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Name: Ricca
Status: student
Grade: 6-8
Location: N/A



Question:
How are bioplastics made?


Replies:
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 case).

Hope this helps,
Burr Zimmerman


Hi Ricca,

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 traditional plastics.

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.

Regards,
Bob Wilson



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