Rubber

1. The technical service magazine for the rubber industry Volume 254, No. 2
MAY 2016
www.rubberworld.com
127
years
EPDM sponge profile formulations:
New approach with metallocene elastomers
by Eric Jourdain, Brian Burkhart and Mark Welker, ExxonMobil Chemical

2. 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 properties
We 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 process
Exxon 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 profile
formulations with metallocene elastomers
by 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 IT0316
properties (ref. 1)
Mooney viscosity
ML 1+4, 125°C
C2 content,
weight %
ENB content,
weight %
MWD
Softening
temperature, °C
Vistalon 7602
65
55
7.5
Medium
NA
Vistalon 8600
81 (ML 1+8)
57.5
8.9
Bimodal
NA
Vistalon 8800
73 (15 phr oil)
53.5
10
Bimodal
NA
IT0316
21
16
0
Narrow
54
and the kinetic balance blow over cure (ref. 2).
Sponge profile formulation and rheology
Exxon 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 properties
Sponge 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
Specificgravity
0.6
0.55
0.5
0.45
0.4
7602 7602
15 phr IT0316
7602
25 phr IT0316
Sponge profile density
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3. 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 EPDM
foaming process
In 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 IT0316
Vistalon 7602 EPDM
rubber
Spheron 5000
Omya BSH (whiting)
Flexon 815
Stearic acid
Active ZnO
PEG 3350
Rhenocure ZAT (70%)
Rhenogran TP/G (50%)
Final:
Rhenogran CaO-80
Sulfur
MBTS (80%)
MBT (80%)
DOTG
ZBEC (70%)
Vulkalent E
Celogen OT
Total phr
Vistalon
7602
-
100
80
20
75
1.5
4.0
1.0
1.5
1.5
2.0
1.5
1.0
0.5
0.2
1.8
0.2
2.5
294.2
7602/15 phr
IT0316
15
85
80
20
75
1.5
4.0
1.0
1.5
1.5
2.0
1.5
1.0
0.5
0.2
1.8
0.2
2.5
294.2
7602/25 phr
IT0316
25
75
80
20
75
1.5
4.0
1.0
1.5
1.5
2.0
1.5
1.0
0.5
0.2
1.8
0.2
2.5
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-02-04
ML t2
ML t5
ML t10
Minimum
MDR arc ± 0.5°, 180°C - TS-02-23
ML
MH
MH-ML
Ts2
T90
(MU)
(min. min.)
(min. min.)
(min. min.)
(MU)
(dNm)
(dNm)
(dNm)
(min.)
(min.)
7602
44
3.5
4.0
4.4
18
1.2
10.8
9.6
0.34
1.8
7602/15 phr
IT0316
40
3.5
4.0
4.5
16
1.0
8.5
7.5
0.37
3.1
7602/25 phr
IT0316
39
3.7
4.3
4.8
14
0.9
7.1
6.2
0.4
2.5
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
CompressionloaddeflectionN/20cm
120
100
80
60
40
20
0
7602 7602
15 phr IT0316
7602
25 phr IT0316
Sponge profile CLD
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4. 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 rheology
To 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 properties
Figure 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 compressibility
Bimodal Vistalon EPDM rubbers offer lower profile load
deflection. Vistalon 8800 profiles are slightly softer than the
30 RUBBERWORLD.COM • MAY 2016
Figure 3 - compression set of sponge profiles made with Vistalon 7602 EPDM rubber
and Exxon IT0316Compressionset,7daysat70°C,
40%deflection,%
40
30
20
10
0
Sponge profile compression set
7602 7602
15 phr IT0316
7602
25 phr IT0316
Best
elastic
recovery
Compressionsetonprofile,
40%deflection,%
40
35
30
25
20
15
10
Compression set and temperature
7602 7602
15 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)
Relativeconcentration
1.E-04
8.E-05
6.E-05
4.E-05
2.E-05
0.E+00
1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Mw (g/mol)
Bimodal grade
Lower MW mode
Higher MW mode
Figure 5 - cure state (MH-ML) of Vistalon
EPDM rubber compounds
Curestate,MH-ML,
MDRat180°C(dN-m)
20
19
18
17
16
15
Sponge formulation comparison
4.0 4.5 5.0
Scorch time, Ts5 at 125°C
7602
8800
8600
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5. Vistalon 8600 profiles, and both are softer than Vistalon
7602.
