A method for refining bottle grade PEN ? 1

[clandestinho]

Hi all polymer people,
this question is way outside my field so please bear with me if it's trivial or just impossible:

I am trying to find out if there's a way to refine a bottle grade PEN (polyethylene naphthalate) resin into a higher I.V. grade?
For example, is it possible to take a medium I.V. grade with a wide molecular weight distribution, melt, and somehow separate this into a lower and a higher molecular weight resin?

Higher grades of PEN is in short supply due to a strategic decision by the main manufacturer not to supply these grades.
I will need to have this done to 10 - 20 MT so a method must be reasonably efficient. If there is a way I will need to find a company in the US that could do this for me and I need to know what to look and ask for.

Many thanks

 

[patprimmer]

No you can't separate them physically.

With some resins, if you have the correct equipment and if you know what your doing, you can do solid state polymerisation to increase the molecular weight by restarting the polymerisation process. It certainly works for PET. I have no idea if it works for PEN.

To solid phase polymerise PET you need to heat it under high vacuum.

Regards
Pat
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[Demon3]

The standard way to increase molecular weight of polyesters is to add Joncryl, an epoxy from BASF. Contact person in the US is Alex Sokolowski.

Chris

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[clandestinho]

Patprimmer, thanks for the advice, I did some reading and it seems it can be done with PEN, only its a little more difficult to control due to the higher barrier of PEN which may cause volume expansion of the pellets. The process may also need an inert athmosphere to avoid oxidizing the surface. It seems worth a try.

Chris, thanks for the idea. I have never heard of Joncryl and I don't know what side effects this may have, if any. The application requires both the higher barrier and higher modulus of PEN. I will look into this.

Thank you, both of you.

Best regards,
Claus

 

[Demon3]

The epoxy groups react with the polyester chains gluing them together to increase molecular weight. It's very well proven technology.

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[patprimmer]

Increasing MW will not impact much if any on modulus or barrier.

Adding flake type fillers is the normal way to do that, or by increasing degree of crystallisation by use of a hot mould. Once again I know increased crystallinity works for PET, but I don't know for PEN. Both would destroy transparency unless you fill with nano particles of less than 40 nano particle size.

Regards
Pat
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[clandestinho]

Hi Patprimmer, Hi Chris,
let me provide some background. The resin is for filament fiber spinning. Normally high IV (>0.9 dL/g) PEN resin is used for this but Teijin which i believe is the only manufacturer of these grades has reserved their resins for their own films and fibers.
Lower MW will reduce the young's modulus of the fiber and I am trying to find out if I can refine a lower IV grade to something that can be used for fiber extrusion. The retention of mechanical properties such as tensile strength, modulus and flex life are very important. PEN fibers are used for tire cord among others and are expected to perform for years.

Although I do not necessarily need to reach the full specs of highest grade PEN yarns I would still be worried about 'shortcuts' to a higher MW if this could afect the long term performance of the fiber. On the other hand, any thermal treatment that might lower Tg is also an issue.

Does this change the picture? I am currently in favour of trying the solid phase polymerisation route, mainly because I dont know how the epoxy link will affect the properties over time.

Does someone know where to find some specs for the Teijin PEN resins? Thet are not on their website, probably as they took the resins off the market, I can't find them on IDES prospector either.

regards,
Claus

 

[Demon3]

And you don't think that BASF has already checked the long term properties of using Joncryl which has been on the market for probably a decade or more?

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[clandestinho]

Hi Chris,
I much appreciate this advice and I will follow up on this and see what BASF thinks about my application. If this is doable it would be a much easier route to take.
What I was trying to say was that PEN is used for a variety of purposes, from short life food containers to high performance tire cord which will be under load for years and simply must not fail. My application is not tire cord but there is still a liability issue if the fiber fails, thats what makes me opt for the safer route, whatever that is. I will ask BASF if they have experience with Joncryl for fiber extrusion.

regards,
Claus

 

[patprimmer]

I have been out of the spinning chips market for about 17 years now but solid phase polymerisation was the normal method for preparing PET spinning chips then to produce yarns for all sorts of applications including seat belts, tyre cord and conveyor belt reinforcements

The final properties of the yarn as opposed to single fibre tests where as much to do with spinning and after-treatments as they where with the polymer itself. We made what we called high efficiency yarns. They where out of 0.9 IV just like the other yarns, but had more time spent on stretching and annealing processes to get greater stability and better load sharing between filaments when the final article was produced.

Regards
Pat
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[clandestinho]

Thanks Pat,
interesting, and I agree that drawing, relaxing etc is just as important as polymer properties.

Since you have this experience I would like to ask if there's a way to estimate yarn (or better, single filament) properties, primarily youngs modulus, from IV values of the PEN resin, other than experience and trial and error?
I dont have any formulas for this and I dont know if I could use practical experience with PET and somehow convert to PEN? My aim is a modulus of 200 gf/den (opposed to 250 for Teijin PEN fibers) and I could save $$ on the pilot line if I could calculate what IV to try to reach. The yarns will be FDY from 250 - 1500 den, 35-200 filaments.

Any input will be much appreciated !

Claus

 

[patprimmer]

You now have as much as I have on this subject. My only direct experience is with PET

Regards
Pat
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[clandestinho]

Pat, Chris, thanks a lot, I now have something to work from. I will try both directions.