Air-tight storage boxes for nylon filament?

[Ama-fessional Molder]

That filament dryer is one of the least effective methods of drying materials I have ever seen. It continuously draws in moist air from the environment. Proper drying systems are closed loop.

Yes, it is true that with a desiccant in there the air will dry. If you have a layer of desiccant in the bottom that the air has to draw through it might be reasonably effective, and it will probably dry it enough that you will likely see decent results.

My concern with it however is that keeping filament at temperatures high enough to encourage molecular movement of the water is also high enough to oxidize the material. This is commonly called "over drying" the material (although that is not the correct term), and if you leave it in there too long you will wind up with brittle, unusable ABS.

Furthermore, when drying plastics, relative humidity is an almost useless number. 10%? At 10% RH many plastics are well above their minimum water content for processing. RH changes with temperature, and the critical number is dew point. When we dry plastics professionally, and without degradation, it is done at a fixed temperature for a set number of hours and at a dewpoint of -20 to -40F. This ensures that the air is actually dry, unlike RH, which does nothing of the sort.

With nylon of almost any grade, this type of drying cannot get it suitably dry without degrading the material and giving you brittle filament. Either you will have semi-moist filament, or you will see degradation. I know this to be true because we have a few old school dryers that are basically this exact method, except with the addition of airflow through the material, and that's the results we get with those dryers no matter what the grade. Nylon is a very finicky material to dry and process. It has a pretty narrow window between melt temp and degradation temp, and time is the most critical factor when drying or processing almost any material.


TLDR version of this post is that for many applications that type of dryer will be suitable, but at bare minimum and I promise you that better results are possible. The problem is being able to build a proper forced air dryer for a reasonable enough price for home users.

I suspect it can be done with manually changed and recycled desiccant beds, for a reasonable enough cost that the average home user can build one.

I wonder if I should just start a discussion thread on drying plastics. I have a lot of resources available to share on the subject. Mjolinor's link up there is a good start. The first method listed is what the bucket is. Just heating air from the environment and passing it through the plastic. This is less than ideal.

[Mjolinor]

I think that people too readily blame their results on wet plastic. Obviously on injection moulding water is a catastrophe but from experience and from reading it seems that the effect on FDM printing is small apart from a few very specific plastics like the Stratasys dissolvable filament, that just makes strings of small balloons when it's wet.

[Ama-fessional Molder]

Oh, yeah I should probably clarify that wet plastic is only one variable.

Even in injection molding most plastics can survive being processed wet with little more than cosmetic issues. When it comes to things like PET though it is catastrophic.

I would imagine with such small diameters of filament that it would diminish the effects a fair bit. My primary concern when I rant about drying is the degradation of the material, and that doesn't come from the water but rather the drying methods.

[sdtag]

I was thinking about trying this:
http://www.harborfreight.com/3-pack-vacuum-storage-bags-95613.html

[Ama-fessional Molder]

That would be a good way to store the material, it isn't a perfect vacuum, but if you put in a bit of desiccant gel or beads along with the spool it should be suitable.

[RobDistrupol]

Nylon needs to be dried at 80deg C for 2-4 hours - you need to aim for <0.25% moisture content. A dessicant dryer is always best - hot air does work but you can just end up blowing hot (humid) air around the place.
If the nylon has been exposed to atmosphere for over a day, you really need to be looking at 24+ hours of drying time to - dependent upon relative humidity of course.

To answer your initial question - there is no ideal solution, though a vacuum-bag with a dessicant sac in it will be better than nothing.

[djprinter]

I keep my filament in an air tight box with paper bag full of drierite desiccant. The box is mounted on the wall above my printer with teflon tubes feeding the printer from the rolls within the box.

I live in seattle, and humidity is usually around 50% at night, but it's only 4% inside the box.

[djprinter]

That filament dryer is one of the least effective methods of drying materials I have ever seen. It continuously draws in moist air from the environment. Proper drying systems are closed loop.

Yes, it is true that with a desiccant in there the air will dry. If you have a layer of desiccant in the bottom that the air has to draw through it might be reasonably effective, and it will probably dry it enough that you will likely see decent results.

My concern with it however is that keeping filament at temperatures high enough to encourage molecular movement of the water is also high enough to oxidize the material. This is commonly called "over drying" the material (although that is not the correct term), and if you leave it in there too long you will wind up with brittle, unusable ABS.

