVC membranes began to be used in the US after
having been widely used in Europe since the 1960. ASTM changed linear dimensional requirement for EPDM as a result of field performance issues PVC membranes began using scrim reinforcement and higher molecular weight and solid plasticizers to address field performance issues 1990 2000
2015 2006 TPO ASTM adjusted UV requirements higher as a result of field performance issues. TPO entered the roofing market. 2011 TPO ASTM adjusted Thermal requirements higher 2003 ASTM Adopted D6878 for
TPO 2002 ASTM established D6754 for PVC sheets with a minimum of 50% KEE polymer by weight of the polymer content of the sheet. 13 ACCELERATED AGING STANDARDS For All Single Ply Roofing Membranes Roofing Membrane EPDM (black) EPDM (white) PVC TPO (2003)
TPO (Current) ASTM Reference Standard Required Ultraviolet Aging [kJ(m2nm)] Required Heat Aging Temperature (oF) Duration (Days) D 4637 D4637
D 4434 D6878 10,080* 2,520 6,480 ** 5,040 240 240 176 240 28 28 56 28 D 6878 10,080
240 224 * ASTM has approved a ballet proposal to increase EPDM to 10,080 kJ(m 2nm) in 2015. it was previously 5,040 kJ(m2nm). ** UV requirements for a Xenon Arc, PVC ASTM allows for both Xenon Arc and QUV (12,240 kJ(m2nm) ). 14 EPDM EPDM Linear Dimensional Failures Industry Actions - Reduced Linear Dimensional Product Standard to 1%. - Changed termination of membrane to parapet.
Accelerated Product Standards Remained the same from 1980 to 2014. UV was updated in 2015. 15 PVC PVC Industry Actions Shattering PVC - Reinforced PVC membrane - High molecular weight and solid plasticizers Accelerated Product Standards
Remained the same 1980 16 TPO TPO Industry Actions Thermal Stability, mid-1990s UV Stability Solar impact - White TPO - Magnesium Hydroxide replace Brominated Fire retardants - Improved Stabilization Accelerated Product Standards
Changes made as recent at 2011 17 TPO Aging UV Weathering & the ASTM 2003 TPO ASTM D6878 Adopted UV Xenon Arc Minimum: 5040 kJ/m2-nm 60% Retention of Physical Properties Visual Inspection at 7X over a Mandrel for cracks 2006 TPO ASTM D6878 Updated UV Xenon Arc Minimum: 10,080 kJ/m2-nm 60% Retention of Physical Properties Visual Inspection at 7X over a Mandrel for cracks 2008 TPO ASTM D6878 Updated UV Xenon Arc Minimum: 10,080 kJ/m2-nm 60% Retention of Physical Properties Visual Inspection at 7X over a Mandrel for cracks SINGLE PLY UV REQUREMENTS UV Performance EPDM
PVC* TPO 5,040 kJ(m2nm) TWICE that of EPDM 6,480 kJ(m nm) 2 More than 1.5X that of PVC 10,080 kJ(m2nm) * The ASTM for PVC allows for the use of both the Xenon Arc and QUV for UV testing. Comparison here was done using Xenon Arc so that direct comparison could be made. QUV testing would result in 12,240 kJ(m2nm). 19
CURRENT TPO vs. PRE-2008 TPO Question: Were the formulations stabilized enough for UV? <2008 >2008 35000 Started in 2009. 35000 30000 30000 Started in 2007.
