09/09/1997

AU Researcher Studies a Process to Convert Solid Waste to Plastic

AUBURN, Ala. - Plastics have become essential in our lives, providing safety and convenience, but more than 35 billion pounds of non-biodegradable plastic waste are discarded by Americans each year, causing environmental problems both on land and in water.

There is a process, though, that can convert municipal and agricultural cellulosic waste to a plastic that is completely biodegradable, killing two birds with one environmentally friendly stone, according to Tom McCaskey, professor of animal and dairy sciences in Auburn University's College of Agriculture.

"Polymer scientists have discovered a way to make plastic out of lactic acid," he said.

Cellulose, which is a component of wood, paper and plant matter, can be broken down into glucose by acid or enzymes produced by microorganisms.

After cellulose is converted to glucose, this sugar can be fermented by microorganisms to lactic acid, a safe organic chemical most commonly used as a food preservative and found in most living things. The biologically active lactic acid, designated L(+) lactic acid, then can be made into polylactic acid plastic.

The plastic has characteristics similar to plastics made from petrochemicals, but because polylactic acid plastic is 100 percent biodegradable it is much more environmentally friendly, McCaskey said.

In addition to the benefits of being biodegradable and making use of discarded solid waste, using this type of plastic would reduce Americans' dependance on petroleum products, from which conventional plastics are made, he said.

"It's really an environmentally friendly process," he said.

McCaskey is working in cooperation with scientists at the Tennessee Valley Authority in Muscle Shoals, Ala., to improve this process so that it can be used economically on a large scale industrial basis. His role is to find microorganisms which convert glucose to lactic acid most efficiently and with the highest yield.

"I determine how best to treat the acid digested municipal solid waste by removing inhibitors and adding nutrients to encourage rapid growth of the organisms," McCaskey said.

He adds calcium hydroxide (hydrated lime) and filters the acid digest to remove compounds that inhibit the bacteria, and then he adds nitrogen compounds which are necessary for the growth of the bacteria. The sugar which is fermented by the bacteria to lactic acid comes from cellulose in the municipal solid waste.

Polylactic acid plastic is being produced commercially from corn, but municipal solid waste would be a more economical alternative because corn has more valuable uses such as human food and livestock feed, he said.

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Office of Ag Communications & Marketing

Auburn University College of Agriculture
Alabama Agricultural Experiment Station
3 Comer Hall, Auburn University
Auburn, AL 36849
334-844-4877 (PHONE) 334-844-5892 (FAX)

Contact Jamie Creamer, 334-844-2783 or jcreamer@auburn.edu
by Anna M. Lee

September 9, 1997