Polymer Recycling and Disposal

Synthetic polymers are arguably the most important materials made by chemists and used in modem society. Chapter 30 Synthetic Polymers expands on the foundations of polymers discussed in earlier Chapters 15 and 22. Of significance is emphasis on the environmental impact of polymer synthesis and use, discussed in sections on Green Polymer Synthesis (30.8), Polymer Recycling and Disposal (Section 30.9A), and Biodegradable Polymers (Section 30.9B). 

So how do we balance the increasing pressure to introduce even more plastic objects into our lives while minimizing the impact on our environment This is an extremely important question, one that we will address when we discuss issues surrounding the recycling and disposal of polymers in Chapter 9. 

The synthesis as well as the recycling and disposal of halogenated compounds such as Polyvinylchloride (PVC), flame retardants (for example Tetrabromobisphenol A), y-Hexachlorocydohexane (y-HCH), Hexachlorobenzene (HCB) leads to the formation of byproducts and residues. Polymers, for example, as well as printed circuit boards or shredder residues include problematic substances which, for ecological reasons, cannot be passed on to the environment but have to be supplied to a specific and proper recycling or disposal process. Prior to this background so called "Supercritical Fluids" are of special interest. Supercritical fluids can be used for the synthesis of polymers in an enviromentally friendly way as well as for recycling and disposal processes. 

Recycling polymers is one way to minimize the disposal problem, but not much recycling occurs at present. Only about 25% of the plastic made in the United States is recycled each year, compared with 55% of the aluminum and 40% of the paper. A major obstacle to recycling plastics is the great variation in the composition of polymeric material. Polyethylene and polystyrene have different properties, and a mixture of the two is inferior to either. Recyclers must either separate different types of plastics or process the recycled material for less specialized uses. Manufacturers label plastic containers with numbers that indicate their polymer type and make it easier to recycle these materials. Table 13-5 shows the recycling number scheme. 

The Macro porous polymer (MPP) system is an ex situ technology designed to remove hydrocarbon pollutants from process water, groundwater, and wastewater. This technology uses a patented, porous polymer containing an immobilized extraction fluid that assimilates the hydrocarbons into the polymer structure. The particles are regenerated with an in situ heating cycle, and the contaminants are recovered for reuse, recycle, or disposal. 

Reclaim is a passive, in situ technology that uses a hydrophobic porous polymer to attract, adsorb, and concentrate petroleum hydrocarbons and volatile organic compounds (VOCs) from soils and/or groundwater. Reclaim is considered a passive treatment technology because it requires no mechanical equipment remediation consists of placing polymer-filled canisters in recovery wells and allowing the containers to attract and adsorb organic contaminants. Reclaim canisters are then recycled and contaminants recovered for analysis and/or disposal. This polymer extracts contaminants whether they are in liquid phase, vapor phase or dissolved phase in water. 

Biodegradable materials are created specifically with recyclability or disposal in mind. Recycling techniques for post-consumer biodegradable plastic products have two important features, which distinguish them from conventional polymers their biodegradability or compostability and the use of renewable resources in their manufacture. 

Apart from providing a solution to a disposal problem, we can look at polymer recycling as turning waste into valuable products, namely chemicals and fuel. We should consider plastic waste as a cheap source of raw materials in times of accelerated depletion of natural resources. 

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