Hartshorn salt and 'baking' solves a serious environmental problem

Polyester is the second most used textile in the world and an environmental menace, especially because most of it never gets recycled. The fabric, a blend of plastic and cotton, has been difficult for the industry to separate and therefore recycle. Now, a group of young chemists from the University of Copenhagen has invented a green and surprisingly simple solution using a single household ingredient.

From clothes to sofas to curtains, polyester dominates our everyday lives, with a staggering 60 million tons of this popular fabric produced annually. However, polyester production takes a toll on the climate and the environment, as only a mere 15% of it is recycled, while the rest ends up in landfills or incinerated, being responsible of more carbon emission.

Recycling polyester poses a significant challenge, particularly in separating the plastic and cotton fibers that the blend fabric is made of without losing either of them in the process. Conventional recycling methods often prioritize preserving the plastic component, resulting in a loss of cotton fibers. Moreover, these methods are costly, complex, and generate metal waste due to the use of metal catalysts, which can be cytotoxic and contaminate the process.

In a remarkable breakthrough, a group of young chemists has unveiled a surprisingly simple solution to this pressing problem, potentially revolutionizing the sustainability of the textile industry.

"The textile industry urgently requires a better solution to handle blended fabrics like polyester/cotton. Currently, there are very few practical methods capable of recycling both cotton and plastic -- it's typically an either-or scenario. However, with our newly discovered technique, we can depolymerize polyester into its monomers while simultaneously recovering cotton on a scale of hundreds of grams, using an incredibly straightforward and environmentally friendly approach. This traceless catalytic methodology could be the game-changer," explains postdoc Yang Yang of the Jiwoong Lee group at the University of Copenhagen's Department of Chemistry, who serves as the lead author of the scientific research article.

Hartshorn salt and 24 hours in the 'oven'

The new method requires no special equipment -- just heat, a non-toxic solvent, and an ordinary household ingredient.

"For example, we can take a polyester dress, cut it up into small pieces and place it in a container. Then, add a bit of mild solvent, and thereafter hartshorn salt, which many people know as a leavening agent in baked goods. We then heat it all up to 160 degrees Celsius and leave it for 24 hours. The result is a liquid in which the plastic and cotton fibers settle into distinct layers. It's a simple and cost-effective process," explains Shriaya Sharma, a doctoral student of the Jiwoong Lee group at the Department of Chemistry and study co-author.

In the process, the hartshorn salt, also called ammonium bicarbonate, is broken down into ammonia, CO2 and water. The combination of ammonia and CO2 acts as a catalyst, triggering a selective depolymerization reaction that breaks down the polyester while preserving the cotton fibers. Although ammonia is toxic in isolation, when combined with CO2, it becomes both environmentally friendly and safe for use. Due to the mild nature of the chemicals involved, the cotton fibers remain intact and in excellent condition.

Previously, the same research group demonstrated that CO2 could serve as a catalyst for breaking down nylon, among other things, without leaving any trace. This discovery inspired them to explore the use of hartshorn salt. Nevertheless, the researchers were pleasantly surprised when their simple recipe yielded successful results.

"At first, we were excited to see it work so well on the PET bottles alone. Then, when we discovered that it worked on polyester fabric as well, we were just ecstatic. It was indescribable. That it was so simple to perform was nearly too good to be true," says Carlo Di Bernardo, doctoral student and study co-author.

While the method has only been tested at the laboratory level thus far, the researchers point to its scalability and are now in contact with companies to test the method on an industrial scale.

"We're hoping to commercialize this technology that harbors such great potential. Keeping this knowledge behind the walls of the university would be a huge waste," concludes Yang Yang.

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Team recycles previously unrecyclable plastic

PVC, or polyvinyl chloride, is one of the most produced plastics in the United States and the third highest by volume in the world.

PVC makes up a vast amount of plastics we use on a daily basis. Much of the plastic used in hospital equipment -- tubing, blood bags, masks and more -- is PVC, as is most of the piping used in modern plumbing. Window frames, housing trim, siding and flooring are made of, or include, PVC. It coats electrical wiring and comprises materials such as shower curtains, tents, tarps and clothing.

It also has a zero percent recycling rate in the United States.

