An introduction to plastics

I'm just guessing that everyone out there knows what plastic is. We call plastics plastic because they are pliable, that is, they can be shaped and moulded easily. As plastics become easier to mould and shape when they're hot, and melt when they get hot enough, we call them thermoplastics. This name can help you tell them apart from cross-linked materials that don't melt, called thermosets. But like I said, everyone knows what plastic is, …

…raincoats. The seams are welded by ultrasonic vibration. 10. A Special Note About Styrene Foam. Styrene foam is made in little pellets. To make blocks of styrene foam, or complicated shapes like a cycle helmet, they scoop lots of pellets into a mould and heat it with steam. The steam makes the pellets swell up and stick together. When you break a moulded block you can see how all the pellets have squashed into each other.