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Pollution

Recycling needs a revamp

Chemical and biochemical approaches take aim at plastic pollution

by Sam Lemonick
June 15, 2018 | APPEARED IN VOLUME 96, ISSUE 25

Credit: Jesse Lenz

 

What could be easier than recycling? Almost everywhere you go these days, there’s a convenient bin for your empty water bottle.

Yet plastic trash continues to accumulate in the environment. A 2015 study in Science estimated that the oceans may hold 155 million metric tons of plastic by 2025, double the current amount (DOI: 10.1126/science.1260352). Turns out those convenient recycling bins aren’t always being used. Americans are doing better than ever but still submit only about one-third of their plastic waste for recycling.

An even more fundamental problem with plastics becomes apparent if you look past the recycling bin. Only about 10% of plastic packaging worldwide—as well as in the U.S.—ends up getting remade into a new product, according to a 2016 World Economic Forum report. Another 14% from around the globe is burned, sometimes to generate energy. And the rest ends up in a landfill or the environment.

And it stays there, preserved. Plastic’s durability is one reason it has become so widely used. When it becomes trash, however, that durability is a curse. Most plastics are made from fossil-fuel-derived polymers, made of molecular chains that can reach thousands of covalently bonded repeating units.

Of the plastic that does get recycled and reborn, a majority of it ends up in a lower-quality product because the most widespread, popular recycling technology involves mechanically shredding, melting, and re-forming plastics. “Polymers tend to degrade at high temperature,” says Megan Robertson, a chemical engineer at the University of Houston. “So we’re essentially downgrading the material as it’s recycled.” A mere 2% of the plastic that starts out in a drinking water bottle will be recycled into a new plastic bottle. The rest of the plastic that gets recycled typically ends up as carpet fibers or outdoor furniture.

Other factors are exacerbating the plastic pollution problem, particularly in the U.S. China, which has for decades collected and processed recyclable waste from around the world, announced in 2017 that it would limit imports of foreign trash. Now some U.S. waste management facilities have to send recyclable plastic straight to the landfill because there’s not enough domestic recycling capacity. Reflecting a growing awareness of the plastic trash problem, in May the American Chemistry Council announced its goal that by 2040 all plastic packaging used in the U.S. will be recycled or made into other products.

09625-cover1-loop.jpg
Broken cycle
Eighty-six percent of plastic packaging produced globally is never collected for recycling, according to a 2016 World Economic Forum report. Another 4% is lost during the recycling process, 8% is recycled into lower-quality products like carpet fiber or plastic lumber, and just 2% is recycled into equivalent products.
Sources: World Economic Forum; Ellen MacArthur Foundation
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As the mountains of discarded plastic continue to grow, science has begun to offer some solutions. Chemists, including Robertson, are working on new chemical methods to break down current plastics to their building blocks for reuse, and they’re designing new plastics that could be easier to recycle. Researchers are also working slowly toward biocatalyzed plastics recycling, using microbes or enzymes to degrade polymers. In the excitement about Mother Nature playing a possible role in solving the plastics problem, however, some news reports about plastic-munching critters have oversold progress.

Read the other stories in this package (here and here) for a few visions of what the future of plastics recycling might—or might not—look like.

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Comments
Leiming Li (June 18, 2018 9:17 AM)
Recycling is the process of converting and reusing used and waste materials. In addition to our daily recycling of used plastic, paper, glass, etc., industrial recycling is also worth mentioning. A good example is the vehicle dismantling industry that recycles old cars. In the petroleum industry, the so-called “produced water”, or the underground salty water produced with oil and gas, is one of the major waste streams, estimated to be about 21 billion barrels per year in the United States alone. Technologies exist that can use produced water in the fracking operations (see, for example, “A Review of Crosslinked Fracturing Fluids Prepared with Produced Water”, Petroleum 2(4), 313-323, 2016), saving a lot of valuable fresh water to therefore become another good example of recycling.
James Castro (June 18, 2018 1:18 PM)
"Plastics," as we chemists all know, is a loose term that covers a multitude of different substances. However, they can be broken down into two general classes: those that consist of carbon and hydrogen with or without oxygen, and those containing halogens, nitrogen, or other elements. The former may be burned to produce heat and/or electricity while producing little or no pollution; the latter cannot.
Most of the polyethylene, polypropylene, polyester, and other CHO plastics are made originally from petroleum. Following their use as containers, wrapping film, etc., why shouldn't they be burned to produce usable energy? Such use would displace an equivalent amount of oil or natural gas and would yield no net increase in carbon usage. It should be possible to design and build burners and boilers to take these materials while producing little or no air pollution.
Consider the fact that most of the plastic in the oceans comes from a handful of Southeast Asian countries, and that most of those countries are short on energy sources. Instead of dumping their plastic refuse on the shores, they could be obtaining useful energy from it and helping their balances of payments by importing less petroleum and coal.
Plastics like vinyls, acrylics, and nylons would still need to be recycled or landfilled, but they would account for a much smaller volume of plastics.
MICHAEL MCHENRY (June 19, 2018 11:56 AM)
The recycling consumer packaging plastics is energy intense and dirty environmentally. This is well known to people in the industry. The better end use for consumer plastics is burning them for energy. It is after all petroleum derived. The plastics used in food packaging is devoid of hazardous additives. It would be simple matter to restrict additives in other package types eg motor oil
Drew Speer (June 20, 2018 10:10 AM)
I think it is important to recognize the value of plastics. We don't have a "plastics" problem we have a human behavior problem. A material can be perfectly recyclable and that won't do a bit of good if someone chooses to litter.
Mary Tuttle (June 20, 2018 8:11 PM)
Thank you C&EN for reminding us that chemistry can be part of the solution to a problem of this magnitude, rather than just be blamed for it by the popular lay media.

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