Reduce, Reuse, and Rethink Plastic Recycling

The widespread use of plastic combined with low recycling rates have made it a pressing environmental issue. Reusable alternatives have become trendy on both a corporate and personal level, but some products are simply not able to do away with plastic packaging in this manner. Additionally, recycling is not profitable due to limited options, high transit and sorting costs-only 9% of all plastic ever produced has been recycled . [1]

Beyond that, trying to clean up waste is a major challenge, as ocean cleanup efforts account for less than .5% of the plastic that ends up there annually. Any change needs to be systematic and deal with the problem of plastic at its source, as recycling from a landfill is challenging with the introduction of myriad contaminants. However, some emerging technologies seek to address the hurdles associated with recycling. This includes solutions designed to reduce dumping and improve existing recycling methods.

Better sorting methods for plastic can potentially aid with sorting recyclable from non-recyclable materials. Often, any contamination means that any recyclable materials are instead dumped in a landfill. One potential solution involves a collection system aimed to collect more low-grade “mixed plastic” (HDPE, LDPE, PE, PP etc.) that is unlikely to be recycled normally. This term covers any plastic packaging without bottles (PET), common in most households.

Sorting plastic is a scientifically challenging (and interesting) problem because most plastic materials have similar appearances but differ by chemical structure and composition. Currently, recycling centers either hire people to manually sort the waste or use a combination of hydrocyclone (to sort based on bulk density) and X-ray transmission techniques (to sort based on atomic density). [2] In addition to the manual sorting process being unpleasant for the workers with minimum pay, the traditional hydrocyclone and X-ray methods require one to build large facilities and use expensive instrumentations, reducing the incentive for plastic recycling.

To separate materials that are chemically different, density is inevitably an important property to measure. Density-based separation using magnetic levitation (Maglev) has been developed in Whitesides lab and studied by many others. [3,4] The magnetic separation process is simple, cheap, and not affected by the size of the object. W2Plastics, a Netherland-based startup, has shown the viability of magnetic density separation, where flakes of shredded plastic are mixed into a magnetic fluid (water containing iron oxide). [5]

Other technologies seek to aid in biodegradation of mixed plastics and enable them to be recycled. For instance, carbon-eating microbe strains survive off of the carbon in plastic materials and break them down . [6] Some bacteria that live on plastics can be leveraged into an enzyme that digests plastic and enable it to be reused while retaining its quality. This is an improvement over current methods, where recycled hard plastics are less valuable.

Researchers are pursuing additional methods of plastic degradation. PureCycle Technologies has developed a process to break down polypropylene, the second most used plastic in the world . [7] Their method uses a solvent that renders waste into a resin that can then be reconstituted into other plastic products. The resulting product is colorless, odorless, and aims to give new life to a type of plastic that has previously been unappealing to recycle.

Indeed, improving the quality of plastics is a major opportunity for technology companies. Even plastics that technically can be recycled are downcycled, making it less economically appealing for most companies. Researchers have pioneered a new extrusion process for polyurethane plastic that removes air upon the addition of a catalyst, enabling it to flow like a liquid . [8] The machinery required for this can be adapted and used for other purposes in the plastics industry.

Beyond recycling plastic, the process of cold plasma pyrolysis opens the door for plastics to be converted into green energy. This process yields ethylene, which can be rebuilt into other plastics, hydrogen, and methane. The latter two produce fewer harmful byproducts than other fuels and can provide the basis for cleaner energy. On top of that, the process is quick and likely to become cheaper in the future.

Limited options for recycling and a poor economic outlook necessitates the introduction of new technologies to fight plastic waste as it continues to overwhelm landfills and oceans. However, from methods that maintain plastic quality to those that aim to extend the life cycle of these materials as energy or otherwise, there are multiple emerging technologies that are poised to address this issue in the near future.

Sources:

[1] Geyer, R.; Jambeck, J. R.; Law, K. L., Production, use, and fate of all plastics ever made. Science Advances 2017, 3 (7), e1700782.

[2] Gundupalli, S. P.; Hait, S.; Thakur, A., A review on automated sorting of source-separated municipal solid waste for recycling. Waste Management 2017, 60, 56–74.

[3] Ge, S.; Nemiroski, A.; Mirica, K. A.; Mace, C. R.; Hennek, J. W.; Kumar, A. A.; Whitesides, G. M., Magnetic Levitation in Chemistry, Materials Science, and Biochemistry. Angewandte Chemie International Edition 2020, 59 (41), 17810–17855.

[4] Zhao, P.; Xie, J.; Gu, F.; Sharmin, N.; Hall, P.; Fu, J., Separation of mixed waste plastics via magnetic levitation. Waste Management 2018, 76, 46–54.

[5] https://horizon-magazine.eu/article/magnetic-attraction-recycling-plastics.html

[6] Syranidou, E.; Karkanorachaki, K.; Amorotti, F.; Avgeropoulos, A.; Kolvenbach, B.; Zhou, N.-Y.; Fava, F.; Corvini, P. F. X.; Kalogerakis, N., Biodegradation of mixture of plastic films by tailored marine consortia. Journal of Hazardous Materials 2019, 375, 33–42.

[7] https://www.nationalgeographic.com/science/2020/01/partner-content-innovations-in-recycling/

[8] Sheppard, D. T.; Jin, K.; Hamachi, L. S.; Dean, W.; Fortman, D. J.; Ellison, C. J.; Dichtel, W. R., Reprocessing Postconsumer Polyurethane Foam Using Carbamate Exchange Catalysis and Twin-Screw Extrusion. ACS Central Science 2020, 6 (6), 921–927.

Originally published at https://haihuijoyjiang.co.