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Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals

Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals. by Bob Ohm* & Dan Patton Lion Copolymer, LLC Compounding and Development Center 5955 Scenic Highway, Baton Rouge, LA 70805. * Speaker. Outline. Introduction Bloom vs. Iridescence

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Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals

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  1. Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals by Bob Ohm* & Dan Patton Lion Copolymer, LLC Compounding and Development Center 5955 Scenic Highway, Baton Rouge, LA 70805 * Speaker

  2. Outline Introduction Bloom vs. Iridescence 23 Designed Experiment: Filler, Oil & Curative Effect of Cure Temperature & EPDM Polymer Surface Analysis Antioxidant Comparison Final Experiments Summary

  3. Introduction Why weatherseals are based on EPDM Excellent Weatherability Impervious to Ozone Highly Resistant to Heat and Oxidation Highly Extendable Discoloration in Light Initial colors blue / red / green Change to bronze / gold Prior Work

  4. Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals Best viewed at shallow angle A long-standing issue Various “solutions” proposed: Cure system Filler Polymer Additives Root cause & permanent fix elusive

  5. The Iridescent Color depends on the angle of view

  6. Bloom and BleedSurface Discoloration due to powdery solid (bloom) or liquid film (bleed) • The remedy is straightforward: • Remove the material at the surface • Determine the composition of the material removed. • Lower the dose or eliminate the use of the material identified. Gold IridescenceSurface Discoloration due to ??? • The discoloration can not be readily removed. • Methylene chloride removes - but only temporarily!

  7. Thermal Desorption ResultsEric Jourdain, Paper #42, 149th ACS Rubber Division meeting (May 1996)

  8. Thermal Desorption ResultsEric Jourdain, Paper #42, 149th ACS Rubber Division meeting (May 1996)

  9. Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals Five Studies: 1. 23 design for: A/ filler (furnace vs. thermal) B/ plasticizer (par oil vs. poly alpha-olefin), C/ cure system (sulfur vs. peroxide) and D/ cure time at 182°C (1.5 vs. 10 minutes) 2. effect of: A/ diene content (4 vs. 8%), B/ ethylene content (60 vs. 70%) and C/ cure temperature (230 vs. 340°C) 3. surface analysis 4. antioxidant comparison 5. polymer, filler & other variations

  10. 23 Designed Experiment Filler / carbon black Oil / plasticizer Cure System (Sulfur vs. Peroxide) Additive Package (the 3 Amigos)

  11. Filler Comparison • Furnace black: • made from crude oil • made in air • contains aromatic structures (staining) • contains sulfur, nitrogen • Thermal black*: • made from natural gas • anaerobic manufacture (no oxygen) • minimum extractables (aromatics) • little/no sulfur, nitrogen * plus precipitated silica to equalize hardness

  12. Plasticizer Comparison • Parafinnic oil: • made from crude oil • contains aromatic structures • contains sulfur, nitrogen • Poly a-olefin: • made from decene • no residual unsaturation (removed by hydrogenation) • no sulfur, nitrogen

  13. Cure System Comparison • Sulfur cure: • contains sulfur, nitrogen • little/no oxygen • accelerator fragments found on surface • Peroxide cure: • no sulfur, nitrogen • contains oxygen

  14. 3 Am.= 5 3 Am. = 1 Gold Ratings: 1 = best, 5 = worst6 days exposure perSAE J1960 (exterior) *= mat surface develops during light exposure

  15. 3 Am.= 0.5 3 Am. = 1.5 Gold Ratings: 1 = best, 5 = worst6 days exposure perSAE J1885 (interior) * = mat surface develops during light exposure

  16. Summary of 23 Experiment • The filler system is most important for gold iridescence. A thermal black/ppt. silica blend develops a low-gloss (mat) surface during light exposure, minimizing the gold iridescence. • The 3 Amigos are effective, esp./SAE J1885. • A peroxide cure is poorer than the sulfur cure per SAE J1885 (no effect per SAE J1960). • The PAO is better than paraffinic oil per J1960 (no effect or slightly poorer by J1885).

  17. Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals Five Studies: 1. 23 design for: A/ filler (furnace vs. thermal) B/ plasticizer (par oil vs. poly alpha-olefin), C/ cure system (sulfur vs. peroxide) and D/ cure time at 182°C (1.5 vs. 10 minutes) 2. effect of diene content (4 vs. 8%), ethylene content (60 vs. 70%) and cure temperature (230 vs. 340°C) 3. surface analysis 4. antioxidant comparison 5. polymer, filler & other variations

  18. Previous workers = best Previous workers = worst Polymers Evaluated (Cure Temperature = 230 or 340 °C) Light Exposure = 6 days SAE J1885

  19. UV* = 1 3 Am.= 1 UV* = 3 3 Am. = 2 Gold Ratings: 1 = best, 5 = worst Cure Temp. 10’/230, 2’/340 °C = NO EFFECT However, 10’at 340°C = IMMEDIATE GOLD * = heavy white bloom on molded samples

  20. Summary of Second Study • The gold color can be developed by oxidation without light exposure. (However, this method leads to sample embrittlement.) • High diene polymers give lower gold ratings. • Gold ratings can be further lowered by addition of the “Three Amigos”. • Ethylene level and cure temperature have little effect on gold in our laboratory work.

