Ocean plastic research
@cymek and I are working in the Precious Plastic & Parley shipping container in the Maldives til May.
While we’re here one of our focuses is learning about ocean plastic, particularly how the extended exposure to saltwater/UV/contamination affects its recyclability with the PP machines.
We’ll share our research below 🙂
@pauldufour this is very valuable work – and great that you have been doing actual experiments, not just relying on preconceived ideas.
Like @donald I found the UV degradation tests puzzling. The usual “received wisdom” is that the UV breaks down bonds, so that the polymer eventually reverts to its monomer. However, UV can definitely have the opposite effect – in that it can promote cross linking, and hence cure (solidify) some liquid polymers. In fact, this is how liquid stereolithography works.
The video showing the brittle and crumbling nature of the (hdpe?) bottles, that have been exposed to sunlight, will be familiar to most of us that have handled “sun degraded” plastic objects.
However, what if the brittleness wasn’t due to breakdown but due to additional (albeit weak) crosslinks? Looking around the web, I found the following paper:
UV effects on the tensile and creep Behaviour of HDPE (Becerra and d’Almeida, 2016)
What it appears to show is that below a certain intensity, the UV is not able to break C-C bonds – and therefore does not actually shorten any of the basic polyethylene chains. However, it can break lower energy C-H bonds, which creates the free radicals necessary for creating additional weak cross links. It seems that this may be what we are seeing during “UV ageing” and associated embrittlement.
If that is the case, heating/melting and re-moulding the HDPE could essentially “recondition” the long chain molecules, restoring “clean” C-H bonds.
If true, the importance of this discovery should not be underestimated. It makes the reprocessing of some “UV degraded” polymers entirely feasible – despite the all the usual negative warnings 😉
(p.s. I’m an engineer, not a polymer chemist, but have had to work with polymers quite a lot over the decades).
To share what we learned, I made this display board showing the results of recycling plastic waste that people might not typically think of as a “recyclable”. It’s hanging in the workspace next to the injector.
More extensive testing should be done to get a better understanding of how UV degradation affects the properties of plastic, but from this initial test it seems that degraded plastic, once recycled, is still quite strong.
Experiment 06 – Testing Effects of Ultraviolet Degradation
<span style=”color: #313131;”>In addition to experimenting with marine textiles, I wanted to get a better understanding of how ultraviolet degradation (common in ocean plastics) affected the material properties of plastic after it’s recycled.
</span>All over the island there were loads of these yellow bottles in varying degrees of degradation, so I used them as a control for the experiment.
To start, we shredded a good-as-new bottle and the most degraded bottle I could find to compare properties of the most extreme types. The degraded bottle was considerably weaker than the new one – you could tear it apart by hand without much effort.
These are the most promising results I’ve seen on PP. Great job!
The fact that you were able to fairly easily turn some nasty degraded beach plastic (that degraded poly rope looked horrible) into solid material is a great result. I wasn’t sure what the Maldives expedition would achieve but you’ve proven the benefit of on-site research and education. Hopefully you can find products in the local marketplace that are expensive to import but you could make.
Also hopefully Project Kamp does not use up all the PP resources and more of these on-site workshops can be done.
Again, Great Job! your results should also make grant applications more competitive. Thanks
Experiment 01 – Marine Rope
To begin experiments, I collected some frayed marine rope and tested it in the injection machine to see if we could melt it down into a solid form which will be less prone to degradation over time.
For the time being, I’m just using a simple hex mold, but once proven that recycling these materials is possible, there are all sorts of directions we could take this.
Cleaning the rope was pretty easy. By dunking it in a water bath for a couple of minutes, most sand and other contaminants fell right off.
Then I took the degraded parts of the rope that were no longer useful in their current form and loaded it into the injector.
The top band heaters were set to 210 and the nozzle at 220.
The material seems to flow really well without any problems.
Loading it into the injector was kind of a pain. Going to see if shredding beforehand helps. It seems like this material might be good in the extruder – and might work for your surf fins @hylasurf 🙂
Experiment 05.1 – Shredding ocean rope
To see if it’d be easier to feed into the extruder, I shredded the rope before extruding.
Shredding the rope worked pretty well, but since the rope fibers are so thin, they began to heat up and clump together a bit as the machine warmed up.
Feeding the shredded rope into the extruder was better, but still not great. The material is very light, so when it’s clumped together it sometimes sits above the screw gaps instead of falling in, meaning it still needed to sometimes be coaxed in by hand.
Experiment 04 – Transport bag
Another item that’s commonly found degrading are these transport bags.
