{"id":84493,"date":"2021-02-08T06:55:26","date_gmt":"2021-02-08T05:55:26","guid":{"rendered":"http:\/\/rss.nova-institut.net\/public.php?url=https%3A%2F%2Fwww.chemie.de%2Fnews%2F1169595%2Fneuer-weg-zu-chemisch-recycelbaren-kunststoffen.html%3FWT.mc_id%3Dca0065"},"modified":"2021-09-09T19:33:32","modified_gmt":"2021-09-09T17:33:32","slug":"chirik-lab-discovers-transformative-route-to-chemically-recyclable-plastics","status":"publish","type":"post","link":"https:\/\/renewable-carbon.eu\/news\/chirik-lab-discovers-transformative-route-to-chemically-recyclable-plastics\/","title":{"rendered":"Chirik Lab Discovers “Transformative” Route to Chemically Recyclable Plastics"},"content":{"rendered":"

As the planet\u2019s burden of rubber and plastic rises unabated, scientists look to the promise of closed-loop recycling to reduce trash. Researchers in the Chirik Lab<\/a> have discovered a potentially game-changing new\u00a0molecule \u2013 from a material known for over a century and used to make common products like tires and shoe soles \u2013 with vast implications for fulfilling that promise through depolymerization.<\/strong><\/p>\n

The Chirik lab reports in Nature Chemistry<\/em> that during polymerization the molecule, named (1,n\u2019-divinyl)oligocyclobutane, enchains in a repeating sequence of squares, a previously unrealized microstructure that enables the process to go backwards, or depolymerize, under certain conditions. In other words, it can be \u201czipped up\u201d to make a new polymer; that polymer can then be unzipped back to a pristine monomer to be used again.<\/p>\n

\"Paul<\/a>
Paul Chirik, Edwards S. Sanford Professor of Chemistry, and Megan Mohadjer Beromi, postdoctoral fellow in the Chirik lab. Photo by C. Todd Reichart<\/figcaption><\/figure>\n

The molecule \u2013 casually referred to around the Chirik lab as a \u201cpolymer of squares\u201d \u2013 could one day enable the use of plastic products many times over, unlike most of today\u2019s plastic that can only be recycled once. If at all.<\/p>\n

\u201cI honestly think this work is one of the most important things to ever come out of my lab,\u201d said Paul Chirik, the Edwards S. Sanford Professor of Chemistry, of the discovery.<\/p>\n

Collaborator Alex Carpenter simply called it \u201ctransformative.\u201d<\/p>\n

The research is still at an early stage and the material\u2019s performance attributes have yet to be thoroughly explored. But under Chirik, the\u00a0lab has provided a conceptual precedent for a chemical transformation not generally thought practical for certain commodity materials.<\/p>\n

In the past, depolymerization has been accomplished with expensive,\u00a0specialized polymers and only after a multitude of steps,\u00a0but\u00a0never from a raw material as common as this one. The molecule was found in a material called polybutadiene, which has been known for over a hundred years and is used to make rubber and plastic products. Butadiene, its parent material, is an abundant organic compound and a major byproduct of fossil fuel development.<\/p>\n

\u201cTo take a really common chemical that people have been studying and polymerizing for many decades and make a fundamentally new material out of it \u2013 let alone have that material have interesting innate properties \u2013 not only is that unexpected, it\u2019s really a big step forward. You wouldn\u2019t necessarily expect there still to be fruit on that tree,\u201d said Carpenter, a collaborator on the research and a former\u00a0staff chemist with ExxonMobil Chemical.<\/p>\n

\u201cThe focus of this collaboration for us has been on developing new materials that benefit society by focusing on some new molecules that\u00a0Paul\u00a0has discovered that are pretty transformative,\u201d Carpenter added.\u00a0\u201cHumankind is good at making butadiene. It\u2019s very nice when you can find other useful applications for this molecule, because we have plenty of it.\u201d<\/h3>\n

