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acetyl plastic

Brand Names: Delrin, Tecaform, Ultraform, Celcon

Acetal Homopolymer (Delrin®)
Delrin® is a crystalline plastic which offers an excellent balance of properties that bridge the gap between metals and plastics. Delrin® sheets and rods possess high tensile strength, creep resistance and toughness.

It also exhibits low moisture absorption. It is chemically resistant to hydrocarbons, solvents and neutral chemicals. These properties along with its fatigue endurance make Delrin® sheet and rod ideal for many industrial applications. Available in natural and black grades.

  • Natural grade is FDA, NSF and USDA compliant.

Acetal Copolymer (Tecaform™)
Tecaform™ is a semi-crystalline thermoplastic offering high strength, stiffness and toughness. Tecaform™ is resistant to hot water, hydrocarbons and solvents, and it possesses good bearing and wear properties. It is available in natural and black grades. Tecaform™ is commonly used as bushings, rollers, wear strips and other applications requiring a combination of strength, low moisture absorption, chemical resistance and dimensional stability.

  • Natural grade is FDA, USDA, NSF and 3A Sanitary compliant.
  • Black grade is FDA compliant.
  • Medical grades available in colors. (see Medical Technology Materials)

Tecaform™ HPV 13 (Delrin® AF blend alternative)
Tecaform™ HPV 13 is a brown homopolymer acetal with an internal PTFE lubricant. Its low coefficient of friction, excellent PV values, toughness, wear resistance, and machinability make it an exceptional material for use in many industrial and military components with moving parts. Additionally, Tecaform™ HPV 13 has superior chemical resistance and flexural fatigue properties, as well as low moisture absorption associated with acetal materials.

  • Complies with FDA regulations 21CFR 177.2470 and 21CFR 177.105 for use in contact with food.

Differences Between Acetal Products

There are two general types of acetal resins available: Acetal homopolymer and acetal copolymers. Each type of acetal has its own set of advantages and disadvantages. Acetal (polyoxymethylene, POM) is a thermoplastic polymer commercialized in the early 1960's. This material is produced through the polymerization of formaldehyde.

ACETAL HOMOPOLYMER resins are currently made by the DuPont Company under the trade name Delrin®. Acetal homopolymers offer the following advantages over acetal copolymers:

Stiffer than acetal copolymers. Higher flexural modulus at room temperature and elevated temperature applications.

  • Higher impact strengths at room temperatures and low temperatures.
  • Tensile strength is approximately 10-15% higher than comparable copolymers.
  • Slightly higher continuous use temperature than copolymer (95°C vs. 90°C).
  • Slightly harder than copolymer acetals, thus giving the homopolymer acetals a lower coefficient of friction.

ACETAL COPOLYMER (Ultraform®, Celcon®) is made by several companies including BASF and Ticona. Acetal copolymers have the following advantages over homopolymer:

  • Improved dimensional stability over comparable homopolymer formulations due to its lower level of crystallinity.
  • Better chemical resistance with high pH (basic) solutions.
  • Lower centerline porosity than homopolymer in extruded shapes.

In most cases, acetal homopolymer and copolymer can be interchanged because many material properties are within approximately 10% of each other. Typical physical properties are shown in the accompanying table. Perhaps the most significant difference between homopolymer and copolymer acetal relates to the phenomenon known as centerline porosity. It is most prominent in extruded parts, particularly thick slab and large diameter rod stock. Visually, it is a whiter shaded region around the center portion of a rod, which extends down the entire length. In slab, porosity appears as a line along the center of each cut edge. In some cases, the slab may appear to be laminated or glued together. Excessive centerline porosity is undesirable for the following reasons:

  • Cosmetic - inconsistent color appearance in finished parts.
  • Compromises structural integrity.
  • Present routes for leakage of gas and liquids.
  • Provide areas where the bacteria can grow in food processing applications.

The cause of the porosity is shrinkage. During the extrusion process, the outside skin of the shape cools before the interior region. As the interior material cools, there is a corresponding reduction of volume. Since the overall volume change of the shape is restricted due to the solidified skin, voids form to compensate for the loss of interior volume.

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