I ran the same experiment as the others and found that this material can also be recycled using the injection machine.
These bags are made up of a few different components (bag, straps, threading) so I’m curious to see if they can all be recycled together or if they need to be separated.
Experiment 03 – Sunshade
This material is used a lot on boats/beaches as a sunshade. Like the others, once it weakens, it’s often discarded and breaks down into micro plastics.
I washed this using the same method.
The temperature was raised to 240 and 250 to melt the material. Once molten, it flowed quite well and seems to be a pretty sturdy (as do the others).
Like the tarp, this material also began to rise in the barrel once heated – if anyone has any insight as to what’s causing that, it’d be greatly appreciated 🙂
Experiment 02 – Tarp
I ran the same experiment with the plastic tarp I’ve been finding all over the place which also tends to break down.
I washed it the same way as the rope and then loaded it into the injector.
The heat needed to be increased to 240 and 250 to get the material to melt properly, and once molten, it began rising in the barrel towards the hopper – not sure what caused this.
Injecting worked pretty well, it didn’t seem to flow as smoothly as the rope. An increase in temperature might help this.
Then we extruded them into beams to test their strength. The degraded beam’s color was a bit less saturated than the new one, but aside from that they felt pretty similar.
Experiment 05.2 – Swapping the extrusion screw for the old auger
The spacing in the extrusion screw is considerably smaller than that of the old auger we used previously, so I decided to reinstall the auger to see if the larger spacing would make it easier for the rope to load into the machine.
Our shredder broke down (extra strong motor sheared shaft, not during rope shredding) so I’ve only been able to experiment with hand-cut, unshredded rope so far. The results have been promising though – the larger gaps in the auger help considerably and I was able to make a second beam.
The screw was spinning at a low RPM in the beginning, so the beam didn’t fully form, but once I bumped it up to full speed it worked quite well.
I was curious about how big of a difference cleaning the rope actually made, so I used dirty rope for this experiment. As you can see, a simple clean with a quick rinse in a tub helps quite a bit with removing the sand, dirt, etc.
Once our shredder is working again, I’ll test the auger with shredded rope.
That said, I was able to successfully make a short beam using the shredded rope 🙂
Experiment 05 – Extruding ocean rope
Seeing the success of the ocean rope with the injection machine, I wanted to see if we could manage to feed it into the extruder for easier processing.
First I experimented with cut, but unshredded rope. It worked, but it was hard to feed it into the machine at a consistent rate – sometimes the extrusion screw took the material without trouble, but other times it had to be coaxed by hand.
It did work though, so now it’s a matter of figuring out the best way to feed it into the machine.
Then, I sorted through it to get a better understanding of the various categories that make up the sample.
In general, the items can be categorized as following:
–Conventional thermoplastics : oil bottles, etc. We have a pretty good understanding of how to recycle these. The main question is: how does degradation due to sun and sea exposure affect their properties? How do contaminants affect their recyclability?
-Marine textiles : rope, tarp, netting. These materials are often made from thermoplastics such nylon and PP, so in theory we should be able to recycle them.
-Conventional thermosets : rubber, etc. These don’t melt so we can’t recycle these using the same methods we use for thermoplastics.
-Foams / Expanded plastics : These can sometimes be recycled, however it isn’t my expertise so I won’t focus on it for now.
-Foils : Grocery bags, chip bags, etc. Foil compositions vary widely, sometimes being recyclable, sometimes not. Depending on progress in other categories, I might experiment with these but they will not be my main focus.
@pauldufour great work. Here is an article on hdpe arctic ocean plastic
but they did NOT melt the plastic, just compared the strength etc of new plastic and ocean plastic. Their only goal was to use ocean plastic to reinforce concrete and they concluded it was viable. Your research is much more important because it shows remelted ocean plastic is STRONG. Thank you.
After @joandarcy mentioned fumes, I had a little search…
Regardess of whether the polymer involved is nylon or polypropylene, fumes should always be treated with caution – and should always be actively extracted. Have a read of this paper (it is open access):
Interstitial lung disease due to fumes from heat-cutting polymer rope (Sharman and Wood-Baker, 2013)
Abstract Interstitial lung disease (ILD) due to inhalation of fume/smoke from heating or burning of synthetic polymers has not been reported previously. A fish farm worker developed ILD after cutting rope (polypropylene and nylon) for about 2 hours per day over an extended period using an electrically heated ‘knife’. This process produced fume/smoke that entered the workers breathing zone. No other likely cause was identified. This case suggests that exposure to airborne contaminants generated by the heating or burning of synthetic polymers has the potential to cause serious lung disease.
