Is anyone accounting for moisture in materials?

I am very excited about building a RepRap for myself to use at home. I have been running various professional RP machines for years. Anyway as someone who has run FDM machines, and someone who just stumbled upon the RepRap movement. I have to ask. Is anyone keeping their material dry? FDM material is packed in desacent or kept in cartridges for to sole purpose of keeping moisture out of the materials since many polymers are hygroscopic. Moisture in material can really mess up a machine. Just curious.

CUrlrup

I live in a pretty humid environment (Vancouver, BC), and haven't had any problems with it yet. I've mostly been running PLA out here, but I did run about 5 kg of ABS back in Toronto, without issues either.

What are the symptoms of wet plastic?

Wade

The water boils and forms steam bubbles which pop and leave voids in the filament. I have not had any problems myself but Vik has mentioned it. [reprap.org]

Edited 1 time(s). Last edit at 09/25/2009 03:23PM by nophead.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> The water boils and forms steam bubbles which pop
> and leave voids in the filament. I have not had
> any problems myself but Vik has mentioned it.
> [reprap.org]
> nt


Yep you get voids in the build. Just overall not a good sight. I have no idea what chemistries are involved with Stratasys FDM ABS material and the ABS used on a RepRap. RepRap ABS might not be as hygroscopic. Anything really that would use engineering plastics you would want to keep moisture away. If you were injection molding parts you run your material through a dryer first to make sure it is good an dry.

If the plastic is hygroscopic and therefore sucks water out of the air can the process be reversed by cranking up an oven up to 120c and baking the plastic
for a few hours to dry it before use?

The idea is to boil off the water and leave bone "dry" plastic. Then put the plastic into a bag.

Stephen

stephen george Wrote:
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> If the plastic is hygroscopic and therefore sucks
> water out of the air can the process be reversed
> by cranking up an oven up to 120c and baking the
> plastic
> for a few hours to dry it before use?
>
> The idea is to boil off the water and leave bone
> "dry" plastic. Then put the plastic into a bag.
>
> Stephen


I have done that with urethane used in prototype vac-casting with much success and yes any injection molded parts that I have run I would first let the material dry in a low heat oven say 100-110 degrees for 48 hours before heading to the dryer.

Greetings all,

Apparently, moisture in some plastics causes worse problems than steam voids.
If you look at the literature for molding (or recycling) PET plastic (used for 2-liter soda bottles and many other containers), moisture while melting leads to a chemical degradation of the plastic. I tried melting some PET shreds after approx. 2 hours of drying (at approx 150 deg. F), and the plastic discolored -- possibly due to this reaction. My temperature control is crude (recycled toaster oven), so I might have mucked it up during the melt itself, though I think insufficient drying time is more likely.

-- Larry

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Larry Pfeffer,

My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]

Did it go for melting straight after drying, or was there transfer time/exposure to fresh moisture/condensation on cooling etc?

Hazel.

@Hazel,

In my first test, I turned the toaster oven up from 150 deg F, to its max ~450 deg. F, without even opening the door, so there was no exposure to moisture between steps.

I didn't keep it at 150 for as long as specified for drying granular feedstock, and I might have help it at ~450 for too long -- I'm not sure which one was responsible for the discoloration. I'll have to shred more and try again. (And/or get a better thermometer for monitoring the oven.) However the resulting plastic disk, albeit discolored is incredibly strong -- can't flex it at all!

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Larry Pfeffer,

My blog about building repstrap Cerberus:
[repstrap-cerberus.blogspot.com]