Identification and Sorting of Plastics

Clipart provided by RECOUP - promoting plastic bottle recycling 

An alternative is to use mechanised sorting technologies. This works by utilising differences in material properties. For example, the densities of some common plastics are shown in Table 5.3. 

The polyolefin fractions (PP, LDPE, HDPE) all have densities below 1 g/cm. This allows a process called float-and-sink to be used to separate them from the other polymer fractions. Separation is carried out in a flotation tank using water as the separation medium. 

Imagine you have a sack filled with bath sponges and house bricks and you were asked to separate them. Then imagine what would 

Now look again at Table 5.3, PET and PVC have the same density. How can these materials be separated from each other In this case a technique called X-ray fluorescence can be used. Many plastics are made up of the same elements such as carbon and hydrogen. PVC contains chlorine atoms. This technique detects the chlorine and can be used to indicate samples for removal from the waste stream. In this way PVC can be separated. 

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Identification and sorting of plastics in waste materials were reviewed [19,31]. Garbassi [32] has stressed the important role played by polymer analysis and characterisation in plastics recycling. 

In most situations, the manual identification and sorting of plastics parts from automobiles or computer and business equipment housings using fast infi ared techniques has significant throughput limitations. Overall ID and sorting rates of... 

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