Soft-plastic recycling – research and feasibility
Dear Precious Plastic community,
I am intern in Swiss research institute working on waste management. A waste audit in one of our nepalese case studies highlighted the need for treatment solutions for soft plastics (mainly food wrappers, approximately 10kg/day). For the next two month we will be conducting a research in Nepal on Small scale soft plastic recycling.
Among my tasks, I’ll be working with a local NGO to achieve and document the construction of a compression machine.
I’ll keep you updated on our progress through this post and I’m happy to hear about your suggestion, experience, comments, etcetera.
Suscribe to the post to stay updated!
All the best,
Weekly update #1
The goal for this week was to meet stakeholders and to find a workspace. We are happy to share that we’ll work at Nepal communitere; where we can use an container and an equipped makerspace.
We aim on gathering all the material to build the compression this week. We’re now facing a challenge: “european sized” ovens are rare in Nepal; so you can’t really find one in scrap (at least we didn’t find one yet). However, what’s common are there smaller ovens (up to 30 litter).
For the first trials, we are considering using a smaller oven. The quantity of plastic to be treated will thus be limited; but I think that’s OK. However, I’m worried about heat uniformity in these kind of ovens; some films might burn. Has anyone experienced working with these small ovens? Would it be difficult to upgrade a small oven to a bigger one (by reusing the heating element and making a new insulated box)?
Should be possible, as you have a makerspace, to combine a couple of smaller ovens into a larger one.
Or maybe even to build something custom out of them to specifically fit the project.
This might meta-solve the problem, as Nepal is probably not the only community with only small ovens.
I have seen it done before. If you like I can dive into my archives to see if I can find more info, but the ‘make’ should be pretty straightforward.
As for the heat uniformity, as I understand it, you should replace the heat controller of any oven anyway. As the ovens you are using are smaller they won’t have that much of a heat buffer to even out temperature fluctuations, so these fluctuations will be more extreme, and thus more dangerous.
In short: I’d say Build the box!
I’ll see if I can find some building plans, but it should be pretty straightforward, as illustrated with this build:
“Just don’t touch it when it’s hot” lol
Searching for ‘DIY powder coating ovens’ should also give plenty of tutorials, maybe even specific to the kind of ovens you have access to.
Recycling the isolation from the old ovens would give the new build a much higher capacity (up to 400C, after which the isolation will melt) as DIY Powder coating normally maxes out at 200C.
The major producer of noodles produces 2100 packets a minute; so the 1000 a resource is definitely applicable.Before leaving, I had access to an infrared spectrometer and ran tests on 8 random noodle packaging (export grade) and they all matched with polyproylene on the library.Concerning shredding, we’ll start with scissors. Then, I have different creative ideas on the scale-up phase.
If the base film is polypropylene, then at least you should have fewer problems trying to heat-mould packaging than if the material was was PET-based.
An infrared spectrometer… I should also get me one of those… bit expensive though…
Are there any simple alternatives?
I also wonder if it would be possible to build a bigger (tetrapak) “blender” vs shredder, as this might also solve the problem of other ‘mixed’ materials, like dvds and cd if you upscale it, and would possibly need a lot less power, and way less complicated ‘knives’.
A lot of (mixed material) recycling plants seem to use a ‘wet’ process anyway, so why not try?
A blender is kind of a vortex generator, so it could also help with the seperation of the materials… within the same machine…
I’m just thinking out loud, but I kind of have a vision of a ‘solar powered’ wet plastic blender, that works slow but sure (off the grid), is easy to build and maintain, and would cost a fraction of the industrialized shredder, both in build and in use…
If you can find/make a metal fan blade and connect it with a motor on the outside, convection should help quite a bit.
I was just in my shed and I saw my sledgehammer.
I think I solved the problem of shredding my old dvds 🙂
Yep, wet blending could be an alternative and could be combined with the washing step.
@donald About infrared, that’s the benefit of still being a student. I’ll try to document different alternatives for optical identification. But it doesn’t seem there’s a really low cost one.
Excellent point. Washing and shredding!
I actually once build a multiple blade office paper cutter, because I had to cut a lot of same size lamminated badges out of a printed roll (with space in between them).
