Brittle PLA

Question

Has anybody had any issues with PLA going brittle? At work we have a CEL Robox and I've noticed that some white PLA filament that was on the end of a spool and lying around for several months has gone brittle and snaps easily. New filament is much more bendy.

We have a windowless office so it has only seen fluorescent light, so I guess that it's to do with moisture in the air. We keep current filament in ziplock bags with silica gel packs.

I know that PLA is supposed to be bio degradable so maybe it's just degrading? I'm wondering if the same will happen to finished parts? I'm planning to print out some test strips and test them over time, but wondered if anybody has any good info on this and point to a good online resource. I'll also be having a look on the CEL site for info.

I suppose this is possibly another reason for using ABS on my REP RAP bodge-o-matic printer at home! I thought I'd get away with PLA if it wasn't too hot.

Dan.

balearicdynamics · Accepted Answer

You are true Peter, but the reason is more easy; it's the air humidity that tend to make the filament fragile. I use several colours and obvious I alternate them. So maybe one roll I will use if after a month. If I leave it on the machine it spontaneously break and the first 2-3 meters become fragile and I should discard when I restart the machine. This happens mostly if there is circulating air in the room (here it is as it is hot during the day). When I unpack a new roll from its plastic envelop I take apart both the envelop and the silica gel (for humidity absorbing) that is in the package. When I change colour I put the partially finished roll in its original pack and seal it with adhesive tape. Rolls last for months without problems. The 3D Printing factory The filaments roll storage, new and partially used.

balearicdynamics · Answer

Hello Daniel, The problem is not specifically related to PLA, but - in a different measure - it occurs also with ABS. Anyway PLA filament is subject to degrading almost easily than ABS. This is the reason that when you buy a new filament roll it is sealed including inside a small bag of silica get. What makes the difference is the environmental humidity (influenced by the external temperature and rainy weather too. I directly experienced that it is not related to the end of the filament roll or to a specific part. If I leave the filament inside the printer for some days, the filament for the first exposed meter (about) becomes fragile. I have limited to adopt the solution to place the unused rolls in a plastic bag, so I think that your zip bag is a better solution and the problems should never occur. Anyway take in account that every time you reuse a filament (e.g. because you need that colour after a wile) that is not new and originally sealed, it is a best practice to test if it bends. If not, break short pieces of filament until it bend and become unbreakable by hand. Cut is with a scissor and start using it from that point. I have experienced many filament producers / distributors of filament and at the moment the better price/quality I have found is from geeetech.com The reason is simple: they sell printers and filament so it sound strange if they sell low quality plastic having a bad return from the clients that already bought the printers from them This factor is also strongly influenced by the geographic place where you live. Nearby the seaside this problem occurs more frequently (I mean the degradation of the most exposed part will start early) while it occurs few in this period that I am using the 3D printer in the Netherlands. Another detail that it is the worth to consider is the colour: one of the factors that influences in good measure the filament quality degrading is just the pigment added to the plastic base. For some colour this occur in positive, for some others the opposite. I have not personally tested a wide set of samples because I had to buy directly several colour for some small productions (black, white, red, purple, orange, yellow, blue) but the distributors that offer for a very cheap price few meters of all their colour set it is expected that provide better quality than other: with a single small investment you will see immediately the right response to temperature with every kind of pigment. Another detail that I have appreciated in the geeetech products (I suppose they just distribute a good quality product for the reasons above) is that the temperature performances are almost the same with every colour. About the temperatures, ABS works perfectly with 0.4 and 0.4 mm nozzles at 180C with a bed temperature of 90C Enrico

gregoryfenton · Answer

I regularly change the colours of the materials I use meaning that I have lots of partly used rolls. The simple technique I use is to put each roll in a bag, pierce a small hole for the filament to pull through and a hole through either side to mount the spool. Drop a few silica gel packs into the bottom of the bag and you're done. When you want to change the spool for another one push the filament back into the bag, tape over the holes and you're done until next time you need it. This also has the added advantage that dust and other contaminants are kept away from the spool.

dougw · Answer

My experience is that the tendency to become brittle is much more likely in the section of PLA that is in the printer, perhaps because of exposure to heat. Maybe the pigment material starts annealing into clumps or something. I always have at least 3 different colour reels open and awaiting use (black, white and clear). One or more colours may sit out for months without use. I have not had any problem with PLA sitting exposed on a reel for months. Maybe it is a combination of naturally low humidity and I print very regularly. However, the short section that is in the printer can definitely get very brittle and very weak if left there for a few days. I always eject the PLA if I don't expect to be printing the following day, and I cut off the section that is roughened by the feed gear teeth.

