Transcription
Polypropylene, or short PP, is the second most commonly used polymer on earth with some really unique features. There isn’t much information on 3D printing this material around, so in today’s video, we’ll take a look at the printing properties of Polypropylene and run a variety of mechanical tests to find out how it performs in comparison to other 3D printing materials.
Due to its mechanical, chemical, and thermal properties, it’s very commonly used in household items and most parts that use living hinges, so things where a thin film of plastic directly serves as a hinge are made out of Polypropylene. Also, the material is food safe, can be microwaved, and is resistant against most common acids and bases.
There aren’t many manufacturers around that produce PP filament for 3D printing, and I haven’t worked with any so far. Formfutura was so nice to hook me up with a roll of their Clear Centaur PP that I put through its paces. It comes on 500g rolls that sell for around 34€ including tax, which makes it not the cheapest material with almost 70€/kg. But due to its very low density of 0.9g/cm³, a 500g roll of filament will let you print around 40% longer than a 500g roll of PLA, for example, which makes the price at least a little more reasonable.
The filament itself has quite a rough texture and is very flexible and can definitely be put into the semi-flex category. Due to its soft nature, I had to crank the extrusion factor all the way up to 122%. I printed 3D Maker Noob’s test tower with nozzle temperatures from 210°C to 250°C, where the only real difference was that 210°C left a more matt surface finish, so I went with the middle of the range, 230°C, for the rest of the prints. The test tower where I varied the fan speed between 0 and 100% showed that this material definitely needs to be cooled and showed very nice printing results starting from 75% fanspeed.
One thing regarding printing Polypropylene: This material doesn’t like to stick to anything besides itself, so it won’t adhere to most printing surfaces. Fortunately, normal clear packing tape is made from PP and serves as a great printing surface for this material. Removing it though can be a mess, but I later noticed that peeling the tape away when the printbed is still warm will result in way less glue residues on your bed. I printed most of the samples on a 60°C bed, which works great, and only for larger prints, it might be a good idea to raise the temperature to 80 or even 100°C in order to reduce warping.
Let’s continue and take a look at the printing quality. First, the material, even though not totally clear, can be printed to be really translucent with barely any layer lines visible. The overhang test was only okay, and angles printed well up to 55°; anything more didn’t look that good. The stringing and detail test was good, and only in the real upper part, some hair started to show, and some of the details on the tips was lost. Bridging was okay, and the result didn’t really look horrible, but the results are quite far away from PLA, for example. The 3D Benchy still came out quite nice, but you can definitely see the quality problems at overhangs and bridges. I already printed all of the parts at only 40 mm/s and noticed that printing even slower, so increasing the cooling time, can improve the print quality a bit.
Next, let’s take a look at the mechanical properties, which is really interesting. As a start, PP is, in terms of tensile strength, not a strong material because with a maximum strength of 14 MPa, this is far below the strength of other filaments. The thing that still is outstanding is that the material doesn’t break; it just yields and necks, which makes it so suitable for living hinges, for example. One of the outstanding properties is the layer adhesion. The specimens that I printed standing were just as strong as the lying ones that did not fail either. This is something I haven’t seen so far with any other 3D printing material. The material properties weren’t altered during the printing process because the tested filament behaved exactly the same.
I have called Polypropylene a semi-flex material in the beginning, which we can also see at the Young’s Modulus. With 320 MPa, it is around 7 times softer than PLA, for example. The strength of the hook was with 17 kg also not impressive, but due to its flexibility, it just yielded away and even did not break. Most interestingly, and again a first, was that the hook which was printed standing was able to bear the same amount of load and flexed exactly the same. The Izod impact test showed another property of PP very well because its impact resistance is way higher than the one of most other materials, absorbing almost all of the energy of the impact hammer, and again, even the standing specimens performed better than most other materials. Even though I can’t put this into numbers, it’s maybe also an interesting property. I printed this in vase mode and fidgeted with it for a couple of hours without any cracks forming, which shows a bit the fatigue strength of the material.
Last, let’s take a look at the temperature resistance, and this is different to most other materials since it doesn’t fail at a specific temperature but only gets softer and softer with rising temperatures, and even at temperatures above 100°C, doesn’t melt away and deform permanently but only gets really rubbery. As advertised, I also tried boiling water in a microwave in that vase, which worked flawlessly. So you have seen the fancy straw cup, designed by TBS, in the beginning. This material is food safe, but still, I can’t really recommend to use 3D prints for food contact because your hotend could contaminate the part, and bacteria probably really like to grow in the small cracks and layer lines of the parts.
A small tip on the side: The cup wasn’t watertight in the beginning, and I thought about how to fix it. Even though I don’t really have artistic skills, I got myself a 3D printing pen from SUNLU that was kindly provided by Gearbest. With this one, I can adjust the hotend temperature, melt a variety of different materials, and therefore fix holes or fuse 3D prints together, which has become really handy. They aren’t expensive, and if you want to get one yourself, you can buy it using the affiliate link in the description.
Now, what’s my conclusion? I think PP is a really underrated material. It prints fairly well, doesn’t smell, doesn’t absorb moisture, has great interlayer adhesion, and is very tough. The only thing is that it’s quite soft, but if rigidity isn’t an issue for your designs or you want to experiment with living hinges, I can definitely recommend to get a roll for your next projects. It might actually be a good alternative for other flexibles you are currently using. What do you think would be a good application for this material? You can find links to the material and the test methods I use down in the description. The detailed test report together with print profile and all test samples are available for my Patrons. If you enjoyed this video and learned something, then hit the like button and subscribe to the channel for more. If you have suggestions and comments about my methods, please leave them down below and let me know what other material you would like to see me investigate in the future. Until then, thanks for watching, auf wiedersehen, and until next time!