Kind: captions
Language: en
What happens if I heat up this rubber
band? When you heat materials like glass
or plastic, the atoms vibrate faster.
They get slightly farther apart and this
reduces intermolecular forces. So, the
material gets weaker. Under tension, it
stretches. But when I heat up this
rubber band, the opposite happens. It
actually pulls more strongly. The rubber
band contracts and the weight goes up.
So, why does this happen? Well, rubber
is unlike any other material. It's
waterproof. As it's breaking, it
actually becomes tougher, and it can
stretch up to 10 times its length and
bounce back, no worse for wear. These
properties have made it essential for
modern life. It forms the tubes and
seals that carry our gas and water, the
belts that drive our motors, and the
tires on our cars, trucks, and planes.
Even trains use rubber in their
suspension systems. It's a perfectly
engineered material, but we didn't
invent it. All of our most durable
rubber still comes from a single natural
source. This tree, it's a source at risk
of being wiped out. And if that happens,
the results could be devastating.
>> You're talking about a complete global
societal meltdown.
>> This could be considered a national
security issue. You wouldn't think that
we're so dependent on this thing.
>> Well, we are. And most people don't know
that. They're waiting for a disaster to
happen.
>> Rubber comes from the Brazilian rubber
tree. As early as 1600 BC, Mesoamericans
cut the bark to release this milky white
liquid, now known as latex. They noticed
that if they let it dry, it turned into
this stretchy waterproof solid lump. To
see this in person, we sent Veritassin
producer and mechanical engineer Henry
van Djk to the Akran Research and
Development Laboratory where they
specialize in all things rubber. In just
all these racks, even though they look
solid, they're all flowing right now.
Really?
>> If you look behind one of these racks,
you can see these are actually dripping.
>> Oh, wow.
>> They're flowing slower than we can
perceive.
>> Unprocessed rubber is not the rubber
we're used to. it slowly flows and can't
maintain its shape. So, how do you get
this weird material in the first place?
Well, just underneath the bark are
special tube-like cells that carry the
latex. Floating around inside are lots
of isopentinyl pyrophosphate or IP. This
is the building block or monomer of
rubber. In fact, IP is found everywhere
in nature, including inside you.
>> Huge amounts of us are dependent upon
that little molecule. We we make short
chain rubber in our livers. It's called
dol. You're busily making rubber. You
are a rubber factory.
>> How? What do you mean? Why why am I
making rubber? Uh
>> it's essential for for for cell
membranes.
>> Special builder enzymes grab these
monomers to build this long chain with
over 10,000 monomers. They build a
polymer. This is rubber.
>> So I get students to think about if this
is a carbon atom and then I've got my
next carbon atom along the chain next to
it. Yeah. And then I've got my next
carbon atom. How many do we have to make
up the whole length of the chain? Well,
we've got tens of thousands, hundreds of
thousands of carbons along the backbone.
You start going kilometers in distance
from end to end. If each atom is the
size of this tennis ball,
>> but the polymers aren't stretched out
from end to end like that. Instead,
they're all coiled up. If you imagine
the room that I'm in right now and I had
the first ball here in the middle, the
chances of the end of the chain leaving
this room is quite small. So after
you've dried out the latex, you're left
with raw rubber, a jumble of all these
polymers. And this is why it's flowing
because over time all those polymers
slowly slide past each other. Now when
you pull on the rubber and let go, it
bounces back. So why is this?
At room temperature, rubber's polymer
chains are constantly vibrating and
bumping into each other. And other
smaller molecules like air molecules or
trapped water molecules also jostle
around and bump into the chains. Now,
when you stretch rubber, these chains
straighten out. But as you're doing
this, those chains are still being
bombarded by these smaller molecules. So
when you release that stress, there's
nothing holding those chains aligned
anymore. And the constant bombardment
from the smaller molecules and the other
chains kinks those chains back up. So
the rubber snaps back to its original
size. And if you heat the rubber up,
well then everything is vibrating faster
and so the chains are going to get
kinkedked up even more. So the rubber
pulls back stronger. This is why when
you heat up rubber, it shrinks. Rubber
bands. Fascinating to think that when
they sitting on an old package of papers
for a long time holding those papers
together, it's done by a perpetual
pounding pounding pounding of the atoms
against these chains to hold trying to
kink them and trying to kink them. But
there's also another reason why rubber
is so stretchy. If you zoom in on a
chain, you'll see that the monomers are
attached to each other on the same side
of the double bond. This is called cis
attachment and it affects how the chain
folds. On each monomer, there are three
single bonds that can rotate to be at an
angle or in line. But these carbons with
two hydrogens take up a lot of space.
