We've just launched our map. Add yourself by clicking here!


Washing plastic

Mathijs Stroober mathijsstroober

Washing plastic

08/06/2018 at 09:53

For a future project, we are looking for  for waste processing  efficiency (read cleaning, shredding, sorting) and shredder efficiency.

In the coming weeks I will post my findings on washing, solutions for washing and the shredding routine.

More about shredding efficiency you can find here.

20 replies
12 subscribers
8 saved
sort on most likes

In reply to: Washing plastic

08/06/2018 at 11:57

Hey there @mathijsstroober !
I read industries often use caustic soda to remove the paper/glue from the shredded plastic, have you looked into it ? (need good protection though cuz it attacks skin very hard )

In reply to: Washing plastic

11/06/2018 at 12:20

@imuh You are right but you already mention the hazards of caustic soda. We want to keep it as human and environmentalfriendly as possible.

In reply to: Washing plastic

11/06/2018 at 12:56

I did some tests on washing PET and HDPE. I choose these two because of the high abundance of the materials and also because PET does sink while HDPE floats.
I seperated the materials on type and then made two equal batches of the material. One batch PET and one batch HDPE I washed before shredding and one batch of both materials I did wash after.

I figured out that washing before shredding is more time consuming but has some advantages. Especially oily substances are easier to remove on bigger parts by washing them with some cloth. Also it prevents the shredder from getting dirty.

However I think the best process is first cutting and cleaning the dirty products (especially oily substances) than shred than clean in water and then dry.

This is mainly because you can make this in a more streamlined process.

During washing the shreds I noticed some things that can be important in the further research (first picture):
Oil floats (obviously) so it is floats in the same layer as the HDPE.
PET sinks to the bottom of the container resulting that it gets mixed with the dirt.
Microplastics which get in the water should get handled and filtered with care. (see last picture

Right now I will continue on washing process optimization.
Open for feedback 🙂


In reply to: Washing plastic

11/06/2018 at 16:12

First small scale sieve for sieving shreds. The mesh is a little bit too coarse so the shreds ‘leak’ a little. Searching for finer sieve.


In reply to: Washing plastic

13/06/2018 at 10:47

Together with Dave, I came up with the idea to shred and wash plastic at the same time. With siphoning technique you do not need a pump,although how I need to transfer the water back to the top by hand.
The first impressions are pretty good and it will probably further explored in version 4. However, due to time constraints, I am not focussing on this principle.
But it is nice food for thought.

Watch a short video here


In reply to: Washing plastic

13/06/2018 at 13:25

Nice one @mathijsstroober –  I was already thinking about combining those two processes (shredding + cleaning), cool to see it being tested!

For the upward transport of the water, we could use an archimedes screw (maybe using the rotation of the shredder motor to run the screw as well, i think it won’t need a lot of power).
And probably would be good to have some sort of filter there, so the water gets cleaned in between every cycle.

In reply to: Washing plastic

13/06/2018 at 14:03

Yes, you are right. But as mentioned.. this will be for a later research. It maybe needs another frame etc…


In reply to: Washing plastic

13/06/2018 at 15:54

Testing sieve sizes

As a part of the washing research, I did test different sieve meshes.  I wanted to see which mesh is the best for further research. The fabric were different kinds of mosquito meshes. As result I figured out that the meshes do not difer much in filtering qualities: The plastic was caught but the dirt got through. It  looked like plastic did stick less to on of the meshes.
After filtering with one of the three coarse meshes, I also filtered with the finest I could find. Although it caught the same size of plastics, the water stil had signs of microplastic.


In reply to: Washing plastic

13/06/2018 at 17:43

i’m looking into a solution as well. i am evaluating 2 options right now:
1. converting a regular washing machine with a more fitted sieve
2. use sieves in combination with vibrating housing, enabling more easy to built extensions like multi-stages of cleaning

is there are already a certain mesh size you could recommend to get started ?

In reply to: Washing plastic

13/06/2018 at 21:09

Hey @mathijsstroober !
Very interesting to see your results !
I was thinking about a point : after microplastics come nanoplastics 🙁
all the effort you put in there will not manage to seperate micro/nano plastic particles from the dirt or any other things ? Is there a minimal size of “remaining plastic in the sieve” your are aiming for ?

I have sorted to clean up my plastic from glue (mainly) once reduced in size; and i am wondering if the washing wouldn’t be more effective while the plastic is still in its whole piece. The shredding would then operate on a clean plastic and we could imagine a system which vacumes all the output of the shredder and maintains it together. The main cleaning is from glue and dirt, so i think it would take less effort & be less risky to do it before shredding. ( Though the industries tend to shred then wash, they are operating tons of plastic at the same time; being at a much smaller scale, process may be rethought ?)

