Advantages of Peroxide Dispersions in HCR Silicone
Compounding
By
Erick Sharp (Speaker) – ACE Products & Consulting LLC, Uniontown, OH
Presented at the
2016 ACS International Elastomer Conference
October 11th – 13Th 2016
Pittsburg, PA
Abstract
A multi‐factor, general factorial designed experiment was performed to
investigate the processing of HCR silicone molding and extrusion compounds with
silicone bound peroxide dispersions. The factors selected for experiments are
peroxide form and type of peroxide. This study measured dependent variables of
a) MDR properties, b) dispersion and c) physical properties.
Classification of “Silicone Peroxide Dispersion”
Experiment
Equipment
All trials were mixed on a 5 liter tilt body lab mixer with tangential rotor configuration and
milled on a 6x12 lab mill.
Peroxides Evaluated
DBPH ‐ 2,5‐dimethyl‐2,5‐di(t‐butylperoxy)hexane
VULCUP ‐ T‐Butylperoxy‐Diisopropyl Benzene
DICUP ‐ Dicumyl Peroxide
Formulation
Compound A
100 PHR 40 Duro Silicone Base
2 PHR Peroxide
Recipe B
100 PHR 40 Duro Silicone Base
100 PHR 10 Micron Ground Quartz
2 PHR Peroxide
Mix Procedure
Compound A
1. Pass base through mill ten times
2. Add peroxide 3. Blend till dispersed
Compound B
1. Pass base / ground quartz masterbatch 10 times
2. Add peroxide 3. Blend till dispersed
Measurable Values
a. MDR
a. Parameters
i. 6’ at 355°F
b. Values
i. ML
ii. TS2
iii. Tc50
iv. Tc90
v. MH
b. Physical Properties
a. Parameters
i. Prepped 6’ at 355°F
ii. Post cured 4 hours at 400⁰F
b. Values
i. Tensile
ii. Elongation
iii. 100% Modulus
iv. 200% Modulus
v. Tear die b
vi. Compression Set (method B/ Plied)
c. Dispersion
a. Visual
Results
Compound (A) ‐ DBPH
It took 35% additional time on the mill to incorporate the powder DBPH versus the DBPH in
silicone binder. This is due to the difficulty to break down the powder agglomerates.
The T90 on the rheology data was slightly quicker on DPBH‐S then the DBPH –P. This is likely
due to the pre‐dispersed peroxide incorporating better with the polymer.
The DBPH‐S had a 9.14% improvement on the DBPH‐P on compression set.
ML Ts2 Tc90
Compound A ‐ Rheology DBPH‐P 0.88 0.40 0.84
Compound A ‐ Rheology DBPH‐S 0.85 0.40 0.80
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.900
1.000 Compound A ‐ DBPH Rheology
MH
Compound A ‐ Rheology DBPH‐P
6.54
Compound A ‐ Rheology DBPH‐S
6.23
6.0506.1006.1506.2006.2506.3006.3506.4006.4506.5006.5506.600
Compound A ‐ DBPH MH
Durometer, ShoreA
Tensile, psi Elongation, %100% Modulus,
psi200% Modulus,
psiTear Die B, lbs
DBPH‐S 78 958.38 555.99 101.31 182.85 65.6
DICUP‐P 49 495.64 354.99 110.05 206.23 72.3
78
958.38
555.99
101.31
182.85
65.649
495.64
354.99
110.05
206.23
72.3
Compound A Durometer & Tear
Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi
DBPH‐P 958.5 566.71 99.787 183.53
DBPH‐S 958.38 555.99 101.31 182.85
Compound A ‐ DBPH (Tensile, Elongation and Modulus)
53.0
54.0
55.0
56.0
57.0
58.0
59.0
60.0
61.0
DBPH‐P DBPH‐S
DBPH‐P DBPH‐S
Series1 61.0 55.7
Compound A ‐ Compression Set
Compound (A) DICUP
The DICUP –P required 50% additional time on the mill in order to achieve proper dispersion.
This was due to the larger particles of the powder not breaking down.
The rheology data between the DICUP‐P and DICUP‐S was within the margin of error other than
the T90 and ML. The T90 was .12 quicker on the DICUP‐S then the DICUP‐P. This is likely due to
better incorporation with the polymer when using the pre‐dispersed silicone binder. The ML on
the DICUP‐P was lower than the DUCP‐S. This is likely due to the extra mill passes it received.
The DICUP‐S had a 46% improvement in tensile properties over the DICUP‐P. Additionally it
tested out with a 30% greater elongation over the powder version. The DICUP‐P did render
13% better tear properties then the DICUP‐S. Compression set results between the two were
within the margin of error.