So, it's favorable for at least one of
these bonds to be at an angle. That
makes the polymer wiggle in and out like
a folded ribbon. So, when you pull on a
piece of rubber, first all the polymers
line up, but then each chain also
unfolds. The wiggle makes rubber extra
stretchy. But this state is very rare.
All three bonds lined up is only one
possible arrangement for any monomer.
And one polymer usually has thousands of
monomers. So after you release the
stress, the chain goes from an
improbable state, completely aligned, to
a more probable one with wiggles. The
chain itself bounces back. This is where
rubber gets its elasticity from. So
natural rubber straight from the tree is
already stretchy. It's also waterproof
since all those chains are just a bunch
of carbon and hydrogen atoms which are
hydrophobic. But as we've seen, it
eventually loses its shape. Plus, if you
stretch it too much, it breaks quite
easily. So, we need to do more to get
the rubber we're used to today. Early
Mesoamericans improved the rubber
slightly by mixing the latex with juice
from the tropical morning glory, a local
flower. And they used this to form
sandals, bottles, and balls.
But for the next 3,000 years, to the
rest of the world, rubber was little
more than a curiosity. Then in 1770, a
piece of natural latex made its way to
English chemist Joseph Priestley, and he
took this piece and used it to try to
erase pencil marks. He noticed that it
easily quote rubbed them away. In the
following decades, people started
exploring other applications. Up until
then, people used to waterproof fabric
with oil, wax, or tar. But some oils
were extremely flammable and prone to
spontaneous combustion, and wax or tar
would eventually crack with movement.
Similarly, there were no real good
flexible materials at the time. Leather
was the best option, but it had little
give. Rubber had the potential to fix
all those problems. So, for the next 50
years, the use of rubber exploded. In
England, people made waterproof
clothing, and by the late 1820s, the
rubber craze hit the US when everyone
wanted their own pair of Brazilian
waterproof boots. Factories sprang up
all across the country to make new
rubber products, including one New
England factory called the Roxbury India
Rubber Company. In the spring of 1834,
things were looking great for the
company. The previous fall, they had
sold over $20,000 worth of goods, rubber
coats, shoes, and the like. But as the
summer came around, problems started to
emerge.
>> They used to rubberize the fabric to
make it water resistant, which was fine
until you sat down on a wooden bench on
a hot day and you stuck to it.
>> See, all natural rubber has a critical
weakness. It's extremely sensitive to
temperature changes. It melts when it
gets too hot, and it freezes and becomes
brittle when it gets too cold.
This made the coats and shoes
practically useless during the hot
summer, so customers returned their
items on mass. Then things went from bad
to worse. One day, the Roxbury manager
visited the warehouse. When he opened
the door, he didn't see their newest
products. Instead, he was met with a
foul smell and a molten, gooey mess that
covered the entire warehouse. In fact,
when we ordered some raw rubber, we were
in for a similar nasty surprise. A
that is disgusting.
>> The summer heat melted their rubber
products and they started rotting. The
sludge stank so badly the manager had
the employees secretly bury it at night.
But later in that horrible summer, the
manager got a visit from a man named
Charles. Charles previous business had
gone bankrupt and he was deeply in debt.
He stumbled upon a rubber life preserver
and he thought he could make a better
valve. He pitched the Roxbury manager on
his new design, hoping to pay back his
lenders. The manager was impressed, but
couldn't buy Charles's work. He showed
Charles the warehouse full of rotten
rubber. Rubber had potential, but in its
current form, it was just too
problematic. However, he said if anyone
could figure out how to make rubber
stable in a wider temperature range and
non-sticky, well, then that person would
stand to make a ton of money. So,
Charles was determined to become that
person.
