Solution proposed for agricultural plastic scrap. (Plastics).

Penn State agricultural engineer James W. Garthe has created a process to help farmers deal with the disposal of agricultural and domestic plastics by creating burnable, energy-efficient plastic nuggets.

"In plastics recycling there are two unbreakable rules," Garthe says. "You cannot mix types of plastic and the plastics must be clean. This process [avoids] both since mixed plastics burn just fine and the dirt and debris come out with the coal ash anyway."

Agricultural plastics, such as mulch films, greenhouse films and pots, flats and silage wraps are dirty and the cost of cleaning them before recycling is expensive. Also, these items are made from various plastics, such as low-density polypropylene, high-density polypropylene and polyethylene terephthalate, which cannot be mixed in conventional recycling.

Garthe's approach is to convert the various plastics into a plastic nugget that can be burned with coal in coal-fired boilers, refuse-derived fuel burners and cement kilns. Because the process does not involve melting, the plastics can be mixed. Only the outer portion of the nugget is fused, forming a melted jacket that contains compressed plastic waste.

Preprocessing for the prototype plant consists of cutting the plastics and hand feeding them into the hopper. A feed rod then pushes the plastics into the die. The die is heated to melt the outer layer, and a snake of compacted, though mostly un-melted plastic emerges. The system will eventually incorporate conveyors, sizing equipment and automatic cutting of the nuggets.

Although Garthe believes emissions are not a problem for the nuggets, Penn State's Energy Institute is currently testing the nuggets to characterize emissions. A grant from the National Watermelon Promotion Board, U.S. Department of Agriculture, supports the tests.

Garthe has applied for a provisional patent on the process.