POMH (Polyoxymethilene Homopolymer)

POM-C and POM-H: main differences

The first thing, which is important to know, is that we can actually find in the market POMC and POMH too. Both of them are obtained from the same polymeric family, but they have a different molecular structure and, consequently, a different mechanical behaviour.

Their differences are result of a different production method: to prevent unzipping of the polymer chains at high temperature 1) DuPont used an end cap mechanism and the obtained POMH; 2) Celanese opted for incorporation of a comonomer which also stopped the unzipping and the result was POMC.

Trying to avoid chemical circumstances, in this step it is enough knowing their main mechanical differences, which are:

• POM-H offers higher tensile strength, stiffness, creep and fatigue resistance and significantly higher impact resistance in short term application. It is an ideal material in parts designed to replace metal. It combines low-friction and high-wear resistance with the high strength and stiffness such applications require. It provides a wide operating temperature range (-40 °C to 120 °C);
• POMC possesses a linear structure with a highly crystalline quality that provides a variety of characteristics: outstanding wear, long-term fatigue, toughness and creep resistance as well as excellent resistance to moisture, solvents and strong alkalis. Its chemical structure provides a higher stability to thermal and oxidative degradation compared to acetal homopolymers.

POM main properties and characteristics

POM is one of the most versatile plastic materials, it can be used in a huge variety of applications and industries. It assures a good range of properties, such as rigidity, hardness and a smooth surface, which allows POM to be considered a friction material, good for wear and sliding applications. One of the most important characteristics of POM is its dimensional stability, thank to the really low moisture absorption (up to 0,8%).

POM main additives

As usually happens also for other thermoplastic materials, POM can be improved adding additives and fillers during the extrusion process. Ones we can supply are:

• POMC ELS. Acetal copolymer (POM-C) material modified by the addition of a special conductive carbon black. The addition of carbon black creates excellent electrical conductivity in the material. Carbon black filled POM-C offers excellent chemical resistance, high strength and hardness, and high abrasion resistance. In addition, carbon black filled POM-C has good UV and weather resistance. Having exceptional ​wear properties as well, makes this special acetal copolymer an ideal choice also for sliding applications. POMC ELS is anyway more used for conductive applications.
• POM SL. A modified material by the addition of solid lubricants, which assure a very good friction and wear properties. Main additives used are PE (for POMC) and PTFE (for POMH). In both cases also Stick Slip effect is highly reduced;
• POMC GF25. It is a special glass filled acetal with 25% glass fibre reinforcement. In comparison to POM-C unfilled, POM GF25 demonstrates optimised properties in a number of different areas. The properties POM GF25 exhibit, makes it suitable for use in parts that are exposed to high static loads over long periods in high temperature conditions. This glass filled acetal has high mechanical strength, outstanding wear resistance, and has very high dimensional stability. In addition to this, POM GF25 also offers high electrical insulation and exceptional chemical resistance. However,​ as glass fibres tend in some cases to have a marked abrasive effect on mating surfaces, POM GF25 is less suitable for sliding applications. ​
• POMC ID. Inductive detectable POM-C is modified with a metal detectable filler that provides for excellent protection in food environments that use metal detection equipment to monitor for unwanted particulates. For added safety and versatility, this acetal material is colored blue to increase its visibility to optical detection equipment in use many food plants. POMC ID can be used in a variety of food industry applications requiring good strength and toughness, dimensional stability, wear resistance and the ability to operate in a wet environment with little moisture absorption.

Chemical resistance.

UV rays damage the molecular structure of POM; a long-time exposure can in fact deteriorate the material and collapse its physical-mechanical properties.

On the other side, Polyoxymethylene resists to organic solvents, wax, fats and fuels. Only few substances at high temperature can damage the material.

Miscellaneous information

POM is largely used in food processing industry, it can be certified EU 10/2011 and FDA. Acetal is usually available in White, Black and Blue RAL 5002.

Most known brand names

Polyoxymethylene is usually available in sheets, rods and tubes and all our semi-finished materials shapes directly come from the main German and Austrian producers.

This material is known with a huge number of different trade names; most common and known are:

• Zellamid 900;
• Sustarin;
• TECAFORM;
• Ertacetal;
• Delrin (only POMH, from DuPont);
• Hostarm (usually used for injection moulding).

POM in few words.

Special properties:

• High chemical resistance;
• High dimensional stability;
• Low moisture absorption;
• Excellent sliding properties;
• High abrasion resistance ideal combination of strength, stiffness and toughness;
• Little tendency to creep.

Used in:

• Food processing;
• Material Handling;
• Construction;
• Automotive.

Applications:

• Gears;
• Bushing;
• Skid;
• Knife guide.