But when he returned home to start his
experiments, he was met by an angry
creditor who threw Charles into DTOR's
prison for unpaid loans. Charles asked
his wife to bring him raw rubber and her
rolling pin. There, in his jail cell, he
started adding different compounds into
raw rubber. If rubber was naturally
sticky, then why couldn't you add dry
powders to absorb that stickiness? So,
he tried adding magnesia, and he got a
smooth, non-sticky rubber. But over
time, the stickiness returned. After his
release, he tested the wear and tear of
his rubber compounds by walking around
in all rubber outfits. His hands were
always covered with gum elastic. He
playfully said that the only way to rub
rubber off was by rubbing more on. Some
mixtures showed promise, but eventually
they'd all rot into a sticky mess. So he
kept borrowing money to fund his
experiments. But because his mixtures
all eventually failed, he ended up in
DTOR's prison so many times that he
jokingly called it his hotel. But
Charles refused to give up. When a
friend told him, "Rubber is dead."
Charles replied, "I am the man to bring
it back."
In the summer of 1838, he met Nathaniel
Hayward, a businessman and inventor.
Hayward had done his own experiments
with rubber. At one point, he laid out a
sheet of rubber and sprinkled on sulfur
powder. And when he let this sheet set
in the sun, he noticed that it hardened
and had a smooth and non-sticky surface.
But eventually, it would still melt in
the heat and freeze in the cold. He
offered his process to his previous
company, but it was so horribly smelly
that they rejected it. But Charles saw
the possibilities, so he helped Hayward
get a patent, and then he bought it so
that he could use it in his own
experiments.
Then one day in the winter of 1839,
Charles accidentally dropped a piece of
rubber mixed with sulfur on a hot stove.
When he went to scrape it off, he found
that instead of melting, it had charred
and hardened.
His daughter later said, "As I was
passing in and out of the room, I
casually observed the little piece of
gum which he was holding near the fire,
and he was unusually animated by some
discovery which he had made. He nailed
the piece of gum outside the kitchen
door in the intense cold. In the
morning, he brought it in, holding it up
exaltingly. He had found it perfectly
flexible as it was when he put it out.
So, he had made a new rubber with
completely different properties, one
that seemed to be temperature resistant
and much stronger. In fact, we're going
to test out unprocessed rubber against
rubber processed in this way.
>> Okay, so this is unccured rubber and I'm
going to see how I how far I can pull
it.
>> Uncured rubber is very soft and
stretches really far before easily
breaking.
It's going to hurt.
>> We need to cure it.
>> What does it smell like to you?
>> Smells like a barbecue.
>> That smells like a barbecue.
>> The smell of rubber does not seem to be
natural.
>> Like it smells very chemically like it
was made in the factory.
>> Yeah. So, when I was in the factory and
I saw the natural rubber, it smelled
just like like a barbecue. The reason is
they take the sap from the rubber tree,
which is latex, and then they smoke it.
>> They're smoking it?
>> Yeah.
>> Like you'd smoke some salmon?
>> Yeah.
>> They smoke the rubber sheets to get rid
of excess moisture and to preserve it by
getting rid of the bacteria. This gives
most natural rubber a sort of brownish
color.
>> So, step one, add the rubber one at a
time.
>> Next, you add several powders, including
sulfur.
Everything is mixed and heated to get a
much stronger rubber.
>> Just pull it straight off.
[Laughter]
That's what
Yeah. We
>> pretty tough.
>> It is tough. Now, yeah. Now it's like
wicked hard. Yeah. Now, at 393
kilopascals, the unccured rubber broke
after extending just under 900% of its
original length. At the same stress, the
cured rubber had only stretched around
5%. It eventually broke at 14.1
megapascals after stretching nearly 600%
of its original length. So, what was it
about sulfur and heat that changed the
properties so dramatically?
Well, chemically, sulfur powder is just
rings of eight sulfur atoms. On the hot
stove, the sulfur ring broke apart into
smaller pieces. And now, those sulfur
atoms or sulfur chains have free bonding
sites. So they look for places to
attach. What likely happened is they
grabbed onto a carbon atom from a rubber
chain, breaking its double bond and
attached itself. Then with another free
bonding site, it grabbed onto a carbon
atom from a different rubber chain,
breaking its double bond and linking the
two rubber chains together. This
cross-linking forms flexible bridges of
one, two, or even more sulfur atoms in a
row. Now think about what this does to
the rubber. Instead of each chain being
loose and slippery like spaghetti,
they're tied together in a flexible but
connected network. So now if rubber sits
out in the sun on a hot summer's day,
the tight bonds prevent it from melting.
