Forces and stresses

Forces act on materials all the time - even if a material appears stationary it still has a force acting on it. There are five terms used to describe what type of force can act on a material:

Five different forces: Compression; bending; tension; torsion and shear illustrated around a main label saying ‘forces’.

It is very difficult to generalise on the properties of polymers as there are so many. There are seven types of plastic - six are common and are used for everyday objects, and the last type (not listed below) covers the substantial variations remaining that are not common.

Common polymerShorthandCommon use
Polyethylene terephthalatePETPlastic water bottles
High density polytheneHDPEFabric conditioner bottle
Polyvinyl chloridePVCPlastic toys, cling film, blister packs
Low density polytheneLDPEBread bags
PolypropylenePPYogurt pots and pen lids
PolystyrenePSPackaging and coffee cups

Each polymer type from the table above will cope with a force in a different way. If a polymer doesn’t withstand the force needed, a new type of polymer could be created by a chemical engineer. It is important to understand the characteristics of each polymer available to see if it is fit for the intended purpose.