The mesh research would be very interesting for the vacuum bag ? :p need to push the research
Anyhow, these thoughts i just pushed aren’t there to bring you down on the research; cuz we need as much intel as possible to make all this possible !

edit : sorry just saw the video now ! so the sieve would be for that system ok ! i’m curious, what are you adding to you water to clean the shredder plastic ? what is the diameter size of the holes of your schredder sieve there ? Maybe that size impacts also on the amount of micro/nano plastic created through the schredding process; OOoor those micro/nano plastics could get collected in the bucket underneath and be reagglomerated together through a special very very very thin sieve ?!

In reply to: Washing plastic

13/06/2018 at 21:48

Nice feedback, your are right on some points. About micro/nano plastics. I want to have the cleaning water in a pretty closed process. Only it water is really dirty it can be changed. Filtering the water can be done with something like sari cloth. Old sari, is really fine and also able to remove cholera bacteria. Read here more about this.

However, thoroughly cleaning plastic before shredding takes a lot of time and is more difficult because sometimes you need to cut it in small pieces in order to remove all the dirt. Also a great thing to do is to let the pieces scrub itself. Which works better with shreds than cut pieces of plastic. Otherwise all the pieces need to be cleaned by using cloth and wiping all the debris.

One thing to take in to consideration is that except glue and dirt, oil is also something to remove. Right now I think it works best to first clean the oil/ grease and then do shredding and washing (dirt/glue).

Also I know PP is on small scale, but I am researching efficiency to recycle as much as possible. Making it more attractive to wash also after shredding

In reply to: Washing plastic

26/06/2018 at 20:42

Have you though about using a sand filter to remove the micro plastics?

That would be very easy to replicate by other people.

Not sure about speed though.

In reply to: Washing plastic

10/08/2018 at 13:37

mathijsstroober, imuh
I was reading through your posts and wanted to give you an alternative to caustic soda have a look a this thread https://www.quora.com/Are-there-any-alternatives-to-sodium-hydroxide-lye-in-making-soap
I believe I will have an  answer and will post in a few weeks just need to finish tests

In reply to: Washing plastic

11/08/2018 at 13:17

Very interesting topic, points and tests @mathijsstroober.
It might be relevant to mention that we have focused mainly on ocean plastic waste as well as HDPE-cans from gas stations.
Currently we have washed before schredding. My biggest concern about washing after or simultaneously is that the contaminated plastic will dull the knifes in the shredder a lot faster. Any thoughts or empirical indications regarding this?

In reply to: Washing plastic

12/08/2018 at 03:36

Some [semi-random] process thoughts on cleaning and separating the shredded plastic.
* Fluidized beds
* Centrifuging
* Skimming
*Stacked sieves
* something like a fractionating column for density separation?

Some process thoughts on cleaning the wash water.
* Centrifuging
* Skimming
* Flocculation

In reply to: Washing plastic

12/08/2018 at 04:03

@tsayles   We are  filtering the water through charcoal filter and then it is deemed grey water.This then gets used on plants. Will post pics when we have finished our tests.

In reply to: Washing plastic

29/08/2018 at 11:03

I have been using moringa as a suppliment and have been reading about its Amazing benefits. It is very inexpensive to produce and can grow in the harshest enviromment. Current studies have proven the seeds are able to purify contaminated water making it sutible to drink. Combiing it with sand its called F sand increaseing the efficiency of the process while still maintaining its simplicity. if we use F sand to clean the plastic we benefit from the scrub of the sand and the water we use to clean gets purified at the same time. The sand could help remove oil and glue residue possibly too. The sand will scratch the plastic suface according to how coarse it is but is that a problem if its getting melted down. Im attaching links to some articles i have read.


In reply to: Washing plastic

02/09/2018 at 17:23

Hey guys! I was reading and thinking about all ideas concerning filters.
Recently, I’ve heard about an Italian company (Directa Plus) that has developed a graphene filter (called Grafysorber) that can absorb every non-emulsified oil.
Now, I’m not a chemist or a specialized engineer, but I think it can be helpful.
It could be expensive to buy, but it is reusable (so it is not consumed over years), works better with the slow speed of Archimede’s Screw or a slow-speed pump (so the water and oils will not be emulsified while passing through the filter) and if squeezed you can collect filtered oil and dispose of it in the right way.
Maybe exists something similar of other companies around the world. Just to let you know this other possibility, for a brainstorming.

Link to Directa plus website:

Grafysorber video demonstration:

In reply to: Washing plastic

25/09/2018 at 20:27

Any progress on this @mathijsstroober ?
@plastikfantastik, any progress on the biodegradable alternative to caustic soda?

Effective washing of glues, etc… is now the biggest (conceptual, since I haven’t actually built anything yet…) impediment in my project to turn plastic into building materials in the developing world. As it stands, I’ll have to purchase plastic that has already been collected, washed, shredded etc… But once I can wash it in an environmentally friendly and efficient manner, collecting and shredding will be easy and reduce input costs by a factor of 4-5x.

In reply to: Washing plastic

02/12/2018 at 18:54

You can find new experiments from V4 here:


Viewing 20 replies - 1 through 20 (of 20 total)

You must be logged in to reply to this topic.

Support our projects on Patreon so we can keep developing 💪