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The technical service magazine for the rubber industry Volume 254, No. 2

MAY 2016

www.rubberworld.com

127years

EPDM sponge profile formulations:New approach with metallocene elastomers

by Eric Jourdain, Brian Burkhart and Mark Welker, ExxonMobil Chemical

formulate sponge compounds, such as an amorphous, high diene, medium molecular weight, metallocene EPDM rubber grade; two amorphous, bimodal, high molecular weight, con-ventional EPDM rubber grades; blends of EPDM grades with a metallocene propylene-ethylene elastomer; and blends of metal-locene and bimodal EPDM rubber grades. These polymer combinations offer the potential for reduced sponge profile density; optimized sealing attributes, such as load deflection and compression set; and adaptability to meet strin-gent automotive OEM weatherseal specifications. Elastomer propertiesWe selected elastomers with different molecular weight struc-tures and properties (table 1). Vistalon 7602 EPDM rubber is a metallocene EPDM with medium molecular weight and high diene. Vistalon 8600 EPDM rubber is a conventional EPDM with higher molecular weight, bimodal molecular weight distri-bution and high diene. Vistalon 8800 EPDM rubber is a conven-tional EPDM with high molecular weight, bimodal molecular weight distribution, and very high diene. Exxon IT0316 is a propylene-ethylene elastomer that does not vulcanize with sul-fur (no unsaturation).

Exxon IT0316 interaction in the EPDM foaming processExxon IT0316 is a propylene based elastomer. It has a pre-dominantly amorphous structure of ethylene-propylene laced with a network of isotactic polypropylene crystallites. A reduc-tion in crystallinity is obtained through the introduction of amorphous regions of ethylene-propylene in the polypropylene sequences. IT0316 has a lower molecular weight than Vistalon 7602 EPDM rubber. During the mixing stage, it is easily dis-persed in the EPDM compound matrix along with the fillers and plasticizers. Since propylene units dominate the backbone structure of Exxon IT0316, it is not miscible with most EPDM polymers. It is a fully saturated copolymer and does not react with the curing agent due to the absence of double bonds. IT0316 is used to modify the EPDM compound rheology by viscosity reduction

New approach to EPDM sponge profileformulations with metallocene elastomersby Eric Jourdain, Brian Burkhart and Mark Welker, Exxon-Mobil Chemical

EPDM is one of the most widely used rubbers in automotive exterior sealing systems. It is the material of choice for automo-tive sponge weatherstrips around doors, trunks and hoods. Its unique properties of air and ozone resistance, coupled with its compounding versatility, produce high performing profiles at relatively low cost while sealing out water, dirt and noise over the lifetime of the car. Advances in metallocene polymerization technology over the past decade have provided precise control over the molecu-lar architecture and comonomer introduction, enabling the abil-ity to design high performance elastomers with tailored proper-ties. In this article, we present different polymer approaches to

28 RUBBERWORLD.COM • MAY 2016

Table 1 - Vistalon EPDM rubber and Exxon IT0316properties (ref. 1)

Mooney viscosity ML 1+4, 125°CC2 content, weight %ENB content, weight %MWDSoftening temperature, °C

Vistalon 7602

65

55

7.5Medium

NA

Vistalon 8600

81 (ML 1+8)

57.5

8.9Bimodal

NA

Vistalon 8800

73 (15 phr oil)

53.5

10Bimodal

NA

IT0316

21

16

0Narrow

54

and the kinetic balance blow over cure (ref. 2).

Sponge profile formulation and rheologyExxon IT0316 was substituted for 15 phr and 25 phr of Vistalon 7602 in a standard sponge formula-tion (table 2). IT0316 acts as a polymeric process-ing aid, reducing the compound viscosity. Since IT0316 has no unsaturation, the scorch time (Ts5) is slightly increased, while the cure rate and cure state are decreased (table 3). Sponge profile propertiesSponge profiles were produced using an “Omega” shaped die in a semi-industrial extrusion line at

Figure 1 - density reduction of sponge profiles made from Vistalon 7602 EPDM

rubber using Exxon IT0316

Spe

cific

gra

vity

0.6

0.55

0.5

0.45

0.47602 7602

15 phr IT03167602

25 phr IT0316

Sponge profile density

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close a door. The profile’s CLD is virtually unchanged after add-ing 15 phr of Exxon IT0316, despite the lower profile density.The CLD increases at 25 phr, which reflects the natural hardness and increased abundance of IT0316 domains in the compound (figure 2). Compression set reflects the sealing performance over time of a sponge profile held at constant deflection. A compression set improvement is observed using 15 phr of Exxon IT0316, but the data suggest the optimum morphology of the foamed struc-ture requires much less than 25 phr (figure 3). At the higher loading of IT0316, where the thermoplasticity of IT0316 be-comes more predominant and the cure state is reduced, the compression set gets worse.

