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  • [intro ]

  • Look around you --

  • how much plastic is within reach?

  • Plastic is literally everywhere.

  • Seriously, scientists have found it in the deepest depths of the ocean

  • and on top of the most remote mountain peaks.

  • Since the end of World War II,

  • we've produced more than eight billion metric tons of plastic.

  • Of all that, only about 9% has ever been recycled.

  • But it's not just that humans are lazy or bad.

  • So let's take a look at what makes something that's so vital to modern life

  • also difficult to reuse.

  • Think about a plastic water bottle,

  • like the kind you might buy at an airport.

  • It's estimated that around the world,

  • people buy a million plastic bottles every minute.

  • And it's easy to think of a “plastic bottleas being made of a single thing --

  • which is the first problem.

  • We use the generic word plastic

  • to refer to a bunch of chemicals that are actually really different.

  • Broadly speaking, plastics are polymers,

  • which is a fancy way of saying they're repeating chains of molecules.

  • During their formation,

  • they can be processed into arbitrary shapes,

  • which is what gives them such a wide range of applications.

  • Now, every plastic material falls into one of two groups,

  • thermoplastics and thermosets.

  • The individual links in a thermoplastic are held together by relatively weak chemical

  • bonds.

  • When the material is reheated,

  • the molecules can break free from those bonds and take on a new shape.

  • In a thermoset, the polymer chains form intricate networks with tight bonds.

  • Heating these materials enough to break the network destroys the plastic itself.

  • So while thermosets can be very strong, they can be difficult to recycle.

  • There are a lot of different types of thermoplastics in commercial products,

  • but two of the ones most commonly seen in the United States are known as PET and HDPE.

  • Polyethylene terephthalate, or PET, is clear,

  • can withstand moderate temperatures, and resists cracking.

  • High-density polyethylene, or HDPE,

  • can survive more extreme temperatures but generally lacks the transparency of PET.

  • Both of these plastics are used for ordinary bottles.

  • But the trouble is, not all recycling centers accept both of them.

  • So you need to know what kind of plastic you're tossing out

  • and what types your local recycler accepts

  • in order to dispose of one correctly.

  • Even then, you're probably still doing it wrong,

  • because a single product often combines multiple kinds of plastic.

  • For instance,

  • the twist cap on that bottle made of PET can often be made of polypropylene,

  • yet another type of plastic.

  • Since most of us don't carefully disassemble our trash before getting rid of it,

  • recycling plants need a way to separate all the plastics they receive.

  • And it can be critical for this separation to be nearly perfect.

  • For example, if the plastic PVC gets recycled,

  • it can create acids that damage and discolor PET beyond repair.

  • And all it takes is a single PVC bottle

  • in a pallet of 10,000 PET ones to ruin the whole batch.

  • To avoid these problems,

  • recycling plants have a few ways to sort plastics.

  • One approach is to use density -- when immersed in water,

  • PET sinks while some other plastics float.

  • Another option is heat.

  • Different plastics become soft at different temperatures,

  • so precisely heating the mixture can set the various materials apart.

  • But since even a tiny bit of contamination can do a lot of damage,

  • recycling properly gets expensive

  • sometimes too expensive to be worthwhile.

  • For instance, in New York City,

  • every ton of recyclables costs $200 dollars more to recycle

  • than it would cost to toss in a landfill.

  • But here's the thing --

  • even if we invented a process that magically

  • and flawlessly sorted and processed every kind of plastic, recycling it would still

  • be hard.

  • That's because, unlike metal and glass,

  • plastic degrades every time you recycle it.

  • Aluminium, for instance, is an element,

  • so no matter how many times you melt and rework it,

  • you've still just got aluminium atoms.

  • On the other hand, at the microscopic level,

  • plastics are really long chains of molecules.

  • For example, HDPE, one of the plastics we do recycle,

  • can contain up to 100,000 linked ethylene molecules.

  • Every time a plastic is reheated to form it into something new,

  • some of those chains break, reducing the quality of the material.

  • To get around this, manufacturers add new plastic to the mixture,

  • so even recycling plastic requires new plastic.

  • Another technique for prolonging the life of plastic is down-cycling,

  • which turns the material into increasingly less sophisticated products.

  • Plastic that starts as a water bottle might then be turned into fleece for a jacket

  • before ending its life as plastic lumber in a deck.

  • Eventually, even that isn't enough,

  • and whatever's left gets burned for energy or thrown into a landfill.

  • So, in a sense, there is no such thing as plastic recycling --

  • every bit of plastic ever made will eventually end up as waste.

  • And in many cases,

  • it's not possible to do even one round of recycling.

  • That's a big deal considering that,

  • in 2009, about 4% of all the oil and gas extracted worldwide was turned into plastic.

  • And another 3 or 4% was used to create the energy for that production.

  • Now, people probably aren't going to give up plastic

  • and there are some good reasons to keep it around.

  • It has huge benefits for health, accessibility, and food safety.

  • But we can be better about how we use it.

  • And that means developing new recycling techniques that prolong the life of the plastic we have,

  • cutting out single-use products where we can,

  • and being careful about which plastics we use and how we combine them.

  • To find out more about what happens behind the scenes to the plastic you recycle,

  • check out the episode after this.

  • And as always, thanks for watching this episode of SciShow.

  • [ outro ]

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B1 recycling recycle landfill aluminium pvc material

Why We're So Bad at Recycling Plastic

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    林宜悉 posted on 2020/03/30
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