How Many Times Can Plastic REALLY Be Recycled?

In this video, we’re testing the highly debated topic of ‘how many times can plastic be recycled?’. Looking online gives you a whole host of mixed results with a lot of generalisation about ‘plastic’ as a single material. We decided that we were bored of people using this as an excuse as to why ‘recycling doesn’t work’ and decided to test this out for ourselves.

To be super clear about our tests - we’re using recycled HDPE and running it through our machines at 230 degrees celsius. The plastic is only melted for as long as is necessary and doesn’t ever go beyond this temperature. All of our plastic comes from post-consumer waste sources and we are very careful about sorting, separating and cleaning the plastic before we let it enter our material circulation.

We’re fascinated to hear what you think of these results. We absolutely could have gone beyond 30, but we weren’t expecting the plastic to last as well as it did to be completely honest with you! We can also repeat these tests in other materials to see if the results are similar, so let us know if that’s something you’d like to see.

Oh, and here's a link to our carabiners if you fancy one!

#BrothersMake #HDPE #PreciousPlastic #HDPERecycling #RecycledPlastic #RecycledPlasticBottles #PlasticShredding #InjectionMoulding #PlasticRecycling

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FAQ:
➡️ Our workshop is powered 100% by renewable energy. We don’t use any energy from fossil fuels whatsoever.

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Music by Epidemic Sound

[thomascloete]

I think the constraint with the amount of times you can recycle plastic is not necessarily from the recycling process itself (as proven in this great video), but from how the product is used between being recycled. For example if the caribiners were used on a daily basis and exposed to lots of UV (someone who works outside alot, construction etc) the plastic may degrade due to UV exposure and lose strength over time. Other factors such as load stress, temperature and exposure to chemicals need to be taken into consideration between each recycle step. The way in which the product is used ends up defining how long the material will last before degrading to a point where it loses it's virgin properties.

[db]

Australian government should support small plastic recycler businesses instead of exporting plastic to other countries

[JPK]

Maybe you should do a strength test. See how much it can hold before breaking.

[SLNTIGamer]

So I’ve worked in industrial injection molding for 3 years and industrial thermoforming for 5 years. I am quite surprised at the results of this test. Granted I’ve not got a lot of experience with HDPE: mostly with PolyPro, PLA, Nylon (glass-filled and normal), TPE, and TPU. But nonetheless in my current thermoforming job we use our reground material but we mix in %50 virgin material to dilute the degraded plastic. I am curious about the temperature settings for your two machines and how those may have affected the results. If you injected at the lower temperature ranges it would have resulted in somewhat less degradation per run (not sure if the amount is negligible thought). Lastly, those injection and extrusion machines are SO COOL. I’m only used to seeing giant machines with 30ft long barrels, so seeing such small machines is just super awesome to me.

[jjoo]

Another thing to think about is that the carabiners and cups are pretty thick plastic (relatively to the thickness of bottles) - and everything is injection molded, not blow molded. I don't know the exact split, but most of the things that you come in contact with are blow molded, not injection molded. Injection molded parts are definitely going to have more strength in general because they're thicker. In addition, you might see a difference in the tensile strength of the carabiners (though I understand why you might be reluctant to do strength testing of them on camera). But if you make a 1L blow molded bottle and try to do a 3' or 6' drop test, you may see differences MUCH earlier than 30x.

[rorydickens]

You are 100% right about clean and well sorted plastic should have a much higher recycle rate than what is advertised. However the recycling system is broken. With still many items not being cleaned properly, bad labeling and companies creating laminated products containing many materials. The system needs to change! And the only way to do that is through changing our buying habits and supporting the small businesses that make an effort to recycle better, smarter and put in that time! Eg. Brothers Make!

However as for the results dont forget that you guys utilised similarly sourced HDPE, with similar properties. However even the category of HDPE in the industrial recycling system can have a wide variety of additives that would affect your success. Also the carabiner is quite a thick object in injection moulding terms. I wonder what the results would have been on a 1-2mm product and what the results would have been with the standard tensile, compression and lateral load tests. Maybe video 2?

[cmac]

I would love to see a long-term environmental test followed by recycling to see how the plastic degrades (or doesn't) in different scenarios.

Like, put a batch outside for a week, a batch on the window sill getting sun, maybe a batch in and out of the freezer daily to simulate thermal cycling and of course a room temp control group. Shred those batches and re-do the carabiner test to see if any of the plastics are now weaker.

[williambarnes]

Plastic degrades over time. The limit to how many times you can recycle it is because it ages and degrades in a way that melting and recasting doesn't fix, leaving you with decayed plastic in a freshly-injected shape. You can grind it and remelt it and reinject it as many times as you want, that doesn't degrade it. You're not really recycling it because it wasn't used until it decayed and broke over time. It's still fresh plastic. It spends years being a bottle and decaying, then you try to melt the decayed bottle into a cliphook, and you get a cliphook made of decayed plastic, and that breaks. You're making cliphooks out of the same fresh plastic, no matter how many times you grind and melt that plastic. It's still only a few days old. The recycling limit is because used products that get recycled are old, and you're mixing together old decayed plastics to make another thing, which continues aging until it too gets recycled, until it's so far decayed anything you make fails.

