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It feels good to recycle. There’s a certain sense of accomplishment that comes from dutifully sorting soda bottles, plastic bags and yogurt cups from the rest of the garbage. The more plastic you put in that blue bin, the more you’re keeping out of landfills and the oceans, right?

Wrong. No matter how meticulous you are in cleaning and separating your plastics, most end up in the trash heap anyway.

Take flexible food packages. Those films contain several layers of different plastics. Because each plastic has to be recycled separately, those films are not recyclable. Grocery bags and shrink wrap are too flimsy, prone to getting tangled up with other materials on a conveyor belt. The polypropylene in yogurt cups and other items doesn’t usually get recycled either; recycling a hodgepodge of polypropylene produces a dark, smelly plastic that few manufacturers will use.

Only two kinds of plastic are commonly recycled in the United States: the kind in plastic soda bottles, polyethylene terephthalate, or PET; and the plastic found in milk jugs and detergent containers — high-density polyethylene, or HDPE. Together, those plastics make up only about a quarter of the world’s plastic trash, researchers reported in 2017 in Science Advances. And when those plastics are recycled, they aren’t good for much. Melting plastic down to recycle changes its consistency, so PET from bottles has to be mixed with brand-new plastic to make a sturdy final product. Recycling a mix of multicolored HDPE pieces creates a dark plastic good only for making products like park benches and waste bins, in which properties like color don’t matter much.

The difficulties of recycling plastic into anything manufacturers want to use is a big reason why the world is littered with so much plastic waste, says Eric Beckman, a chemical engineer at the University of Pittsburgh. In 2018 alone, the United States landfilled 27 million tons of plastic and recycled a mere 3 million, according to the U.S. Environmental Protection Agency. Low recycling rates aren’t just a problem in the United States. Of the 6.3 billion tons of plastic that have been discarded around the world, only about 9 percent has gotten recycled. Another 12 percent has been burned, and almost 80 percent has piled up on land or in waterways.

With plastic collecting everywhere from the top of Mount Everest to the bottom of the Mariana Trench, there’s an urgent need to reduce the amount of plastic that gets thrown away (SN: 1/16/21, p. 5). Some people propose replacing plastics with biodegradable materials, but those replacements are generally not as strong or cheap to make as plastics (SN: 6/22/19, p. 18). Since, realistically, plastic is not going away any time soon, chemists who understand the ins and outs of all this pesky plastic are working to make it easier to recycle and turn into higher-quality material that’s useful for more things.

“There’s not going to be a single technology that’s going to be the answer,” says Ed Daniels, senior project manager at the REMADE Institute in West Henrietta, N.Y., which funds research into new recycling techniques. Some projects are on the brink of breaking into industry; others are still just promising lab experiments. But all are focused on designing a future where any plastic that ends up in the recycling bin can have a second and third life in a new product.

Picking plastics apart

One of the biggest bottlenecks in plastic recycling is that every material has to get processed separately. “Most plastics are like oil and water,” says chemist Geoffrey Coates of Cornell University. They just don’t mix. Take, for example, a polyethylene detergent jug and its polypropylene cap. “If you melt those down, and I make a bottle out of that, and I squeeze it, it would basically crack down the side,” Coates says. “It’s crazy brittle. Totally worthless.”

That’s why the first destination for plastic recyclables is a material recovery facility, where people and machines do the sorting. Separated plastics can then be washed, shredded, melted and remolded. The system works well for simple items like soda bottles and milk jugs. But not for items like deodorant containers — where the bottle, crank and cap could all be made of different kinds of plastic. Food packaging films that contain several layers of different plastic are particularly tricky to take apart. Every year, 100 million tons of these multilayer films are produced worldwide. When thrown away, those plastics go to landfills, says chemical engineer George Huber of the University of Wisconsin–Madison.

To tackle that problem, Huber and colleagues devised a strategy for dealing with complex mixtures of plastics. The process uses a series of liquid solvents to dissolve individual plastic components off a product. The trick is choosing the right solvents to dissolve only one kind of plastic at a time, Huber says.

