Today's KNOWLEDGE Share: POM (part2)

Today's KNOWLEDGE Share:

POM (part2)

Copolymer and homopolymer acetal plastic differences:

One of the most important differences between homopolymer acetal (POM-H) and copolymer acetal (POM-C) is porosity. Acetal homopolymer may contain a lower-density or porous center. Porosity in a plastic means it may contain small bubbles or voids. These allow gases and liquids to seep into the plastic. Copolymer acetals have little or no porosity at their centers. This makes them the preferred acetal type for food contact or medical applications.

Homopolymer vs copolymer

Copolymers have less outgassing

Homopolymers have better creep resistance

Copolymers have better dimensional stability

Copolymers are less porous in extruded shapes

Homopolymers have higher Rockwell hardness ratings

Copolymers have slightly better overall chemical resistance

Homopolymers have about 10% to 15% higher tensile strength

Homopolymers have slightly higher operating temperature limits

Homopolymers are stiffer at room temperature and high temperatures

Homopolymers have higher impact strength at room temperature and low temperatures

Food grade acetal plastics

Acetal (POM) copolymers and homopolymers are available in formulations suitable for contact with food. These include compliance with FDA, USDA, NSF, Canada AG and 3-A Dairy material standards. While most acetals used for these applications are natural (white) color, there are compliant colorant additives available that can provide color options.

There are also acetal plastics with metal detectable additives. These are made for the food processing and food packaging industries. Metal detectable additives makes it easier to spot plastic particle contamination using conventional metal detection systems.

Glass-filled and glassreinforced acetal plastics:

One other type of acetal plastic that is sometimes used to make flow control parts is glass filled or glass reinforced acetal. The glass used in glass filled and glass reinforced acetal plastics is actually chopped glass fibers. While the terms glass filled and glass reinforced are often used in the same way, there are actually some significant differences between the two.

For glass filled acetals, the glass fibers act as a filler and make the parts stiffer but not necessarily stronger. Fiber reinforced acetals use glass fibers that have been sized and chemically treated to help them stick to acetal plastic. Glass reinforcement provides both stiffness and strength.

Glass filled acetals:

Glass filler adds stiffness but not strength

Intended for general industrial applications

No chemical bonding of the glass fibers with the acetal plastic

Glass reinforced acetals:

Glass fibers provide high stiffness and strength

For parts requiring high or very high stiffness and strength

Glass reinforced acetal is always stronger than glass filled acetal

Requires chemical bonding or coupling of the glass fibers with the acetal plastic

Source:industrialspec.com

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