[tzisorey]

That was always my understanding - the change in strength wasnt from the shortening of polymer chains etc, but from the added impurities after each use, recovery, and processing.
But that not from work in the industry or anything, just what i was told in school in the 80s

[harmless]

My very first search about the topic gave me a link to a paper the abstract of which reads:
"The thermomechanical degradation during processing gives rise to different modifications of the structure depending on the temperature, residence time and applied stress. In general, it is possible to say that if the reprocessing operations are carried out in apparatus with low residence time, the mechanical and rheological properties of the raw materials are only slightly influenced by the recycling operations. Significant degradation phenomena and reduction of some mechanical properties are observed on increasing the number of recycling steps in apparatus with large residence times. By adding antioxidant agents the polymer maintains the initial properties even after several recycling cycles."

[keithhorning]

You do a fine job of keeping the plastic clean, not a good example of post consumer mixed recycling. Maybe that's the point.

[TheDeadKingsRaven]

Would love to see this done with other plastics and also think if you threw everything in a room with a UV lamp on for a few days between recycling steps to see if there’s a noticeable difference in strength of the batches.

Anyways, cool video and enjoyed watching you test this one out.

[rachelpatterson]

Love that you did this this as a bit of self-researcher, myself. It’s always easier to trust your own results than those someone else has done because you control all the variables that matter to your own things.

[Znatnhos]

I think the other thing to consider is that you rarely recycle a product immediately off the production line. It usually spends months on a shelf somewhere, more months or even years being used, and then more months at the end of its life as it's processed, cleaned with harsh chemicals, and finally ground and reformed. All that time likely contributes to the expected degradation of the polymers.

[keithezard]

Great video - boring to do but of such value to the community. I had exactly this question. Thanks very much for your effort!

[rolfbjorn]

This is a great thing you guys are doing. Your test uses clean, on-site, premium post process material. Post consumer material is...glorified trash. The efficiency goes down and so does the $$$$ incentive.

In the industry, enforcing any rules all grinds down : $$. In Metal Fab for example, the most efficient subcontractor wins, whether it's cutting corners, better processes or material costs.

In my region of Canada, recycling and garbage are hard to distinguish, even for educated people, judging by the sheer amount of recyclable matter in the garbage and vice versa.

Glass contaminates the fibrous materials and the plastics, the plastics contaminate the glass and fibrous materials... And since it's expensive to process, the stuff is sent overseas or buried.

Ironically, clean sorted materials are worth $$$, cardboard bales have companies that pay you to pick them up!

It's also a pain to bring back cans and bottles to stores for refund...I wish we could have a local system where it's actually easy to just shove plastics/glass/ferrous/etc down a specific drain where it gets shredded/compacted and picked up by the appropriate industry.
Polystyrene Foam should be easy to recycle, but the very low density makes it a pain. I have the equivalent of a solid cubic meter of accumulated polystyrene packaging dissolved in half a liter of acetone in a couple jars. No kidding.

[Mikemk_]

Chemistry student here. There's two main categories of plastic, thermoplastic and thermoset.

Thermoplastics melt when heated and are much easier to recycle as a result. Sometimes, as in the case of PE [includes HDPE, LDPE], infinitely recyclable barring contamination.

Thermosets harden when heated, making them difficult to recycle. You can't melt them down, so you have to use chemical means of breaking them back apart into their monomers, which isn't always possible.

Also, you got the terminology wrong here. You were saying the carabiners were strong because they weren't breaking, but that's the opposite of the truth. Their elasticity is what allowed them to not break. Strong materials are brittle. When too much force is applied, they snap. Weak materials are elastic. When too much force is applied, they bend. Nothing is perfectly strong or perfectly elastic; real materials exist on a spectrum between the two.

Plastic actually gets stronger when heated or exposed to UV light or ozone. Specifically, the long polymer chains will get cross-linked began two side to side chains. This forms small off color, typically white, thermoset dots in the product. The more you recycle the plastic, the slightly larger these dots become. Because they no longer melt, if you recycle enough times, they'll clog your extruder nozzles. They're also stronger than the original plastic, which makes the plastic less elastic and more brittle.

If you've read this far, you should make an update video looking closely through a magnifying glass and microscope for those dots.

[rainsticklandguitartalk]

I'm still stuck on the fact they took all that time to separate the colours...only to throw them all back in the same bin.

[guybrushX]

Good on you for seeing a lot of conflicting information and deciding to put it to the test so there's more real world data.

[WeebotTheRobot]

A better measurement in material change after each round of recycling would be to put all of the sampled carabiners in a tensile testing machine and seeing how much the yield strength changes over time. It would require more than one of each round's sample to get an accurate average yield strength though.