Washing Plastic (V4)
Washing plastic is essential in the recycling process and at the moment it is mostly done by hand – a very time-consuming process.
While working with plastic films I came in contact with water and plastic and the advantages but also dangers it has to offer. Shredding film has turned out to be a challenge because of overheating and dust. My only solution for this was to work with a water-cooling system. I got familiar with the dangers of microplastic in water, the dirt and chemicals, and filtration processes. I changed my focus and now I am working on everything which has to do with washing. Starting before shredding and ending with a clean and dry workable material.
Washing plastic is a very broad topic and it contains many different steps. Each of them is important and I will spend the next months on researching, experimenting and updating you guys – I hope, together with your help, we can create a way to make it possible, that small workshops are able to work efficiently and save for the environment.
Creating clean plastic demands different machines, which have to function in a workflow. Designing this process seems to me as important as designing the machines so I will also work a lot on how the different work steps could look like.
So what have I done so far:
After gathering all the information from @mathijsstroobers topic washing plastic and some research I have defined and started to work on the different steps – Cutting and prewashing, shredding with water, collecting the shreds in a mesh bag, modifying a washing machine, drying and most important filtering.
At the beginning of January we redefined the scope of this project a bit more broadly to look beyond washing alone and instead design an entire workflow for shredder workspaces. Since washing is one facet of the larger shredding system, it makes sense to look at the process as a whole and design within that. We’re designing the system with our V4 semi-industrial shredder in mind, which means higher volumes of plastic will be processed on a daily basis.
Starting out, we looked at each stage of the current process and identified pain points that we can resolve to make the process more efficient and user friendly. The stages and goals are laid out below:
Collection: Offer an easy way to collect unsorted plastic from community members. Collection method should make sorting easier.
Sorting: Offer a method of sorting plastic that’s flexible and can adapt to the varying volumes of plastic types, colors, and cleanliness that a workspace might receive on any given day.
Pre-washing: Offer a way to efficiently remove loose debris from plastic prior to shredding in order to keep the shredder as clean as possible (wet shredding isn’t an option)
Shredding: Offer a user friendly way to interact with the shredder and shredded plastic, making transport between shredder and wash station easy and efficient.
Washing: Offer an efficient way to clean dirty plastic of various types (kitchen, beach, etc)
Drying: Offer a space efficient way to dry plastic after the wash cycle
Storing: Offer a user-friendly, space efficient way to store plastic once it’s been processed and is ready to sell
Ultimately, the goal is to develop a streamlined workflow that works seamlessly across each of these process stages.
To start, we roughly 3D modeled our initial concept of how the space might look with each station in mind, then built a life-size mockup to test it in real life.
This is probably the most challenging, but also most exciting problem. The plastic we wash is very contaminated with dirt and oil and also loses microplastics in the process. All of this will end up in the water. Many low-key washing facilities around the world are pouring this toxic mixture on the streets or in the sewage, a proper filtering system can be very complex and expensive. I am going to gather information about ways to filter different contaminations, recreate them in a DIY environment find out what works and at the end provide instructions for an easily repeatable filter, so workshops can deal with their own waste.
The first two prototypes are connected between the pump and the dirt-water, this is not an ideal solution but I am trying to work now with one “clean” tank and one dirty one. Perhaps I will introduce an overflow filter between those two.
The filter medium I chose is polyester filling. In my test, I got very good filtering results and the medium can be used for a long time (so far). After it is unusable, we can dry it and for example, put it in a pyrolysis machine or bring it compactly stored to a recycling facility. Attached to the recent filter is a box with activated charcoal to reduce the toxins in the water, this is a very well tested way and I only need to figure out how often I should be using it to get out the most of the activated charcoal.
Cutting and prewashing:
I haven’t done any experiments here yet, but I believe for some sort of products it might be helpful to clean them a little bit before shredding, e.g. oily surfaces or impurities like sand which would be to rough on the shredder. Though the end goal is to make this step obsolete.
Shredding with water:
This is a fairly easy process, as long as your shredder is built from stainless steel or made water-resistant in any other way. I connect a pump (link here) to a water tank, located beneath the shredder from there a pipe leads up to the shredder and the water cools, contains the dust and ends up in the tank again. Of course, you need some sort of sieve or mesh to keep the plastic shreds out of the pump. In my first system I used a fine mesh on the bottom, this way turned out to be prone to failure and clogged up easily.
Warm laundry cycle did the best job of bringing the plastic back to a bright, vibrant white. Cold laundry and the drill mixer results were pretty similar to each other which leads me to believe that warm water is an important variable for cleaning this type of plastic.
