Not all recycling is the same
It is essential for anyone looking into the issue of recycling to gain a more in-depth understanding of the different and sometimes complex methods of recycling waste. These methods are targeted at the various types of plastic waste. Different approaches are used, for instance, for preconsumer and postconsumer waste; clean, source-separated waste; and mixed, unclean waste. Plastic waste is part of the wider value chain, but the problems of commingled waste and low levels of cleanliness are becoming increasingly prevalent throughout the course of the usage chain, which has a significant impact on the recyclability of the waste. Generally, plastics can be mechanically recycled, chemically recycled, or used in energy recovery.
Mechanical recycling involves treating plastic waste in such a way that the plastic’s chemical structure is retained. Used plastics are reprocessed (e.g. melted down, ground, and regranulated) to produce the secondary raw material for new plastic products or to make new molded parts directly. The process takes homogeneous waste from production or processing operations and transforms it into fully functional materials. However, the ability to mechanically recover plastics from used products presents more of a problem. First, they are neither clean nor source-separated. Second, their chemical structures may have been damaged by oxidation, UV radiation, or thermal stress. This considerably limits the quality of the output material and, in turn, that of the products made from it, as well as making these items more expensive due to the high level of effort and expense associated with the recycling process. As a result, an efficient and effective collection system for accurately identifying and sorting waste plastic is an essential prerequisite for mechanical recycling.
Where mechanical recycling is impossible – for instance, in the case of products with differing compositions – recycling specialists attempt to recover the plastics’ low molecular weight constituents for use as raw materials. This process, known as chemical (or feedstock) recycling, involves converting plastics into products with low molecular weight (monomers, high-quality oils, or liquefied petroleum gas) to use in place of fossil fuels (petroleum, coal, or natural gas). This means employing either solvolytic methods, in which polycondensates or polyurethanes are broken down using a suitable solvent, or thermal processes such as pyrolysis, in which the polymer chains are broken down using thermal energy. As a matter of fact, chemically recycled plastics are not currently classified as recycled materials in all EU countries, though it is expected that these regulations will be harmonized across the EU. In the context of recycling, energy consumption is also a subject worth examining. While products made of virgin material consume the largest amounts of energy, energy consumption levels can be significantly reduced in products made of chemically recycled material. However, the most energy-efficient products are made of mechanically recycled material.
Despite all the efforts that have been made, the disposal of waste plastics still results in some residual material that cannot be either mechanically or chemically recycled for technical, environmental, or commercial reasons. However, polymers are high-yielding energy sources, as a considerable amount of the energy used in their production is stored in the form of chemical energy. Consequently, nonrecyclable plastic waste is incinerated with the aim of recovering energy – most notably in industrial combustion systems, kilns in the cement industry, and household waste incineration plants, where plastics are needed to improve calorific values. “Energy recovery from plastic often comes under criticism. Yet plastic is absolutely essential when incinerating household waste, for instance, as we’d otherwise have to add in extra oil during the incineration process. A more sensible source of energy is to replace this with waste plastic, which will ideally have already been used a number of times in the recycling loop,” stresses Bettina Carow, Group Category Manager for Plastics at Greiner Packaging. The very worst method of recycling plastic waste is to put it into landfill or a garbage dump in the natural environment, as this means valuable materials cause pollution instead of at least being used as an energy source.
Plastics are forever
Some plastic products will take around 450 years to completely decompose in the natural environment, although they will still not have biodegraded. Depending on the application and the presence of a waste management system, EN 13432-certified “compostable” plastic packaging – which is correspondingly labeled as industrially and/or home compostable – can provide a solution to prevent microplastics or plastic refuse in general from entering the environment. These materials are usually also readily recyclable. In this context, a clear distinction must be drawn between composting (involving microorganisms) and structural degradation (without microorganisms). The former causes the material to decompose completely, whereas the latter releases microplastics and will not be permitted as a potential solution in the future.