The team tested the technique on a packaging film that contained polyethylene and PET, as well as a plastic oxygen barrier made of ethylene vinyl alcohol, or EVOH, that keeps food fresh.

Stirring the film into a toluene solvent first dissolved the polyethylene layer. Dunking the remaining EVOH-PET film in a solvent called DMSO stripped off the EVOH. The researchers then plucked out the remaining PET film and recovered the other two plastics from their separate solvents by mixing in “antisolvent” chemicals. Those chemicals caused the plastic molecules that were dispersed in the liquids to bunch together into solid clumps that could be fished out.

This process recovered practically all of the plastic from the original film, the researchers reported last November in Science Advances. When tested on a jumble of polyethylene, PET and EVOH beads, the solvent washes recovered more than 95 percent of each material — hinting that these solvents could be used to strip plastic components off bulkier items than packaging films. So in theory, recovery facilities could use this technique to disassemble multiplastic deodorant containers and other products of various shapes and sizes.

Huber and colleagues next plan to look for solvents to dissolve more kinds of plastic, such as the polystyrene in Styrofoam. But it will take a lot more work to make this strategy efficient at sorting all the intricate plastic combinations in real-world recyclables.

Making plastics mix

There may also be chemical shortcuts that allow multilayer films and other mixtures of plastics to be recycled as they are. Additives called compatibilizers help different melted-down plastics blend, so that unsorted materials can be treated as one. But there is no universal compatibilizer that allows every kind of plastic to be mixed together. And existing compatibilizers are not widely used because they are not very potent — and adding a lot of compatibilizer to a plastic blend gets expensive.

To boost viability, Coates and colleagues created a highly potent compatibilizer for polyethylene and polypropylene. Together, those two plastics make up more than half of the world’s plastic. The new compatibilizer molecule contains two segments of polyethylene, interspersed with two segments of polypropylene. Those alternating segments latch onto plastic molecules of the same kind in a mixture, bringing polyethylene and polypropylene together. It’s as if polyethylene were made of Legos, and polypropylene were made of Duplos, and the researchers made a special building block with connectors that fit both types of blocks.

Having two polyethylene and two polypropylene connectors for each compatibilizer molecule, rather than one, made this compatibilizer stronger than previous versions, Coates and colleagues reported in 2017 in Science. The first test of the new compatibilizer involved welding together strips of polyethylene and polypropylene. Ordinarily, the two materials easily peel apart. But with a layer of compatibilizer between them, the plastic strips broke, rather than the compatibilizer seal, when pulled apart.

In a second test, the researchers mixed the compatibilizer into a melted blend of polyethylene and polypropylene. It took only 1 percent compatibilizer to create a tough new plastic.

“These are crazy potent additives,” Coates says. Other compatibilizers had to be added at concentrations up to 10 percent to hold these two plastics together. The new compatibilizer is now the basis for Coates’ start-up, Intermix Performance Materials, based in Ithaca, N.Y.

Good as new

Even if every piece of plastic trash could easily be recycled, that still wouldn’t solve the world’s plastic problem. There are a couple major issues with how recycling currently works that severely limit the usability of recycled materials.

For one thing, recycled plastics inherit all the dyes, flame retardants and other additives that gave each original plastic piece its distinctive look and feel. “The plastic that you actually recover at the end of all this is really a very complex mixture,” says chemist Susannah Scott of the University of California, Santa Barbara. Few manufacturers can use plastic with a random mishmash of properties to make something new.

Plus, recycling breaks some of the chemical bonds in plastic molecules, affecting the strength and consistency of the material. Melting down and remolding plastic is sort of like reheating pizza in the microwave — you get out basically what you put in, just not as good. That limits the number of times plastic can be recycled before it has to be landfilled.

The solution to both problems could lie in a new kind of recycling process, called chemical recycling, which promises to make pure new plastic an infinite number of times. Chemical recycling involves taking plastics apart on the molecular level.