ML Ts2 Tc90 MH
Compound A ‐ Rheology DICUP‐P 0.91 0.40 0.89 6.69
Compound A ‐ Rheology DICUP‐S 1.07 0.38 0.77 6.61
0.000
1.000
2.000
3.000
4.000
5.000
6.000
7.000
8.000
Compound A ‐ Dicup Rheology
Durometer, ShoreA
Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi Tear Die B, lbs
DICUP‐P 49 495.64 354.99 110.05 206.23 72.3
DICUP‐S 49 913.35 505.58 108.23 201.79 62.7
49
495.64
354.99
110.05
206.23
72.349
913.35
505.58
108.23
201.79
62.7
Compound A Durometer & Tear
Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi
DICUP‐P 495.64 354.99 110.05 206.23
DICUP‐S 913.35 505.58 108.23 201.79
Compound A ‐ Dicup (Tensile, Elongation and Modulus)
Compound (A) VULCUP
The VULCUP‐P required 30% additional passes on the mill in order to incorporate. The powder
was platy and had a large particle size.
The ML was 48% higher on the DICUP‐P then the DICUP‐S. This is likely due to the large particle
size on the DICUP‐P. Dramatic increases in ML can result in crepe hardening, poor shelf‐life and
difficulty in processing. The DICUP‐S also had a .61s quicker T90. This is likely due to the better
incorporation of the peroxide with the polymer.
The DICUP‐S had a 14% improvement in tensile properties over the DICUP‐P. Additionally, it
rendered 25% better elongation.
Compression set improved by 24% in comparison to the DICUP‐P
44.5
45.0
45.5
46.0
46.5
47.0
DICUP‐P DICUP‐S
DICUP‐P DICUP‐S
Series1 45.5 46.9
Compound A ‐ Compression Set
ML Ts2 Tc90 MH
Compound A ‐ Rheology VULCUP‐P 1.99 0.35 1.53 7.51
Compound A ‐ Rheology VULCUP‐S 1.03 0.39 0.92 6.56
0
1
2
3
4
5
6
7
8
Compound A ‐ Vulcup Rheology
Durometer,Shore A
Tensile, psi Elongation, %100% Modulus,
psi200% Modulus,
psiTear Die B, lbs
VULCUP‐P 54 652.72 328.19 138.15 310.16 42.1
VULCUP‐S 52 755.38 435.91 118.56 228.62 64.6
54
652.72
328.19
138.15
310.16
42.152
755.38
435.91
118.56
228.62
64.6
Compound A Durometer & Tear
Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi
VULCUP‐P 652.72 328.19 138.15 310.16
VULCUP‐S 755.38 435.91 118.56 228.62
Compound A ‐ Vulcup (Tensile, Elongation and Modulus)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
VULCUP‐P VULCUP‐S
VULCUP‐P VULCUP‐S
Series1 56.6 43.2
Compound A ‐ Compression Set
Compound (B) DBPH
Incorporating the DBPH‐P into Compound (B) was more difficult than incorporating it into
Compound (A). The additional filler loading required extra passes in the mill to get the peroxide
into the matrix. The DBPH‐P required 40% additional blends over the DBPH‐S.
The ML value on the DBPH‐P was much higher than the DBPH‐S gave. While the DBPH‐P had
more time on the mill, it had an overall higher powder content and less polymer content then
the DBPH‐S batch. All other rheology results were within standard deviation.
The DBPH‐P gave 10% better tear while the DBPH‐S gave 10% better compression set. All other
physical properties were closely similar.
DBPH‐P DBPH‐S
ML 2.72 0.94
Ts2 0.33 0.28
Tc50 0.39 0.38
Tc90 0.73 0.79
MH 9.58 9.42
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Compound B ‐Rheology
Durometer, Shore A Tear Die B, lbs
DBPH‐P 62 80.7
DBPH‐S 62 73.0
62
80.7
62
73.0
Compound B ‐ Durometer & Tear
Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi
DBPH‐P 852.66 413.06 227.13 501.28
DBPH‐S 839.04 415.68 212.71 471.42
Compound B ‐ Tensile & Elongation
Compound (B) DICUP
Similar to the DBPH‐P, the DICUP‐P required additional mill work to disperse into Compound (B)
than what was required on Compound (A). The more highly filled a compound is the more
difficult it becomes to incorporate powder peroxides into the matrix. The DICUP‐P required
double the mill blending time than the DICUP‐S.
Tensile on the DICUP‐S improved by 21% over the DICUP‐P. Consequently, the tear on the
DICUP‐S was 16% lower then the tear on the DICUP‐P. Elongation was also 8% lower on the
DICUP‐S. Compression set was improved 10% with the DICUP‐S peroxide.
