Thermoset Plastics vs Thermoplastics

When classified by chemical structure, there are two generally recognized classes of plastic materials: Thermosets, having cross-linked molecular chains, and Thermoplastics, which are made up of linear molecular chains.

Thermoset polymers require a two-stage polymerization process. The first is done by the material supplier, which results in a linear chain polymer with partially reacted portions. The second is done by the molder, who controls final cross-linking. Short chains with many cross-links form rigid thermosets, while longer chains with fewer cross-links form more flexible thermosets. With all thermosets, the polymerization is permanent and irreversible.

Thermoplastic polymers require no further chemical processing before molding. There are two types of thermoplastic polymers: Crystalline and Amorphous. The pyramid graphic located here identifies many of our common thermoplastic materials.

Crystalline Polymers:

  1. Have a relatively sharp melting point.
  2. Have an ordered arrangement of molecule chains.
  3. Generally require higher temperatures to flow well when compared to Amorphous.
  4. Reinforcement with fibers increases the load-bearing capabilities considerably.
  5. Shrink more than Amorphous, causing a greater tendency for warpage.
  6. Fiber reinforcement significantly decreases warpage.
  7. Usually produce opaque parts due to their molecular structure.

Amorphous Polymers:

  1. Have no true melting point and soften gradually.
  2. Have a random orientation of molecules; chains can lie in any direction.
  3. Do not flow as easily in a mold as Crystalline Polymers.
  4. Shrink less than Crystalline Polymers.
  5. Generally yield transparent, water-clear parts.

Long Glass and Short Glass

How long is long?

Long glass is typically 11mm long x .3mm in diameter. Normally the glass fibers lay parallel within the strand.

Short glass is usually 3mm long x .3mm in diameter.

Normally when we make reference to "Glass Filled" we are referring to short glass unless otherwise specified.

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