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::Biodegradable Plastics |
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Bio plastics are biodegradable plastics, whose components are
derived from renewable raw materials. These plastics can be
made from abundant agricultural/animal resources like cellulose,
starch, collagen, casein, soy protein polyesters and triglycerides.
Large scale use of these would help in preserving non-renewable
resources like petroleum, natural gas and coal and contribute
little to the problems of waste management. Biodegradable Plastics
degrade over a period of time when exposed to sun and air.
Though the demand for biodegradable Plastics is increasing,
acceptance of biodegradable polymers is likely to depend on
factors like
1) Customer response to costs.
2) Possible legislation by Governments
3) The achievement of total biodegradability
Immediate application areas identified in India for biodegradable
plastics are Agricultural Mulch, Surgical implants, Industrial
Packaging, Wrapping, Milk Sachets, Foodservice, Personal care,
Pharmaceuticals, Medical devices, recreational etc.
Biodegradable Plastics highlights the Indian efforts in the
direction, as well as activities at some of the major centers
of developmental at USA/Canada, Germany, Scandinavian countries
and Japan.
Plastics that break down
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 plastics made with plant-based materials have
been available for many years. Because of their higher cost
they have never replaced traditional non-degradable plastics
in the mass market.
Indeed, 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 add up these associated costs, traditional plastics
would cost more and biodegradable plastics might be more competitive.
Biodegradable and affordable
If cost is a major barrier to the uptake of biodegradable plastics,
then the solution lies in investigating low-cost options to
produce them.The Cooperative Research Centre (CRC) for Food
Manufacture and Packaging Science is looking at ways of using
basic starch, which is economical to produce, in a variety of
blends with other more expensive biodegradable polymers to produce
a variety of flexible and rigid plastics. These are being made
into 'film' and 'injection moulded' products such as plastic
wrapping, shopping bags, bread bags, mulch films and plant pots.
Mulch film from biodegradable plastics
The CRC has developed a mulch film for farmers. Mulch films
are laid over the ground around crops, to control weed growth
and retain moisture. Normally, farmers use polyethylene black
plastic that is pulled up after harvest and trucked away to
a landfill (taking with it topsoil humus that sticks to it).
However, field trials using the biodegradable mulch film on
tomato and capsicum crops have shown that it performs just as
well as polyethylene film but can simply be ploughed into the
ground after harvest. It's easier, cheaper and it enriches the
soil with carbon.
Pots you can plant
Another biodegradable plastic product is a plant pot produced
by injection moulding. Gardeners and farmers can place potted
plants directly into the ground, and forget them. The pots will
break down to carbon dioxide and water, eliminating double handling
and recycling of conventional plastic containers.
Different polymer blends for different products
Depending on the application, scientists can alter polymer mixes
to enhance the properties of the final product. For example,
an almost pure starch product will dissolve upon contact with
water and then biodegrade rapidly. By blending quantities of
other biodegradable plastics into the starch, scientists can
make a waterproof product that degrades within 4 weeks after
it has been buried in the soil or composted.
Composting the packaging with its contents
Compost may be the key to maximizing the real environmental
benefit of biodegradable plastics. One of the big impediments
to composting our organic waste is that it is so mixed up with
non-degradable plastic packaging that it is uneconomic to separate
them. Consequently, the entire mixed waste-stream ends up in
landfill.
By ensuring that biodegradable plastics are used to package
all our organic produce, it may well be possible in the near
future to set up large-scale composting lines in which packaging
and the material it contains can be composted as one. The resulting
compost could be channeled into plant production, which in turn
might be redirected into growing the starch to produce more
biodegradable plastics.
An Olympic effort - recycling 76 per cent of waste
For anyone who thinks such schemes aren't feasible, you only
have to look at the recycling success of the Olympics to see
that where there's a will, there's a way. More than 660 tonnes
of waste was generated each day at its many venues. Of this,
an impressive 76 per cent was collected and recycled. Part of
this success was due to the use of biodegradable plastics used
in the packaging of fast food, making the composting of food
scraps an economic proposition as it eliminated the need for
expensive separation of packaging waste prior to processing.
With intelligent use, these new plastics have the potential
to reduce plastic litter, decrease the quantities of plastic
waste going into landfills and increase the recycling of other
organic components that would normally end up in landfills.
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