49.0
49.5
50.0
50.5
51.0
51.5
52.0
52.5
53.0
53.5
54.0
DBPH‐P DBPH‐S
DBPH‐P DBPH‐S
Series1 54.0 50.9
Compound B ‐ Compression Set
DICUP‐P DICUP‐S
ML 3.06 3.18
Ts2 0.33 0.33
Tc50 0.38 0.38
Tc90 0.71 0.83
MH 10.41 9.91
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Compound B ‐Rheology
Durometer, Shore A Tear Die B, lbs
DICUP‐P 64 71.7
DICUP‐S 63 59.9
64
71.7
63
59.9
Compound B ‐ Durometer & Tear
Compound (B) VULCUP
Similar to all the other powder peroxides there was considerable difficulty getting the material
worked into the compound. The VULCUP‐P required double the mill blending time versus the
VULCUP‐S. Of the powder peroxides, the VULCUP‐P was the most difficult to blend in.
Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi
DICUP‐P 593.78 218.5 260.99 551.38
DICUP‐S 752.45 311.68 239.32 539.55
Compound B ‐ Tensile & Elongation
41.0
42.0
43.0
44.0
45.0
46.0
47.0
48.0
DICUP‐P DICUP‐S
DICUP‐P DICUP‐S
Series1 47.2 43.2
Compound B ‐ Compression Set
The ML of the VULCUP‐P was much higher than the value for the VULCUP‐S. This likely
correlates with the processing difficulty we saw on the mill. The silicone carrying the VULCUP‐S
helped wet it out into the mixture, which improved processability and reduced the ML. The T90
on the VULCUP‐P was nearly half the rate of the VULCUP‐S. The VULCUP‐P acted as though
there was inhibition effecting the cure rate.
The VULCUP‐S had a slight decline in physical properties in comparison to the VULCUP‐P other
than tear. The VULCUP‐S had a 30% improvement in tear properties over the VULCUP‐P.
Compression set between the two were similar.
VULCUP‐P VULCUP‐S
ML 4.66 0.86
Ts2 0.32 0.29
Tc50 0.40 0.40
Tc90 2.15 0.92
MH 11.64 10.89
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Compound B ‐Rheology
Durometer, Shore A Tear Die B, lbs
VULCUP‐P 65 49.1
VULCUP‐S 65 69.6
65
49.1
6569.6
Compound B ‐ Durometer & Tear
Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi
VULCUP‐P 799.11 292.1 326.82 652.78
VULCUP‐S 759.35 284.34 282.66 596.55
Compound B ‐ Tensile & Elongation
Conclusions
The powder peroxide dispersions were more difficult to disperse into the compounds. This
difficulty magnified as the fill increased in the compounds. Longer mill blends were the result
of this issue. All the powder dispersions took longer to mix in comparison to their silicone
dispersed alternatives.
The fact that we added the peroxides in a secondary mill blend allowed for discretionary
blending of the peroxides to ensure proper dispersion. When mixing on a mixer, it is more
difficult to measure the dispersion of the powder peroxides. Some mixing technologies have
less shear than others. This can also effect the ability to break down the powder agglomerates
and disperse them into the low viscosity silicone polymer. Worn out mixers or poor mixer
tolerances will only hinder the ability to blend in powder peroxides.
We recommend blending powder peroxides into the polymer before large filler additions if
possible in order to ensure good polymer interaction. This allows the peroxide to work into the
polymer before all the available sites are consumed with filler. Being that silicone dispersed
peroxides are already in a polymer matrix, this makes it easier to work into any compound
50.0
51.0
52.0
53.0
54.0
55.0
56.0
57.0
VULCUP‐P VULCUP‐S
VULCUP‐P VULCUP‐S
Series1 56.2 52.2
Compound B ‐ Compression Set
without having to find available polymer sites. Having the peroxide in a silicone binder ensures
there is always available polymer with which to link.
The DICUP showed the greatest gain in physical properties when using the silicone binder. All
others evaluated showed minimal difference either way in general physical properties.
Compression set was always improved or equal when using the silicone bound dispersions.
Silicone bound peroxide dispersions processed better than their powder equivalents. There
was less inhibition in cure with the silicone bound dispersions. Other than in DICUP, there was
little difference in physical properties. The silicone bound dispersions provided measureable
improvement in compression set. Silicone bound peroxide dispersion do provide several
advantages over their powder equivalents.
Acknowledgements
A special thanks to Polychem Dispersions for use of their laboratory resources to perform this
study.
A special thanks to HB Chemical, Lianda and Graphic Arts for contributing raw materials for this
study.
