Environmental Engineering Reference
In-Depth Information
particularly attractive as means to overcome limitations inherent to bioproces sing.
These are particularly desirable for their potential to remove products as they are
synthesized, alleviating the nearly universal problem of product inhibition in culture
media.
E.
P
OLYACTIDES
•
Development of LCIA Tools
. One of the greatest challenges facing the production of
truly environmentally-benign plastic materials, PLA and otherwise, is the evaluation
of net environmental impacts, beginning with feedstock production (agriculture or
collection of biomass wastes), including processing steps (production of lactide and
subsequent polymerization) and ending with the emissions resulting from
biodegradation. Specific processes chosen at each stage, particularly concerning
conventional vs. sustainable methods, are likely to have dramatic impacts on the net
environmental profiles of individual materials, yet the tools with which to evaluate
these differences are not yet fully refined. These metrics are needed urgently, both to
guide research and development of bioplastics and to advocate use of the truly
environmentally beneficial materials. Consequently, a top priority in the
development of environmentally benign plastics is the continuation of efforts to
develop tools and standards within the context of LCIA that will make comparisons
transparent and meaningful.
•
Improvement of Physical Properties
. Presently, PLA and other biopolyesters suffer
from two important deficiencies that limit their use. The first of these is their
relatively low heat distortion temperatures, and the second is their relatively high
permeabilities toward a number of substances, particularly water. As current, best-
available LCIA analyses have indicated that PLA is indeed environmentally benign,
continued research into biological, chemical, and physical transformations of PLA-
based materials to improve these properties is warranted. In particular,
nanocomposite technologies (Chapter III.D.) hold promise of improving both
temperature distortion and permeation characteristics, as they have in conventional
plastics, and should be investigated. Microcomposite technologies are related,
already well-established approaches to achieve similar improvements in conventional
plastics. In addition, plant microparticles derived from waste agricultural residues
and simple grasses can be used directly as microparticles, providing both economic
and environmental advantages. Alternatively, blending and trans-reacting PLA-based
plastics with starch- or triglyceride-based materials (Chapter III.D.) may improve
performance while maintaining biodegradability, with the result that these techniques
also deserve further investigation. Recently, copolymerization of cellulose acetate
with PLA has demonstrated that the heat distortion temperature can be increased. In
this interesting case, both constituents of the plastic material come from renewable
resources. This suggests that copolymerization of PLA, especially with other
polymers based on renewable resources, can provide a viable route towards improved
performance.
