Everyone knows those small bags of forbidden “Do not eat” candy that come with fresh rolls of FDM filament as well as a wide range of other products. Containing usually silica gel but sometimes also bentonite clay, these desiccant bags are often either thrown away or tossed into bags of FDM filament with a ‘adding one can’t hurt’ attitude. As [Stefan] over at CNC Kitchen recently figured out, adding an already saturated bag of desiccant into e.g. an airtight container with a freshly dried spool of filament can actually make the humidity in the container spike as the desiccant will start releasing moisture. So it’s best to dry those little bags if you intend to reuse them, but what is the best way?
Among the ‘safe’ contenders are an oven, a filament dryer and the ‘filament drying’ option of [Stefan]’s Bambu Lab FDM printer. These managed to remove most of the moisture from the desiccant in a few hours. The more exciting option is that of a microwave, which does the same in a matter of minutes, requiring one or more ~5 minute sessions at low power, which effectively also used less power than the other options. Among the disadvantages are potentially melting bags, silica beads cracking, the bentonite clay desiccant heating up rather dangerously and the indicator dye in silica beads may be damaged by the rapid heating.
After all of this testing, it would seem that there are many good options to reuse those desiccant bags with a bit of care, although for those who happen to have a vacuum chamber nearby, that might be an even faster option.
They’re too small to keep around IMO. But if you have a need methinks putting them in the sun takes care of them.
Mix with explosives in a model kit?
What about using a food dehydrator? (I don’t have the ability to test that myself)
It will likely perform similarly to the filament dryer.
Food driers are a lot more aggressive that the filament driers.
Larger capacity, higher temperatures, more powerful (loud!) fans.
Yes, but of you already have one, which use is mainly seasonal, it would be a reasonable option. But, I have a “beater” microwave oven out in the garage already.
A former workplace had us discard any silicon gel packets that fell on the floor, or ones that arrived with incoming equipment, so I ended up with several “gallons” worth that they allowed me to take home. Those packets typically held 3/4 cup of crystals.
I run mine on 135F for about two hours to get bone dry desiccant. I also get free used pouches at work whenever I want them so it works out!
i didn’t know they an indicator dye in, I guess mine have aways been “dry enough”
Not all of them do. Some of the use cobalt chloride as part of the indicator which can apparently be toxic.
i used a lot of desiccant living in rain forest conditions (se alaska). i usually dry them on my gpu exhaust, in my network cabinet or sometimes in a light fixture. its generally on a leave them there until you need them basis, so they are usually pretty dry. never had to dry silica right now, and never thought to use a microwave.
Nice info, but practically speaking reuse of dessocant packs is extremely easy. Toss them in a bag instead of the trash. Once you’ve got a few dozen of them spread them out on a baking sheet and bake at low temp for like 15mins (exact numbers can be found on the internet). Store in dry bag. Done. I put dessicants in everything simply because they’re so plentiful and easy to reuse. I never have moisture problems with electronics or 3D prints.
I’ll eat them if I damn well please!
Not that I have any need to it, but couldn’t one use them to make Aerogel by soaking up as much water as possible, then freeze drying them or using a vacuum outgasser? I wonder if there’s anything useful that can be done by then spluttering them with metal?
they are not really toxic, they just print that on there so they are off the hook when a kid thinks its a pack of chicklets and chokes on it.
Uh, have you seen what happens when a silica gel ball hits liquid water? Whether it’s thermal shock from the high temperature rise or the stress from absorbing water quickly, the resulting razor-sharp shards would be very unwelcome in a stomach.
They’ll pass right through, honestly. Humans are built to eat worse.
In the lab, we dry them in an oven at 80°C for a few hours and store them in airtight containers afterwards. In many of our applications we move to molecular sieves instead, but these can’t be dried.
I thought molecular sieves could be dried but that it was much harder (higher temps and for longer).
Yes, technically you can dry them, but it requires very high temperatures (>200°C?), so lots of energy. Moreover, the bags holding the molecular sieve probably don’t tolerate these high temperatures.
plastic moulding factories run the colour changing silica gel beads in a drier temp at 120 C until whole batch is same colour. Timewise about the same time as your 80C. Granted, the amount was 3 kg if memory serves.
I tried re-using the desiccant packs with filament by putting 3 of them along with a color changing pack in a vacuum sealed bag. They didn’t last long, probably needed a lot more and still would have to unseal the bag to recharge.
Tired of resealing and re-drying filament before use, started using ‘air-tight’ plastic cereal containers with a 3D printed cup that holds 50g of color changing beads and a cheap hygrometer. Filament stays dry and can swap out the desiccant based on the hygrometer reading.
For seldom used filaments, I place the filament after drying in a vacuum bag with 75g of desiccant. The beads are in two 2 condiment cups with poked holes sitting in the spool center.
Explain how my PETG and PLA sit, opened, in my livingroom for months and print perfectly fine when I live 200 yards from the sea. The minimum humidity in my house is 40%
Maybe because the level at which you rate “perfectly” is lower than others?
I do have used PLA filaments left exposed to open air for months, and they printed very well. But when i tried to dry same filaments for the first time, prints were even better: less visible/smoother layers, less strings when head moving without printing between 2 locations…
Also, you can usually hear some crackling noise when printing undried filaments, and absolutely no noise with dried ones. This noise is from water inside filament being vaporized, and in addition to noise, it also causes some internal pressure inside the printing head that pushes small amount of melted filament out of the nozzle even when no extrusing/printing should occur (mouvements), so more stringing, and less even flow of extrusion.