Possible mechanism of Exxon IT0316 interaction in the EPDMfoaming processIn compounds containing Exxon IT0316, the chemical blowing

ExxonMobil. Profiles were extruded at approximately 4 meters/minute and then cured using a UHF oven followed by a hot air oven. The increased thermoplasticity of Exxon IT0316 reduces the pressure at the extruder head. The final density of the profile was also reduced by about 10% (figure 1). It appears that IT0316 allows the blowing agent to expand more easily, while the re-duced diene content lowers the cure rate and cure state. These effects may also be influenced by soft thermoplastic domains from the IT0316 dispersed into the compound. Compression load deflection (CLD) is a measure of stiffness and serves as a proxy for the seal’s influence on the effort to

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Table 2 - model compound formulations for automotive sponge

Formulation and mixing

Masterbatch:Exxon IT0316Vistalon 7602 EPDM rubberSpheron 5000Omya BSH (whiting)Flexon 815Stearic acidActive ZnOPEG 3350Rhenocure ZAT (70%)Rhenogran TP/G (50%)

Final:Rhenogran CaO-80SulfurMBTS (80%)MBT (80%)DOTGZBEC (70%)Vulkalent ECelogen OTTotal phr

Vistalon 7602

-100

8020751.54.01.01.51.5

2.01.51.00.50.21.80.22.5

294.2

7602/15 phr IT0316

1585

8020751.54.01.01.51.5

2.01.51.00.50.21.80.22.5

294.2

7602/25 phr IT0316

2575

8020751.54.01.01.51.5

2.01.51.00.50.21.80.22.5

294.2

Table 3 - rheology of Vistalon 7602 EPDM rubber/ Exxon IT0316 model compounds

Rheology

Mooney ML (1+4) 100°C on MV2000E - TS-02-02 ML (1+4)Mooney scorch 125°C - TS-02-04ML t2ML t5ML t10MinimumMDR arc ± 0.5°, 180°C - TS-02-23MLMHMH-MLTs2T90

(MU)

(min. min.)(min. min.)(min. min.)

(MU)

(dNm)(dNm)(dNm)(min.)(min.)

7602

44

3.54.04.418

1.210.89.6

0.341.8

7602/15 phr IT0316

40

3.54.04.516

1.08.57.5

0.373.1

7602/25 phr IT0316

39

3.74.34.814

0.97.16.20.42.5

agents have more latitude to expand. IT0316 decreases “green strength,” reduces the cure rate, creates thermo-plastic domains and lowers the crosslink density. As a result, a lower profile density can be achieved when using the same amount of blowing agent. Alternative-ly, the same density can be obtained with less blowing agent. Since IT0316 has higher crystallinity than the EPDM rubber, the sponge profiles with IT0316 also have a higher stiffness at similar densities, resulting in a higher compression load deflection. Alternatively, a similar compression load deflection can be obtained at a lower density. A surprising effect is seen in the compression set at 70°C, which maintains similar performance despite lower crosslink density and lower profile density. It appears that the Exxon IT0316 improves the cell structure, creating more open cells of smaller size, which improves the compression set in a sponge pro-file.

Figure 2 - compression load deflection of sponge profiles made with Vistalon 7602

EPDM rubber and Exxon IT0316

Com

pres

sion

load

defl

ectio

n N

/20

cm

120

100

80

60

40

20

07602 7602

15 phr IT03167602

25 phr IT0316

Sponge profile CLD

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Sponge formulations with bimodal Vistalon EPDM rubber ExxonMobil’s bimodal EPDM elastomers are composed of a major polymer fraction with narrow MWD with a controlled level of very high molecular weight component (figure 4). Since their introduction in the 1990s, bimodal EPDM grades have been very successful in extrusion applications, as they offer the elastic performance of a high molecular weight EPDM with the processing capability of a medium molecular weight polymer (ref. 3).