And in the cold, the cross links make it
harder for the rubber to fully freeze,
so it's less brittle and harder to
break. And when you pull on the rubber,
the chains stretch just as before. But
as you release it, everything returns to
its original position because it's all
connected. So the cross links make the
rubber stronger, more resistant to
temperature changes, and more elastic.
In fact, by tweaking the number and
properties of these cross links, you can
change the properties of rubber. If you
have a lot of cross links, all the
rubber chains are bound tightly
together, so the rubber becomes harder
and stiffer. Great for things like shoe
soles and tires that need to be durable,
but still a little flexible. If you have
shorter cross links, each link is harder
to break, so the rubber is more
resistant to heat and weathering. This
is useful for seals and insulators. And
if you have longer cross links, the
rubber chains can move more freely, so
you can stretch it more before it
breaks. That's perfect in the medical
field for soft and flexible
applications.
So, the cross links are essential to
stabilizing rubber.
When Hayward sprinkled sulfur powder on
rubber sheets, the heat from the sun did
cause some cross linking, but only on
the surface. When Charles kneaded in
sulfur and then heated the entire
mixture, the cross lengths grew
throughout the entire sample. So now the
results were much better. Eventually
this process was called vulcanization
after the Roman god Vulcan who was
associated with heat and sulfur in
volcanoes. Over the next 5 years,
Charles perfected his method of
vulcanization and then he patented it in
1844. With this, he transformed rubber
from a curiosity into a material of
endless possibilities. Little did he
know that he actually wasn't the first
to discover it. The Mayans or the Aztecs
used like created rubber. Were they also
vulcanizing rubber or was this the
>> They actually were.
>> In fact, Charles discovery was very
similar to what the Mesoamericans have
been doing for thousands of years. They'
taken the juice from the morning glory
which contained sulfur, mixed it with
natural latex, and then by laying it out
in the sun, it would heat up and
actually naturally create the cross
links that he discovered in his kitchen.
>> Why did the Europeans like why did they
have to reinvent the whole thing? Why
did they just ask?
>> Well, they hadn't even noticed, I don't
think.
>> No.
>> In the decades after Charles's
invention, tons and tons of products
were invented or improved with rubber.
>> Richards makes bold claim he could cross
Pacific in this outfit. The inflatable
bicycle tire arrived in 1888, the first
rubber gloves for medical purposes in
1890, and the first car tire in 1895.
And all of this was thanks to Charles
invention.
But despite almost single-handedly
transforming the rubber industry, he
never made much money. I mean, he spent
thousands of dollars defending his
inventions in patent disputes. And when
he passed away in 1860 at the age of 59,
he was over $200,000 in debt. That would
be around 7.7 million today. 38 years
later, American entrepreneur Frank
Sebring founded a tire company and
decided to name it in honor of Rubber's
inventor, Charles Goodyear. Today, the
Goodyear Company makes $18.9 billion a
year in revenue, and it's the third
largest tire manufacturer in the world.
For the past h 100red years, tires have
consumed the most natural rubber out of
any application. But vulcanized rubber
alone isn't strong enough and would wear
down quickly, lasting only around 8,000
km. So in the early 1900s, car and tire
companies started experimenting with
additives, including something called
carbon black.
>> Start with natural rubber, we got carbon
black reinforcement,
>> which is going to add the cross linking.
>> This doesn't do the cross linking. No,
it doesn't. So this is the reinforcement
and filler.
>> This makes it durable and resilient.
>> Nowadays, passenger car tires last about
100,000 km. Carbon black is what gives
them their color and durability.
>> But carbon black has another benefit. It
conducts electricity.
>> That's hugely important because as
you're driving down the road, you're
charging up the vehicle. If you didn't
dissipate that static charge, then you
get a shock when you earth the car, when
you touch the car. But later, some
companies wondered if they could reduce
rolling friction by using a different
additive. So they tried silica instead,
making a whitish looking tire. But
silica is a poor conductor and rubber
itself is an insulator. So now as the
car moved, it would slowly build up
charge. As you go to refuel the car, you
have a highly charged static electricity
charged vehicle. You put an earth
conductor, the fuel hose into the tank,
you create a spark in the tank, car
explodes. There's a very vital uh
characteristic of tires is that they
should be conductive. The other benefit
is if you're in a if you're in a
thunderstorm and you're struck by
lightning, the lightning will hit the
car. It will act as a Faraday cage. It
will completely protect you and it will
dissipate down to the ground. So, people
have stuck to using carbon black for
most of the tire and only a little
silica in the treads.
