What causes brittle filament?

[smorgana 0]

I have an Ultimaker 2+ that I've kept in my basement for years...   Though it's not as dry down there as it should be, I never had an issue with leaving spools on the printer for weeks or months at a time..

 

 

Since last summer I moved the printer to a room upstairs...   and since then, lets say I put a new spool on, print for a few days, and leave the spool on the printer for a couple weeks,

What happens is next time I print the print fails because the filament became brittle inside bowden tube, and up to the first wind on the spool.

 

So what causes that?   It's not any more humid in that room as it was in the basement...    The room is a sun room. so it's all windows whereas the basement had no sunlight.

Is it possible that lots of sunlight is causing the filament to go brittle?

 

[Smithy 998]

I have the same issue from time to time and I think it can have several reasons. When PLA gets too dry it breaks easily. So maybe the room is too dry - check the humidity there.

 

Another reason could be how old the filament is. PLA gets brittle over the time.

 

And from my personal experiences it depends on the filament type/brand. For example a spool of Colorfabb matte PLA is brittle as hell and I opened the spool some weeks ago, so not too old. 

 

I am also sure the sun light is now the best for the filament. So when you only print from time to time, unload it and store it somewhere else. 

 

My PLA spools are just in cupboard without a bag or box and there are all fine, also after several months or even years.

[geert_2 524]

Indeed, PLA changes crystal structure into more crystaline as it ages, becoming more brittle; this is reversible. Also, it degenerates due to water-absorption, this is not reversible.

 

I also found that if a string of filament is stretched for a longer time, like in the bowden tube, micro-cracks tend to form. This also makes it brittle. Probably this is what you have?

 

Also, some colors and brands are worse than others.

 

So, I remove the roll after printing, and store it in a plastic box with bags of desiccant.

 

These bags can be re-used by heating them. They are sold in car-accessory shops, used for drying cars and campers in winter. The blue dot turns pink when wet.

 

Micro-cracks in filament:

 

Idem, seen through a microscope:

 

[smorgana 0]

Thank you both for the good advice...   I keep my unused spools in a tupperware bin with a re-chargable desiccant .   From now on I'll be taking the spool off the printer when I'm done printing.