Science Friday - Flame Retardant From Cocoa Pod Husks | The Oozy Physics Of Oobleck

Episode Date: December 20, 2023

Flame Retardant Could Be Made From Discarded Cocoa HusksOn cocoa farms around the world, cocoa beans are pulled from their pods, and the hard husks are discarded, leaving 20 million tons of plant waste to biodegrade and potentially harm future crops. These husks are a source of lignin, a substance that gives plants their rigidity. It’s extremely abundant—but often wasted.A new study published in the journal ACS Sustainable Chemistry and Engineering found that the lignin processed from leftover cocoa pod husks could have a new use as an ingredient in flame retardant.“Lignin is pretty special, as it is very soluble in organic solvents,” said study co-author Dr. Nicholas Westwood, a professor of chemistry and chemical biology at St. Andrews University in Scotland, in an email. This means lignin can be chemically manipulated to create a number of useful substances relatively easily.Because of lignin’s malleability, Westwood and his coauthors were able to add a flame-retardant molecule to the processed substance, and found that the modification increased its already naturally high ability to smother flames.That’s just one possible application. While lignin hasn’t found widespread industrial use yet, scientists hold hope for it to become a greener alternative for fuel and a biodegradable plastic instead of just being leftovers. Processing biomass for food or fuel also produces a massive amount of lignin as a byproduct, which has been converted to materials like activated charcoal or carbon foam. “There are endless possibilities,” Westwood said.​​Joining Ira to talk about lignin and its potential uses is Dr. Rigoberto Advincula, a materials scientist with the Oak Ridge National Laboratory and the University of Tennessee in Knoxville.The Oozy Physics Of OobleckYou may be familiar with a common science demonstration done in classrooms: If you mix cornstarch and water together in the right proportions, you create a gooey material that seems to defy the rules of physics. It flows like a liquid, but when you try to handle it quickly, it stiffens up.This kind of material is called an oobleck, and it’s a type of non-Newtonian fluid, meaning its viscosity changes under pressure or stress. Oobleck-like materials include human-made things like Silly Putty and paint, but are also found in nature; blood and quicksand are both non-Newtonian fluids.For a long time, it’s been hard to prove exactly why these materials act the way they do. But recently, scientists developed a better understanding of the underlying physics. A new study conducted in collaboration between the James Franck Institute and Pritzker School of Molecular Engineering at the University of Chicago was able to demonstrate this mechanism.“The findings from this study are important because they provide direct experimental evidence for one of the mechanisms proposed for strong shear thickening,” says Dr. Heinrich Jaeger, professor of physics at the University of Chicago. “Namely, frictional interactions as the particles in the liquid are sheared into contact.” Jaeger is a co-author of the study, which was led by postdoctoral researcher Dr. Hojin Kim.Jaeger and Kim speculate that a better understanding of non-Newtonian fluids could help in the development of new, advanced materials. The potential ranges from flexible speed bumps to impact-resistant clothing. Jaeger joins Ira to talk about it.Transcripts for each segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

What do ketchup, yogurt, and quicksand all have in common? They're non-Newtonian fluids, or ooblek. Non-nutonian fluid really is a fascinating material that can adapt and dramatically change its behavior all by itself depending on how it is forced to flow. It's Wednesday, December 20th, but just like every day, today is Science Friday. I'm SciFRI producer Kathleen Davis. we're used to a certain level of consistency in life. If I reach for the orange juice day after day, I assume it's going to be the same liquidy goodness each time. There's a class of materials that don't operate this way.

They may fool you into thinking they're a liquid, but with a little pressure, they move into solid territory. We'll talk about the science of Ublec in just a bit, but first how cocoa bean husks could get a new life as a renewable resource. On cocoa farms around the world, husks are stripped off cocoa beans, leaving 20 million tons of plant waste to biodegrade. These husks are a source of lignin, the substance that gives plants their rigidity. A new study published in ACS, sustainable chemistry and engineering, says that lignin from the leftover cocoa bean husks could be an alternative for lots of different fossil fuel-based products like plastics and flame retardants. Joining me to talk about this is my guest, Dr. Rigoberto, Advincula, material scientist with the Oak Ridge National Laboratory and the University of Tennessee in Knoxville.

Welcome to Science Friday. Well, thank you so much, Ira. I'm happy to be with your show. Thank you. Let's talk about Lignin. What do we currently use it for? Well, Lignin is actually a byproduct of the pulp industry. It's well known in the biosphere.

sciences that you need lignin to hold the cellulose and basically give the rigidity in plants. But right now, a lot of it is thrown away. Huh. And so we want to save it from the cocoa husks. Yes. So like any other agro industry, they have a lot of biomass that includes lignin and cellulose. And they've been finding that there are many uses for lignin for variety of including plastics, flame retardants, adhesives, and so on. Give us an idea and how you extract it from the cocoa husks and other plants. So basically, LinkedIn binds the cellulose, hemicelios derived from a big unit called fibriel,

and you have to do some chemical treatment, desolution with a solvent. And when you do that, you fractionate them basically into the cellulose, and the lignin, which in our language basically is a mess. Ligdin is a very heterogeneous molecule or biomolecule, but when you process it or spiralize it properly, you get all sorts of very useful stuff that, for example, can be used for making further complex and very useful chemicals. You said it was a mess.

