Announcer

Welcome to Brain Stuff from howstuffworks.com where smart happens.

Marshall

Hi, I’m Marshall Brain with today’s question: how do plastics work and what is actually in a plastic; what’s it made out of? If you were to crawl under your house and poke around, chances are that you would find quite a bit of a white plastic pipe. This pipe is made of a very common, long lasting, strong plastic called PVC or polyvinyl chloride. PVC plastic can be found in lots of other places around the home, including vinyl siding and vinyl windows. Then there’s the fake leather made of vinyl found in everything from furniture to jackets to shoes. And many toys are made of vinyl as well. And that is just one kind of plastic.

Polyethylene is even more popular. You find polyethylene in everything from plastic containers to plastic bags; from garbage cans to garbage bags. You can even make bulletproof protection out of it if you make it thick enough. There are many other types of plastics in common use. There’s PET plastic for example, found in clear plastic bottles for soda as well as carpeting, clothing. ABS plastic makes everything from pipes to Lego bricks. Polystyrene makes Styrofoam as well as plastic forks and containers.

The bottom line is that we find these different plastics everywhere we look and almost any product we touch on a daily basis. To understand how useful plastic is, think about where we would be if plastic had never been discovered. Let’s say you want a container for some shampoo. If there’s no plastic, what do you use to make the container? There’s wood, paper, pottery, glass, fabric and metal. You can make the container out of glass, but what if you drop it? Or what about a computer keyboard? You can make it out of metal, but now it’s a lot heavier and more expensive. Plastics are obviously handy. They’re inexpensive, lightweight and strong.

Where do they come from and what makes them so popular? Let’s start with polyethylene since it is both the most common plastic as well as the simplest. A plastic like polyethylene starts with crude oil. If you look at crude oil, it contains chains of carbon atoms decorated with hydrogen atoms. Polyethylene begins with an ethylene molecule derived from crude oil and this molecule contains two carbon atoms and four hydrogen atoms. To make polyethylene, chemists have to link these ethylene molecules together into long chains that are hundreds of units long. That’s where the name polyethylene comes from. You’re chaining together these ethylene molecules to make incredibly long chains. The long chains then knit together to create a strong flexible plastic. If you think about it, polyethylene plastic is really nothing more than solidified gasoline. It contains exactly the same atoms, just slightly rearranged and organized into much longer chains.

Therefore, polyethylene is gonna cost about the same as gasoline by the pound and it’s also going to burn like gasoline. There’s even a company that makes a machine to turn plastic bags back into liquid oil to be reused. PVC is very similar to polyethylene except one of the hydrogen atoms is replaced by a chlorine atom. About half of the weight of PVC comes from chlorine, so you need less oil to make PVC. And that chlorine atom also adds some concerns when PVC gets thrown out. When PVC is incinerated it produces dioxins, which are good for neither animals nor people.

Some countries are therefore working to phase out PVC either all together or in certain kinds of products. The environmental problem is the only real downside to most plastics. One of the things that makes plastics so appealing is that they’re strong and long lasting, but if plastics escape into the environment, those assets become liabilities. The plastics can last for centuries and they are accumulating in the Pacific and the Atlantic oceans in areas called garbage patches. While the patches grow, there’s no real proposed solution to eliminating them.

The best defense against plastic pollution is collection and recycling. If labeled with a recycling symbol, it’s easy to tell what kind of plastic you’re holding in your hand. The symbol 1 or the letters PET denote PET plastic. HDPE or 2 is high density polyethylene. PVC or 3 is polyvinyl chloride. LDPE or 4 is low density polyethylene. PP or 5 is polypropylene. PS or 6 is polystyrene and 7 stands for everything else. The next time you pick up or touch a piece of plastic, which will probably be about three seconds from now, keep in mind what you’re holding. It’s a piece of solidified crude oil molded into the object you need.