Glass so strong you can jump on it, a rubber-like coating tough enough to absorb a bomb blast, endless varieties of plastic. Scientists and engineers have created virtually indestructible versions of common materials by manipulating the chains of interlocking atoms that give them strength—but have they made them too tough? Host David Pogue explores the fantastic chemistry behind the everyday materials we depend on, and how the quest for durability can be balanced with products’ environmental impact. (Enjoy this program with Audio Description.)
Beyond the Elements: Indestructible
PBS Airdate: February 10, 2021
DAVID POGUE (Science and Technology Author): What’s it take to make our modern world?
I’m David Pogue. Join me on a high-speed chase through the elements and beyond.
Oh, my god.
As we smash our way into the materials, molecules and reactions…
AMANDA CAVANAGH (University Of Illinois, Realizing Increased Photosynthetic Efficiency [RIPE)]): It’s a really cool enzyme, because it makes life on Earth possible.
DAVID POGUE: …that make the places we live, the bodies we live in and the stuff we can’t seem to live without.
The only thing between me and certain death is chemistry? From killer snails…
MANDË HOLFORD (Hunter College): Just when you think you’ve heard of everything, nature will surprise you.
DAVID POGUE: …and exploding glass to the price a pepper-eating Pogue pays…
There’s got to be some easier way to learn about molecules.
…we’ll dig into the surprising way different elements combine together and blow apart.
In this hour, we swing from the molecular chains and surf the atomic webs that give some materials unique abilities…
…the moldable molasses of molten glass…
…the built-in “boing” of rubber…
The G-forces are indescribable.
…and the menagerie of modern plastics that these days is both a miracle…
…and a menace.
JASON LOCKLIN (University of Georgia, New Materials Institute): People want to do the right thing, but it’s really difficult to know exactly what to do.
DAVID POGUE: Beyond the Elements: Indestructible, right now, on NOVA.
Ah, the periodic table: the Who’s Who of atoms, the stuff everything is made of, with familiar names like hydrogen, oxygen, carbon and iron.
But what if every substance were made of just one kind of atom, one kind of element? What if a human were made only of carbon? What if water were made only of hydrogen? And what if salt were made only of poisonous chlorine?
Luckily, nearly all elements like to stick together. It’s through the combination of different elements that our world exists. And we’ve made it an even richer place by learning to harness, and even make those combinations, to create new materials that have shaped our modern world, such as rubber or plastic, materials we’ve come to depend on. But that sometimes come with difficult environmental downsides.
But let’s start with one of the oldest and most chemically interesting. Look at the buildings in any city today and you’ll see, or see through, one of the signature materials of our times: glass.
The Corning Museum of Glass, in Corning, New York, is home to “an internationally famous collection of glass” with examples that range from antiquity to contemporary art, from the functional to the fantastic.
The museum also runs demonstrations of glassblowing.
GLASS BLOWING PRESENTER: She’s applying glass color to that molten glass.
By holding it to the ground, gravity takes hold, and she gets that beautiful ruffled edge.
DAVID POGUE: Some include opportunities for novices, like me, to get into the act.
ERIC MEEK (The Corning Museum of Glass): We’re going to be making something called the Roman bottle.
Good. Keep going, keep going. All right, stop.
DAVID POGUE: The kind of glass I’m working with is the most common sort, “soda-lime glass,” the stuff of windows, drinking glasses and glass bottles.
ERIC MEEK: Give the pipe a tap.
DAVID POGUE: Woo hoo! I am good at this.
Eric Meek, one of the hot glass program managers, breaks down the ingredients in soda-lime glass for me.
ERIC MEEK: So, these are the raw materials that we use to make glass. The first main ingredient is silica sand. You can see this is a beautiful white, pure silica sand. This will make really nice, clear glass for us.
DAVID POGUE: Silica is a network of silicon and oxygen atoms, where each silicon atom shares electrons with neighboring oxygens in what are called covalent bonds.
ERIC MEEK: To get this to melt at a lower temperature, we add soda ash, so that’s sodium carbonate.
DAVID POGUE: Sodium carbonate: two sodiums, electrically attracted to three oxygens, sharing electrons with a carbon atom.
ERIC MEEK: If we melted pure silica, it would melt at nearly 4,000 degrees. If you add soda ash, it drops the melting temperature down to around 2,000 degrees Fahrenheit.
DAVID POGUE: So, easier for us to bring about?
ERIC MEEK: Easier for us to bring about.
And then the final ingredient, over here, is crushed limestone or calcium carbonate.
DAVID POGUE: Like sodium carbonate but with a calcium instead.
ERIC MEEK: Calcium carbonate will help to stabilize the glass over time.
DAVID POGUE: Wow, and you just sort of mix that up in a pot…
ERIC MEEK: Yep.
DAVID POGUE: …and put it over a medium flame, and…
ERIC MEEK: It’s that easy. You mix these together, put it in a crucible, melt it at about 2,000 degrees, and you have glass.
