de-oxygenated plastic

[CRmolding]

Is there an of-the-shelf solution to drying plastic in an oxygen free environment? This would be used prior to N2 blanketing.

 

[Pud]

Hi,

Why would you want to dry plastic in an entirely oxygen-free atmosphere?

Vacuum dryers give a 'reduced' oxygen atmosphere (e.g Maguire for a fast one, countless others for conventional).

Rgds

Harry

 

[CRmolding]

We are molding parts that need to be very inert. The Maquire LPD vacuum drier uses air to dry and convey. I need to remove surface O2 as well as moisture. The material is not hygroscopic.

My initial thought was to vacuum dry but it becomes complicated because the drying and conveying need to be done in an inert gas. The vacuum bleed-off would need to be done with N2 and the intake of the blower would need to be fed N2... not a practical solution.

My thought was to use a desiccant system that used N2 as the make-up air source. Another possibility would be a compressed air type drier using N2 but I am trying to minimize N2 consumption.

 

[patprimmer]

Vacuum is the only way I know to meet your requirements

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CRmolding]

Thanks. I'm not sure that the vacuum system will be practical in continious use. In a batch oven, I think that the N2 atmosphere would be easy.

How closed is a "closed-loop" drier? If a standard plastic-pellet desiccant-drier was fed N2, could this system dry and remove surface O2?

 

[patprimmer]

The O2 on the surface will reach equilibrium with it's surroundings.

The exact amounts will depend on relative affinities for the plastic and the nitrogen atmosphere.

I strongly suspect the work to determine the affinity of plastics for O2 will not be available.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Pud]

Hi,

I might be missing something, but assuming you have your material dried in a batch oven, how do you mould it without exposing it to O2? How do you keep the moulded parts in an inert atmosphere?

Harry

 

[CRmolding]

I have developoed a system to flow N2 into the feed throat of the molding machine and monitor the atmosphere in that area. The cavity is also purged of O2 before plastic is injected.

 

[CRmolding]

I have talked to the material supplier and they say that it can and is done. They have data in regard to surface O2 levels.

They work with companies that have come up with proprietary methods of removal.

 

[CRmolding]

Oxidation is the issue. The molded parts are not exposed to heat.

 

[patprimmer]

Do you need to remove only oxygen, or do you need to also remove moisture.

I presume others have patent protection or the supplier cannot disclose the process as used by others.

Do you know anything about their "proprietary" methods.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

Do they have graphs with relative oxygen level on the surface of the plastic vs the oxygen content of the environment at very low oxygen levels in the environment.

What I mean is, will the oxygen expelled from the surface be enough to prevent all oxygen from coming off. If so, how many flushes at what volume to surface area will you need.

How far does the oxygen permeate into the plastic, and what is the diffusion rate and how is this effected by temperature and concentration gradient.

This sounds like you are working on something quite new or very specialised. I guess it is very confidential.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CRmolding]

I think that I am going to move ahead with a compressed-air type drier and modify to run with an inert gas.

I can't be real specific using this forum.

Again, if there is someone that knows of an of-the-shelf plastic drier that can provide a nitrogen or argon environment I would be interested in this info.