Sponge profile formulation and rheologyTo aid comparing the performance of different Vistalon EPDM rubber grades, it is useful to target a similar compound viscosity (ML, 1+4, 100°C). Therefore, we used the same formulation for Vistalon 7602 and Vistalon 8600. Because Vistalon 8800 has higher molecular weight, we formulate it with a higher filler loading (30% EPDM content vs. 33%) and a lower carbon black to oil ratio (ref. 4). The cure package has been modified for each EPDM grade’s

properties in order to have compounds with a similar scorch time (table 4).

Compound rheology and profile propertiesFigure 5 shows a high cure state for Vistalon 7602 EPDM rub-ber compound, as measured by MDR at 180°C. This is related to the uniform molecular structure of metallocene EPDM, which improves ENB efficiency during vulcanization. Figure 6 shows the effects of the high molecular weight and bimodal EPDM structure on profile properties, including smooth surface aspect, low profile density, low CLD and low compression set. The Vistalon 8800 EPDM rubber compound has a higher filler content and a lower carbon black to oil ratio. Its profile has similar performance to a Vistalon 8600 EPDM rubber-based profile. This illustrates the advantage of selecting a very high molecular weight EPDM to formulate sponge compounds.

Sponge profile compressibilityBimodal Vistalon EPDM rubbers offer lower profile load deflection. Vistalon 8800 profiles are slightly softer than the


Figure 3 - compression set of sponge profiles made with Vistalon 7602 EPDM rubberand Exxon IT0316

Com

pres

sion

set

,7 d

ays

at 7

0°C

, 40

% d

eflec

tion,

%

40

30

20

10

0

Sponge profile compression set

7602 760215 phr IT0316

760225 phr IT0316

Bestelasticrecovery

Com

pres

sion

set

on

profi

le,

40%

defl

ectio

n, %

40

35

30

25

20

15

10

Compression set and temperature

7602 760215 phr IT0316

■ 24 hours/80°C, %■ 70 hours/70°C, %■ 24 hours/100°C, %

Figure 4 - typical GPC trace of a bimodal EPDM grade (140°C - trichlorobenzene -

refractive index detector)

Rel

ativ

e co

ncen

tratio

n

1.E-04

8.E-05

6.E-05

4.E-05

2.E-05

0.E+001.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Mw (g/mol)

Bimodal gradeLower MW mode

Higher MW mode

Figure 5 - cure state (MH-ML) of Vistalon EPDM rubber compounds

Cur

e st

ate,

MH

-ML,

M

DR

at 1

80°C

(dN

-m) 20

19

18

17

16

15

Sponge formulation comparison

4.0 4.5 5.0Scorch time, Ts5 at 125°C

7602

8800

8600

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Vistalon 8600 profiles, and both are softer than Vistalon 7602. The following improvements were noted with the bimodal EPDMs: •LowCLDwiththemodifiedformulations(figure7) •Reducedlowtemperaturestiffeningduetolowethylene content(figure8) •LowerCLDlossuponheatagingundercompression (figure8)duetohighcrosslinkdensity

Sponge formulations with blends of Vistalon EPDM rubberBlends of Vistalon 7602 EPDM rubber and Vistalon 8800EPDMrubbercanbedevelopedtooptimizecost/performancebalance.Inthecomparativeexamplebelow,formulationshave


Table 4 - sponge formulations comparing Vistalon EPDM rubbers

Ingredients, phrEPDM rubberCarbon black FEF N550CaCO3Paraffinic oil high viscosityZnOStearic acidPEG 3350CaO-80Sulfur 80%MBT 80%MBTS 80%ZDEDC 80%TMTDS 80%DPTTS 80%ZDBDC 80%DPG 100%Vulkalent EOBSHTotal phr

