A Guide
to Acetal
Reference
Sheet
Material Safety Data Sheet -
Copolymer
Material Safety Data Sheet -
Homopolymer
What is acetal?
Acetal, or
polyoxymethylene, refers to two distinct yet similar products:
acetal homopolymer and acetal copolymer. The main
molecular chain of acetal homopolymer is the backbone of the
acetal copolymer chain, as acetal copolymer adds ethylene
oxide randomly throughout the acetal homopolymer chain.
What are the properties of
acetal?
The simple
nature of the molecular nature of the acetal homopolymer chain
allows a very stable crystalline structure. This
crystallinity leads to high heat resistance, high modulus,
excellent wear resistance, and resistance to solvents.
The added ethylene linkages of acetal copolymer increase the
thermal stability, elongation, and toughness but decrease the
stiffness and strength. These changes are likely a
result of the decreased crystallinity that results from adding
the ethylene oxide groups to the molecular chain. The
carbon to oxygen bonds in the main molecular chain are not as
thermally stable as the carbon to carbon bonds found in other
polymers. Thus, processing of acetal requires special
attention to be paid to temperature during molding as
exceeding the thermal degradation point (the temperature at
which the material will begin to break down) will produce
rapid decomposition resulting in formaldehyde gas. The
temperature at which this degradation occurs is less for
acetal copolymer than for acetal homopolymer. The
properties of acetal can be summarized as follows:
- excellent wear resistance
- very good strength,
stiffness
- good heat resistance
- excellent chemical
resistance
- opaque
- moderate to high price
- somewhat restricted
processing
A practical
difference between the copolymer and the homopolymer is that
the copolymer can accept reinforcement much better than the
homopolymer. Thus, the strength of the copolymer can be
increased far more easily than that of the homopolymer.
Both types can be modified by additives such as PTFE
(Teflon®) to increase the resistance to wear.
What are the applications
of acetal?
- gears, cams, and bearings
- light-weight industrial
wheels
- plumbing fixtures
- carburetor components
- conveyor components
- pens and buckles
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