Environmental Engineering Reference
In-Depth Information
In efforts to synthesize completely biodegradable nanocomposites, so-called green
nanocomposites have been successfully fabricated from cellulose acetate powder,
biodegradable triethyl citrate (TEC) plasticizer, and organically modified clay. Varieties with
20 weight percent plasticizer and 5 weight percent organoclay showed better intercalation and
an exfoliated structure than the counterpart having 30-40 weight percent plasticizers, while
the tensile strength, modulus, and thermal stability diminished with increasing plasticizer
content from 20-40 weight percent. Of special note, the nano-reinforcement at the lower
volume fractions (phi ≤ 0.02) reduced the water vapor permeability by 50 percent [49].
2.4.4.3. Polysaccharide nanocomposites
. Renewable nanocomposites have also been
made using microbially-derived polysaccharide polymers, such as polysaccharide fillers as
the reinforcing phase for a poly(3HO) [45, 50]. The mechanical properties of poly(3HO) are
significantly improved by the addition of certain polysaccharides (up to 50 percent starch by
weight or up to 6 percent cellulose by weight). The aspect ratio of the reinforcing phase is a
critically important variable. Improved nanocomposites are possible by transreacting the
hydroxyl groups of polysaccharides with functional groups in PHA, again demonstrating the
importance of chain functionalization [45, 50].
3. Research Priorities
3.1. Basic Biosciences
From a long-term perspective, continued support for basic biosciences that allow the
manipulation of plants at the genetic level is absolutely essential. Only through continued
development of genetic and physiological engineering techniques will the possibility of
inducing organisms to produce polymers directly, and thereby reducing the cost of bioplastics
by minimizing processing steps, be realized. In addition, the preference for anaerobic
processes among microbial fermentations should be recognized due to the minimization of
carbon loss from feedstocks. In the context of the plant-based plastics described in this
section, the required tools include the genetic engineering of the cellulose-lignin and oil
distribution in plants. Such basic genetic manipulation of plants is supported by the USDA.
Specific strategies for pollution prevention are necessarily more narrow and should focus on
developing cost-effective methods for producing plastics from plant-based matter.
3.2. Biodegradable Plastics
Within the realm of starch-based plastics, commercial interest and success is currently
carrying the development of compostable disposable packaging, including garbage bags, food
wraps, diapers, as well as disposable food service items such as plates, cups, and utensils.
Commercial research and development is even leading to improvements in water resistance
and durability of starch-based materials, with the result that these are not considered to be
high priorities for federal research funding. In contrast, the possibility of vastly improved
strength, lightness, durability, and heat and water resistance offered by natural fiber-
reinforced composites, particularly nanocomposites, cause this area to be highly attractive for
additional effort. Low-cost polysaccharide-based plastic materials have the greatest potential
to displace significant amounts of petroleum-based plastics.
