Intro to the Chemistry of Plastics

Ever wonder how chemicals become plastics?

It’s magic. Kidding … Actually, it’s science in action. Specifically, chemistry. Plastics are the result of the very real marriage of raw materials, engineering, and energy—all brought together through chemistry.

Here’s a brief introduction to how chemists make modern plastics possible. No worries if you didn’t ace your chemistry class. While plastics can be high tech, advanced materials, understanding their basic construction is easy. Well, at least for me …

To make today’s plastics, chemists start with various elements (atoms such as carbon, hydrogen, oxygen and so on) derived from natural resources. Remember that magnificent, elegant periodic table of chemical elements that lists the building blocks of everything on earth? That’s the list of ingredients.

Chemists combine various atoms to make molecules, which are simply two or more atoms held together by chemical bonds. When making plastics, these molecules generally are called monomers. These monomers then are combined by chemical bonds into a chain or a network—this is called polymerization. And the resulting materials are called polymers. Or plastics.

(As you see, chemical bonds are rather important—and not simply to enable modern plastics. They also organize all those elements that combine to make up everything in the universe—including we humans. Without chemical bonds, life would simply be a chaotic maelstrom of elements. Not much of a life, actually …)

If the monomers join together lined up like a chain (picture a string of pearls), the polymer is called a thermoplastic. This plastic behaves sort of like an ice cube: it melts when heated and solidifies when cooled … like water, over and over again. Polypropylene (the stuff butter tubs often are made of) is an example of a thermoplastic.

If the monomers connect in a three-dimensional network, the polymer is called a thermoset. This plastic behaves sort of like an egg: once it sets and “cures” (or in the egg’s case, once it’s cooked), it cannot return to its gooey, liquid state. An epoxy from the hardware store that hardens and cures when applied is an example of a thermoset.

Because thermosets are a three dimensional network of monomers, they can be very tough. For example, your car tires are made with thermoset plastics (often called synthetic rubber).

Thermoplastics are tough, too, but they often are used in less intense settings, such as lightweight bottles for soft drinks that are not subject to massive heat and friction like tires.

Chemists (along with other smart people) over time have come up with many ways to combine ingredients to make new polymers … and even to combine polymers. The molecules can be fashioned with various properties depending on what we need: sticky or slippery or lightweight or soft or hard or foamy or stretchy or … well, you get the point. That’s why plastics are used in so many helpful everyday products, from spatulas to car bumpers and from medical implants to fabrics for clothing.

And this is only the beginning, as chemists are constantly developing innovative new plastics—to help make aircraft lighter, hearts pump longer, food stay fresher, homes more energy efficient and so on.

Thus ends the chemistry lesson. See, that was easy.

Read more about science and innovations in plastics here. And if you have a question for me, submit it and I’ll get back to you as soon as possible.