To put it basically plastics fit into two different types:
Thermoforming plastics can be heated and formed repeatedly.
Thermosetting plastics, once heated, cannot be re melted.
The science bit:
Synthetic plastics all have a starting point of carbon – oil, gas or coal. The process of chemically making plastic is all about linking chains of monomers to create polymers.
Thermosetting plastics are interlinked like a net which, makes them more rigid. Thermoforming plastics are linked together as long chains making them easy to reheat and remould.
Just to add to the confusion there are several subtypes in those two sorts of plastic.
Thermosetting plastics are more rigid, they are highly resistant to heat which makes them suitable for electrical parts and pan handles. They are often cast into shapes from a liquid mix which hardens and cannot be reformed:
Melamine: Camping plates, worktops.
Epoxy resin: A two part resin and hardener that sets when mixed, Araldite glue, casting resin.
Phenol formaldehyde: Pan handles, bottle tops.
Urea formaldehyde: Plug sockets, electrical switches, door handles.
Polyester resin: Car bodies, boats.
In your exam you need to try and remember the difference between the two and be able to quote some examples. Help try to figure out which is which by having a look around your house and categorise the plastic you find using the descriptions above. Look closely at bottle labelling, it often tells you what type of plastic it is.
Thermoforming plastics generally make the bendy types of plastic, they aren’t very resistant to heat so can be melted easily. They are easy to recycle by grinding them down into pellets and reforming them:
Polythene HDPE (high density): Milk crates, buckets, plates.
Polythene LDPE (low density): Food packaging, carrier bags, washing up and shampoo bottles.
Polypropylene PP: Syringes, reusable food containers.
High impact polystyrene HIPS: Casing on vacuum cleaners, radios etc
Nylon: Hinges, combs, clothes.
Poly vinyl chloride PVC: Pipes, shoe soles, tablet packaging.
Acrylic (Perspex): Baths, machine guards.