Thermoplastics:   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.

Properties: Thermoplastics 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.

Processing: The most common methods of processing thermoplastics are injection molding,  extrusion, and thermoforming.

Advantages: Thermoplastics 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.

Disadvantages: Thermoplastics 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.

Engineering Thermoplastics: Engineering 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.