In cracking you always make and alkene and an alkane
This is where we use heat to crack a molecule. This is how most cracking is done.
Plastics are very large molecules. They are made of small building blocks called monomers. These are always alkene showing that they have double bonds. They join to form a long chain called a polymer.
Plastics are non-biodegradable. This means they do not deteriate. It is a problem to burn plastics because they give out toxic fumes and take a lot of energy to burn. It is a problem recycling plastics because its hard to identify different types of plastics.
Thermosoftening plastics have no cross links, melt and are flexible and stretchy.
Thermosetting plastics burn (don’t melt) and are rigid and because they have hard cross links.