Light-Induced Gold Iridescence (Sunburn) of EPDM Weatherseals

by Bob Ohm* & Dan PattonLion Copolymer, LLC

Compounding and Development Center5955 Scenic Highway, Baton Rouge, LA 70805

* Speaker

Outline

IntroductionBloom vs. Iridescence23 Designed Experiment: Filler, Oil & CurativeEffect of Cure Temperature & EPDM PolymerSurface AnalysisAntioxidant ComparisonFinal ExperimentsSummary

IntroductionWhy weatherseals are based on EPDM

Excellent WeatherabilityImpervious to OzoneHighly Resistant to Heat and OxidationHighly Extendable

Discoloration in LightInitial colors blue / red / greenChange to bronze / gold

Prior Work

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

The Iridescent Color depends on the angle of view

Bloom and BleedSurface Discoloration due to powdery solid (bloom) or liquid film (bleed)

The remedy is straightforward:1. Remove the material at the surface2. Determine the composition of the material removed.3. 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!

???

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

Non-exposed Side

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Time

Ab

un

dan

ce

O

S C N

C

O

OH

O

NH

NH

N

S

HO

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

Sun Exposed Side

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Time

Ab

un

dan

ce

NH

Light-Induced Gold Iridescence (Sunburn) of EPDM WeathersealsFive 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 analysis4. antioxidant comparison5. polymer, filler & other variations

23 Designed Experiment

Filler / carbon black

Oil / plasticizer

Cure System (Sulfur vs. Peroxide)

Additive Package (the 3 Amigos)

Filler Comparison

A. Furnace black:– made from crude oil– made in air– contains aromatic structures (staining)– contains sulfur, nitrogen

B. Thermal black*:– made from natural gas– anaerobic manufacture (no oxygen)– minimum extractables (aromatics)– little/no sulfur, nitrogen

* plus precipitated silica to equalize hardness

Plasticizer Comparison

A. Parafinnic oil:– made from crude oil– contains aromatic structures– contains sulfur, nitrogen

B. Poly -olefin:– made from decene– no residual unsaturation

(removed by hydrogenation)– no sulfur, nitrogen

Cure System ComparisonA. Sulfur cure:

– contains sulfur, nitrogen– little/no oxygen– accelerator fragments found on

surface

B. Peroxide cure:– no sulfur, nitrogen– contains oxygen

Gold Ratings: 1 = best, 5 = worst6 days exposure per SAE J1960 (exterior)

3, 2 5, 4

5, 4 3, 2 (PO)

-2

-1

0

1

2

-2 -1 0 1 2

Filler (-1 = thermal black*, +1 = furnace black)

Cu

re S

yste

m,

(-1

= p

erox

ide,

+1

= s

ulf

ur)

SulfurCure

PeroxideCure

ThermalBlack*

FurnaceBlack

3 Am.= 5

3 Am. = 1

* = mat surface develops during light exposure

Gold Ratings: 1 = best, 5 = worst6 days exposure per SAE J1885 (interior)

2, 3 5, 5

3.5, 3.5 1, 2.5 (PO)

-2

-1

0

1

2

-2 -1 0 1 2

Filler (-1 = thermal black*, +1 = furnace black)

Cu

re S

yste

m,

(-1

= p

erox

ide,

+1

= s

ulf

ur)

SulfurCure

PeroxideCure

ThermalBlack*

FurnaceBlack

3 Am.= 0.5

3 Am. = 1.5

* = mat surface develops during light exposure

Summary of 23 Experiment

A. 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.

B. The 3 Amigos are effective, esp./SAE J1885.

C. A peroxide cure is poorer than the sulfur cure per SAE J1885 (no effect per SAE J1960).

D. The PAO is better than paraffinic oil per J1960 (no effect or slightly poorer by J1885).

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 analysis4. antioxidant comparison5. polymer, filler & other variations

Polymers Evaluated

EPDM563/501

EPDM556

EPDM509

EPDM505

3

5

7

9

50 55 60 65 70 75 80

Ethylene Content, %

Die

ne

Co

nte

nt,

%

Previous workers= best

Previous workers= worst

(Cure Temperature = 230 or 340 °C)Light Exposure = 6 days SAE J1885

Gold Ratings: 1 = best, 5 = worst

4 3

2 2

3

5

7

9

50 55 60 65 70 75 80

Ethylene Content, %

Die

ne

Co

nte

nt,

%

UV* = 1 3 Am.= 1

UV* = 3 3 Am. = 2

Cure Temp. 10’/230, 2’/340 °C = NO EFFECT

However, 10’at 340°C = IMMEDIATE GOLD

* = heavy white bloom on molded samples

Summary of Second Study

A. The gold color can be developed by oxidation without light exposure. (However, this method leads to sample embrittlement.)

B. High diene polymers give lower gold ratings.

C. Gold ratings can be further lowered by addition of the “Three Amigos”.

D. Ethylene level and cure temperature have little effect on gold in our laboratory work.

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 analysis4. antioxidant comparison5. polymer, filler & other variations

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

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

10 m10 m

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 onlysiloxane

(mold release).

