Advantages of Peroxide Dispersions in HCR Silicone Compounding

Transcription

1 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 11 th 13 Th 2016 Pittsburg, PA

2 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.

3 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

4 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)

5 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 Compound A DBPH Rheology ML Ts2 Tc90 Compound A Rheology DBPH P Compound A Rheology DBPH S

6 Compound A DBPH MH Compound A Rheology DBPH P Compound A Rheology DBPH S MH Compound A Durometer & Tear Durometer, Shore A Tensile, psi Elongation, % % Modulus, psi % Modulus, psi Tear Die B, lbs DBPH S DICUP P

7 Compound A DBPH (Tensile, Elongation and Modulus) Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi DBPH P DBPH S Compound A Compression Set DBPH P DBPH S DBPH P DBPH S Series

8 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. Compound A Dicup Rheology ML Ts2 Tc90 MH Compound A Rheology DICUP P Compound A Rheology DICUP S

9 Compound A Durometer & Tear Durometer, Shore A Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi Tear Die B, lbs DICUP P DICUP S Compound A Dicup (Tensile, Elongation and Modulus) Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi DICUP P DICUP S

10 Compound A Compression Set DICUP P DICUP S DICUP P DICUP S Series 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

11 8 Compound A Vulcup Rheology ML Ts2 Tc90 MH Compound A Rheology VULCUP P Compound A Rheology VULCUP S Compound A Durometer & Tear Durometer, Shore A Tensile, psi Elongation, % % Modulus, psi % Modulus, psi Tear Die B, lbs VULCUP P VULCUP S

12 Compound A Vulcup (Tensile, Elongation and Modulus) Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi VULCUP P VULCUP S Compound A Compression Set VULCUP P VULCUP S VULCUP P VULCUP S Series

13 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. Compound B Rheology DBPH P DBPH S ML Ts Tc Tc MH

14 Compound B Durometer & Tear Durometer, Shore A Tear Die B, lbs DBPH P DBPH S Compound B Tensile & Elongation Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi DBPH P DBPH S

15 Compound B Compression Set DBPH P DBPH S DBPH P DBPH S Series 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.

16 Compound B Rheology DICUP P DICUP S ML Ts Tc Tc MH Compound B Durometer & Tear Durometer, Shore A Tear Die B, lbs DICUP P DICUP S

17 Compound B Tensile & Elongation Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi DICUP P DICUP S Compound B Compression Set DICUP P DICUP S DICUP P DICUP S Series 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.

18 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. Compound B Rheology VULCUP P VULCUP S ML Ts Tc Tc MH

19 Compound B Durometer & Tear Durometer, Shore A Tear Die B, lbs VULCUP P VULCUP S Compound B Tensile & Elongation Tensile, psi Elongation, % 100% Modulus, psi 200% Modulus, psi VULCUP P VULCUP S

20 Compound B Compression Set VULCUP P VULCUP S VULCUP P VULCUP S Series 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

21 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.