V86001008040604

1.522

1.51

0.51.50.8

11.30.40.2

2299.7

V88001159040604

1.522

1.50.51.51.50.8

11.30.40.22.5

325.7

V76021008040606

1.522

1.51.5

-1.70.8

11.20.4

-2

301.6

Figure 6 - sponge profile comparisons of Vistalon EPDM rubber compoundsP

rofil

e su

rface

ro

ughn

ess,

Ri,

um

8

7

6

5

4

Sponge profile comparison

0.60 0.65 0.70

Profile density (g/cm3)

7602

88008600

Com

pres

sion

load

de

flect

ion

N /

20 c

m

1501401301201101009080

Sponge profile comparison

10 15 20 25 30

Compression set, 7 days/70°C (%)

7602

88008600

Figure 7 - CLD of Vistalon EPDM rubber compounds at room temperature

Com

pres

sion

load

de

flect

ion,

N/2

0 cm

120

100

80

60

40

20

0

Sponge profile CLD at RT

-- Vistalon 7602-- Vistalon 8600-- Vistalon 8800

0 10 20 30 40 50

Profile compression in % of initial height

Figure 8 - CLD of Vistalon EPDM rubber compounds at -20°C and after heat aging

Com

pres

sion

load

de

flect

ion,

N/2

0 cm

120

100

80

60

40

20

0

Sponge profile CLD at -20°C


0 10 20 30 40 50


Sponge profile CLD lossafter aging 21 days at 70°C

Load

defl

ectio

n lo

ss, % 0%

-20%

-40%

-60%

-80%

-100%

0 10 20 30 40 50



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been adjusted to obtain similar compound viscosity and cure parameters (table 5). When blending Vistalon 7602 EPDM rubber, having a me-dium molecular weight distribution, with Vistalon 8800, which has a bimodal molecular weight distribution, profile properties such as density and compression set are impacted. However, the Vistalon 7602 content can be easily adjusted to meet or exceed the aspect and sealing requirements of many sponge specifica-tions (figure 9).

ConclusionsThe rubber formulator can conveniently select the most appro-priate Vistalon EPDM rubber grade or blend to produce finely tailored automotive sponge profiles according to the particular technical specification desired (figure 10). Replacing 15 phr of Vistalon 7602 EPDM rubber with Exxon IT0316 is a novel approach to formulating EPDM sponge compounds. Since the blowing agent becomes more ef-ficient, Exxon IT0316 blends provide a convenient route to cost and performance improvements through lower profile densities and/or reduced use of blowing agents. Blends of Vistalon 7602 EPDM rubber with bimodal Vistal-on 8800 further improve sponge profile properties such as den-sity and compression set. Vistalon 7602/8800 blends offer a convenient route to optimize the cost/performance balance of a profile. The highest performing automotive sponge profiles are

achieved with the high molecular weight bimodal Vistalon EPDM rubber grades. Vistalon 8600 and Vistalon 8800, which are the grades of choice to produce the best performing sponge profile, have unique molecular architectures to consistently produce the highest quality low density profiles of complex geometry and best compression load deflection and compres-sion set over a wide range of temperatures. This article is based on a paper presented at the 188th Tech-nical Meeting of the Rubber Division, ACS, October 2015.


Table 5 - formulation and rheology of Vistalon EPDM rubber compounds

IngredientsVistalon 8800Vistalon 7602Carbon black FEF N550CaCO3Paraffinic oil high viscosityZnOStearic acidPEG 3350CaO 80%Sulfur 80%MBT 80%MBTS 80%ZDEDC 80%TMTDS 80%DPTTS 80%ZDBDC 80%DPG 100%Vulkalent EOBSHTotal (phr)Mooney viscosity ML (1+4) 100°C (MU)Mooney scorch (1+29 ) 125°C - EEB Ms t2 (min. min.) Ms t5 (min. min.) Ms t10 (min. min.) Minimum (MU)MDR arc ± 0.5°, 180°C ML (dNm) MH (dNm) MH-ML (dNm)Ts2 (min.) T90 (min.)

