bioplasticsMAGAZINE_1406

3D printing
Fig. 2: Brittle fractured surface of printed PLA test bars (80x10x4 mm).
ISO 179 Charpy impact test (left); ISO 178 three-point bending test
(right). PLA/PHA does not show brittle fracturing.
PLA/PHA Blend
for 3D-Printing
The Institute for Natural Materials Technology (IFA-Tulln)
has many years of experience in injection molding and
extruding PLA. Due to the rising consumption of PLA in
the 3D-printing community the institute has adapted its approach
to these new demands.
Most 3D printers for home use are based on an open source
technology which is called Fused Filament Freeforming (FFF).
A filament of thermoplastic resin is pushed through a heated
nozzle which moves in two directions to form a solid layer.
This is repeated for many layers until the part is finished.
PLA is very popular because it does not require a heated
bed for good print bed adhesion. The use of unmodified PLA
in FFF can lead to several inconveniences such as oozing,
warping or a brittle filament. The Institute has developed a
PLA/PHA blend which solves these problems.
Oozing
Oozing refers to the problem of uncontrolled leaking
of material which leads to strands between separated in
printing areas. This can be reduced by retraction of filaments
if the printing vector is interrupted and a lower printing
temperature. Still this leads to a reduction in quality and does
not completely prevent the oozing. The captive ball test (Fig. 1)
was used as an accurate indicator for the oozing tendency of
the material.
Warping
There are two different kinds of warping. Warping of the
first layer and warping of overhanging areas. Both can cause
a collision with the extruder nozzle and may destroy the print.
The warping of the first layer can be prevented by good print
bed adhesion and a heated print bed. Warping of overhangs is
more difficult to reduce. These need a well set temperature
profile or an active cooling. Since most desktop open source
printers do not have active cooling the material’s warping
tendency must be reduced.
Mechanical Properties
When it comes to mechanical properties PLA’s biggest
weakness is its brittleness. Brittle filaments often break
in the feed, which prevents the print from being finished.
Further, good mechanical properties of the final printed part
are always desired and need to be tested and improved. To
test the material’s mechanical properties test specimens for
the ISO 178 three point bending test were printed (Fig. 2) and
injection molded.
Blending PLA with PHA
To improve the 3D printing properties PLA was blended with
PHA. This led to superior properties compared to a regular
PLA filament.
Tests have shown that an ISO 1133 melt flow rate
(190 °C/2.16 kg) below 10 g/10 min would be optimal for a PLA
based filament to prevent oozing. Unfortunately a low MFR
has an adverse effect on warping of overhangs. Therefore
a PLA/PHA blend was used which showed less oozing and
would still not warp on overhangs.
PLA/PHA blends also avoided brittle fracturing of the
filament. A printed PLA/PHA specimen showed an ISO 178
bending strength of 85 MPa and an ISO 179 Charpy impact
strength of 18 kJ/m². Blending PLA with PHA increased
the mechanical properties, print bed adhesion and oozing
behaviour while remaining completely bio-based and biodegradable.
www.ifa-tulln.boku.ac.at
By:
Bernhard Steyrer
University of Natural Resources and Life Sciences
Department for Agrobiotechnology, IFA-Tulln
Institute for Natural Materials Technology
Vienna, Austria
Fig. 1: Captive ball test on the left shows strong oozing
with high-MFR PLA/PHA compared to a fine print on the
right with low-MFR PLA/PHA (edge length 20 mm).
22 bioplastics MAGAZINE [06/14] Vol. 9