RESEARCH
In the realm of bioplastics, similar
‘
Its processes have made
problems will nearly always arise - renewable
crops need somewhere to grow and even
in the mid-west, an acre of land devoted to
PLA more competitive with
bioplastic feedstocks is an acre of land not
devoted to food. A partial exception may be
conventional plastics
’
PHAs (polyhydroxyalkanoates), which are
produced by certain classes of bacteria grown
on specifi c nitrogen-free substrates.
The absence of nitrogen leads the bacteria
to lay down stores of energy for the future,
just as hibernating animals store up fat for
the winter. The energy stores contain PHA,
which, after extraction and processing,
have similar properties to polyethene and
polypropene and can be produced to have the
same tensile strength and melting point as
polyolefi ns. The drawback: it's currently much
more expensive than existing materials.
But there's always hope, in that respect.
sulphate waste. Its processes have made PLA of staples upwards, without making serious Just as Cargill developed technology that
more competitive with conventional plastics; inroads into gasoline or diesel consumption. overcame the self-neutralising issue with
the other main output is ethyl lactate, a non- As well as chlorine-based chemicals, PLA, so may an enterprising company come
toxic and biodegradable solvent, which is Greenpeace is also concerned about the up with the goods for PHA. Its qualities
used in applications like paints and industrial implications of growing crops for plastics. make it a useful material and, while it also
solvents. "Sony and other Japanese companies requires organic resources like sugar cane,
The low toxicity and high biodegradability are moving over to bioplastics," says the indications are that it seems to make more
of PLA itself has been valued for a number Iza Kruszewska, toxics campaigner for effi cient use of them - so the impact on food
of years for use in dissolvable sutures and Greenpeace International. "The problem with resources may be less than PLA.
in controlled release devices in surgery and going that way is the use of land." Finally, what of recycling? Paradoxically,
medicine. Its drawback has been expense in Speaking at the PCD Congress in Paris biodegradable plastics may seem attractive
production and the challenge of overcoming earlier this year, professor of bio-polymer but because they degrade, their suitability for
a particular sticking point: as condensation science and engineering, Stéphane Guilbert, recycling is very low. PVC-free petroleum-
polymerisation proceeds, a competing concurred that use of certain materials can based plastics are available - and in
depolymerisation takes place and the higher be accompanied by unwelcome ethical widespread use, in applications like computer
the degree of polymerisation, the lower the consequences. Sugarcane and cornstarch are monitors and cabling. Wire insulation was for
rate until the two competing processes are in both important food sources and companies a long time a problem; plastics with bromide
balance. Cargill resolved the confl ict at over that claim to be - and are - environmentally softeners and fl ame retarders did the job
100,000 tons per annum, through the use of a conscious may be infl ating food prices so well. However, the electrical industries
tin oxide catalyst. in developing countries through using overcame the problems with lead-free solders
The main source for polylactic acids isn't bioplastics. He also implied that some and some seem to have now done the same
milk, despite the name; it's corn (maize) claims for 'biodegradability' can be infl ated with going bromide-free. And most plastics in
starch. Cargill's primary plant in Nebraska, - bioplastics are not biodegradable in soil use today are recyclable, some of them many
is handily placed for the vast prairies of the and need special treatment. And the most times over.
American mid-west, where corn is grown in abundant potential source of corn starch Now; the question is: why should there be
abundance - which is just as well, as 40,000 for PLA may be GM (genetically modifi ed) that dilemma at all? PLA is not the ultimate
bushels a day equates to over 1000 tonnes of maize - and as the American mid-west is GM answer, but at least it is one of a range of
corn, to produce 140-150,000 tonnes of PLA Central, such concerns may not be misplaced. alternatives.
annually. The use of plant stocks for biofuels So what about alternatives?
produced a shortage of food during
2008 - which pushed prices
SUSTAINABLE SOLUTIONS April/May 2009 49
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