DAVID POGUE: …at high temperatures, all those powdery ingredients melt together to form a viscous liquid that cools into glass.
But there’s more to the story.
Most solids are crystalline, like frozen water, the ice in your glass. In ice, the water molecules are arranged in a regular pattern. If we heat it to its melting point, ice quickly turns to liquid, with water molecules sliding past each other. And then, if we drop the temperature, the water refreezes and the regular crystalline structure returns.
Silica sand, the primary ingredient in common glass, typically also has a regular crystalline structure. As you heat it up, it, too, will melt, just like ice does, more or less all at once transitioning from a solid to a liquid, with the network of silicon and oxygen atoms sliding around chaotically.
But this is where glass gets weird. When you cool our liquid silica down, it doesn’t find its way back into a crystalline structure. Instead, it becomes an increasingly viscous liquid with jumbled rings of atoms. When it finally cools down enough, that warped irregular structure becomes locked in place into what’s called “an amorphous solid.”
The range of temperatures in which glass remains a viscous goopy liquid that we can manipulate is one reason it’s such important material and has made possible the amazing art of glassblowing.
When most of us talk about glass, we mean silica-based glass, ordinary glass. But glass is also the term scientists use for any material that exists as an amorphous solid material, that unlike a crystal, have an irregular structure and when heated, pass through a phase that’s not exactly liquid and not exactly solid, a phase I call “gooey.”
ERIC GOLDSCHMIDT (The Corning Museum of Glass): So, glass comes in many forms.
DAVID POGUE: Eric Goldschmidt, a flame worker, demonstrates that glass doesn’t have to be, well, glass, using a piece of hard candy.
ERIC GOLDSCHMIDT: And it actually acts a lot like glass that we use out of our furnaces here. So, I’m softening this material with some heat, getting those atoms moving around, and it simply will never have the opportunity to come back to a crystalline network. So we can soften it a little bit, start to inflate it.
DAVID POGUE: Start to inflate it?
Come on! Dude, you’re making a Roman bottle out of a Jolly Rancher.
ERIC GOLDSCHMIDT: In theory, it can be shaped into just about anything, because of its ability to, sort of, transition from really fluid to fairly, fairly rigid.
DAVID POGUE: Would it still taste like candy?
ERIC GOLDSCHMIDT: I don’t think we’ve cooked the sweetness out of it.
DAVID POGUE: Is it too hot?
ERIC GOLDSCHMIDT: It should be cool enough to touch.
DAVID POGUE: Excuse me.
My gosh. I feel like I’m eating the wrapper. I’ve never had candy that light and flaky.
ERIC GOLDSCHMIDT: And I don’t think I’ve ever had anybody eat a piece of glass that I’ve inflated either.
DAVID POGUE: This is gorgeous. This is clearly going to be worth something.
ERIC MEEK: It’s straight out.
DAVID POGUE: Okay.
ERIC MEEK: There you go.
DAVID POGUE: Okay. Maybe if I stop talking and keep working.
There’s an underappreciated aspect of glassblowing that I learned about firsthand.
ERIC MEEK: Here we go. Comes right off.
DAVID POGUE: After you shape a piece of glass while it’s hot, it has to cool slowly in an annealing oven that gradually ramps down the temperature. For something this size, it takes about 12 hours. Otherwise, differences in thickness mean differences in cooling, leading to stresses that can cause the piece to crack.
But what happens if you cool some glass really fast? Then, you get these: “Prince Rupert’s drops,” named for Prince Rupert of the Rhine, who brought them to England, in 1660, as a scientific curiosity.
ERIC MEEK: So, I’m going to have you take this hammer and try to break this drop.
DAVID POGUE: Are you nuts? It’s glass.
ERIC MEEK: All right. So, just grab it down here, by the tail, all right? And set it down there on the table, and just make sure you hit the thick end.
DAVID POGUE: Just shatter it?
ERIC MEEK: Yep.
DAVID POGUE: Come on. No. Wow. I broke your table. That’s insane.
We’ve established that this glass is indestructible. Congratulations.
ERIC MEEK: We have, but there is an Achilles’ heel. There is a way to break this.
DAVID POGUE: Considering this glass just dented a steel table, I’m skeptical.
ERIC MEEK: So, snap it down in the tail.
DAVID POGUE: So, this is me, trying to snap off the tail of this unbreakable glass.
What? Where’d it go?
What just happened?
Well, let’s rewind a little, to the key moment, when the drop of hot glass enters the cold water. The outside of the glass immediately cools and locks into shape, but the inside cools more slowly, gradually contracting, trying to pull in the rigid outside glass, creating a tremendous amount of stress, placing the outer layer under compression.
ERIC MEEK: A lot of materials under compression are very strong, including glass.
DAVID POGUE: So strong, you can’t break it with a hammer. But there’s an Achilles tail, because that part is so thin, when it enters the water, it cools just about all at once: no compression effect, no super strength. I can break it with my hands. And that surface fracture races through the rest of the compressed material.
ERIC MEEK: Once that compressive layer is compromised, there’s so much energy in there, the whole thing will crack.
