Environmental Engineering Reference
In-Depth Information
4. Renewable Polymer Production
Conceptually, three tiers of polymer production from renewable resources exist, as shown
in Figure 6 [10]. Polylactic acids (PLAs) and Sorona polymers are produced in a three-stage
process. The feedstock is first harvested in the form of crops, crop residuals, or other biomass,
and refined to yield plant sugars (primarily glucose and xylose). A secondary stage of
production consists of forming the subunit monomers via fermentation and separation.
Finally, the third stage consists of traditional chemical processing to form the polymers that
will ultimately be molded into plastic parts.
In a two-stage production system, plant sugars are used as substrates to support growth of
bacteria that synthesize polymeric materials directly to store their own excess energy, much
as an animal synthesizes glycogen. Such materials are being developed by a number of
groups and corporations around the globe, including Proctor and Gamble (under the trade
name Nodax, www.nodax.com) and Metabolix, Inc. (www.metabolix.com)—both of which
now claim the ability to provide commercial scale samples. It can also be argued that the
many interesting and useful materials being made from soybean and other plant oils [6] fall
into the two-stage production scheme, but with the second stage consisting of chemical rather
than biochemical transformation.
Figure 6. Systems for the production of materials by bioengineering [10].
In single-stage production, the material of interest is grown directly within the plant. This
technology is the most futuristic of the three but holds the greatest promise for additional
environmental benefits, particularly the direct capture of atmospheric CO
2
within the plastic;
it is now being pursued energetically by Metabolix, Inc. for production of PHA within both
