Bioplastics and biodegradable plastics
Last updated: March 12, 2010.
From cars to food wrap and from planes to pens, you can make
anything and everything from plastics—unquestionably
the world's most versatile materials. But there's a snag. Plastics are
synthetic (artificially created) chemicals that don't belong in our
world and don't mix well with nature. Discarded plastics are
a big cause of pollution, cluttering
rivers, seas, and beaches, killing fish, choking birds, and making our
environment a much less attractive place. Public pressure to clean up
has produced plastics that seem to be more environmentally friendly.
But are they all they're cracked up to be?
Photo: A typical biodegradable bag made
from Eco Film™ by Cortec Corporation.
The global plastics problem
Plastics are carbon-based polymers (long-chain molecules
that repeat their structures over and over) and we make them mostly
from petroleum. They're incredibly versatile—by definition: the word
plastic, which means flexible, says it all. The trouble is that plastic
is just too good. We use it for mostly disposable, low-value items such
as food-wrap and product packaging, but there's nothing particularly
disposable about most plastics. On average, we use plastic bags for 12
minutes before getting rid of them, yet they can take fully 500 years to
break down in the environment (quite how anyone knows this is a
mystery, since plastics have been around only about a century).
Getting rid of plastics is extremely difficult. Burning them can
give off toxic chemicals such as dioxins, while collecting and recycling them responsibly is also
difficult, because there are many different kinds and
each has to be recycled by a different process. If we used only tiny amounts of plastics that wouldn't be so
bad, but we use them in astounding quantities. In Britain alone (one
small island in a very big world), people use 8 billion disposable
plastic bags each year. If you've ever taken part in a beach clean,
you'll know that about 80 percent of the waste that washes up on the
shore is plastic, including bottles, bottle tops, and tiny odd fragments known as
"mermaids' tears".
We're literally drowning in plastic we cannot get rid of. And we're
making most of it from oil—a non-renewable resource that's becoming
increasingly expensive. It's been estimated that 200,000 barrels of oil
are used each day to make plastic packaging for the United States alone.
Photo: A biodegradable fruit and vegetable bag produced by
d2w®
for the UK's Co-op chain of grocery stores.
Making better plastics
Ironically, plastics are engineered to last. You may have noticed
that some plastics do, gradually, start to go cloudy or yellow after long
exposure to daylight (more specifically, in the ultraviolet light that
sunlight contains). To stop this happening, plastics manufacturers
generally introduce extra stabilizing chemicals to give their products
longer life. With society's ever-increasing focus on protecting the
environment, there's a new emphasis on designing plastics that will
disappear much more quickly.
Broadly speaking, so-called "environmentally friendly" plastics fall into three types:
- Bioplastics made from natural materials such as corn starch
- Biodegradable plastics made from traditional petrochemicals, which are engineered
to break down more quickly
- Eco/recycled plastics, which are simply plastics made from recycled plastic materials rather
than raw petrochemicals.
We'll look at each of these in turn.
Bioplastics
Photo: Some bioplastics can be harmlessly composted.
The theory behind bioplastics is simple: if we could make plastics
from kinder chemicals to start with, they'd break down more quickly and
easily when we got rid of them. The most familiar bioplastics are made
from natural materials such as corn starch and sold under such names
as EverCorn™and NatureWorks—with a distinct emphasis on environmental
credentials. Some bioplastics look virtually indistinguishable from
traditional petrochemical plastics. Polylactide acid (PLA)
looks and behaves like polyethylene and polypropylene and is now widely
used for food containers. According to NatureWorks, making PLA saves
two thirds the energy you need to make
traditional plastics. Unlike traditional plastics and biodegradable
plastics, bioplastics generally do not produce a net increase in carbon
dioxide gas when they break down (because the plants that were used to
make them absorbed the same amount of carbon dioxide to begin with).
PLA, for example, produces almost 70 percent less greenhouse gases when it degrades
in landfills.
Another good thing about bioplastics is that they're compostable:
they decay into natural materials that blend harmlessly with soil. Some
bioplastics can break down in a matter of weeks. The
cornstarch molecules they contain slowly absorb water and swell up,
causing them to break apart into small fragments that bacteria can
digest more readily.
Biodegradable plastics
If you're in the habit of reading what supermarkets print on their
plastic bags, you may have noticed a lot of environmentally friendly
statements appearing over the last few years. Some stores now use what
are described as photodegradable, oxydegradable, or
just biodegradable bags (in practice, whatever they're called, it often
means the same thing). As the name suggests, these biodegradable
plastics contain additives that cause them to decay more rapidly in the
presence of light and oxygen (moisture and heat help too). Unlike
bioplastics, biodegradable plastics are made of normal (petrochemical)
plastics and don't always break down into harmless substances:
sometimes they leave behind a toxic residue and that makes them
generally (but not always) unsuitable for composting.
Photo: A typical message on a biodegradable bag. This one, made
from Eco Film™, is compostable too.
