Environmental Engineering Reference
In-Depth Information
pound. As discussed further below, biobased plastics are already economically competitive
with conventional petroleum based plastics because of the higher price they can command
when they have specific materials properties. It can be argued that industrial bioengineering
for commodity production will first be utilized on the most economic targets and that plastics
are more economically attractive than fuels.
Pursuing economically viable plastics using bioengineering techniques can also affect
fuel prices to a substantial degree. This economic impact is due to several factors. Presently
about 65 percent of petroleum goes to transportation fuels, [3] however, if the 5-10 percent of
petroleum going into plastic materials can be substituted, the marginal cost of petroleum
could decrease significantly. This is due to the fact that market surpluses and shortages are, in
fact, relatively small perturbations on a large base number. Perhaps more significantly,
producing bioplastic materials provides an opportunity for economic integration. That is, by
having integrated biorefineries in which high-margin plastics are coproduced with biofuels,
economic production of the lower-margin fuel products can be produced.
There are a number of materials that can be made that start with renewable resources and
use bioengineering techniques. These include thermoplastics, thermosets, foams, pressure
sensitive adhesives, various biocomposites, and coatings. This document focuses on the
emerging material classes where bioengineering techniques play the largest role; that is,
where engineered organisms play a prominent role. Only a brief synopsis of materials
available from bioresources using more traditional chemical routes is given; several excellent
monographs are available that discuss biobased plastics and composites [4-6].
2. Conventional Plastics
Considerable environmental pollution occurs as a result of the production, use, and
disposal of conventional plastics. The absolute mass of plastics produced in a given year is
small compared to that of fuels; however, due to their persistence they present unique
challenges when released into the environment. Current polymer materials are nearly all
derived from petrochemical sources, contributing significantly to greenhouse gas emissions
during both production and incineration [7, 8]. Because producing plastics from renewable
resources provides a real economic opportunity, perhaps the best possible substitution
strategy would be to make non-degradable, persistent plastics from renewable resources; this
strategy could provide at least a relative sequestration of CO
2
from the atmosphere, thereby
mitigating effects of global climate change [9].
3. Plastics from Renewable Resources
Through application of bioengineering in conjunction with traditional chemical
processing techniques, bioplastics production is proving viable in a number of commercially
produced materials. Most notable are the production of PLA by Cargill-Dow under the trade
name of Natureworks
TM
(http://www.packexpo.com/ve/82489/main.html); the production of
Sorona
TM
polyesters, which contain a 1,3 -propanediol monomer derived from renewable
feedstocks, by DuPont (http://www.dupont.com/sorona/backgroundsoronapolymer.html); and
the production of PHA by Metabolix, Inc. (www.metabolix.com).
