Electrostatic separation of plastics by friction mixer with rotary blades

Abstract

A mixture of plastic pellets or waste plastic pieces is electrostatically separated. The mixture is charged by friction in a mixer and falls through a horizontal electric field of 4 kV/cm into three zones under the field. A mixture of two kinds of plastic pellets is separated with a purity of not less than 90%. A mixture of three kinds of pellets is separated to some extent in the zones at the extreme ends in the first separation, according to the locations of the different kinds of pellets in the triboelectric charging sequence. This mixture will be separated in successive separations following the first one into the respective pellet types. A mixer made of suitable plastic material and adapted to enhance the friction between different kinds of pellets assures easy and reliable separation. Proper mixing time, a high rotational speed of the mixer, and low humidity increase the purity of the separated pellets. Since the effect of blended additives of pellets on charging characteristics appears with good reproducibility, pellets and waste plastic pieces with such additives may likewise be successively separated into the respective plastics. © 1999 Scripta Technica, Electr Eng Jpn, 127(3): 33–40, 1999