Specialty plastics for practitioners – Properties, resistance and application examples

Specialty plastics are used when applications place high demands on the material or special properties are required. They frequently have insulating properties and their high resistance to water and chemicals makes them a reliable, low-maintenance material. It is then no wonder that specialty plastics are used in many technical fields and also in fasteners such as screws and nuts. The following article provides an overview of various specialty plastics and their applications.

What are specialty plastics?

Specialty plastics are designed to meet requirements that ordinary plastics cannot meet. The special properties are for example achieved by modifying the chemical composition or by special-purpose manufacturing processes. Specialty plastics, or high-performance plastics, are often specialized in terms of one property.

Manufacturing process for specialty plastics

When producing specialty plastics, the material composition is important to achieve the ultimately desired properties. The following example describes the production of PTFE:

Production process using PTFE as an example

Polytetrafluoroethylene, or PTFE, is made of chlorinated hydrocarbon. It can be produced by two methods, which differ depending on the desired starting product (powder or dispersion). Fluorides are partially added to the chlorinated hydrocarbon, which initially generates the gasses chlorine difluoromethane and tetrafluoroethylene. The tetrafluoroethylene is then dissolved in an aqueous phase, while excluding oxygen and exerting high pressure, and is then polymerized to PTFE by adding an aqueous initiator solution. Because PTFE is not water soluble, it precipitates in the aqueous phase. The PTFE is then obtained in the form of a powder by filtration and drying. If a dispersion is to be obtained as the starting product, a dispersant is added to the aqueous solution before the addition of the initiator.

Types of Specialty Plastics

There are a number of plastics that are suitable for producing components for specialized applications, such as plastic screws. At MISUMI, we offer a wide range of components made of the following plastics:

Advantages and disadvantages of plastic

Plastic connecting elements have the following advantages:

• They usually have an insulating effect, both thermally and electrically.
• They often expand similarly to natural materials.
• They are often resistant to water and many chemicals.

When compared to metal fasteners, their disadvantages are that they often have lower resistance to tensile and compressive forces, as well as lower maximum application temperature. This should be taken into account, for example, when selecting plastic washers.

Chemical resistance of selected plastics

The following table provides an overview of the chemical resistance of selected plastics:

Application example: Plastic sleeves and plastic washers

Spacer sleeves are used in many designs to create a distance between two components. They are cylindrical and can for example consist of rubber, metal or plastic. The purpose can be to insulate, reduce friction, or control movement. Plastic spacer sleeves offer several advantages over metallic spacer sleeves: They are insulating (thermally or electrically depending on the material) and are similar in properties to natural materials. Plastic sleeves expand, for example, to a similar extent as wood and other soft materials.

The insulating properties make plastic sleeves the ideal component in electrical engineering, e.g. for securing electronic components on a printed circuit board or for correct alignment and for maintaining safe distances between components. Spacer sleeves are also often used in mechanical engineering to accurately hold components in position or to dampen vibrations and noises. Another option would be as a bearing sleeve or mounting aid for light components.

• 1 - Plastic sleeve with guide
• 2 - Rotary shaft
• 3 - Timing pulley
• 4 - Ball bearing
• 5 - Bearing housing with bearing
• 6 - Drive wheel

If plastic discs are to be used that need to be conductive, MISUMI offers conductive and antistatic versions made of MC nylon in addition to standardized versions.

Various plastics are also used in washers. Here too, thermal and electrical insulation is the key criterion for their use. MISUMI for example also offers plastic discs with gliding properties. Discs and sleeves made of fluoroplastics for example reduce friction resistance in hinge designs. Due to their excellent thermal insulating properties (melting point is up to 300°C, depending on the strength and composition), Polyether Ether Ketone (PEEK) discs can in turn be used in heating and cooling lines.