Evaluation of DISPERSIX™ in HCR Silicone Compounding

By

Erick Sharp (Speaker) – ACE Products & Consulting LLC, Uniontown, OH

Miles Dearth – The SEFA Group, Lexington, SC

Bill Black – The SEFA Group, Lexington, SC

Presented at the

2016 International Silicone Conference

A Rubber and Plastic News Event

May 17th & 18th

Akron, OH

Abstract

A multi-factor, general factorial designed experiment was performed to investigate the

processing of highly extended HCR silicone molding and extrusion compounds with

aluminosilicate ceramic (ASC) microspheres. The factors selected for experiments are the

presence, particle size, dose level and grade of microspheres. This study measured dependent

variables of a) cycle time, b) MDR properties, c) dispersion, d) physical properties and e) mold

release. Introduced in this study is DISPERSIX™ a new line of inorganic multi-functional process

aids which the data in this study indicate have significant effects on processing efficiency and

the balance of property improvements not previously available to silicone compounders.

Introduction of DISPERSIX™ Microspheres

DISPERSIX™ aluminosilicates are recovered from various mining and post-industrial byproduct

streams and converted to micro-spherical ceramics by a patented thermo-oxidative

process. Once returned to their pristine mineral state they are size classified and modified with

inorganic and organic reactants for faster processing and superior properties.

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.

Figure 1 Figure 2

Raw Materials

Molding Trial

Figure 3

Extrusion Trial

Figure 4

Formulation

Molding Trial

Figure 5

Extrusion Trial

Figure 6

Mix Procedure

Molding Formulation

1. Add JFD 2041, JFD 0620, Precipitated Silica and DISPERSIX™ (except for control)

a. Mix to 117°F

2. Add ACE-SD-BIO, ACE-SD-HS2, ACE-SD-MR1, VTEO and ½ Minusil10

a. Mix to 130°F

3. Add remaining Minusil 10

4. Drop at 135°F

5. Ten passes on lab mill

Extrusion Formulation

1. Add JFD 2041, JFD 2071, ACE-SD-HS9, ACE-SD-CaO, ACE-SD-MgO, ACE-SD-MMO

a. Mix 30 seconds

2. Add ½ Minusil 10 and DISPERSIX™ (except for control)

a. Mix to 125°F

3. Add remainder of Minusil 10

a. Mix to 150°F

4. Add DCBP

a. Mix 60 seconds and drop

5. Ten passes on lab mill

Measurable Values

a. Mixing Cycle Time

a. Seconds

b. MDR

a. Parameters

i. Molding formulations: 6’ at 355°F

ii. Extrusion formulations: 6’ at 250°F

b. Values

i. ML

ii. TS2

iii. Tc50

iv. Tc90

v. MH

c. Physical Properties

a. Parameters

i. Molding formulations prepped 6’ at 355°F

ii. Extrusion formulations prepped 6’ at 250°F

b. Values

i. Specific Gravity

ii. Tensile (Mpa)

iii. Elongation

iv. 100% Modulus

v. 200% Modulus

vi. Tear die b

vii. Compression Set (method B/ Plied)

d. Other

a. Amp Draw

Results

Cycle Times

Total mixing cycle times were reduced by over 40% with the DISPERSIX™ microspheres in the

molding formulation compound (Figure 7).

Figure 7

MDR Data

Compared to the control, compounds containing DISPERSIX™ ASC microspheres exhibited lower

Tc90 cure times by 6 seconds, 11.4 seconds and 9.6 seconds, respectively (Figure 9). This is

thought to be due to the improved dispersion of the peroxide curing agent because DISPERSIX™

spheres act similarly to type II co-agents. It is likely that the amounts of peroxide could be

reduced when using the DISPERSIX™ microspheres.

Mooney-High (MH) as shown in FIG. 10 increases less than two Mooney units when DISPERSIX™

microspheres are present. Relative MH differences between versions of DISPERSIX™

microspheres are thought to be the result of differences in the cure network from different

surface treatments.

FIG. 8

00.20.40.60.8

11.21.41.61.8

Control Dispersix4PC

Dispersix4PC 3

Dispersix4PC 4

Ts2 0.38 0.38 0.37 0.37

Tc50 0.64 0.65 0.61 0.63

Tc90 1.63 1.53 1.44 1.47

Min

ute

s

MOLDING SCORCH DATAFIG. 9

19

19.5

20

20.5

21

21.5

Control Dispersix 4PC Dispersix 4PC 3 Dispersix 4PC 4

MH 20.02 21.43 21.22 20.62

MH - MOLDINGFIG. 10

2.6

2.7

2.8

2.9

3

3.1

3.2

Control Dispersix4PC

Dispersix4PC 3

Dispersix4PC 4

ML 2.81 3.17 3.07 2.98

ML - MOLDINGFIG. 11

EXTRUSION COMPOUNDS

Total mixing cycle times (Figure 13) were reduced by over 12% with the DISPERSIX™

microspheres in the extrusion formulation compound (figure 12).

