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.
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 MateÂ®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:
Â· 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.
Â· 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.