What are the challenges of biorefining these materials? How do you get high-quality lignin? Yes. So lignin is a class of what we call heterogeneous penolics or alcohols. They are highly branched. And depending on the plant source, they can be very different in terms of the aromatic content and the amount of phenolic content. So one has to carefully understand the heterogeneity or the,

variants of chemical intermediates you can extract from this various plant sources. So, for example, with cocoa and coconut and wood, they have different fractions, which has to be separated in order to use them for a variety of chemical intermediates. And you already mentioned the possibility of using them for plastic, flame retardants. Are there any other kinds of sustainable materials that might show? up. Yes, so cellulose obviously is a type of polysaccharide, you know, the same as the class of starch that we eat, but cellulose is the stuff that is not easily digested. They've been finding many uses for cellulose beyond the paper industry, including nanomaterials, including different

types of bioderibed plastic. On the other hand, the lignin is actually a rich source. of chemical intermediates when derivatives, for example, with phosphonate groups or lots of nitrogen, that's what makes it very useful, for example, in flame-retardant applications. So depending on the type of biomass, basically you have to classify the type of lignin chemistry you can derive, and therefore the biorefining, solvolysis, pyrolysis, these are all steps that are done in order to make them more useful. Now, we've heard about bioplastics, but bioplastics are still plastic, right?

Does extracting lignin from cocoa husks solve this problem? So the cellulose actually has been around for a long, long time. It's basically your natural polymer, natural polymer, natural plastic, and therefore biodegradable in many cases. Polylactic acid, which is derived from other plant or even bacterial sources, is actually a biodegradable plastic that is useful for packaging these days. Liglin, on the other hand, is a different kind of plastic. Because of the phenolic and alcohol groups present, one has to do some type of condensation polymerization to convert them into what we call thermosum. So when we say thermoset, these are plastics that are not easily molded and reformed with temperature.

A good example of a thermoset is epoxy. And epoxy has many uses, for example, in the fiber composite industry. So in this case, lignin really is a rich, rich playground to do more chemistry to derive different types of plastics and materials. Is there a business then that needs to. to be set up to extract and reuse all these husks that are lying around? Yes, good question. So a lot of the value depends really on the use of catalyst and the lower energy, meaning less cost to convert them into something useful.

So, for example, many companies, normally they would just consider this as waste. but then the new chemistries that are being developed even with some startup companies, and they've been finding ways to efficiently extract the useful intermediate and therefore get more value out of it. So a good example is the lignin can be derived into what we call monolignins, essentially very small molecules derived from lignin. These are closer to other types of aromatic intermediates that we use for solvents, for use in shampoo or plasticizers, for different types of chemical intermediates to make more complex molecules. So the more they can be purified into monoligins, the more they become useful as replacements for fossil-derived chemical intermediates.

It's fascinating, fascinating. Good to hear about this, and I hope we get to see some products made from the husks soon. Yes, yeah, exciting, because that means you can take any waste, biomass waste, and derive value out of it. Yeah, yeah, well, that's what we'd like to do. Thank you, Dr. Rigoberto at Vinculav, material scientists with the Oak Ridge National Laboratory, and the University of Tennessee in Knoxville. Thank you. My pleasure.

You may be familiar with a common science demonstration done in classrooms. Here it is. If you mix cornstarch and water in the right proportions, you wind up with a material that seems to defy the rules of physics. It flows and settles like a liquid like you would expect it to, but when you try to pick it up quickly or stir it, it stiffens up. The same thing happens with silly putty, quick sand and paint. This type of material is called a non-Newtonian fluid. It also has a more fun name, Ublec. And for a long time, it's been hard to prove why exactly this material acts like this. But now scientists have a better understanding of the underlying mechanism, and this understanding could help us create new smart materials. Joining me to talk about this is my guest, Dr. Heinrich Yeager, Professor of

Physics at the James Frank Institute at the University of Chicago. This study, was done in collaboration with the James Frank Institute and the Pritzker School. Thank you for joining us. Thank you, Ira. Thanks for having me. Nice to have you. You know I have done this many times. I love creating quick sand with cornstarch and water, and if you put your hand in it, and if you lift it up slowly, you can easily remove your hand, but if you try to jerk it up quickly, the cornstarch your water becomes like a solid. Please explain what exactly is going on here. What is a non-Newtonian fluid? Yes. So non-Nutonian fluid really is a fascinating material that can adapt and dramatically change its behavior all by itself depending on how it is forced to flow. And what I want to do

to explain that is contrasts that with what we would call a Newtonian fluid. Typically, that's a pure liquid like water. And how easily it flows depends on its resistance. its viscosity, which is simply a material property. So it does not depend on how you handle it. Imagine you move your hand through water. It puts up some resistance to flow, and that is this viscosity. But a non-Newtonian fluid now can adapt its viscosity. Smartly, it can flow more easily, for example, when we push it,

or it can dramatically resist a flow when we push it. And these are two extreme cases of non-utonian fluids that we call either sheer thinning or sheer thickening. Can you explain that exactly what's going on in the particles inside that dish where my hand is? Yes. So the prototypical non-nutonian fluid is dispersion or suspension of small particles in a liquid. And you might think that liquid lubricates these particles as they flow past each other. Right, exactly. And that can happen, right?

