How "green" are
green plastics?
Leland Teschler, Editor
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Careful, it's a trick question, at
least according to a study from
Athena Institute International, a
nonprofit that does R&D on sustainable building practices.
Recently it compared the environmental burdens of consumer
packaging made from common
plastics such as PET and
polypropylene (PP) to those associated with polylactide (PLA), a widely used corn-based plastic.
Athena's study looked strictly
at five packaging items: 16-oz
cold-drink cups, two-piece deli
containers, envelope window
film, foam meat trays, and 12-oz
water bottles. It calculated the
total energy consumed, the
amount of postconsumer solid
waste generated, and the amount
of greenhouse gases created
both with ordinary packaging
and from versions made from
PLA. When the final tallies were
in, packaging made from PLA
wasn't necessarily better than
that from PET, PP, or high-impact
and general-purpose polystyrene
(HIPS and GPPS).
The reasons why are interesting. It takes about as much
energy to form packaging made
from PLA as from petroleum-based resins. This stands to
reason: An operation that turns
PLA pellets into packages looks a
lot like one using pellets of
ordinary resins.
Surprisingly, PLA packaging
also creates about as much solid
waste as the ordinary kind. The
main reason is that the PLA
packages in the study weighed
more than all but one of the
petroleum-based packages.
There is just more PLA needed
for a given package. This is a big reason PLA packaging consumes
more energy from fabrication-to-grave. But a contributing factor is
an extra drying step necessary
for PLA that ordinary plastics
don't need.
One might also think the
disposal options for PLA would
be "greener" than those for conventional plastic. But claims
about how easily bioplastics
break down are only conjecture
at this point, says the report. To
back up its claim, Athena points
to evidence that PLA degrades
only with difficulty and not at all
in home-composting setups. That
means any effort to reduce PLA
into simpler compounds would
have to be a commercial effort.
And burning the stuff doesn't
help. Incinerating PLA gives off
the same by-products as incinerating conventional plastics: The
greenhouse gas CO2, water, and
other compounds get released
into the atmosphere. Of course,
PLA is theoretically recyclable,
but there is a catch here, too. For
one thing, the material can't be
mixed with other plastics for
recycling. In fact, mixing PLA
bottles with PET bottles could
harm the existing infrastructure
for reusing PET.
It's likely that newer bioplastics will have the same kinds of
disadvantages as PLA. So
whether these materials are a
better way of deploying
resources than ordinary plastics
is debatable. After all, land used
to grow crops for bioplastics
can't be used for producing food
or ethanol. And even if we completely eliminated the use of hydrocarbon-based polymers, the
result would only be a 3% drop in
the production of oil and natural
gas.