The molecules that make up plastics are called polymers, which are made of smaller monomers. Using heat and chemicals, it is possible to disassemble polymers into monomers, separate those building blocks from dyes and other contaminants, and piece the monomers back together into good-as-new plastic.

“Chemical recycling has really started to emerge as a force, I would say, within the last three or four years,” says University of Pittsburgh’s Beckman. But most chemical recycling techniques are too expensive or energy intensive for commercial use. “It’s not ready for prime time,” he says.

Different plastics require different chemical recycling processes, and some break down more easily than others. “The one that’s farthest along is PET,” Beckman says. “That polymer happens to be easy to take apart.” Several companies are developing methods to chemically recycle PET, including the French company Carbios.

Carbios is testing enzymes produced by microorganisms to break down PET. Researchers at the company described their work on one such enzyme last April in Nature. Microbes normally use the enzyme, called leaf-branch compost cutinase, to decompose the waxy coating on plant leaves. But the cutinase is also good at breaking PET down into its monomers: ethylene glycol and terephthalic acid.

“The enzyme is like a molecular scissor,” says Alain Marty, chief scientific officer at Carbios. But because it evolved to decompose plant matter, not plastic, it’s not perfect. To make the enzyme better at snipping apart PET, “we redesigned what we call the active site of the enzyme,” Marty says. This involved swapping out some of the amino acids along that PET docking site for others.

When the researchers tested their mutant enzyme on colored plastic flakes from PET bottles, applying 3 milligrams of the enzyme per gram of PET, about 90 percent of the plastic broke down in about 10 hours. The original enzyme had maxed out at about 50 percent. Using the terephthalic acid monomers produced in that process, the researchers made new plastic bottles that were just as strong as the originals.

Carbios is now building a plant near Lyon, France, to start chemically recycling PET later this year.

Milder conditions

But other plastics, like polyethylene and polypropylene, are much harder to break down via chemical recycling. Taking apart polyethylene molecules, for instance, requires temperatures over 400° Celsius. At such high heat, the chemistry is chaotic. Plastic molecules break down randomly, generating a complex mixture of compounds that can be burned as fuel but not used to make new materials.

Scott, the UC Santa Barbara chemist, proposes partially breaking down these sturdy plastics in a more controlled way, under milder conditions, to make other kinds of useful molecules. She and colleagues recently came up with a way to transform polyethylene into alkylaromatic compounds, which can be used as biodegradable ingredients in shampoos, detergents and other products. The process involves placing polyethylene inside a reaction chamber set to 280° C, with a catalyst powder containing platinum nanoparticles.

Polyethylene is a long molecule, in which hydrogen atoms are connected to a carbon backbone that can be thousands of carbon atoms long. The platinum is good at breaking carbon-hydrogen bonds, Scott says. “When you do that, you generate hydrogen in the reactor, and the platinum catalyst can use the hydrogen to break the carbon-carbon bonds [in the molecule backbone]. So it actually chops the chain into smaller pieces.”

Since this reaction takes place at a relatively mild 280° C, it happens in an orderly fashion, snapping long polyethylene molecules into shorter chains that are each about 30 carbons long. Those fragments then arrange themselves into the six-sided ring structures characteristic of alkylaromatic compounds.

After 24 hours in the reaction chamber, “most of the products are liquids, and most of the liquids are alkylaromatics,” Scott says. In experiments, about 69 percent of the plastic in a low-density polyethylene bag was converted into liquid. About 55 percent of a high-density polyethylene bottle cap was transformed. The process produces hydrocarbon gases too, which could be used to generate heat to run the reaction at a recycling plant, Scott says.

For now, this is just a lab demo, and like many new recycling strategies, it’s still a long way off from commercialization. And no single upgrade to the recycling pipeline will rid the world of its growing mountains of plastic trash. “We’re going to need a suite of technologies to meet this challenge,” says Daniels, of the REMADE Institute. But each new technology — whether it’s focused on making plastics easier to recycle, or transforming them into more useful materials — could help.

