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SSP is compulsory when recycled PET will go for food applications..
 
This is the only known way to get rid of monomers and toxic chemicals that, doesn't matter how good washing line is, must be removed for FDA approval.
 
Here some of the methods commonly used and few words about a more economical emerging one.

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 Solid State Polycondensation

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Solid State Polycondensation applies to crystal polymers (mainly PET and PC)
What Polycondensation does, is not only upgrading the IV of the polymer, that's important anyway, but also remove monomers and other dangerous chemicals, specially when raw material is made out of scraps.
There are two know ways to do the job.
First one is the continuous one, very effective, high capacity etc.
Second is the batch system.
Advantages of first method are the ones of every continuous line meaning, when the process is started and all parameters adjusted, everything run smooth.
Of course, it does if raw material at the inlet point has a fixed characteristic, meaning if you set the line to upgrade the IV by 0,2, for example, and you feed the system with a polymer with IV 0,6 the result will be 0,8.
So, with virgin polymers or, in other words, if you handle a steady characteristic product, the result will be perfect.
Can this apply to recycled polymers ?
You answer it.
So, let's talk about batch system.
The batch system SSP is nothing but a "container" where pellets (or flakes) are heated up under vacuum for the period of time variable necessary to get to the required viscosity.
This means that whatever you feed into, you get what you want in terms of IV because the IV increase is directly proportional to the residence time that's under your control.
Does this sound better ?
We do think so.
We did talk about pro's but there are some con's:
Running SSP means losing almost 20% by weight and this happens because acids, momomers etc. are gone.
Few companies now are now selling some silicon based "extenders" to increase mechanical properties of the polymer directly into extrusion.
Some of them got also FDA approval for material at the end of the process so you may take this into consideration.