The following improvements were noted with the bimodal
EPDMs:
• Low CLD with the modified formulations (figure 7)
• Reduced low temperature stiffening due to low ethylene
content (figure 8)
• Lower CLD loss upon heat aging under compression
(figure 8) due to high crosslink density
Sponge formulations with blends of Vistalon EPDM rubber
Blends of Vistalon 7602 EPDM rubber and Vistalon 8800
EPDM rubber can be developed to optimize cost/performance
balance. In the comparative example below, formulations have
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Table 4 - sponge formulations comparing
Vistalon EPDM rubbers
Ingredients, phr
EPDM rubber
Carbon black FEF N550
CaCO3
Paraffinic oil high viscosity
ZnO
Stearic acid
PEG 3350
CaO-80
Sulfur 80%
MBT 80%
MBTS 80%
ZDEDC 80%
TMTDS 80%
DPTTS 80%
ZDBDC 80%
DPG 100%
Vulkalent E
OBSH
Total phr
V8600
100
80
40
60
4
1.5
2
2
1.5
1
0.5
1.5
0.8
1
1.3
0.4
0.2
2
299.7
V8800
115
90
40
60
4
1.5
2
2
1.5
0.5
1.5
1.5
0.8
1
1.3
0.4
0.2
2.5
325.7
V7602
100
80
40
60
6
1.5
2
2
1.5
1.5
-
1.7
0.8
1
1.2
0.4
-
2
301.6
Figure 6 - sponge profile comparisons of Vistalon EPDM rubber compounds
Profilesurface
roughness,Ri,um
8
7
6
5
4
Sponge profile comparison
0.60 0.65 0.70
Profile density (g/cm3)
7602
8800
8600
Compressionload
deflectionN/20cm
150
140
130
120
110
100
90
80
Sponge profile comparison
10 15 20 25 30
Compression set, 7 days/70°C (%)
7602
8800
8600
Figure 7 - CLD of Vistalon EPDM rubber
compounds at room temperature
Compressionload
deflection,N/20cm
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
Compressionload
deflection,N/20cm
120
100
80
60
40
20
0
Sponge profile CLD at -20°C
--Vistalon 8600
--Vistalon 8800
--Vistalon 7602
0 10 20 30 40 50
Profile compression in % of initial height
Sponge profile CLD loss
after aging 21 days at 70°C
Loaddeflectionloss,%
0%
-20%
-40%
-60%
-80%
-100%
0 10 20 30 40 50
--Vistalon 7602
--Vistalon 8800
--Vistalon 8600
Profile compression in % of initial height
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6. 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).
Conclusions
The 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.
32 RUBBERWORLD.COM • MAY 2016
Table 5 - formulation and rheology of
Vistalon EPDM rubber compounds
Ingredients
Vistalon 8800
Vistalon 7602
Carbon black FEF N550
CaCO3
Paraffinic oil high viscosity
ZnO
Stearic acid
PEG 3350
CaO 80%
Sulfur 80%
MBT 80%
MBTS 80%
ZDEDC 80%
TMTDS 80%
DPTTS 80%
ZDBDC 80%
DPG 100%
Vulkalent E
OBSH
Total (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.)
