#materials science

"New research has made encouraging progress in tackling not one but two of the biggest problems facing our planet right now: plastic pollution and the use of fossil fuels as part of drug manufacturing processes.

Scientists from the University of Edinburgh in the UK have used Escherichia coli bacteria to convert molecules from the widely used polyethylene terephthalate (PET) plastic into the painkiller acetaminophen (also known as paracetamol).

Like a lot of drugs today, acetaminophen is mostly made out of fossil fuels. Switching those ingredients for waste products – like plastic – could offer an ingenious way of addressing two major environmental problems in one.

It's going to take a while to scale this up and prove it can be effective at an industrially and commercially viable level, so we shouldn't get too far ahead of ourselves, but there's a lot of potential in the new technology.

"This work demonstrates that PET plastic isn't just waste or a material destined to become more plastic – it can be transformed by microorganisms into valuable new products, including those with potential for treating disease," says biotechnologist Stephen Wallace from the University of Edinburgh.

The process starts by chemically degrading PET bottles. The resulting molecules are then fed to engineered E. coli, which use phosphate as a catalyst to convert the molecules into an organic compound containing nitrogen. Finally, these compounds are turned into the active ingredient of acetaminophen.

Among the numerous advantages of the process are that it can be completed in 24 hours in a compact laboratory setup, and that it works at room temperature, so there's no need for excessive heating or cooling. What's more, the team has managed to get it working at an impressively efficient 92-percent yield...

The reaction makes use of a well-established chemical reaction called the Lossen rearrangement, named after German chemist Wilhelm Lossen, who discovered it in 1872. Here, the reaction is made biocompatible so it can work in cells and living bacteria.

This was all done using PET bottles, but the plastic is also used extensively in food packaging, furniture, and manufacturing. This type of plastic is estimated to account for more than 350 million tons of waste per year, adding to the plastic pollution burden.

The same approach might also work for other types of bacteria and other types of plastic, according to the researchers, so there's potential here for more environmentally friendly recycling and drug production options.

It's a powerful example of how both natural and synthetic chemistry can be combined to find solutions to problems and drive innovation, and it may ultimately mean that E. coli plays a part in the production of our pain relief in the future...

The research has been published in Nature Chemistry.

In a study published in the Journal of the American Chemical Society, they report a new type of plastic made from plant cellulose, the world's most abundant organic compound. The new plastic is strong, flexible, and capable of rapid decomposition in natural environments, setting it apart from other plastics marketed as biodegradable. Microplastics are a global contaminant found in nearly every ecosystem, from the soil and the ocean to the animals and plants that live there. They have even been found in human tissue and the bloodstream, where they likely have adverse effects.

Steel is great, it's probably the third most important thing ever invented after vaccines and antibiotics. However, in nuclear fusion, we're running up against the limits of modern steel technology – it performs poorly under high neutron radiation. This happens for a lot of reasons, but I'm going to focus on helium embrittlement here.

When you bombard a material with fast neutrons, you can induce nuclear transmutation. This is often bad, because the transmutation products mess with the material properties (e.g. tungsten transmutes in rhenium and osmium, which make tungsten brittle). This is a big problem in fusion reactors, which are usually designed to produce lots and lots and lots of fast neutrons.

Figure 1. Several types of neutron radiation damage in metal. The production of a helium atom through transmutation circled in magenta; this particular mechanism is the focus of this post. Figure adapted from Das 2019.

These transmutation reactions often involve alpha decay. Because an alpha particle is a helium nucleus, this means that helium gas will start to build up inside the metal, as shown in Fig. 1. Over weeks or months or years, depending on the metal and the neutron environment, this helium gathers into tiny bubbles. This makes your metal very hard and brittle. That's not good!

(Note that these reactions can also produce hydrogen, but in many cases the amount of hydrogen you get from transmutation is dwarfed by the amount that's absorbed directly from fusion plasma or tritium-bearing breeding fluid).

A lot of otherwise excellent steel alloys are very susceptible to helium embrittlement, but one potential solution is these newfangled oxide dispersion-strengthened (ODS) alloys.

Figure 2. Yttrium-titanium-oxide nanoparticles (dark gray dots) dispersed in steel (gray background). Oxide nanoparticles can entrap helium, which prevents it from migrating and forming large helium bubbles. Figure adapted from Lu et al. 2017.

Basically, you take a bunch of very small metal oxides nanoparticles – I've seen people use yttrium oxide a lot, in combination with titanium and halfnium, or borides – and mix them in with steel powder, which is then sintered into solid metal, as shown in Fig. 2. Helium is still produced by transmutation, but it's stopped cold by the nanoparticles and never coalesces into large bubbles. There's even evidence to suggest that these helium "nanobubbles" will strengthen the metal!

There's still a lot of development to be done with ODS steel – it's hard to produce in large pieces, and it's tricky to weld or bond without destroying the nanoparticles. You can 3D print it, which is cool but hard to scale up. Still needs to be tested in larger quantities too. But this is a really exciting area of research that a lot of people are pursuing with great interest!

Image sources:

Das, S. Recent advances in characterising irradiation damage in tungsten for fusion power. SN Appl. Sci. 1, 1614 (2019). https://doi.org/10.1007/s42452-019-1591-0

A surprising new method finally makes teflon recyclable

New research has identified a straightforward and environmentally friendly way to decompose Teflon, one of the most resilient plastics in use today, and convert it into valuable chemical ingredients. Scientists at Newcastle University and the University of Birmingham have created a clean, energy-saving process for recycling Teflon (PTFE), which is widely recognized for its role in non-stick cookware and in products that must withstand high temperatures and harsh chemicals. The team found that discarded Teflon can be broken apart and reused with only sodium metal and mechanical movement by shaking -- all at room temperature and without toxic solvents.

the copper-aluminum equilibrium phase diagram is a good illustration of why a lot of alloys are in the “90% A, 5% B, <1% each of C, D, E, etc” category

once you get into that middle area, not only do does your equilibrium phase composition get more intricate, but it also gets way hard to predict the true microstructure you will get (phase diagrams do not capture kinetics)

some elements like nickel don't even have "the" standard refining process because it's found in close association with a number of other metals, meaning what works differs on where you got your nickel from. others do have standard processes, but they might require valuable resources (rare, expensive elements as catalysts, for example) or the most efficient process comes with negative side effects like mercury getting into groundwater.

platinum and palladium are incredibly rare but also highly important as catalysts for many different things and cannot be replaced. so depending on costs and available funding, you might need to use a different process that's worse for the environment when you cannot afford a platinum or palladium catalyst. (additionally, while catalysts technically come out 'unchanged' at the end of a reaction, repeated high intensity use will still erode them.)

metals like aluminium might seem to be available in abundance, but they aren't. you need expensive industrial infrastructure to refine aluminium in large amounts and get a high quality product. that means space, high energy costs, qualified workers, complicated set-ups, additional materials, storage opportunities, ability to have large amounts of unrefined aluminium delivered on a regular basis, and people buying your aluminium once it's a finished product.

there are thousands of uses for seemingly abundant elements that do not have an alternative, so they are prioritized, and using it for "simple solutions" for other problems is not feasible. it's just not.