DAVID POGUE: Ka-blammo! Total drop destruction!
Turns out, the surprising strength of a Prince Rupert’s drop plays a role in how we make glass today. Manufacturers take advantage of the strength of glass under compression to make a special kind, called “tempered” glass.
ERIC MEEK: So, this is a piece of commercial tempered glass. And rather than being cooled with water, this one is just cooled with jets of air on the surface.
The jets of air, sort of, make the skin of the glass rigid, and stiffens the surface of the glass. The core of this cross-section is left to cool a little bit more slowly, and so it pulls away from the surface, and that creates a compressive layer on the surface.
DAVID POGUE: So, it’s sort of compressing itself from the inside?
ERIC MEEK: From the inside, exactly.
DAVID POGUE: So then, what is this, like, Prince Rupert’s sidewalk?
It may seem counterintuitive…
Every cell in my body is saying this is a bad idea.
…but by cooling the glass to create compressive stress, generally more than 10,000 pounds per square inch, it becomes physically stronger. I can walk, even jump on this tempered piece that’s about a half-inch thick.
Oh, my gosh! Dah! They could make diving boards out of this stuff. Oh, man!
Even pouring molten glass on it doesn’t make it shatter immediately, but give it a minute…
That’s some strong glass.
ERIC MEEK: It is.
DAVID POGUE: …or four.
Oh, man, that was cool! It was like “poof!”
The molten glass finally compromised the surface, and all that built-in stress broke up the entire sheet. But the remaining shards are relatively safe.
ERIC MEEK: Because of that tension, when it does break, it breaks all the way out to the edge, and it all breaks into these little bits. They make these nice little cubes that aren’t nearly as dangerous as a big, broken shard of glass.
DAVID POGUE: The miracle of glass is made possible in part by the element silicon, the second most common element in the earth’s crust, after oxygen. Silicon atoms have 14 electrons, arranged in three shells. Because the outermost shell has four electrons, silicon can share those, to form up to four bonds with other atoms.
But one thing that it doesn’t do well is form a chain with other silicon atoms to create a compound with a silicon backbone. It’s just too reactive. In water, the backbone easily falls apart.
The element with the best ability to do that trick sits just above silicon. Carbon can also form up to four bonds with other atoms, but luckily, it can also form strong bonds with other carbon atoms.
The result is not only you and me, and all life on Earth, but also a plethora of other molecules and materials that shape our lives and can even put a bounce in your step.
First up: rubber.
It turns out that more than half of the world’s rubber ends up wrapped around the wheels of vehicles: motorcycles, trucks and cars. So, I’ve come to a place that’s rolling in it: the Indianapolis Motor Speedway.
It’s 11 days away from the running of one of the most famous car races in the world, the Indy 500. The competing teams are here, doing practice runs. And some end better than others.
Before the teams hit the track, some fortunate fans get a taste of the race. They get to ride in a specially adapted two-seater Indy car. At the wheel, the legendary champion, Mario Andretti.
He’s one of the most successful American drivers in the history of the sport. He’s the only pro ever to win the Indianapolis 500, the Daytona 500 and the Formula One World Championship.
And now, it’s my turn. Imagine riding a roller coaster at over 180 miles an hour, with no rails, flying around the curves, while wondering why we’re not smashing into the wall.
I’ve had enough after a couple of laps. How do these drivers do 200 of them?
Oh, man. The G forces are just indescribable. I mean you’re pressed against the side and then pressed against the back. And when he takes the curves, I mean there’s a concrete wall coming at you, just…
So, what’s the secret ingredient to staying alive out there? To find out, I head to the garage that supplies the tires in the weeks leading up to the Indy 500.
In 2019, each team received 36 sets of tires for practice, qualifying and the race: 6,000 tires in all.
It’s also a chance to talk to the expert himself.
What I was surprised at most was the lateral forces, obviously, as a layman. So, is it the rubber that’s keeping us from flying into that wall?
MARIO ANDRETTI (Racecar Driver): That’s it, that’s what it is. That’s, the tire is obviously the most important aspect of the racecar. These are the babies you want to kiss after a run.
DAVID POGUE: At speeds up to 230 miles an hour, a driver experiences about five Gs of force during the turns. That’s more than what an astronaut experiences during a space launch, so you know the tires take a beating.
Do you know enough about the chemistry to know what kinds of things they can do to the compounds? Like, what sorts of things do they add?
MARIO ANDRETTI: If they would tell me that, they would have to kill me.
DAVID POGUE: Hopefully, that’s not a blanket policy, because I’ve come to Akron, Ohio, looking for some answers.
Harvey Firestone founded the Firestone Tire and Rubber Company here, in 1900. Bridgestone Corporation bought it in 1988, becoming Bridgestone/Firestone.
This is one of its research facilities, and Laura Kocsis is one of its scientists. According to her, it all starts with this.
I’ve got to say this feels rubbery. Oh, man, it’s also stinky!
