Plastic recycling is a minefield. Here's why it's so difficult and how we can make it easier

Jun 15, 2023

Why is it that after nearly 40 years of kerbside recycling in this country, figuring out which plastics can and can't go in your recycling is still so difficult?

A major problem is that plastics just aren't plastics.

PET is different to HDPE, which is different to PVC, PP and PS, and then soft plastics (LDPEs) are something else altogether.

There's also no unified national standard for dealing with plastic — the processing facilities and guidelines vary from council to council.

To that end the best we can do is give you a rough guide to what's in and what's out when it comes to your recycling bin.

Because of their different chemistry, some types of plastic are pretty easy to recycle, whereas until something changes, landfill is the only destination for others.

So we've enlisted polymer chemist Bronwyn Laycock to help us understand what plastics we're dealing with, and whether they're broadly recyclable or not.

First up, there's a reason PET or polyethylene terephthalate tops this list. Because it's literally number "1".

You know the little triangles made from arrows with the number inside, that you find stamped on plastic things? That triangle doesn't mean the product can or cannot go in your recycling bin. It's a code for the type of plastic the thing is made from.

The numbers range from 1 to 7, and PET which is used for everything from water and food containers to sleeping bags, is designated 1.

It's also, as far as plastics go, one of the easiest to recycle in its pure form.

On that note, for each plastic type we're going to test your recycling chops. Here's the first challenge:

Does your clear, single-use plastic water bottle stamped with a 1 go in the recycling bin or landfill?

Of course it goes in the recycling.

OK an easy one to start with (they'll get harder).

Recycling is broadly mechanical or chemical. Mechanical recycling is where the plastic is sorted into its type, ie PET, then shredded, melted and reused.

But chemical recycling involves reducing plastics back to their starting monomers.

So if we back up for a bit of chemistry here — all plastics are made up molecules called monomers, bonded together to form chains called polymers.

How easy or hard a plastic polymer is to chemically recycle basically comes down to how hard it is to break apart the bonds between the monomers.

The reason PET is pretty easy to chemically recycle is that its monomers are joined by what are called ester linkages or bonds that can be easily broken apart.

"You can chemically recycle PET very, very easily," says Professor Laycock of the University of Queensland.

"You can break it down to monomers, which are the starting materials [of plastic], or oligomers, which are sort of half way down to starting materials."

By using those monomers or oligomers to build new PET polymers, you get no degradation in the quality of the new plastic. In other words, you can chemically recycle it over and over again.

The other bonus of PET having those ester bonds is that they act like a "signature". A load of mixed plastic can be infrared scanned, and the ones with the esters are easily identified as PET.

This means you can get a pure or "clean" stream of PET, which can then be recycled — ground down and re-melted — without being contaminated by other plastics.

Mechanical recycling is much less expensive than chemical recycling, but the downside is it can only be done a limited number of times due to declining plastic quality with each cycle.

Products branded with a number 2 are made from high density polyethylenes or HDPEs, and include your cloudy milk bottles.

OK, so it's challenge time again: You're standing at your bins. Which one does the milk bottle go into?

If you said the recycling bin, you're correct. Again, pretty easy.

But will it be recycled? Not necessarily. Quite possibly not back into a milk bottle anyway.

"The problem is that you can't chemically recycle HDPEs very easily," says Professor Laycock, "because [the polymer is made of] very stable bonds of just carbon and hydrogen."

Which leaves mechanical recycling — melting and reshaping. But that comes with problems, says Professor Laycock.

"If you've got HDPE in a clean product stream (without any other plastic types in it), you can melt that fairly easily.

"But if you've got any sort of contamination, and that's common for polypropylene then it becomes much harder."

The upshot is your milk bottle may well end up being "down-cycled" to an impure or compromised plastic and used for say, a park bench, decking, or even a rubbish bin.

Number 3 plastics are the PVCs — the world's third most commonly used plastic.

