Identifying Plastics for Easy Sorting - recycling - Brief Article

USA Today (Society for the Advancement of Education), June, 1999

A device designed to identify plastics quickly and easily so they can be sorted for recycling has been developed by researchers at Purdue University, West Lafayette, Ind. It could help to save billions of pounds of plastics that are landfilled or incinerated every year, suggests Edward Grant, professor of chemistry.

"One of the primary obstacles in recycling today is the lack of sufficient means to avoid cross-contamination during collection. Polymers of different composition are incompatible when melted together, and a ton of mixed plastic is a ton of garbage."

The RP-1 Polymer Identification System "can be used to sort plastic components in cars, synthetic fiber resins in carpets, and a number of plastics used in the building and construction industry. It also can be used to sort plastic films, such as those found in dry cleaning bags, shrink wrap, and packaging material." Only a small fraction of these materials are being recycled, primarily because of difficulties in identifying and separating the various types of plastics, Grant points out.

The SpectraCode device consists of a handheld probe, which looks like a hair dryer, connected to a mobile console. The probe illuminates a solid object with a laser and collects the light scattered from the sample, much like a bar-code scanner. When a sample is illuminated with the laser, its molecules vibrate. The vibrations, in turn, cause the light to scatter in a pattern that is specific for each type of plastic. The scattered light is recorded and analyzed by a computer, which displays the result on a color monitor located on the console.

The entire identification cycle requires less than one second. Used with an automated system designed to trigger the probe when plastics are placed on a conveyor belt, the device is capable of identifying the chemical composition of plastic parts and scrap at rates of more than 100 pieces per second, or 500 tons per day. That means it could be used to screen commercial and post-consumer waste in factories, warehouses, recycling centers, and scrap yards.