We use plastics for so many things, water bottles, milk
牛奶壶 用来装杂货的塑料袋 叉 刀
jugs, plastic bags to carry our groceries, forks, knives,
coffee-cup lids, even shopping carts.
We use plastics for so many things.
With so much plastic all around us, have you ever thought,
what is a plastic?
If we zoom in really close on a plastic,
we would find that it looks like a chain of small units.
One of these little units is called a monomer.
Each of these little units, or monomers,
are connected to other monomers forming a long chain.
This chain is called a polymer.
Lots of these polymer chains get grouped together,
sort of like spaghetti on a plate,
and that makes up the plastic.
Plastic polymers are usually made
from oil, which is the same stuff that makes
the gas we use in our cars.
Well, how long does it take all of this plastic
we use to break down?
It takes 1,000 years or more for plastic
to break down when we throw it away.
What if we could engineer new materials that
could break down easier?
Well, fruits and vegetables break down or rot very
easily when they’re left out over time.
In fact, they only take three to four weeks
to break down when they’re thrown away.
What if we could make plastic out of fruits and vegetables?
So today, we’re going to make potato plastic.
We’re going to make it in the lab here,
but these are all ingredients that you
can find in the grocery store and do this yourself at home.
If you decide to do this at home,
make sure you have an adult supervisor.
This is our starch.
This will be the backbone of our plastic.
It is a molecule that’s made up of a chain of sugars,
and you can get this from potatoes when you boil them.
It’s that milky, white water.
你也可以从玉米 稻谷 或木薯粉中找到它
You can also find starch in corn, rice, or tapioca.
We’re going to use water to mix up all the ingredients
and help loosen up all of those long starch chains
to help make our plastic.
Vinegar helps break the starch chains
into smaller sizes, which make them more manageable
while creating plastic.
Glycerin helps make the chains of starch slip
along each other, which help make the plastic material more
We’ll also need vegetable oil and food coloring just
for our baking needs.
Measure out 10 grams, or about 1 tablespoon, of potato starch.
Add the starch to the beaker.
To this we’ll add 60 milliliters of tap water.
Add 5 milliliters of vinegar.
Add 5 milliliters of glycerin.
It’s very thick, so it might take a while to pour out.
Add three drops of your favorite food coloring to make
a very exciting plastic.
To get this solution to turn into plastic,
we’re going to add heat.
When you’re doing this at home on a stove,
be careful not to touch any hot surfaces
or handle hot liquids directly.
Stir the solution continuously on heat.
As it starts to thicken, raise the heat
from low to medium up to high.
This might take some time, so consider asking a friend
to help you stir.
Once it finally thickens, allow the solution
to boil on medium-high heat for another five minutes.
You can see how the solution has darkened a lot
and has become very thick and hard to move around.
Allow the mixture to cool for a couple minutes
so it’s easy to handle.
Grease the pans or molds that you’ll
use to scoop out your plastic with a little bit of oil.
This will make it easy to remove the plastic once it’s dry.
Scoop the mixture into your mold and go ahead
and spread it out as thin or thick as you
want your final plastic to be.
Stick the plates into the oven at 65 degrees
Celsius, or 150 degrees Fahrenheit,
for one to two hours.
Now let’s zoom in and take a look
at what’s happening to our polymer.
So earlier we talked about an oil-based plastic.
But here we’ve made our plastic from potato starch.
The dried starch powder is a bundle of polymers.
We add it to water to loosen up those bundles.
Some of the starch polymer has branches on it,
which makes it difficult to form a good plastic.
We add vinegar to cut off those branches
and make a linear polymer called amylose.
If we just made plastic from this linear polymer amylose,
we would get a very rigid plastic.
We add glycerin to make the plastic more flexible.
Now let’s go see what it looks like when we take
the plastic out of the oven.
If you add less glycerine, you’ll
get a plastic that’s somewhat hard and rigid.
If you add more glycerin, you’ll get a plastic that’s
more flexible and bendable.
So depending on how much glycerin you add,
you can create plastics depending on your needs.
Now, the key reason why we chose to use starch as our polymer
is that it’s biodegradable.
That means natural organisms like bacteria
are capable of breaking down the material into smaller parts.
In this case, we take a polymer, our starch,
and break it down into its monomer parts,
in this case, simple sugars.
Sugars are a vital energy source for all living organisms.
因此 许多生物体 从细菌到人类
As a result, many organisms, from bacteria to humans,
have enzymes that break starch into simple sugars.
Let’s take a closer look at how this is done.
The starch polymer is made up of chains of simple sugar
monomers called glucose.
The bonds that connect them are called glycosidic bonds.
An enzyme called amylase helps break the sugars apart
from each other by fitting between two monomers.
A water molecule is absorbed in order
to break the glycosidic bond between two monomers
in a process called hydrolysis.
Let’s test whether our bioplastic is biodegradable.
To do this in the lab, we’ll need an amylase enzyme,
which will help break down the starch into simple sugars.
This is actually a concentrated form
of the same stuff you’ll find in your own spit.
Add the amylase enzyme to water, give the mixture a stir,
and finally add the potato plastic to the mixture.
We left this sample overnight, along with a control sample
with just water.
The control is there to see if water alone breaks up
Notice how the plastic in the amylase breaks up.
Here, let’s take a closer look.
This is what our plastic looked like before we
And this is what they look like after we biodegraded them.
Again, notice how the sample that was in the amylase enzyme
broke apart and degraded much faster than the plastic that
was just in water.
So we’ve just demonstrated that we
can make a plastic that degrades in a matter of days as opposed
to thousands of years.
So with a little bit of thought, it’s possible for us
to engineer better plastics for our planet.