Page 117 - Engineering Plastics Handbook

Polyacetals 91

TABLE 5.5 Acetal Homopolymer and Copolymer Property Values*
Property Homopolymer Copolymer
Specific gravity, g/cc 1.41 1.41
Tensile strength, MPa (psi) 72 (10,500) 65 (9460)
0.32 cm (0.125 in)
Tensile modulus, GPa (psi) 3.0 (436,500) 2.5 (365,000)
Flexural strength, MPa (psi) 105 (15,275) 89† (13,000)
0.32 cm (0.125 in)
†
Flexural stress at 5% strain
Flexural modulus, GPa (psi) 3.0 (436,500) 2.6 (375,000)
0.32 cm (0.125 in)
Elongation at break, % 50 60
0.32 cm (0.125 in)
Shear strength, MPa (psi) 34 (5000) 53 (7700)
Impact strength, Izod notched, 90 (1.7) 80 (1.5)
J/m (ft⋅lb/in)
Hardness, Rockwell 95 85
M scale
Taber abrasion, mg/1000 cycles 12 14
1000-g load CS-17 wheel
DTUL/1.82 MPa (264 psi) 145 (293) 120 (248)
°C (°F)
DTUL/0.45 MPa (66 psi) 180 (356) 160 (320)
°C (°F)
Melt flow index, g/10 min 22 9
Water absorption, %
Equilibrium at immersion 0.7 0.7
24-h room temperature 0.2 0.2
HB HB
Flammability UL 94
Limiting oxygen index, % 18 16
UV radiation resistance Poor Poor
Other radiation resistance Poor Poor
3
Dielectric constant, 10 Hz 3.5 4.0
Dielectric strength, kV/mm (V/mil) 23 21
Volume resistivity, Ω⋅cm 10 16 10 15
17 15
Surface resistivity, Ω/sq 10 10
3
Dissipation factor (tan ∂), 10 Hz 0.0045 0.009+
Mold shrinkage, % 2.0
Flow/transverse
*Average typical properties (unmodified grades) at room temperature unless
indicated otherwise.
†Values are generally based on ASTM D20 test methods, which usually show
a range.

hardness, stiffness (rigidity), fatigue resistance, tensile strength, flexural
strength, and creep resistance and lower percent of elongation. Higher-MW
homopolymers can have higher toughness and percent of elongation.
Modified acetal homopolymer compounds are formulated for resistance
to hydrolysis at 82.2°C (180°F), similar to acetal copolymer hydrolysis