TPU Stringing Issues  

TPU Stringing Issues

Hello! I have recently started trying to work with TPU filament, and have run into various issues when printing. My main concern has been stopping stringing, and I have run 6 different tests and got a similar result each time. I threw together a model designed to highlight stringing, and did 6 separate prints, with results shown in the image attached. I have listed the settings changed in order from left to right.

Prints done on 9/6/22:

1) All preset settings for everything, Generic FLEX filament, only modification being extruder temperature at 230°C

2) Set the extruder temperature to 215°C

3) Set the retraction length to 1.4mm

4) I tightened the idler slightly (which was out way more then it should be, still poking out a bit now) and set the print speed to 75% on the printer. (I shouldn't change 2 variables at once I know, but for some reason I thought it would be a good idea)

Prints done on 9/7/22:

5) Enabled keep fan always on, which defaulted to a speed of 70%

6) Disabled keep fan always on, set the retraction length to 2mm

As you can see, I have gotten just about the same results for each print, although both the prints that were done today are arguably worse. My best guess has to be that the TPU absorbed a lot of moisture in the air, as I was printing with the window open and a fan blowing out as a crude form of ventilation. I live in a generally humid area, and I do not have any form of enclosure. I also don't have access to any way to dry the filament, whether that be a specialized filament dryer, or an oven. I am going to let it sit in my bin of silica gel for a few days and just hope it works. The only idea I have left after that is decreasing the temperature further, maybe to 200°C or 190°C, since that's the lowest this filament says it can go. It appears that the printer is always extruding something at all times, I just don't know which setting to tweak to prevent it. I have never seen stringing like this before, and don't know how to tackle this. If anyone has suggestions or insights, they would be greatly appreciated! Thank you So much for your time!

Other things to note:

I am using a bearing based spool holder that sits above the printer. 

The TPU was bought on January 1, 2020, sealed, and only opened on September 5, 2020. The brand is Priline, and probably not a brand I intend to get again.

I am using the i3 MK3S+ printer, as well as PrusaSlicer.