LAURA KOCSIS (Bridgestone Americas): Yep. So, that’s natural rubber.
DAVID POGUE: Oh. This is what comes out of the tree?
LAURA KOCSIS: Yep. So, it comes out of the tree, we process it, and it turns it into what you have in your hands right now.
DAVID POGUE: It becomes this?
LAURA KOCSIS: Yes.
DAVID POGUE: Natural rubber begins as sticky, runny, white liquid, called latex. It’s found in more than 2,000 plants including dandelions, but most of the world’s natural rubber comes from trees like these, the Hevea brasiliensis, better known as the rubber tree.
Natural latex is about 55 percent water with particles of rubber suspended in it. And if you could zoom into one of the particles, you’d see it’s like a tangled bunch of spaghetti. Each noodle is a long molecular chain called a polymer.
LAURA KOCSIS: To get to a polymer, you start with monomers, which is one chemical unit. And that’s represented by these paperclips, here.
DAVID POGUE: This, here, is one chemical unit?
LAURA KOCSIS: Yep, consider that one chemical unit.
DAVID POGUE: Meaning what? A molecule?
LAURA KOCSIS: Yep, one molecule.
DAVID POGUE: So, for natural rubber, what, what molecule are we talking about?
LAURA KOCSIS: So, we’re talking about isoprene.
DAVID POGUE: Isoprene. Okay.
Here’s what isoprene looks like. It’s a molecule with five carbons bonded to each other and to eight hydrogens. In natural rubber, isoprenes are bonded together, one after another, to make a chain, a polymer, just like the chain of paper clips Laura showed me.
LAURA KOCSIS: Once you get to tens of thousands of these units linked together, you end up with natural rubber.
DAVID POGUE: Oh, tens of thousands?
LAURA KOCSIS: Yep.
DAVID POGUE: Okay.
LAURA KOCSIS: Tens of thousands.
DAVID POGUE: In their natural state, the rubber polymer chains can become easily entangled, as they coil up. But when you stretch them out, the chains straighten out and align themselves in the direction of the stretch. Let them go, and the molecules return back to their coiled-up states, giving rubber its signature “boinginess.”
So, if it’s rubber, it should be a little boingy.
LAURA KOCSIS: Yep. It’s going to bounce.
DAVID POGUE: Okay. That’s very boingy. I’m sure here at Bridgestone, you use that as a chemical property, the “boinginess.”
LAURA KOCSIS: Yes. Very technical.
DAVID POGUE: Oh, man!
Natural rubber is often an ingredient in tires, but it’s not the only one. Today, many tires include synthetic rubber, made out of other monomers, not found in latex.
Oh, ho. I’m sensing more polymers.
LAURA KOCSIS: Yes.
DAVID POGUE: More chains of molecules. What do these represent?
LAURA KOCSIS: So, these are different configurations of polymers that we can make in our laboratory. Natural rubber is made of only one type of monomer. Here, we can use different types and bring them together, with our chemistry.
DAVID POGUE: And each way of linking them together produces different qualities in the tire that will result?
LAURA KOCSIS: Yep. So, maybe the amount of monomer can make a difference in the properties, how they’re configured can make a difference. And that’s basically what we do here is find different ways of putting them together, so that we can achieve the properties that we want.
DAVID POGUE: Wow.
Natural rubber, synthetic rubber, turns out, there’s even more that goes into “tire” rubber. Here in the test lab, technicians mix all the ingredients together, like carbon black and silica, which reinforce the tire. Another key ingredient is sulfur, element number 16 on the periodic table.
The resulting blob then gets rolled into sheets, cut into squares, for testing, and baked at high temperature, in a process called “vulcanization.”
Charles Goodyear discovered the process, in 1839, when he accidentally spilled a mixture of rubber and sulfur on a stove. He named it after Vulcan, the Roman god of fire.
Cooking the rubber-sulfur mixture causes the sulfur to chemically bond the rubber’s polymer chains to each other, forming crosslinks between them. Bill Niaura, Bridgestone’s Director of Innovation, shows me the result.
So, this little bowtie, this was cut out of one of those squares before vulcanization?
BILL NIAURA (Bridgestone Americas): It was.
DAVID POGUE: And this is what rubber looks like after that vulcanization?
BILL NIAURA: Correct.
DAVID POGUE: So, the only difference between these two is this one was super-heated for a while?
BILL NIAURA: Correct.
DAVID POGUE: All right. And, according to you, something property-wise has changed?
BILL NIAURA: It has. Why don’t you take the uncured one and stretch it.
DAVID POGUE: All right, this guy, just pull it. Oh, wow.
BILL NIAURA: What you’ll feel are the polymer chains flowing apart, it’s acting like a liquid. It’s viscous.
DAVID POGUE: It feels…
BILL NIAURA: When you…
DAVID POGUE: …exactly like gum, stretching gum.
BILL NIAURA: And when you release the force, you’ll see that it’s flowed apart and the energy that you put in has not been recovered, and the piece has been permanently deformed.
