The properties of products made from recycled plastics are in partdetermined by the level and types of impurities found in the primaryplastic. The removal of other plastics is essential if the propertiesare to approach those of virgin resin. Purification of plastic resins isachieved by exploiting differences in material properties of thedifferent plastic types. Differences in density and surface propertieshave been shown to allow for the separation of a number of plasticmaterials. In many cases, streams of recycled plastic are composed offlakes of a wide variety of colors. The flakes can also range from clearto opaque. Separation of plastics into groups of similar colors cangreatly increase their value because they can be colored to meetreasonable specifications much more easily. Sometimes, the differentcolors might correspond to different types of plastics, so theirseparation is desirable. For these reasons, the sorting of plasticsbased on color may prove to be a valuable separation technique forrecycled plastic flakes. In this study undertaken jointly by theAmerican Plastics Council and MBA Polymers, color sorting was applied tothe separation of white, gray and black plastics from end-of-lifeelectronic equipment. The composition dependence of sorting wasinvestigated experimentally and compared with a theoretical model.Results indicate that increased levels of impurities decrease thethroughput rate and result in increased impurity levels in both productand reject streams. The removal of black from a mixture of black andgray flakes was also demonstrated as a way to control productcolor
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