Old idea of using bioplastics gets a new lease of life

Researchers are following Henry Ford's footsteps by developing food-based plastics as oil prices rise
Lee Bruno, The Guardian 10 Jul 08;

Landfills and plastics don't mix well. It takes several hundred years for an oil-based plastic bottle to breakdown in a landfill. And plastics can consume as much as 25% of the landfill space, according to the US government's Energy Information Administration.

Those two problems are helping drive innovation into new bioplastic packaging material at research institutions including Missouri University Science and Technology. There, researchers are cooking up recipes for super-biodegradable plastics that decompose in a few months.

These bioplastics are welcome improvements for US cities running out of landfill capacity over the next two decades.

In several states - such as Alaska, Connecticut, Delaware, North Carolina, New Hampshire and Rhode Island - capacity is expected to run out in just five years.

Dr KB Lee, professor of chemical engineering at Missouri S&T, and his team are investigating super-biodegradable plastic recipes made up of fillers, such as starch and fibres. Those natural building blocks make it possible for living organisms to break down waste material. Not only do these fillers accelerate the decomposition, but they also reduce the cost in a variety of commercial applications.

Wear, tear and weather

Lee's team is experimenting with renewable polymers such as glycerol, a byproduct of biodiesel manufacturing, and polyactic acid, a byproduct of ethanol fermentation. By combining and creating blends of polymers, the researchers believe the formulations will be suitable for applications such as agricultural films, bottles, biomedical and drug delivery devices.

Researchers agree that bio-based plastics have shortcomings, including being more expensive than petroleum plastics to produce and having limited mechanical strength properties. "It would be hard to expect a plastic product with excellent resistance against wearing, tearing, and weathering during its service life to also have biodegradability after usable service life," says Lee.

The challenges of higher prices are not new. Early in the 20th century, American inventors Henry Ford and George Carver tested formulations of plastics derived from foodstuffs in their labs. But they found the material wasn't cost-competitive with cheap oil-based plastics.

Today, the rising price of oil, coupled with innovative bio-plastic formulations, has improved the commercial outlook for these products. For example, bioplastics are considered good fits for different types of single-use products, such as low-grade stuffing materials, agricultural product containers and bags and packaging for materials with short expiration dates.

US-based market research body Freedonia Group estimates that demand in the $330m (£161m) US market in degradable plastic will grow 13.7% each year as prices and properties become more competitive with conventional polymers.

Other research efforts are focused on improving the strength of these bioplastic materials. Dr David Grewell, assistant professor of agriculture and biosystems engineering at Iowa State University and colleagues are tackling the mechanical weakness by reinforcing bioplastics with nanoclays. These tiny pieces of clay are between just 10- and 20-billionths of a metre in thickness.

The Iowa State researchers are using zein - natural proteins derived from corn and soy plants - which have stronger mechanical properties. One application for bioplastic formulations, says Grewell, is for garden plant pots. The bioplastic pots can be placed in the ground with the plant, thus supplying nutrients to the plant as it breaks down. Other potential applications for bioplastics made from crop proteins include disposable wraps for hay bales and packaging for the food industry. Another application is making green, biodegradable lubrication sticks from soy grease: Grewell and the Cornell researchers are working with prototypes as part of a 20-month pilot project.

Another research effort, 1,000 miles to the east of Iowa State, is based at Dr Emmanuel Giannelis' lab at Cornell University. The researchers there are also using nanotechnology techniques to build composite materials with properties that permit them to decompose faster, yet have mechanical strength and durability. "What we're trying to do is make biodegradable plastics far more attractive," says Giannelis.

Giannelis and his team have used a natural polymer called poly 3-hydroxybutyrate (PHB) to make a bin bag. The microbes produce the material as a way to store energy in the same way the human body produces fat to store energy.

Mad munching microbes

The Cornell team's composite material behaved as a clear plastic polymer but broke down almost completely in compost at room temperature within seven weeks. The rapid breakdown is enhanced by small spaces between the particles, which make the material more vulnerable to chemical attack and consumption by microbes. What's more, the material can also tolerate higher temperatures, thus making it suitable for a broader range of applications.

The outlook for bioplastics research is encouraging. The two most promising areas of research are in the use of polymer-clay nanocomposites (PCNs) and using nanoparticles or nanostructured materials as modifiers, compatibilisers and fillers. With new legislation under consideration across the US for raising landfill prices, plus the increasing cost of oil, the market opportunity for bioplastics may have its day, long after Ford and Carver tinkered with recyclable plastics.