There's been a lot of hype, even "greenwashing", around the
development of plastics made from plants, such as corn, potatoes or sugar cane.
What's the potential of these new materials for design
engineers?
Developers of one material, called Mirel, say it's the real deal.
"Mirel is readily injection moldable for durable applications," says Bob
Findlen, vice president for sales and marketing for Telles, a joint venture
established by Archer Daniels Midland and Metabolix to develop Mirel, which is
a polyhydroxoxyalkanoate (PHA).
Mirel PHA has a heat distortion temperature (HDT) as high as
290F (143C) and physical properties that Findlen compares to ABS, a crossover
resin between commodity and engineering plastics. He says Mirel has good
hydrolytic stability, a drawback to starch-based plastics.
The catch is that it costs $2.50 a pound compared to less
than a dollar a pound for petroleum-based ABS and $1 to $1.25 to polylactic
acid, an aliphatic polyester made from corn starch or corn sugar that has
weaker thermal properties than Mirel. Oh, and you will need more material for beefier
walls and maybe ribs to obtain necessary impact strength.
The value proposition for Mirel, and to some extent other
bioplastics is twofold, and evolving.
At first, say even a year or two ago in North
America, the pitch was biodegradability. But that was messy.
Biodegradable in what? Many marketers wanted consumers to believe their
material would biodegrade in landfills, which, in fact are scientifically
designed to prevent biodegradation. And what's the impact of a biodegradable
product on an existing plastics recycling stream? Often, not good.
"One thing that has changed," says Findlen, "is that people
are becoming a lot more aware of the life cycle assessment. People want to make
sure the life cycle of a material they are considering is no worse, and
hopefully better, than the material they are presently using."
Life cycle assessment refers to a determination of the total
carbon dioxide generation used by a product during its life.
Substantial Premium
So, in the case of Mirel, you pay a premium of 2.5X over the
price of ABS and you can market your product as biodegradable and a carbon
footprint improvement.
The biodegradable argument for Mirel works like this:
1) Findlen
says Telles is targeting applications in which there is not an established
plastics recycling stream. So for example, replacement for PET bottles is not
on the table.
2) Telles
does not pretend its material can biodegrade in a landfill. But the composting
argument is tricky, because composting capabilities differ widely around the
world. Findlen says Germany
uses industrial composters to process waste. California may move in a similar direction.
For the rest of North America, the pitch is
that people can put waste in home composters, or just bury it in their
backyards.
The main target is packaging, but there are some indications
that the pitch is working for durable injection molded products.
Newell Rubbermaid will market three types of Paper Mate®pens whose Mirel housings can be separated from the inner
workings and disposed of in the ground. "Mirel can simply be placed in your
backyard garden or compost," says a Paper Mate promotion. Labcon North America,
a manufacturer of laboratory supplies, is using Mirel in its new Pagoda pipette
reloading system. Mirel is injection molded into a tray that holds pipettes in
place.
"There has been growing concern within our industry that the
disposal of traditional plastics is too wasteful ...," says Jim Happ, president
of Labcon. "Labcon previously supplied conventional plastic trays that were
thrown away or reclaimed through Labcon's recycle program. Now we are planning
to launch a composting program to complement this initiative."
Bioverse is using Mirel to produce a new biodegradable
version of its AquaSphere PRO pond and lake treatment system for golf courses.
The AquaSphere is a submersible, plastic-enclosed water treatment system.
The big payoff for Mirel and products like it will be in
consumer product applications, such as computer housings and keyboards, cell
phone housings, personal digital assistants and automotive parts.
Hewlett-Packard, a leader in trying more environmentally
materials, tested starch-based plastics, which failed in even minimal heat
tests.
"What's held us back so far is that we're working out of a
small pilot plant in Clinton,
IA," says Findlen. But the
capacity to produce Mirel from the factory will soon grow from 25,000 lb per
month to 110 million lb per year early in 2010. Infrastructure is in place to
boost capacity fourfold. Metabolix CEO Rick Eno estimates that the potential
revenues from a fully developed plant are more than $1 billion.
Another potential problem is the feedstock source for Mirel
in Iowa - corn
sugar via a fermentation process. Here's how Metabolix deals with the corn
issue:
· At full capacity, it says the
Telles production plant in Clinton,
IA that produces Mirel will use
less than 0.05 percent of the global production of corn annually.
· Locally grown field corn will be
used as the feedstock.
DuPont
is also using corn as a feedstock for a major dive into biobased plastics, but
its marketing approach is different from the one used by Metabolix. "Our goal
from the very beginning was to develop materials that offered equal or superior
performance to the competitive materials," Marsha A. Craig, DuPont's global
business manager for renewably sourced materials, told Design News in an interview at last June's National Plastic
Exposition.
DuPont is using its corn-based polymer as part of an alloy
that mostly contains petroleum-based plastics. That's an approach also being
taken in Japan
for components in cars and cell phones. That approach disregards one of the two
arguments employed by Telles - biodegradability, and totally focuses on the
carbon footprint issue. That approach has two other big advantages: it improves the economics of the bio option,
and improves mechanical properties for engineering applications.
DuPont's
Sorona will be priced in the $2-$3 range, and offers better engineering
properties than the moldable Mirel.
The
long-range plan at Metabolix is to produce PHA within plants such as
switchgrass, sugarcane and industrial oilseeds using modern biotechnology. Switchgrass yields 3.7 percent
of polymer within its leaves and 1.2 percent in the total plant. Researchers
hope to move away from a crop viewed as a food source, and also to improve the
economics of their PHA.
Nobody
said it is easy being green, but for some applications - and possibly many - they
increasingly may make sense.
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