Africa’s electricity capacity is expected to double by 2030 — and with the rapidly dropping cost of renewable energy technologies, the continent might seem poised to go green. But a new analysis suggests that fossil fuels will still dominate Africa’s energy mix over the next decade.

The scientists used a machine learning approach that analyzes what characteristics, such as fuel type and financing, controlled the past successes and failures of power plants across the continent. Their findings suggest that renewable energy sources such as wind and solar power will make up less than 10 percent of Africa’s total electrical power generation by 2030, the team reports January 11 in Nature Energy.

In 2015, 195 nations pledged to reduce their fossil fuel emissions to limit global warming to “well below” 2 degrees Celsius by 2100. To achieve that goal, the world would have to reduce its emissions by 2.7 percent each year from 2020 to 2030 — but current pledges are nowhere near enough to achieve that target (SN: 11/26/19). And the energy demand from developing economies, including many on the African continent, is expected to increase dramatically by 2030 — possibly leading to even more fossil fuel emissions over the next decades.

However, the price of renewable energy technologies, particularly wind and solar energy, has rapidly dropped over the last few years. So many scientists and activists have said they hope that African countries might be able to take advantage of these technologies, leapfrogging past carbon-intensive coal or oil-based energy growth and straight into building renewable energy plants.

Whether that’s a realistic scenario hasn’t been clear, says Galina Alova, a sustainability scientist at the University of Oxford. There is a lot of uncertainty about how and why new and planned energy projects might succeed or fail on the continent, she says. “We wanted to understand whether Africa is actually heading in the direction of making that decisive leap, but we wanted to do it looking at the data.”

So Alova, along with Oxford sustainability scientists Philipp Trotter and Alex Money, amassed data on nearly 3,000 energy projects — both fossil-fuel based and renewable — that were commissioned over the last 20 years across Africa’s 54 countries. Those projects included both successful and failed energy plants. The data include a variety of characteristics for the different plants, such as how much energy a particular plant can produce, what type of fuel it uses, how well it’s connected to an energy grid, who owns the plant and how it’s financed.

Then, the team used a machine learning approach creating a computer algorithm to identify which of these characteristics were the best predictors of success in the past. Finally, the scientists analyzed the chances for success of almost 2,500 projects now in the pipeline, based on those features as well as on different country characteristics, such as the strength of the economy, population density and political stability.

Those country-level factors do matter, but they weren’t the biggest predictors of a project’s success, Trotter says. “We do see some truth to good governance, but project-level [factors have] been consistently more important.”

Those factors include the power plants’ size and whether the plants had public or private financing, for example. Smaller renewable energy plants tended to have a better chance of success than larger projects, as did plants with financing from large public funders, such as the World Bank, which are less likely to pull out in the face of delays or roadblocks. As for fuel type, there has been a recent uptick in the chances for success for solar energy in particular, the team found — but overall, oil and gas projects still have a much greater chance to succeed.

What this adds up to, the team found, is that by 2030, fossil fuels will still account for two-thirds of all energy generation on the continent. Renewable energy, particularly wind and solar, will account for less than 10 percent, with the remainder, about 18 percent of the power mix, coming primarily from hydro-electric power.

The findings were “both quite surprising and unsurprising to me,” says Wikus Kruger, a researcher in the African power sector at the University of Cape Town in South Africa who was not involved in the new study. The finding that project-level factors, particularly financing, are very significant tracks with research he and others have done, he says. But, he says, he is less convinced that the decreasing cost of renewables won’t be a bigger factor.

“We are seeing this massive disruption [to the energy market], in terms of costs of renewables. It’s just completely changed the way that planning is done. What’s exciting about this disruptive moment is that these smaller renewable energy projects are in conflict states that have historically struggled to get anything done,” Kruger says. “But these are smaller, more modular projects, and people are willing to put smaller amounts [of money] into projects that spread the risks out across a wide variety of countries.”

One other factor that could change the renewable energy outlook, Alova says, is if many of the fossil fuel plants now in the pipeline were to be canceled, what the team calls a “rapid decarbonization shock.” But that wouldn’t occur just due to a drop in the cost of renewable energy technologies alone.