Did work, but if you don’t need ‘same size’ you’re way faster just chopping them up with one cutter.
I’ve also tried to cut thin foil with an office cutter (for shrink wrap packaging).
Foil just folded over the edge, along the knife (unless you close it really fast).
A build like this might work better (with some tweaks (like using razor blades)):
Could also be hand cranked…
This is the shredder I used on the coffee & linseed wrappers. It is quite old, and was acquired for free a long time ago from someone who had bought a better one. The rating plate says 220-250v ~0.5A 50Hz, and that it shouldn’t be run for more than 2 minutes without a 30 minute cool-down. It was made in China.
Conversely, where I work, we have a large document shredder that can also shred DVDs – so much more powerful machines do exist.
Yes, some of these cheap shredders already overheat just showing it a piece of paper!
Re: dvds – as the plastic is not flexable, it almost needs to be grinded to dust for simple (non-extruder) uses. Most office shredders I know are merely meant to destroy the disc, so it can no longer be used, not to shred them into small pieces, like the paper, but I would love to stand corrected on this.
I’ll try to find a second-hand blender to test cds/dvds also according to the tetrapak setup. Would be easier if the printed foil did not have to be removed…
For starters I’m going to make pave part of my garden with plastic bricks (no, not gonna pave paradise, just the pathways 😉 ).
Why is this important to mention?
Well experiments are fun, but you should always aim for a product you can actually use, instead of crap you’re just gonna melt again !
P.S. mostly in research mode this week.
Weekly update #2
Our second week is going well!We finally got this big oven; so we won’t have to build it ourself (precious time is saved!). We just removed the circuits we didn’t need (the four electric plates) and are now experimenting with the electronics. We also got the metal and car jack for the compression frame.
I saw in V2 compression video that the oven was flipped by 90°, having the heating elements on the side. Is that better? We planned to use the oven racks to nicely melt our plastic in molds, on grids.
Also, if we don’t rotate the oven, I considered only using the lower heating element to avoid foil burning on the top, as it occured in previous experiments of this community. Any inputs?
We are looking forward to build this oven soon, and start crazy-melting stuff!
I think you answered your own question 🙂
Having the heating on the side would give a more even heating when looked at top to bottom.
i believe most top ‘heaters’ are actually grills, meant to put a brown colour to the top of your ‘turkey’, and as such not very usefull for even heating.
Could differ per over though (but I know mine does this).
I guess the best guess would be to experiment.
If you get even heating (using only the bottom heater) in the upside down oven, great. If it goes sideways, go sideways!
Also scored some noodle packages that might fit your description to do some testing on (like washing it in a blender). If anything usefull comes from this, I’ll let you know.
If it doesn’t work for plastic (are you going to heat it?), then it can always be used for food…
Or paper (with some modifications).
Or the actual answer, which is ‘bean burgers’, but hush, don’t tell anyone!
‘Extruder’ is fully metal, so would be interesting to try…
Gotta love vintage tech!
@marcvdv , I used our kitchen oven a couple of times for experiments. Even with the windows open and a fan on, the fumes were an issue. I’ve stopped using that oven for that reason.
Hopefully you have several temperature sensors/readouts you can use during your experiments. I found oven temperatures vary significantly. Are you planning to use your own controllers? I would sill consider adding a fan of some kind.
Those range top heating elements may be useful for directly heating molds.
The fumes are not always obvious smoke. That container is a small volume.
Thank you all for your feedback, comments and enthousiasm. We decided to start working only with the lower heating element to limit the risk of burning the top layer of films.
@s2019: Yes, we are adding a thermocouple connected to a PID controller (temporary/testing setting on the picture down there, it seems to work pretty well!). You mentionned “several” controller. We just have one. Would you still recommend adding a fan in the oven?
@donald True, I didn’t plan the timer. I’ll look for one or I’ll use my phone.
Sure, I know the banger of smoke. We’ll experiment gradual temperature increase, work with open doors and windows and use the good masks I have with me. Moreover, as we’re in a co-working space (next neighbors are maybe 10m from the oven, we’ll be really precautious and communicate a lot on our activities.
