Plastics are polymers (large molecules), made of long chains of smaller molecules, which are called monomers. Plastics are produced by polymerization, where millions of monomers are joined together to form a polymer chain. Much of the plastic we use is derived from petrochemicals, although plastic from plants (mainly corn starch) can be made. These are termed biopastics and decay more easily in the environment. Bioplastics differ from biodegradable plastic, which may be made from petrochemicals.
There are two main types of plastics – thermoset (permanent shape once molded) and thermoplastic (will melt under heat so can be molded again and again).
Thermoset plastic can be compared to a boiled egg. Once you’ve boiled it, you can’t ‘unboil’ it. It’s strong and durable and is used in vehicle manufacture and construction.
Thermoplastic can be compared to an ice cube. You can melt it, and then refreeze it into any shape you want. Same with thermoplastic. Thermoplastics are common in the food packaging industry because they can be quickly formed into any shape, for example milk and soda drink bottles.
Plastic has to be processed and shaped into the finished article and there are a variety of different methods to do this. Extrusion is a continuous process which forms sheets and pipes, such as gutters. Plastic granules are heated in a chamber, then forced out of the end of the chamber through a small hole to form the shape of the finished product. Injection molding can produce intricate high quality 3D shapes. Molten plastic is forced into a mold which is the shape of the finished product. This process is used to make such items as bottle caps and yogurt containers. Blow Molding is used to manufacture hollow plastic products such as carbonated soft drink bottles. And expanded bead blowing produces expanded polystyrene.
So that’s where plastic comes from. An equally important question is ‘where does it go’? Plastic is an amazing product – lightweight, strong and durable. It’s also very long lasting in the environment, and getting rid of it is a real headache. Fortunately plastic can be reused easily, and this is a very valid option, as it saves valuable natural resources and reduces greenhouse gas emissions. Most plastic is downcycled (i.e. it becomes a product of lesser value than the original).
If you can’t reuse the plastic, then send it for recycling. But this is a labor-intensive process and unfortunately some plastics are still difficult to recycle (or it’s not economically worthwhile to) so the first choice is always to reuse.