How are bioplastics made?
There are many different kinds of bio-based polymers ("polymer" is term many
scientists prefer to use instead of "plastic"). Biopolymers are like
petroleum-based polymers in that they both are made of lots of subunits
("monomers") connected together to form a long chain (the "polymer"). Some
biopolymers are made by organisms (starch and cellulose are biopolymers made
from glucose). We collect the biopolymers from the organisms that made them
(e.g. corn starch from corn, cellulose from trees, etc.). Other times, the
monomers are made by an organism (such as lactic acid), and then processed
through traditional chemical means into a polymer (poly-lactic acid in this
Hope this helps,
The actual answer to your question would occupy many books! The term
"bioplastics" is a rather "fuzzy" term that generally means plastics
that are made only from biomass sources.
The class of plastics called "Cellulosics" were the first of this
type, and were first made nearly a century ago. They are derived from
plant cellulose. Others that are nearly as old are (or I should say
"were") made from soy beans, and the milk derivitive casein. Of these,
only the cellulosics (mainly cellulose acetate) are in use today, and
are a cheap, low-performance family of plastics. Screwdriver handles,
for example, are often made of cellulosic plastic. To make them,
cellulose is extracted from plant sources, and reacted chemically to
make cellulose acetate. The first cellulosic plastic was cellulose
nitrate, but it is extremely flammable, and has not been used for 60
years or more.
There are some new types of bioplastics that have been developed more
recently, but so far they have not found much use. Manufacture is
complex (much too complex to go into it here), and with the exception
of the cellulosic family of plastics, bioplastics at present are
usually too expensive to see general usage, and generally speaking,
the performance of bioplastics does not come close to that of many
One interesting type of bioplastic is plain ordinary polyethylene
(such as is used to make Tupperware and milk jugs). Rather than making
it from petroleum sources, it is possible to use ethanol as a
feedstock. The ethanol can be made by fermenting corn or sugar cane.
This does have the disadvantage of using foodstuffs to make plastic,
which does not sound like a smart thing to do!
Another point to remember is that although bioplastics may be made
from renewable sources, but their manufacture generally requires a lot
of energy that is, of course, supplied by fossil fuels. There is also
some controversy about the environmental damage that could be done if
bioplastics were ever produced on the huge scale that would be needed
to replace petroleum-derived plastics. The worry is that excessive
deforestation may result in order to supply the feedstock needed for
such large amounts of these plastics.
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Update: June 2012