And in particular, this can happen for so-called shear thinning fluids. But there's also the case, particularly when you add a lot of particles, where they get pushed together to a point that actually the liquid between them is expelled and they get into direct contact. And now they interact by friction. And that can dramatically increase the resistance to flow. In fact, it can even solidify. Yeah, yeah, now I get it. That was good. Do you find these kinds of non-Newtonians in nature or are they all man-made? No, they, in fact, they exist in nature. So I told you that typically pure liquids are Newtonian, so they don't display that behavior. But when particulate matter is added, then this non-neutonian behavior emerges. And example, it's blood.

Blood. Blood, for example, is sheer thinning. It flows more easily if it's forced harder. Then there's paint. Paint also often is formulated by putting editors in there such that it will flow more easily when you brush it. That's what you want to get it off the brush onto the wall. But then when it's on the wall, you don't want it to keep flowing. You want it to resist flow. And that's exactly a sheer thinning behavior, right? So the opposite. of UBLIC. Yeah. This is Science Friday from WNYC Studios. Why has it taken so long to understand how these UBLICs work? In part, you know, these sheer thickening UBLEC type, non-utonian fluids, they're rarer, and they are so utterly counterintuitive. Just imagine any material I force it, I push it, I would imagine it should get weaker.

Ublech is now doing exactly the opposite. It becomes stronger. It potentially even solidifies, right? Right. And it does that even reversibly. It goes back and forth. If I take the forcing off, if I don't push it, it just reverses back to a liquid. And this counterintuitive behavior is as complex.

It has been hard to understand. And maybe historically that had also to do with the fact that two very different communities were looking at that. Initially, it was the rheology community. And I think they started basically from the idea I'd take pure liquid, like water, and I add particles, a few, and see what might happen, right? Right. Did you know that the person who was one of the first to calculate what would happen if you would put a few particles in illiquid and how its viscosity would change was, no other than Albert Einstein? Really?

That was his, that's a part of his PhD thesis, in fact. Wow, that's something I'm sure a lot of us didn't know. But we like to know that now. You suggest that now that we better understand how non-Newtonian fluids work, that they could be used to make new materials. Well, what kinds of materials are you thinking of? Well, so we are very much interested in making materials, materials, formulating materials that all by themselves, if you want autonomously, adapt to

changes and conditions, right? You don't need a computer to tell the material what to do, no feedback. So, you know, if you want an eublich-like material, you want one that becomes more resistive to flow. And that could be useful, for example, for impact mitigation. Think of wearable garments impregnated by fluids like that, that would take up impact, that would help you maybe protecting against sport injuries, injuries at the workplace, you know, prevent you from hurting yourself when you fall. There are other applications that have been proposed. One that I like in particular is speed bumps.

Speed bumps. Oh, yeah. Now I see it. It's like lying squishy flat when it's not being touched, but then you hit it in the car and now it's suddenly a speed bump. Exactly. So the idea with this non-Newtonian sheer thickening fluid is that the harder you force it, the more resist if it gets, right? So a car rolling over one of those at low speed would essentially just push the fluid aside and roll right over or through it. And if you go at faster speeds,

the pump would get solid and you would notice. That is cool. I like that. So you, you say it could be used in clothing. What other kinds of uses, let's say in clothing, you know, stab resistant because it would harden up? What other uses possibly if wearable stuff? Well, I should explain maybe a little bit more. Of course, there are many ways of protecting yourself against impact, let's say, doing sports, right? But typically, this implies a garment or a part of a garment that is relatively rigid. And that could, also then prevent you in terms of mobility. And what would be really nice is a protective system

that is very much not affecting your mobility when nothing happens, but then suddenly hardens up the moment, there's an actual impact. And that's exactly what such a non-notonian fluid could do. So we would combine the fluid with another fabric, obviously, into a protective system. system. That's all the time we have for today. I'd like to thank my guest, Dr. Heinrich Yeager, Professor of Physics at the James Frank Institute at the University of Chicago. This study was done

in collaboration with the James Frank Institute and the Pritzker School. Thank you, Ira. Thanks for having me. And that's all the time that we have for now. A lot of folks help make the show happen, including Annie Niro, Emma Gomez, Charles Bergquist, Danielle Johnson, and many more more. Next time, how one author is working to make romance novels a bit more scientific. But for now, I'm SciFRI producer Kathleen Davis. Thanks for listening.