is significantly greater than that of wood or coal. Many plastics can also be thermally or chemically depolymerized into monomer(s), petrochemical feedstocks, and fuels. The end result is that several forms of plastics recycling can be defined. D5033-00 describes the following:
Primary recycling is the "processing of scrap plastic product into a product with characteristics similar to those of the original product."
Secondary recycling is the "processing of scrap plastic into a product that has characteristics different from those of the original product."
Tertiary recycling is the "production of basic chemicals or fuels from segregated plastic scrap or plastic material that is part of a municipal waste stream or other source."
Quaternary recycling is the "useful retrieval of the energy content of scrap plastic by its use as a fuel to produce products such as steam, electricity, and so forth."
Primary and secondary recycling are often referred to as mechanical recycling since the principal recycling processes involve cleaning and separation of the plastic by mechanical rather than chemical or thermal means. Quaternary plastics recycling is not universally recognized by government agencies in the United States or Europe as a form of plastics recycling. Energy recovery in the form of steam, hot water, or electricity by direct, controlled combustion of plastics as well as via the intermediate production of liquid, gaseous, or solid fuels from scrap plastic by thermal or chemical methods are often referred to as resource recovery processes rather than recycling. In Japan, quaternary recycling is often referred to as thermal recycling and is included in the broad definition of plastics recycling.
There is also uncertainty in the regulatory status of tertiary recycling when it does not result in the direct production of monomers suitable for polymerization into new plastic. The European Commission has at times supported the chemical recycling (depolymerization) of condensation polymers such as polyethylene terephthalate back to monomer (e.g., dimethyl terephthalate) as recycling for the purpose of government-mandated plastics recycling rate calculations, but not the liquefaction of polyolefin plastics back to petrochemical feedstocks for reprocessing in a refinery. Discussions around these types of definitional issues, and their environmental and economic implications, are likely to continue for many years to come.
Lastly is the subject of postconsumer and preconsumer plastics. In the United States for the purposes of making recyclability or recycling content claims for products, it is important to differentiate postconsumer from preconsumer plastics (16 CFR Part 260 Guides for the Use of Environmental Marketing Claims, available from U.S. Federal Trade Commission, www.ftc.gov). The paper industry now widely differentiates between postconsumer fiber and preconsumer fiber. The following definitions of postconsumer and preconsumer plastics are contained in ASTM D5033-00:
Postconsumer plastic: "Plastic material or finished product that has served its intended use and has been diverted or recovered from waste destined for disposal, having completed its life as a consumer item."
Preconsumer plastic: "Plastic material diverted from the waste stream following an industrial process, but excluding reutilization of material such as rework, regrind, or scrap generated in a process and capable of being reclaimed within the same process."
The term postuse plastic is sometimes used to cover both postconsumer or preconsumer plastics. The above definitions are in line with the recycling industry's position that scrap destined for recycling is not waste.
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