Catalysis with Iron<\/h3>\n

The Chirik lab explores sustainable chemistry by investigating the use of iron \u2013 another abundant natural material \u2013 as a catalyst to synthesize new molecules. In this particular research, the iron catalyst clicks the monomers together to make oligocyclobutane. Normally, enchainment occurs with an S-shaped structure that is often described as looking like spaghetti.\u00a0\u00a0But with oligocyclobutane, the monomers click together in a chain of squares.<\/p>\n

To bring about\u00a0depolymerization, oligocyclobutane is exposed to a vacuum in the presence of the iron catalyst, which reverses the process and recovers the monomer. The Chirik lab\u2019s paper, published this week,\u00a0identifies this as a rare example of closed-loop chemical recycling.<\/p>\n

The material also has intriguing properties as characterized by Megan Mohadjer Beromi, a postdoctoral fellow in the Chirik lab, together with chemists at ExxonMobil\u2019s polymer research center. For instance, it is telechelic, meaning the chain is functionalized on both ends. This property could enable it to be used as a building block in its own right, serving as a bridge between other molecules in a polymeric chain. In addition, it is thermally stable, meaning it can be heated to above 250-degrees C without rapid decomposition.<\/p>\n

Finally, it exhibits high crystallinity, even at a low molecular weight of 1,000 grams per mol (g\/mol). This could indicate that desirable physical properties \u2013 like crystallinity and material strength \u2013 can be achieved at lower weights than generally assumed. The polyethylene used in the average plastic shopping bag, for example, has a molecular weight of 500,000g\/mol.<\/p>\n

\"Darmon-graphic[9]\"
Iron-catalyzed [2+2] oligomerization of butadiene produces (1,n’-divinyl)oligocyclobutane, a new polymer that can be chemically recycled. Figure by Jon Darmon<\/figcaption><\/figure>\u201cOne of the things we demonstrate in the paper is that you can make really tough materials out of this monomer,\u201d said Chirik. \u201cThe energy between polymer and monomer can be close, and you can go back and forth, but that doesn\u2019t mean the polymer has to be weak. The polymer itself is strong.<\/p>\n

\u201cWhat people tend to assume is that when you have a chemically recyclable polymer, it has to be somehow inherently weak or not durable. We\u2019ve made something that\u2019s really, really tough but is also chemically recyclable. We can get pure monomer back out of it. And that surprised me. That\u2019s not optimized. But it\u2019s there. The chemistry\u2019s clean.\u201d<\/p>\n

Ditching the ethylene<\/h3>\n

The project stretches back a few years to 2017, when C. Rose Kennedy, then a postdoc in the Chirik lab, noticed a viscous liquid accumulating at the bottom of a flask during a reaction. Kennedy said she was expecting something volatile to form, so the result spurred her curiosity. Digging into the reaction, she discovered a distribution of oligomers \u2013 or nonvolatile products with a low molecular weight \u2013 that indicated polymerization had taken place.<\/p>\n

\u201cKnowing what we knew about the mechanism already, it was pretty clear right away how this would be possible to click them together in a different or continuous way. We immediately recognized this could be something potentially extremely valuable,\u201d said Kennedy, now an assistant professor of chemistry at the University of Rochester.<\/p>\n

At that early point, Kennedy was enchaining butadiene and ethylene. It was Mohadjer Beromi who later surmised that it would be possible to remove the ethylene altogether and just use neat butadiene at elevated temperatures. Mohadjer Beromi \u201cgave\u201d the four-carbon butadiene to the iron catalyst, and that yielded the new polymer of squares.<\/p>\n

\u201cWe knew that the motif had the propensity to be chemically recycled,\u201d said Mohadjer Beromi. \u201cBut I think one of the new and really interesting features of the iron catalyst is that it can do [2+2] cycloadditions between two dienes, and that\u2019s what this reaction essentially is: it\u2019s a cycloaddition where you\u2019re linking two olefins together to make a square molecule over and over again.<\/p>\n

\u201cIt\u2019s the coolest thing I\u2019ve ever worked on in my life.\u201d<\/p>\n

To further characterize oligocyclobutane and understand its performance properties, the molecule needed to be scaled and studied at a larger facility with expertise in new materials.<\/p>\n

\u201cHow do you know what you made?\u201d Chirik asked. \u201cWe used some of the normal tools we have here at Frick. But what really matters is the physical properties of this material, and ultimately what the chain looks like.\u201d<\/p>\n

