Page 212 - Engineering Plastics Handbook

Polyphenylene Ether (PPE) Blends and Alloys 185

■ PPE resins with very high heat distortion temperatures (HDTs) can
readily raise the HDT of polystyrene polymers to over 212°F (100°C),
which is a significant temperature because this allows the material
to be used for many boiling water applications.
■ Styrene polymers, with ease of processing and well-established impact
modification, balance the refractory nature of PPE resins.
■ PPE resins bring inherent flame retardance and facilitate making of
nonhalogen flame-retardant blends.
■ PPE resin and styrene polymers both have excellent water resistance
and outstanding electrical properties.
■ In addition PPE/PS blends exhibit lower specific gravity than many
other engineering thermoplastics.
Modified PPE resins are relatively resistant to burning, and judicious
compounding can increase their burn resistance by using nonbrominated,
nonchlorinated flame retardants, making them ECO-label compliant.
Modified PPE resins are especially noted for their outstanding hydrolytic
stability. They have no hydrolyzable bonds. Their low water absorption
rates—both at room temperature and at elevated temperatures—allow the
retention of properties and dimensional stability in the presence of water,
high-humidity, and even steam environments. In addition, modified PPE
resins are generally unaffected by a wide variety of aqueous solutions,
detergents, acids, and bases.
Modified PPE resins will soften or dissolve in many halogenated and aro-
matic hydrocarbons. Laboratory data are available on the chemical resist-
ance of plastics. However, such data should only be used as a screening
tool. If a material is found to be incompatible in a short-term test, it will
usually be found to be incompatible in a similar end-use environment. The
converse, however, is not always true. Favorable results in a short-term
test are no guarantee of actual performance in long-term, end-use condi-
tions. The amount of molded-in stress found in any particular part will
have a pronounced effect upon the relative chemical compatibility of a
polymer. The acceptable chemical compatibility of a polymer in an appli-
cation can be determined only by exposure or immersion of prototypes and
suitably stressed samples in this type of environment under actual oper-
ating conditions [21].
The combination of various PPE/PS levels with other additives provides
a family of resins covering a very wide range of physical and thermome-
chanical properties. General characteristics include high heat resistance,
excellent electrical properties over a wide temperature and frequency
range, low density, hydrolytic stability, chemical resistance to most acids,
dimensional stability, low mold shrinkage, and very low creep behavior at
elevated temperatures.