I have not had any problems with printed parts becoming brittle or weak.

The colour additives definitely alter the mechanical properties of PLA. I find white hardest to work with after printing. Black is much better, clear is probably the best.

Robert Peter Oakes · Answer

I find the same issue if I leave it mounted on my printer for a week or two without use, I need to cut off the part that was off the roll and re-insert to the printer, if I dont it will snap too easily. If I remove from the printer after use and pack back int he bag with silica gell then I dont have the problem Hope this helps or at least confirm your not alone / Peter

tjwitman · Answer

It doesn't degrade that fast. It is absorbing moisture out of the air and getting brittle. You MUST keep PLA in a sealed container with some form of drying agent like those little packets that come with it. Damp Rid works well. I have a reusable version. Don't leave it out! I keep all my rolls is a large gasketed plastic box made by Zip Loc and I put this dehumidifier in it >> https://smile.amazon.com/Improved-Eva-dry-E-333-Renewable-Dehumidifier/dp/B000H0XFCS/ref=sr_1_9?s=home-garden&ie=UTF8&qi…

brucekline · Answer

I have experience with optical fiber and it has the same problem! Water can make glass fiber brittle if there is stress. But it takes both. Water attacks the micro-cracks on the surface of a stressed fiber. No stress, the water can't get into the glass. No water, the micro-cracks do not grow. Most optical fiber has a moisture barrier plus a clearly stated minimum bend radius to avoid stress. My experience with PLA shows very similar behavior. Only the filament under stress (the straitened portion in this case) is susceptible to humidity. The fiber that is still coiled on the reel without stress is not absorbing moisture (at least not fast enough to matter). The timer starts when the filament is unreeled, straightened, and put under stress. The heating and printing process relaxes the stress making the printed object immune to the effects of moisture. The cooling object does shrink a bit which might cause stress but I have not experienced nor heard of any problems with spontaneous fracture. Here's an experiment I think I'll try: Unwind enough filament while on the printer to relieve the stress; let it coil to a more stress free state. I'm hoping that the filament within the printhead has been warmed enough for stress relief. Someone else should try this too.

jw0752 · Answer

Hi Daniel, While this may not be the cause of your brittle filament I wanted to highlight something that you alluded to. The fluorescent light with its higher UV composition does work on plastics much as sunlight does albeit more gradually. In the industry of my vocation, dental equipment, we used to see both color and composition changes in the plastic parts of the equipment even when they were only exposed to florescent lighting. John

Robert Peter Oakes · Answer

On my CEL Robox I find the PLA or ABS will break if I leave it connected but not used for a few weeks, it is always right at the entry to the machine, not the roll, and the roll remains fine.I think perhaps it is interacting with materials in the build of the machine ???

dougw · Answer

I have made brackets for outdoor Christmas lights that have been out in the rain and snow for several years and still work. This is an application where strength gets tested every season. (They have lasted longer than commercial injection molded plastic brackets I had been using)

danielw · Answer

This is interesting as I've been taking the reel off and putting it in the bag with silica gel. We have had a contractor in who has years of experience with plastics and injection moulding who has overruled me and said it's not an issue (until now!) Despite having no prior experience with 3D printers. This is someone who knows that raw material has to be dried before used in an injection moulding machine but sees the printer as a simple and poor relation to injection moulding. Interesting that he took the printer to his office as was sat next to it working and commented on the fumes. I did say that is smells and that's why I keep it in the lab area and not in the main office at work... Good to hear about your experience with actual printed parts being ok over time! Dan.

andzer9 · Answer

I have two identical prusa i3, side by side. I have on the left one PLA transparent and on right PLA Orange. I have always the same behavior. The orange filament has no problem, though is on the printer several days, but the transparent one became brittle after 2- 3 days, always in or over the extruder..

daveoutlaw · Answer

I stumbled across this post in a web search . Here is my opinion It seems that the idea that moisture causes brittleness is an assumption that may have no proof . If I read through the post I do see a common thread of it possibly being caused by heat . Wet material may produce poor quality prints but it may not be the root cause of the brittleness . Material stored in the summer in warehouses is exposed to heat that may enhance the brittle conditions . It seems that the community may have used the web post to validate the cause and copied them to answer others leaving a trail of bogus misinformation . I would suggest we validate our the theory before making the assumption that other have .

