Pushing the Boundaries of Fluorosilicone Rubber. Dr. R. A. Drake, Dr. L. M. Tonge, P. J. Griffith, Dr. K. B. King

Transcription

1 Pushing the Boundaries of Fluorosilicone Rubber Dr. R. A. Drake, Dr. L. M. Tonge, P. J. Griffith, Dr. K. B. King

2 Topics Overview of Fluorosilicone Rubber (FVMQ) Dow Corning Innovation in FVMQ High Resilience & Low Compression technology New Bases High Temperature & Fluid Resistance technology Acid Acceptors Peroxide Effects Redox Stabilisers Adhesion 2

3 FVMQ Definitions and benefits: Fluorosilicone Chemistry VMQ CH=CH 2 CH 3 CH 2 CH 2 CF 3 CH=CH 2 FVMQ Si O Si O Si O Si O n m m n CH 3 CH 3 CH 3 CH 3 Replacing one CH 3 with CH 2 CH 2 CF 3 gives: Improved resistance to non-polar hydrocarbon fuels, oils, and solvents Increased specific gravity Improved solubility in polar fluids such as esters and ketones Improved lubricity Lower use temperature by eliminating polymer Tm crystallization A 10x increase in viscosity at the same molecular weight very cold aggressive fluids very hot We are improving FVMQ here 3

4 Typical Automotive FVMQ applications Some examples Fuel line safety seals Oil system seals Turbocharger hoses Membranes O-rings Gaskets... 4

5 Dow Corning Innovation in FVMQ Global Development Team Multi-generational approach making improvements across our fluorosilicone supply chain Focus on material performance and durability in application Resilience Compression Set Thermal Stability Fluid Stability Oil, Acid Gas Condensate Fatigue Life FVMQ adhesion to VMQ 5

6 HIGH RESILIENCE & LOW COMPRESSION SET 6

7 High Resilience & Low Compression Set Developments New bases have been launched meeting the following needs: High resilience/rebound Low compression set High fuel resistance Reduced stickiness when unwrapping and mill handling Globally available as U-stock bases or in compounds Blending can cover 40 to 70 durometer range Designed for molding applications such as o-rings, diaphragms, and other fuel contact applications 7

8 Silastic LS-2940 U / LS-2970 U Blends Formulation, Parts Silastic LS-2940 U Fluorosil Rubber Silastic LS-2970 U Fluorosil Rubber DBPH Test 1 Physical Properties 2 Unit ASTM D2240 Hardness Shore A ASTM D412 Die C Tensile strength MPa ASTM D412 Die C Elongation at break % ASTM D412 Die C Modulus 100% MPa ASTM D2632 Bashore Resiliency % Rebound ASTM D624B Tear Strength kn/m ASTM D395 Compression Set 3 % ASTM: American Society for Testing and Materials. 2 Properties obtained using 1.0 phr DBPH-50 (DHBP) (2,5-bis (tert-butylperoxy) 2,5 dimethyl hexane) on 1.91mm (0.075 inch thick) slabs; as molded 10 minutes at 171 C (340 F); postcured 4 hours at 200 C (392 F). 3 Tested according to method B, type II (6mm), plied disks, 22hrs 177 C. 8

9 Fluid Resistance Data Formulation, Parts LS-2940 U LS-2970 U DBPH Fluid Resistance, Volume Swell per ASTM D471 Reference Fuel B, 24 C Reference Fuel C, 70 hrs at 23 C Reference Fuel C, 168hrs at 60 C FAM B Fuel, 168 hrs at 60 C Properties obtained using 1.0 phr DBPH-50 (DHBP) (2,5-bis (tert-butylperoxy) 2,5 dimethyl hexane) on 1.91mm (0.075 inch thick) slabs; as molded 10 minutes at 171 C (340 F); post cured 4 hours at 200 C (392 F). 9

10 Mill Handling Performance 10 10

11 THERMAL STABILITY 11

12 FVMQ Degradation Various degradation mechanisms occur in FVMQ on heating F - promoted chain cleavage and depolymerisation Oxidative cleavage of cross-links and side groups Changes to filler / polymer interactions CF 3 Range of environments Dry heat 70h to C C plus C Oil Dexron VI used as an aggressive test oil, C Compression set 3 & C Fuel Acid Gas Condensate Si O * * n Me 12

13 Analysis of Heat Age Conditions 40 & 60 Duro 13

14 Effects of Temperature and Time 14

15 Tensile Strength MPa Tensile Strength MPa Acid Acceptors HF can form during heat aging and this leads to siloxane depolymerisation Addition of the correct type and amount of an acid acceptor can significantly improve thermal performance Can have conflicting impacts on stability in fluids and interactions with other components that need to be managed Days at 250 C AA 1 AA 2 AA 3 AA 4 No AA 4 Level 1 AA4 Level 2 AA4 Days at 250 C 15