And since Goodyear's invention, we've
made over 70 billion tires. If they were
stacked on top of each other, they could
go to the moon and back 21 times.
And almost all of these tires needed
natural rubber. But fueling the rubber
boom came at a price, especially early
on. In the late 19th century, the Amazon
region supplied over 90% of the world's
rubber. But wild rubber trees were often
separated by hundreds of meters. So to
keep up with growing demand, rubber
barons began to exploit natives, killing
roughly 40,000 people in the Pudomeo
region alone and likely over a 100,000
across the wider Amazon region between
1879 and 1911. The humanitarian activist
Roger Casease casement said that it was
first called India rubber because it
came from the Indies and the earliest
European use of it was to rub out or
erase. It is now called India rubber
because it rubs out or erases the
Indians.
>> Is one of the most appalling instances
of genocide and sickening ill treatment
of native peoples.
>> But other countries like England weren't
happy with Brazil's monopoly. So in
1876, the biopirate Henry Wickham
managed to smuggle 70,000 rubber seeds
back to England. The British Empire
planted these seeds all over Southeast
Asia, which had a similar climate. Only
now, instead of having just a few rubber
trees here and there, they made farms of
acres and acres of nothing but rubber
trees. These plantations produced far
more than the Amazon. Brazil's share of
the rubber supply dropped from over 80%
in 1907 to 1.6% at 6% just over three
decades later. By the mid1 1930s, over
90% of all rubber came from the British
colonies in Southeast Asia.
And 2/3 of that rubber went into making
car tires. One of the largest car
manufacturers at the time was Ford,
which made an average of 1.5 million
cars every year. And Henry Ford wasn't
comfortable with England's monopoly. So
in 1928 he bought 10,000 square
kilometers of land from the Brazilian
government to build a utopian town. He
called it Fordia. It had Cape Cod
cottages, a hospital, swimming pools, a
golf course, and little red fire
hydrants. It was an American city in the
middle of the Amazon. It could house
10,000 people, all working to plant
millions of rubber trees.
>> Ford Plantation is a successful
enterprise, a tribute to skill and
science.
But in the early 1930s, things started
to go wrong. Every morning, the workers
would wake up, walk to the line of
rubber trees, and they'd notice black
spots.
Just a few at first, little specks on
the unders sides of the leaves, like
flexcks of soot. But by the afternoon,
they'd spread to cover the leaves
entirely. And the next morning, the
leaves were falling off. Shortly after
that, the tree died. Every day another
row of trees was infected and dying.
>> People who've seen it say it looks like
a firefront. You have the infected trees
and it's green on one side and black on
the other. And you see that black line
move day by day. You you could virtually
watch it move, leaving dead trees behind
it.
>> The trees were infected by the South
American leaf blight, a fungus native to
South America. This blight ruined the
3.6 6 million rubber trees from Ford's
plantations by the early 1940s, turning
it into a disaster.
When planting his rubber trees, instead
of separating them by hundreds of meters
like they were in the wild, he planted
them several meters apart, 200,000 of
them.
>> They're all touching. The roots are
touching, the leaves are touching, the
branches are touching, and so it's just
like a plague run straight through the
plantation. Ford tried relocating the
project to a town downstream, Belterra,
planting another 16,000 acres with
rubber trees, but these two all died.
Ford's son eventually abandoned the
project in 1945.
The Ford Landio buildings still stand in
Brazil, abandoned, and to this day,
there is no cure for the leaf blight.
The blight is so fatal to rubber trees,
they can't grow in plantations in their
native country. That's why South America
makes up less than 2% of the rubber
supply. Over 90% comes from Asia, which
is why it is so essential to prevent the
spread of the leaf blight to Southeast
Asia.
Virtually all of the rubber trees in
Southeast Asia came from those seeds
Henry Wickham stole, and newer trees are
just clones of the old ones. So, the
farms are essentially just one big
monoculture. As a consequence of that,
we are particularly prone to potential
outbreaks of funguses and things like
that. If you get a fungal infection in
Malaysia, then you would end up
dramatically reducing global production
of rubber.