DAVID POGUE: I broke your rubber sample.
BILL NIAURA: I’m okay with that.
DAVID POGUE: With all the new ingredients, our unbaked tire mixture is far less “boingy” than the rubber I saw in Laura’s lab. When you stretch it, the mixture’s loosely coiled polymer strands slide past each other and keep on sliding. Only weak interactions hold the network of strands together, so, under stress, it pulls apart.
Okay. And then after vulcanization, the same test?
BILL NIAURA: Indeed.
DAVID POGUE: Oh, man, it’s much harder to pull.
BILL NIAURA: And when you release the force…
DAVID POGUE: Oh.
BILL NIAURA: …you’ll see that it’s recovered its original shape. And that’s a characteristic of elasticity.
DAVID POGUE: Stretch out this vulcanized interconnected web of strands, and instead of ripping apart, the network springs back to its original shape.
But as Bill shows me, with cross-sections from different tires, vulcanization doesn’t just connect up individual rubber molecules, it connects up everything in the whole tire mixture.
BILL NIAURA: As we cure the tires, we heat it. That vulcanization reaction not only cures the rubber within a compound, it cures across compounds, to connect all of that into one unit. In the end, it’s essentially one molecule.
DAVID POGUE: The whole tire?
BILL NIAURA: It is.
DAVID POGUE: The whole tire is a molecule?
BILL NIAURA: It is.
DAVID POGUE: Well, how is that a molecule?
BILL NIAURA: So, a molecule is a collection of atoms that are chemically attached.
DAVID POGUE: Yeah.
BILL NIAURA: We’ve done that through polymerization. We’ve attached monomers to make polymers, and then, through vulcanization, we’ve attached the polymers to make the finished product.
DAVID POGUE: So, I guess, therefore, since this is all connected, molecularly-linked to molecularly-linked, it is one giant molecule?
BILL NIAURA: It’s beautiful.
DAVID POGUE: Now that I know just how much engineering goes into those giant tire-shaped molecules, I have a new appreciation for the rubber that keeps us all on the road and for the people behind it, like Cara Adams, Director of Race Tire Engineering and Production for Bridgestone/Firestone.
She oversees the race tire operation, including Indy, although interviewing her at the office turns out to be tough.
CARA ADAMS (Bridgestone Americas): One of the things you’re trying to look at with a racecar is aerodynamics. If you think about a tire, it’s the only point of contact between the cars and…
That was a very small, four-inch wide…
This is what you get for trying to film at a racetrack.
DAVID POGUE: Yes, exactly.
So we move to a somewhat quieter place.
We think of car racing as excitement and adrenaline, really cool. How much actual science is there to tires?
CARA ADAMS: Well, there’s a lot of science and chemistry that actually goes in the tires. So, we have engineers that work with physics, to make sure the tires are strong enough; and then we have people that are really smart in chemistry, and they are actually able to design those tread compounds that are running at 240 miles per hour and adhering to the ground. It’s really exciting.
DAVID POGUE: So, are you trying to tell me that the only thing between Mario and me and certain death is chemistry?
CARA ADAMS: Chemistry and physics, absolutely.
DAVID POGUE: Both the natural rubber and synthetic rubber used in tires are elastomers, polymers with elastic properties. They allow tires to be both flexible and durable marvels of engineering. But they have their limits.
So, what if you need an elastomer that can hold it together no matter what you throw at it? Michael Tidd, from the company LINE-X, has invited me here, a lift, in a back lot, in West Springfield, Massachusetts, to see an elastomer that can be a protective coating.
The day begins with a tale of two pumpkins.
Pumpkins seem like they are already blessed with a certain degree of protection.
MICHAEL TIDD (LINE-X Protective Coatings, Ltd.): Nature has provided a pretty good membrane, but I don’t know if it was in the original design to drop it from 50 feet.
DAVID POGUE: Well, let’s do a scientifical test.
MICHAEL TIDD: We could always give it a try and see what happens.
DAVID POGUE: On three, ready? One, two, three!
Well, no surprise here.
It’s a squashed vegetable and a floor wax.
MICHAEL TIDD: That was the control of an uncoated pumpkin, as you would find them in nature, yes?
DAVID POGUE: Now it’s time for a pumpkin covered with Michael’s protective LINE-X coating.
I have to say, it feels a little bit like plastic.
MICHAEL TIDD: It is a lot like plastic. It has characteristics of plastic. However, it is an elastomer, which means it could be stretched, but it will return to its original shape.
DAVID POGUE: Uh, let’s see if this has any better effect. One, two, three!
The LINE-X-coated pumpkin flexes to absorb the impact then springs back into shape. We try a few more household objects.
This experiment is entitled, “When Pigs Fly.”
Can you guess what will happen to the egg when we drop it?
The flower pot’s last moments.
And I run a few comparisons myself.
Finally, bringing out the big guns.
Okay I get it. The stuff is tough. But what’s going on inside that coating? Did the objects survive intact?
Michael cuts open our dropped pumpkin to see the state of affairs.