Recycled plastics
One neat solution to the problem of plastic disposal is to recycle
old plastic materials (like used milk bottles) into new ones (such as
items of clothing). A product called ecoplastic is sold as a
replacement for wood for use in outdoor garden furniture and fence
posts. Made from high-molecular polyethylene, the manufacturers boast
that it's long-lasting, attractive, relatively cheap, and nice to look
at.
Photo: This "wooden" public bench looks much like any other until you look at the grain really closely. Then you can see the wood is actually recycled plastic. The surface texture is convincing, but the giveaway is the ends of the "planks," which don't look anything like the grain of wood.
Trendy Welsh outdoor clothing firm Howies has been trying to turn
recycled plastic into a selling point, and now offers recycled
polyester board shorts and all-weather jackets as part of its
range. But there's a problem with recycled
plastics. You can't automatically assume they're better for the
environment unless you know they've been made with a net saving of
energy and water, a net reduction in greenhouse gas emissions, or some
other overall benefit to the environment. And that's true of all
"environmentally friendly" plastics.
Are bioplastics good or bad?
Anything that helps humankind solve the plastics problem has to be a
good thing, right? Unfortunately, environmental issues are never quite
so simple. Actions that seem to help the planet in obvious ways
sometimes have major drawbacks and can do damage in other ways. It's
important to see things in the round to understand whether
"environmentally friendly" things are really doing more harm than good.
Bioplastics and biodegradable plastics have long been
controversial. Manufacturers like to portray them as a magic-bullet
solution to the problem of plastics that won't go away. Bioplastics,
for example, are touted as saving 30-80 percent of the greenhouse gas emissions you'd
get from normal plastics and they can give food longer shelf-life in
stores. But here are some of the drawbacks:
- When some biodegradable plastics decompose in landfills, they
produce methane gas. This is a very powerful greenhouse gas that adds
to the problem of global warming.
- Biodegradable plastics and bioplastics don't always readily
decompose. Some need relatively high temperatures and, in some
conditions, can still take many years to break down. Even then, they
may leave behind toxic residues.
- Bioplastics are made from plants such as corn and maize, so land
that could be used to grow food for the world is being used to "grow
plastic" instead. By 2014, almost a quarter of US grain production is
expected to be turned over to biofuels and bioplastics production,
potentially causing a significant rise in food prices.
- Some bioplastics, such as PLA, are made from genetically modified
corn. Most environmentalists
consider GM (genetic modification) crops
to be inherently harmful to the environment.
- Bioplastics and biodegradable plastics cannot be easily recycled.
To most people, PLA looks very similar to PET (polyethylene
terephthalate) but, if the two are mixed up in a recycling bin, the
whole collection becomes impossible to recycle. There are fears that
increasing use of PLA may undermine existing efforts to recycle
plastics.
How to cut down on plastics
Why is life never simple? If you're keen on helping the planet,
complications like this sound completely exasperating. But don't let
that put you off. As many environmental campaigners point out, there
are some very simple solutions to the plastics problem that everyone
can bear in mind to make a real difference. Instead of simply sending
your plastics waste for recycling, remember the saying "Reduce, repair,
reuse, recycle". Recycling, though valuable, is only slightly better
than throwing something away: you still have to use energy and water to
recycle things and you probably create toxic waste products as well.
It's far better to reduce our need for plastics in the first place than
to have to dispose of them afterwards.
Photo: Recycling, though sensible, is not always the best option. Generally it's better to reduce, reuse, and repair if you can and recycle only if you can't do these things.
You can make a positive
difference by actively cutting down on the plastics you use. For
example:
- Get a reusable cotton bag and take that with you ever time you go
shopping.
- Buy your fruit and vegetables loose, avoiding the extra plastic
on pre-packaged items.
- Use long-lasting items (such as razors and refillable pens)
rather than disposable ones. It can work out far cheaper in the long
run.
- If you break something, can you repair it simply and carry on
using it? Do you really have to buy a new one?
- Can you give unwanted plastic items a new lease of life? Ice
cream tubs make great storage containers; vending machine cups can be
turned into plant pots; and you can use old plastic supermarket
bags for holding your litter.
- When you do have to buy new things, why not buy ones made from
recycled materials? By helping to create a market for recycled
products, you encourage more manufacturers to recycle.
One day, we may have perfect plastics that break down in a trice.
Until then, let's be smarter about how we use plastics and how we get
rid of them when we've finished with them.
Further reading
General articles
- Research questions the environmental credentials of 'degradable' plastics: A Defra (British government) study published in March 2010 concludes that "some plastics marked as 'degradable' might not be as environmentally-friendly as consumers think."
- Packaging: The Riverford organic food company describes efforts to make its packaging greener. Includes an interesting comparison of the prons and cons of plastic and paper bags and whether "bioplastics" are really all they seem. Riverford has tried and shunned specially made bioplastic bags, opting instead for collecting the plastic bags it gives out and then recycling them.
News articles
Manufacturers' sites
Websites produced by biodegradable bag manufacturers are well worth a look. Most contain information about the plastics problem and explain how the different mechanisms of biodegradable bags actually work.