Warm laundry cycle was the only method that removed the oily residues from the plastic. Warm water seems to be a very important variable for this type of plastic as well.
Sand remained on the plastic after using all of the listed methods. That said I did find the sand very easy to remove by lightly scrubbing the pieces pre-shred with water and a brush. None of the methods completely removed the algae, however the warm laundry cycle did a better job than the other methods.
Experiment | Using a paint mixer to clean shredded plastic
This morning I experimented with using a multi-purpose mixer to clean shredded plastic in a bucket of water.
The mixer creates a lot of turbulence, which seems like it could be pretty effective for cleaning plastic. The mixer’s turbulence seems like it’d be a good counterpart to the centrifugal force created by the washing machine, which is better for forcing particulate/water out once it’s already been agitated.
Switching back and forth between rotation directions seems to be a good way to continually agitate the plastic. You could potentially have 2 or 3 mixers installed into a single, large container, rotating in opposite directions to really stir things up.
Louis and I discussed the possibility of a two-phase process earlier and it seems like the mixer and washing machine might be a good combination for such a process.
Phase 01: Use turbulence of the mixer to agitate and aggressively clean/separate particulate from plastic.
Phase 02: Use centrifugal force of the washer to force remaining particulate and water out of the mix through a mesh.
More experimenting to do, of course, but interested in exploring this route – In this scenario, it might even be possible to simplify the washer down to a rotating drum that’s rigged up to some sort of motor/bicycle.
Each topic is covered only very vague and I will post more detailed later about them, but right now I am testing, researching and could really use some input about your experiences with cleaning plastic, filtering water, drying and everything around. One problem for me at this point is to find good methods to control how well I am able to clean the plastic and the water. To see the results in plastics I will start with one very simple method. In a small mold, I press and the test sample in a sheet of roughly 1 mm thickness and control it over a light table for seeable contaminations, how I can find oils and other alien materials is still a mysterium for me. A similar process can be used for the water.
If you have tips, questions, critics please answer in the topic and I will get back to you!
Modifying a washing machine:
A household laundry washing machine provides me with many features I can take advantage of. I can use the different programs, temperatures and especially the centrifugation function, which will help a lot to get the plastic dry after its clean. All whats then still necessary is to hang up the bag for a little bit and the plastic is ready to use. Connected to a water pump and tanks the machine manages to run autonomous and I can contain the dirt and microplastic in a filter, before adding the greywater to the sewage or even water plants. To save energy and reduce material damage the pump is controlled by a relay which turns on when the inlet valve of the washing machine opens up. How effective this process is gonna be I still have to find out in the next weeks with many experiments and ways to proof the cleanliness of the plastic.
Collecting shreds in a mesh bag:
For the next system, I am trying bags made out of mesh. They will be connected directly to the shredder, collect the plastic, but let out the water and the dirt. For these bags, I am trying differently sized mashes to see what works the best for what kind of plastics and shredders. Changing to bags can help to keep a necessary cleanliness, they are used from shredding to washing to drying and also for storing.
A color system could help to keep the individual bags dedicated to one certain kind of plastics.
In regards to your workshop, I would like to share our experience for the last 1 year. In total we have collected 967,32 kg of plastic.
When we started we collected unsorted plastic, soon we realized we couldn’t manage the quantities received.
Our moto for the last year has been “recycling begins with your choices in the supermarket”
Collection: we have established a collection point at the back of our shop, where neighbours bring households plastic items washed, dry and separated by themselves into the four main plastic resin categories (normally found in a house).
Sorting: The main sorting is done by colours and in the case of PET bottles of water or soft drinks, by brands.
Pre-washing: We have the system that you develop, very similar (hope to post a picture soon)
Washing: ultrasonic washing
Drying: We have a very simple drier machine we build.
Storing: Beside the storing area we have overflow storing space
When dirty plastic is collected, it sometimes has loose debris such as food waste or other contaminants. We want to keep these materials out of the shredder as much as possible to reduce the need for shredder maintenance.
We experimented with a number of agitation methods in the previous month and found that using a paint mixer drill attachment works well for removing loose debris from unshredded plastic.
After deciding to use the drill mixer as our pre-wash method, we designed a pre-wash station to further test the concept. To save space, we designed the station so that the water reservoirs, filters, and pumps used for the washing process can be stored underneath the pre-wash station. The pre-wash reservoir drains directly into the dirty water reservoir where it can be filtered and recycled in the closed system.
