Value added color sorting of recycled plastic flake from end-of-life electrical and electronic equipment

Abstract

The properties of products made from recycled plastics are in part determined by the level and types of impurities found in the primary plastic. The removal of other plastics is essential if the properties are to approach those of virgin resin. Purification of plastic resins is achieved by exploiting differences in material properties of the different plastic types. Differences in density and surface properties have been shown to allow for the separation of a number of plastic materials. In many cases, streams of recycled plastic are composed of flakes of a wide variety of colors. The flakes can also range from clear to opaque. Separation of plastics into groups of similar colors can greatly increase their value because they can be colored to meet reasonable specifications much more easily. Sometimes, the different colors might correspond to different types of plastics, so their separation is desirable. For these reasons, the sorting of plastics based on color may prove to be a valuable separation technique for recycled plastic flakes. In this study undertaken jointly by the American Plastics Council and MBA Polymers, color sorting was applied to the separation of white, gray and black plastics from end-of-life electronic equipment. The composition dependence of sorting was investigated experimentally and compared with a theoretical model. Results indicate that increased levels of impurities decrease the throughput rate and result in increased impurity levels in both product and reject streams. The removal of black from a mixture of black and gray flakes was also demonstrated as a way to control product color.