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Polypropylene
thermoplatsic resins are produced from propylene gas, a by-product of petroleum
refining. The natural resin is
semitranslucent and milky white in color and has excellent colorability.
Most propylene parts are produced by injection molding, blow-molding,
or extrusion of either unmodified or reinforced compounds.
Other applicable processes for polypropylenes are structural- foam
molding and solid phase and hot flow stamping of glass reinforced sheet stock.
Molding and extruding resins can be pigmented by any conventional method.
Polypropylene
is a low-density resin that offers a good balance of thermal, chemical, and
electrical properties, along with moderate strength.
Strength properties are increased significantly with glass fibre
reinforcement. Increased toughness
is provided in special, high-molecular weight, rubber modified grades.
Electrical
properties of polypropylene are affected to varying degrees of service
temperature. Dielectric constant is
essentially unchanged, but dielectric strength increases and volume resistivity
decreases with increased temperature.
Polypropylene
has limited heat resistance, but heat-stabilized grades are available for
applications requiring prolonged use at elevated temperatures. Useful life or
parts molded from such grades may be as long as five years at 250 degrees F, ten
years at 230 degrees F, or for 20 years at 210 degrees F.
Polypropylene
resins are inherently unstable in the presence of oxidated conditions with UV
radiation. While all grades are
stabilized to some extent, specific stabilization systems are often used to suit
formulation for a particular environment. Polypropylenes
resist chemical attack and staining and are unaffected by aqueous solutions of
inorganic salts or mineral acids and gases, even at high temperatures.
They are not attacked by most organic chemicals, and there is no solvent
for the resin at room temperature. The
resins are attacked, however, by halogens, fuming nitric acid and other active
oxidizing agents, and by aromatic and chlorinated hydrocarbons at high
temperatures.
Unreinforced
polypropylene is used for packaging applications such as blow-molded
pharmaceutical, medical, cosmetic, and food containers.
Structural-foam grades are used for furniture and for automotive
seatbacks.
Both
reinforced and unreinforced grades are used in automotive, appliance, and
electrical applications. Examples
are:
Automotive
Battery Cases
Fan Blades
Lamp
Housings
Vegetable Bins
Blower
Wheels
Sole support for:
Fan
Shrouds
Current-carrying Electrical Parts
Fender
Liners
Coil Bobbins
Glove
Boxes
Cable
Covers
Appliance
Pumps
TV Yokes and Insulators
Blower
Housings