3D printing Fig. 2:
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
3D printing Extruding of the thermoplastic Bio-PU out of a 0.5 mm nozzle (Photo: Merseburg Univ. Appl. Sc. /D. Glatz) Rapid prototyping methods for bio-based plastics Merseburg University develops procedures and devices Today rapid prototype parts are required in all areas and are vitally important for the product development process. The wide range of Rapid Prototyping (RP) procedures and thus the choice of the materials to be used are limited. FABIO (FAbrication of parts with BIOplastics) is an R&D project funded by the German Federal Ministry of Food and Agriculture (BMEL) through its project management agency, the Agency for Renewable Resources (FNR). As part of this project, scientists from Merseburg University of Applied Sciences (Merseburg, Germany) have developed a test facility for rapid prototyping, using the so called fused extrusion prototyping (FEP), for processing bioplastics. This technology, which is considered important for the industry, could not be used so far with biopolymers. Specific values for the processing of the bioplastics were determined by carrying out different analyses. The extrusion unit was developed to enable processing of all sizes of granulates. Temperature ranges are adjustable up to 300 °C. Particular attention was paid to the extruder feeder, the optimum melting and discharge of the biopolymers considering the influences of the cylinder and screwconstruction, screw clearance, screw speed and head and nozzle geometry. The necessary cooling facilities were also taken into consideration. Different settings were tested using selected bio-plastics and any deficiencies disrupting the process could be remedied. Some complex and individual parts for the internal design of the equipment were produced on RP machines, belonging to the university. The rack could be provided with inside superstructures, among other things, changing devices, a heating system, a cooling system, a granulate material supply, a construction platform, and procedural units in an X-, Y-, Z-direction. The interaction of control mechanisms and software could be tested, irrespective of the materials used. The implementation of FABIO technology is imminent. FABIO technology makes it possible to choose from a wide range of thermoplastic granulates such as Polyamide, Polyhydroxybutyrate, Polyurethane, Polylactide and starch. After successful completion of the project, the aim is to take the innovative idea, which was a spin-off from Merseburg University of Applied Sciences, and turn it into a service platform for prototype parts. Other topics this service platform for rapid prototyping with bioplastics will deal with are PSP (Photo Sensitive Polymerisation of thermoset materials) and material modifications for the SLS process (Selective Laser Sintering). MT www.hs-merseburg.de Info: The complete final report (German language only) and a short project description can be downloaded from www.bioplasticsmagazine.de/201406 bioplastics MAGAZINE [06/14] Vol. 9 23
