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
todays video we’ll take a look at the printing
properties of Polypropylene and run a variety
of mechanical test to find out how it performs
in comparison to other 3D printing materials.
Due to it’s 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 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 it’s
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 put
into the semi-flex category. Due to its soft
nature I had to crank the extrusion factor
all the up to 122%. I printed 3D Maker Noobs
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 rise 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, lets 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 deformes
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 save but still I can’t really recommend
to use 3D prints for food contact because
your hotend could contaminate the part and
bacterial 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 sample 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!