Furthermore, when drying plastics, relative humidity is an almost useless number. 10%? At 10% RH many plastics are well above their minimum water content for processing. RH changes with temperature, and the critical number is dew point. When we dry plastics professionally, and without degradation, it is done at a fixed temperature for a set number of hours and at a dewpoint of -20 to -40F. This ensures that the air is actually dry, unlike RH, which does nothing of the sort.

With nylon of almost any grade, this type of drying cannot get it suitably dry without degrading the material and giving you brittle filament. Either you will have semi-moist filament, or you will see degradation. I know this to be true because we have a few old school dryers that are basically this exact method, except with the addition of airflow through the material, and that's the results we get with those dryers no matter what the grade. Nylon is a very finicky material to dry and process. It has a pretty narrow window between melt temp and degradation temp, and time is the most critical factor when drying or processing almost any material.


TLDR version of this post is that for many applications that type of dryer will be suitable, but at bare minimum and I promise you that better results are possible. The problem is being able to build a proper forced air dryer for a reasonable enough price for home users.

I suspect it can be done with manually changed and recycled desiccant beds, for a reasonable enough cost that the average home user can build one.

I wonder if I should just start a discussion thread on drying plastics. I have a lot of resources available to share on the subject. Mjolinor's link up there is a good start. The first method listed is what the bucket is. Just heating air from the environment and passing it through the plastic. This is less than ideal.

It doesn't matter how dry the air it is matters how absorbent it is. Which is why RH is all that matters.

A moist sponge will suck up more water than a dry piece of metal.

[Ama-fessional Molder]

Incorrect.

I have a formal education on the subject. As much as it makes me look like an ass to say that, I have a practical, working knowledge of plastics drying. I do it every single day on medical and high precision components that require exacting mechanical characteristics.

A lower actual moisture content makes air more readily able to absorb water. RH can be low even though the moisture content of the air is higher than the plastic. At this point no more moisture will migrate out of the plastic and into the air, in fact it will go the opposite direction - into the plastic.

http://www.conairgroup.com/assets/Kn...rying-0410.pdf

10% RH at 75f is a lot less water than 10% at 120f, and both of them are far more water than a dewpoint of 0 or less. Precisely zero professional plastic processors utilize RH as a metric, because the point is to get the air dryer than the material to encourage molecular water transfer.

You can have a 10% RH and still have more water in the air than your Nylon, which will actually cause the Nylon to absorb water from the air. It is similar to the process of heat exchange. Areas of higher heat will flow to areas of lower heat, and areas of higher water content will flow to areas of lower water content.


It might very well be "enough" for a home user, but I assure you that RH is not the correct factor to look at if you want reliable results.

I see a lot of people using RH on a lot of forums, then posting results that clearly indicate too high a water content in their materials.

[Ama-fessional Molder]

An example, from this paper:
http://www.simar-int.com/files/vortrag_engl.pdf

example 25 °C temperature and 80 % R.H. the air is containing19 g H2O / cbm air! Heating up the air from 25 °C to more than80 °C is reducing the R.H to less than 10 % but there are still 19 g ofwater per cbm drying air

Heating the air reduced the RH, but the water content remained exactly the same, and in many cases the actual water content can still remain above the recommended moisture content of the plastic. If that is true, then you will never be able to suitably dry the plastic no matter how long it stays in the box, or how far you increase temperature to reduce RH.

Furthermore, elevated temperatures are absolutely necessary to begin the process of drying any hygroscopic materials. The water actually binds to the polymer chains of hygroscopic materials, and heat is required to break the water molecules free.

So, while you can achieve very dry air at 5c and 5% RH, the air temperature is not sufficient to unbind the water from the plastic at the molecular level. All you will do with those parameters is reduce the surface moisture.

I just took this picture less than a minute ago. This is the control panel of a several thousand dollar industrial plastic dryer. It uses heated air and dual desiccant beds with automated bed regeneration to maintain a specific dewpoint, in this case -40 degrees. The plastic being processed here is polysulfone, which has a melt processing point of approximately 630f or 330c, hence the high drying temperature.



You will note that RH is nowhere to be seen. In fact these units don't even have the ability to measure or display RH.


I'm also extremely enthusiastic about my work, in case you haven't noticed.