Plastic Sorting-A personal project

Greetings from Denmark, albiet from an Indian citizen.
My name is Aniruddha and I am a student of Industrial Design. I’ve been a huge fan of the Precious Plastics project and was wondering if and how I could add to this wonderful body of work.
So here is my pitch for a idea. I’ve tried making a video but I can’t say I’m proud of it.

So i’ll try and summarise my thoughts through words.
I want to make the sorting of plastic waste into a playfull and rewarding experience, especially for children. For doing so I hope to get public sector educational bodies involved in the movement.
Being a forigner in Denmark, I believe I can view the waste management cycle here in a fresh perspective.
The economy in my adopted country is mostly knowledge based with little production of any kind. Most of the processes of creating and disposing products are outsourced overseas.
There is a strong public sector and a will to be a sustainable system in my region. But as the ‘dirty work’ happens overseas, I believe we citizens may not be completly aware of the problem.
At the moment I’m just starting with the legwork of visiting local waste management bodies and educational museums. More to follow soon.
In the meantime I would love to hear your opinion on the matter.


Hi @ani0555. Nice you made a video, don’t be harsh. The more you make the better they will get! Sounds like an interesting project you’re starting. Keeps us posted on the proces! Would love to see some information/pictures about your visits to the waste management!

Thanks for sharing. It is very interesting, the work that you are doing. I unfortunately am not able to view the link you have shared.
I would love to see pictures sometime. The ‘marker’ method is something I too had to use on occasion to tell LDPE & HDPE apart.


ABS is is relatively newly invented plastic. The 1-6 numbers on the plastic items do not include ABS. ABS goes into category 7. Most post-consumer category 7 plastics are sadly not recycled.

thanks Andy – for reminder that testing is IMPORTANT. so annoying that so many widely used consumer products can be made from several different plastics.

(just linking some topics for the AIs and those interested)

Also see

Sorting LDPE and PP apart

for a more current discussion on (part) of the topic.



“6. I also teach them that bottle caps wth hinges are always PP because it is good at repetitive bending.”


This is called a ‘living hinge’ and while PP is usually regarded as the best material for this, it’s no guarantee the item is PP. HDPE is often used for living hinges, (particularly in larger items like blow molded tool cases), even PET can be used.

The best document on float sorting plastic I found is a middle-school lesson plan.

I work on a small scale in Haitian villages. I want to show people low cost ways to use the local “garbage.” and a shredder is expensive and electricity is intermittent. So instead, I show people how to sort unshredded plastic.  We collect lots of bottle caps and small things.

Some things that work for me:
1. do water float first.
2. for things that sink, instead of glycerin (expensive, hard to get) I use 2 cups vinegar with 1/8 cup salt.  The PS floats and the PET and PVC sink.
3. By the way, ABS has a specific gravity very close to PS, so both float in my salty vinegar. Very little ABS in Haiti, so doesn’t matter to me. But am interested in what would separate them.
4. we don’t use the pvc and PET.
5. use veg oil to separate the PP (it floats).
6. I also teach them that bottle caps wth hinges are always PP because it is good at repetitive bending.
7. wash the hdpe and ldpe to get the oil off, then float in alcohol. I use isopropyl alcohol 92%, with equal parts water, to make alcohol 46%.
8. I also reject the bottle caps that have obvious liners – clearly 2 kinds of plastic, so we won’t use them.
9. The difficulty is that the alcohol is stinky, and evaporates, so you get things that neither float nor sink.
10. My answer is 2 bottle caps, one I know is ldpe, and one I know is hdpe.  I toss them in, one floats, the other sinks. They are my markers.  I toss in handfuls of plastic and most are clear floaters or sinkers. After a while, stuff begins to neither sink nor float, so I add a little alcohol, making sure that my two markers stay in place.
11. Obviously not a fast production method. Bur for people with time and few resources, it works.

Hey Marco,


Thanks for taking a look through my work and for sharing your thoughts. Yes, I do believe what you have drawn can be achieved through a little ingenuity. That valve/spout combo you need may be tricky to achieve but I’d encourage you to go ahead and create mock-ups.

I eventually replaced the Archimedes Screw with a combination of bottle-brushes and a belt drive. I can’t remember if I shared that on the forum, but I will share it here again once I can find the photos. (*edit images added :-))

Think hard about why you wish to automatize the process. These tanks work as a fun learning tool about plastics and density. But they will not be able to consistently sort out a large quantity of mixed plastic.


Here to help

-Ani 🙂


Hey! I was thinking and reading all your posts…  I just conceived this primitive Plastic sorting system. Ok it’s very rough, but what I wanted to do is give an alternative (or ispiring it) to the Archimede’s Screw problem. Hope this will bring you a new perspective.

P.s: the cube tank in the second picture is one of the main tank shown in the first picture. The second picture shows only the way you can collect floating plastic and bring them to the second tank. Still looking how to automatize this.

Hey @davehakkens ,
Its been a while. Yep, finally put made one. 🙂
It works fine as a educational tool. The students enjoyed themselves and so did the chemistry teachers. The archimedes screw wasn’t good enough in the end but I do have another option planned.
At the moment the sorted plastic isn’t pure enough for an application like say the extrusion machine as we has discussed in Feb. But should be fine for injection moulding.
As an academic project its deadline is past. But as a personal project I am still hoping to tweak the experience a bit further. I may also take a leaf from your book and make a tutorial on how it can be made.

Here are some videos of mechanisms I tested. I now want to add gears and a drivetrain to the second option.

Cool! you made it! Looks good. So how did it work, is it a good way to seperate plastic?

last set

some more

Here are some images of a workshop I conducted with the tanks at a local adult education school. Please feel free to ask me any questions.
I am also looking to develop simple mechanisms to move the plastics between tanks. I’ll post some examples asap, nevertheless I would love your input as well.

Hey @chrismcgowen-com ,
Its all trial and error at the moment. The hot air gun was to make sure that any liquid on the surface of the shreds evaporates and does not alter the density of the liquid in the next tank.
But if you have any suggestions I would love to get your input on it.

I have now conducted a few test sessions with students. I’ll upload make the images available to the community asap.

Love your thinking of the multiple trays pulling off sorted materials – elegant. I don’t understand the need for the hot air and can see more problems than benifits. Is it to move the material along to the next stage?

Now the question was how to make this sorting process a fun, enjoyable activity. To do so I imagined the experience you can see in conceptual video here:

I’d advise you to turn up the volume a bit.

I am at the stage where I am building mock-ups with various configurations and trying to identify which one would best fit the experience.

Your inputs would be most welcomed.

Its been a while since I last gave the forum an update. I have been keeping myself rather busy.
So to cut to the chase, Through my research I discovered the following.

Each type of plastic has a specific density. Using a series of liquids of corresponding densities I would be able to seperate the 6 common types of plastic.

Its a model that shows how all house-hold waste is sorted. When school children or new clients visit they are given a demonstration.
Its a manual mini version of this
Complete with magnets and a foot powered air pump.

thanks for sharing this here @ani0555! Very interesting to see your visits and read about them!