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 Discoloration in Light
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
Initially, the light-induced discoloration appears as blue, red or rainbow iridescence like the sheen of a film of oil on water.
With continued light exposure, this subtle color of the weatherseal changes to bronze or gold. The appearance depends on the angle of view and strength of illumination. When examined perpendicular to the surface, black predominates. When viewed at an angle, the blue / red / gold colors are more evident. Moderate light conditions are best to view the iridescent colors

6. Gold Iridescence Surface Discoloration due to
Bloom and Bleed Surface 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 Iridescence Surface Discoloration due to
???
Many rubber articles can develop a powdery solid surface discoloration, known as bloom. The remedy to bloom is straightforward: the material at the surface is removed, its composition determined and the dose of the material(s) identified either lowered or their use eliminated. Similarly, “bleed” is the appearance of a liquid at the surface, and the procedure to resolve the undesired film is the same.
In contrast, iridescence cannot be readily removed for identification. Only with enough force to physically abrade away the surface can be the iridescent colors be removed. Some powerful solvents for EPDM, e.g. methylene chloride, can temporarily seem to remove the colors. However, as soon as the solvent evaporates and the puffed-up part surface returns to its normal flat configuration, the iridescent colors reappear
The discoloration can not be readily removed.
Methylene chloride removes
- but only temporarily!

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

8. Thermal Desorption Results Eric 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: Thermal 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. Gold Ratings: 1 = best, 5 = worst 6 days exposure per SAE J1960 (exterior)
3 Am.= 5
3 Am. = 1
* = mat surface develops during light exposure

15. Gold Ratings: 1 = best, 5 = worst 6 days exposure per SAE J1885 (interior)
3 Am.= 0.5
3 Am. = 1.5
* = 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. Light Exposure = 6 days SAE J1885
Polymers Evaluated
(Cure Temperature = 230 or 340 °C)
Light Exposure = 6 days SAE J1885
Previous
workers
= best
Previous
workers
= worst

19. Gold Ratings: 1 = best, 5 = worst
Cure Temp. 10’/230, 2’/340 °C = NO EFFECT
However, 10’at 340°C = IMMEDIATE GOLD
UV* = 1
3 Am.= 1
UV* = 3
3 Am. = 2
* = 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
SEM
TOF-SIMS
XPS
AFM
Scanning Electron Microscopy
Time of Flight - Secondary Ion Mass Spectroscopy
X-Ray Photoelectron Spectroscopy
Atomic Force Microscopy

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

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

25. XPS - Black Area
Carbon
Oxygen

26. XPS - Gold Area
Oxygen
Carbon

27. XPS Oxygen Results - 2nd Study

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

29. XPS Zinc Results - 2nd Study

30. High Resolution AFM Surfaces
Black
Gold Shiny
Gold Matt

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 Antioxidants in the Three Amigos
Blank Bisphenolic ODPA TMQ
No AO (liquid)
Light Exposure = 6 days SAE J1885

34. Comparison of Antioxidants in 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 variations Gold Ratings = cured / uncured
Peroxide Cures of:
N762 black
N990 black & KE clay
EPDM 4345 (DCPD)
5/5
1/1
EPM 404 Copolymer
5/4
2/2
EPDM 509 (ENB)
4*/5
EPDM 509 / sulfur cure
5*/4
rainbow/ws
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. Final Experiment Photo of Test Pad with Gold Iridescence Middle portion clamped 1 week at RT removes gold.
10 mm
However: gold returns on oven aging or more light exposure.

38. Optical Properties of Nano Particles Chad A. Mirkin, George C
Optical Properties of Nano Particles Chad A. Mirkin, George C. Schatz, et. al., Science, 294, pages (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. Particle Size of Additives
Gold Region
N990
N774
Carbon
Black
Hard
Clay
Soft
Whiting
Zinc
Oxide
Precipitated Silica

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

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

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