One issue that often occurs during pre-wash is cleaning the inside of closed objects such as bottles. To solve this, we attached a hooked knife blade to one of the vertical posts on the pre-wash station which can be used to easily cut open bottles prior to putting them in the water.
Plastic is usually sorted by type, color and cleanliness. There’s a huge variety of possible plastic that a workspace could receive on any given day, so we want to offer a solution that’s flexible and can adapt to any situation, whether they receive one huge supply of a single plastic or many smaller amounts of various types.
We designed these bags and frames to hold between 10-30 kg of plastic depending on the density of the contents. The idea is that a workspace could have several of these to sort out their plastic from the collection bins before shredding.
So if one day the workspace receives six bags worth of clean, red PP and 2 bags worth of dirty, green PE, but on the following day receives a very different combination of types, they can easily sort accordingly without the problem of wasted space or mixed assortments by using the bags however necessary rather than having just a few big bags which would result in less flexibility.
The frames are placed on casters so that they can be rolled around the workspace to collection, washing, and shredding stations, but they’re also designed to be carried if casters aren’t an option. The rods sewn into the top of the bags help stabilize the bag’s structure and also act as handles for carrying.
The bag pattern is very easy to replicate – three rectangular panels which can be constructed with two seams.
Below is a breakdown of the work we’ve done within each stage so far:
Currently, the best method we have for collecting plastic waste are these massive bags, which work well in the beginning of the process (collecting) but kind of suck when you have to reach into the bottom of the bag to get the color/type you’re looking for.
To solve this, we modified the bag by attaching zippers to the front panel which make accessing the contents of the bag much easier at all levels.
Warm water seems to be a pretty important variable in order to completely clean the various types of plastic, however for certain cases where complete cleanliness (brightness, etc) isn’t necessary, cold water can work. From these tests, it seems the warm laundry cycle is the best method to effectively clean plastic. In cases where laundry machines aren’t available, the drill mixer could be a good low-tech alternative.
Experiment | Testing various methods with various types of dirty plastic
Next, we tested the various cleaning methods on different types of dirty plastic to see if there’s a “one-size-fits-all” technique or if different types of “dirty” require different cleaning methods.
Cleaning methods used
– wet shred
– warm laundry cycle
– cold laundry cycle
– drill mixer
Dirty plastic types
– household: food contamination
– commercial kitchen: oil, etc.
– beach: sand and algae
Once the plastic plates were rinsed, I wet-shred them (shred them while spraying water into the shredder). Then I mixed the shreds in a bucket for a total of thirty minutes, removing samples at five minute intervals in order to learn how much time is needed to effectively clean the plastic with the mixer. After 30 minutes, I washed the remaining plastic in a mesh bag in the laundry machine to see how it’d compare.
Below are some images of the results. The plastic was partially cleaned, but some residue remained on many of the pieces.
Conclusion: Leaving the pieces in their original form seems to be less effective than shredding (at least when contained in the mesh bag) since it makes it more difficult for the water to reach every surface. Smaller pieces got trapped in larger containers which also caused complications.
I’ve been exploring uses and solutions for non-recyclable plastic over the past couple of months for V4 (see more here)
A lot of the plastic I’ve encountered hasn’t truly been “non-recyclable”… we just don’t have an efficient way to clean it properly right now, so it ends up being discarded rather than recycled. I’m teaming up with Louis to develop a cleaning method to take care of this problem.
Experiment | Cleaning unshredded plastic waste with washing machine
To start off, I experimented by collecting dirty (moldy), household plastic waste to see how well it’d be cleaned in the washing machine without shredding beforehand.
Hi all, we are a charity starting a project to do some local recycling and need to crack this washing nut too.
@pauldufour, do you have a Bill of Materials for any of those systems you tested so far?
Especially the sand-based filter – what kinds of fittings did you use to be compatible with both your water pump and washing machine?
That translucent hose going into your filter barrel looks like a much wider bore than typical water hoses found on the back of washing machines here. Is an adapter involved?
Have any of you recorded any observations on water quality coming out of your filters after pouring into a settling tank?
Ideally the filter would allow you to continually recycle water through the machine, only binning filter sand after a long period, but I guess that there would actually be a build-up of soap in the water from oils dissolved with lye, and that solution would need to be disposed of via sewage.
I’m also wondering how well sticker adhesives are able to escape through the woven bag on a hot wash, and whether they could block up the machine itself.
Keen to get started 😀
Throughout building the mockup, our concept evolved to look a bit more like the rendering below (numbers of units in each stage will change depending on workspace). Things are still shifting, but we ran a test this morning with some very dirty plastic and the system did a good job of cleaning it.
