New filament makes brittle prints

0

I recently bought 5 spools of white 1.75 mm PLA off Amazon. However, I experienced some very strange behavior when I started to print with it. First, the filament wouldn't stick to the print bed. I'd had no such trouble with the past several batches of filament (all from different makers, I think - my usual supplier is closed for COVID), but this filament refused to stick - or rather, it failed partway through three consecutive prints. I squished the first layer into the bed, but it didn't help. Not sure what else to do, I applied glue stick to my print bed (despite having a special print surface that has worked quite well on its own for over a year). Well, it worked - too well. The next print adhered firmly to the print bed, and applying pliers and a vise succeeded only in explosively shattering the parts, leaving most of the bottom few mm still stuck fast to the print surface. I finally managed to remove the remains by letting it cool, then heating the bed quickly to ~75 °C and applying steady moderate torque with pliers for 5-15 seconds.

That was not a desirable outcome, so I cleaned the print surface with water and then alcohol. Unfortunately, the next print I did had the same problem, and snapped during attempted removal.

This leads into the second, somewhat more fundamental problem with this filament - I don't have numbers, but it seems way more brittle, and a little weaker, than the average filament. The parts I printed were ones I've printed before, and they generally hold up to more abuse than the ones I've printed with this new filament. If I had to put a number on it - the new filament has maybe 50 %-75 % of the strength of most filament I've used, and/or is 150 % as brittle? Yeah - I just tried to shave off an edge with a deburring tool, and rather than form nice little plastic curls, it crackled and shot tiny chips of plastic. (Except for one corner, which was well behaved some of the time?)

Can anyone diagnose my filament from these symptoms? Is there something I can do to fix it (e.g. bake it for 8 hours or whatever), or should I just return it?

Erhannis

Posted 2020-09-12T02:39:02.417

Reputation: 181

At least the removal problem is your technique. You should never be putting force on the print to remove it. Use the "putty knife" tool or similar to separate it slowly from bed starting from edges. – R.. GitHub STOP HELPING ICE – 2020-09-12T03:55:01.637

@R..GitHubSTOPHELPINGICE A metal tool would likely damage my print surface, and a plastic tool almost certainly wouldn't make it under the print to start with - wouldn't have an edge both strong and thin enough to fit. Do you have any suggestions? Note that I've removed hundreds of prints from the bed before, and this is the first time any prints have been so stuck. – Erhannis – 2020-09-12T04:14:55.493

What type of build surface do you have? A putty knife type tool should be fine on buildtak clones and glass at least, and I would expect on other types too. You run the blade along the surface similar to how you use a razor blade to clean adhesives off glass or burnt-on mess off a flat-top electric stove, not downward in a way that would dig in. – R.. GitHub STOP HELPING ICE – 2020-09-12T04:45:15.863

As for your problem with brittleness and adhesion before using the glue, I wonder if the filament just has poor size accuracy. If the diameter is slightly too low, you'll have underextruson that would explain all these issues. Do you have a high-precision caliper (better than 0.1 mm) you can use to measure and see? – R.. GitHub STOP HELPING ICE – 2020-09-12T04:46:45.610

@R..GitHubSTOPHELPINGICE I have one from geckotek.co - it's a ~2.5 mm layer of some kind of plastic (reminds me of nylon, maybe?). A metal knife would risk scratching or gouging the surface. (The build surface instructions recommend against metal tools.) Yeah, I have calipers that measure to two decimal points - I got 1.76 mm at several points on the filament when I just checked, and 1.75 mm in at least one spot. – Erhannis – 2020-09-12T05:17:56.110

1Sounds like the print temp might be off. different materials like different temps, so play around with that setting, say +20 and -20 from what you have now, and see what's worse and better, then hone in. – dandavis – 2020-09-15T20:57:57.187

No answers