Air Classification of Mixed Plastics

Plastics collection poses a quandary: if one wishes the easiest collection, the citizen must be given very simple instructions as to what plastics to set out; if the maxi­ mum collection of the many recyclable plastics is desired, one must accept mixed plastics. In either case, process­ ing is necessary: in the first, to control contamination; in the second to separate the polymers. Many sophisticated technologies are being developed for mixed plastics pro­ cessing: solvent extraction, melt technologies, X-ray de­ tection, etc. These are too sophisticated for primary sepa­ ration at a local MRF. This work focuses on the applica­ tion of air classification to the separation of mixed plas­ tics at the MRF level. Air classification has the advan­ tage over hydro-cyclones of being a dry operation. The differences in densities and in shredding behavior are em­ ployed. The air classifier and methods for its analysis are those developed by Stessel. Interesting interactions have been observed between tensile strength governing shred­ ding behavior, the resulting particle sizes, and material density. Laboratory separation data are presented and an­ alyzed. Implications for the employment of air classifiers for separation of plastics at the MRF are discussed.