  21. Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals Five Studies: 1. 23 design for: A/ filler (furnace vs. thermal) B/ plasticizer (par oil vs. poly alpha-olefin), C/ cure system (sulfur vs. peroxide) and D/ cure time at 182°C (1.5 vs. 10 minutes) 2. effect of diene content (4 vs. 8%), ethylene content (60 vs. 70%) and cure temperature (230 vs. 340°C) 3. surface analysis 4. antioxidant comparison 5. polymer, filler & other variations

  22. Surface Analysis Methods Scanning Electron Microscopy SEM TOF-SIMS XPS AFM Time of Flight - Secondary Ion Mass Spectroscopy X-Ray Photoelectron Spectroscopy Atomic Force Microscopy

  23. 10 m 10 m Surface Analysis of Molded Test Pads Scanning Electron Micrograph (SEM)

  24. Found only siloxane (mold release). XPS X-RayPhotoelectronSpectroscopy* * or ESCA, electron scattering for chemical analysis Surface Analysis Techniques TOF-SIMSTime of Flight Secondary Ion Mass Spectroscopy

  25. Carbon Oxygen XPS - Black Area

  26. Carbon Oxygen XPS - Gold Area

  27. XPS Oxygen Results - 2nd Study

  28. contains aMSDPA amine antioxidant XPS Nitrogen Results - 2nd Study

  29. XPS Zinc Results - 2nd Study

  30. Gold Matt Gold Shiny High Resolution AFM Surfaces Black

  31. Surface Analysis Summary • Molded samples under SEM appear to develop raised nodules. • TOF-SIMS was not successful in identifying the composition of the nodules. • XPS finds the gold surface is enriched in oxygen and, to a lesser extent, nitrogen and zinc. • AFM finds black regions are smooth; light-exposed gold regions, especially low-gloss, are rough – nano structure.

  32. Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals Five Studies: 1. 23 design for: A/ filler (furnace vs. thermal) B/ plasticizer (par oil vs. poly alpha-olefin), C/ cure system (sulfur vs. peroxide) and D/ cure time at 182°C (1.5 vs. 10 minutes) 2. effect of diene content (4 vs. 8%), ethylene content (60 vs. 70%) and cure temperature (230 vs. 340°C) 3. surface analysis 4.antioxidant comparison 5. polymer, filler & other variations

  33. Comparison of Antioxidantsin the Three Amigos Blank Bisphenolic ODPA TMQ No AO (liquid) Light Exposure = 6 days SAE J1885

  34. Comparison of Antioxidantsin the Three Amigos (continued) aMSDPA Sulfonated Bisphenol NBC Diphenyl- Phosphite amine Blend

  35. Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals Five Studies: 1. 23 design for: A/ filler (furnace vs. thermal) B/ plasticizer (par oil vs. poly alpha-olefin), C/ cure system (sulfur vs. peroxide) and D/ cure time at 182°C (1.5 vs. 10 minutes) 2. effect of diene content (4 vs. 8%), ethylene content (60 vs. 70%) and cure temperature (230 vs. 340°C) 3. surface analysis 4. antioxidant comparison 5. polymer, filler & other variations

  36. Polymer, filler & other variationsGold Ratings = cured / uncured The filler system of N990 & KE clay give a dull surface After SAE J1885 exposure, similar to N990 & ppt. silica. * Rating improves where Mylar film adhered.

  37. 10 mm Final ExperimentPhoto of Test Pad with Gold Iridescence Middle portion clamped 1 week at RT removes gold. However:gold returns on oven aging or more light exposure.

  38. Optical Properties of Nano ParticlesChad A. Mirkin, George C. Schatz, et. al., Science, 294, pages 1901-1903 (2001),as taken from Chemical & Engineering News, page 10 (Dec. 2, 2001) Silver nanoprisims scatter red light. Gold nanorods scatter orange light. Gold nanospheres scatter green light.

  39. Summary • Compression of the surface can remove the gold iridescence. • However, this is not a practical solution because the gold is redeveloped during brief oven aging or additional light exposure. • For future work, a permanent solution may require both chemical and physical (structure) control.

  40. Thanks for your attention Any Questions?

  41. The papillo butterfly’s wings are covered with small textured scales (above right)… Tiny concavities within these scales (below left) create color through constructive interference… In the scales of the green portion of the papillo’s wings, each concavity reflects bright yellow while the outer edges reflect bright blue…

  42. The Three Amigos

  43. Gold Region N990 Carbon Black N774 Soft Clay Hard Clay Zinc Oxide Precipitated Silica Particle Size of Additives Whiting

  44. gold sample A C-O C=O C-N control sample A -O-C=O High Resolution XPSMain Peak = C-(C1H)

  45. 30 mm AFM Surface Analysis Black Surface Shiny Sample Black Surface of Matt Sample Gold Shiny Surface Gold Matt Surface

  46. Gold Matt Gold Shiny 350 nm 0 -350 475 nm 665 nm 350 nm 0 -350 130 – 250 nm 0 2 4 6 mm 0 2 4 6 High Resolution AFM Surfaces Black

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