Figure 12

FIG. 13

0

0.1

0.2

0.3

0.4

0.5

0.6

Ts2 Tc50 Tc90

Control 0.28 0.32 0.56

4PC 0.26 0.31 0.53

Min

ute

s

EXTRUSION SCORCH DATA6 MIN @ 250° F

FIG. 14

2.322.342.362.38

2.42.422.442.462.48

2.52.52

ML

Control 2.39

4PC 2.51

ML - EXTRUSIONFIG. 15

8.9

9

9.1

9.2

9.3

9.4

9.5

9.6

9.7

9.8

9.9

MH

Control 9.26

4PC 9.84

MH - EXTRUSIONFIG. 16

Physical Properties

Conventional process aids are typically designed to improve productivity but sometimes result in

a sacrifice in physical properties. The research done by SPHERIX Mineral Products has focused

on the development of aluminosilicate ceramified microspheres that improve productivity while

maintaining or improving physical properties at low dosages. Surface modification of these

microspheres optimizes adhesion and crosslinking to the matrix elastomer for enhanced mixing,

dispersion, and flow efficiencies along with reinforcement in the cured state without significant

changes in hardness, scorch and cure rate. Molding formulations containing 5 phr DISPERSIX™

microspheres outperformed the control compound on every physical property measured. The

experimental extrusion formulations exhibited physical properties that were comparable to the

control with a notable improvement in mixing efficiency.

75

76

76

77

77

78

78

Durometer

Control 76

Dispersix 4PC 77

Dispersix 4PC 3 78

Dispersix 4PC 4 77

SHO

RE

A

Molding HardnessFIG. 17

800.0

820.0

840.0

860.0

880.0

900.0

920.0

940.0

960.0

980.0

1000.0

Tensile, psi

Control 875.9

Dispersix 4PC 943.7

Dispersix 4PC 3 990.7

Dispersix 4PC 4 932.2

PSI

Molding TensileFIG. 18

195.0200.0205.0210.0215.0220.0225.0

Control Dispersix 4PC

Dispersix 4PC 3

Dispersix 4PC 4

Elongation % 205.5 211.6 223.7 210.2

%

Molding Elongation %FIG. 19

100% Modulus 200% Modulus

Control 410.5 861.5

Dispersix 4PC 438.5 889.6

Dispersix 4PC 3 435.4 896.3

Dispersix 4PC 4 434.7 891.3

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

1000.0

Molding ModulusFIG. 20

85.090.095.0

100.0105.0110.0115.0

Tear Die B, lbs

Control 93.8

Dispersix 4PC 100.2

Dispersix 4PC 3 110.1

Dispersix 4PC 4 109.6

Molding TearFIG. 21

Method B, Plied

Control 33.6%

Dispersix 4PC 27.1%

Dispersix 4PC 3 28.9%

Dispersix 4PC 4 27.0%

Molding CompressionFIG. 22

Durometer

Elongation%

100%Modulus

200%Modulus

Tear DieB, lbs

Control 80 241.8 379.8 782.6 177.1

4PC 79 258.0 356.4 746.4 176.1

0

200

400

600

800

1000

Extrusion Physical PropertiesFIG. 23A

Specific Gravity Tensile, (Mpa)

Control 1.524 6.6

4PC 1.489 6.7

0

2

4

6

8

Extrusion Physical PropertiesFIG. 23B

Energy Consumption

The physical dispersive action of the microspheres is enhanced by surface chemistry and

improved silica reinforcement while the Amperage draw during compounding decreased by up

to 50% compared with the control.

02468

1012

Average AMP Draw

Control 12

Dispersix 4PC 6

Dispersix 4PC 3 7

Dispersix 4PC 4 7

Amp Draw - MoldingFIG. 24

Dispersion

By visual observation the compounds with the DISPERSIX™ microspheres had better dispersion

and less powder agglomerations in the milled slab.

Control Batch

DISPERSIX™ Batch

FIG. 25

FIG. 26

Conclusions

HCR silicone compounds containing DISPERSIX™ microspheres consistently processed cleaner,

quicker and with better dispersion. The mixer body was cleaner and the batch discharged

better with the DISPERSIX™ microspheres compounds. The DISPERSIX™ microspheres acted in

a ball bearing like effect to break down the raw materials and improve dispersion. This had a

dramatic improvement on the mixing cycle time. The cycle time improvement seems to be

greater on formulations that have a higher level of reinforced filler being added. When molding

slabs for testing the compounds with DISPERSIX™ microspheres had better release from the

mold. This was a consistent observation throughout the entire study.

The development objectives of SPHERIX Mineral Products as demonstrated by the foregoing

experimental mixes in obtaining process improvements without an adverse effect on the

rheology and physical properties have been apparently achieved. The better dispersion

apparently further enhanced the rheology. It is likely that the peroxide level could be slightly

reduced when used in DISPERSIX™ compounds. In molding compounds with a high level of

precipitated and ground silica, significant improvements in physical properties and process

efficiency were demonstrated. Experiments with predispersed fumed silica-containing

extrusion compounds showed comparable physical properties with processing efficiency

benefits in the use of DISPERSIX™ microspheres. Further study in the dispersion of fumed silica

in silicone base compounds is warranted.

The data in the foregoing studies supports the general conclusion that DISPERSIX™

microspheres provide substantial cycle time improvements, enhanced dispersion and reduced

power load, while maintaining equal or better physical properties in the finished compound.

Acknowledgements

A special thanks to John Summers and Polychem Dispersions for their assistance in running

these trials.

A special thanks to HB Chemical for providing raw materials for these trials.