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2-Plants: The myth of 'green' plastic

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TITLE:  The myth of 'green' plastic
SOURCE: The Times, UK, by Nigel Hawkes
DATE:   June 23, 1999

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The myth of 'green' plastic

None of us wants to leave the cupboard of natural resources bare
for our descendants. But just how sustainable is the idea of
sustainability? An analysis in this month's issue of Nature
Biotechnology, by Professor Tillman Gerngross of the Thayer
School of Engineering at Dartmouth College in New Hampshire, is
illuminating. Critics of the plastics industry complain that it
is unsustainable because it is based on a finite resource, fossil
fuels. Much better, they argue, to produce plastics from plants,
using fermentation. Professor Gerngross outlines the process by
which plastics called polyhydroxyalkanoates, or PHAs, can be made
from maize. They are broadly equivalent in properties to the
conventional plastic polystyrene. Maize must be grown, harvested,
then processed to extract glucose and fermented to convert the
glucose to PHA. The cells containing PHA are washed and spun in a
centrifuge, then broken open to release PHA, which is washed and
centrifuged again before final concentration and drying.

He shows that the fermentation route consumes 22 per cent more
steam, 19 times more electricity and seven times as much water as
the chemical manufacture of polystyrene. Producing PHA by
fermentation "consumes significantly more energy, releases more
greenhouse gases and therefore is no more sustainable than
petrochemical polymer production," he concludes. To produce 1kg
of polystyrene requires 2.26kg of oil: 1kg to generate the energy
needed and the other 1.26kg to serve as the feedstock for
conversion into plastic. The fermentation route involves growing
maize using fertiliser, insecticide and herbicide - all of which
need energy - and processing requires yet more energy, so that
even by the most optimistic calculations, 2.39kg of fossil fuel
are needed to produce 1kg of PHA. Furthermore, PHA production
requires the combustion of the entire 2.39kg for energy, while
the chemical route involves burning only 1kg. This means that the
polluting effects of the green approach are greater than those of
the traditional.

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