I know there are warnings about fume inhalation elsewhere in these forums, but this is a reminder to take those warnings seriously.
@frogfall you may not be a chemist, but it sure is pragmatic scientific proof @pauldufour delivered according to your reasoning.
It’s not the (bulk of the) plastic that’s degrading, just the bonds…
In a way making it even more urgent to recycle the Ocean plastics as under the influence of UV they seem to degrade into even more dangerous microplastics (long chains vs short chains).
Or at least how I understand it.
I’m not even an engineer 😉
Hello Paul, Thank you for your research and putting out the information for us to know more. Your whole project is so inspiring and amazing. I study MA sustainable design and I am doing my major project on local river plastics and recycling them into products helpful for local community. This detailed description really helped me envision how I can proceed with my research now.
Also, anyone from London who own these machines i can contact with? Your response is appreciated 🙂
Very interesting indeed and quite unexpected.
Is there a chemist who could make sense of this?
Does the heat of melting re-strenghten the chemical bonds?
We used a hydraulic press to test the beams’ flexibility and compression strength.
We applied 12,000 metric tons of force and there didn’t seem to be a substantial difference between the behavior of the beams. Perhaps I was wrong in my previous research (http://onearmy.world/community/forums/topic/non-recyclable-plastic-waste-v4-2/)
Of the plastics I collected, the category that caught my attention most was marine textiles – for a few reasons.
-Ubiquity : They’re used in huge quantities by shipping vessels all over the world for many different purposes – rope, storage bags, fish net, sunshade.
-Degradation : Because they’re made up of small fibers, they fray and degrade very easily into micro-plastics which are released into the environment.
-Useless : Once they start to break down, they’re rendered “useless” in their current form and often discarded once they reach this point. If we can recycle them, we could help prevent this form of pollution from happening as much.
-Knowledge : When speaking with people around the island about marine textiles, they’re usually surprised to find out that they’re made of plastic. Showing that they’re recyclable could give people more knowledge about materials that are so ubiquitous in their community, and hopefully help them make more informed decisions about how to use it in the future.
Below are some examples of degrading marine textiles I found on a 100-meter stretch of beach.
@pauldufour great research og great thread with lot of very relevant insight!
I have been making stuff from ocean plastic for about a year, using the compression method.
My experience too is that brittle UV-exposed plastic will re-strengthen to a certain degree, suprisingly well. The faded color too seem to fade back by remelting it to some extent. This goes for HDPE, PE – as well as PP which I use the most. PP get very brittle very fast compared to HDPE, in my experience.
One concern I have has to do with exposure to fumes. Some studies apparently find that some ocean plastic will attract pollutants and chemicals due to static electricity. So what this means regarding exposure in the long run is for me a open and somewhat troubling question. I use a good mask, but still. https://cen.acs.org/articles/90/web/2012/08/Ocean-Plastics-Soak-Pollutants.html
I also get this oil-like residue in my oven – smells somewhat like oil.
more info on process and stuff here https://www.instagram.com/sjolove.plastfangst/
From my research about the fumes, mostly PS has the most issues concerning with toxic fume production, because melting can create styrene and similar aromatic compounds in the air. PE and PP creates much less fume when heated because it is essentially a refined wax. Fortunately, we have some masks available commercially which is 3M ABEK filter respirator which filters organic vapours above 65C, inorganic gases, acid gases and ammonia. These filters need to be changed after 40 hours of use (around 15USD for a pair).
Our group [email protected] started out researching the flux of plastic in North West Scotland. We set up a beach clean bin at our local beach, cleaned the beach weekly and counted and surveyed our finding. A very simple method to get some good empirical data.
Please see our website https://www.plasticatbay.org/category/resource/
We have got some funding so now we employ a Beach Ranger to help. We have also started doing microplastic surveys, we are getting involved with a study to monitor the incorporation of plastic in seabird nests and we have sent off nurdles for toxicology reports
We got into the recycling side of things as 80% of what we collect is fishing ropes and nets and we were sick of putting them in landfill and we need money to do more research.
Do you know someone to contact in the UN, we would be happy to pass on what we know so far….
Of course the “origin” results might be strangely affected by the years of “waste export” across the world. See (BBC) Recycling: Where is the plastic waste mountain?
But some waste can be very traceable – such as on this image from a beach on the Scottish island of Eigg – as the fish processing company named is located on the west coast of Ireland. Although, I guess, the people dumping the box ties could be customers of the fish packers – located in another country.
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