New lightweight material is stronger than steel

Using a novel polymerization process, MIT chemical engineers have created a new material that is stronger than steel and as light as plastic, and can be easily manufactured in large quantities.

The new material is a two-dimensional polymer that self-assembles into sheets, unlike all other polymers, which form one-dimensional, spaghetti-like chains. Until now, scientists had believed it was impossible to induce polymers to form 2D sheets.

Such a material could be used as a lightweight, durable coating for car parts or cell phones, or as a building material for bridges or other structures, says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of the new study.

“We don’t usually think of plastics as being something that you could use to support a building, but with this material, you can enable new things,” he says. “It has very unusual properties and we’re very excited about that.” The researchers have filed for two patents on the process they used to generate the material, which they describe in a paper appearing today in Nature. MIT postdoc Yuwen Zeng is the lead author of the study.

Two dimensions

Polymers, which include all plastics, consist of chains of building blocks called monomers. These chains grow by adding new molecules onto their ends. Once formed, polymers can be shaped into three-dimensional objects, such as water bottles, using injection molding.

Polymer scientists have long hypothesized that if polymers could be induced to grow into a two-dimensional sheet, they should form extremely strong, lightweight materials. However, many decades of work in this field led to the conclusion that it was impossible to create such sheets. One reason for this was that if just one monomer rotates up or down, out of the plane of the growing sheet, the material will begin expanding in three dimensions and the sheet-like structure will be lost.

However, in the new study, Strano and his colleagues came up with a new polymerization process that allows them to generate a two-dimensional sheet called a polyamide. For the monomer building blocks, they use a compound called melamine, which contains a ring of carbon and nitrogen atoms. Under the right conditions, these monomers can grow in two dimensions, forming disks. These disks stack on top of each other, held together by hydrogen bonds between the layers, which make the structure very stable and strong.

“Instead of making a spaghetti-like molecule, we can make a sheet-like molecular plane, where we get molecules to hook themselves together in two dimensions,” Strano says. “This mechanism happens spontaneously in solution, and after we synthesize the material, we can easily spin-coat thin films that are extraordinarily strong.”

Because the material self-assembles in solution, it can be made in large quantities by simply increasing the quantity of the starting materials. The researchers showed that they could coat surfaces with films of the material, which they call 2DPA-1.

“With this advance, we have planar molecules that are going to be much easier to fashion into a very strong, but extremely thin material,” Strano says.

Light but strong

The researchers found that the new material’s elastic modulus — a measure of how much force it takes to deform a material — is between four and six times greater than that of bulletproof glass. They also found that its yield strength, or how much force it takes to break the material, is twice that of steel, even though the material has only about one-sixth the density of steel.

Matthew Tirrell, dean of the Pritzker School of Molecular Engineering at the University of Chicago, says that the new technique “embodies some very creative chemistry to make these bonded 2D polymers.”

“An important aspect of these new polymers is that they are readily processable in solution, which will facilitate numerous new applications where a high strength to weight ratio is important, such as new composite or diffusion barrier materials,” says Tirrell, who was not involved in the study.

Another key feature of 2DPA-1 is that it is impermeable to gases. While other polymers are made from coiled chains with gaps that allow gases to seep through, the new material is made from monomers that lock together like LEGOs, and molecules cannot get between them.

“This could allow us to create ultrathin coatings that can completely prevent water or gases from getting through,” Strano says. “This kind of barrier coating could be used to protect metal in cars and other vehicles, or steel structures.”

Strano and his students are now studying in more detail how this particular polymer is able to form 2D sheets, and they are experimenting with changing its molecular makeup to create other types of novel materials.

https://web.mit.edu/

Scientists Develop Recyclable Plastics Based on Sugars

Researchers from the University of Birmingham, U.K., and Duke University, U.S., have created a new family of polymers from sustainable sources that retain all of the same qualities as common plastics but are also degradable and mechanically recyclable.

The scientists used sugar-based starting materials rather than petrochemical derivatives to make two new polymers, one which is stretchable like rubber and another which is tough but ductile, like most commercial plastics.

The researchers made the new polymers using iodide and isomannide as building blocks.  Both these compounds are made from sugar alcohols and feature a rigid ring of atoms.  The researchers found that the suicide-based polymer showed a stiffness and malleability similar to common plastics, and a strength that

is similar to high-grade engineering plastics such as Nylon-6. Despite suicide and isomannide only differing by the 3D spatial orientation of two bonds, known as stereochemistry, the isomannide-based material had similar strength and toughness but also showed high elasticity, recovering its shape after deformation. Notably, the materials retained their excellent mechanical properties following pulverization and thermal processing, which is the usual method for mechanically recycling plastics.