You'll recognise them from such adventures as the pipes beneath your kitchen sink, the pipes beneath your toilet, or the pipes strutting Parisian catwalks or Hollywood Boulevard in the form of tight fitting vinyl pants.

That's right, PVC is the plumbing-haute-couture crossover the world didn't need.

I'm going to take a wild guess and say you're two from two on the recycling challenge so far.

You've been working hard. Go grab a drink of cordial. Make sure it's the brand that starts with a "C". You know the one with the kids marching through the orchard singing about the fruit their dads' pick?

You finish the bottle. Right, now you're holding the clear, plastic bottle by the handle, above the bins. Which one do you put it in? Which one? Be honest — which one would you have put it in if you didn't suspect this was a set up?

You put it in the recycling bin? Nooooooooooo.

As well as plumbing and pants, PVC is used for some food and beverage packaging, like the cordial you just finished, and it's a real problem to recycle.

"[PVC] has got a few issues," Professor Laycock says. "It's quite thermally stable, so it takes quite a lot of energy to melt it back down ... [but] it degrades to form hydrochloric acid.

"So if you have any trace of PVC in say, a polypropylene stream, that contaminates the stream and makes it much harder to repurpose. You've got to be really careful with PVC."

Plastic shopping bags, disposable coffee cup linings, some layers of Tetra Paks, some squeeze-able juice, jam and honey containers, bin bags, even some fishing lures: these are just a few of the places you might find plastic number 4 — low-density polyethylenes (LDPEs) or soft plastics.

Can they go in the recycling bin? You might know the answer: REDcycle.

When soft-plastics recycling scheme REDcycle went under last year, it left thousands of tonnes of LDPEs that are still sitting in warehouses and may end up in landfill or sent overseas.

Recycling is a business. Waste is sorted into streams and either recycled onsite or sold to a recycler, who will chemically or mechanically process it into a feedstock — the base form of the plastic.

That feedstock is then sold to say, a bottle manufacturer, who will use it to make new bottles.

But the recycler has to compete with feedstocks made from virgin materials, mostly crude oil, natural gas or coal derivatives. If the sorting and recycling process is too expensive, the virgin materials get chosen in preference.

It's not that the technology to chemically recycle or down-cycle soft plastics doesn't exist, but Australia "isn't well set up for it yet", Professor Laycock says — certainly not in an economically competitive way.

The reason soft plastics are hard and expensive to recycle is partly because they're often a mix of several plastic types.

But even LDPE in its clean form is problematic.

"Because it's lightweight and thin, it entangles the machinery and it's challenging to work with," says Professor Laycock.

"It's really hard to shred a plastic bag because it's so tough and elastic."

In the case of REDcycle, their buyers would have been down-cycling the LDPE plastic they received to lower grade materials.

There's a funded project underway right now to develop Australia's first operational advanced chemical recycling (ACR) facility in Victoria, for soft plastics.

The company behind the project estimates it's about 16 months away from becoming operational, and will be using hydrothermal liquefaction (hot, pressurised water) to "take plastic back to the oil it originally came from".

Cash money. That's where you're probably most familiar with polypropylene or plastic number '5'. And the good news is, when our bank notes reach their end of life, they're shredded, melted into pellets and down-cycled.

Because cash literally has monetary value, it doesn't end up in landfill and unless you get lucky you'll almost never find it blowing around on the street or getting washed out to sea.

But polypropylene can also be used for things like ice cream and yoghurt containers, plastic chairs, bottle lids and those plastic pots you get your plants in.

So can they all go in the recycling bin?

Challenge time again: You're holding a polypropylene lid from a milk bottle, and an ice cream container and a plant pot that are both stamped with a number 5. Which bin do they go in?

The answer is pretty simple.

If you're in say, Geelong, the polypropylene bottle lids can go in the recycling bin if they're bigger than a credit card; if you're in the Hornsby Shire Council, they can't; in Sutherland Shire Council, polypropylene bottle tops must be bigger than a business card or be still attached to the bottle. In most councils around Australia the ice cream containers can go in the recycling, but plant pots generally can't.