Increasing the share of renewable energy in Africa’s electricity mix “will not happen automatically by some invisible hand,” Trotter says. “It’s something that has to happen from the top, from African governments and the international development community.” The danger, he says, is that once a fossil fuel power plant enters production, it will stay in operation for 20 or 30 years, “so it’s really important not to be locked into these. What is clear from our dataset is that we have to act now [to cancel those fossil fuel plants]; this is not something we can postpone any longer.”

Lying low

During Africa’s dry season, when mosquitoes are scarce, malaria parasites in human blood turn their genes on and off to keep numbers low so infection doesn’t set off alarm bells for the immune system, Erin Garcia de Jesus reported in “How malaria parasites hide from the human immune system” (SN: 11/21/20, p. 8).

“How on Earth does the malaria parasite know it is the dry season from within the moist human body?” reader Elizabeth McDowell asked. “The human body must maintain moisture levels year-round.… What signals the parasite to alter gene activity?”

The mechanism remains unclear, Garcia de Jesus says, “but the researchers are searching for answers.” One hypothesis is that mosquito bites play a role. “Perhaps some protein in mosquito saliva tells the parasites, ‘Hello, I’m here to take you to your next victim,’ and the parasites adjust gene activity to ramp up their numbers,” she says.

E.T. phone home?

New methods are ramping up the search for alien intelligence, Maria Temming reported in “New search methods are ramping up the hunt for alien intelligence” (SN: 11/21/20, p. 18).

Many readers were intrigued. The story “challenged my memory on the search for messages from aliens with [Temming’s] statement: ‘So far, SETI scientists haven’t picked up a single alien signal,’ ” reader David Cosson wrote. “My recollection was that NASA launched the two Voyager spacecraft in 1977 each carrying a golden record that included 90 minutes of world music, including Bach, Mozart and Chuck Berry’s ‘Johnny B. Goode.’ I thought I recalled a press report … that NASA had received a reply from aliens who had played the record. The message was: ‘Send more Chuck Berry.’ Perhaps my memory is faulty, but I recall the reporter as somebody named Steve Martin,” Cosson joked.

Reader Bob Johnson remains puzzled by some researchers’ efforts to detect radio frequency signals. “It is highly unlikely other civilizations are, like us, going through the first 100 years of communication evolution,” Johnson wrote. “We should be hunting for signals in the ultraviolet, X-ray and gamma-ray frequencies. Even though older technologies work, they are displaced by new methods. Looking for [radio frequency] signals from E.T. is analogous to listening for … modem tones as an indication of intelligent life.”

Watery skies

Water high up in Mars’ atmosphere splits apart within a few hours, leaving hydrogen atoms to float away, Lisa Grossman reported in “Chemical reactions high in Mars’ atmosphere rip apart water molecules” (SN: 12/5/20, p. 14).

Reader Lorenza Zamarron wondered what happens to oxygen. “Where does the oxygen go? If the oxygen is heavier, does it fall back down to Mars? Is it destroyed?”

At least some oxygen breaks free of Mars’ gravity in a process called photochemical escape, says Shane Stone, a planetary chemist at the University of Arizona in Tucson. “Additionally, some oxygen would inevitably be transported down toward and around the planet,” Stone says. “Many scientists believed that atmospheric chemistry would, over very long time periods, balance the escape of hydrogen and oxygen to match the 2:1 ratio that these elements are found in water. However, some of us are rethinking this concept in light of this discovery of water transport directly to the upper atmosphere,” Stone says. That oxygen is slow to escape could partly explain why the Red Planet is red. “Oxygen in the atmosphere reacts with minerals on the surface to produce iron oxide (rust), which is responsible for the reddish-orange color that is so indelibly Martian,” Stone says. “In other words, Mars is oxidized.”

Correction

In “Meet 5 Black researchers fighting for diversity and equity in science” (SN: 12/19/20 & 1/2/21, p. 26), the name of a BlackAFinSTEM group member was incomplete. Her name is Anna Gifty Opoku-Agyeman.

