Pushing the Boundaries of Fluorosilicone Rubber Dr. R. A. Drake, Dr. L. M. Tonge, P. J. Griffith, Dr. K. B. King
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
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
Typical Automotive FVMQ applications Some examples Fuel line safety seals Oil system seals Turbocharger hoses Membranes O-rings Gaskets... 4
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
HIGH RESILIENCE & LOW COMPRESSION SET 6
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
Silastic LS-2940 U / LS-2970 U Blends Formulation, Parts Silastic LS-2940 U Fluorosil Rubber... 100 70 50 30 0 Silastic LS-2970 U Fluorosil Rubber... 0 30 50 70 100 DBPH-50 2... 1 1 1 1 1 Test 1 Physical Properties 2 Unit ASTM D2240 Hardness Shore A 42 49 56 62 71 ASTM D412 Die C Tensile strength MPa 8.8 9.5 10.0 10.8 10.4 ASTM D412 Die C Elongation at break % 360 320 300 289 241 ASTM D412 Die C Modulus 100% MPa 1.2 1.8 2.3 3.0 4.2 ASTM D2632 Bashore Resiliency % Rebound 31 28 26 26 25 ASTM D624B Tear Strength kn/m 15 17 20 19 19 ASTM D395 Compression Set 3 % 6 10 6 7 8 1 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
Fluid Resistance Data Formulation, Parts LS-2940 U 100 0 LS-2970 U 0 100 DBPH-50.. 1 1 Fluid Resistance, Volume Swell per ASTM D471 Reference Fuel B, 24 hrs @23 C 19 19 Reference Fuel C, 70 hrs at 23 C 21 19 Reference Fuel C, 168hrs at 60 C 24 22 FAM B Fuel, 168 hrs at 60 C 34 29 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
Mill Handling Performance 10 10
THERMAL STABILITY 11
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 14 days @ 250-275 C 700 hours @ 220 C plus 70 hours @ 240 C Oil Dexron VI used as an aggressive test oil, 7 days @ 150 C Compression set 3 & 7 days @ 200 C Fuel Acid Gas Condensate Si O * * n Me 12
Analysis of Heat Age Conditions 40 & 60 Duro 13
Effects of Temperature and Time 14
Tensile Strength MPa Tensile Strength MPa Acid Acceptors 10.0 9.0 8.0 7.0 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 6.0 5.0 4.0 3.0 2.0 1.0 0.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 5 10 15 Days at 250 C 0 5 10 15 AA 1 AA 2 AA 3 AA 4 No AA 4 Level 1 AA4 Level 2 AA4 Days at 250 C 15
Elongation at Break % Tensile Strength MPa Peroxide Choice 12.0 10.0 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 8.0 6.0 4.0 2.0 0.0 0 5 10 15 Days at 250 C 500 450 400 350 300 250 200 150 100 50 0 0 5 10 15 Days at 250 C Peroxide 1 Peroxide 2 Peroxide 3 Peroxide 4 Peroxide 1 Peroxide 2 Peroxide 3 Peroxide 4 16
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+1+ + 2 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
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 12 12 Student's t-test 14d @ 250 C Hardness 61.8 64 Yes 50% Modulus, MPa 1.79 1.81 No 100% Modulus, MPa 2.91 2.99 No Tensile Strength, MPa 4.5 4 Yes Elongation, % 181 152 Yes Δ Hardness (Shore A) 10.3 12.4 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 700h @ 220 plus 70h @ 240 C Hardness 61 62.3 No 50% Modulus, MPa 1.56 1.64 Yes 100% Modulus, MPa 2.62 2.85 Yes Tensile Strength, MPa 5 5.3 Yes Elongation, % 212 201 Yes Δ Hardness (Shore A) 8.8 10.5 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
A: Redox 3 Design-Expert Software Factor Coding: Coded EB, 14d @ 250 C Design Points 100 1.00 EB, 14d @ 250 C 2 270 X1 = B: Redox 1 X2 = A: Redox 3 0.50 160 Design of Experiment methodology used to study redox stabiliser interactions See variable interactions depending on stabilisers used and properties studied 0.00-0.50-1.00 180 200 220 240 240 220-1.00-0.50 0.00 0.50 1.00 B: Redox 1 19
Elongation at Break % Tensile MPa Expanded Boundaries - 60Shore FVMQ 12 10 8 6 4 2 0 Initial 7d at 225 C 3d @ 250 C 3d @ 260 C 3d @ 275 C Old FSR New FSR Graphs show performance of a new FVMQ material using the technology discussed vs. an older FVMQ 400 350 300 Available for evaluation 250 200 150 100 50 Old FSR New FSR Further development of new heat stabilised bases ongoing 0 Initial 7d at 225 C 3d @ 250 C 3d @ 260 C 3d @ 275 C 20
Tensile Strength Mpa Heat Aging Benchmark - Tensile 21 18 15 12 9 6 3 Hose Grade FKM Higher Fluorine FKM LS-2860 Dev FSR 1-60 Shore Dev FSR 2-60 Shore 0 0 5 10 15 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
VMQ FVMQ ADHESION 22
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
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 6 5 4 3 2 1 Hose grade FKM/VMQ Higher Fluorine FKM/VMQ Current FSR/VMQ Development FSR/VMQ FSR breaks 0 0 5 10 15 Days at 225 C 24
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
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