"In plastics recycling there are two unbreakable rules," says James W. Garthe, instructor in agricultural engineering and cooperative extension specialist. "You cannot mix types of plastic, and the plastics must be clean. This process does 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 universally dirty, and the cost of cleaning them before recycling would be expensive. Also, while mulch and greenhouse films are generally low-density polyethylene, nursery pots are polypropylene and soda bottles and milk jugs are polyethylene terephthalate and high-density polyethylene respectively. The plastics found on farms, nurseries and landscape yards are a variety of plastics that would never be mixed in conventional recycling.
Garthe's unconventional approach is to convert the various film and solid plastics into a plastic nugget that can be burned with coal in coal fired boilers, refuse-derived fuel burners and even cement kilns. The process can mix plastic types, because it does not melt the plastic. Only the outer portion of the nugget is fused forming a melted jacket that contains the compressed plastic waste.
"Because the plastic is not completely melted, calculations show that only about one eighty-fifth of the energy released when the plastic nuggets burn is used to create the nugget," says Garthe. "Even if these plastics could be remelted and remolded, which they cannot, conventional recycling requires much higher energy input."