I don't know about you, but I take recycling for granted.

You finish your drink, and you just toss the plastic bottle into a bin marked "Recycling".

Then, something happens to it, and you're told it's good for the environment,

and then you feel good because you're saving the planet

in your own small way by not throwing that bottle into the garbage.

But how does recycling really work?

What happens to that plastic, or that can,

or that piece of paper I toss into that little bin with the arrows on it?

Recycling is, basically, the process of collecting waste materials and

breaking them down into building blocks that can be turned into new products.

Since each material is made of different things, it needs to be broken down in its own way.

Paper, for instance, becomes wood fibres, but glass is just crushed into tiny pieces.

And, since 1973, scientists and engineers have been working on the best ways

to separate clean and processed recyclables at "Material Recovery Facilities".

They're also known as "MRFs", for short, which is a much more awesome and fun name that we will be using from now on.

There are, typically, two kinds of MRFs:

"Single Stream Recycling Plants" and "Dual Stream Recycling Plants".

Dual Stream Recycling means that the curb-side bins are split into two categories:

"Mixed Paper" and "Everything Else".

These two categories are kept separate in the truck,

dumped into two separate piles, and offloaded onto two separate conveyor belts.

Single Stream Recycling, on the other hand, means exactly that.

Everything is thrown into the same recycling bin

and sorted later by a combination of people and high-tech machines.

Less than half of all Material Recovery Facilities use this method,

but that number is growing.

So here's how it works: almost anything can be recycled,

but some materials, like computers, batteries and light bulbs are too complex,

too large, or contain too many toxins, to properly recycle at any given MRF.

If they show up in the recycling pile, they're either thrown away or

taken to different, specialised facilities.

Single Stream Recycling focuses on five different kinds of waste:

Paper, steel, glass, aluminium, and plastic.

As they make their way through the plant, each of these materials is separated from the mixture,

and is processed.

The paper and the cardboard come first,

thanks to a series of rubber, star-shaped wheels

called "Rotary Screen Separators".

With the help of blown air pushing them along,

the cardboard and paper ride the wheels at a 45° incline,

up to a higher conveyor belt,

while the more three-dimensional, heavier objects,

like containers and bottles, fall through the gaps in the wheels

and land back on the main conveyor belt.

That cardboard and paper is sorted by workers

who remove any remaining contaminants, or stray plastics,

and separated the materials into bins for

newspaper, mixed paper, and corrugated cardboard.

Paper is made out of two basic ingredients:

cellulose fibres from wood, and water.

So, to recycle it, you need to break it down to those two component parts and let it reform.

Plus, there are contaminants, like ink and dirt, that need to be filtered out.

So, first, the paper is compacted, baled, sent to a mill and placed in a hot water bath.

This bath quickly breaks the paper down into tiny strands of cellulose fibre,

creating a mushy substance called "pulp",

basically, wet, lumpy paper.

That pulp is still dirty though,

so it's forced through screens that filter out any remaining residues,

like glue or bits of plastic.

It's then sent to the "De-inker",

which is another bath containing air bubbles and soap-like chemicals called surfactants

that separate the paper from the ink.

Air bubbles carry the ink up to surface, while the pulp, which is heavier,

sinks to the bottom.

That pulp, now clean, can be formed into new paper products.

You might have even eaten from a recycled cereal box this morning.

Meanwhile, back at the MRF,

anything that didn't make it up the rotary separator

enters another sorting line.

What's left on the conveyor belt is moved through a "cross-belt magnet",

which is a high-powered magnet that attracts iron-containing metals,

mostly steel.

Aluminium gets left behind because aluminium isn't usually magnetic.

Steel isn't all that hard to recycle,

it's just crushed and baled and sent to foundries where it's melted down.

After that, it's ready to be mixed with new steel

and refashioned into cans, or cars, or beams, or anything else made of steel.

So, now all we have left at the MRF are glass, aluminium, and plastic.

They're separated using an "Air Classifier",

which is a fan that pushes lighter goods, like aluminium and plastic,

toward a higher conveyor belt,

while allowing glass, which is heavier, to fall down to a lower conveyor belt.

Then the glass takes a ride through a "Rolling Drum".

It's shattered into pieces

and filtered through sieve-like screens

that ensure that no glass piece is larger than 5cm wide.

Those glass pieces are then sorted by colour:

clear, brown, and green.

The different colours are important.

They make recycling tricky because they're permanent.

Glass is made of silica, plus a bunch of other ingredients, depending on the colour,

that's been melted by high heat and then rapidly cooled.

Around 60% of all the glass in the U.S. is clear,

it's the easiest glass to make because it's just silica, limestone and soda ash.