It’s pumpkin pudding!
MICHAEL TIDD: A lot of damage.
DAVID POGUE: So, the pumpkin is gone, but the coating did just fine?
MICHAEL TIDD: Correct.
DAVID POGUE: But when would you care about not protecting the guts of something but the outside is fine?
MICHAEL TIDD: A lot of times. We will put it on a membrane, such as a wall or a floor, where we’re trying to protect what’s on the other side.
DAVID POGUE: Here’s a test of that idea: this simulated car bomb blows down an exterior wall. But with a coating of LINE-X on the outside and the inside of the wall, it becomes more of a dust-up.
So what is this stuff?
Well, there’s more than one flavor of LINE-X, but the coating on our power pumpkins is the result of a reaction between two ingredients. The first is a highly reactive molecule. At each end of its carbon backbone, there’s a nitrogen, carbon and oxygen group called an isocyanate that acts like a hook to lock onto the second chemical ingredient. It’s a polyamine, a member of a chemical group called resins.
LINE-X heats the two ingredients and feeds them, under pressure, to this sprayer, which mixes them just as they exit. Immediately, the first ingredient hooks on to part of the resin, and all those linkages create long entangled polymer chains, similar to rubber, so that they’re flexible but also much tougher. The resulting elastomer is called a “polyuria,” a cousin to the more familiar polyurethanes.
So, that’s the general idea, though they tweak the chemistry for different applications.
Most of LINE-X’s consumer business is in spray-on truck bed liners, not so much for protecting produce or making kid’s toys last forever.
The main ingredients for LINE-X and synthetic rubber come from fossil fuels like refined crude oil. When we pump oil from the ground, it’s a rich soup of molecules, built around that Tinkertoy® wonder element, carbon.
They come in chains, rings, trees and other shapes. Refining separates those molecules by kind, and in some cases, breaks up bigger ones, turning them into smaller more useful molecules, like gasoline.
Refining also supplies industry with the basic building blocks for another group of synthetic polymers that came to dominate our way of life in the 20th century: plastics.
Today, plastic is everywhere. You can find it in teabags, ribbon, the inside of paper coffee cups, sunscreen, toothpaste, sponges, most clothing, the fish you eat and even salt.
Malika Jeffries-EL plays with the molecular building blocks of plastic for a living. She’s a polymer chemist at Boston University.
So, clearly, there’s all kinds of different plastics, but is there something that unites them all that makes a plastic a plastic?
MALIKA JEFFRIES-EL (Boston University): Plastics are a subset of polymers, in that they are known, not just for having their macromolecular structure, but the processing and mechanical properties that come from a result of that structure.
DAVID POGUE: Like bendy-ness and strength.
MALIKA JEFFRIES-EL: Exactly, strength, exactly, flexibility; rigidity would be another property.
DAVID POGUE: Like rubber, all plastics are polymers, long molecules made up of subunits called monomers. What makes each of these polymer-based materials distinct, are the combinations of the different monomers used to make them.
MALIKA JEFFRIES-EL: For example, this is actually really hard and rigid, and one of the units in here is styrene, and this is polystyrene.
DAVID POGUE: Not hard and rigid at all.
MALIKA JEFFRIES-EL: Not hard and rigid at all. But when you blend in the other molecules, you get different properties.
DAVID POGUE: Wow.
But it’s not all chemistry. Processing can turn the same plastic into very different products.
MALIKA JEFFRIES-EL: And in this case, these were actually molded and blown into this bottle shape. And, in this case, really small fibers were spun from the polymer and then…
DAVID POGUE: Wow.
MALIKA JEFFRIES-EL: …processed to make this.
DAVID POGUE: And it comes out soft and comfortable.
MALIKA JEFFRIES-EL: Comes out soft and comfortable.
DAVID POGUE: Our “Age of Plastics” isn’t very old.
It was this guy, Leo Baekeland, who gets credit for the first fully synthetic plastic. He called it Bakelite, and by the 1920s it had become a big hit, in all kinds of products, from radios to kitchenware to kids’ toys, and coming in a variety of colors.
Malika has offered to whip up some of this landmark plastic. It’s made from two monomers, phenol—a ring of six carbon atoms bonded to five hydrogens, and an oxygen bonded to a hydrogen—and formaldehyde, one carbon atom bonded to two hydrogens and double-bonded to an oxygen.
After dissolving the solid phenol into the formaldehyde solution, Malika adds two acids to start up the process. Then we wait.
MALIKA JEFFRIES-EL: There should kind of be this “aha” moment, and it should just go.
DAVID POGUE: Are you saying it’s going to harden?
MALIKA JEFFRIES-EL: Yeah. It should get cloudy, and polymer should come crashing out. I feel like it’s getting pinker, which is an indication that the chemistry is changing.
DAVID POGUE: Oh, did you see that? Like, instantaneously.
Right before our eyes, the phenol and formaldehyde molecules link up, giving off water molecules while creating long polymer chains.
You made plastic.
Look at that: genuine, crusty, hard, hard plastic.
