Page 116 - Engineering Plastics Handbook

90 Engineering Plastics

TABLE 5.3 Typical Properties of Polyacetals
Abrasion and wear resistance
Low coefficient of friction
Low moisture absorption
Stiffness, rigidity (flexural modulus)
Hardness
Dimensional stability
Creep resistance
Stress crack resistance
Impact-resistant
Dynamic fatigue-resistant
Fuel (gasoline, diesel, oxygenated) resistance
Water resistance
Solvent, chemical resistance to oil, grease, dilute acid, alkalies, detergents (not phenols).
Attacked by acids, bases in solution
Property retention at elevated temperatures
Relatively low smoke (particulate) emissions
High T m
High gloss
FDA, NSF, USDA, EU compliant grades
FDA-compliant grades for repeated food contact to 121°C (250°F)
Excellent machinability of rod and slab with conventional brass turning lathes, cutting
tools

Acetal homopolymer and copolymer property values are relatively dif-
ferent for many properties, as shown in Table 5.5. Both polyacetals pos-
sess hardness, toughness, stiffness, abrasion, and wear resistance and
resistance to many of the same chemicals, and they compete for many of
the same applications. These properties are largely due to the high degree
of crystallinity of polyacetals. Acetal homopolymers generally have slightly
better mechanical properties; the copolymer shows better oxidative and
thermal stability. Unmodified acetal homopolymers generally show higher

TABLE 5.4 Typical Resins, Compounds, and Composites
Unreinforced
Impact-modified, unreinforced
Glass-fiber-reinforced, 10%, 20%, 25%, 30%
Glass-bead-reinforced and filled
Carbon-fiber-reinforced, 10%, 20%, 30%
Graphite-fiber-reinforced, 10%, 20%, 30%
Aramid-fiber-reinforced
Stainless-steel-reinforced, 7%, 10%
Mineral-reinforced (chemically coupled) and filled, e.g., 10% CaCO 3
Glass-fiber- and mineral-reinforced
®
PTFE (Teflon ) including powder, 5%, 10%, 15%, 20% lubricated
Silicone-filled, 2%
PTFE (18%) + silicone (2%)-filled
TiO 2 -filled
Recycled