Page 284 - Handbook of Plastics Technologies

ELASTOMERS

4.76 CHAPTER 4

These polymers resist burning and ignite in air only at temperatures of about 400°C or
more. When they do burn, relatively sturdy silica structures form, which are good insula-
tors and are functional in wire insulation, even for a short time, in fire.
Uses of Silicone Rubbers. Because of their high cost, silicone elastomers are used
only in applications where other elastomers fail. They are mainly used in applications re-
quiring high heat resistance and extreme low-temperature flexibility. These elastomers are
used in the electrical, electronic, aerospace, automotive, mechanical equipment, lighting,
cable, and textile industries. They are also used in pharmaceutical and medical applica-
tions for components in contact with food. They are now used in high-temperature cook-
ing utensils (e.g., scrapers and spatulas).
Silicone elastomers are used in the automotive industry in such applications as ignition
cables, coolant and heater hoses, O-rings, and seals. In aircraft applications, they are used
in seals, connectors, cushions, and hoses. In home applications, they are used in O-rings,
seals, and gaskets. There are also uses in naval and other applications.
4.5.3.16 Fluoroelastomers (FKMs). Fluoroelastomers can be prepared by co- or terpo-
lymerization of the following monomers:

Hexafluoropropylene

Tetrafluoroethylene

1-Hydropentafluoropropylene

Perfluoro(methyl vinyl ether)
An example of such a copolymer is given by the chemical structure shown here:

Other comonomers such as vinylidenefluoride and chlorotrifluoroethylene are used,
generally in smaller amounts. In addition, some fluoroelastomers incorporate bromine-
containing curing-site monomers and can be vulcanized with peroxides.
Fluoroelastomers are prepared by emulsion polymerization at elevated temperatures in
the presence of peroxides as initiators.
Different grades (prepared from different monomer mixtures) require different types of
vulcanization chemistry, with different curing systems. Examples of curing agents are (1)

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