How do plastics work? What is actually in a plastic?

Plastics have become so ubiquitous that we often take them for granted, but have you ever wondered where these popular materials come from? In this episode, Marshall explains what plastics are made of.

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Episode Transcript

Speaker 1 (00:00):
Welcome to Brainstuff from house stuff works dot com where
smart happens. Hi. I'm braining 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

(00:21):
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 PBC. Plastic can be
found in lots of other places around the home, including
vinyl siding and vinyl windows. Then there's the fake leather

(00:44):
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 and everything from plastic
container is two plastic bags, from garbage cans to garbage bags.
You can even make bulletproof protection out of it if

(01:06):
you make it thick enough. There are many other types
of plastics in common use. There's pet plastic, for example,
founding clear plastic bottles for soda, as well as carpet
and clothing abs. Plastic makes everything from pipes to lego bricks.
Polystyrene makes styrofoam as well as plastic forks and containers.

(01:27):
The bottom line is that we find these different plastics
everywhere we look, in 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?

(01:48):
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

(02:08):
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

(02:29):
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. Your chaining together these ethylene molecules to make

(02:51):
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 going to cost

(03:12):
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

(03:34):
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 altogether or

(03:55):
in certain kinds of products. The environmental problem is the
only real down side 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

(04:17):
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 one
or the letter's PET denote pet plastic. HDPE or two

(04:41):
is high density polyethylene PVC, or three is polyvinyl chloride
l DPE or four is low density polyethylene pp or
five is polypropylene ps or six is polystyrene, and seven
stands for everything else. The next time you pick up
or touch a piece of plastic, which will probably be

(05:01):
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. Be sure to check out our new
video podcast, Stuff from the Future. Join how Stuff Work
staff as we explore the most promising and perplexing possibilities
of tomorrow. The House Stuff Works iPhone app has arrived.

(05:24):
Download it today on iTunes.