bioplasticsMAGAZINE_0703

Basics
Figure 1, microscopic thin
section of microbes with
white nodules of PHA. The
microbe is 80% plastic,
just prior to recovery.
Figure 2, parts made of
Mirel before and after
60 days submersion in
the ocean.
1: Chemtec, Biodegradable
Plastics from plants, 1996,
38-44, Oliver Peoples et al
2: American Chemical Society,
ACS Symposium Series 939
June 2006, Ramani Narayan
ful emissions, such as greenhouse gases like carbon
dioxide, during its manufacturing and disposal. Finally,
we want plastic that minimizes the use of “non-renewable”
resources like fossil fuels. Before we discuss the
functionality of PHA, we should summarize the environmental
aspects:
• They can reduce greenhouse gases: since PHAs are
made from renewable resources, they can be produced
and used in ways that can actually remove
greenhouse gases from the atmosphere, not just reduce
emissions! In most end of life scenarios, use
of the right PHA instead of a fossil based plastic will
reduce greenhouse gas emissions by 80% to 100%.
For a more complete discussion of the carbon cycle,
please read Ramani Narayan’s treatise 2 on the
subject. It is important to understand the life cycle
assessment of both the process used to make PHA
and the usage of the material to understand its true
impact on greenhouse gases. Early processes used
to make PHA were energy intensive and released
significant amounts of greenhouse gases, but new
processes have superseded them, resulting in breakthroughs
that make PHA economically and environmentally
viable.
• PHAs will quickly return to nature at the end of their
usefulness: since PHAs are made by the “cousins”
of naturally occurring microbes found broadly in nature,
and since these cousins already have the enzymes
required to digest PHA, they will be digested
and returned to nature in virtually any environment
supporting a healthy microbial population such as
soil, lakes, rivers, oceans, home and industrial composting
systems. Figure 2 shows samples of Mirel
bioplastic, made from PHA, before and after 60 days
submersion in the ocean. Though these Mirel bioplastics
quickly return to nature, they are durable in
use.
• PHAs can considerably reduce fossil energy usage.
Depending upon how they are manufactured, PHAs
can significantly reduce the amount of fossil energy
used to produce them compared to the traditional
plastic they replace. Mirel Bioplastics reduce fossil
energy usage by over 90% in some applications.
The future seems even brighter, since this remaining
fossil energy is used to harvest the feed stocks, and
much of this fossil energy can and probably will be
converted to renewable fuels in the future.
Mirel bioplastic is a family of PHA resins that can replace
fossil fuel based plastics in a growing variety of
applications. There are various grades of Mirel being
developed. Some have “film like” properties with the
look and feel of low density polyethylene. Other grades
perform more like polystyrene or polypropylene in injection
molded applications such as soil stabilization
stakes, caps and closures, food containers or cosmetic
cases. Grades have been developed for coating paper
board to replace polyethylene in cups and food containers
and still other grades for sheet used in thermoforming
applications such as storage containers, lids, and
other food service items. Future grades are being developed
for foam and fiber applications replacing polystyrene
and polyester. Figure 3 depicts some common
applications under development.
Beyond the production of PHA in microbial bio-factories,
research is continuing to find ways to make PHA
commercially viable using waste products as feed stock
or by growing the plastic in sugar cane or in non food
crops such as switch grass. Although these potential
pathways are most likely years from commercialization,
they demonstrate the variety and environmental potential
some of the production methods for this new family
of plastics.
bioplastics MAGAZINE [03/07] Vol. 2 35