Chemical recycling and promising new technologies need to be more fully explored. Mechanical recycling is the only method now commonly used for the large-scale treatment of solid plastic waste. Because every type of plastic differs in terms of chemical composition, mechanical behaviours, and thermal properties, however, conventional mechanical recycling requires pre-sorting to separate non-plastic items and different varieties - which can be costly and time-intensive. In addition, the two types of plastic that can currently be mechanically recycled, polyethylene terephthalate, or “PET,” and some grades of polyethylene, together make up less than half (46%) of all annual plastic production. In order to make recycled plastic products, old PET or polyethylene is blended with virgin plastics in an expensive, energy-intensive process that ultimately results in lower-quality finished material. Further innovation is therefore essential, ideally with a focus on both mixed mechanical recycling and chemical recycling. The latter uses thermolysis (applying heat) or catalysts to break down plastics into their component parts, which can then be re-built into new plastics. Complete depolymerisation involves breaking a plastic down to monomers (molecules), which can enable multiple recycling loops with lower energy requirements - all while maintaining the material properties of the finished product. In general, chemical recycling is under-explored - though it is also the most feasible approach for dealing with PET (it is also expected to become possible for biodegradable and compostable polyesters). Innovative recycling technologies that enable the direct processing of mixed plastic waste without pre-sorting may offer other potential solutions. This would require a means to stabilize the behaviour of mixed plastic waste during the recycling process - and would have to be facilitated by better design of the ways that plastic products reach their “end-of-life.” Plastics additives and impurities can interfere with recycling, and policies that make plastic producers responsible for the impact of the entire product lifecycle may help commit more manufacturers to better design, while improving the economics of current end-use options. Some positive related signs include Unilever’s pledge that by 2025 all of its plastic packaging will be fully reusable, recyclable, or compostable. Moves like this are more necessary than ever before, as new plastics can create problems for mixed waste recycling; for example, PET and the bio-polymer PLA (polylactic acid) can each compromise the recycling of the other if they are mixed. In 2015, an environmental engineer at the University of Georgia named Jenna Jambeck published a groundbreaking study that used available data to estimate that 8 million tons of plastic enter the world’s oceans every year. The amount of plastic produced is carefully safeguarded within companies, meaning that the actual amount of plastics filling up the oceans and landfills is likely much higher than Jambeck’s estimate. Despite global efforts to recycle plastic products, there are numerous barriers: Consumer-facing plastics come in different varieties, they’re often coated with labels or print, and they have colors and other features added. The mess of waste—used iPhone cases, empty shampoo containers, soda bottles—can’t be easily managed at scale, so a lot of it piles up. An emerging chemical process to break down a wide variety of plastics into usable propane offers a new solution to recycle plastic en masse. Researchers at SLAC National Accelerator Laboratory and the National Renewable Energy Laboratory used a microporous material called a zeolite that contains cobalt nanoparticles as a catalyst to break down different polymer molecules. The majority could be turned into propane. At the University of Texas at Austin, researchers used a machine learning model to generate novel mutations to natural enzymes that allow bacteria to break down the plastics found in soda bottles and most consumer packaging. The enzyme, called FAST-PETase (functional, active, stable, and tolerant PETase), could operate efficiently and work at an industrial scale. The first real-world application: setting the enzyme loose to clean up landfills.
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