Moisture Detection and Measurement in Vacuum Oven (Plastic Dryness)

J

jjames

#1
Hi

I have a vacuum oven to dry a project plastic tube 0.075in ID and 100in in length. Due to the material of the plastic I intend to dry it at around 80 to 120 degF in somewhere near 30 inHg.

1. My question is how to define dryness of the plastic tube? How long will I have to keep to dry out the entire water content in the tube? What kind of moisture sensor can I use inside the vacuum oven for this purpose?
2. Is it possible to take reading of vacuum gauge to find the deflection in vacuum pressure when there is steam and set a dryness standard instead of using moisture sensor?
3. What is a good position inside the oven for the plastic tube opening to be so that I can get faster rate of evaporation?

I understand the term "dryness" can not be justified properly. I will be doing KF titration after this process to further determine any trace of water.

Ultimate aim of the project is to prove the plastic tube is dry without the need of visual inspection.
Any help is highly appreciated.

Thank You.

*I APOLOGIZE IF THIS IS THE WRONG PLACE TO POST THIS THREAD. I'M NEW HERE AND JUST FINDING MY WAY AROUND*
 
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NikkiQSM

Quite Involved in Discussions
#2
I work for medical plastics compounder so I may be able to help.

The "dryness" you are looking for depends on the grade of plastic that was used to produce the tubing. For example, if they are made from Pebax - the manufacturer recommends 0.100% moisture of lower. If the material is Pellethane or other type of TPU, the manufacturer recomments 0.020% moisture. I would base the "dryness" on what the manufactuer states.

We use 6 vacuum ovens in our R&D department to dry samples for testing. I would not imagine that are 120F you would produce must steam, especcially when drying tubing. Secondly, we have dried material at much higher temps and have seem a fluctuation in the pressure of the vacuum oven. Although, maybe you are using a different kind / type that we are not familiar with.

I would suggest you purchase a moisture analyzer. I am not familiar with any moisture testing that can be conducted inside the vacuum chamber. We have both loss in weight moisture analyzers and a sensor based. The sensor based (Arizona Instruments VaporPro) is much more accurate and is recommended to test moisture sensitive materials like TPU. Whereas the loss in weigh versions(Ominmark Mar 3), less expensive, but great for testing Pebax and other General House resins like ABS, PC, or PP, HDPE.

Besides the use of a moisture analyzer, I can not see how you could determine the dryness accurately.

Just my :2cents:.

Hope this helps in some way.
 
J

jjames

#3
Hi NikkiQSM,

Thanks a lot for your help. It sure does answer some of my questions. I will be using Pebax tube inside my oven.

The water pro moisture analyzer you are talking about wouldnt be able to accommodate the whole tube to test the level of moisture presence, I assume. Or if I'm wrong, could you explain how it works? I don't want to destruct my tube while doing a moisture testing. I did think of loss in weight moisture analyzer but I couldn't find any manufacturers that made highly sensitive and high capacity scales.

Also I did come across electrolytic P2O5 moisture sensor which detects moisture and show a deflection in current reading, but could not come across any info on how safe is it to mount in a vacuum oven.

I have a Thermo Scientific vacuum oven with me. Its an older model, and they don't sell that product anymore.

So yea hoping you would have some more answers for me.

Thanks again for trying to help me out.
 
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