Introduction to Fluorosilicone Rubber
Fluorosilicone rubber (FVMQ) is a fluorinated variant of silicone rubber (VMQ), produced by incorporating fluoroalkyl groups (e.g., trifluoropropyl) into the siloxane backbone. This modification, typically achieved through copolymerization of fluorinated silanes, enhances hydrocarbon resistance while retaining silicone's core properties. Developed in the 1950s for aerospace applications, FVMQ is cured via peroxide or platinum systems. Grades vary by fluorine content (around 30-40%) and durometer (40-80 Shore A), with options for high-purity or low-compression-set formulations. It is compounded with reinforcing fillers like fumed silica, and sometimes carbon black, to optimize strength. FVMQ is more expensive than standard silicone but offers superior performance in fuel-exposed settings.
Characteristics of Fluorosilicone Rubber
FVMQ bridges the gap between silicone's temperature range and fluorocarbon's chemical resistance, with balanced properties for harsh conditions. Here are its key characteristics:
- Mechanical Properties: FVMQ has moderate tensile strength (5-15 MPa), high elongation at break (200-500%), and good tear resistance. It exhibits excellent compression set resistance (low even after heat aging) and flexibility, similar to silicone, with good vibration damping. However, it is generally harder than VMQ and has fair abrasion resistance, often requiring reinforcement for dynamic applications.
- Chemical Resistance: Superior resistance to fuels, oils, solvents, hydrocarbons, and di-ester lubricants due to fluorine groups, outperforming standard silicone. It also resists ozone, UV, weathering, and dilute acids/bases. However, it has limited resistance to ketones, esters, and superheated steam, and is not as chemically inert as full fluorocarbons like FKM.
- Thermal Properties: Exceptional wide temperature range from -60°C to +200°C (or up to +230°C for short exposures), maintaining elasticity without embrittlement at low temperatures or softening at high ones. It has low thermal conductivity and good heat aging resistance, comparable to silicone.
- Durability and Aging: Excellent long-term stability against ozone, weathering, and radiation, with low gas permeability and inherent flame retardancy. It has good electrical insulation properties and biocompatibility in some grades. Compression set is low, but it can be affected by prolonged fuel exposure without proper formulation.
- Processing and Cost: Processed via injection molding, extrusion, or compression molding, with good mold flow and release. It adheres well to metals with primers. FVMQ is costlier than VMQ (2-5 times) due to fluorine, but its durability reduces replacement frequency in critical uses.
- Other Properties: Low specific gravity (1.4-1.6), transparent or colorable, non-toxic, and sterilizable. It offers good dielectric strength and low outgassing, suitable for vacuum applications. However, it may swell in silicone fluids and requires careful compounding to avoid contamination.
In formulations, FVMQ is often used neat or with minimal fillers, and can be blended with silicone for cost optimization, though compatibility with organic rubbers is limited.
Applications of Fluorosilicone Rubber
FVMQ's fuel resistance and temperature stability make it ideal for aerospace, automotive, and industrial sectors:
- Aerospace and Aviation: Used in fuel system seals, O-rings, gaskets, and diaphragms for jet engines and fuel tanks, handling aviation fuels and extreme temperatures.
- Automotive Industry: In fuel emission control systems, turbocharger hoses, valve seals, and O-rings, resisting biofuels, oils, and heat in engines.
- Oil and Petroleum: Employed in seals, hoses, and gaskets for pumps and valves exposed to crude oil, solvents, and chemicals.
- Military and Defense: For seals in fuel handling equipment and protective gear, leveraging its chemical and thermal resilience.
- Industrial Seals: In static and dynamic seals for chemical processing, HVAC, and vacuum systems where oil resistance is needed without sacrificing flexibility.
- Other Uses: Medical devices (e.g., seals in equipment), electronics insulation, and food/pharma applications in FDA-compliant grades. It's also in O-rings for diving gear and automotive sensors.
FVMQ production focuses on high-purity grades for emerging electric vehicle and renewable energy applications. It's a niche material with growing demand in fuel-related industries.
