Endless Exploration EX7 (March 2025) A nylon alternative?
It's not nylon, but Polyketone (POK or PK) is marketed as a nylon alternative. Now there are many grades of nylon, but when I think of nylon, I think of weedwhacker or fishing line. Durable and a bit flexy. Nylon is often relatively heat resistant, but with moisture absorption which affects both printing and part performance. Wet nylon crackles and pops when printing. Wet nylon gains impact resistance but looses stiffness. Nylon is also often characterized by high shrinkage, exceptional lubricity, not sticking well to itself or build plates, good chemical resistance, and poor UV resistance.
Enter PK: It shares many characteristics of the the nylon I described above. On the plus side, PK absorbs less (minimal) moisture so the performance is less variable both when printing and afterwards. A shrinkage of almost 2% makes printing without fibers problematic so we improved printability by adding glass fibers (GF - below right) and carbon fibers (CF - below right) to reduce shrinkage to about 0.8 and 0.4% respectively. Once adding fibers, PK feels a lot like carbon fiber-filled PETG. Turns out PK has a similar stiffness, impact resistance, and strength to CF-PETG, but a higher max use temperature of up to about 150 C (geometry and load dependent).
We included PETG-CF7, Protopasta's Carbon Fiber PETG, with March's shipment to make your own comparison to this already available material. With the lower heat resistance of PETG, you can also print at lower temperatures and with less shrink + distortion as long as a max use to about 75 C is enough. Given the challenges we had producing PK, we won't be making more straight away (if at all). In the meantime, PETG-CF7 is a great alternative. For use up to 150 C, consider HTPLA-CF with the added step of heat treating or Rigid TPU for unfilled nylon-like chemical and impact resistance.
Why both CF and GF? PK-CF is more rigid and breaks more abruptly, but also shrinks and weighs less with a density of about 1.14 g/cm3. PK-GF is more forgiving in flex, but also shrinks more and has a higher density of about 1.28 g/cm3. You can feel the difference when bending the filament though PK-CF still has enough flex to be durable in both handling and use. We recommend printing like nylon (little to no fan) with glue stick (included) on PEI or similar with a 90-120 C print bed for parts like below.
We printed the above on a Bambu P1S with 100 C bed and 0.4 mm hard steel nozzle (below right) after wearing our a 0.4 mm stainless steel nozzle (below left). PK degrades at 260+ C, but we printed up to 290 C. Why? Because 290 C yielded better layer adhesion and at higher rates. Just because the set temperature is 290, that doesn't mean the filament necessarily reaches 260+ C or is that hot for too long.
On the contrary, being too hot for too long is what we struggled with when making filament, but our filament extruders are larger, introduce sheer, and have more complex inner geometry than 3D printer hotends. You may notice some black flecks in the PK-GF. That's some charred polymer, evidence of the challenge we had producing the material. To be honest, we weren't sure if it was going to work out, but we pulled it off. Whew! Lucky for you, printing PK is easier than making the filament!!! ;-)
PK is also low odor and has a reduced carbon footprint compared to many other high performance polymers. Pretty cool, huh? There's still lots to learn about PK, but we're excited to see what's possible. Show us what you make on social (links below).
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Take care and enjoy the pasta,
Alex and the Protopasta Team
