Sorting of waste plastics

The collected plastics have to separate according to their types. Plastic waste can divide in to seven types. The Society of the Plastics Industry (SPI) established a classification system in 1988 to allow Consumers and recyclers to identify different types of plastic. That is as follows,

Code	Name	Examples
	Polyethylene Terephthalate	Used to make many common household items like beverage bottles, medicine jars, rope, clothing and carpet fibre.
	High-Density Polyethylene	Items made from this plastic include containers for milk, motor oil, shampoos and conditioners, soap bottles, detergents, and bleaches.
	Polyvinyl Chloride	PVC is used for all kinds of pipes and tiles, but is most commonly found in plumbing pipes.
	Low-Density Polyethylene	Items such as cling-film, sandwich bags, squeezable bottles, and plastic grocery bags are made from LDPE.
	Polypropylene	Used to make lunch boxes, margarine containers, yogurt pots, syrup bottles, prescription bottles. Plastic bottle caps are often made from PP.
	Polystyrene	Items such as disposable coffee cups, plastic food boxes, plastic cutlery and packing foam are made from PS.
	This is used to designate miscellaneous types of plastic not defined by the other six codes	Polycarbonate and Polylactide etc.

Not only that the separation is doing according to the color of the plastic. So there are different sorting methods used in the plastic recycling industries. The common method used in small scale industries in Srilanka is manual sorting method. It is mainly based on practice and experience of workers. When using this method most times human errors can be happen. So we can say that is in effective method. But it is cost effective in Srilanka as woman engaged in those works in low labor cost. When we consider large scale industries in the world used many developed methods for sorting. Most of them required high initial cost and maintenance cost.

There are density based sorting methods like centrifugal sorting, dry separations, Sink-float tanks, Sink-float by preferred solvent absorption, Sink-float by hydrophobicity, Froth flotation etc. Automated optical sorting methods are there like color sorters, color cameras, infrared cameras etc. Not only that advance spectroscopic based sorting methods, X ray fluorescence, electrostatic sorting techniques, sorting using softening temperature methods, selective dissolution methods also are there.