How badly does moisture effect PLA?

[insta]

I'm printing structural parts for a customer of mine, the samples always turn out fine, and the "full run" a few days later aren't strong enough. We are using PLA because of the extra stiffness over ABS is necessary for these parts. The process is:

1) Unbag a spool of PLA, print a tray of parts (little plus shaped things). Put the batch of 20 into the mail, send to customer.
2) Get feedback "these look great, send the rest"
3) Hit "go" on the machine 10 times over the next few days, same gcode. Put wad of them in the mail, send to customer.
4) Get feedback "these turned out like crap"
5) Rinse, repeat

The best I can come up with at this point is humidity. It's very humid where I am, averaging 80% RH, and the PLA is exposed to the air for about a week. Could this cause noticably weaker layer bonding?

[Jules]

Don't know if it can affect the PLA in so short a time, but just in case ('cause it's generally over 80% RH here too), I keep mine in 5 gallon buckets with removable GammaSeal lids and a cheap bag of white rice that has been Food Saver-ed and then had a bunch of tiny holes poked in it with a large bore needle.

The rice does the same thing that it does in a salt shaker - sucks up the moisture in the bucket overnight. Just pop a bag on top of the rolls then close it up. And it doesn't need to be renewed, which is why I use it instead of dessicant packs.

Haven't had any issues with the PLA so far doing it that way - and they've all been opened for a lot longer than a week.

The only tedious thing is having to search through several buckets to find the roll you need, since you can't see into 'em. Might want to go with a see-through bin instead, although I don't know how air-tight those are.

[Bratag]

I'm printing structural parts for a customer of mine, the samples always turn out fine, and the "full run" a few days later aren't strong enough. We are using PLA because of the extra stiffness over ABS is necessary for these parts. The process is:

1) Unbag a spool of PLA, print a tray of parts (little plus shaped things). Put the batch of 20 into the mail, send to customer.
2) Get feedback "these look great, send the rest"
3) Hit "go" on the machine 10 times over the next few days, same gcode. Put wad of them in the mail, send to customer.
4) Get feedback "these turned out like crap"
5) Rinse, repeat

The best I can come up with at this point is humidity. It's very humid where I am, averaging 80% RH, and the PLA is exposed to the air for about a week. Could this cause noticably weaker layer bonding?

I don't know if this is relevant or not but I have run into a similar issue with some eSun natural filament. I am pretty sure its not moisture as it happened with both a brand new roll fresh out of the bag and the same roll after spending some quality time in an airtight container with some dryRid. The print would come off the bed fine but a short while later it would simply de-laminate. Actually kind of cool (in a son of a &*^$ way) as I ended up with pretty much a pile of perfectly formed hair thin spaghetti. I have 4 other rolls from them that print great, but its not limited to eSun stuff as I had the same problem with a roll of yellow and one of red when I was printing in 3mm. It just seems like some filament doesn't want to bond.

I was able to get slightly better results by bumping the print temp.

[Tim]

A proper failure analysis would be tricky. The only thing I can think of besides moisture that would end up being time-dependent over the course of days is dust accumulation. Possibly, if you run your first test print during the day but let the larger set run overnight, then you might end up with some differences due to the change in ambient temperature. Moisture seems like a likely candidate, but then I've kept spools of PLA on my printer for weeks at a time and never noticed much change (but then, the humidity around here, in my basement, usually stays below 50%).

Try moving to Arizona.

[insta]

Try moving to Arizona.

That might be the more cost-effective measure at this point.

[Rich]

Great printer-mounted humidity control idea:
viewtopic.php?t=1386&p=4224 Great on-printer humidity control idea

[jsc]

How is your client testing them? What does "crap" mean in this instance?

I noticed from one of your posts in the "can't print this thing" thread that your temperature for PLA seemed abnormally low to me. Have you tried going hotter?

[insta]

I'm trying them at 220C, 80mm/sec, no fan, 60C bed, 0.2 layers, 4 perimeters, 40% infill, 1.2 extrusion multiplier right now. If this doesn't work, I give up. I don't know how to make PLA stronger.

The parts are actually structural tools used to hold open an interlock of some sort, so they insert them into the interlock and twist. This causes the layers to delaminate when they are twisting it. I'm not sure why it spontaneously holds up sometimes.

[jsc]

I found a baggie of some demo filament labeled PLA+. I think it may have come with my esun PETG preorder. Maybe some "enhanced PLA" is what you're looking for? You could also just keep upping the temperature until it stops delaminating. You can also try larger layer heights, which have better Z strength (fewer layer to layer bonds). With a .35mm nozzle, you can probably get up to .3mm layer heights.

[Jules]

I'm trying them at 220C, 80mm/sec, no fan, 60C bed, 0.2 layers, 4 perimeters, 40% infill, 1.2 extrusion multiplier right now. If this doesn't work, I give up. I don't know how to make PLA stronger.

The parts are actually structural tools used to hold open an interlock of some sort, so they insert them into the interlock and twist. This causes the layers to delaminate when they are twisting it. I'm not sure why it spontaneously holds up sometimes.

If they are torquing the parts like that, try rotating them 45° or 22.5° on the bed before printing. Sounds weird, I know, but I discovered by accident the other day that the direction that the part faces on the bed makes a big difference on the structural strength. If you don't let the infill (or walls) print in one direction in long straight runs, they tend to delaminate less. Might increase the printing time a bit though.

I'd drop it to 1 perimeter as well. Multiple perimeters don't make the outside of the part stronger, they make for more long straight runs that can come off if the bonding isn't quite right, and the cross strength of the infill actually holds the perimeter on better. 40% infill is plenty strong. (I print all PLA at 218°, so 220C should be good.) I also hit PLA with as much fan as I can, it likes to cool off quickly. 40° bed temp.