Moisture content analysis - PA6 1

[fankyfranki]

Hi everyone,

I am trying to find the right parameters for testing the moisture content in PA6 plastic. I use the RADWAG MA 50.R device for this. I am thinking about the appropriate temperature parameters for this test. Lowering the temperature will significantly extend the test time, however, I am afraid to raise this temperature - possible impact on the material (however it's not NDT). Will exceeding some limit value of temperature for PA6 affect the results? In addition to the moisture in nylon, can other compounds escape that disrupt the result?

I did tests for 100C and the drying time for saturated nylon was around 6 hours, for dry nylon it was about 90 min. How high can I raise the temperature? I'm trying now with 115C. Does anyone have experience with testing moisture content in nylon?

(sorry for my english - it's not my native language)

Thanks anyone for response!

 

[vt2012]

The potential disruptions to your moisture measurement really depends on the type of instrument you are using. From a quick google it looks like the RADWAG MA 50.R is a loss-in-weight device? i.e. heat it up and see how much weight your sample loses due to evaporation of volatiles?

If it is based on loss-in-weight, the only thing typically in PA6 to worry about is residual caprolactam. This should not be volatilized at testing temperatures, but I have seen it come out of nylon-6 pellets and powders at 180-200 degrees C. I'm not sure why. Check your PA6 SDS to see if there is much residual capro or any other volatiles.

The other thing to consider is at temperatures approaching 170 degC you will start to further polymerize the nylon, joining chain ends (solid-state polymerization), and giving off water from the reaction.

All that being said, I have successfully tested nylons with various instruments at temperatures up to 180 degrees C. There is definitely some SSP happening, but the test is so quick it should be insignificant. I would say you are safe to go up to about 150 to speed up testing, maybe higher. The speed of the test also depends on whether the moisture of your molded part/pellet is surface moisture (picked up quickly by the nylon from the atmosphere) or embedded in the polymer matrix from production or long periods exposed to the atmosphere.

Your English is great!

 

[fankyfranki]

Thank You so much for Your response, it was very helpful.

My research focuses only on the moisture content since it is mostly the reason of our quality issues (low moisture content - brittle fracture). I will do some attempts with 130 and 150 deg C. If after some time weight will stabilize - then I will have my answer. If moisture content will reach aprox. 0% but the weight will continue to drop - then it will mean that something else is happening to the material... I think.

Thanks again.
Best regards

 

[dgallup]

We have several nylon parts that need to distort a bit in assembly. Dry as molded parts will break, we specify that the parts must be conditioned to at least 50% relative humidity prior to assembly. Usually this is accomplished by putting a damp sponge inside the bag the parts are packaged in before they are shipped to us. The days or weeks in the bag are quite sufficient to humidify the parts. If we get some parts that are too dry and we have to use them immediately manufacturing has been know to put them in boiling water for a short time.

Most people doing moisture content measurements are trying to do the opposite, ensure that the pellets are sufficiently dry to ensure good molding.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[fankyfranki]

Putting in boiling water for a short time will cause the outside layer of part to have a very high moisture content in opposition to inner layers. In time some of this moisture will enter inside of the wall cross-section and some of it will escape in to air. But if it works it's good.

I tried to condition parts in salt spray chamber using distilled water. I managed to get up to 8% moisture content. I wanted to check if any parts we had at this time were made from nylon 66 insted of nylon 6. Nylon 66 has lower maximum moisture content.

Today I compared the dependence of moisture content on the impact strength of different nylons from different suppliers. Nylon 6 from factory A can be much much better then from factory B for the same moisture content. My components had about the same 2.5% but the results from the impact test were completely different.