Page 113 - Engineering Plastics Handbook

Polyacetals 87

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®
thermoplastic compounds includes Polypenco polyacetals, Tecaform AH
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polyacetal copolymer, and Tecaform polyacetal homopolymer. Also in
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Ensinger’s stable are Tecamid and Tecast polyamides, Tecanat poly-
™
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cabonate, Tecaran ABS and Tecanyl modified PPE, TPI, PAEK, PPS,
PEI, and PSU.
Compounder RTP Company adds perfluoropolyether (PFPE) modifier,
an internal lubricant system, to increase the wear resistance of polyacetal
and nylon. Typically, less than 1% PFPE loading is adequate, and in some
polyacetal wear-resistant applications, less than 1% PFPE performs sim-
ilar to 15 to 20% PTFE, according to RTP. According to the company, other
advantages of PFPE are that it (1) eliminates plate-out associated with
PTFE; (2) improves fatigue resistance, especially for gears; (3) improves
processing by enhancing melt flow, which increases throughput; and (4)
serves as an internal mold release agent. The PFPE modifier meets USP
Plastics Class VI requirements, and it is NAMSA-tested for use in med-
ical devices and tubing. Besides gears and clean-room applications, PFPE
modified polyacetal compounds are used for automotive weatherstripping,
airbag doors, seals, and bushings [13].
When 2% silicone is added to acetal copolymer, as an internal lubricant,
the compound has good rigidity and toughness, creep resistance, low coef-
ficient of friction, and resistance to most solvents; but it also has disad-
vantages associated with unmodified acetal copolymer, high mold
shrinkage, and poor resistance to UV radiation [14]. Typical thermal prop-
erties for 2% silicone lubricated acetal copolymer include T of 190 to 210°C
m
(374 to 410°F), maximum service temperature of 90°C (194°F), deflection
temperature under load (DTUL)/1.82 MPa of 110°C (230°F), mold tem-
perature of 60 to 120°C (140 to 248°F); and flammability UL HB. Typical
94
applications include gears, bearings and bearing bushings, sprockets, con-
veyor belt components, drive chains, snap-fit parts, pulley wheels, and
spring studs [14].
Acetal homopolymer with PTFE lubricant shows good solvent resistance
typical of standard-grade homopolymer, good hydrolytic stability, and
lower coefficient of friction than unmodified grades. Disadvantages include
poor resistance to UV radiation, acids, and bases; and lower stiffness,
toughness, and strength properties compared with unmodified acetal
homopolymer [12]. Thermal properties include a T of 210 to 230°C (410
m
to 446°F), maximum service temperature of 90°C (194°F), DTUL/1.82 MPa
of 118°C (244°F), mold temperature of 70 to 110°C (158 to 230°F); and flam-
HB [12].
mability UL 94
TiO -filled, UV-resistant polyacetal compounds are used for outdoor
2
consumer products such as ski boot bindings, tennis racket handles,
windsurfing board frames, and toys.
On a different front, Quadrant Engineering Plastics Products man-
ufactures plastic stock shapes—plate, sheet, rod, and tube [15]. The