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A plastic material consist of many, many repeating groups of atoms or molecules linked in long chains (called polymers). These polymers combine all different kinds of elements. Some examples would be hydrogen, oxygen, nitrogen, carbon, silicone, fluorine, and sulfur. These elements and their amount directly effect the physical and mechanical properties.

There are two main groups of plastic materials: Thermosets and Thermoplastics

 

Thermoset plastics:

Examples: amino, epoxy, phenolic, and unsaturated polyesters.

Reaction when heated:

  • Heating a thermoset degrades the material so that it cannot be reprocessed satisfactorily.
  • Because processing of this material causes the permanent cross-links between adjacent molecules, movement (shaping) is prevented at any temperature

 

 

 

 

Thermoplastic:

Examples: Acetal, acrylic, cellulose, acetate, nylon, polyethylene, polystyrene, vinyl, and nylon.

Reaction when heated:

  • becomes soft and moldable, solidifies when cooled; (thermoplastic elastomers* or TPE's remain flexible even when cooled).
  • the linked chains of molecules are able to flow into a different shape because they can move relative to each other when heated.

Reaction when the cycle is repeated:

  • recycling reduces mechanical properties and appearance.

* Elastomers = flexible materials that can be stretched to about double their length and returned to their original length when released. They are often used in the place of rubber and can be added to rigid thermoplastics to improve the impact strength.

Relevant categories of thermoplastics:

  • Amorphous (noncrystalline) : include polycarbonate, polystyrene, ABS(acrylonitrile butadiene-styrene), SAN (styrene-acrylonitrile, and PVC (polyvinylchloride)

unorganized structure of polymer chains

Reaction to heat: softens over a range of temperature (no apparent melting temperature)

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  • Crystalline: include acetal, nylon, polyethylene, polypropylene, and polyester

Organized structure of polymer chains

Crystalline thermoplastics have:

  1. higher melting temperatures
  2. higher shrinkage
  3. higher warpage factors

................Then amorphous plastics

Reaction to heat: fairly distinct melting temperature

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  • Liquid crystalline polymers (LCP):

Highly ordered rod-like structures

Liquid crystalline plastics:

  1. are highly chemical resistant.
  2. are highly dimensionally stable
  3. posses high mechanical property values
  4. are easy to process

..........As a result they have the lowest shrinkage and warpage of the three types of thermoplastics.

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Sonic & Thermal Technologies, Inc.
84 Research Drive
Milford, CT 06460
Tel: (203) 878-9321 Fax: (203) 878-6786

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