Stay tuned

In 1970, researchers thought Earth’s magnetic pole reversals might be to blame for long-ago extinctions of single-celled organisms called Radiolaria (10 living species shown below). But no strong evidence of a direct link has turned up, Jonathan Lambert reported (SN: 11/21/20, p. 4) in an update to the article “Effects of Earth’s magnetic field” (SN: 11/21/70, p. 392). Reader Doug Pruner joked: “Radiolarian extinctions? Of course. The reversals caused interference with their radios.”

A distant galaxy has been caught in the act of shutting down.

The galaxy, called CQ 4479, is still forming plenty of new stars. But it also has an actively feeding supermassive black hole at its center that will bring star formation to a halt within a few hundred million years, astronomers reported January 11 at the virtual meeting of the American Astronomical Society. Studying this galaxy and others like it will help astronomers figure out exactly how such shutdowns happen.

“How galaxies precisely die is an open question,” says astrophysicist Allison Kirkpatrick of the University of Kansas in Lawrence. “This could give us a lot of insight into that process.”

Astronomers think galaxies typically start out making new stars with a passion. The stars form from pockets of cold gas that contract under their own gravity and ignite thermonuclear fusion in their centers. But at some point, something disrupts the cold star-forming fuel and sends it toward the supermassive black hole at the galaxy’s core. That black hole gobbles the gas, heating it white-hot. An actively feeding black hole can be seen from billions of light-years away and is known as a quasar. Radiation from the hot gas pumps extra energy into the rest of the galaxy, blowing away or heating up the remaining gas until the star-forming factory closes for good (SN: 3/5/14).

That picture fits with the types of galaxies astronomers typically see in the universe: “blue and new” star formers, and “red and dead” dormant galaxies. But while examining data from large surveys of the sky, Kirkpatrick and colleagues noticed another type. The team found about two dozen galaxies that emit energetic X-rays characteristic of an actively gobbling black hole, but also shine in low-energy infrared light, revealing that there is still cold gas somewhere in the galaxies. Kirkpatrick and colleagues dubbed these galaxies “cold quasars” in a paper in the Sept. 1 Astrophysical Journal.

“When you see a black hole actively accreting material, you expect that star formation has already shut down,” says coauthor and astrophysicist Kevin Cooke, also of the University of Kansas, who presented the research at the meeting. “But cold quasars are in a weird time when the black hole in the center has just begun to feed.”

To investigate individual cold quasars in more detail, Kirkpatrick and Cooke used SOFIA, an airplane outfitted with a telescope that can see in a range of infrared wavelengths that the original cold quasar observations didn’t cover. SOFIA looked at CQ 4479, a cold quasar about 5.25 billion light-years away, in September 2019.

The observations showed that CQ 4479 has about 20 billion times the mass of the sun in stars, and it’s adding about 95 suns per year. (That’s a furious rate compared with the Milky Way; our home galaxy builds two or three solar masses of new stars per year.) CQ 4479’s central black hole is 24 million times as massive as the sun, and it’s growing at about 0.3 solar masses per year. In terms of percentage of their total mass, the stars and the black hole are growing at the same rate, Kirkpatrick says.

That sort of “lockstep evolution” runs counter to theories of how galaxies wax and wane. “You should have all your stars finish growing first, and then your black hole grows,” Kirkpatrick says. “This [galaxy] shows there’s a period that they actually do grow together.”

Cooke and colleagues estimated that in half a billion years, the galaxy will host 100 billion solar masses of stars, but its black hole will be passive and quiet. All the cold star-forming gas will have heated up or blown away.

The observations of CQ 4479 support the broad ideas of how galaxies die, says astronomer Alexandra Pope of the University of Massachusetts Amherst, who was not involved in the new work. Given that galaxies eventually switch off their star formation, it makes sense that there should be a period of transition. The findings are a “confirmation of this important phase in the evolution of galaxies,” she says. Taking a closer look at more cold quasars will help astronomers figure out just how quickly galaxies die.