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What is Polyacetal?
In the 1920s, a German chemist, Staudinger studied the polymerization and structure of Polyoxymethylene (POM) to research the theory of giant molecule. However, due to lack of thermal stability, POM was not commercialized. In 1948, DuPont started basic research and studied molding, finishing, and application to commercialize POM by improving the thermal stability. At last, "plastic replaces metal," the company issued DELRIN in 1956, and produced to sell the product since the 1960s.

Celanese completed its study on copolymer in 1960, and started producing CELCON in 1962. Since then, Acetal was divided with homopolymer produced by Dupont's technology and copolymer produced by Celanese's technology.

Establishing a limited partnership, Ticona with a German company, Heochst, Celanese started producing Hostaform in 1963. In 1968, Celanese established Polyplastics with a Japanese company, Daicel Chemical, and started producing Duracon. Since the expiration of patent on basic technology of Dupont and Celenese, many companies strived to develop new technology. BASF (ULTRAFORM) of Germany, Asahi Kasei of Japan, and Mitsubishi Gas Chemical also joined the production of POM.

In Korea, Korea Engineering Plastics Co. started producing KEPITAL by acquiring technology from Mitsubishi Gas Chemical. Kolon established KTP Industries Inc. with Toray of Japan, and introduced KOCETAL to the market in 1998.
Characteristics of Polyacetal
*Mechanical property
The resin is highly crystalline, and has a great combination of toughness and rigidity. It is also resistant to fatigue, creep, and to abrasion thanks to its property of self-lubrication.

*Thermal property
Heat deflection temperature under load and deterioration are other properties to be considered with polymer. Amorphous resin deflects over the heat deflection temperature, but polyacetal that is crystalline, doesn't deflect a lot even over the heat deflection temperature. Thus, the limit of temperature should be considered after calculating the amount of creep deflection, depending on the design requirement.

The estimated life of resin can be extrapolated by measuring the change of property by temperature and using Arrhenius Plot. Because thermal stability of acetal copolymer resin can be improved by addition of stablilizer, each grade shows different thermal stability. Homopolymer is more easily deteriorated than copolymer.

*Chemical resistance
The chemical resistance of a resin can be judged by examining the solubility to chemicals, the increase of weight through absorption, and the influence of chemicals on creep fracture.

Polyacetal isn't penetrated by organic solvents due to its crystalline property, but gains its weight slightly to aromatic, chlorine, ketonic, and ester solvents, which can change its mechanical property and size. Exceptionally, hexafluoroacetone dissolves polyacetal. Polyacetal is resistant to gasoline and lubricant, but if acid additive is used to improve the performance, it may become less resistant. Copolymer is resistant to alkali, but homopolymer is not resistant to alkali chemicals. Polyacetal is generally resistant to inorganic chemicals, but can be penetrated by ZnCL2 depending on temperature and concentration.

The life of resin should be decided by considering the concentration of chemicals and temperature. In case of resistance to hot water, if used for one year, the limit of temperature for copolymer is 90, and is 65 if used for ten years. Due to its chemical structure, homopolymer has fairly shorter life than copolymer.

*Weatherability
Polyacetal resin is not resistant to ultraviolet, but can be improved by adding light stabilizer and ultraviolet absorber. The resistance to ultraviolet can be enhanced by staining carbon black and using proper pigment. However, in case of exterior use, the resin can be deteriorated by ultraviolet and influenced by SOx, NOx, ozone, etc. Therefore, serious consideration is needed for weatherability.
The accelerated weather resistance test is carried out by using Weather-O-Meter, Xenon arc, and Fade-O-Meter. Good result doesn't guarantee any crack or discoloration caused by exterior conditions.
Homopolymer and Copolymer
Distinct property should be considered when selecting material between homopolymer and copolymer.
Homopolyer ... Excellent mechanical strength than copolymer for the short term
Copolymer ... Excellent flexibility but lower strength and rigidity than homopolymer
Homopolyer ... 10higher melting point than copolymer and heat deflection temperature under load
Copolymer ... Highly resistant to hot water and alkali. Especially excellent thermal stability at high temperature
Copolymer ... Good thermal stability and broad range of molding temperature in molding process.

Property Unit Homopolymer Copolymer
Specific Gravity 1.42
(0.051262)		 1.41
(0.050939)
Tensile strength   700
(9956.34)		 630
(8960.706)
Tensile elongation   30 60
Flexural strength   980
(13938.88 PSI)		 910
(12943.24 PSI)
Flexural modulus   28800
(409632.3 PSI)		 26400
(375496.3 PSI)
Impact strength Notched Izod   7.5
(1.3776)		 6.5
(1.19392)
Rockwell hardness  M scale 94 80
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