VITON® Fluoroelastomer
Product introduction
VITON® fluoroelastomer was launched in 1957 to meet the aviation industry's demand for high-performance sealing elastomers. Since
then, the applications of VITON® fluoroelastomers have quickly expanded to many other industrial sectors, notably the automotive, hydraulic transmission,
household appliances and chemical industries. After more than thirty years of actual field use, VITON® fluoroelastomers have
become known for their excellent performance in very hot and corrosive environments.
VITON® fluoroelastomers are available in three series: A, B and F. VITON®A series is a dimer composed of vinylidene fluoride (VF2) and hexafluoropropylene
(HFP). B and F series are
terpolymers made of vinylidene fluoride (VF2), hexafluoropropylene (HFP) and tetrafluoroethylene (TFE) in various proportions .
The main difference between the three VITON® series is their resistance to fluids, particularly corrosive lubricants and oxygenated
fuels , such as methanol and ethanol automotive fuel blends.
The differences in the fluid resistance properties of these different series of VITON®
are caused by the different fluorine content in the polymer backbone as shown in the table. Fluid resistance generally
increases with increasing fluorine content, however, as the fluorine content increases, the low-temperature flexibility of the polymer decreases, so
a trade-off must be made between the fluid resistance and low-temperature flexibility of A, B and F Series VITON®.
DuPont Graft also manufactures specialized grades of VITON®, some of which contain vinyl ether monomers in the polymer backbone.
The low-temperature flexibility temperature of this polymer vulcanizate is lowered by several degrees Celsius, such as VITON® GLT and GFLT. Compared with ordinary
varieties of FKM polymers, their low-temperature flexibility has been significantly improved.
Especially in low molecular weight oxidizing solvents or highly corrosive lubricants (containing strongly alkaline additives),
there is a significant difference in the resistance to volume change or performance degradation of different series of VITON®.
Typical physical properties of ITON® fluoroelastomer
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Special varieties
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A
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B
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F
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GLT
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GFLT
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| Nominal fluorine content (weight), % |
66
|
68
|
70
|
64
|
67
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| Volume change over 168 hours in fuel C at 23°C, % |
4
|
3
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2
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5
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2
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| Volume change in methanol at 23°C for 168 hours, % |
90
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40
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5
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90
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5
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| Low temperature flexibility, TR-10, °C |
-17
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-13
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-6
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-30
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-twenty four
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Product features
High and low temperature resistance
Thermal - VITON® outperforms most other elastomers in its ability to withstand high temperatures while maintaining good physical and mechanical properties. Oil and
chemical is also relatively unaffected by rising temperatures.
VITON® compounds remain indefinitely when exposed to laboratory air aging up to 204°C (400°F) , or intermittently exposed to test conditions up to 260°C (500°F).
Effective flexibility. Continuous use limits are generally as follows:
·3,000 hours at 232°C (450°F)
·1,000 hours at 260°C (500°F)
·240 hours at 288°C (550°F)
·48 hours at 316°C (600°F)
Cold-VITON® is typically used under dynamic conditions as low as -18°C - -23°C, but is specially formulated for
use under static conditions as low as -54°C (-65°F). The effect of VITON on static seals used under low temperature conditions close to absolute zero
is also satisfactory.
·Resistant to the degradation of more than 300 fluids, the fluid resistance is no less than that of any commercial rubber and has excellent resistance to oil, fuel, lubricants and most mineral acids.
·Exceedingly low transmission rates for a wide range of substances, including oxidized automotive fuels.
·Resistant to many kinds of aliphatic and aromatic hydrocarbons that act as solvents for other rubbers.
·Excellent compression set value at high temperatures.
·Excellent resistance to atmospheric oxidation, sunlight and weathering. Excellent anti-mildew and anti-fungal properties.
·Good electrical properties in low voltage and low frequency applications. Low flammability; more flame resistant than any other hydrocarbon rubber.
Product processing
Processing Another formulation variable that has a significant impact on the processing and physical properties of VITON® vulcanizates is the cure system.
Diamine vulcanizing agents were introduced by DuPont in 1957 for vulcanizing VITON® A (DIAK No. 1). Although this type of
vulcanizing agent (DIAK No.1, No.3, No.4) has a relatively slow vulcanization speed and poor compression set resistance, they
do provide some rare advantages, such as excellent performance with metal inserts. Excellent adhesive properties and high hot tear strength.
Most FKM polymers today are cured with bisphenol AF. This vulcanizing agent was launched by DuPont in 1970 in the form of VITON® E60C, which is a premixed compound of VITON® E60, accelerator and bisphenol AF. VITON® rubber compounds using this vulcanizing agent cure quickly, have excellent rubber burning safety and resistance to compression set.
In 1989, DuPont introduced an improved bisphenol vulcanizing agent, which was made into several different premixes: VITON® A201C, A202C, A401C and A402C. Compared with the original bisphenol curing system used in VITON®
E60C and E430 , the improved system speeds up vulcanization, improves mold release properties, and slightly improves compression set resistance.
In 1976, with the introduction of VITON® GLT, peroxide curing of FKM polymers became possible for the first time. Using
peroxide to vulcanize polymers such as GLT and GFLT has fast vulcanization speed and excellent physical properties. However,
it is not easy to vulcanize these polymers using diamine or bisphenol vulcanization systems. For polymers that can be vulcanized with both peroxide and bisphenol systems, such as
VITON® GF and GBL 900, peroxide vulcanization can improve the resistance to corrosive automotive lubricants, steam and
acid resistance. There is no significant difference in the resistance of VITON® polymers cured with peroxide to
other fluids and chemicals compared to the same polymer cured with bisphenol .
The table below shows the comparison of various processing properties and physical properties of rubber compounds using different vulcanization systems.
Comparison of different vulcanization systems used in vulcanized VITON®
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Vulcanization system
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Diamine
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bisphenol
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Peroxide *
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| Processing safety (scorch) |
Poor-Medium
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excellent
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excellent
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| Rapid vulcanization |
Poor-Medium
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excellent
|
excellent
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| Demolding/scaling |
Difference
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Good-Excellent
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middle
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| Release tear strength |
excellent
|
good
|
good
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| Bonding to metal inserts |
excellent
|
good
|
good
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| Resistance to compression set |
Difference
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excellent
|
good
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| Resistance to steam, water and acid |
middle
|
good
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excellent
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| Flex life |
good
|
good
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good
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