Cutting edge computational modeling simulated how the polymer chains pack and interact to produce such different polymer properties. The unique 3D shapes of the sugar derivatives facilitate different movements and interactions of the long chains causing the huge difference in physical properties that were observed.

By creating copolymers that contain both iodide and isomannide units, the researchers found that they could control the mechanical properties and degradation rates independently of one another. Hence, this system opens the door to using the unique shapes of sugars to independently tune the degradability for a specific use without significantly altering the properties of the material.

The chemical similarity of the polymers means that, unlike a lot of current commodity plastics, they can be blended to yield materials with comparable or improved properties.

Dr. Josh Worch, from Birmingham’s School of Chemistry, and a co-author in the research said: “The ability to blend these polymers to create useful materials, offers a distinct advantage in recycling, which often has to deal with mixed feeds”.

Dr. Connor Stubbs, also from Birmingham’s School of Chemistry, added: “petrol-based plastics have had decades of research, so catching up with them is a huge challenge. We can look to the unique structures and shapes that biology has to offer to create far better plastics with the same expanse of properties that current commercial plastics can offer”

Duke University professor Dr. Matthew Becker said: “Our findings demonstrate how stereochemistry can be used as a central theme to design sustainable materials with what truly are unprecedented mechanical properties.”

Professor Andrew Dove, who led the research team from Birmingham, noted: “This study shows what is possible with sustainable plastics. While we need to do more work to reduce costs and study the potential environmental impact of these materials, in the long term it is possible that these sorts of materials could replace petrochemically-sourced plastics that don’t readily degrade in the environment.”

A joint patent application has been filed by the University of Birmingham Enterprise and Duke University.  The researchers are now looking for industrial partners who are interested in licensing the technology.

https://otc.duke.edu/

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Tonnes of Used Face Masks to Be Turned into Energy

The authors of the research claim that their technology could turn waste that is difficult to recycle into raw materials, according to a study published in the Journal of Energy Storage.

Researchers say that during the coronavirus pandemic people on the planet started using more than 130 billion masks every month, which turn into hundreds of tonnes of polymer waste. When burned it emits toxic gases, so the task of recycling this waste is particularly urgent.

Scientists at NUST MISIS, together with their foreign colleagues, have developed a new technology for producing cost-effective batteries from used masks, where waste drug blister packs are also used as a shell. Thus, medical waste forms the basis for creating batteries; all that needs to be procured is graphene.

The new technology enables the production of thin, flexible, low-cost batteries that are also disposable, due to their low cost. They are superior in several ways to heavier, metal-coated conventional batteries, which require more manufacturing costs. The new batteries can be used in household appliances from clocks to lamps.

“To create a battery of the supercapacitor type, the following algorithm is used: first the masks are disinfected with ultrasound, then dipped in ‘ink’ made of graphene, which saturates the mask. Then the material is pressed under pressure and heated to 140°C (conventional supercapacitor batteries require very high temperatures for pyrolysis-carbonation, up to 1000-1300°C, while the new technology reduces energy consumption by a factor of 10).

A separator (also made of mask material) with insulating properties is then placed between the two electrodes made of the new material. It is saturated with a special electrolyte, and then a protective shell is created from the material of medical blister packs (such as paracetamol)”, Professor Anvar Zakhidov, scientific director of the infrastructure project “High-Performance, Flexible, Photovoltaic Devices Based in Hybrid Perovskites” at NUST MISiS, said.

Compared to traditional accumulators, the new batteries have a high density of stored energy and electrical capacity. Previously, pellet batteries created using a similar technology had a capacity of 10 watt-hours per 1 kg, but scientists at NUST MISIS and their foreign colleagues have managed to achieve 98 watt-hours/kg.

When scientists decided to add nanoparticles of inorganic perovskite of CaCo oxide type to the electrodes obtained from the masks, the energy capacity of the batteries further increased (208 watt-hours/kg). They have achieved a high electrical capacity of 1706 farads per gram (This is significantly higher compared to the capacity of the best-carbonized electrodes without the addition of graphene (1000 farads per gram).

Scientists have tried before to use various porous natural materials and waste products to make electrodes for supercapacitors. These included coconut shells, rice husks, and recently even newspaper waste, car tire waste, and others. However, working with these materials always required high-temperature annealing (charring) in special furnaces. Masks turned out to be an easier and cheaper material to process since graphene saturation is sufficient to give them unique properties.

In the future, the scientific team plans to apply the new technology for the production of batteries for electric cars, solar power stations, and other applications.

https://en.misis.ru/

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