Plastic is easily the most common manufacturing material in the world. We interact with it so often that we don’t think about it. Interestingly enough, the key to making plastic so useful is also what makes it so troubling. If you do not know what that key is, it can be encapsulated in a single word: polymers.
A polymer is a substance made up of a series of large molecules bonded together in a chain. Polymers are abundant in nature. However, they can also be created synthetically. Such is the case with plastic. Though it is possible to make bio plastics using organic polymers, nearly all the plastic the world produces are made synthetically from crude oil.
Polymers and Plastic
Plastic is a lightweight and durable material that can be easily molded into just about any shape. The key to its high strength-to-weight ratio is the polymer. Find the right molecules and bond them together in long chains and you end up with an extraordinarily strong substance. That is exactly what happens when a manufacturer makes plastic.
An easy way to understand how and why plastic polymers are so tough is to compare them to the individual fibers that make up a length of rope. If you break rope down to its smallest components, you have very thin threads incapable of supporting much weight on their own. But spin those threads together to create larger threads and you have the building blocks of rope. Twist multiple threads together and you create a rope more than capable of supporting a lot of weight.
Plastic polymers work on the same principle. You take individual molecules, known as monomers, and bind them together using a chemical catalyst. Bonding multiple monomers together creates a polymer chain. Then, you bind those chains together to create polymer groups. You end up with a strong substance that doesn’t weigh a lot.
Breaking the Bonds Is Difficult
It should be apparent that polymers are that which makes plastic what it is. You could say they are the best thing about plastic because they guarantee its toughness and durability. But guess what? That is also why polymers are the worst thing about plastic. The chemical bonds that keep molecules and polymer chains together are exceedingly difficult to break.
Bury a piece of paper in the earth and it will decompose fairly quickly. The chemical bonds holding the paper’s molecules together are easily broken by water and chemicals in the soil. Not so for plastics. Some forms of plastic can lay in the ground without decomposing for hundreds of years. The chemical bonds are so strong that not even the universal solvent (water) can break them.
Mechanical Plastic Recycling
The difficulty in breaking down polymers explains why mechanical recycling is the most utilized form of plastic recycling. Mechanical recycling involves chopping, grinding, and shredding plastic to create material that can be mixed with new plastic in the manufacturing process. Tennessee’s Seraphim Plastics, a company that buys and mechanically recycles industrial scrap plastic in seven states, says that mechanical recycling is cost-effective and profitable.
On the other hand, chemical and thermal depolymerization is expensive and difficult. It reduces plastic down to its individual polymers, but it also reduces the integrity of those polymers. Neither process is nearly as common as mechanical recycling.
Polymers are what make plastics so useful as a manufacturing material. But they are also the reason plastics do not break down in landfills. Polymers are both the good and bad of plastics. But until we can find a better way, we have to make do.