MALIKA JEFFRIES-EL: So, this is an example of a thermoset plastic. Once it’s set into place with heat, you can’t reform it or reshape it with additional heat.
DAVID POGUE: Oh, okay, so unlike a plastic drink bottle…
MALIKA JEFFRIES-EL: That’s right.
DAVID POGUE: …you can’t melt this down and reform it into something else.
MALIKA JEFFRIES-EL: No.
DAVID POGUE: This is Bakelite now and forever.
MALIKA JEFFRIES-EL: That’s stuck like that forever. Yep.
DAVID POGUE: In a thermoset plastic like Bakelite, the bonds between the polymer chains are extremely strong. By the time you’ve applied enough heat to break them, the chains themselves have decomposed, so you can’t re-melt thermoset plastics or reshape them for recycling.
But not all plastics are thermoset. There’s nylon, the first commercially successful plastic that wasn’t. It came to public attention at the 1939 World’s Fair as a substitute for silk in women’s stockings, and its importance grew during World War II.
At the time, the main source of silk for parachutes was America’s enemy, Japan, so the military recruited nylon as a replacement.
Malika offers me some firsthand experience making nylon.
If you want to make nylon, don’t you need, like, a factory?
MALIKA JEFFRIES-EL: Well, if you want to make a lot of nylon, yeah, then you’re going to need a factory. But if we’re just going to do a demo, we’ve got to make a little bit of nylon, and we can do it in a little beaker.
DAVID POGUE: All right, like for mouse stockings?
MALIKA JEFFRIES-EL: Yes, exactly. To do this we’re going to mix together two chemicals.
DAVID POGUE: There are lots of variations on nylon. Our two key components will be two molecules that are simpler than they sound, hexamethylenediamine and adipoyl chloride.
Since they each have a six-carbon chain, we’re making what’s called “nylon 6.6”
MALIKA JEFFRIES-EL: So, the first thing we’re going to do is we’re going to add the hexamethylenediamine.
DAVID POGUE: So, mostly colored water.
MALIKA JEFFRIES-EL: Mostly colored water, with some cool organics in there. And then we’re going to add our organic layer of the adipoyl chloride solution. And because the density of this is less than that of the water, it should float on the surface of the water.
DAVID POGUE: Kind of like oil and vinegar.
Where the two liquids meet, the molecules of the hexamethylenediamine and adipoyl chloride link up, one after another, releasing hydrogen chloride as a gas.
Malika gives me the honor of pulling the newborn nylon polymer out of the beaker, and as more of the two liquids come into contact, they make more nylon.
Do you have a ladder, Malika? Look at that, freshly baked, free-range nylon. Amazingly, this really is a junior version of how bulk nylon is manufactured.
All right, anyone need stockings?
Unlike Bakelite, nylon is an example of a thermoplastic, which we can reheat and reform. That’s the basis of some plastic recycling.
Malika wants to show me one more example.
And this time what are we going to make?
MALIKA JEFFRIES-EL: So, for this demonstration, I thought I would show you how we make polyurethane foams.
DAVID POGUE: And what do we use polyurethane foam for in the world?
MALIKA JEFFRIES-EL: Polyurethane is used in, like, seat cushions and also insulations. You think about blown foams and things like that.
DAVID POGUE: Oh yeah, “E.T. blown foam.” Yeah, I remember that.
There are two key reactants. First up is a type of molecule with an oxygen-hydrogen hook at either end. Aside from its role in polyurethanes, this one shows up in paintballs and laxatives, too.
The other reactant we’ve already met at LINE-X,.that carbon-backboned isocyanate molecule with the nitrogen/carbon/oxygen hooks at either end.
MALIKA JEFFRIES-EL: And we stir those together. And so, you can already see, it’s starting to react, because it’s starting to get milky, and it’s starting to grow. And you can see it’s rising up a little bit.
DAVID POGUE: The two molecules begin to link up to form a polyurethane polymer. At the same time, one ingredient also reacts with some water-generating carbon dioxide gas. That’s what causes the bubbling and, ultimately, the foam, when the polyurethane grows rigid.
I know I’m tacky, but…Oh! And the cup’s entombed inside there.
MALIKA JEFFRIES-EL: Yeah, the cup is gone.
DAVID POGUE: Pretty cool, but it’s just a start, because “when in foam, do as the foam-mans do?”
Years of snowman training.
We’ll open a 529 plan; we’ll buy some diapers.
MALIKA JEFFRIES-EL: Nothing but the best for you. He has your smile.
DAVID POGUE: At this point…
MALIKA JEFFRIES-EL: Polycarbonate…
DAVID POGUE: …you are probably getting the idea…
MALIKA JEFFRIES-EL: …polyethylene terephthalate, PETE…
DAVID POGUE: …that there are lots of different plastics,
MALIKA JEFFRIES-EL: …polyvinyl chloride, P.V.C.…
DAVID POGUE: …each made out of polymers…
MALIKA JEFFRIES-EL: …these are examples of polyamides, commercially known as “nylon.”