16 Elongation at Break % Tensile Strength MPa Peroxide Choice Choice of peroxide influences the cured network and thus the thermal stability Also has an effect on oil stability and compression set Dialkyl or Diacyl peroxides are preferred for FVMQ cure and thermal stability Days at 250 C Days at 250 C Peroxide 1 Peroxide 2 Peroxide 3 Peroxide 4 Peroxide 1 Peroxide 2 Peroxide 3 Peroxide 4 16

17 Redox Stabilisers FVMQ is typically stabilised with Cerium complexes The use of other redox active metals is known for stabilisation of siloxanes against thermal decomposition Redox stabilisers thought to work by decomposition of peroxides formed from O 2 oxidation thus preventing branching chain reactions, though much debate in literature R + M x+1+ R + + M x+ 4 M x+ + O 2 4 M x O 2- Oxygen diffusion and sample thickness are important parameters in thermal stability In the absence of any added redox stabiliser will get rapid decomposition at elevated temperature 17

18 Metal Oxide Redox Stabilisers A wide range of redox active oxides are available These show variable performance for stabilisation of FVMQ The initial oxidation state, particle size and shape all play a role in obtaining good redox stabilisation Variable interactions between combinations of redox stabilisers Stabiliser Redox 1 Redox 2 Significant Difference Number of samples Student's t-test 250 C Hardness Yes 50% Modulus, MPa No 100% Modulus, MPa No Tensile Strength, MPa Yes Elongation, % Yes Δ Hardness (Shore A) Yes Δ Weight (%) -4.80% -5.10% No Δ 50% Modulus (%) 82% 87% No Δ 100% Modulus (%) 65% 74% No Δ Tensile Strength (%) -50% -55% Yes Δ Elongation (%) -50% -58% Yes 220 plus 240 C Hardness No 50% Modulus, MPa Yes 100% Modulus, MPa Yes Tensile Strength, MPa Yes Elongation, % Yes Δ Hardness (Shore A) Yes Δ Weight (%) -3.90% -3.30% No Δ 50% Modulus (%) 60% 69% No Δ 100% Modulus (%) 51% 64% Yes Δ Tensile Strength (%) -44% -40% Yes Δ Elongation (%) -41% -45% No 18

19 A: Redox 3 Design-Expert Software Factor Coding: Coded EB, 250 C Design Points EB, 250 C X1 = B: Redox 1 X2 = A: Redox Design of Experiment methodology used to study redox stabiliser interactions See variable interactions depending on stabilisers used and properties studied B: Redox 1 19

20 Elongation at Break % Tensile MPa Expanded Boundaries - 60Shore FVMQ Initial 7d at 225 C 250 C 260 C 275 C Old FSR New FSR Graphs show performance of a new FVMQ material using the technology discussed vs. an older FVMQ Available for evaluation Old FSR New FSR Further development of new heat stabilised bases ongoing 0 Initial 7d at 225 C 250 C 260 C 275 C 20

21 Tensile Strength Mpa Heat Aging Benchmark - Tensile Hose Grade FKM Higher Fluorine FKM LS-2860 Dev FSR 1-60 Shore Dev FSR 2-60 Shore Days at 250 C Standard Dow Corning FSR bases such as LS-2860 do not heat age well at 250 C Development FSR materials show considerable improved heat stability with good tensile strength retention on aging FKM shows higher initial tensile but worse heat aging performance in the case of the higher fluorine grade 21

22 VMQ FVMQ ADHESION 22

23 Turbocharger Hoses Turbocharger hoses can be multilayer construction using fluoro-polymers and VMQ Similarity between FVMQ and VMQ, chemical nature of siloxane backbone, cure chemistry, and cure speed make an ideal combination Strong and durable adhesion between the layers is required Dow Corning has a patented solution for chemical adhesion between MVQ and FVMQ 23

24 180 Peel Adhesion kn/m FVMQ-VMQ adhesion Adhesion is obtained via interfacial reaction FVMQ / VMQ combinations with improved initial and aged adhesion are available Hose grade FKM/VMQ Higher Fluorine FKM/VMQ Current FSR/VMQ Development FSR/VMQ FSR breaks Days at 225 C 24

25 Summary The boundaries of FVMQ performance have been extended across a range of properties Resilience Compression Set Thermal Stability Fluid Stability Oil, Acid Gas Condensate Fatigue Life Adhesion to VMQ FVMQ ready to help address your needs very cold aggressive fluids very hot We have improved FVMQ here 25

26 Thank You! The information provided in this presentation does not constitute a contractual commitment by Dow Corning. While Dow Corning does its best to assure that information contained in this presentation is accurate and fully up-to-date, Dow Corning does not guarantee or warranty the accuracy or completeness of information provided in this presentation. Dow Corning reserves the right to make improvements, corrections and/or changes to this presentation in the future. 26