Highly crystalline resins that have the repeating group (OCH2)x. The resins are polyformaldehyde. The natural acetal resin is translucent white and can be readily colored. There are two basic types: a homopolymer, such a Du Pont's Delrin, and a copolymer, such as Hoechst Celanese's Celcon. In general, the homopolymers are harder and more rigid and have higher tensile, flexural, and fatigue strengths, but lower elongation. The copolymers are more stable in long-term high-temperature service and have better resistance to hot water. Glass-filled acetals provide greater strength and stiffness, and tetrafluoroethylene (TFE)-filled acetals provide low friction and high wear resistance. The 500 Series of Glidestar, from EM Corp., consists of acetal-based self-lubricating (oil or TFE) compounds.
Acetals are among the strongest and stiffest of the thermoplastics. Their tensile strength ranges from 8,000 to about 13,000 lb/in 2 (55 to 89 MPa), the tensile modulus of elasticity is about 500,000 lb/in 2 (3,445 MPa), and fatigue strength at room temperature is about 5,000 lb/in 2 (34 MPa). Their excellent creep resistance and low moisture absorption (less than 0.4%) give them excellent dimensional stability. They are useful for continuous service up to about 220 F (104 C). Acetals' low friction and high abrasion resistance, though not as good as nylon's, rates them high among thermoplastics. Their impact resistance is good and remains almost constant over a wide temperature range. Acetals are attacked by some acids and bases, but have excellent resistance to all common solvents. They are processed...
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