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| Fig. 1: Approximate distribution of plastic waste disposal. [1] (Image source: J.Smith) |
Since the middle of the twentieth century, plastic production has increased more quickly than most manufactured materials. [1] Plastics are chemicals called polymers: they are chains of repeating individual chemical units called monomers. Commonly used plastics include polyethylene, polypropylene, polystyrene, polyvinylchloride (PVC), polyester, and acrylic. [1] The chemical monomers used to produce these plastics, such as ethylene and propylene, are overwhelmingly derived from fossil fuels. [1] Plastics are used in a variety of sectors. Producing packaging utilizes the most plastic, followed by the construction industry. [1]
By 2017, approximately 8300 Mt (million metric tons) of primary (from raw materials, not recycled) plastic had been produced. [1] At the end of 2015, 6300 Mt of plastic waste had been produced. [1]
Of this plastic waste, approximately 9% has been recycled, 12% has been incinerated, and 79% is found in landfills or elsewhere in the environment, such as in the oceans (Fig. 1). [1]
Different sorts of plastic, serving different purposes, remain in use for varied amounts of time. [1] While packaging is often disposed within a year of production, plastics used in electronics may last between 5 and 10 years, and plastics used in construction can have usage lifetimes of decades. [1] It is approximated that 30% of plastic that has been generated in the world remains in use today. [1]
More than 90% of plastic recycling is currently "open-loop," meaning that the plastic obtained from recycling is used to make a different product than the one from which it was recycled; for example, PET from plastic bottles is used to make polyester for clothing. [2] This is partly due to the fact that plastic recovered from recycling is often contaminated with toxins that can be difficult to remove: it is thus unsafe for the recycled products to be used for applications like food packaging and medical supplies. [2] Most current recycling involves mechanical techniques in which recycled plastics are shredded, cleaned, and then separated via processes like floatation, filtering, exposure to magnets, and spectroscopy. [2] Currently, many recycling plants still must relegate approximately 30% of their recycled plastic to waste because it is too challenging to properly separate or decontaminate. [2]
Approximately 6% of oil consumed globally is presently devoted to plastic production, and this is projected to increase to 20% by 2050. [3]
Approximately 4.5% of the world's greenhouse gas emissions in 2015 resulted from the plastic industry. [4]
It is estimated that approximately 6% of the world's oil consumption is used for plastic production. [3]
In 2021, 94088 thousand barrels of oil were consumed in the world per day. [5]
Therefore, in 2021, the number of barrels of oil consumed for plastic production was:
| 0.06 × 89877 × 103 barrels × 365 days | = | 1.96 × 109 barrels |
Currently, plastic generally has a life-cycle that corresponds to the principles of a linear economy, in which the plastic materials are generated, utilized (often only once - these are referred to as "single-use plastics") and then thrown away. [2]
In an effort to reduce the greenhouse gas emissions and pollution from plastic production and waste, many researchers are developing models for paths towards a circular economy for plastic. [2-4] Although the term "circular economy" does not have a single, clear-cut definition because the concepts involved are still in progress, the general goal of a plastic circular economy is to reduce the amount of plastic that becomes waste. [2] In addition to improving and increasing recycling, a circular economy aims to produce plastic products that are high quality and last for as long as possible, so they do not need to be replaced as frequently. [2] It also aims to make plastic from renewable resources. [2] Working towards a circular economy also involves considerations such as addressing environmental harms that have already been created by plastic production, and considering social impacts of implementing changes to plastic production, such as on the work force involved. [2]
Models that scientists have proposed for achieving a circular economy and reducing greenhouse gas emissions from plastic production often involve a combination of strategies. These include using biomass as a source for generating plastic monomers such as ethylene and propylene, thereby replacing fossil fuels and sequestering some carbon from organic materials in the plastic products. [3,4] Replacing some or all landfilling with recycling - particularly increasing the use of pyrolysis, a process in which plastics are heated in the absence of oxygen to break them down for reuse - is also proposed. [2-4] It is also suggested to implement carbon capture technology to use carbon dioxide from the plastic production process as a methanol source for further monomer generation. [3]
Although a successfully implemented circular plastic economy could reduce the environmental impact of plastic production and contribute significantly to the world economy, scientists readily acknowledge the challenges associated with achieving this. [2-4] For instance, achieving a low-emission circular economy requires access to decarbonized electricity to power the processes involved in plastic production and recycling within the circular economy. [3,4] Sustainable methods of biomass production that are conscious of land-use, existing ecosystems, and nitrogen emissions are also needed. [4] Furthermore, even if recycling is very effective, the amount of waste available for recycling is insufficient for the expected demand for plastic production going forward. [4] Achieving a circular economy would also require policy changes and economic incentives that make biomass use and recycling more attractive and accessible for companies and governments. [2-4]
© Jordyn Smith. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] R. Geyer, J. R. Jambeck and K. L. Law, "Production, use, and fate of all plastics ever made," Sci. Adv. 3, e1700782 (2017).
[2] D. G. Bucknall, "Plastics as a materials system in a circular economy," Phil. Trans. R. Soc. A. 378, 20190268 (2020).
[3] R. Meys et al.,"Achieving net-zero greenhouse gas emission plastics by a circular carbon economy," Science 374, 71-76 (2021).
[4] P. Stegmann et al.,"Plastic futures and their CO2 emissions," Nature 612, 272-276 (2022).
[5] "BP Statistical Review of World Energy 2022," British Petroleum, June 2022.