Plastic
contains polymers, molecules that are linked into long chains. Under a
microscope, polymers resemble a bowl of tangled spaghetti.
If you looked at the plastic in your sneakers under a high-powered
microscope, it would resemble cooked spaghetti, with each noodle tangled
in the others.
Plastics are made of groups of many atoms — the smallest building
block of any element — linked together into molecules. Molecules, in
turn, are the smallest complete unit of any chemical. In plastics, the
molecules are linked into long chains called polymers.
Polymers “become entangled with each other much like a single strand
of cooked spaghetti gets tangled up with other spaghetti strands in a
bowl of pasta,” explains Annette Jacobson, a chemical engineer at
Carnegie Mellon University in Pittsburgh.
That entanglement makes it hard to break plastic, which is a good
thing when it’s in your sneakers, toothbrush, bike helmet or hundreds of
other products we use every day. But plastic’s strength is also its
weakness — at least when it comes to the environment.
The reason: Plastic takes years, sometimes centuries, to completely
disintegrate. So our garbage dumps fill up with discarded plastic —
bags, food containers, tattered soccer balls and, yes, even old
sneakers.
Some plastic products even end up in the ocean, where currents gather the trash into what’s known as the Great Pacific Garbage Patch.
Marine animals get tangled up in plastic and sometimes mistake plastic
bags for food, because they look a lot like jellyfish. Scientists have
found plastic in the stomachs of dead seabirds, fish and turtles.
“Recycling programs address some of those concerns, but not everyone
recycles,” says Art Ragauskas, a Georgia Institute of Technology chemist
in Atlanta who is working to make plastics safer.
Problems with plastics
Some of the chemicals used to make plastic, such as plasticizers, do break down.
Plasticizers are chemicals used to make materials flexible. But as
plasticizers’ molecules break off or slide out of the plastic, they can
end up in the air and on surfaces around our homes and the environment.
People can breathe in plasticizers. If they come from a plastic used to
package or serve foods, plasticizers could even end up tainting what we
eat and drink. Scientists worry about the effects that these pollutants
may have on our health.
Phthalates
(THAAL’ ehtz) are one family of plasticizers. Though widely used,
phthalates have been linked to serious health problems, including
certain types of cancer and birth defects.
American, Canadian and European governments have banned several types
of phthalates in children’s toys. But phthalates are still used in
products such as shower curtains, car parts and food packaging. That
means most of us are exposed to phthalates every day.
Another major problem with plastics is that most are made using oil
and gas. Remember those polymer spaghetti noodles? Well, they don’t
occur naturally. Chemists manufacture polymers out of hydrocarbons,
which are ingredients of oil and gas.
Currently, about 4 percent of the crude oil (oil in its natural
state, before processing) used by industrialized countries is converted
into plastic. Another 4 percent is used to run equipment in the
factories that make plastic.
Getting that oil out of the ground often involves cutting down trees
and digging up the ground, destroying the habitat of many wild animals.
And oil and gas are nonrenewable resources, which means once they’re
gone, they’re gone.
“We all know the oil fields eventually will be empty,” says
Ragauskas. “Do we really want to hinge our economic success for our
children’s children on a resource that’s becoming more and more
difficult to find? I think the answer is no.”
How much plastic?
Because people use so much plastic, its effect on the environment is a
big deal. There were 1.5 million metric tons (3.3 billion pounds) of
transparent plastic sold in North America in 2010, and by 2015, that
number could reach 1.8 million metric tons. In the United States, sales
of plastics total more than $374 billion each year.
Plastic
is everywhere: in sneakers, straws and sandwich wrappers, to name a
few. But the handy material’s strength is also its weakness – plastic’s
durability means it lingers on land and at sea. Scientists are exploring
using plants in plastic for more Earth-friendly materials. Credit:
Sharon Oosthoek
“Go to any grocery store and look at what is plastic and you’ll go ‘Holy smokes!’” says Ragauskas.
But chemists are working to reduce the volume of this
hydrocarbon-based, hard-to-degrade material that can release potentially
toxic ingredients into the environment.
Some of the more promising research involves green plants.
Ragauskas, for instance, is using wood or the stalks and husks from
corn instead of oil and gas to make plastics. Using plants means we can
avoid digging up the earth in search of oil. And plastics that rely on a
material that is biodegradable, or able to naturally break down,
shouldn’t last for decades or longer in our landfills and oceans.
Another benefit of substituting green plants for oil and gas is that
plants are renewable. Once harvested, new plants can grow to replace old
plants. Oil and gas, on the other hand, comes from the decayed residues
of plants and animals buried underground. It takes many millions of
years for their remains to turn into oil.
However, using plants to make plastic is easier said than done. One
reason: Plant polymers have a very different chemical structure than the
polymers made from oil. And things that have different chemical
structures behave differently.
For example, plant polymers don’t generally repel water, as oil-based
polymers do. That’s why we use oil-based polymers in plastic containers
that hold food and drinks. Imagine buying milk in a plastic bag that
wasn’t waterproof.
The power of enzymes
At the University of Toronto in Canada, biochemist Emma Master is
trying to figure out how to alter plant polymers to make them repel
water. She’s using enzymes, which are proteins found in nature that act
as catalysts. Catalysts work by increasing or decreasing the rate of a
chemical reaction.
“We are using enzymes to generate [new] plant polymers, some of which
might be useful in plastic-replacing materials,” says Master. “And what
is nice about enzymes is that they are biodegradable,” she adds.
Master is especially interested in using plants to make plastic
products we tend to use once and then throw away, like food wrappers and
the materials used to package products such as batteries and pens. Her
research involves creating new materials from wood and farm crops. She
does this by extracting cellulose — a structural material in wood and
plant fibers. Then she experiments with enzymes to make the cellulose
behave more like the hydrocarbon-based polymers that are traditionally
used to make plastics.
Already, there are plastic drinking cups and bags made from
corn-based polymers combined with traditional, oil-based polymers that
repel water. While that’s a step in the right direction, such bags don’t
always easily biodegrade.
Another example of a plastic product with both plant- and oil-based
polymers is the combination wood and plastic boards being sold to make
decks and playground equipment.
Still, making bike helmets or computers out of plant-based plastic
may be far off in the future, because these products must be completely
waterproof and unbreakable. “Those things have to be engineered for high
performance,” notes Ragauskas.
But chemists are also working hard to make a difference in the
persistence of hydrocarbon-based products. They are trying to develop
bacteria that produce plastic-eating enzymes, which would decompose
plastic products once we are done with them.
“Bacteria have evolved to degrade most things,” says Master. “The
challenge is in promoting the transformation of the more harmful
components in plastic to environmentally harmless compounds.”
Power words
atom: The basic unit of matter. Or, to put it another way, the smallest building block of any element.
element: A substance containing atoms of the same
type. Hydrogen and aluminum are two examples. Elements are the building
block of all chemicals.
hydrocarbon: Any of a range of large molecules
created by chemically bound carbon and hydrogen atoms. Crude oil, for
example, is a naturally occurring mix of many hydrocarbons.
molecule: The combination of two or more atoms,
forming the smallest unit of any chemical. For instance, two hydrogen
atoms make up a hydrogen molecule. Add an oxygen atom to that hydrogen
molecule and you now have a molecule of water.
polymer: A very large, chainlike molecule with
identical links that consist of a tinier molecule. Even though a polymer
is considered a large molecule, it is not visible to the eye without
the use of a high-powered microscope.
catalyst: A substance that increases or decreases the speed of a chemical reaction.
bacteria: Living organisms, each consisting of a single cell.
phthalate: A chemical added to plastic to increase its flexibility.