For that, Chirik traveled to Baytown, Texas last year to present the lab\u2019s findings to ExxonMobil, which decided to support the work. An integrated team of scientists from Baytown were involved in computational modeling, X-ray scattering work to validate the structure, and additional characterization studies.<\/p>\n

Recycling 101<\/h3>\n

The chemical industry uses a small number of building blocks to make most commodity plastic and rubber. Three such examples are ethylene, propylene, and butadiene. A major challenge of recycling these materials is that they often need to be combined and then bolstered with other additives to make plastics and rubbers: additives provide the performance properties we want \u2013 the hardness of a toothpaste cap, for example, or the lightness of a grocery bag. These \u201cingredients\u201d all have to be separated again in the recycling process.<\/p>\n

But the chemical steps involved in that separation and the input of energy required to bring this about make recycling prohibitively expensive, particularly for common consumer products. Plastic is cheap, lightweight, and convenient, but it was not designed with disposal in mind. That, said Chirik, is the main problem with it.<\/p>\n

As a possible alternative, the Chirik research demonstrates that the butadiene polymer is almost energetically equal to the monomer, which makes it a candidate for closed-loop chemical recycling.<\/p>\n

Chemists liken the process of producing a product from a raw material to rolling a boulder up a hill, with the peak of the hill as the transition state. From that state, you roll the boulder down the other side and end up with a product. But with most plastics, the energy and cost to roll that boulder backwards up the hill to recover its raw monomer are staggering, and thus unrealistic. So, most plastic bags and rubber products and car bumpers end up in landfills.<\/p>\n

\u201cThe interesting thing about this reaction of hooking one unit of butadiene onto the next is that the \u2018destination\u2019 is only very slightly lower in energy than the starting material,\u201d said Kennedy. \u201cThat\u2019s what makes it possible to go back in the other direction.\u201d<\/p>\n

In the next stage of research, Chirik said his lab will focus on the enchainment, which at this point chemists have only achieved on average up to 17 units. At that chain length, the material becomes crystalline and so insoluble that it falls out of the reaction mixture.<\/p>\n

\u201cWe have to learn what to do with that,\u201d said Chirik. \u201cWe\u2019re limited by its own strength. I would like to see a higher molecular weight.\u201d<\/p>\n

Still, researchers are excited about the prospects for oligocyclobutane, and many investigations are planned in this continuing collaboration towards chemically recyclable materials.<\/p>\n

\u201cThe current set of materials that we have nowadays doesn\u2019t allow us to have adequate solutions to all the problems we\u2019re trying to solve,\u201d said Carpenter. \u201cThe belief is that, if you do good science and you publish in peer-reviewed journals and you work with world-class scientists like Paul, then that\u2019s going to enable our company to solve important problems in a constructive way.<\/p>\n

\u201cThis is about understanding really cool chemistry,\u201d he added, \u201cand trying to do something good with it.\u201d<\/p>\n

 <\/p>\n

Read the full paper here:\u00a0https:\/\/www.nature.com\/articles\/s41557-020-00614-w<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

As the planet\u2019s burden of rubber and plastic rises unabated, scientists look to the promise of closed-loop recycling to reduce trash. Researchers in the Chirik Lab have discovered a potentially game-changing new\u00a0molecule \u2013 from a material known for over a century and used to make common products like tires and shoe soles \u2013 with vast […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"","nova_meta_subtitle":"","footnotes":""},"categories":[17143],"tags":[11966,12593,10453],"supplier":[3322],"class_list":["post-84493","post","type-post","status-publish","format-standard","hentry","category-recycling","tag-plastics","tag-polymer","tag-recycling","supplier-princeton-university"],"_links":{"self":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/84493","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/comments?post=84493"}],"version-history":[{"count":0,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/posts\/84493\/revisions"}],"wp:attachment":[{"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/media?parent=84493"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/categories?post=84493"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/tags?post=84493"},{"taxonomy":"supplier","embeddable":true,"href":"https:\/\/renewable-carbon.eu\/news\/wp-json\/wp\/v2\/supplier?post=84493"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}