8800
115
-
90
40
60
4
1.5
2
2
1.5
0.5
1.5
1.5
0.8
1
1.3
0.5
0.2
2.5
325.8
49
4.00
4.62
5.20
20
1.27
16.5
15.2
0.34
2.3
8800/7602
57.5
50
90
40
65
4
1.5
2
2
1.5
0.8
0.8
1.5
0.8
1
1.3
0.4
0.2
2.5
322.8
49
4.08
4.70
5.27
20
1.28
17.3
16.1
0.33
2.4
Figure 9 - profile properties of Vistalon EPDM rubber compounds
Surfaceroughness,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
8800
7602/8800
Compressionload
deflection,40%N/20cm
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
Profileproperties,
indexbasedon
density,CLDand
compressionset
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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7. References
1. 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.
FOLLOW US ON TWITTER @rubberworld 33
Appendix 1 - Exxon IT0316 modification
Eclipse Number
Profile properties
Density,
g/cm3
Profile dimensions
Height, mm
Width, mm
Wall thickness, mm
Surface roughness
Ra, m
Rt, m
Ri, m
Physicals
Modulus 25%, MPa
Modulus 100%, MPa
TS, MPa
EB, %
Compression set
7 days/70°C/40% deflection, %
Retest
Load deflection
RT/40% deflection, N/20cm
112201208
7602
0.56
16.2
16.2
3.4
2.4
21
4.5
0.2
0.6
2.2
370
37
32
72
7602 w/
15 phr
IT0316
0.52
16.7
16.1
3.3
2.8
21
4.9
0.3
0.7
2.1
354
28
27
70
7602 w/
25 phr
IT0316
0.52
15.8
16.2
3.3
3.8
28
6.5
0.3
0.8
2.2
352
37
38
101
Appendix 2 - Vistalon EPDM rubber grade
comparison
Sponge profile properties
Dimensions
Height
Width
Thickness
Density
Surface roughness
Ra
Rt
Ri
Compression set, 40%
compression
7 days at 70°C
Compression load
deflection
40% deflection
Physical properties on
sponge profile
Modulus 25%
Modulus 50%
Modulus 100%
Tensile strength
Elongation at break
mm
mm
mm
g/cm3
mm
mm
mm
%
N/20 cm
MPa
MPa
MPa
MPa
%
7602
15.7
14.2
3.0
0.67
3.9
31
7.0
29
138
0.3
0.5
0.9
3.2
350
8600
15.8
15.4
3.0
0.63
3.3
23
5.6
18
111
0.4
0.6
1.1
3.3
270
8800
15.8
14.8
3.0
0.64
3.1
21
5.2
18
104
0.3
0.5
1.1
3.1
270
Appendix 3 - EPDM rubber
Sponge profile properties
Dimensions
Height
Width
Thickness
Density
Surface roughness
Ra
Rt
Ri
Compression set, 40%
compression
7 days at 70°C
Compression load deflection
40% deflection
Physical properties on
sponge profile
Modulus 25%
Modulus 50%
Modulus 100%
Tensile strength
Elongation at break
mm
mm
mm
g/cm3
mm
mm
mm
%
N/20 cm
MPa
MPa
MPa
MPa
%
8800
16.2
15.0
3.0
0.63
2.8
21.0
4.9
19
89
0.4
0.6
1.2
3.0
240
8800/7602
16.3
14.8
2.9
0.64
3.0
19.6
5.0
21
101
0.4
0.6
1.1
2.9
250
Appendix 4 - test methods
Test methods
Compound Mooney viscosity
Compound Mooney scorch
Compound MDR
RPA
Density
Profile surface roughness
Compression set sponge profile
Compression load deflection sponge
Physical properties
Test methods - technical data sheet
EPDM Mooney viscosity
EPDM Mooney stress relaxation
Ethylene content
ENB content
ExxonMobil
reference
TS 02-02
TS 02-04
TS 02-03
TS 02-22
TS 03-45
TS 05-17
TS 03-21
TS 03-23
TS 03-05
ASTM
D 1646
D 1646
D 3900
D 6047
Appendices
Profiles detail properties and test methods used.
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