Thermoplastics    

Plastics come in two broad types. Thermoplastics, which are the types often found in schools and can be easily recycled. Thermosetting plastics which cannot be recycled usually and rely on mixing chemicals together to create a new substance. A good example of this would be epoxy resin glue (such as Araldite) which does not harden until the two tubes are mixed together. For more detailed information see the animation below.