Having several temperature measurement locations will help you understand the oven, the temperature gradients, and what the plastic is seeing. They are not that expensive online, but I’m not sure what is easy to get in your location. You could even use a grilling/cooking thermometer if it has a remote probe sensor.
If available a fan in the oven would only help avoid burning the plastic because of uneven temperature.
For the fumes, keeping the oven near the door and a floor fan if available should help.
Or place the oven outside before you use it.
Especially when still testing…
My outdoors is part of my workspace, just for this reason…
Weekly update #3 (On week 4)
I didn’t update you last week. I was busy solving the overheating issues of our SSR. I think we managed it now : we added an heat sink and will have an additional fan on our electronic box.
We didn’t melt any plastic yet, but we made slow but steady progress: The compression frame is almost built, our first mold is ready to use (a bit a dodgy setting of two stainless steel kitchen pots that should allow us to make bowls), our supply in plastic should be insured thanks to a local women association of waste pickers and the cleaning procedure is established.
We decided to work on these “thin arrowroot” biscuits and these “waiwai” noodle packagings.
Our oven has poor insulation and is degraded on top (rust and hole); so it’s not really energy efficient. I needed 25min to go from 27°C to 200°C; and the SSR heat sink was really hot after 45 min. Moreover, we never reached a temperature higher than 214°C and I saw several case studies of melting PP at 220°C.
Oven insulation is hard to find in Nepal; but I found this box containing some foam at home. I don’t really know what material it’s made of: Will it be temperature resistant? Can it start burning if I use an inappropriate one? Otherwise, do you guys have a solution for “DIY” insulation of an oven?
Picture of the insulation material mentionned above.
Well always best to err on the side of caution.
You could of course try to heat it (outside) and see what happens.
But why don’t you use wool?
Could also be the solution for anyone else who has no access to industrial isolation materials (or their labels).
The general recommendation on some of the ebay type SSR is to have a healthy margin on amperage. Otherwise some heatsink compound and lots of airflow. If it is overheating mostly during the long initial warmup, you could add a switch so the warmup just goes through the original oven thermostat and once it gets warm you manually switch to the SSR for PID control.
Do you have a strategy on how to separate your double pot mold if it sticks? Maybe weld some more reinforcement around the rims and maybe use the nuts you are using as spacers to also work as jack screw locations. Also make sure the outside of the inner pot is smooth.
If electricity is at a premium, for smaller batches, you may want to build a smaller enclosure that uses the heating elements from the top of the stove and some sheetmetal, insulation and your PID/SSR as a mini oven.
Weekly update #4
Upgrading the oven
We decided to add the insulation we found and it just works well. While re-insulating, we understood why we were struggling to achieve a higher temperature: the upper side of the oven was in really bad condition (see photo). As a temporary solution, we removed some of the rust and wrapped the top with aluminium foil before covering it with insulation material.
@s2019 Thank you also. The second switch idea sounds to be a good alternative. We added a fan on the other side of the heat sink and there’s no longer overheating (see picture 2; the casing is temporary). Concerning the healthy margin, is there a way to estimate the amperage of an oven in advance (I mean, without using a multimeter). By the size of the heating elements, maybe?
We don’t really have a strategy if the lid gets tuck. We have plastic supply issues and didn’t gather enough plastic yet to fill this mold.
Other nice upgrades would be to have a window anda light to follow the melting process without opening the oven.
As a reminder, we are conducting trials on two different packages, which each have three model/brand variations : Transparent biscuit packages and metallized noodle packages.
We were expecting PP, but the biscuit packages seem to be made of PET: It melts around 260°C and leads to a brittle product that sinks in water.
The three different packages melt at the same temperature and bind well together, which may allow us to play, to some extent with the different colors. You’ll see hereafter that the small batch we produces isn’t the most aesthetic. However, focussing on a waste managment perspective, I am convinced we can have an impact by finding the appropriate end-product.
Has anyone an experience on recycling PET wrapper? What would be the minimal thickness for a resistant end-product? We have produced small pieces up to 3-4 mm only, they are all pretty easy to break.
(To be continued)
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