See how easy that is?

A federal government report from 2021 estimated about 13,500 tonnes of plastic plant pots get dumped in landfill each year.

So why can ice cream containers go in and plant pots not? Because of the colour.

Many automated recycling facility sensors use near-infrared scanning to sort plastics and they don't pick up black.

Even if they do, in places like the ACT for instance, the plastic is too low grade to be processed at their facilities.

Right now there's a push to establish a national polypropylene plant pot recycling scheme, and some garden centres and hardwares will take back used pots.

Last challenge: Can polystyrene go in the recycling bin?

No. You knew that.

Poly Styrene was the stage name of '70s punk frontwoman Marianne Joan Elliot-Said of X-Ray Spex. She chose the name because it encapsulated what she thought of pop stars — "lightweight and disposable".

The former quality is part of what makes polystyrene so useful. The latter, is what makes it so problematic. While it might be discarded, like some pop stars this plastic (number 6) is really hard to get rid of.

It comes in two forms — expanded and rigid. Expanded polystyrene or EPS is what we get in packaging and takeaway containers, whereas the rigid form might be CDs or yoghurt containers.

Its chemical, physical, and thermal properties — it was used in napalm-B in the Vietnam war — all make it one of the hardest plastics to recycle.

Both forms are chemically stable, but while mechanical recycling of the rigid form is fairly straightforward, expanded foam is problematic, says Professor Laycock.

Food contamination is common, and it takes heaps of space to stockpile.

"For EPS, the problem with mechanical recycling is that it is mostly air — 98 per cent. So it's lightweight and bulky."

Though it can't go in your recycling bin, a spokesperson for the expanded polystyrene industry in Australia says there is a network of EPS recyclers here.

"Some 30 per cent of expanded polystyrene packaging, which is predominantly imported from overseas, is diverted from landfill and reused in the Australian construction sector, a figure which is growing."

According to the spokesperson it is:

But there are also alternatives for almost all its uses, and the National Plastics Plan includes winding down most of its use here.

Polystyrene containers — things like coffee cups and disposable plates — were supposed to disappear from shelves in Australia by the end of 2022. So was loose packaging foam.

By 2025 the phase-out will also include moulded packaging for small to medium electronics.

However, we'll still see it in things like insulation and some business-to-business uses.

Polycarbonates, polyamolines, polyurethanes ... number 7 is a catch-all for all the other plastics.

Rather than give you a rundown on all of them, it's probably time to think outside the Tetra Pak box.

If this article has achieved anything so far, it's probably just reinforced what a minefield plastic recycling is.

Plastic waste is clearly a huge problem that we need to do something about.

But although it's not a problem that we the consumers have solely created, it can feel like we're burdened with the lion's share of responsibility for its solutions.

But what if products didn't come as a mix of plastic and cardboard like disposable coffee cups and Tetra Paks?

Planet advocate and prankster Craig Reucassel takes a deep dive into Australia's waste crisis. Tune in on Tuesdays at 8.30pm on ABC TV and catch up on ABC iview.

What if where feasible, only easily recyclable plastics were used in packaging and were clearly labelled? And what if there were clear and consistent guidelines for what goes into the recycling bin?

Or what if, again where possible, products were packaged in returnable or reusable containers?

It's called product stewardship, and it's a core tenet of circular economy strategies, including in Australia.

The idea is that the responsibility for the recovery and reuse or recycling of the product is put back on the producer — the one who profits from its use.

The federal government's Australian Packaging Covenant Organisation has the following voluntary targets, which are meant to encourage plastic circularity:

If these targets are met it could at least take some of the headache out of choosing between bins.

Editor's note 31/07/23: article has been updated to include information about polystyrene recycling.

Watch War On Waste on ABC iview or on Tuesdays at 8:30pm on ABC TV.