Now, University of Michigan researchers, led by study first author Danielle Fagnani and principal investigator Anne McNeil, have discovered a way to chemically recycle PVC into usable material. The most fortuitous part of the study? The researchers found a way to use the phthalates in the plasticizers -- one of PVC's most noxious components -- as the mediator for the chemical reaction. Their results are published in the journal Nature Chemistry.

"PVC is the kind of plastic that no one wants to deal with because it has its own unique set of problems," said Fagnani, who completed the work as a postdoctoral researcher in the U-M Department of Chemistry. "PVC usually contains a lot of plasticizers, which contaminate everything in the recycling stream and are usually very toxic. It also releases hydrochloric acid really rapidly with some heat."

Plastic is typically recycled by melting it down and reforming it into the lower quality materials in a process called mechanical recycling. But when heat is applied to PVC, one of its primary components, called plasticizers, leach out of the material very easily, McNeil says.

They then can slip into other plastics in the recycling stream. Additionally, hydrochloric acid releases easily out of PVC with heat. It could corrode the recycling equipment and cause chemical burns to skin and eyes -- not ideal for workers in a recycling plant.

What's more, phthalates -- a common plasticizer -- are highly toxic endocrine disruptors, which means they can interfere with the thyroid hormone, growth hormones and hormones involved with reproduction in mammals, including humans.

So, to find a way to recycle PVC that does not require heat, Fagnani began exploring electrochemistry. Along the way, she and the team discovered that the plasticizer that presents one of the major recycling difficulties could be used in the method to break down PVC. In fact, the plasticizer improves the efficiency of the method, and the electrochemical method resolves the issue with hydrochloric acid.

"What we found is that it still releases hydrochloric acid, but at a much slower, more controlled rate," Fagnani said.

PVC is a polymer with a hydrocarbon backbone, Fagnani says, composed of single carbon-carbon bonds. Attached to every other carbon group is a chlorine group. Under heat activation, hydrochloric acid rapidly pops off, resulting in a carbon-carbon double bond along the polymer's backbone.

But the research team instead uses electrochemistry to introduce an electron into the system, which causes the system to have a negative charge. This breaks the carbon-chloride bond and results in a negatively charged chloride ion. Because the researchers are using electrochemistry, they can meter the rate at which electrons are introduced into the system -- which controls how quickly hydrochloric acid is produced.

The acid can then be used by industries as a reagent for other chemical reactions. The chloride ions can also be used to chlorinate small molecules called arenes. These arenes can be used in pharmaceutical and agricultural components. There is material left from the polymer, for which McNeil says the group is still looking for a use. Fagnani says the study shows how scientists might think about chemically recycling other difficult materials.

"Let's be strategic with the additives that are in plastics formulations. Let's think about the during-use and end-of-use from the perspective of the additives," said Fagnani, who is now a research scientist at Ashland, a company focused on making biodegradable specialty additives to consumer goods such as laundry detergents, sunscreens and shampoos. "Current group members are trying to improve the efficiency of this process even more."

The focus of McNeil's lab has been to develop ways to chemically recycle different kinds of plastics. Breaking plastics into their constituent parts could produce non-degraded materials that industry can incorporate back into production.

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Collectors in the prehistoric world recycled old stone tools to preserve the memory of their ancestors

A first-of-its-kind study at Tel Aviv University asks what drove prehistoric humans to collect and recycle flint tools that had been made, used, and discarded by their predecessors. After examining flint tools from one layer at the 500,000-year-old prehistoric site of Revadim in the south of Israel's Coastal Plain, the researchers propose a novel explanation: prehistoric humans, just like us, were collectors by nature and culture. The study suggests that they had an emotional urge to collect old human-made artefacts, mostly as a means for preserving the memory of their ancestors and maintaining their connectedness with place and time.

The study was led by PhD student Bar Efrati and Prof. Ran Barkai of the Jacob M. Alkow Department of Archaeology and Ancient Near Eastern Cultures at TAU's Entin Faculty of Humanities, in collaboration with Dr. Flavia Venditti from the University of Tubingen in Germany and Prof. Stella Nunziante Cesaro from the Sapienza University of Rome, Italy. The paper appeared in the journal Scientific Reports, published by Nature.