>> So, what's the outcome if we were cut
off from rubber?
>> If SAL gets established in Southeast
Asia and you lose natural rubber, then
you're talking about a complete global
societal meltdown. You're left now with
making synthetic rubber tires at the
most. Worst case, they can't make them.
You can't make a truck tire. You won't
have any airplanes. But the real
potential is is urban famine. Over 50%
of the world's population is in cities.
How will you move food into the cities
to feed them?
>> But something like this did wipe out a
large part of the rubber supply just 6
years ago. In 2019, two different
diseases jumped from palm trees to
rubber trees in Thailand. In 6 months,
these diseases had spread across seven
countries and a million acres of trees.
And the next year saw a 10% drop in
production.
>> And the only reason it didn't destroy
more trees was because of a different
outbreak that we all remember.
>> CO comes in early 2020. It stopped the
spread of these diseases as as a
byproduct of trying to stop the spread
of CO. If CO hadn't hit there, how far
would that have gone? How many more
millions of acres would have in effect
been killed or seriously compromised by
these two leaf bllightes?
>> Granted, it's hard to predict what would
happen if we ran out of natural rubber.
Some say the impact could be
catastrophic. Grounded planes, failed
railways, even famine. And any
disruption to the oil supply chain would
send shock waves through synthetic
rubber products. But oil is such a
polarizing and politically charged topic
deeply tied to global power struggles
and hidden incentives that it's hard to
know what's truly at stake. That's why
we specifically asked Ground News to
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roughly 20% of the world's oil. What
happens when they threaten to close it
amid US strikes on their nuclear sites?
Well, on the topic, USA Today ran oil
hits five-month high after US strikes
key Iranian nuclear sites. But the New
York Post led with US stock surge after
restrained Iran attack on US base. One
headline warned to a looming energy
crisis, the other stock market rally and
strategic restraint. It's the same
event, but completely different
conclusions. In times of uncertainty,
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I'd like to thank Ground News for
sponsoring this video. And now back to
rubber.
We take Natural Rubber for granted in a
huge number of different products. So if
you take a typical car, there's
something close to 250 to 300 rubber
components within the car. You would
have a nightmare trying to re-engineer
all of those out of synthetic materials.
If we were to lose natural rubber and
just rely on synthetic rubber, would it
still be possible to do those
applications?
>> So, this has happened in the past. If
you think about it, all of these
synthetic polymers come from that
initial thought process that we can't we
can't get natural rubber. We have to
create other stuff. It's a national
security issue.
>> That's wild.
>> You're just like, "Oh, it's a tire." But
think about it. If you don't have tires,
you can't move a military.
>> Yeah. Yeah,
>> the obvious question is if natural
rubber is so great, why can't we just
replicate it in the lab? And that's the
exact thing that the US tried when
during the Second World War, Japan cut
it off from roughly 97% of the world's
natural rubber supply.
>> Modern wars cannot be won without
rubber. What then happened was an
enormous investment by the US equivalent
to 11.1 billion in today's terms uh into
synthetic rubber and growing uh
alternative natural rubber crops. That's
roughly a third of the Manhattan
project. It was a complete gamble, but
the four big US tire companies were able
to improve and manufacture a synthetic
rubber called styrene butadene in less
than 3 years. Unlike natural rubber,
styrene butadene is made from two
monomers, roughly 25% styrene and 75%
butadene. Both usually come from crude
oil refining. The monomers are dispersed
in water and combined into long chains
in a random arrangement. Then the rubber
is vulcanized. Now compared to natural
rubber, it doesn't wear down as quickly
under friction, but it has a much lower
tensile strength. In 1942, the US used
99.6% natural rubber and 0.4% synthetic.
But in 1945, it was practically reversed
at 14% natural and 86% synthetic.
Now almost 70% of all rubber consumed is
synthetic. And the most common one is
still styrene butadine.
But there are some things that natural
rubber is just better at. If you think
about airplane tires, it's absolutely
incredible that they're up there at
degrees below zero before they start to
come into land. And then you've got this
huge weight of the airplane on these
dinky little tires that increase in
temperature enormously over an
incredibly small space of time. And only
natural rubber can do it. So airplane
tires are essentially 100% natural
rubber and you can't land if you've got
synthetic in the tire.