012771130.spe: control sample A Evans East01 Dec 17 Al mono 350.0 W 0.0 50.0° 187.85 eV 2.0460e+005 max 4.50 minSur1/Full/1

200400600800100012000

0.5

1

1.5

2

2.5x 10

5 012771130.spe

Binding Energy (eV)

c/s

-C

KL

L

-Z

n2

p1

-Z

n2

p3

-O

KL

L -

O K

LL

-Z

n L

MM

-O

1s

-Z

n L

MM

-Z

n L

MM

-C

1s

-S

i2s

-S

i2p

-F

1s

-N

1s

-Z

n3

p3

-Z

n3

s

XPS - Black Area

Oxygen

Carbon

012771120.spe: "gold" sample A Evans East01 Dec 17 Al mono 350.0 W 0.0 50.0° 187.85 eV1.8553e+005 max 4.50 minSur1/Full/1

200400600800100012000

0.5

1

1.5

2

2.5x 10

5 012771120.spe

Binding Energy (eV)

c/s

-C

KL

L

-Z

n2

p1

-Z

n2

p3

-O

KL

L -

O K

LL

-O

1s

-Z

n L

MM

-Z

n L

MM

-N

1s

-C

1s

-S

2s

-S

2p

-S

i2s

-S

i2p

-Z

n3

p3

-Z

n3

s

XPS - Gold Area

Carbon

Oxygen

XPS Oxygen Results - 2nd Study

0

5

10

15

20

25

Royalene505

(GR=2)

Royalene556

(GR=3)

Royalene563/501(GR=4)

R-505 +UV Stab.(GR=1)

R-505 + 3AmigosGR=1)

10 min @650F

(GR=10)

Oxy

gen

Co

nce

ntr

atio

n,

% black surfacegold surface

XPS Nitrogen Results - 2nd Study

0.0

0.5

1.0

1.5

2.0

2.5

EPDM505

(GR=2)

EPDM556

(GR=3)

EPDM563/501(GR=4)

505 + UVStab.

(GR=1)

505 + 3AmigosGR=1)

10 min at340ºC

(GR=10)

Nit

rog

en C

on

cen

trat

ion

, %

black surface

gold surface

contains MSDPA amine antioxidant

XPS Zinc Results - 2nd Study

0.0

0.5

1.0

1.5

2.0

2.5

EPDM505

(GR=2)

EPDM556

(GR=3)

EPDM563/501(GR=4)

505 +Ciba

(GR=1)

505 + 3AmigosGR=1)

10 min @650F

(GR=10)

Zin

c C

on

cen

trat

ion

, % black surface

gold surface

Gold Matt Gold Shiny

High Resolution AFM Surfaces

Black

Surface Analysis SummaryA. Molded samples under SEM appear to

develop raised nodules.

B. TOF-SIMS was not successful in identifying the composition of the nodules.

C. XPS finds the gold surface is enriched in oxygen and, to a lesser extent, nitrogen and zinc.

D. AFM finds black regions are smooth; light-exposed gold regions, especially low-gloss, are rough – nano structure.

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 analysis4. antioxidant comparison5. polymer, filler & other variations

Comparison of Antioxidantsin the Three Amigos

Blank Bisphenolic ODPA TMQNo AO (liquid)

OH

CH3

CH2H19C9

OH

C9H19

CH3

NH

C8H17

C8H17

N

CH3

CH3

CH3

H n

Light Exposure = 6 days SAE J1885

Comparison of Antioxidantsin the Three Amigos (continued)

MSDPA Sulfonated Bisphenol NBC Diphenyl- Phosphite amine Blend

NH

CCH3

H3C

CH3C

CH3

SO2

H3C

NH

NHNi

S

S

C

S

N (C4H9)2

C N (C4H9)2

S

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 analysis4. antioxidant comparison5. polymer, filler & other variations

Polymer, filler & other variationsGold 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 1/1

EPDM 509 / sulfur cure 5*/4 rainbow/ws

The filler system of N990 & KE clay give a dull surfaceAfter SAE J1885 exposure, similar to N990 & ppt. silica.

* Rating improves where Mylar film adhered.

Final ExperimentPhoto 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.

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 nanoprisimsscatter red light.

Gold nanorodsscatter orange light.

Gold nanospheresscatter green light.

SummaryA. Compression of the surface can

remove the gold iridescence.

B. However, this is not a practical solution because the gold is redeveloped during brief oven aging or additional light exposure.

C. For future work, a permanent solution may require both chemical and physical (structure) control.

Thanks for your attention

Any Questions?

In the scales of the greenportion of the papillo’s wings,each concavity reflects bright yellow while the outer edges

reflect bright blue…

The papillo butterfly’s wingsare covered with small textured

scales (above right)… Tinyconcavities within these scales(below left) create color through

constructive interference…

The Three AmigosOH

CH3

CH2H19C9

OH

C9H19

CH3

Naugawhite

R

OH

CH2

OH

R

HO

OH

R

CH2 OH

n

Schenctady SP-1066 Phenolic Resin

HO O OHn

Carbowax 3350Polyethyleneglycol

Gold RegionGold Region

250 500 1000 1500

Particle Size, nm

Particle Size of Additives

HardClay

SoftClay

ZincOxide

Precipitated Silica

Whiting

N990N774Carbon

Black

High Resolution XPSMain Peak = C-(C1H)

control sample A-O-C=O

gold sample AC-O

C=O C-N

AFM Surface AnalysisBlack Surface Shiny Sample Black Surface of Matt Sample

Gold Shiny Surface Gold Matt Surface30 m

Gold Matt Gold Shiny

High ResolutionAFM Surfaces

0 2 4 6

350

nm 0

-3500 2 4 6 m

350

nm 0

-350

Black

475 nm665 nm 130 – 250 nm