Bar Efrati explains that stone tools with two lifecycles have been found at prehistoric sites all over the world, but the phenomenon has never been thoroughly investigated. In the current study the researchers focused on a specific layer at Revadim -- a large, open-air, multi-layered site in the south of Israel's Coastal Plain, dated to about 500,000 years ago. The rich findings at Revadim suggest that this was a popular spot in the prehistoric landscape, revisited over and over again by early humans drawn by an abundance of wildlife, including elephants. Moreover, the area is rich with good-quality flint, and most tools found at Revadim were in fact made of fresh flint.

Bar Efrati: "The big question is: Why did they do it? Why did prehistoric humans collect and recycle actual tools originally produced, used, and discarded by their predecessors, many years earlier? Scarcity of raw materials was clearly not the reason at Revadim, where good-quality flint is easy to come by. Nor was the motivation merely functional, since the recycled tools were neither unusual in form nor uniquely suitable for any specific use."

The key to identifying the recycled tools and understanding their history is the patina -- a chemical coating which forms on flint when it is exposed to the elements for a long period of time. Thus, a discarded flint tool that lay on the ground for decades or centuries accumulated an easily identifiable layer of patina, which is different in both color and texture from the scars of a second cycle of processing that exposed the original color and texture of flint.

In the current study, 49 flint tools with two lifecycles were examined. Produced and used in their first lifecycle, these tools were abandoned, and years later, after accumulating a layer of patina, they were collected, reworked, and used again. The individuals who recycled each tool removed the patina, exposing fresh flint, and shaped a new active edge. Both edges, the old and the new, were examined by the researchers under two kinds of microscopes, and via various chemical analyses, in search of use-wear marks and/or organic residues. In the case of 28 tools, use-wear marks were found on the old and/or new edges, and in 13 tools, organic residues were detected, evidence of contact with animal bones or fat.

Surprisingly, the tools had been used for very different purposes in their two lifecycles -- the older edges primarily for cutting, and the newer edges for scraping (processing soft materials like leather and bone). Another baffling discovery: in their second lifecycle the tools were reshaped in a very specific and minimal manner, preserving the original form of the tool, including its patina, and only slightly modifying the active edge.

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Paper recycling must be powered by renewables to save climate

 Recycling paper may only be helpful to the climate if it is powered by renewable energy, according to a new modelling study by researchers at UCL and Yale.

The study, published in Nature Sustainability, found that greenhouse gas emissions would increase by 2050 if we recycled more paper, as current methods rely on fossil fuels and electricity from the grid.

The researchers modelled various scenarios for increasing recycling of wastepaper by 2050 and the impact this would have on greenhouse emissions. They found that if all wastepaper was recycled, emissions could increase by 10%, as recycling paper tends to rely more on fossil fuels than making new paper.

However, the researchers found that emissions would radically reduce if paper production and disposal were carried out using renewable energy sources rather than fossil fuels.

Making new paper from trees requires more energy than paper recycling, but the energy for this process is generated from black liquor -- the low-carbon by-product of the wood pulping process. In contrast, paper recycling relies on fuels and electricity from the grid.

Researchers found that modernising landfill practices, for instance by capturing methane emissions and using them for energy, also had a positive effect -- although not as profound as moving to renewables.

Lead author Dr Stijn van Ewijk (UCL Institute for Sustainable Resources and Yale Center for Industrial Ecology) said: "Our study shows that recycling is not a guaranteed way to address climate change. Recycling of paper may not be helpful unless it is powered by renewable energy.

"We looked at global averages, but trends may vary considerably in different parts of the world. Our message isn't to stop recycling, but to point out the risk of investing in recycling at the expense of decarbonising the energy supply and seeing very little change to emissions as a result."

Senior author Professor Paul Ekins (UCL Institute for Sustainable Resources) said: "The recycling of some materials, for instance metals, can lead to a very large reduction in emissions. But we need to be careful about assumptions that recycling, or a circular economy in general, will always have a positive effect on climate change."

The researchers emphasized that recycling has benefits beyond combatting global warming. Co-author Professor Julia Stegemann (UCL Civil, Environmental & Geomatic Engineering) said: "Our exponentially increasing consumption of global resources has many seriously damaging environmental impacts beyond climate change, and conserving resources, including by paper recycling, remains critical for sustainability."

