TPO Roofing Membranes: TPO Roofing: Stability and Performance Stability and Performance Dr. Kimberly Deaton Johns Manville
Outline TPO Roofing Membrane What is TPO Degradation Modes Protection Performance
TPO Formulations Polymer PP (Polypropylene) and EP (Ethylene-Propylene) Rubber Weldability Ethylene-propylene copolymer comprising an amorphous phase of EPR and a single crystalline phase of polypropylene Fire Retardant Magnesium Hydroxide and others. Pigment Titanium Dioxide Top & bottom Carbon black -Bottom UV Stabilizers Thermal Stabilizers (Antioxidants) Top & bottom Polymer 50-75% Antioxidants 1-2% UV Stabilizers Antioxidants Recycled Pigment 3-5% 3-5% CAP Top Over Scrim CORE Bottom Under Scrim 0-20% Pigment 3-5% Fire Retardant 15-35%
TPO Structure & Features CH 3 CH 3 CH 3 CH 3 CH 3 m Polypropylene n Ethylene Propylene Good TPO Polymer TPO Polymer Schematic: Blue = Polypropylene (rigid) Red = Ethylene Propylene (flexible)
TPO Features Current ASTM D 6878-08 Physical Properties Weathering Performance (UV) Min: 10,080 kj/m 2 -nm @ 340 nm ~ 4000 hrs Visual inspection for cracks (7x) Heat Aging 240 F (116 C) for 28 days Retention of physical properties Only Proposed Change Proposed Changes No Proposed Changes UV Enhancement Not Considered Heat Aging 275 F (135 C) for 56 days Visual Inspection TPO Service Temp Range Under Solar Panel Littleton, CO Current ASTM Proposed ASTM Polypropylene Melt Range 158 F 176 F 194 F 212 F 230 F 248 F 266 F 284 F 302 F 320 F 338 F 356 F
TPO Modes of Degradation Photo (light-uv) Thermal (heat-temp) Processing heat Weathering Environmental Wind, rain, hail, snow, frost Atmospheric gases and pollutants Soiling
Difference Between UV & Thermal Energy Too much Sun = sunburn! Using Wein s Law for Black Body Radiation: 340 nm of UV radiation is equal to 14,883 ºF
TPO Photo Degradation Photo Degradation Good TPO Polymer UV + "Broken" TPO Polymer Or + "Broken" TPO Polymer Radical Reactive Site =
TPO Thermal Degradation UV "Broken" TPO Polymer "Broken" TPO Polymer Radical Reactive Site = Degradation initiated by UV radiation continues in the presence of heat and oxygen.
TPO Thermal Degradation "Broken" TPO Polymer Radical Reactive Site =
TPO Degradation Propagation Reactive TPO Polymer can attack good polymer.
TPO Degradation Propagation Propagation: single chain to 2-4 - 8-16 etc.flaking!
TPO Roof Failures Cap Flaking Cap Flaked & Gone Core Begins to Flake
TPO Protection with Stabilizers UV Protection Absorbers Pigments (TiO 2, Carbon Black) Stabilizers Hindered Amine Light Stabilizers (HALS) LMW HMW NOR HALS Thermal-Oxidative protection Antioxidants Phenolic Phosphites HALS (Below 248 ºF)
UV Stabilizers: Stopping Photo Degradation Hindered Amine Light Stabilizers (HALS) Low Molecular Weight Will Migrate High Molecular Weight Lower Migration Standard HAL: LMW R is short chain HMW R is long chain R NOR HALS (newest and best) Effective Thermal Additives at 248 ºF or lower N O R' NOR HAL: can have long or short chain for R and R is proprietary.
HMW vs. LMW HALS
Thermal Protection: Antioxidants Phosphites can reduce thermal peroxy radicals to more stable alcohols.
Thermal Protection: Phenolic Antioxidants OH "Repaired" TPO Polymer Hindered Phenols can stop peroxy radicals produced from thermal oxidation.
Critical to TPO Performance UV Protection Stabilizers Hindered Amine Light Stabilizers (HALS) LMW HMW NOR HALS Absorbers Pigments (TiO 2, Carbon Black) Thermal-Oxidative protection Antioxidants Phenolic Phosphites x x x x
TPO: What You Need Xenon Arc performance Higher than ASTM minimum (10,080 kj/m 2 ) Look for 2x ASTM minimum or more: over 20,160 kj/m 2 Heat Aging Add an elevated test that does not exclude the advantage of HALS as thermal protection ( 248 ºF) Consider 248 ºF (120 ºC) for 128 days as a possibility Thickness Thicker is better! 60 mil minimum
Questions???? Sources Dr. Majid Hindi (Johns Manville) August 2, 2010 Dr. Joseph Fay (BASF) October 18, 2010 Articles: Hans-Rudolf Beer, Sarnafil International AG, Longevity and Ecology of Polyolefin Roof Membranes, Proceedings of the Fourth International Symposium on Roofing Technology. September 17-19, 1999. Bobbijo van Beusichem, Michael Ruberto, Ciba Specialty Chemicals, Introduction to Polymer Additives and Stabilization, a presentation to Product Quality Research Institute, December 2005. R. V. Todesco, Ciba-Geigy Limited, HATS: The Future of Long Term Thermal Stabilization of Polypropylene, Maack Business Services, PP 94: Session II. October 4-5, 1994.