So yes, drying most of the time can improve printing quality, but it depends on many factors (including filament and printer quality), so YMMV.
Same settings on my Prusa for new filament out of the packaging or sitting for 6+ months with no difference in print quality. I print at 0.35 for prototpes and 0.2 for final products. No issues at all. No pops or anything that I read others talking about.
This isn’t it, but I’d point out that the maximum humidity measured right next to seawater is generally given as 80% because saltwater has less vapor pressure than freshwater. And that’s at the temperature of the surface water, not the temperature inside or outside the house – and the ocean has enough thermal mass that it can easily be quite a bit cooler than the air for the day. So it can actually be more humid further inland as the plants transpire in the sun and such, which is nice to know.
Wow, I don’t live near sea (lot of forests and lakes around), but I have to run dehumidifier to get below 50%. Typical is 70%.
As a AV integrator by trade I keep the big bags of used Desiccant packs from speakers and toss them into my tool box. Keeps my tools rust free since they’re in a Van in Florida weather. Before doing this after a few days of rainy weather my tools would start rusting up.
The traditional method for drying them is overnight in a 200F oven. That probably would not work well for the plastic modules. A modern air fryer with the ability to set more drying cycles than I can count would be better. A cheap vacuum pump and a modified pressure cooker would be an excellent final step.
As for use cases, they are an excellent way to turn 91% isopropyl alcohol into 99+%. May require some means of removing fine particles by filtering and sedimentation in the manner that telescope mirror makers used to get the very fine grits they need. Transfer the decanted liquid at intervals to another container and settle out finer particles. The older books give tables of how long it takes for each grit size to settle out. In this case you merely need to know how long it takes for the smallest particle you can tolerate.
If the silica gel is in a filter paper container and alcohol added slowly so as not to stir up particles, there shouldn’t be a particulate issue and letting the 99% IPA settle in a glass container will both verify that there are none and remove any that are present. Settling times of many days for superfine particles. This is extreme old school filtering, as in hundreds of years old.
I wonder if that work work with ethanol? I appreciate what you say about losing/filtering the sediment.
“Crystal cat litter” is silica gel with blue indicator crystals. Available in any Walmart/Kroger/pet store, cheap enough to throw away after use. Not as fine as the stuff that’s in the throwaway bags; whether that’s an issue depends on how it’s to be used.
I drill a bunch of small holes in a peanut butter jar, fill with silica gel, place into the container holding whatever needs to be kept dry. Use a medication bottle for smaller jobs.
The version I inspected was filled with crushed siliga gel spheres. As i recall, silica gel dust alledgedly does not play nice with your lungs, so unless an avid smoker, wouldnt bother with it.
You are correct that SiO2 that is fine enough to be breathed in is a hazard, especially for something like cat litter, which is stirred around by the cat in use, and by the (cat-owned) human when scooping. I would suggest checking the labeling of the bag. FWIW the Kroger brand I bought has no warnings about breathing in fine silica. That labeling is required for materials that do contain significant amounts of inspire-able SiO2 dust, so it’s unlikely to be an issue with cat litter.
As we are Manufacture of Sorbipaks Silica Gel, I Would you like advice on specific types of desiccants Reusing desiccant bags efficiently involves reactivating them after they’ve absorbed moisture. Here’s a step-by-step approach to make this process effective:
Monitor Saturation Levels:
Color-Indicating Desiccants: Some desiccants, like silica gel, change color when they are saturated (e.g., turning from blue to pink& Orange to green). This helps identify when they need reactivation.
Time-Based Monitoring: If you use standard non-indicating desiccants, track the duration and conditions of use to estimate when they may be saturated (e.g., in high humidity areas, reactivation may be needed sooner).
Reactivation Process:
Desiccants can be dried and reused by heating to remove absorbed moisture. Here’s how:
Oven Method:
Preheat your oven to 250°F to 300°F (120°C to 150°C).
Spread the desiccants in a single layer on a baking sheet.
Heat them for 2 to 4 hours, depending on the size and type of desiccant.
Allow them to cool before storing.
Microwave Method (Silica Gel Only):
Place desiccants in a microwave-safe container.
Microwave for 5-10 minutes on medium heat.
Check periodically to avoid overheating.
Nice to see some research on this. I’ve been keeping them for many years, primarily the silica gel type, as the dessicant bags seem to come in every other thing I buy, be it filament, electronics, tools, medications, etc. Heck, I think even the last few pairs of shoes I’ve bought had ’em.
The best re-use I’ve found for them is in storing carbon composition resistors. I’ve made a side hobby of finding these types (usually for virtually or actually nothing), and “baking” them back into their tolerance specifications. Boy is that a lost art…but for good reason. LoL I don’t use them for anything precision or important, of course, but it’s fine for stuff like old tube radios, and keeps the aesthetic consistent.
Anyhow, I keep those resistors in well cleaned-out jelly jars, which are decently airtight, along with dessicant bags. I see a few other posters here are using just about the same method I do for drying the dessicant: around 130 to 140 °C in a toaster oven, for a few hours. I’ve never tried a microwave oven to do this, and don’t intend to try, as I’ve always seen it as being too intense for the job at hand. They need a long, slow heating, hot enough to ensure any moisture is completely driven away, so above the boiling point of water, and long enough to allow a) the heat to penetrate the entire mass, and b) the water to escape (hopefully without causing excessive thermal stress).