What Are Thermoplastics?
are organic materials that melt when heated. They should be differentiated from
thermoset materials which cure, or become set, when they are heated.
Thermoplastic materials are melt processable, that is they are formed when they
are in a melted or viscous phase. This generally means they are heated, formed,
then cooled in their final shape.
have wide ranging properties. Depending upon their chemistry they can be very
much like rubber, or as strong as aluminum. Thermoplastics are light weight,
with densities of .9 to 2 gm/cc. Some high temperature thermoplastic materials
can withstand temperature extremes of up to 600 F, while others retain their
properties at -100 F. Some Thermoplastic materials have no known solvents at
room temperature. Most thermoplastic materials are excellent insulators, both
electrical and thermal. On the other hand thermoplastic composites can be made
to be electrically conductive with the addition of carbon or metal fibers. In
general the combination of light weight, high strength, and low processing costs
make thermoplastics well suited to many applications.
most common methods of processing thermoplastics are
injection molding, extrusion, and
have a good range of properties and are energy efficient both in their
manufacture and processing. Thermoplastic components can be made in very high
volume with high precision and low cost. Thermoplastics can replace metals with
a considerable weight savings , providing proper care is taken in design. Most
thermoplastics have better fatigue properties than metals and will tolerate
larger deflections than metals without deforming.
melt. Some degrade in direct sunlight or under high U.V. light levels. Many
materials have poor resistance to hydrocarbons, organic solvents, and highly
polar solvents but others have excellent resistance to these materials.
Thermoplastics suffer from creep, a relaxation of the material under long term
loading. Many thermoplastic materials, especially composites, tend to fracture
rather than deform under high stress levels.
Plastics is a marketing term used to distinguish higher performance/ higher cost
materials from basic commodity materials like Polyethylene, Polypropylene,
Polystyrene, and PVC. Engineering materials generally include Nylons,
Polyesters, Polycarbonates, etc. Far more materials fall into this category
than would fall into the commodity category.
In general, an Engineering material has a tensile strength of over 7,500 psi,
and costs over $2.00 per pound.