>> So what can natural rubber do that we
just can't replicate?
>> Okay. What I want you to think about is
you start to stretch it. This first
movement hardly it's very easy to
stretch that bit.
>> That first bit very simple. Now think
about how much force you're using to
continue to stretch it.
>> Yeah. It gets harder.
>> It gets harder and harder and harder and
harder.
>> Yeah.
>> And then eventually you'll get to a
break point.
>> Yeah.
>> But what's happening, why it's getting
harder is that the rubber is getting
stronger as you stretch it. As you
stretch the polymers, they start to
align and stick together through weak
intermolecular forces called Vanderwal's
forces. When they are packed tightly
enough, the polymers freeze together in
thin sheet-like crystals aligned in the
direction you stretch. And as you keep
pulling, more and more polymers join the
crystal structure. Each crystal acts as
a new cross link, making the rubber
harder and stronger. That ability to
form crystallites prevents tear. Um, so
if you have crack propagation, it hits a
crystal and can't go any further.
>> In a sample without a crack, the stress
is evenly distributed. But if there is a
crack, more load flows right to the
edge, so the rubber stretches more. That
area forms more crystals, so it becomes
harder to break. The crystals stop the
crack growth until a threshold is
reached, and then it breaks. This is
what makes natural rubber so durable.
It's self-reinforcing under stress,
stopping cracks in their tracks.
Crystallization is what makes natural
rubber so good for tough applications.
The plane can weigh 5 600 tons.
So if you think about that, you've got
a, you know, each tire is taking 20 tons
and it's coming from a very cold
temperature up there. Yeah, it's -50 -
60 depending exactly how high you've
been flying. And you go from zero
rotational speed to quite fast, very
fast. You get generate a lot of
frictional heat really quickly as well.
There's a reason why they make tires for
planes out of natural rubber and that's
because it's really demanding
application and the crystallization
helps a huge amount preserve those tires
and help them last. One study notes that
experiment has shown that no detectable
crack propagation occurs in rubber
undergoing crystallization until the
stress is so high as to generate abrupt
catastrophic fracture.
[Music]
>> Oh,
that was fast.
>> And then eventually you'll get to a
break point and yeah, you finally
overcame it.
>> When you pull on a rubber sample, you're
applying a stress. The polymers realign
and the wiggle unfolds. So the piece
deforms and gets longer. The per unit
change in length is known as strain and
we can plot this on a stress strain
curve. Lots of materials are elastic
around low stresses. You stretch it a
little and the spacing between atoms
changes. But when you remove the force,
it goes back to its original shape. But
eventually you hit a stress where there
is permanent deformation. That's called
the yield point. The material can't go
back to the same shape after. And if you
keep going, it will fracture.
But the stress drain curve for rubber is
a little weird. It starts out stretching
very far with very little force. That's
the easy part. But then as you keep
pulling, the stress shoots up really
fast.
>> So stretch stretch it fast. What do you
notice?
>> It's a little warm. Maybe
>> it's hot. It's gone up in temperature by
10°.
>> That section where it gets really hard
to pull it any further and it gets
hotter, that's right where rubber starts
to crystallize. The rubber warms up
because as those new bonds form, they
release a bit of energy as heat. Then if
you keep stretching it, you get to the
point where the crystal can no longer
hold it and it breaks. But something
strange happens if you stop right before
that fracture point. Then the rubber
bounces back, but on a lower curve.
>> Keep it stretched. Keep it stretched.
Wiggle it around.
>> Now relax it.
>> Touch it to your lips. What do you got?
Now it's like much cooler.
>> Yeah. Yeah. So you went from
crystallization from you stretched it.
You crystallized. That's an exothermic
reaction.
>> Wow. Okay.
>> You then allowed it to cool down to room
temperature in the stretch state and you
relaxed it and you dissolved the
crystals.
>> That's weird.
>> How do you dissolve the crystals? You've
got to take energy from somewhere to
dissolve crystals. You cool the rubber
band down.