The researchers reported that paper accounted for 1.3% of global greenhouse gas emissions in 2012. About a third of these emissions came from the disposal of paper in landfills. Researchers said that in coming years, use of paper would likely rise, with the move away from plastics leading to increased demand for paper packaging.

The study looked at how different levels of recycling, renewable energy use and more environmentally friendly landfill practices might affect our ability to reduce emissions in line with a target to avoid a 2-degrees Celsius temperature rise by 2050.

It found that if past trends continued, emissions would slightly increase from the 2012 level (721 metric tonnes of carbon dioxide equivalent in a year) to 736 metric tonnes in 2050, with efforts to reduce emissions outweighed by increased demand for paper.

A radical programme of recycling, with landfill and energy uses remaining on the same path, would increase this still further by 10% (to 808 metric tonnes), with savings due to a decrease in total energy use outweighed by an increase in the use of high-carbon electricity.

On the other hand, radically modernising landfill practices would reduce emissions to 591 metric tonnes, while moving to renewables, with recycling and landfill practices remaining on the standard path, would reduce emissions by 96% to 28 tonnes.

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Get over it? When it comes to recycled water, consumers won't

If people are educated on recycled water, they may come to agree it's perfectly safe and tastes as good -- or better -- than their drinking water. They may even agree it's an answer to the critical water imbalance in California, where the northern third of the state holds 75% of the water despite 80% of the demand coming from the southern two-thirds.

But that doesn't mean they're going to use recycled water -- and it sure doesn't mean they'll drink it. And the reason lies in the word "disgust."

That's the result of a series of studies by UC Riverside psychology researchers Mary Gauvain and Daniel Harmon published recently in the journal Basic and Applied Social Psychology.

Past research by Harmon and Gauvain explored whether people sense a difference in taste among recycled water, conventional tap water, and commercially bottled water. That study, released in spring 2018, was based on a blind taste test and found people actually preferred the taste of recycled water over conventional tap water.

However, "The idea of recycled wastewater in general evokes disgust reactions," Harmon said at the time.

This idea was addressed in the psychologists' latest research. If people disgusted by the notion of recycled wastewater are educated on its safety and benefits, will their attitudes change? And, will they change their behaviors?

In the research paper, "disgust" is defined as "a strong repulsion to a potentially harmful substance." In addition to disgust, the research considered other factors that dissuade people from using recycled water. Those included misinformation, ignorance, and peoples' desire to conform to social norms.

The research involved three separate studies and a total of 886 participants.

In study one, half of the subjects viewed a brief, pro-conservation internet video. The other group watched a short video about water, but not conservation, about the urban myth that crocodiles live in the sewer system of New York City.

Researchers found both groups failed to budge in their willingness to endorse sustainable water. Ninety-six percent of participants cited disgust as the reason. Distilling the reasoning even more, the researchers asked if participants were motivated by cleanliness or fear of illness. Sixty-five percent said cleanliness.

In study two, the videos were used again. But this time, an educational video demonstrating recycled wastewater is contaminant-free was also shown to address the disgust reaction. The pro-conservation and disgust videos had a "small but unsubstantial effect on peoples' willingness to use recycled wastewater" the research found.

In the last study, participants viewed all three videos. But this time, after completing a post-video survey, they were offered a bottle of water labeled "SMARTdrop -- Pure Recycled Water" and asked to sign a conservation petition.

Researchers hypothesized participants who watched the video addressing disgust would be more likely to accept the water and sign the petition. In fact, a similar number across all three groups -- about two-thirds -- took the water bottle and signed the petition.

The results of the three studies run counter to previous findings that assert media information can influence peoples' water conservation attitudes. Instead, they show internet messages may encourage people to view water sustainability more positively, but they do not encourage more sustainable water behaviors.

The article drawn from the research, "Influence of Internet-Based Messages and Personal Motivations on Water-Use Decisions," discourages using pro-recycled wastewater internet videos about water scarcity and conservation alone. Instead, researchers urge a focus on the more visceral roadblock of disgust. As an example, the researchers suggest a video stressing the extent of water purification in recycling plants as part of larger campaigns to change behaviors.

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