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The Breakdown of Plastic Waste In The Ocean Studied
April 24, 2020

Creating plastic containers that easily degrade in sea water would be a dream solution to the growing problem of plastic waste in the ocean, but a team of Penn State New Kensington researchers suggest that, at least for now, recycling and finding plastic alternatives may still the best way of handling this waste.

According to information, in a study, the researchers used a machine learning algorithm to classify more than 110 types of plastics, including commercial and lab-made varieties, to better understand how they might degrade in the ocean, said Robert Mathers, professor of chemistry.

“One of the things we were interested in finding out is what is going to happen to the large quantity of plastic that is in the ocean,” said Prof. Mathers. “This study took a wide range of physical property data, in combination with a metric that would quantify the composition of molecular structures and used that to try to figure out the most important aspects of plastic degradation in the ocean.”

According to the Ocean Conservancy, there are more than 150 million metric tons of plastic in the ocean, with 8 million metric tons more entering the ocean each year. The researchers, who released their findings in a recent issue of Nature Communications, said a number of factors in the ocean can help break down this plastic, including ultraviolet radiation from the sun, wind, waves, seawater, water temperature and bacteria. They found that certain types of plastics did break down quicker than others when subjected to these conditions.

While knowing the molecular structure of the more susceptible plastics could give engineers a chance to develop plastics with less environmental impact, Prof. Mathers said that economics of producing those plastics at scale would still be an issue.

“Others have suggested the possibility of putting a weak link in the molecular structure of a plastic that could accelerate the degradation of that strand of atoms,” said Prof. Mathers. “Now, that is a great idea, but, right now, it may not be an economically feasible option. It’s just hard to economically compete with polyethylene and polypropylene, which are the most-used plastics in the world. So, we probably want to keep focusing on recycling because that offers the most immediate help.”

The team approached the problem of plastic in the ocean by gathering as much data on the molecular structure of the various plastics and information on how these plastics behave in sea water, both in the field and in laboratory conditions.

“From the literature, we were able to get information about the physical properties of the plastic that are in the ocean, for instance, molecular weights, the glass transition temperature, the amount of crystallinity, but considering the molecular composition was an overlooked opportunity. In this regard, we figured out how to translate molecular structure into a metric that we called hydrophobicity, which is how much is the material likely to absorb water or want to be in contact with water,” said Prof. Mathers.

After experimenting with a few different models of machine learning, the researchers opted for a decision tree, machine learning approach. Members of the Institute for Computational and Data Sciences and Materials Research Institute helped the team by providing access to machine learning tools.

According to Prof. Mathers, the study also showed how data science and materials science can contribute to solving issues that may have once been considered outside of their fields.

“I had been interested in sustainability, sustainable materials and this idea of green chemistry for a long time,” said Prof. Mathers. “And when we looked at the studies in the current literature, we found there were a lot of people investigating plastics in the ocean and most of these researchers were oceanographers, marine biologists, ecologists, and marine biologists. They were doing real interesting work, but from a materials standpoint, no systematic studies were available.”

He added that more work needs to be done to investigate plastics in the ocean, including adding more data.

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