0 A B C D A B C D Xenon Arc weathering tests for 45 mil membrane. Crack investigation at 40X magnification.
Market samples (blinded). E F TPO Heat Aging & ASTM 2003 TPO ASTM D6878 Adopted Oven Aging (D573) at 240 F (116 C) for 28 days 90% Retention of Breaking strength and elongation 60% Retention of Tearing Strength 2011 TPO ASTM D6878 Updated Oven Aging (D573) at 240 F (116 C) for 224 days 90% Retention of Breaking strength and elongation 60% Retention of Tearing Strength 2012 -2015 TPO ASTM D6878 higher temperature Proposed revisions are being review. Mandrel wrap at 7x magnification for cracks. SINGLE PLY THERMAL PERFORMANCE
Thermal Performance EPDM PVC TPO 28 days @ 240oF 56 days @ 176oF 8 times longer than EPDM 50x more heat exposure than PVC 224 days @ 240oF 22 ADDRESSING THE ISSUES Changes to the product standards have been made as a reaction to field failures EPDM
Membrane Shrinkage PVC Shattering Membrane TPO Early 2-3 year failures due to heat exposure of black TPOs 5-year failures associated with UV and flame-retardants have been eliminated 7-year failures associated with combined heat and UV have been eliminated WHAT IS NEXT? 23 PREDICTING WHAT IS NEXT? Increasing the Accelerated Aging Temperature to 275oF Scientific Accelerated Aging verses Torture Test Example of Torture Test BP Lubricants USA., the maker of Castrol
EDGE oil, comparative advertising campaign. 24 TORTURE TEST BACKGROUND Case Study - Advertising campaign pitted BPs product against Exxon Mobils Mobil 1. - The advertising depicted two cars on a dynamometer running at 75 miles per hour on a 7% grade fully loaded at 1,600 lbs. Which is equivalent to driving a fully loaded car continuously up one of the steepest mountain passes suitable for a vehicle for a distance of 9,000 miles. - They pushed the cars for 5 straight days and on the 5th day the Mobil 1 engine failed and the Castrol EDGE engine continued to run. - ExxonMobil filed a complaint and although they did not dispute the results argued that this test represents a torture test. - The National Advertising Division opinion was that the test conditions did not represent conditions to which consumers would ever subject a cars engine too. Essentially, just because the oil worked well in these tortuous conditions, it not mean that the oil would last longer in normal service conditions. 25
TAKING TPO TO 275oF Arrhenius Equation, applied to TPO degradation, states that the rate of degradation doubles about every 18oF Temperatures 240oF 258oF 276oF Degradation Time 224 days 112 days 56 days Moving to 56 days at 275oF benefits manufactures in terms of shorter testing times but could introduce some new and unknown variables or unintended consequences. 26 POTENTIAL DIFFERENCE Between Aging at 240oF/224 days and 275oF/56 days
Youngs Modulus (Stiffness) of Unreinforced TPO Membrane Samples 27 DSC CURVES FOR TPO CAP MATERIALS Current ASTM 240oF 275oF 28 FLEXIBILITY CONCERNS TPO membranes have already lost 90% of their polymer stiffness at 240oF. They will lose another 50% at 275oF Melting point of TPO formulations are around 295-298oF. Is the TPO Membrane really the same at 275oF as it is at in-service
temperatures? 29 STABILIZER CAPABILITIES Melt Processing Stability Long Term Thermal Stability Hindered Amine Hindered Phenol Thiosynergist Phosphite Hydoxylamines 0 100
200 300 400 500 600 Temperature (oF) 30 STABILIZER CONCERNS TPO Stabilizer packages are designed to perform at service temperatures Some additives start to lose efficacy at higher temperatures Formulating for higher testing temperatures may require the use of alternate thermal stabilizers, and we dont
know how well they work at service temperatures. 31 WELD STRENGTH AT 1150oF Weld Strength at 1150 degrees F @ 14' per min 80 Peel Strength (lbf) 70 60 50 40 30 20 10 1 2
3 4 Supplier 32 WELD STRENGTH AT 800oF 33 WELD WINDOW FROM 800 - 1150oF Weld Variability Through Temperature Adjustments 80 Peel Strength (lbf) 70 60
50 40 30 20 10 1 2 3 4 Supplier 34 INSTALLATION DIFFERENCES Competitive Weld Window vs Days to Weight Loss > 1.5% Maximum Load (lbf)
80 140 70 120 60 100 50 80 Days to Weight Loss > 1.5% 40 60 30 40 20
20 10 0 1 2 800F @ 14' per min 3 1150F @ 14' per min 4 Weight loss > 1.5% 0
35 INSTALLATION CONCERNS Membranes that perform well at the 275oF accelerated test appear to show greater variability in low temperature weld strength Cold welds were also observed in some of the samples tested. 36 RISK & BENEFITS RISK TPO has lost 90% of its stiffness at test temp. Stabilizers may need to be optimized for higher temps. Weld variability is increased with high
temperature TPOs BENEFIT Shorter testing time Lower testing costs 37 SUMMARY Roofing membranes have all experienced early life failures Product Standards have been modified and updated to address those early field failures Test of Time Changing Product Standards to address one aspect of product performance could result in unintended consequences. Is the benefit of the change worth the risk? 38 TPO Weathering
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