vacuum drying PLA

Vacuum Drying PLA Pt.1

Polylactic acid (PLA) is a popular filament for beginning 3D printers. It prints at low temperatures (180 – 220 C) does not give of fumes (unlike ABS) and comes in a wide range of colors. It can be printed without a heated build plate, which is attractive to low-cost and kit built 3D printers.

PLA is made from corn starch in the USA, and other food sources around the world.

Being made from a food product, it has one main weakness. PLA is hygroscopic, meaning that it will absorb water from the air over time.

For printers that buy PLA in bulk, this can present a storage problem. It is always a good idea to store PLA in an airtight box with a desiccant (a chemical that dries out the air) or used a vacuum seal bag.

You can buy desiccant online, or you can find them in the laundry aisle of a grocery store. Painters desiccant may be found in humid climates to help house paint dry. If you know a science teacher or professor, you may be able to find desiccant through a science supply company. Shipping supply companies also sell desiccant packets that are good for beginning 3D printer

As you take PLA filament in and out of the box to print, it will be exposed to the warm air around your 3D printer. Over time you will find the quality of your PLA filament may degrade.

PLA should be stored with desiccant (green) in an airtight box when not in use.
Vacuum Drying PLA Pt.1 2

If your PLA starts to bubble and pop as it comes out the hot end, or becomes brittle and snaps, then your filament may have absorbed too much water.

In looking online I found a few ideas on how to dry out PLA.

The first method involves uncoiling the PLA and putting it on aluminum foil. Then you bake your PLA in an electric (not gas) oven at 77 C (170 F) for an hour.

I’m hesitant to try this method after all the hassle I went through heat treating Proto Pastas’ HTPLA. When I did put PLA in an oven, I did not get much of a result. I also do not want to take a chance of making a mess in my oven.

The second method I found happens at room temperature. Take your stale PLA and put into an airtight container with plenty of silica desiccant. Then leave it sealed in the airtight box for 2-3 weeks.

This method is more appealing, but I wanted to see if I can use a chemistry trick to speed it up.

Walter White is my favorite anti-hero - vacuum seal bag
What I hope to apply my science education skills to a good use.

About the same time I purchased my first 3D printer I also purchased a 10 spool package of 1.75 PLA from MakerBot.

After a year of printing and getting good performance from the filament, it recently started going bad. After some bad prints and a lot of feeding issues I never encountered before, I decided to try to dry out the filament. I’d like to keep my investment in filament printable.

A lot of PLA, and a Tweak of Chemistry

I like the second method of using a desiccant to dry out PLA. However I don’t want to wait 2 – 3 weeks.

There may be a way to use a vacuum to increase the rate of vaporization of the water in the filament.

My hypothesis is that by lowering the air pressure and vapor point of the water in the filament, I can get it to come out of the filament quicker.

In Denver, Colorado the air pressure averages around 84.0 kPa (0.83 atm) and the room temperature is around 23 C. At that point, water is a liquid and it would be difficult to draw out from the PLA.

Phase diagram, triple point. - vacuum seal bag
Water phase diagram. By changing the temperature or air pressure, you can change the state of matter of a liquid.

What I want to do is to drop the air pressure around the PLA below 1.01 kPa (0.01 atm). At 23 C, any water in the PLA should vaporize. When I combine it with a desiccant to absorb the moisture away, I hope this process will quickly dry out the PLA so I can print with it again.

While a large vacuum chamber would be ideal, I will use a vacuum seal bag that is used to store clothing to hold the PLA in a vacuum.

Materials Required: Vacuum seal bag. You find these used for storing clothing, closet dehumidifier, air-tight box, household vacuum.

For this experiment I found the airBOss closet dehumidifier canisters in the laundry aisle of my grocery store. I also found DampRid at a hardware store, which I may use in the future to store PLA.

airBOss dehumidifier that I found in the laundry aisle of the grocery store.
Vacuum Drying PLA Pt.1 3

AirBOss dehumidifiers are sold in handy units as closet dehumidifiers to help keep your cloths fresh. Buy the unscented ones though, as the lavender ones smell strong.

vacuum seal bag

Procedure: For this I first put all the spools of PLA into a vacuum seal bag.

I then put the closet dehumidifier at the end of the stack of spools.

PLA and dehumidifier (green) placed inside vacuum bag.
Vacuum Drying PLA Pt.1 4

I carefully put the whole unit inside the air tight box, with the vacuum valve for the bag oriented up so I could draw the air from it.

Finally I closed the bag and used the vacuum cleaner to draw out as much air as possible from the vacuum bag. I do not have a vacuum pressure gauge, so I don’t know how much of a vacuum I can draw with my cleaner.

PLA and dehumidifier vacuum sealed together. I hope by lowering the vaporization point of the water in the filament, it will leave the PLA and be absorbed by the closet dehumidifier.
Vacuum Drying PLA Pt.1 5

I will let this set for a week, checking the bag and drawing air out daily.

As a control, I put a small 250 g spool of PLA inside the airtight box and will check the vacuum dried filament against it.

Next week I’ll do a test print from the PLA and see if there is any improvement. Please check back next week to see if my chemistry trick works.

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