8800115

-9040604

1.522

1.50.51.51.50.8

11.30.50.22.5

325.8

49

4.004.625.20

20

1.2716.515.20.342.3

8800/760257.5

509040654

1.522

1.50.80.81.50.8

11.30.40.22.5

322.8

49

4.084.705.27

20

1.2817.316.10.332.4

Figure 9 - profile properties of Vistalon EPDM rubber compoundsS

urfa

ce ro

ughn

ess,

um

5.5

5.3

5.1

4.9

4.7

4.5

Sponge compound with EPDM blendsSponge compound with EPDM blends

0.60 0.61 0.62 0.63 0.64 0.65

Profile density

7602/8800

88007602/8800

Com

pres

sion

load

de

flect

ion,

40%

N/2

0 cm

8800

120

110

100

90

80

70

60 15 17 19 21 23 25

Compression set, % (7 days/70°C, 40% deflection)

Figure 10 - Vistalon EPDM rubber selection and sponge profile performance

Pro

file

prop

ertie

s,in

dex

base

d on

de

nsity

, CLD

and

co

mpr

essi

on s

et

Sponge grade positioning

7602/ IT0316 Blend 7602/

8800

7602

8800

8600

Compound processibility,index based on MLRA/ML and compound

viscosity

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References1. Vistalon EPDM rubber technical data sheet.2. Eric Jourdain and Caroline Szala, "A new approach in EPDM sponge profiles with metallocene elastomers," IRC 2015.3. Eric Jourdain, Guy Wouters and Mark F. Welker, "New EPDM grade with improved processing characteristics," DKT 12 Conference.4. Brian Burkhart, Milind Joshi and Eric Jourdain, "A metal-locene EPDM grade for use in automotive and industrial sponge applications," 186th Technical Meeting of the Rubber Division, ACS, October 2014.


Appendix 1 - Exxon IT0316 modification

Eclipse NumberProfile properties

Density, g/cm3

Profile dimensions Height, mm Width, mm Wall thickness, mmSurface roughness Ra, m Rt, m Ri, mPhysicals Modulus 25%, MPa Modulus 100%, MPa TS, MPa EB, %Compression set 7 days/70°C/40% deflection, % RetestLoad deflection RT/40% deflection, N/20cm

1122012087602

0.56

16.216.23.4

2.4214.5

0.20.62.2370

3732

72

7602 w/ 15 phr IT0316

0.52

16.716.13.3

2.8214.9

0.30.72.1

354

2827

70

7602 w/ 25 phr

IT0316

0.52

15.816.23.3

3.8286.5

0.30.82.2

352

3738

101

Appendix 2 - Vistalon EPDM rubber grade comparison

Sponge profile propertiesDimensionsHeightWidthThicknessDensitySurface roughness Ra Rt RiCompression set, 40% compression7 days at 70°CCompression load deflection40% deflectionPhysical properties on sponge profile Modulus 25% Modulus 50% Modulus 100% Tensile strength Elongation at break

mmmmmm

g/cm3

mmmmmm

%

N/20 cm

MPaMPaMPaMPa

%

7602

15.714.23.0

0.67

3.9317.0

29

138

0.30.50.93.2350

8600

15.815.43.0

0.63

3.3235.6

18

111

0.40.61.13.3

270

8800

15.814.83.0

0.64

3.1215.2

18

104

0.30.51.13.1

270

Appendix 3 - EPDM rubber

Sponge profile propertiesDimensionsHeightWidthThicknessDensitySurface roughness Ra Rt RiCompression set, 40% compression 7 days at 70°CCompression load deflection 40% deflectionPhysical properties on sponge profile Modulus 25% Modulus 50% Modulus 100% Tensile strength Elongation at break

mmmmmm

g/cm3

mmmmmm

%

N/20 cm

MPaMPaMPaMPa

%

8800

16.215.03.0

0.63

2.821.04.9

19

89

0.40.61.23.0

240

8800/7602

16.314.82.9

0.64

3.019.65.0

21

101

0.40.61.12.9

250

Appendix 4 - test methods

Test methods

Compound Mooney viscosityCompound Mooney scorchCompound MDRRPADensityProfile surface roughnessCompression set sponge profileCompression load deflection spongePhysical propertiesTest methods - technical data sheetEPDM Mooney viscosityEPDM Mooney stress relaxationEthylene contentENB content

ExxonMobil referenceTS 02-02TS 02-04TS 02-03TS 02-22TS 03-45TS 05-17TS 03-21TS 03-23TS 03-05

ASTMD 1646D 1646D 3900D 6047

AppendicesProfiles detail properties and test methods used.

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