Recycling color sorting

Most end-use markets for recycled plastic bottles require that they be separated by resin type and color. This ensures high end-use value for new products incorporating substantial amounts of the recycled resin. PVC bottles, like PET bottles, are very recyclable. Manual sorting of nonpigmented PVC and clear PET bottles is difficult because they look alike. When the two types are received commingled, the reprocessor can experience quality deficiencies due to rheological incompatibilities between these two resins. Therefore, all attempts to separate and remove these two resins must be made prior to recycling. 

Hamos GmbH of Penzberg, Germany, also has an IR-based plastics identification system for recycling applications. The compaw also manufactures equipment for color sorting that can be used in recycling processes. ... 

Clear/Color Sorting System for Recyclable Containers. Presentation at Conference on Solid Waste Management in the Midwest Chicago, IL. 1990. 

Petra 140 (Allied Signal) is a 40 percent glass-reinforced polyethylene tereph-thalate from recycled soda bottles. It has a tensile strength of 26,000 psi and a heat-deflection temperature of 225°C at 264 psi. PC23MS-200 (MCR Polymers) contains at least 25 percent recyclate from personal computer compact disks and polyethylene terephthalate beverage bottles. DMDA-1343NT polyethylene (Union Carbide) contains 28 percent color-sorted recyclate and has physical properties similar to those of virgin stock. Encore resins (Hoechst Celanese) are a family of plastics based on 100 percent reclaimed thermoplastics such as acetal, polyester, polyphenylene sulfide, nylon 6/6, and liquid crystal polymer. 

Care should be exercised with this procedure. Quaternary ammonium ion can be extracted from the montmorillonite with methanol (particularly the Cloisite lOA, which is exchanged past the CEC). The organic content needs to be checked by thermal analysis after this procedure. The recycled PET was a color-sorted grade from Polymer Institute Brno. The DSC signature of the PET was confirmed as similar to virgin PET. The miniextruder and injection molder from DSM were used to prepare the polymer-montmorillonite composites and test samples ... 

To efficiently use recycled plastics in molded parts, it is beneficial to work with several recycling suppliers to obtain a resin that is as close to the color of the product as possible. The resin that most closely matches the product may cost more per pound due to special sorting necessary to obtain a special color. This resin will probably cost less to use since it will require less corrective colorant to adjust the recycled resin to match the target. Recycled resins that are farther off color will require much more pigment to overpower the colorants in the recycled resin. 

In most cases, before attempts are made to recycle plastic resins, the used parts must first go through a series of sorting processes. The purpose of these sorting processes is to separate the desired recycle plastic from possible contaminants in the incoming stream. These contaminants can take many forms. They include dirt, paper, glue, and metal as well as other recyclable plastics and even the same desired plastic but of a different color. The most postconsumer recycled plastic today is PET. This is the plastic from which all plastic soft drink beverage bottles are made. 

One task a chemist often handles is the separation of the components of a mixture based on one or more physical properties. This task is similar to sorting recyclable materials. You can separate glass bottles based on their color and metal cans based on their attraction to a magnet. Techniques used by chemists include filtration, which relies on particle size, and distillation and evaporation, which rely on differences in boiling point. 

Traditionally, glass recycling has involved the collection and sorting of glass by color for use in the manufacture of new glass containers... 

In a few communities, recycled materials are placed into bags (usually blue in color) and collected in the same vehicles, standard compactor trucks, and at the same time as the garbage. When the load is dumped, the blue bags (and sometimes other readily identifiable recyclable materials) are sorted out. While some of these systems seem to work reasonably well, others have experienced significant contamination problems. Even without losses... 

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