Biodegradable Plastics
Biodegradable plastics made with plant-based
materials have been available for many years. Their high cost, however, has
meant they have never replaced traditional non-degradable plastics in the
mass market. Our whole
world seems to be wrapped in plastic. Almost every product we buy, most of
the food we eat and many of the liquids we drink come encased in plastic.
Packaging is the largest market for plastics, accounting for over a third of
the consumption of raw plastic materials.
Plastic packaging provides excellent protection for the product, it is cheap
to manufacture and seems to last forever. Lasting forever, however, is
proving to be a major environmental problem. Another problem is that
traditional plastics are manufactured from non-renewable resources – oil,
coal and natural gas.
In an effort to overcome these shortcomings, biochemical researchers and
engineers have long been seeking to develop biodegradable plastics that are
made from renewable resources, such as plants.
The term biodegradable means that a substance is able to be broken down into
simpler substances by the activities of living organisms, and therefore is
unlikely to persist in the environment. There are many different standards
used to measure biodegradability, with each country having its own. The
requirements range from 90 per cent to 60 per cent decomposition of the
product within 60 to 180 days of being placed in a standard composting
environment.
The reason traditional plastics are not biodegradable is because their long
polymer molecules are too large and too tightly bonded together to be broken
apart and assimilated by decomposer organisms. However, plastics based on
natural plant polymers derived from wheat or corn starch have molecules that
are readily attacked and broken down by microbes.
biodegradable plastic products currently on the market are from 2 to 10
times more expensive than traditional plastics. But environmentalists argue
that the cheaper price of traditional plastics does not reflect their true
cost when their full impact is considered. For example, when we buy a
plastic bag we don’t pay for its collection and waste disposal after we use
it. If we added up these sorts of associated costs, traditional plastics
would cost more and biodegradable plastics might be more competitive.