I’m not talking about making waterproof, foodsafe or dishwasher safe objects here (that’s a topic for later), I’m wondering about storage conditions for filament before I print with it. I’ve read a number of statements that suggest ambient humidity can be a problem.
PLA is hygroscopic. It absorbs moisture from the air. Here’s a patent application that discusses it as a problem for plastics engineering. When PLA with moisture in it runs through the hot end nozzle of a RepRap printer at nearly twice the boiling point of water, the moisture turns to tiny little bursts of steam. Its a bit like shaking a bottle of carbonated soft-drink, then trying to pour it into a thimble. Not exactly precise.
“In-line drying is required. A moisture content of less than 0.025% (250ppm) is recommended to prevent viscosity degradation. Typical drying conditions are 4 hours at 175 degrees F (80 degrees C) or to a dew point of –30 degrees F (-35 degrees C), with an airflow rate greater than 0.5 cfm/lb of resin throughput. The resin should not be exposed to atmospheric conditions after drying. Keep the package sealed until ready to use and promptly reseal any unused material.”
Now that sounds pretty heavy duty, and is aimed at factory production. I’m guessing ‘viscosity degradation’ means ‘gets sticky and clogs’, but I could be wrong. More directly relevant to me is the RepRap wiki page on PLA, which I mentioned above. It states
“PLA can absorb moisture from the air. When it is heated this moisture can turn to steam bubbles which with certain hot end (extruder head) designs can interfere with printing. The symptom is that when the extruder motor stops the PLA kept coming out. When the stepper starts again there is a significant delay. Occasionally the tip may blow a bubble with a tiny puff of what looked like steam.
Small amounts of PLA filament (Natureworks PLA4043D has been tried) can have some moisture removed by putting it on a piece of aluminum foil in an oven heated to 170F for an hour. The filament in the oven is floppy, but sticks to itself only slightly. Flexing the coils after cooling unsticks them from each other. Heating a whole spool this way has not been tried, and may result in the spool becoming unusable, so caution is advised.”
“Sticks to itself only slightly” does not sound like a success to me, given how important consistent feed rate is for reliable smooth objects.
I don’t know how common this problem is, but I’m worried anyway. I live in a humid subtropical area where in summer the thunderstorms can drop a foot or so of rain over a couple of days, then the sun comes out and temperatures reach 37 degrees Celsius (98 degrees F?). Humidity >95%. We have no air conditioning. Mould on the ceiling is a problem if we don’t keep the doors and windows open for airflow. I understand that most people in developed countries tend to have air-conditioning, and I wonder if that, more than extruder head design, is what has been protecting most folks.
At our last remaining real photographic store in town I saw a small bar-fridge sized glass-fronted dehumidifying cabinet. I know photographers locally who have big problems keeping their lenses (some of which cost more than my printer) free of mould. Especially the two guys who live in the rainforest… That cabinet costs $400. Plus electricity to run it. I’m wondering what DIY options might work. A sealed fishtank with a small incandescent bulb and some desiccant? Am I just being paranoid, trying to think of things I can do before my MakerGear printer kit arrives?
All suggestions gratefully received.