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 The washing of plastic scraps


In our dictionary the word "Washing" means to remove dirt from whatever it is and this sounds absolutely obvious.
Well, not that much.
For example, most of everybody calls tanks "washing tanks"
Now you can check by yourself putting a piece of plastic into water, and feel free to add even some soap, leave it there for few hours, or a day, and see how clean it is after this.
It has exactly the same amount of dirt it was before this "washing" treatment.
In other words, to remove dirt from plastic flakes, it takes some other action.
Now, what about doing what it has been done for centuries to wash cloths: brushing and/or beating with stones or something like this, in other words making friction to remove dirt.
In the 21st century the way of washing didn't change much, unless for the fact soaps are different and performing better.
The end of the story is make as much possible friction (we're speaking about pieces of plastic and not an expensive piece of cloth) in presence of something that can trap dirt into it (detergent).
Do all plastic need detergents ?
Not at all.
If contamination is, for example, paper, sand or something that remains on the surface, detergents are useless because the process will be only to remove them from the surface while, speaking of oil, glue or other sticky dirt, matter can be different.
Sometimes, with some materials, contamination even help to make polymer to look better; for example if you leave some PPM of oil into LD-HDPE or PP you'll get a beautiful looking pellet, shining, so why to remove all of it ?
Or why to remove all paper contamination if your pellets will be used to make lumbers ? A little bit of paper will "expand" the profile, and nails and screws will go into much easier than a solid profile.
Of course we're talking about a very little amount that should remain inside the scrap but, again, sometimes a little bit of contamination helps to make you product better or better performing.
Most of scraps anyway, need to be perfectly clean and here we'll be talking about the meaning of "perfect"
It needs to perfect when a certain kind of contamination really bother being there and needs to be removed all the way.
Let's make the example that, in our opinion, suite the best this concept:    glue into PET washed bottle flakes.
Many year ago, asking to the chief engineer of the biggest company in the world recycling PET which was the maximum amount of glue allowed, he just said: don't know and don't care.
So, in the years we found out the reason for this:
Glue doesn't effect PET itself but it just turns the color of pellets anywhere from yellow to brown because melting point is a lot different and glue, normally PU based, release oxygen to PET and turns it yellow.
So, if you're looking for perfectly clear material or you have to make a precise color with recycled flakes, you need to remove all glue content while, for some other application, you only need a flake with no dirt and careless about glue content.
Everybody now knows how to remove glue while not many understand how much it does cost.
And also, after flakes are gone into any process using caustic, flakes need a good rinsing (otherwise your flakes will turn yellow anyway) adding another cost.
For the purpose of washing we did develop our own technology that is a friction washer where the amount of friction and residence time of flakes can be adjusted by the operator.
The machine is controlled by a simple electronic device that keep the amperage of main motor constant to the level set by operator and residence time will be accordingly.
This machine does not require steam of heater bands of any kind to make water hot because it does it by itself, just by the friction created by the rods spinning inside.
We have been told it is too simple to perform well but we do like simple things.  (and well working)