Our focus moving forward is to test the workflow/cleaning methods to identify opportunities for improvement. Some of the main questions we need to answer at this point are:
– how long can the filter run before needing to be cleaned?
– how many times can the water be recycled before it’s no longer usable?
– are the bags durable enough for their intended use?
– how well does the system work with various types of dirty plastic?
To complete the experience, we designed the bags to close with a roll-top, which compacts the plastic and creates a handle to make them easier to carry. The handle can also be used to hang the bags on a storage rack so that they can continue to air dry and are easily accessible when ready to sell.
At first, we thought it might be necessary to lay the shredded plastic out to cover a wide surface area to allow it to dry after washing, so we designed the bags to lay flat on a drying rack to allow the plastic to dry. After some testing, it seems that running the plastic through a centrifuge cycle in the washing machine does a good job of quickly drying the plastic. The moisture that’s left to dry is probably ok to be completed in the storage stage.
One tricky thing about the bag system is figuring out which materials work best during the washing phase. The bags have to withstand quite a bit of weight and force (10kg of plastic and 1250 rpm during the centrifuge phase)
We’ve found that meshes tend to break under the force. So far it seems that woven polyester or cotton is best at withstanding the forces of the process.
At first we experimented with a roll-top to keep the design of the bag simple, but found that it wasn’t secure enough to stay closed during the washing cycle. We added a zipper to the top which seems to do a good job of withstanding the forces so far.
Plastic is usually shredded into some sort of bin/container. We decided to try using bags instead, since that would enable us to more easily transport the plastic granulate from the shredder to the washing machine without having to pour the plastic from one container to another, eliminating a pretty big pain point in the process.
We designed the bags to hold roughly 10 kg of plastic – about as much as a laundry machine can comfortably handle. This standard amount also makes it easy to keep track of how much plastic you’ve processed later in the process when the bags are stored – count your bags and multiply by 10 to calculate.
Great study. If you are going to do additional testing, it may be interesting to add a warm or hot water pre-soak. I think there are many places where warm to hot water is readily achieved through simple solar heating (though perhaps not in Eindhoven right now). It may be useful to know what the minimum effective temperature is. Hot water may also soften or release some of the label adhesives.
If you clean food containers before shredding, is the waste water from that initial cleaning considered simple gray water that can be disposed of? That may influence the sequence. I think you want to generate as little contaminated water as possible.
Your use of wet shredding is interesting. It would be informative to wet shred some clean material and measure the amount and size distribution of the microplastic in the water. You may end up selecting different shredder speeds for different plastics based on the microplastic issue.
Some other agitation methods that may work: tumbling in a barrel (think cement mixer), air bubbles, water jet, etc.
Hope this work continues and also looks at the label removal issue.
Thank you for all the work.
You don’t speak about any kind of washing additives. When you have greasy stuff on your plastic (eg foodplates) an emulgator (soap) is efficient to bind water and grease.
Experiment | Using a sander to agitate
Another method we experimented with was agitation using the vibration of a sander – we made a quick and dirty prototype by strapping an old sander to the bottom of a bucket of water. The sander agitated the water quite a bit, however plastic remained dirty after ~15 minutes of agitation.
The biggest observable differences in cleanliness are between the shredded but uncleaned plastic and the five minute mix – There seems to be a diminishing return once you past the five minute mark. There was also a large difference between the 30 minute mix and the laundry cycle. The laundry cycle brought the plastic back to a bright, vibrant white, which the mixer failed to do.
As a starting point, I selected plates with a range of dirtiness from pretty clean to very dirty to see if there’s a limit to the mixer’s effectiveness. Some of the plates had a lot of contamination so I put them through a mix cycle prior to shredding them in hopes that it might remove some of the large, loose contaminants. This method turned out to be a good way to remove loose contaminants prior to shredding, however it did result in some plastic shreds being created and left behind in the water (the plates were extremely thin – i don’t think this would be an issue with thicker plastics)
To get a better understanding of how well the mixer worked, we collected some dirty plastic waste from local dumpsters – a majority of the waste was contaminated with food. We found a large amount of the same type of dirty plastic (white plates w/ tomato sauce) so we decided to use these as a control for our first tests with the mixer.
I am working on a line to clean agricultural mulch films on a 3-5 tons per day basis.
I am in an arid climate with scarce water resources.
I am looking at using a dry cleaning process.
Here is one company that offers a line based on heat and friction.
Here is another.
I wonder about scaling this down for smaller plastic workshops.
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