DAVID POGUE: …constructed sort of the same way…
MALIKA JEFFRIES-EL: Polystyrene…
DAVID POGUE: …but out of different subunits…
MALIKA JEFFRIES-EL: …polypropylene, P.P.…
DAVID POGUE: …to obtain very different material properties.
MALIKA JEFFRIES-EL: …low-density polyethylene, L.D.P.E.…
DAVID POGUE: And then if you start throwing in additives and fillers…
MALIKA JEFFRIES-EL: …Polyvinyl alcohol, P.V.A.…
DAVID POGUE: …like colorants…
MALIKA JEFFRIES-EL: …high-density polyethylene, H.D.P.E.…
DAVID POGUE: …flame retardants, glass or carbon fibers…
MALIKA JEFFRIES-EL: …Polymethyl methacrylate, P.M.M.A.…
DAVID POGUE: …you end up with tens of thousands of “grades” of plastic…
MALIKA JEFFRIES-EL: …polyoxymethylene, POM.
DAVID POGUE: …each tailored for a specific purpose, which has created the problem: what do we do with them when that job is finished?
Mostly, we throw them out. Ninety-one percent of all the plastic we make ends up in landfills or burned or just escapes into the environment. The remaining nine percent is recycled.
But first, the plastic has to be carefully separated by type, those recycling number symbols. Any mix-up there can contaminate any otherwise reusable plastic, rendering it worthless. And there aren’t many places willing to do that separating work.
In 2018, China stopped accepting shipments of bulk unsorted plastic from the U.S. or anywhere else in the world. With the economics of recycling in turmoil, lately the discussion has shifted to single-use plastics, about half of all the plastic we produce. Much of it is food related.
To learn more, I travel to the University of Georgia, to meet Jason Locklin, a chemistry professor and the director of its New Materials Institute.
Well, thanks for meeting me here, Jason. I brought you breakfast.
JASON LOCKLIN: All right.
DAVID POGUE: Well, breakfast and a bag of single-use problems.
JASON LOCKLIN: This is called a clamshell container. Less than one percent of all polystyrene is recycled globally. If this makes its way into the landfill, which is exactly where it’ll go, it’ll persist there forever.
We have a plastic straw.
It’ll stay there for hundreds, if not thousands, of years. Is that really a way to design packaging, to have a material that you use for 10 seconds, and then it goes to a landfill for a thousand years?
DAVID POGUE: Even packaging that looks recyclable, like paper takeout containers, may not be because, well, they have to hold food.
JASON LOCKLIN: If you put food into a paper towel, what happens to it?
DAVID POGUE: It’s going to get soggy and fall apart.
JASON LOCKLIN: Exactly. So, in order to make this a takeout container, we have to coat it with plastic. It essentially prohibits our ability to recycle it.
DAVID POGUE: Wow. So, is there any solution to that problem?
JASON LOCKLIN: So, here’s just an example. If you pull the film off that plastic, this is about what it looks like, but this film is made out of a material called P.H.A.
DAVID POGUE: P.H.A.s, polyhydroxyalkanoates, are a type of plastic produced from polymers harvested from certain bacteria. For the bacteria, the polymers are essentially, kind of, like fat, a way to store energy. But because they come from bacteria, P.H.A.s have a huge advantage. They’re completely biodegradable.
Researchers in Jason’s lab are among several scientists and companies around the world developing a P.H.A.-based coating that could replace the traditional plastics that often make our takeout boxes unrecyclable, although the cost of P.H.A.s still needs to come down to be competitive.
And, finally, what does Jason think about that eco-friendly-looking green bag I brought breakfast in.
JASON LOCKLIN: This is a great example of some absolute “green washing.” “Biodegradable.” You see it in big, bold claims. If you read the fine print, it says 49.28 percent biodegradation in 900 days under non-typical conditions, no evidence of further biodegradation.
DAVID POGUE: Come on. That sounds like a total scam. But look at the size of the green leaves. That makes me feel good about myself. It has a leaf on it.
JASON LOCKLIN: This is simply adding to the confusion of people like yourself, people in the general public that want to do the right thing. This makes it really difficult to know exactly what to do.
DAVID POGUE: Oh! Did you see that?
When it comes to creating new materials, we may be the victims of our own success.
It was like “poof!”
We’ve invented some that are useful and so durable that they last more than a human lifetime, and now we’re drowning in them.
But attitudes are changing, with engineers and chemists harnessing biology to combat the problem. In the end, the human ingenuity that helped create the current crisis may help solve it, as well…
The only thing between me and certain death is chemistry?
…as we move Beyond the Elements.
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This program was produced by WGBH, which is solely responsible for its content. Some funders of NOVA also fund basic science research. Experts featured in this film may have received support from funders of this program.
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- Cara Adams, Mario Andretti, Eric Goldschmidt, Malika Jeffries-EL, Laura Kocsis, Jason Locklin, Eric Meek, Bill Niaura, David Pogue, Michael Tidd