Peroxide Dispersions in HCR Silicone Compounding · Advantages of Peroxide Dispersions in HCR...

transcript

Advantages of Peroxide Dispersions in HCR Silicone

Compounding

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

ii. TS2

iii. Tc50

iv. Tc90

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

1.000 Compound A ‐ DBPH Rheology

Compound A ‐ Rheology DBPH‐P

Compound A ‐ Rheology DBPH‐S

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

958.38

555.99

101.31

182.85

65.649

495.64

354.99

110.05

206.23

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)

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

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

495.64

354.99

110.05

206.23

72.349

913.35

505.58

108.23

201.79

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

DICUP‐P DICUP‐S

Series1 45.5 46.9

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

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

652.72

328.19

138.15

310.16

42.152

755.38

435.91

118.56

228.62

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)

VULCUP‐P VULCUP‐S

Series1 56.6 43.2

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

Compound B ‐Rheology

Durometer, Shore A Tear Die B, lbs

DBPH‐P 62 80.7

DBPH‐S 62 73.0

Compound B ‐ Durometer & Tear

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.

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

DICUP‐P 64 71.7

DICUP‐S 63 59.9

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.

DICUP‐P 593.78 218.5 260.99 551.38

DICUP‐S 752.45 311.68 239.32 539.55

DICUP‐P DICUP‐S

Series1 47.2 43.2

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.

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

VULCUP‐P 65 49.1

VULCUP‐S 65 69.6

6569.6

VULCUP‐P 799.11 292.1 326.82 652.78

VULCUP‐S 759.35 284.34 282.66 596.55

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

Series1 56.2 52.2

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.

Peroxide Dispersions in HCR Silicone Compounding · Advantages of Peroxide Dispersions in HCR...

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