- Washing of scraps coming
from municipal collection
mixed plastics we mean the light fraction
of municipal plastics separation.
- The results
are normally not very exiting in terms
of purity because what can be found
into this mixture is what follows:
- LD, LLDPE and HDPE film coming
from shopping bags, packaging etc. and
- Heavy printed PP film that's the
eye catching wrap of most food products.
- PVC film and blister pack that's
- Multi-layers films used in the food
industry to preserve perishable food.
- PS trays both vacuum molded and
- Same trays out of PET
- Cellophane, leather, cleaning pads,
cotton fabrics, wood, some old shoes,
you name it.
- So, with a "raw material"
like this you shouldn't expect much
and here is why:
- First, to make a system delivering
a good quality product at the end will
cost a fortune, and nobody will make
any money out of it.
- Second because, even thinking to
the most sophisticated unit for the
separation of whatever you expect as
normal contamination, there will always
be something you didn't expect and quality
will be spoiled anyway.
- The matter has many variables and
a lot depends by the starting point.
- If you get the "all plastics"
to be separated by yourself, you will
have some valuable PET bottles out of
the stream, some HDPE bottles, drums
etc, that's a good material to be recycled
and going deeper with some manual sorting,
a stream of LDPE by its own that after
washing and separation will be good
for film applications.
- The rest is the material we were
talking about before so, making an average
value, this material is the one you
have been paid for. (when you got it)
- If you have only this material,
meaning somebody else took the good
part of the mixture and left the garbage
to you, you better ask for a fair
amount of money before messing with
- And now, how to handle it and what
you should expect as final product.
- Even with the very best, sophisticated
set up that will remove all PVC, PET,
PS and other sinkable plastics, with
a set of washers and dryers to remove
all paper, foamed materials, some wood
etc, what remains is still contaminated
by some multi-layers film, cleaning
pads, foamed Polyurethane that will
not break apart and surely something
- All this will be a pelletizing and
- And this is only what's related
to separation while, like any other
film washing line, the other two difficult
points are cutting and drying.
- Cutting because heavy contamination
will make your cutting system to be
maintained pretty often and drying because
films are getting thinner day by day
and, as you may understand, the thinner,
the more difficult to dry.
- Cutting first: the only approach
in this case will be the single shaft
shredder that's described in the machinery
section of this site, because it is,
specially for high production rates,
the less expensive machine in terms
of "currency" per Kg.
- One of the things we didn't mention
yet is this kind of system should be
sized for production rates not less
than 1 ton/hour and, if more, much better.
- Drying is the other issue; mechanical
centrifugal dryer are performing well
if thickness of film is over 40/45 microns,
while if thickness is less, like it
normally is in this case, together with
the high throughput required, moisture
content you should expect at the end
is well over 10%, meaning no extruder
will handle it.
- You will say hot air drying system
will fix the problem and you're surely right
but how much it cost ? (we don't like
- In our opinion, the best ratio energy/drying
effect is achieved by the continuous
agglomerator that's described in the
machinery section of this site.
- Doesn't matter how much (till 1800
Kg/hour - 4000 lb/hour) and which level
moisture content, up to 20% this machine
will deliver to the extruder a melted
material with a residual mixture content
of less than one % all extruder can
- Little space required, continuous,
no pipes jamming, no possibility to
go on fire, no operator required. What
you think ?
- Let's go now to the final stage
of the line that's filtering and pelletizing.
- Which kind of extruder should be
used for this purpose ?
- A single extruder will do it, no
question, considering the fact that
single screw extruders don't mix materials
- A twin screw extruder, much better
for compounding but delivering less
pressure and making filtration a little
- To state what's best it is compulsory
to know which quality material is getting
out of washing line and see if quality
is to the level to try to get a good
pellet, at least for injection molding
- So, difficult to say and to be evaluated
time to time according with what you're
- Back to extrusion, the best way
to go, is a combination of the two extruder;
first twin screw extruder will provide
for compounding and first filtration
( backflushing filter with a screen
0,5 mm) and a second single screw, a
short L/D one, for further filtration,
down to 0,2 mm and pelletizing.
- This, of course, if your customer
will pay for the higher quality.
- As far as filtration, once again,
you can get more details into "polymer
filtration", in the machinery section
and, as we say there, the "very
best" device is yet to be invented
but everyday somebody finds something
new about it so let's keep the window
open and see what happens next.
- If you need any more deeper information
about one of the different steps of
the process please write to: