Plastics

Plastics are non-metallic polymer materials that are manufactured on an entirely or partially synthetic basis from organic Carbon compounds. During polymerisation, chemical reactions cause reactive and monomeric small molecules to link together and form linear, branched or crosslinked macromolecules.

Depending on their thermomechnical properties, plastics are classed as either thermoplastics, Thermoset materials or elastomers.

The properties of a plastic depend on its molecular structure.

• Chain and thread-like molecules exhibit a weak linkage between the chains that becomes smaller under the influence of heat and causes the molecules to become mobile relative to each other. This results in thermoplastic properties such as suitability for thermoforming and/or welding (thermoplastics).
• Crosslinked chain molecules exhibit a stronger bonding effect at the crosslinkages. The molecules cannot be moved, but can be stretched (elastomers).
• Three-dimensional network molecules are tightly intermeshed by strong bonding, such that they cannot be displaced or moved against each other (thermoset materials).

Polymers have a low density and mass and usually good chemical Resistance to acids, alkalis and saline solutions, as well as a low Modulus of elasticity. Their Strength is highly dependent on temperatures and they can become brittle at low temperatures. Their coefficient of Thermal expansion is high and they can be susceptible to Creep and stress fatigue (relaxation), due to their visco-elastic behaviour.