by Shijie (Jenny) Deng
In modern cities like Los Angeles, convenience and efficiency seem to be people’s permanent pursuit, which opens the market for plastic products especially single-used plastics for packaging and utensils. As a matter of fact, people’s undiminished obsession with single-use plastic packaging is not hard to understand. For instance, the pre-weighed and pre-packed food and drinks in the grocery stores make the shopping process more hygienic and expeditious for the customers. Plastic food containers make it possible for restaurants to deliver food to you via DoorDash (an online food ordering company), for example. Moreover, online shopping, where you can almost get anything you want by a click of a fingertip, cannot guarantee a promptly delivered and undamaged package without tons of plastic bubble wrap. Although plastics are now such an indispensable part of our daily lives, we have reached a point where we really need to start thinking about where these substantial amounts of plastic would end up and what is their impact on our environment.
The hazards of plastic waste
Due to the tremendous consumption of plastic commodities, plastic waste accumulates exponentially in the natural environment, both on land and in the oceans. Plastics are polymers, a huge molecule made from a number of identical small molecules, which are rather stable chemically and it takes ages for mother nature to eradicate them. When plastic bags and bottles are discarded in the ocean, they gradually break down into small pellets by the wind and ocean current. These pellets can be mistakenly swallowed by marine animals, filling their stomach, and eventually preventing them from any food intake. And when plastic pellets are broken down to even smaller sizes, the result is microplastics, which are invisible and intractable. The insidious hazards of microplastics are still under study, but scientists have revealed that microplastics can absorb toxic chemicals on their surface [1}. The small size of microplastics makes them ubiquitous, which could easily make their way into the circulation system of marine animals and then diffuse into the ecosystem through the food chain.
Plastic waste treatment
To reduce the accumulation of plastic waste, there are currently various methods to decompose and recycle them. Since plastics are not degrading easily in landfills, incineration is so far the only way to exterminate plastic waste, but the stench generated during the combustion is another problem that must be taken into account. Considering the mass and exponentially increasing production of plastics, it is best to recycle them rather than simply destroy them. Although some plastic products are labeled as recyclable, the huge discrepancy between recyclable and recycled still exists. Currently, mechanical recycling is now the major way to recycle plastic waste. Recycling factories sort plastic waste before grinding them into resins, and the resins can then be modeled into plastic products. Chemical recycling is another emerging recycling method. Chemists are making every effort to develop catalysts that are capable of breaking the robust chemical backbone of plastics and degrading them into reusable feedstocks or even chemicals with higher value. Despite that chemical recycling is still at an early stage, it is a promising method to eradicate plastic waste.
However, the overall amount of plastic recycled is far from satisfactory. As of 2015, approximately 6300 Mt of plastic waste had been generated, only around 9% was recycled, and the majority 79% was accumulated in the environment or landfill [2].
Biodegradable plastics made from bio renewable feedstocks.
Environmentally friendly plastics
At present, the plastic type we use as food containers and packaging are mainly PE (polyethylene) and PP (polypropylene), which are petroleum-based. These plastics have a backbone composed of very strong chemical bonds, making the chemical decomposition arduous. Scientists are now expanding their efforts in designing plastics that can be produced from sustainable feedstocks and can degrade much more easily. Our lab led by Prof. Diaconescu at UCLA has been working on developing catalytic systems that can synthesize biodegradable plastic with tailored structures and enhanced properties for years. PLA (polylactic acid) is a prominent biodegradable plastic that has been commercialized- it uses cornstarch as a feedstock and degrades much faster than petroleum-based plastics. Nonetheless, the major drawback of PLA is its brittleness, which limits its utility and application.
We are trying to combine the brittle and biodegradable PLA with other softer materials to eventually make environmentally friendly substitutes for petroleum-based plastics. We, and other labs, are also working on expanding the feedstock scope that can be exploited in the manufacturing of biodegradable plastics. Chemicals derived from trees, fruits, and the greenhouse gas CO2 are prospective building blocks toward greener biodegradable plastics. Up till now, the durability of biodegradable plastics like PLA still needs to be reinforced to attain wider application. As for decomposition however, according to Sustainability at UCLA [4], biodegradable plastics like PLA will end up in landfill, because recycling facilities do not process these materials and they do not decompose fast enough at industrial composting facilities. This shows there is still a long journey ahead to recycle biodegradable plastic or produce value out of the waste.
By and large, it is now imperative for us to come up with a practical and scalable system to decompose or recycle our plastic waste. Meanwhile, our plastics should be upgraded to be more environmentally friendly. Most importantly, we need to resist the temptation of convenience and reduce our consumption of single-use plastic; this seems to be the best way to make our own individual contribution to protecting our environment at this time. Bornscheuer et. al [3] proposed the ‘6 R’ principles: rethink, refuse, reduce, reuse, recycle, replace. The journey of a thousand miles begins with one step. Reducing our consumption of single-use plastics is that one step we can all make.
References
1. A. L. Andrady, Marine Pollution Bulletin, 2017, 119, 12–22.
2. R. Geyer, J. R. Jambeck and K. L. Law, Sci. Adv., 2017, 3, e1700782.
3 . R. Wei, T. Tiso, J. Bertling, K. O’Connor, L. M. Blank and U. T. Bornscheuer, Nat Catal, 2020, 3, 867–871.
4. https://www.sustain.ucla.edu/zero-waste/faqs/#Q17
Shijie (Jenny) is part of the 2018-2019 INFEWS program cohort and a PhD candidate in the Department of Chemistry and Biochemistry at UCLA. Her research focuses on developing electrochemical systems using redox-switchable catalysts for the synthesis of biodegradable, block co-polymers.
This article is part of the INFEWS Social Media Series.