Environmental Engineering Reference
In-Depth Information
of new catalyst systems for polymerization, improving characterization with new analytical
techniques, and investigation of new medical applications [9].
Recently, the need for more biofriendly polymers has led to the study of additional
catalyst systems, new types of copolymers, and polymerization mechanisms. In the early
1990s, methods were developed for the continuous production of both lactide and PLA. A
major step in the commercialization of PLA occurred when Cargill Corporation developed its
method to produce PLA in a continuous process [10-13]. A joint venture of Cargill with Dow
Polymers (CDP) was then formed in 1997 to develop further the potential of PLA as a
commodity polymer. A production facility opened in 2002 and was built in Blair, Nebraska
with the capability of producing approximately 300 million pounds of PLA per year. Large-
scale production of PLA has dramatically decreased the cost of PLA resins and is now
enabling it to compete with established petroleum-based materials (Wall Street Journal, “One
Word of Advice: Now it's Corn,” October 12, 2004). Dow Chemical recently exited the joint
venture in 2004 and the Blair facility is operated by a wholly owned subsidiary of Cargill
called Natureworks (www.natureworksllc.com). This corporation is now producing and
selling large quantities of plastics being used in products ranging from clothing to food
packaging.
2. PLA Biosynthesis, Biodegradation, and Environmental Impact: Overview
PLA is presently commercially produced utilizing corn as the feedstock according to the
process diagramed in Figure 7. Corn first undergoes the traditional milling process to produce
unrefined glucose (dextrose), after which microorganisms ferment the glucose to lactic acid.
Importantly, this fermentation process is anaerobic: a wide variety of literature suggests that
anaerobic fermentations hold great advantage over aerobic fermentations when CO
2
balance
is of concern (discussed below). After fermentation, the resulting lactic acid is formed into
cyclic lactide through dimerization using reactive distillation. The lactide ring is then
polymerized to produce PLA.
Figure 7. Commercial route to biobased PLA plastics.