But, clear glass can sometimes cause the substance inside to degrade

due to light exposure from the sun.

Beer, for example, has a light-sensitive chemical called "isohumulone" inside of it

that breaks down into free radicals when struck by ultraviolet light.

The side effect of this reaction is a skunky smell and some carbon monoxide.

Generally, not what you're looking for in a beer.

That's why we have brown and green glass,

which act like sunglasses and protect the contents from UV rays.

But they also have ingredients in them to make them that colour,

like nickel, iron, and sulphur.

This means that the brown and green colours can't be removed from glass,

so the need to be recycled separately.

Once the glass is all separated, it's crushed into tiny pieces,

called "cullet".

These cullets melt at a lower temperature than new glass,

because the ingredients and have already been mixed and fused together when that glass was initially made.

Back at the MRF, we've only got aluminium and plastic left.

We are almost done.

Aluminium can be separated from the plastic using a machine called an "Eddy Current Separator".

It's a big drum with a spinning rotor that contains magnetic poles,

which creates a really strong, magnetic field called an "induction field".

Remember how I said that aluminium isn't magnetic?

Well, that is true, most of the time.

This induction field is so powerful

that it causes electrons in a conductor, like aluminium,

to create their own magnetic field.

The two fields repel each other and the aluminium is pushed away to a different conveyor belt,

while the plastic continues on.

Like steel, there isn't much to do when it comes to making the aluminium reusable.

It's shredded, washed, and turned into chips,

which are melted in a large furnace, and poured into moulds.

These moulds are shipped to manufacturers,

where they're melted again, and rolled out into thin sheets

that can be cut, and bent, and shaped into new products,

like cans, and licence plates, and aluminium foil.

So now all we have left is the plastic.

Kinda.

It turns out the plastics are made of one of six different kinds of chemicals,

which correspond to the numbers 1 through 6, that you'll see on the bottom

of that soda bottle, or yoghurt container.

Sometimes, you'll also see a "7",

but that just means it's made of any one of the less popular types.

Each kind of plastic has a different molecular structure,

which determines the physical properties of the plastic.

It also means that some plastics are a lot easier to recycle than others.

Plastic is made out of long, carbon chains.

Usually, the hydrocarbon molecules are extracted from fuels,

like crude oil, or natural gas,

then linked up, forming big, repeating structures called "polymers".

Take PET, for example,

which corresponds with code number 1.

It's made of a polymer called "polyethylene terephthalate",

which has rings of carbons separated by chains of carbons,

some of which have single and double bonds, to oxygen atoms.

Those rings and double bonds don't give PET much flexibility,

so the polymers tend to pack closely together, and are harder to melt.

Since PET will soften at temperatures more than a hundred degrees below that high melting point,

it's easy to reshape, without damaging its molecular structure.

That's pretty helpful when you're trying to recycle it.

Then there's code number 3, PVC,

which is made of a polymer called "polyvinyl chloride".

It's a strong and durable plastic

often used in piping or in bottles of shampoo.

It's also known as "the poison plastic"

because, when it's melted, it can release a corrosive and toxic gas called,

yeah, hydrochloric acid.

Most of the time, recycling PVC involves

grinding into a powder at a specialised plant,

and then mixing it with additives so that it can be reused.

But you definitely do not want it contaminating the rest of your plastic,

which is just one reason why all the different kinds of plastic are separated at the MRF.

More importantly, separating plastics by types preserves their special properties.

For example, PET is harder to shatter, while PVC is more resistant to harsh chemicals.

In most plants, the separation is done using human sorters

but, in newer plants, there are infrared sensors

that identify the plastics based on the spectrum of light they reflect.

Since each type of polymer reflects light differently,

the sensors can identify which plastic is which.

Once identified, little puffs of air blast those plastics

onto different conveyor belts.

Depending on the MRF's capabilities, plus other factors, like market demands,

some of these plastics are recycled, while others are thrown away.

Take "expanded polystyrene", for example,

which you know as "Styrofoam".

While it can technically be recycled, it's not particularly practical,

because a truck full of lightweight, air-filled Styrofoam

doesn't melt down into a lot of polystyrene.

But soda bottles, which are made of PET plastic, are recycled at almost all MRFs.

They can be melted down, mixed with new plastic,

and used to create things like

clothing, and carpet, or even to fill pillows.

So that soda bottle you just recycled?

Some day, you might end up wearing it.

Thanks for watching this SciShow Infusion,

which was brought to you by our patrons on Patreon,

who make SciShow possible for free for everybody.

If you want to help us keep making videos like this,

you can go to Patreon.com/SciShow,

and don't forget to go to YouTube.com/SciShow, and subscribe.

[Outro Music]