daveoutlaw · Answer

Thanks Douglas for the input wall sections and design may impact the brittleness as well . I wonder if 3 mm as opposed to 1.75 mm has less brittleness and if there is a pattern to the brittleness based on size of the wall or diameter of the filament. The other issue is the static condition of the printed objects may not be inducing any stress to cause the brittleness to be a factor

shabaz · Answer

Interesting topic. I don't know if this is useful, but there's a long article here: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1541-4337.2010.00126.x some snippets like this seemed interesting to me, but probably worth reading in full: One problem is that most information out there concerns PLA for non-3D-printing applications, like food packaging, or medical use inside humans since it biodegrades safely. So for example, the above snippet refers to PLA sheet, but I don't know if bendy PLA filament is acceptable to consider as a sheet.. I think it is, but it's a guess for me. I don't have any hard conclusions (and I don't own a 3D printer or PLA so I have no personal experience, but it's still an interesting topic for me to learn more from others) but from some of the research from non-3D-print applications, it seems that for PLA, moisture, or moisture and heat together, can cause some irreversible effects, and some reversible effects. Some things can be controlled, but realistically many people are working in environments that easily approach or exceed 50% RH, and cooling is to room temperature fairly quickly unlike a controlled environment like an oven. It's very cool that people have found out some mitigation like removing unused filament and wrapping it up, or cutting off the heated end, etc. Even if the precise underlying physics isn't know, that experience is valuable. For example, when I cut acrylic, I can see that the melted acrylic is more brittle, but I don't know the physics to it. I just know I really need to avoid it getting toward melting stage, otherwise I can't machine that area further (apparently additives can reduce brittleness with such heat scenarios with some plastics, according to https://www.bpf.co.uk/plastipedia/additives/default.aspx - anyway it's a digression). Also maybe if PLA in filament form is really just considered as a consumer hobby material by some manufacturers, there could be less controls, or alternatively might have their own mixes with additives to help with the brittleness? Just speculation : ( Also, as an idea, maybe design-level things can be done to mitigate too, e.g. have 3D printed shapes with thicker regions to change cooling rate (if that is an issue) or curves in multiple planes, to minimize flex of the completed item during use, i.e. perhaps design the item slightly differently if using a specific plastic.

danielw · Answer

Crikey! I never imagined this thread coming back to life. In the years that have gone by we still use the robox white PLA at work. In general we've stopped bagging the filament at night and the filament still goes a bit brittle (think dry chewing gum) by the end of the roll if it's been on for a while. Maybe its a brand thing? It is supplied in a bag with a silica gel, and more recently the bags have become foil bags. And there have been discussions on the CEL forum about drying filament and the filament becoming brittle. We generally make prototypes and some Jigs / location / assembly tools and it isn't really an issue. We've even made replacement parts for hand crimp tools and not knowingly had an issue. And in any case, we can always print a replacement part. I have a gluing jig I made when we first got the printer and it's still working admittedly there is a point where the jig was supposed to flex a little that cracked but I've seen the assembly team brutally over stressing the parts so it was probably that that caused the crack. I've also seen web pages and you tube videos about how rugged PLA can be, as dougw has proven. I've also seen content that describes how bio-digradable PLA isn't. I never did do any testing at the time, I have a couple of prototypes I'm about to get rid of, I might put one in some water and one in a desiccant bag and leave it for a while and see what happens. I'm Interested to hear more about this UV curing resin COMPACT Dan.

danielw · Answer

Hi Bruce, That makes some sense, I had tried printing some parts and kept one in a sealed bag with desiccant, and another in water, After 2 to 3 months I would say they behaved similarly. Unfortunately the company went into administration. I left and the test pieces will have been thrown away in the clear out. I wonder if the results would have been different if I'd stressed the parts. I knew about the minimum bend radius and had thought that it was just a factor of the cracks scattering the light. I didn't know about moisture effects, you learn something new every day! Dan.

fortknoxis · Answer

it is because there is moisture in the air. The quality of the material can be degrading. try buying it from a Canadian source. Their products are better. Not from China. if you need a supplier, let me know.

Brittle PLA

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