The reason the two curves are different
is because it takes more energy to align
the polymers than it does for the
polymers to curl back up. And this
energy difference is exactly the heat
that's released over a full cycle. We've
seen that natural rubber is built using
these building blocks, but the technical
monomer is actually isoprne, which looks
like this. It's the same atoms, but with
some groups and bonds moved around. So,
the technical term for rubber is cis4
poly isoprne.
And we've actually been able to make
synthetic cis4 polyisoprene. You can
take isoprne and polymerize it. So it
should behave exactly like natural
rubber. Right.
>> And that one is the closest, but it
doesn't perform nearly as well because
it's not structurally as perfect as
natural rubber.
>> See, there are two ways for the monomers
to attach. In natural rubber, they
attach on the same side. The cis
attachment. the percentage of cyst in in
in the molecular chain that nature can
provide is is really accurately. It's
99.99%
something of that sort of scale. But
with synthetic rubber, it's easy for
monomers to attach on the opposite side
of the double bond. That's the trans
attachment. But now there's more room
for them to lay flat. They don't have
that extra wiggle, so they stretch less
and don't crystallize very well. And
when you make the synthetic equivalent,
it's pretty good, but it's 98%
uh cis polypin. There is, you know, one
or two% is going to be transpoly ice
cream and therefore isn't so susceptible
for crystallization
and it's not as good and hasn't got the
same strength properties that natural
rubber would have.
>> In a tensile test, a synthetic rubber
also stretched to around 600% before
breaking. But it only took around 9.1
megapascals compared to over 14.1
megapascals for natural rubber. But
there are a few areas where synthetic
rubber is actually better than natural.
Under low stress where crystallization
doesn't happen, natural rubber loses the
advantage. So synthetic is preferred for
the tread of passenger car tires for
better abrasion resistance. Nitral
rubber, a synthetic rubber used for
gloves, also blocks harsher chemicals
from passing through. So in polyisopilm
we used to see let's say in um
chemotherapy agents maybe 80 90%
permission in night trial we see maybe
10 20.
>> Wow.
>> So it's much better.
>> That's huge.
>> That's huge for a cancer center worker.
That's huge.
>> Nitrial gloves were developed in the
late 1980s during the global AIDS
pandemic in response to the growing
latex allergy. Surprisingly, gloves
weren't required for every single
procedure until the CDC published a
mandate to prevent HIV transmission in
1987.
After the demand for gloves went from
300 million to over 36 billion by the
end of the 1980s, well, dozens of new
latex glove factories sprang up to meet
the demands. Typically, after a mold is
dipped in latex, the glove is leeched
and lots of proteins from the tree are
just washed away. But then they got rid
of that step. This meant that all of
those soluble proteins were left in the
glove.
>> So when nurses or doctors were putting
on or taking off these unleashed
powdered gloves, they would disperse all
of those proteins into the air.
>> The nursing staff were breathing those
particles in, breathing that dust in
through their entire shifts and into
their lungs. At the patients, you've got
these pro these gloves with loads of
proteins washing that away around in
your inids. Thousands of people were
exposed enough to become allergic to
latex.
>> In the early '9s, they said if you have
if you've had four surgical procedures,
you almost certainly have type 1 latex
allergy. If you have if you've had 10,
you do.
>> So eventually manufacturers received
enough complaints that they started
leeching again. But by then it was too
late. Even if something's been properly
leeched, if someone has that type 1
latex allergy, they're still going to
react to it. Nitral gloves help combat
that allergy. But for long surgeries,
some doctors still prefer the softer and
more comfortable glove that comes from
natural latex. So, Dr. Cornish has been
working on alternative natural rubber
from the Wuli plant, which doesn't have
the proteins that people are allergic
to. This plant can grow in desert
climates, and it makes a stronger,
softer rubber than even the Brazilian
rubber tree. Not only does scaling up
Guauli help with the latex allergy, it's
also a safeguard in case the blight ever
makes its way across to Southeast Asia.
Transportation, healthcare,
construction, there are so many
industries that are dependent on natural
rubber. There are regulations around
South American leaf blight control and
it's difficult to get a direct flight
from Brazil to Southeast Asia, but not
impossible. It seems short-sighted to
leave the industry vulnerable to like
one bad flight. For a material that only
became useful around 200 years ago, it's
now hard to imagine life without it.
When Henry Ford developed Ford Landia,
he didn't consult a single rubber tree
expert who could have told him about the
blight. So, let's not make that same
mistake again.