VMQ compounds advantages
- Excellent thermal and heat stability
- Best cold flexibility
- Excellent weather, aging and ozone stability
- Good resistance in oils and hydraulic fluids
- Temperature range from –50 °C to +200 °C
- Temperature special grades up to 300 °C
The term silicone covers a large group of materials with high molecular weight poly-organo-siloxanes as central ingredient. Silicones in general are unusual among synthetic rubbers as they are partly organic and partly inorganic in nature.
Chemically, their backbone consists of siloxanes with, depending on type, vinyl, methyl, trifluoropropyl and phenyl substituent groups on polymer chain.
MQ rubber compounding
MQ,the most basic silicone (red frame) have only methyl substituents in polysiloxane chain. By replacing small amounts of these methyl groups significant variations in properties can be achieved.
The presence of vinyl groups, forming
VMQ rubber compounding
VMQ (blue frame) improves vulcanisation rate, compression set, resilience and oil resistance. These elastomers have excellent cold flexibility (can reach temperatures of -50 °C) as well as high thermal resistance (up to 200°C, with special compounding up to 300°C for short periods of time).
They have very good resistance to ageing and attack by oxygen, ozone and sunlight. They also have excellent dielectric and anti-adhesive properties as well as low toxicity and can therefore be used in many food and medical applications since they do not impart odour or taste. In general they have poor tensile strength (<15MPa) and tear resistance compared to conventional rubber.
Resistance to mineral oils (depending on grade) and fuels is moderate however, but they have good resistance to animal and vegetable fats and oils, brake fluid and engine oils. The most admirable property of this polymer is its very wide service temperature range. Silicones also show poor gas impermeability.
FVMQ rubber compounding
FVMQ, as their name suggests, have similar polymer structure as VMQ, but with the additional trifluoropropyl substituent group on the polymer chain (yellow frame). This extra substituent gives the end product excellent resistance to many fuels (aliphatic and aromatic), solvents (benzene, toluene, ..), oils (animal, vegetable, mineral, silicone, …) and chemicals which would severely degrade VMQ and most other polymers.
The mechanical and physical properties are very similar to VMQ. However, FVMQ offer poor hot air resistance when compared with VMQ. Compared to Fluorocarbon rubbers fluorosilicones provide a much wider operational temperature range as they can reach temperatures up to 175°C and go as low as -70°C. In some cases, however, high temperature range in fluids is limited due to possible degradation of fluid and formation of harmful acids.
FVMQ Is for example used in:
- Automotive parts including diaphragms, O-rings, gaskets and seals
- Aircraft gaskets, seals, hoses, bellows, diaphragms and connectors
- General industrial gasket and seals
- Moulded parts exposed to heat, oil or solvents
PVMQ rubber compounding
PVMQ have phenyl, vinyl and methyl substituent groups on the polymer chain. They show improved low temp flexibility (they can reach temperatures as low as -95°C) and resistance to high-energy radiation (up to 10^7 rad).
Polycomp is able to produce a wide variety of different (fluor-)silicone compounds to suit your particular need and application.
More information about VMQ rubber compounds
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