Plastics are polymers, meaning that on the molecular level, thousands of like molecules, or monomers (for plastics, this usually translates into long, long, chains of hydrocarbons, with some other molecules mixed in here and there, which I'll get to in a minute) join forces to create one giant molecule.
Plastics make up one group of synthetic (or man made) polymers, the other being rubber. However, naturally occurring polymers are far more prevalent than all the manufactured rubber and plastic products in the world, combined! Natural polymers include wood, cotton, leather, and wool, which man has long used to build homes and make clothing; the synthetic polymers available today serve to complement these naturally occurring substances.
Left to its own devices, the chemical reaction that causes polymerization would continue unchecked, creating infinitely long chains of hydrocarbons, which would produce so much heat and energy that they would eventually self-combust. This is where the other elements come in; they serve as book ends, if you will, to an otherwise never-ending polymer. Some plastics might contain molecules of chlorine, fluorine, oxygen, or nitrogen, so the make up (and eventual breakdown) of plastics vary drastically from one type to the next.
Okay, so by now we all know that it's important to recycle plastics. But what many people don't know is that some types of plastics are more easily recycled than others, and discerning which containers should go in a blue bin can be downright confusing. Fortunately for us Chicagoans, the city's recycling program accepts six out of the seven basic types of plastics used for packaging and containers: #1-5 and #7.
So what does this mean? Each number represents a category by which plastics can be sorted, and for all intensive purposes, the lower the number, the easier the plastic is to recycle. The good news is that all plastics can be recycled, but the bad news is that not all plastics can be easily recycled. Adding to the bad news is that the composition of plastic changes when exposed to heat, which causes the polymers to break down, the single bonds within the hydrocarbon chains to weaken, and sometimes chemicals within the polymer leach out of the plastic itself. This is especially troubling in the case of plastic bottles or containers for food or beverages.
The other troubling thing about plastic is that, unlike recyclables made from more natural substances such as aluminum and paper, plastic cannot be recycled back into plastic, which means that we have to find other uses for recycled plastics. Without a market for products made from recycled plastics, all the recycling in the world won't do us any good! Stay tuned in the coming months for a breakdown of the seven main types of recyclable plastics, including the common uses and resulting byproducts for each.